U.S. patent application number 11/016137 was filed with the patent office on 2006-01-12 for method for operating and individually controlling the luminance of each pixel in an emissive active-matrix display device.
Invention is credited to Walter Edward Naugler, Damoder Reddy.
Application Number | 20060007249 11/016137 |
Document ID | / |
Family ID | 38701564 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060007249 |
Kind Code |
A1 |
Reddy; Damoder ; et
al. |
January 12, 2006 |
Method for operating and individually controlling the luminance of
each pixel in an emissive active-matrix display device
Abstract
System and method for controlling luminance of pixel in display.
Method includes storing transformation between digital image gray
level value and display drive signal that generates luminance from
pixel corresponding to digital gray level value; identifying target
gray level value for particular pixel; generating display drive
signal corresponding to identified target gray level based on
stored transformation and driving particular pixel with drive
signal during first display frame; measuring parameter
representative of actual measured luminance of particular pixel at
a second time after the first time; determining difference between
identified target luminance and actual measured luminance;
modifying stored transformation for particular pixel based on
determined difference; and storing and using modified
transformation for generating display drive signal for particular
pixel during frame time following first frame time. Control system
and circuits for controlling the luminance of a picture element or
pixel in a display device.
Inventors: |
Reddy; Damoder; (Los Gatos,
CA) ; Naugler; Walter Edward; (Cedar Park,
TX) |
Correspondence
Address: |
DORSEY & WHITNEY LLP
555 CALIFORNIA STREET, SUITE 1000
SUITE 1000
SAN FRANCISCO
CA
94104
US
|
Family ID: |
38701564 |
Appl. No.: |
11/016137 |
Filed: |
December 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60583744 |
Jun 29, 2004 |
|
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|
Current U.S.
Class: |
345/690 |
Current CPC
Class: |
G09G 2320/0233 20130101;
H01L 27/3272 20130101; G06F 3/0412 20130101; G09G 2360/148
20130101; G09G 3/3275 20130101; G06F 3/042 20130101; G09G 2310/066
20130101; G09G 2300/0842 20130101; H01L 27/288 20130101; H01L
27/3227 20130101; G09G 2320/0693 20130101; G09G 2320/043 20130101;
G09G 2360/142 20130101; H01L 27/3269 20130101; H01L 27/1446
20130101; H01L 2251/5315 20130101; G09G 2300/0852 20130101; G09G
2320/0295 20130101; G06F 2203/04109 20130101; G09G 3/3291 20130101;
G09G 2320/029 20130101; G09G 3/3233 20130101; G06F 3/0386 20130101;
G09G 2300/0819 20130101; G09G 2360/147 20130101; G09G 2320/045
20130101; G06F 3/03542 20130101; H01L 27/323 20130101 |
Class at
Publication: |
345/690 |
International
Class: |
G09G 5/10 20060101
G09G005/10 |
Claims
1. A method for controlling the luminance of a picture element
(pixel) in a display device, the method comprising: storing a
transformation between a digital image gray level value and a
display drive signal that generates a luminance from a pixel
corresponding to the digital gray level value; identifying a target
gray level value for a particular pixel; generating a display drive
signal corresponding to the identified target gray level based on
the stored transformation and driving the particular pixel with the
drive signal during a first display frame; measuring a parameter
representative of an actual measured luminance of the particular
pixel at a time after the first display time; determining a
difference between the identified target luminance and the actual
measured luminance for the particular pixel; modifying the stored
transformation for the particular pixel based on the determined
difference; and storing and using the modified transformation for
generating the display drive signal for the particular pixel during
a frame time following the first frame time.
2. A method as in claim 1, wherein the first display frame is any
display frame designated by software programming or by the display
user or by a combination of the programming and the user.
3. A method as in claim 1, wherein the frame time following the
first frame is any subsequent frame time.
4. A method as in claim 1, wherein the first display frame is any
display frame designated by software programming or by the display
user or by a combination of the programming and the user.
5. A method as in claim 1, wherein the first display time may be
either a single continuous period of time or comprised of a
plurality of discontinuous periods of time, and wherein either of
the continuous period of time and the discontinuous periods of time
may occur during a single frame time or over multiple frame
times.
6. A method as in claim 1, wherein storing and/or the using of the
modified transformation for generating the display drive signal for
the particular pixel is applied at any subsequent portion of a
single frame or at different frames.
7. A method as in claim 1, wherein storing and/or the using of the
modified transformation for generating the display drive signal for
the particular pixel may be either at single continuous period of
time or comprised of a plurality of discontinuous periods of time,
and wherein either of the continuous period of time and the
discontinuous periods of time may occur during a single frame time
or over multiple frame times.
8. A method as in claim 5, wherein storing and/or the using of the
modified transformation for generating the display drive signal for
the particular pixel may be either at single continuous period of
time or comprised of a plurality of discontinuous periods of time,
and wherein either of the continuous period of time and the
discontinuous periods of time may occur during a single frame time
or over multiple frame times.
9. A method as in claim 1, wherein the stored transformation
comprises a transformation stored in a gray level logic functional
block of a display system.
10. A method as in claim 1, wherein the stored transformation
comprises a transformation stored in a gamma table for a display
device.
11. A method as in claim 1, wherein the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a voltage
measurement corresponding to a number of electrons accumulated or
released from a charge storage device.
12. A method as in claim 1, wherein the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a current
measurement corresponding to a number of electrons accumulated or
released from a charge storage device.
13. A method as in claim 1, wherein the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a charge
measurement corresponding to a number of electrons accumulated or
released from a charge storage device.
14. A method as in claim 11, wherein the charge storage device
comprises a capacitor.
15. A method as in claim 14, wherein the electrons are accumulated
or released in proportion to a resistivity or conductivity of a
sensor element having a resistivity or conductivity that changes in
response to a flux of photons incident on the sensor.
16. A method as in claim 15, wherein the proportion is a direct
proportion.
17. A method as in claim 1, wherein the frame time following the
first frame time is the next subsequent frame time.
18. A method as in claim 1, wherein the frame time following the
first frame time is any subsequent frame time.
19. A method as in claim 1, wherein the frame time following the
first frame time is a next display device power on time.
20. A method as in claim 1, wherein the frame time following the
first frame time is a frame time at a predetermined or dynamically
determined time interval.
21. A method as in claim 1, wherein a different transformation is
stored for each pixel in the display device.
22. A method as in claim 1, wherein a different transformation is
stored for each different gray level that may be displayed for each
separately addressable pixel in the display device.
23. A method as in claim 1, wherein the first display time is the
duration of time a pixel is turned on in the display.
24. A method as in claim 1, wherein the display time is
substantially any time between 8 milliseconds and 36
milliseconds.
25. A method as in claim 1, wherein the display time is
substantially any time between 10 milliseconds and 20
milliseconds.
26. A method as in claim 1, wherein the portion of the frame time
comprises substantially the row address time.
27. A method as in claim 1, wherein the portion of the frame time
comprises a time between the row address time and the frame
time.
28. A method as in claim 1, wherein the measuring of a parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises measuring a
voltage stored on a capacitor that has either been charged toward
or discharged from a known voltage and the amount of charging or
discharging is proportional to a photon flux emitted from the
emitter within the particular pixel onto a sensor within the same
particular pixel.
29. A method as in claim 1, wherein the steps of identifying,
generating, measuring, determining, modifying, and using are
repeated for every pixel in the display.
30. A method as in claim 1, wherein the determining of a difference
between the identified target luminance and the actual measured
luminance for the particular pixel is based on a reference
integrated photon flux on the particular pixel sensor determined
during a display calibration procedure performed during manufacture
or when initially used.
31. A method as in claim 1, further comprising a display
calibration procedure that determines and stores an initial
transformation for every pixel and every gray level the display may
be commanded to display.
32. A control system for controlling the luminance of a picture
element (pixel) in a display device, the system comprising: a
stored pixel gray level to display pixel drive signal
transformation for each pixel and each gray level the pixel may be
commanded to display, the stored transformation based on
performance characteristics of the display pixels during a prior
display frame time period; a display drive signal generator
responsive to a control that receives a command to display a
particular gray level for a particular pixel location and generates
a drive signal to the particular pixel using the stored
transformation during a first frame time; a luminance measurement
circuit for each separate pixel in the display for measuring
parameters representative of an actual measured luminances of each
of the plurality of particular pixels at the end of the first
display time; a comparator circuit for determining a difference
between the identified target luminance and the actual measured
luminance for the particular pixel; transformation update logic for
modifying the stored transformation for each particular pixel based
on the determined difference during the first frame time; and using
the modified transformation for generating the display drive signal
for the particular pixel during a frame time following the first
frame time.
33. A system as in claim 32, wherein the stored transformation
comprises a transformation stored in a gray level logic functional
block of a display system.
34. A system as in claim 32, wherein the stored transformation
comprises a transformation stored in a gamma table for a display
device.
35. A system as in claim 32, wherein the luminance measurement
circuit measures a parameter representative of an actual measured
luminance of the particular pixel at the end of the first display
time and comprises a voltage measurement corresponding to a number
of electrons accumulated or released from a charge storage device
separately for each pixel of the display.
36. A system as in claim 35, wherein the charge storage device
comprises a capacitor.
37. A system as in claim 36, wherein the electrons are accumulated
or released in proportion to a resistivity or conductivity of a
sensor element having a resistivity or conductivity that changes in
response to a flux of photons incident on the sensor.
38. A system as in claim 37, wherein the proportion is a direct
proportion.
39. A system as in claim 32, wherein the frame time following the
first frame time is the next subsequent frame time.
40. A system as in claim 32, wherein the frame time following the
first frame time is any subsequent frame time.
41. A system as in claim 32, wherein the frame time following the
first frame time is a next display device power on time.
42. A system as in claim 32, wherein the frame time following the
first frame time is a frame time at a predetermined or dynamically
determined time interval.
43. A system as in claim 32, wherein different transformation is
stored for each pixel in the display device.
44. A system as in claim 32, wherein a different transformation is
stored for each different gray level that may be displayed for each
separately addressable pixel in the display device.
45. A system as in claim 32, wherein the first display time is the
duration of time a pixel is turned on in the display.
46. A system as in claim 32, wherein the display time is
substantially any time between 8 milliseconds and 36
milliseconds.
47. A system as in claim 32, wherein the display time is
substantially any time between 10 milliseconds and 20
milliseconds.
48. A system as in claim 32, wherein the portion of the frame time
comprises substantially the row address time.
48. A system as in claim 32, wherein the portion of the frame time
comprises a time between the row address time and the frame
time.
50. A system as in claim 32, wherein the measuring of a parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises measuring a
voltage stored on a capacitor that has either been charged toward
or discharged from a known voltage and the amount of charging or
discharging is proportional to a photon flux emitted from the
emitter within the particular pixel onto a sensor within the same
particular pixel.
51. A system as in claim 32, wherein the steps of identifying,
generating, measuring, determining, modifying, and using are
repeated for every pixel in the display.
52. A system as in claim 32, wherein the determining of a
difference between the identified target luminance and the actual
measured luminance for the particular pixel is based on a reference
integrated photon flux on the particular pixel sensor determined
during a display calibration procedure performed during manufacture
or when initially used.
53. A system as in claim 32, further comprising a display
calibration procedure that determines and stores an initial
transformation for every pixel and every gray level the display may
be commanded to display.
54. A system as in claim 32, wherein the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a current
measurement corresponding to a number of electrons accumulated or
released from a charge storage device.
55. A system as in claim 32, wherein the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a charge
measurement corresponding to a number of electrons accumulated or
released from a charge storage device.
56. A system as in claim 32, wherein the first display frame is any
display frame designated by software programming or by the display
user or by a combination of the programming and the user.
57. A system as in claim 32, wherein the frame time following the
first frame is any subsequent frame time.
58. A system as in claim 32, wherein the first display frame is any
display frame designated by software programming or by the display
user or by a combination of the programming and the user.
59. A system as in claim 32, wherein the first display time may be
either a single continuous period of time or comprised of a
plurality of discontinuous periods of time, and wherein either of
the continuous period of time and the discontinuous periods of time
may occur during a single frame time or over multiple frame
times.
60. A system as in claim 32, wherein storing and/or the using of
the modified transformation for generating the display drive signal
for the particular pixel is applied at any subsequent portion of a
single frame or at different frames.
61. A system as in claim 32, wherein storing and/or the using of
the modified transformation for generating the display drive signal
for the particular pixel may be either at single continuous period
of time or comprised of a plurality of discontinuous periods of
time, and wherein either of the continuous period of time and the
discontinuous periods of time may occur during a single frame time
or over multiple frame times.
62. A system as in claim 59, wherein storing and/or the using of
the modified transformation for generating the display drive signal
for the particular pixel may be either at single continuous period
of time or comprised of a plurality of discontinuous periods of
time, and wherein either of the continuous period of time and the
discontinuous periods of time may occur during a single frame time
or over multiple frame times.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. 119 and/or 35 U.S.C. 120 to U.S. Provisional Patent
Application Ser. No. 60/583,744 (Atty. Docket. No. 186051/US
[474125-20]) filed Jun. 29, 2004 naming as inventors Damoder Reddy
and W. Edward Naugler, Jr., and entitled High-Impedance to
Low-Impedance Conversion System for Active Matrix Emission Feedback
Stabilized Flat Panel Display, which application is incorporated by
reference in its entirety.
[0002] This application is also related to the following
applications, each of which is hereby incorporated by reference:
U.S. Utility application Ser. No. ______, (Atty. Docket. No.
186051/US/4 [474125-21]) filed 17 Dec. 2004 and entitled System And
Method For A Long-Life Luminance Feedback Stabilized Display Panel;
U.S. Utility application Ser. No. ______, (Atty. Docket. No.
186051/US/2 [474125-22]) filed 17 Dec. 2004 and entitled Feedback
Control System and Method for Operating a High-Performance
Stabilized Active-Matrix Emissive Display; U.S. Utility application
Ser. No. ______ (Atty. Docket. No. 186051/US/3 [474125-23]) filed
17 Dec. 2004 and entitled Active-Matrix Display And Pixel Structure
For Feedback Stabilized Flat Panel Display; U.S. Utility
application Ser. No. ______, (Atty. Docket. No. 186051/US/5
[474125-25]) filed 17 Dec. 2004 and entitled Method For Operating
And Individually Controlling The Luminance Of Each Pixel In An
Emissive Active-Matrix Display Device; U.S. Utility application
Ser. No. ______, (Atty. Docket. No. 186051/US/6 [474125-26]) filed
17 Dec. 2004 and entitled Device And Method For Operating A
Self-Calibrating Emissive Pixel, and U.S. Utility application Ser.
No. ______ (Atty. Docket. No. 186051/US/7 [474125-27]) filed 17
Dec. 2004 and entitled High-Performance Emissive Display Device For
Computers, Information Appliances, And Entertainment Systems; each
of which applications is hereby incorporated by reference.
FIELD OF THE INVENTION
[0003] This application pertains generally to emissive flat panel
displays and more particularly to systems, devices and methods for
making, calibrating, and operating emissive pixel flat panel
displays to provide uniform light emission level and color over the
surface of the display initially and throughout its operational
life and to extend the operational life of such displays.
BACKGROUND
[0004] Active matrix (AM) emissive displays and active matrix
organic light emitting diode (AMOLED) displays in particular rely
on current levels in the light emitting diode to produce luminance
levels (light emission level) in a matrix of pixels (picture
elements). Each pixel is a separate light emitting diode that is
directly addressed and wherein each pixel has a sample and hold
circuit so that a voltage can be applied to the Organic Light
Emitting Diode (OLED) display driver continuously over the duration
of the frame.
[0005] The function of a flat panel display is to produce an image
in various shades of light and dark in correspondence to voltage
levels representing the original image, or an image created by
computer software. These light and dark shades may form or generate
colors when they are rendered as different pixel types such as in
red, blue, and green through the use of different colored emissive
pixels or diodes or through the use of same colored or white pixels
and filters. Sometimes the set of three pixels used together to
render a color by additive combination of their respective photon
flux are referred to as subpixels, but in the description to
follow, little distinction is made between pixels and subpixels as
the subpixels are pixels in their own right and sets of pixels that
are controlled as a set are merely cooperative sets of subpixels.
Operation of sets of pixels or emitters to generate color are known
in the art and not described in greater detail. The translation of
the voltage image data into current generated OLED photon emission
(flux) levels presents several complex issues involving the
manufacture of the display and the aging of the display during
operation and use by a user or consumer in the field.
[0006] In the case of a typical conventional OLED display, an image
or data voltage is placed on the gate of a power transistor
(current source) in the display pixel, which feeds and controls the
amount or magnitude of current to the OLED pixel. The higher the
gate voltage is, the higher will be the current and therefore the
brighter or more emissive will be the pixel. Typically voltages
(the signal data) supplied to thin-film semiconductor transistors
(TFTs) having source, drain, and gate terminals are used to control
the current to the pixel emitter elements to render an appropriate
gray level or pixel image luminance.
[0007] The circuits, methods of control, and even materials
heretofore used in conventional implementations have significant
limitations so that OLED display panel performance has suffered and
has limited the application of such OLED technology for larger
high-performance displays at consumer acceptable price.
[0008] A primary problem in such systems and devices is that it is
conventionally extremely difficult if not impossible to produce
uniform current from pixel-to-pixel in a display using voltage
image data applied to TFTs in this manner. This problem becomes
particularly acute as the displays become physically larger, have
larger numbers of pixels, are driven to high current and luminance
levels, and/or are operated either continuously or intermittently
for longer periods of time (they age). This problem arises at least
in part because the current delivered by a TFT at a particular gate
voltage depends on many parameters, such as for example the TFT
threshold voltage, the effective electron mobility, and current
gain of the TFT device (which may vary from TFT device to TFT
device as a result of manufacturing variations, environmental
exposure during operation, and/or operational history. These three
parameters (threshold voltage, effective electron mobility, and
current gain) may in turn depend, for example, on inter-grain and
intra-grain trap densities, semiconductor thickness, and
semiconductor-to-gate dielectric trap densities. Other factors
include: gate dielectric thickness, dielectric constant of the
insulators, the TFT geometry, electron/hole mobilities, and other
factors alone and in combination.
[0009] Among the problems at issue are how voltages (e.g. TFT
voltages) to be applied are determined and how that voltage is
placed on the power TFT to give the right current level to produce
the correct gray level. Some studies have suggested a particular
way or ways to use a particular luminance of a pixel to correct the
voltage supplied to the pixel power TFT (See for example, U.S. Pat.
No. 6,518,962 B2 by Kimura and assigned Seiko-Epson; U.S. Pat. Nos.
6,542,138B1 and 6,489,631B2 assigned to Philips, and the paper by
Eko T. Lisuwandi at MIT (See "Feedback Circuit for Organic LED
Active-Matrix Display Drivers, by Eko T. Lisuwandi submitted to the
Department of Electrical and Computer Science in Partial
Fulfillment of the Requirements for Degrees of Master of
Engineering in Electrical Engineering and Computer Science at the
Massachusetts Institute of Technology, May 10, 2002). However,
these conventional attempts to improve OLED (or indeed other active
emission display technologies) have not been entirely effective and
are in one way or another flawed.
[0010] For example, U.S. Pat. No. 6,542,138 B1 (assigned to
Philips) describes a method that at most attempts to make pixels
tend to be uniform to some extent over a frame duration but does
not describe or suggest that exact emission levels corresponding to
a series of gray levels can be controlled. This invention described
in this patent for example, uses a light sensitive discharge device
across the signal hold capacitor that maintains the gate voltage on
the OLED current driving TFT during the frame time. The photon
emission from the OLED causes the light sensitive discharge device
to discharge the voltage on the holding capacitor thus turning off
the current driving TFT and thus extinguishing the OLED. The rate
of extinguishment is dependent on the level of photon emission;
therefore if the pixel over-produces photon emission the OLED will
be extinguished faster than were the pixel to under-produce photon
emission. As a further refinement of such a system, the
photosensitive discharge device is a photo-transistor, the gate of
which is controlled by the current passing through the OLED. The
circuit is designed so that at high current through the OLED the
photo-transistor is in the off condition because the voltage to the
gate of the photo-transistor is close to ground due to the high
OLED current, but the photo-transistor while in the off condition
acts like a reverse biased photo-diode and the charge on the
holding capacitor is slowly leaked to ground, causing the current
through the OLED to be reduced as the current is reduced. Due to
the declining voltage on the storage capacitor the voltage rises on
the gate of the photo-transistor. When the current decrease to a
certain point the threshold voltage of the photo-transistor is
exceeded causing the photo-transistor to turn on and dump the
remaining charge in the storage capacitor and thus shut off the
OLED. The rapidity, and thus, the perceived luminance of the OLED
is determined by the luminance level of the OLED. The higher the
luminance of the OLED the faster is the OLED shut off.
[0011] There are several objections to this approach. Firstly, the
turning on of the photo-transistor to shut off the OLED depends on
the threshold voltage of the photo-transistor. One of the problems
that this approach is supposed to correct is the variable threshold
voltages of the TFTs used in the pixel circuitry. This means that
the time when the OLED is shut off will vary from pixel to pixel
and thus actually contribute to the non-uniformity between
different pixels of the display. Secondly, at low emission values
the voltage applied to the gate of the photo-transistor will be
close to the threshold voltage at the beginning of the frame time.
Any variations in threshold voltage are therefore greatly magnified
and the uncertainty of the actual luminance values is not well
controlled at all. Thirdly, the actual brightness perceived by the
viewer depends on the total photon emission during the frame. The
total photon emission during the frame depends at least in part on
the initial value of the data voltage supplied to the storage
capacitor, the rate of discharge of the storage capacitor during
the off time of the photo-transistor (which is dependent on the
emission level of the OLED caused by the initial voltage), the
threshold voltage of the current controlling TFT whose gate is
controlled by the voltage stored on the storage capacitor, current
gain of the current controlling TFT, the effective electron
mobility of the current controlling TFT, the age point of the OLED
materials, the color spectrum of the OLED materials and the
threshold voltage of the photo-transistor. All these mentioned
controlling parameters are not well controlled in the manufacturing
process and therefore the pixel uniformity is not well controlled
using the structures and methods of described or inferred by the
U.S. Pat. No. 6,542,138 B1 (Philips) reference.
[0012] U.S. Pat. No. 6,518,962 B2 by Kimura (assigned to
Seiko-Epson) describes circuits in which current levels are
obtained by certain pixel associated sensors in the short address
time allocated for making a measurement. These are essentially
instantaneous measurements and the measurement time is too short to
give a practically acceptable signal-to-noise ratio so that useful
information for determining the voltage or current to be supplied
to the TFT (or OLED pixel) can be extracted from the measurement.
The signal extracted is expected to be on the order of a few
nano-volts (10.sup.-9 volts) and the noise is expected to be on the
order of several volts due to the long conductor line terminated
essentially by an open circuit for a signal-to-noise ration (SNR)
of less than about 0.1 percent Furthermore, it is also expected
that different noise characteristics may arise for different
regions of a display owing to the different localized
electromagnetic fields and to the same pixels at different
times.
[0013] Another limitation of Kimura et al (U.S. Pat. No. 6,518,962
B2) is that the system and method as described appears to apply a
predetermined signal to the signal data line and it then alters
this signal by the voltage control unit to make the light level
come close to the reference value. The predetermined data signal
therefore appears to cause a luminance that is an incorrect
luminance because it varies from the reference and is subsequently
altered by the voltage-adjusting unit to produce luminance that is
only "close" to the reference. Kimura therefore does not appear to
actually match the reference or any other target luminance.
[0014] The work of Lisuwandi et al., which is generically and
conceptually similar to U.S. Pat. No. 6,518,962 B2 has too long a
feedback settling time (greater than 150 ms) and thus, is not
practical, especially for displays that have dynamic content that
changes from frame to frame for normal computer screen, television,
and similar applications.
[0015] Conventional systems and methods that have attempted to
control pixel luminance, have by-and-large attempted to measure
instantaneous light or luminance levels that have been too small
and too noisy to accurately and precisely provide such control.
They have therefore been ineffective and their limitations will be
even more severe as the size and performance expectations of OLED
displays increases.
[0016] These performance problems may likely be even more severe
when amorphous silicon (a-Si) is used for the display electronics.
Amorphous silicon is the semiconductor used by the LCD industry and
has billions of dollars invested in the infrastructure. It is,
therefore, desirable for the major display manufacturers to use
amorphous silicon. Early development of OLED active-matrix displays
has employed the use of poly-silicon due to its higher speed and
better stability. There is very little investment in poly-silicon
infrastructure and the costs are high as opposed to amorphous
silicon.
[0017] Recall that there are three forms of silicon conventionally
used in electrical integrated circuits. Crystalline silicon used in
monolithic integrated circuits (ICs). This type of silicon has no
grain boundaries since the material is a solid crystal. This type
of silicon (x-Si) has only one area for electrical charge to
accumulate, and that area is at the interface between the gate
dielectric and the silicon surface contacted by the dielectric. The
area of this interface is just the width and length of the gate
dimensions.
[0018] Poly-silicon (p-Si) is made up of course grains of silicon
having more or less intimate contact with each other. In order for
electrons to go from grain to grain and thus, travel through a p-Si
channel in a field effect transistor (FET), a certain amount of
energy must be added. Also, the interface between grains can
collect stray charges (both positive (holes) and negative
(electrons) stray charges) just like the interface between the
dielectric and the silicon crystal in the x-Si material, but now
the area has greatly expanded. The intergranular area in the p-Si
is inversely proportional to the grain size. Therefore, the smaller
the grain size, the greater the interfacing area will be and the
greater the chance for stray charges to build up.
[0019] In the case of amorphous silicon (a-Si) the grain boundary
area is magnitudes greater than for p-Si. Trapped charge is
normally the dominant characteristic that determines electron
mobility and threshold voltage for a-Si devices and therefore any
changes in the charge density at the inter-grain boundaries causes
fluctuation in the electron mobility and threshold voltage with
much greater effect in the amorphous silicon (a-Si) as compared to
the poly-Silicon (p-Si) or crystalline silicon (x-Si).
[0020] As display size increases, there is great desirability to
use amorphous silicon rather than poly-silicon or crystalline
silicon. However, due to the differences and fluctuations in
electron and hole mobility characteristics, stray electrical charge
accumulation characteristics, and threshold voltage
characteristics, it is increasingly difficult to maintain a desired
and uniform display luminance characteristics over a large display
surface at any single moment in time and as the display device is
used with amorphous silicon.
[0021] Various attempts have been made to overcome the uniformity
problem in emissive displays, including some that have involved
circuit-based, some of which are still in use today. These attempts
have not been entirely successful and do not meet the needs and
application requirements of the current and next generation of
emissive display applications, particularly OLED display
applications.
[0022] One scheme attempts to control photon emission by using a so
called "current mirror" at the pixel, rather than using image
voltages to drive or control the current through the OLED and hence
control the OLED pixel luminance. Image currents are used in an
attempt to force a luminance level current through the power TFT
that feeds the OLED.
[0023] Another scheme compensates for TFT threshold variation by
providing a circuit that determines the power TFT threshold voltage
and then adds the TFT threshold voltage to the image data voltage
thus compensating for the threshold voltage so that variations or
changes in the TFT threshold voltage do not result in variation of
the current supplied to the OLED pixel luminance
[0024] These circuit based schemes are complex and expensive to
produce and have not been entirely satisfactory in maintaining
pixel luminance uniformity, because they do not compensate for the
OLED material degradation, but only certain limited variations in
the TFT.
[0025] It may be appreciated that for some devices in which OLED or
other emissive pixels are employed, the cumulative pixel on-time
may be relatively short as compared to the age of the device
carrying the display, such as cell phones and personal data
assistant (PDA) devices, because the display is normally on only
when there is an active call or user interaction. By comparison, an
OLED display for a flat panel television may be on and displaying a
dynamically changing image for five to ten hours a day. The
requirements for luminance and color uniformity are also greater
for the television which must render accurate continuous tone
images as compared to a small cell phone display which may
acceptably provide luminance uniformity and color accuracy at
considerably lower levels.
[0026] It is known in the art that OLED displays that use different
materials for the red emitter, green emitter, blue emitter of a
three color subpixel set, will age or degrade at different rates so
that after a period of operation such pixels in the displays
(without correction) will have an observable color offset or shift
that may depend on pixel luminance value. It may also be
appreciated that as the color and luminance change will be specific
to the individual pixel (subpixel) and overall or global change to
a particular color channel drive circuit will generally be
ineffective unless the cumulative effect on each pixel is the
same.
[0027] Other schemes attempt to achieve a measure of uniformity by
making a correction based on a comparison of a measured pixel
luminance to a reference luminance. One scheme of this type has
already be discussed relative to U.S. Pat. No. 6,518,962 B2 by
Kimura and assigned to Seiko-Epson. According to this scheme as
described in the patent, the brightness of the pixel is measured
and compared with the brightness of a reference pixel brightness to
generate a difference signal or value. (It is noted that although
the term "brightness" is commonly used, brightness is a subjective
measure and may require the consideration of a human viewer to be
interpreted, whereas luminance is an objective measure.) The
difference signal or value is then used to alter the signal voltage
that drives the TFT supplying current to the pixel with the
intention of adjusting the pixel brightness in order that the final
or "settled" brightness (really luminance) comes "close" to the
reference value. This scheme has several problems and does not
solve the uniformity problem. Three problems are paramount with
this scheme: (i) pixel brightness (really luminance) variation or
"ringing" before stabilizing at a settled value, (ii) inaccuracy
due to a low signal-to-noise level and noise, and (iii)
insufficient resolution as a result of lack of pixel isolation.
These problems better understood by reviewing the structure of one
of the Kimura pixel structures.
[0028] Kimura et al. (U.S. Pat. No. 6,518,962) shows (See Kimura
FIG. 19) what is described as a block diagram showing an entire
arrangement of a display apparatus according to a twelfth
embodiment his invention and including a circuit diagram of a
pixel. This Kimura pixel circuit structure 61 has been redrawn and
relabeled as presented in FIG. 1A so that an appropriate comparison
may subsequently be made with an embodiment of the pixel circuit
structure 62 of the present invention. It is noted that the
photodiode D1 of Kimura is connected to the voltage supply line for
its voltage. This approach is problematic from at least the
standpoint of pixel luminance stability and repeatability because
the exact voltage on that voltage supply line depends on the
current being used by the lines nearer the voltage supply for that
voltage, because all the pixels attached to the line (in the
column) are drawing current which drops the voltage on the line.
This voltage drop depends on what pixels are turned on and to what
level of current draw they are experiencing. In other words, the
voltage that drives each of the Kimura pixels are dependent on the
image data presented for display at other pixels of the display. It
will also be noted that the Kimura pixel lacks any isolation of the
thin film diode. This means that all the sensor photodiodes in the
column are contributing current to the sensor read line at the same
time.
[0029] Again, this photodiode configuration and the pixel structure
that contains it is problematic because there is no information as
to where the current (or charge, or voltage) originates from.
Reference to the original FIG. 19 of Kimura suggests that all the
sensor read lines go into a shift register, and each line appears
to be read in series (rather than in parallel) with the next one.
Performing a serial read operation for each line would have to done
during the address time which implies an exceedingly fast read rate
and would permit only a very short time to make the current
measurement. Such short measurements are susceptible to imprecision
and the effects of noise and may generally support only a very
small signal to noise ratio.
[0030] Other conventional approaches also fail to overcome
conventional limitations. A particular luminance level produces a
photocurrent in the sensor, and the size or magnitude of the
photocurrent is an indication (in some instances is proportional or
directly proportional to) of the luminance (photon flux through the
sensor). Either the current or a voltage created across a resistive
element (such as a resistor) by the current that is measured to
identify the luminance.
[0031] First, the pixel luminance will "ring" or oscillate for a
time around the reference value before stabilizing and reaching a
stable luminance point. This stabilization takes time, time is
important, and more time than allowed by the short address time
(t.sub.A) which for most display applications (such as OLED
displays having an array in the range of 640.times.480 pixels) is
the display frame time (t.sub.f) divided by the display number of
lines (N.sub.L). For a relatively small 160.times.120 pixel display
such as may be used in a hand-held computer or information
appliance, the address time is about 0.13 ms and for relatively
larger 800.times.600 pixel display such as may be used in a Lap-top
computer the address time is about 0.027 ms. By comparison, the
time to stabilize (t.sub.s) such a feedback system has been
calculated by Eko T. Lisuwandi at MIT (See "Feedback Circuit for
Organic LED Active-Matrix Display Drivers, by Eko T. Lisuwandi
submitted to the Department of Electrical and Computer Science in
Partial Fulfillment of the Requirements for Degrees of Master of
Engineering in Electrical Engineering and Computer Science at the
Massachusetts Institute of Technology, May 10, 2002) to exceed 100
ms. This settling time is therefore unacceptably long for practical
active-matrix type displays. The problems and limitations described
here are typical of conventional closed-loop feedback systems and
methods, where a parameter or value is measured, sensed, or read
and the reading fed-back to a control means that changes the read
parameter (or a parameter derived from it), and applies or
otherwise uses the changed parameter for operation. In this
particular display context, since for any display that displays
changing display content, the frame rate must exceed 30 frames per
second to prevent flickering. For most displays that display moving
images the frame rate is 60 frames per second (fps). The frame
duration (reciprocal of fps) will be less than about 20 ms, a
closed-loop feedback control scheme such as described by Kimura
cannot be realized for displays operating with display content that
changes at rates faster than about 6 to 8 fps, as do normal video
speeds for television, computer displays.
[0032] A second problem with this scheme is that the scheme relies
on a direct reading from the light sensors in the pixels by a
current measurement circuit physically located outside the display
area (or off glass). The current measurement circuit conventionally
needs to be physically located outside the display area because
integrating high speed circuitry directly on the display glass has
been to costly in yield loss and added expense to be practical at
this time; so it has not been merely a design choice as to where it
is located. These conventional devices have used a reverse biased
PIN diode as the sensor. Due to the high impedance value of the
sensor (typically between about 1000 MegOhms and 1 MegOhm), noise
picked up by the wires or conductors attached to the sensor and
subsequently to the measuring equipment off the glass will
seriously obscure accurate reading of the pixel luminance. For
example, the sensed signal may be a signal voltage in the range of
a few millivolts (mv) and the noise on this signal when it reaches
the measuring equipment may typically be in the range between about
a few millivolts and about several volts. Since the pixel
uniformity requirement for a 8-bit grayscale display may be 0.4
percent, any noise greater than that will prevent achieving the
required uniformity. Since, the signal voltage is a few millivolts
a noise level of millivolts to volts far exceeds the signal to
noise ratio (which can be no worse that 1 to 1) required to make a
measurement with any accuracy at all. Third, this scheme generally,
and the particular approach described in U.S. Pat. No. 6,518,962 B2
(Kimura), does not describe and gives no consideration for
isolating the sensors for individual rows thus, also failing to
isolate the reading of the sensors since all sensor readings in
display array column appear to be combined into one current that is
conducted to the measurement circuit off the glass. All the pixels
in a column are on in an active-matrix display (as opposed to a
passive-matrix display where the rows are on only one at a time);
therefore, since the sensor line travels vertically up the display
all the sensors in a column are connected to the sensor line for
that column and each pixel's sensor will contribute to the total
current in the sensor line making it impossible to determine the
current contributed by any one pixels.
[0033] Therefore there remains a need for system, device, method,
and computer program and computer program products that solve the
afore described problems and limitations in the prior art,
including the problems of settling times for conventional
closed-loop control, noise interference, and sensor isolation.
SUMMARY
[0034] Systems, devices and methods for making, calibrating, and
operating flat panel displays to provide uniform pixel and display
luminance emission levels (sometimes referred to as brightness) and
colors over the surface of the display initially and throughout the
operational life of a display and to extend the operational life of
such displays.
[0035] A stabilized feedback display system and method for
maintaining uniform pixel luminances in a display device. System
includes a display device having a plurality of emissive picture
elements (pixels) each formed from at least one electronic circuit
device, a display driver circuit receiving a raw input image signal
from an external image source and applying a corrected image signal
to the display, a display luminance detector generating at least
one display device luminance value, and a processing logic unit
receiving the at least one display device luminance value and
communicating information to the display driver circuit, the
display driver circuit using this communicated information to
generate a transformation for generating the corrected image signal
from the raw input image signal.
[0036] System and method for controlling luminance of pixel in
display. Method includes storing transformation between digital
image gray level value and display drive signal that generates
luminance from pixel corresponding to digital gray level value;
identifying target gray level value for particular pixel;
generating display drive signal corresponding to identified target
gray level based on stored transformation and driving particular
pixel with drive signal during first display frame; measuring
parameter representative of actual measured luminance of particular
pixel at a second time after the first time; determining difference
between identified target luminance and actual measured luminance;
modifying stored transformation for particular pixel based on
determined difference; and storing and using modified
transformation for generating display drive signal for particular
pixel during frame time following first frame time. Control system
and circuits for controlling the luminance of a picture element or
pixel in a display device.
[0037] System, device, and method for operating active-matrix
emissive pixel display device. Method includes storing calibration
value for pixels and gray levels displayed by pixels in memory;
storing transformation in memory for transforming first
representations of gray level values to second representations;
receiving first gray level representations of image pixel gray
level values; transforming first representations to second
representations for each pixel; generating image data and control
signals for driving pixels during present display frame time;
generating integrated photon flux signal for pixels in display
indicative of integrated photon flux during portion of present
display frame time; comparing plurality of integrated photon flux
signals with calibration values on pixel-by-pixel basis and
generating plurality of comparison results indicating difference;
and identifying deviation for each pixel and directing change in
stored transformation to be applied during subsequent time. System
provides a gray level logic, calibration memory, a comparator, and
pixel deviation logic.
[0038] An emissive pixel device having integrated luminance sensor
and a method of operating an emissive pixel device having an
integrated luminance or photon flux sensor. Device includes light
or photon emitting device, drive circuit generating current to
drive light emitting device to predetermined luminance
corresponding to an image voltage and applying drive current to
light emitting device during frame time, photo sensor that exhibits
change in electrical characteristic in response to change in
incident photon flux disposed near the light emitting device to
intercept measurable photon flux when light emitting device is in
emitting state, charge storage device coupled with sensor for
accumulating or releasing charges and exhibiting capacitance charge
and voltage proportional to the charge at a time; and control
circuit controlling charging and discharging of charge storage
device in response to changes in electrical characteristics of
sensor during at least a portion of the frame time.
[0039] Self-calibrating emissive pixel circuit, device and method
for operating pixel. Method for operating includes: establishing
sensor capacitor at predetermined starting voltage, delivering
current to photon emitting device to cause photons to be emitted at
predetermined target photon emission level, exposing sensor having
electrical properties that vary according to photon flux on sensor
to the emitted photon emission during at least portion of display
frame time, permitting sensor capacitor to either charge or is
discharge from predetermined starting state through the sensor so
that portion of frame time and resistance of sensor during portion
of frame time determine amount of charge on sensor capacitor,
measuring voltage or charge remaining on sensor capacitor at end of
portion of frame time as indication of integrated photon flux and
pixel luminance, and modifying image voltage and/or current applied
to pixel during any subsequent display frame time using measured
voltage as feedback parameter.
[0040] Information appliance device and method for operating
display associated with information appliance. Information
appliance includes display device comprising plurality of
active-matrix pixels arranged as two-dimensional array, each pixel
including a photon emitter, emitter drive circuit receiving input
image data for each pixel and generating pixel drive signal
intended to produce a corresponding target pixel luminance during
frame time, and emitter luminance sensor and measurement circuit
that measures electrical parameter indicative of actual luminance
of each pixel over portion of measurement display frame time; and
display logic coupled to display and receiving pixel luminance
related electrical parameter for each pixel and generating
correction for application subsequent time period to input image
data for each pixel based on difference between target pixel
luminance and measured pixel luminance. Photon emitter may be OLED,
electroluminescent, plasma or other emissive device in flat panel
display. Information appliance may include a television monitor, a
television receiver, a CD player, a DVD player, a computer monitor,
a computer system, an automobile instrument panel, an aircraft
instrument display panel, a video game, a cellular telephone, a
personal data assistant (PDA), a telephone, a graphics system, a
printing system, a scoreboard system, an entertainment system, a
domestic or home appliance, a copy machine, a global positioning
system navigation display, a dynamic art display device, and/or
devices combining these devices and systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1A and FIG. 1B are illustrations showing a comparison
between an exemplary conventional pixel structure and a structure
of a pixel according to an embodiment of the invention.
[0042] FIG. 2 is an illustration showing an embodiment of a
Steadylight.TM. emissive pixel and display calibration and
stabilization circuit.
[0043] FIG. 3 is an illustration showing a first embodiment of a
feedback control system for operating an active matrix display
device with individual pixel sensor integrated flux detection
feedback
[0044] FIG. 4 is an illustration showing an embodiment of a second
embodiment of a feedback control system for operating an active
matrix display device with individual pixel sensor integrated flux
detection feedback and including a calibration memory and pixel
deviation memory for modifying and controlling operation of a gray
level logic unit.
[0045] FIG. 5 is an illustration showing an embodiment of a pixel
sensor and integrated photon flux detection and measuring circuit
using a voltage sensing amplifier.
[0046] FIG. 6 is an illustration showing an embodiment of a pixel
sensor and integrated photon flux detection and measuring circuit
using a charge amp-trans-impedance amplifier.
[0047] FIG. 7 is an illustration showing a first embodiment of an
active matrix pixel including emitter, sensor, and photon-flux
integrator elements.
[0048] FIG. 8 is an illustration showing a second embodiment of an
active matrix pixel including emitter, sensor, and photon-flux
integrator elements.
[0049] FIG. 9 is an illustration showing an embodiment of a first
calibration procedure that may be executed to calibrate an active
matrix display according to the invention during the display
manufacturing process.
[0050] FIG. 10 is an illustration showing embodiment of a second
calibration procedure that may be executed to calibrate an active
matrix display according to the invention after the display has
been manufactured such as during a first time boot-up or
power-on.
[0051] FIG. 11 is an illustration showing an embodiment of a
procedure for operating a display according to embodiments of the
invention.
[0052] FIG. 12 is an illustration showing an embodiment of an
active-matrix emissive pixel display device incorporating features
of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0053] The present invention is directed to systems, devices and
methods for making, calibrating, and operating flat panel displays
to provide uniform luminance emission levels and colors over the
surface of the display initially and throughout the operational
life of a display and to extend the operational life of such
displays.
[0054] U.S. Utility patent application Ser. No. 10/872,268 (Atty.
Docket. No. 34133/US/2 [474125-8]) filed May 6, 2004 naming as
inventors Damoder Reddy and W. Edward Naugler, Jr., and entitled
Method and Apparatus for Controlling Pixel Emission (which
application is incorporated by reference in its entirety) describes
and teaches the value of sensor arrays to improve organic light
emitting diode (OLED) or other emissive pixel image quality,
increase display life, and lower manufacturing costs. The
innovations described in this patent application generate emission
measurements utilizing photo resistors and or photodiodes and
phototransistors to send voltage or current signals to data
processing circuits located off the display substrate.
[0055] In one of the circuits described therein and shown in FIG.
2, and referred to as the Steadylight.TM. calibration and
stabilization circuit 40 (Steadylight is a trademark of Nuelight
Corporation), a voltage ramp 55 is placed on the source of thin
film transistor TFT T1 41. The voltage from output pin P3 42 of
voltage comparator VC1 43 is high so that TFT T1 41 conducts the
voltage ramp to the gate of TFT T2 46 and storage capacitor C1 47.
This causes OLED D1 48 to emit light with increasing intensity,
which causes the resistance 49 of optical sensor S1 50 to steadily
decrease. As the resistance of sensor S1 50 decreases the voltage
across ground resistor R1 51 steadily increases placing an
increasing voltage on pin P1 44 of voltage comparator VC1 43. At
the beginning of the addressing cycle a reference voltage 46 is
placed on pin P2 47 of voltage comparator VC1. The reference
voltage represents the desired emission value from OLED D1 48. When
the voltage on pin P2 47 reaches the same voltage as the reference
voltage on pin P2 the output voltage on pin P3 42 switches from a
positive "on" voltage to a negative "off" voltage, thus turning off
TFT T1 41 and freezing the voltage to the gate of TFT T2 46, and
thus, freezing the emission from OLED D1 48 at the desired emission
level. One difficulty is that the resistance of optical sensor S1
50 is in the gig-ohm range causing the voltage across ground
resistor R1 51 to possibly fluctuate with any voltage noise near
the circuit. One of the greatest source of voltage noise comes from
the digital processing circuitry used to process the data from the
optical sensor S1. The reason for this is that the currents
required to produce significant voltage are typically very small in
a high impedance circuit. Therefore, the impedance should
advantageously be confined to the location of the pixel before a
noise free measurement can be made.
[0056] The present invention now described provides device, system,
method, and other means to overcome the limitations associated with
conventional active matrix displays generally, with any emissive
display type (including for example, electroluminescent devices,
plasma emission devices, or any other controllable emissive device)
more particularly, and with organic light emitting diode (OLED)
displays in particular, by providing a means to measure and track
the photon emission or luminance of a pixel (the integrated photon
flux over a defined period of time) and to use that information to
ensure that any degradation mechanisms, whether they be pixel
driver circuitry degradation due to gate threshold drift as in the
case of amorphous silicon, or degradation of the OLED materials
themselves, is compensated.
[0057] It will also be appreciated in light of the description
provided herein, that even when the emissive device is an organic
light emitting diode (OLED) there are several types, including but
not limited to small molecule OLEDs, polymer OLEDs (PLEDs),
phosphorescent OLEDs (PHOLEDs), and/or any other organic light
emitting diode constructed from any organic material in any
combination of single or multiple layers of organic materials and
electrodes.
[0058] Among the advantages of the invention, the invention
provides a system and method for measuring the luminance or photon
flux over time (the time duration of the frame) and storing that
information to be used at a later time by the display to maintain
uniformity, color balance and to extend life. The use of a photon
flux integrator (sensor S1 coupled with a capacitor C2 in a
particular circuit configuration) reduces noise found on feedback
systems operating with instantaneous photo currents and with
instantaneous feedback to the voltage drive system.
[0059] Among the advantages of the present invention, this
invention recognizes that the instantaneous photocurrents generated
by light emitted (actually the photon flux emitted) by the OLED
material in a pixel are too small to be used for controlling the
voltages on the pixel and thus, we devised an in-pixel photon flux
integration circuit so that rather than trying to measure the
instantaneous photon flux emitted by the pixel the invention
provides a device that integrates that flux over the time length of
a display frame. This causes the random instantaneous noise
fluctuations in the photon flux to cancel out over the frame time.
The invention also provides a system and display panel that
utilizes this pixel device structure, and methods for calibrating,
controlling, and operating the display. The invention therefore
overcomes the problems associated with conventional systems and
methods that have attempted to control pixel luminance using
low-magnitude, noisy, and fluctuating measured instantaneous light
or luminance measurements. The in-pixel nature of the integrated
photon flux measurements also compensates for pixel device material
and electrical characteristics, operating environment, and
operating history.
[0060] In at least one embodiment of the invention, a particular
luminance level produces a photocurrent in the sensor, and the size
or magnitude of this photocurrent serves as an indication of the
luminance (photon flux through the sensor). In at least one
embodiment of the invention, the photocurrent is proportional
(linearly or nonlinearly) to the luminance, and in at least one
embodiment the photocurrent is directly proportional to the
luminance, or linearly proportional within an acceptable non-linear
error. In one embodiment, either the current or a voltage created
across a resistive element (such as a resistor) by the current that
is measured to identify the luminance. In other embodiments,
voltage accumulated on charge storage devices, such as capacitors,
are measured to identify the luminance.
[0061] Embodiments of the invention are capable of maintaining a
pixel photon flux within one gray level (higher orders of accuracy
can be obtained if the bit level is increased--this is a matter of
cost) of an absolute photon flux reference level, and
pixel-to-pixel photon flux uniformity to within the same accuracy,
over the life of the display. The inventive system, device, and
method are also capable of adjusting the integrated photon flux
level of each and every pixel element (and hence also the pixel
color and display color balance) so that the life-time of a display
can be extended (and/or so that the aging or degradation can be
controlled in a preplanned manner), in spite of the known
degradation characteristics of OLED displays, over a relatively
longer period of time than in conventional systems and methods.
[0062] One convention associated with defining the life time of a
display is to use the time from an initial time (t.sub.0) when the
luminance is maximum to a half-life time (t.sub.x) which is the
time when the luminance has fallen to one-half of the initial
luminance. Thus, if the display has a 10,000 hour life time (time
t.sub.x) it conventionally means that the display will be one-half
as luminant (or have one-half the luminance) as it was in the
beginning (at time t.sub.0).
[0063] The inventive device, system, and method can actually extend
the practical lifetime of a display and display system by extending
the length of time to one-half of maximum luminance (by
compensating for the degradation that leads to one-half luminance).
For example, the inventive device, system, and method may extend
the period of time to half-life by a factor of 2, 3, 4 or more (to
2 t.sub.x, 3 t.sub.x, 4 t.sub.x, or more). In one embodiment, this
is accomplished by programming the display to permit a controlled
degradation over time. Recall, that the inventive device, system,
and method can actually compensate 100% (and of course for any
lesser amount of degradation) for the degrading of the luminance,
but the display will last longer if it is permitted to slowly
degrade. Achieving a 100% compensation requires that additional
voltage be available to apply to the gate of the OLED current
driving TFT. The available voltage determines just how long
degradation can be fully compensated. If, however, the aging is
partially compensated the display will eventually reach half
luminance, but is a longer time than an un-compensated display.
[0064] Uniformity as used here means that the normal or average
viewer will not usually be able to visually detect an aberrant
pixel luminance (where luminance or more loosely "brightness" is
used to describe the characteristic in some conventional systems)
or integrated photon flux (as a particular manner of characterizing
luminance according to embodiments of invention described in
specification) difference or color difference relative to other
pixels in the display. In the context of the invention to be
described, embodiments of the invention are able to maintain a
calibration so that no pixel is more than one-half gray level from
a reference level. In one embodiment, having 8-bit per pixel per
color data (256 levels of gray), the uniformity is maintained to at
or better than one gray level or .+-.0.4 percent. This is a pixel
quantization level of the display calibration, wherein if the pixel
is determined to have a luminance or integrated photon flux that is
different from the reference luminance or integrated photon flux,
the system and method drive the pixel to the gray level luminance
or integrated photon flux nearest the reference. Other embodiments
of the invention may quantize at a finer level of calibration, but
normally the human visual system will not detect a variation even
at the one-half gray level difference in a video display.
[0065] Recall that "brightness" is a subjective term. Luminance is
an objective term that has physical meaning and actual physical
units. The most common actual physical units used units today being
cd/m2 (candelas per square meter), which is the so called `nit`. In
the inventive device, system, and method, the sensor operates by
intercepting photons and turning them into charge carriers (holes
and electrons) making the material of the sensor a better conductor
and thus having lower resistance. In an embodiment of the
invention, the lower resistance of the sensor drains the charge on
a capacitor (C2). The amount of drained charge is directly
proportional to the number of photons that strike the sensor during
the frame time. That is, the photons are counted (integrated)
during the frame time. This integrated photon count is
quantifiable.
[0066] A numerical example is now presented, without benefit of
rigorous theory and by way of example to illustrate aspects of the
operation of embodiments of the inventive device, system. The
capacitance of the sensor capacitor (C2) is in the Pico farad (pf)
or 1.times.10.sup.-12 Farad range. If the capacitor has a
capacitance of 1.times.10.sup.-12 Farad, and if capacitor C2 drains
from an initial voltage of 10 volts at the beginning of the frame
to ending voltage or 4 volts at the end of the frame, then
6.times.10.sup.-12 coulombs of charge has passed to ground through
the sensor. (Actually the starting and ending voltages may be
selected at any value, however, voltage magnitude values in the 1
to 10 volt range are typical.) The corresponding amount of charge
is 6.times.10.sup.-12 coulombs. This is equal to about 37,745,000
electrons. Since it only takes 0.25 electron volts to promote an
electron into the conduction band and each light photon has an
energy of about 2 to 3 electron volts (depending for example upon
the photon wavelength or energy) it can be calculated that a red
photon has the ability to put about 8 electrons into the conduction
band and a blue photon has the ability to put about 12 electrons
into the conduction band. This means that the 37,745,000 electrons
would mean that about 4,681,000 red photons hit the sensor during a
16.7 ms frame time or that about 3,121,000 blue photons hit the
sensor in the same frame time. The above values and numbers are
provided as examples so that the principles may be understood and
are not provided as exact values determined via rigorous
calculation. The actual promotion of electrons into the conduction
band depends on many factors. Among the most important is quantum
efficiency, which is the amount of photon energy that promotes
electrons into the conduction band versus the amount of photon
energy converted into heating the semiconductor material.
[0067] It may therefore be appreciated that the invention operates
as a photon flux integrator for the capacitor, sensor, and frame
duration integration time. The photon flux is a flow of photons
through a unit area (the area of the sensor) and the total photon
count is the photon flux integrated over the sensor area and over
the frame or other appropriate partial frame or other integration
time. The invention also provides isolation so that the measurement
of parameters from one pixel do not impact the measurement of
parameters from another pixel.
[0068] The invention has several aspects that may be used
separately or for optimum effect in combination to provide a
greater synergistic effect. Some of these are listed below, while
others will be apparent from the description of the embodiments of
the invention and from the drawings.
[0069] In one aspect, the invention provides a Feedback Control
System and Method for High-Performance Stabilized Active-Matrix
Emissive Display. In another aspect, the invention provides an
Active-Matrix Display and Pixel Architecture for Feedback
Stabilized Flat Panel Display. In another aspect, the invention
provides a Method for Calibration of an Active-Matrix Display and
Pixel. These three aspects in particular, may advantageously be
combined so that a display panel having the inventive pixel and
sensor architecture and circuitry may be operated with off display
glass (or other display substrate) circuitry such as an off-display
integrated circuits (ICs) to provide a uniform and stable display
system.
[0070] In still another aspect, the invention provides a
High-Impedance To Low-Impedance Conversion System For Active Matrix
Emission Feedback Stabilized Flat Panel Display.
[0071] In even still another aspect, the invention provides a
High-Impedance to Low-Impedance Conversion Circuit for
Active-Matrix Display Pixel and Sensor.
[0072] In another aspect, the invention provides a Structure for
and Method of Design of a High-Stability Integrated Light Sensor
for Use in Feedback Control System and Method For Making Same.
[0073] In even another aspect, the invention provides Long-Life and
High-Stability Feedback-Stabilized Amorphous Silicon Photoconductor
Based OLED Display.
[0074] In another aspect, the invention provides computer programs,
computer program products, data structures and other computer
constructs and machines that may be embodied in tangible media or
memory devices and either executed within or stored on a computer
or other processor or hardware, including a processor and processor
coupled memory of either general purpose of special purpose
computers.
[0075] These and other aspects and features of the invention will
become clear in light of the description provided herein and the
referenced drawings.
[0076] Attention is first directed toward a comparison of an
embodiment of the inventive display pixel with a conventional pixel
structure so that aspects of the inventive pixel may be appreciated
prior to describing the manner in which its operation is
controlled. Then aspects of the closed-loop feedback control system
that may be used for the inventive display and pixel structure and
architecture as well as for other display and pixel structures.
Then several exemplary pixel structures, each having an emitter and
a sensor, are described that may be utilized with the inventive
control system. A method for calibrating the sensors to establish
reference integrated photon flux levels is then described as well
as some design methodology for designing sensors that have an
appropriate capacitance and dark and illuminated resistance to
provide the desired operation and support the inventive calibration
and operational procedures and methods. Operation of the calibrated
display and electronics so that stable and uniform operation is
maintained is then described.
[0077] When the pixel is on and radiating it emits photons at a
particular rate such that at any point in time there is an
instantaneous luminance. In the prior art the "brightness" referred
to that has been measured has been the instantaneous brightness. As
suggested in the Background section, one problem associated with
conventional systems and methods has been that the amount of photo
power intercepted by a sensor in a pixel is that the photon power
has been so small that random and/or non-random noise sources swamp
out the instantaneous signal. This is particularly problematic when
the read time for the pixel is small and such problems are
compounded when the read signal from one pixel cannot be
distinguished from other pixels. Note that power is the time rate
of energy and power is an issue in the prior-art as compared to the
instant invention. Photon flux and luminance are more-or-less
interchangeable terms in that both of these terms are power
terms.
[0078] With further reference to FIG. 1A, recall that the Kimura et
al. pixel structure connects photodiode D1 to the voltage supply
line for its voltage, and that this approach is problematic because
the exact voltage on that voltage supply line depends on the
current being drawn by all the other pixels attached to the line in
the same column. There is a voltage drop that depends on the on-off
state and gray level value of other pixels in the display column.
Recall also that a Kimura pixel lacks any isolation of the
photodiode TFTs for different pixels. This means that all the
sensor photodiodes in the column are contributing current to the
sensor read line at the same time and individual pixel sensor
values cannot be determined. Finally, recall that the Kimura pixel
and display configuration permits only a very short time to make a
current measurement (the current measurement is essentially
instantaneous) and that instantaneous measurements are imprecise
due to low power, low signal strength, and high noise levels.
[0079] By comparison, the embodiment of the inventive pixel in FIG.
1B overcomes at least these problems. The inventive device, system,
and method solve the problems associated with delivery of voltage
to the emissive diode, the sensor isolation problems, and the noise
and low power problem. The structure and operation of this pixel
and others are described in detail elsewhere in this
specification.
[0080] The photon flux integrator operates to store the energy
(which is the integral of power) delivered by the OLED to the
sensor in a capacitor. What this means is that a weak photon flux
is integrated over time for a duration of the display frame time,
for example the photon energy is integrated for 16.7 milliseconds
(16.7 ms) or 16700 microseconds (16700 .mu.s). In conventional
devices and systems, the energy is measured over a portion of the
row address time, which is typically about 5 microseconds (5
.mu.s). This means that in the inventive device, system, and
method, the power of the signal has been magnified by 16.7 ms
divided by 5 .mu.s microseconds for a gain factor of about 3,333
times. This represents a gain of about 35 db.
[0081] Furthermore, while the signal-to-noise ratio is greatly
increased by the 35 db of gain, the random noise is effectively
cancelled because on average during this lengthy integration time
there may generally be expected to be substantially as many
positive noise contributions as negative noise contributions of the
same magnitude. By integrating the signal over time random noise is
cancelled. These are significant advantages over conventional
systems and methods which require and therefore attempt to obtain
an accurate measurement of instantaneous luminance, however, they
do not succeed in obtaining an accurate measurement because the
signal to be detected is always plus or minus the random noise and
the magnitude of the random noise is at least comparable to the
magnitude of the signal to be measured. If, in addition, the
photo-sensor employed in the pixel has an impedance in or on the
order of the gig-ohm (10.sup.9 ohm) or greater range, the voltage
noise can be at the volt level, which would be a thousand times
greater than the signal.
[0082] As described elsewhere in the detailed description, an
additional difference between the inventive device, system, and
method as compared to conventional schemes is that the invention no
longer attempts to control the luminance of a pixel during the
identical pixel write time or cycle. In fact, in embodiments of the
invention, the integrated photon flux that is determined as an
indication of the pixel luminance during one display frame time (or
a portion of the display frame time) is used to control the
integrated photon flux (and by extension the pixel luminance)
during some subsequent display pixel frame time (or portion of such
pixel display frame time). In one embodiment, the subsequent
display time is the next frame time or a portion thereof, while in
other embodiments it is any future display time, such as a time
that is an integer multiple of frame times for that pixel, or a
subsequent time that is triggered by an event such as by display
power on. Therefore, although the control and adjustment may appear
to be real-time and be indistinguishable to the display user (e.g.
may lag by a frame time such as a 16.7 ms frame time) from a
real-time feedback based measurement and control, some
interpretations would suggest that it is not real time. On the
other hand, the measurement in one frame write cycle and the use of
the measurement to generate the pixel drive signal is in the next
frame write cycle are sufficiently close in time such that other
interpretations may consider such operation to be real-time or
near-real time. Where many minutes, hours, or days were allowed to
pass between the measurement of integrated photon flux and
adjustment of the pixel drive signal to take the measurement into
account, then the device, system, and method are less likely to be
characterized as real-time.
[0083] It will be appreciated that as OLED pixels (and other active
photon or luminance emitters) used in displays my typically change
over tens or hundreds of hours from a previous operating
characteristic, once a particular pixel has been adjusted, the need
to update a pixel's drive characteristic every frame diminishes.
Therefore, performing the measurement and adjustment every frame is
not normally necessary.
1. Exemplary Control System and Method Description
[0084] An exemplary display system 200 is illustrated in a first
embodiment of a feedback control system of FIG. 3 and includes two
primary components, a display device 201 having a plurality of
picture elements or pixels 202 and photon flux integrator circuits
203, and display driver and control electronics (optionally
including software and/or firmware) 204 to drive and control the
display device 201. The drive and control electronics are
responsible for converting image data 205 into the appropriate
pixel drive and control signals 206 to the pixels 202 so that their
apparent gray level or integrated photon flux (and their color for
a color display) within the image is correct or match a commanded
integrated photon flux and color. It will be appreciated that where
the basis set of OLED materials are appropriately chosen,
maintaining the proper color basis set (for example Red, Green, and
Blue) integrated photon flux will also maintain the color balance
of the pixel. The display device 201 also includes sensors and
sensors coupled with capacitors to form novel photon flux
integrators (in one embodiment sensor S1 coupled with capacitor C2)
associated with each individual pixels for measuring a
characteristic of the perception of luminance based on an
integrated photon flux over an integration period T.sub.PFI. The
sensors 203 generate a sensor output signal 207 (and in one
embodiment a plurality of sensors generate a plurality of sensor
signals) that is (are) communicated to the display drive and
control electronics 204 and used by the drive and control
electronics 204 to modify the pixel drive and control signal(s) 206
as necessary to achieve and maintain individual pixel photon flux
levels and achieve uniformity performance between and among the
plurality of pixels in the display. In one embodiment there is a
sensor 203 associated with and located within or adjacent to each
pixel 202 so that the pixel integrated photon flux and uniformity
is achieved on a pixel-by-pixel basis rather than globally for the
entire display.
[0085] The inventive device, system, and method also advantageously
provide for the measurement of the integrated photon flux for each
pixel separately and such measurement is not limited to the
measurement of a row of pixels, a column of pixels, or any other
set of collection of pixels together. Embodiments of the invention
also provide for separate pixel senor output signals so that it is
not necessary to sense or measure a current, voltage, or other
indication of photon flux, integrated photon flux, or luminance
serially over a common sensor line.
[0086] This pixel-by-pixel approach is particularly advantageous as
it permits adjustments and corrections to each and every pixel to
account for operational history differences of each and every pixel
so that in spite of these historical operational differences, the
same or any desired pixel integrated photon flux can be achieved.
For OLED display pixels or other display types where the integrated
photon flux and other operational parameters at any point in time
are highly dependent on past operational history at the individual
pixel level, this solves the display aging, display and pixel
"burn-in" problem, and other operating or age related problems.
[0087] Another embodiment of the invention incorporates at least
some of the features of the FIG. 3 embodiment as well as additional
features. In this embodiment, the image data 205 is received from
or generated by an analog image source 208 that provides an analog
signal, such as an RGB composite signal, separate component red
(R), green (G), and blue (B) signals, a monochrome or black/white
signal, or any other source or type of graphical, text, symbolic,
image, picture, or other data. This data may be dynamic (that is
changing over time) or static. Examples of such image data are
television (TV) analog or digital signals, computer display signals
(such as half-VGA, VGA, super-VGA, any of the digital display
interfaces, and the like), cellular or mobile telephone display
data, watches, appliances, automotive electronics display data
(such as for example automotive instruments, navigation, and
entertainment), aircraft avionics and in-flight entertainment,
fixed and portable gaming devices, billboards and other large
displays, and any other type of display and data.
[0088] When the image data is in the form of sequential or serial
frames or segments of analog data (such as a conventional
television signal), the data signal 205 (See FIG. 3) is processed
by serial-to-parallel (S/P) and analog-to-digital (A/D) processor
circuitry or logic 209 to generate digital red (R.sub.D) digital
green (G.sub.D), and digital blue (B.sub.D) signals. It may be
appreciated that monochrome or black/white signals may be achieved
for a color display by providing the same integrated photon flux
levels from adjacent R, G, and B emitters or pixels (sometimes
referred to as RGB subpixels). Alternatively, where only a
monochrome display is provided, then only a single pixel signal
representing the display image is required rather than three (RGB)
signals. Furthermore, where the image data is already in parallel
and/or digital form, either or both of the serial-to-parallel and
analog-to-digital conversion or processing may be eliminated. For
ease of description it will be assumed for purposes of this
description that the display is a color display and uses Red 210-1,
Green 210-2, and Blue 210-3 signals which will conveniently be
referred to as the digital image input data 210; however, it will
also be clear that the invention applies to monochrome displays
with only one digital input data signal. The description will also
user the more usual nomenclature of R, G, B, or simply RGB signals
to describe the three signals or data sets typically associated
with a color display or image. Whether such signals or data are
analog or digital will be apparent from the context of the
description. The RGB nomenclature will also stand for any set of
color dyes, phosphors, filters, or materials the form a color or
colors, or other basis sets (independent on number of color basis
element) that may be used to produce a true, false, or pseudo-color
display.
[0089] Normal display operation is carried out by the blocks in
FIG. 4 namely, Analog. Image Data 208, Image A/D converter 209,
Gray level logic Z103 (modified to accept an inventive input),
Display Controller Z104, Column Drivers 238, Row Select 240, and
the Active matrix Emissive display 292, 293, 294. Optionally the
Analog Image Data Block 208 and the Image A/D converter 209 may be
replaced by the Digital Image Data Block 208a. In either case,
digital image data is fed into the Gray Level Logic block.
[0090] A top level description of each of the blocks in the FIG. 4
embodiment is provided, followed by additional detail where
warranted. The Display controller Z104 controls all timing signals,
converts image voltage data into display voltage data. Column
drivers 238 down loads or otherwise communicates display voltages
to the rows. Row Select logic 240 enables the rows one at a time to
receive data from column drivers. Sample and Hold block Z101
samples and holds the sensor data from each row as it is addressed
by the row select. Analog-to-Digital (A/D) converter 270 is
responsible for converting the analog data at the Sample and Hold
block Z101 to digital data. Multiplexer (MUX) 270a coverts the
parallel data at the A/D converter into a serial data stream.
Calibration Memory 250 stores the original sense data that was
taken when the display was first manufactured, by pixel and by gray
level. Comparator 260 is responsible for performing a comparison
(such as a magnitude or difference arithmetic comparison) between
the pixel emission data and the calibrated data. The Digital or
Pixel Deviation Memory Z102 stores the deviation from calibration
for each pixel and gray level. Gray Level Logic Block Z103 may be
responsible for (i) determining a gray level strategy (simple
voltage, spatial and/or temporal dithering or the like for
achieving a desired luminance), (ii) for determining when to send
corrections to display driver controller, (iii) and for determining
or identifying how to correct the display driver controller using
the data stored in the digital deviation memory. Analog Image Data
block 208 sources image data in an analog format when the data is
provided in this form (becoming obsolete). Digital Image Data 208a
sources image data in a digital format (more and more prevalent
today) Image A/D Converter 209 converts the analog image data to
digital.
[0091] The Gray Level Logic block Z103 converts the digital image
data into a form which can be used by the Active-Matrix emissive
display to recreate an image faithfully corresponding to the image
data. Although functional blocks having some of the features of the
Gray Level Logic block of the invention are known in the art, they
are not the same as used in the inventive system and method, at
least in part because the inventive Gray Level Logic block Z103
includes an input for receiving values from Pixel Deviation Memory
Z102 (described in greater detail below) and structural and
methodological means for using both the output of image A/D
converter 209 and outputs from the pixel deviation memory Z102 to
provide novel inputs to Display controller Z104.
[0092] The Gray Level Pixel Logic function block Z103 may be any
circuit, logic, digital function (optionally including software
and/or firmware) or any other hardware, software, or hybrid
hardware/software means that converts the digital gray level
determined by the inputted image data to a voltage calculated to
cause the pixel specified to emit luminance at the same gray level
as required by the image.
[0093] It is understood in light of the description provided here
that there are many ways to reformat the image data to be able to
produce a display image with proper gray levels and colors. For
example, the Gray Level Logic block may include a gamma function
which transforms image voltage data into display voltage data that
will produce the proper luminance changes from one gray level to
another. Another function that may optionally be included in the
Gray Level Logic block would be a system to effect gray levels by
using temporal dithering; that is, by dividing each frame into two
or more sub-frames. Operating on x number of gray levels using just
one sub-frame (the other always remaining in the dark state) would
allow the doubling of the levels by using both sub-frames in the on
state. The Gray Level Logic block may also arrange to use spatial
dithering for gray levels. This means that each pixel would have an
array of sub-pixels, which would be turned on or off depending on
the gray level. Some limited forms of this approach are already
used color displays in order to use the three primary colors to
reproduce all the colors in the visible spectrum. The Gray Level
Logic block could also use a combination of temporal and spatial
dithering to accomplish the gray level function.
[0094] The data that emerges from the Gray Level Logic block is
sent to the Display Controller Block. The Display Controller block
literally runs the display. It provides all the timing signals that
control sending the display voltage data to the column drivers, and
it provides the timing of the row selection driver so that the
proper row is selected for the particular line of data being down
loaded to the display from the column drivers. The Gray Level Logic
block Z103 determines what voltages will be down loaded, and the
Display controller determines when the voltages will be down
loaded. The Column Drivers receive the digital voltage level for
the first row of the frame, converts the digital data to analog
data, and downloads the data to the first row of pixels which has
meanwhile been selected by the row select driver under the command
of the Display Controller. Since this is an active-matrix display
the data voltages are stored on a storage capacitor and to the gate
of the current controlling TFT, thus turning on the OLED in the
pixel. The display controller then sends the next row of data and
selects the next row of the display and so on until all rows in the
frame have been activated. There is then a retrace to the first row
and the next frame commences to be down loaded by the Display
Controller. These aspects of display operation are known in the art
and no further detail provided here.
[0095] The functional blocks and structure relating separately and
in combination to aspects of the invention are the Sample and Hold
Z101, the A/D converter 270, the multiplexer or MUX 270a, the
Comparator 260, the Calibration Memory (Cal Mem) 250, and the Pixel
Deviation Memory Z102. The Gray Level Logic block Z103 is also a
modified version of conventional gray level logic because it
includes structural and method components that permit it to accept
and utilize the output of the pixel deviation memory which are
themselves based on the results of comparator 260. In this
embodiment of the invention there are two memory blocks the
Calibration Memory 250 and the Pixel Deviation Memory Z102. In
other embodiment there may be more memory block or less. In the
interest of lower cost, the less memory the better. It is, however,
easier to understand the principles of invention by referring to
the two memory block in this embodiment. Other embodiments my
readily use a single memory. In the invention a photo-sensor system
called a photon flux integrator has been added to the pixel. When
the pixel is activated by the data sent by the column drivers light
is emitted in the form of a photon flux from the OLED. A portion of
that photon flux is intercepted by the photo-sensitive material in
the photon flux integrator, converted to electrons and collected by
the capacitor in the photon flux integrator. The collection of
photo-electrons continues for the full duration of the frame (at a
60 Hz frame rate this is a time duration of 16.7 ms). On the next
frame, the charge or voltage on the photon flux integrator
capacitor is read by the Sample and Hold Function out side the
display area. In one embodiment the voltage on the capacitor is
read and in another embodiment the charge on the capacitor is read.
The charge and voltage on the capacitor is proportional and is some
embodiments it is directly proportional to the luminance of the
pixel during the frame time.
[0096] While there are many ways to read voltage and charge known
in the art, FIG. 5 and FIG. 6 give examples of two embodiments.
These circuits and variations of them are described relative to
embodiments in FIG. 7 and FIG. 8. It will be appreciated that the
circuits and methods for reading voltage and charge (or current)
are known in the art and that the circuits and methods described
here may be applied to a variety of different pixel circuits and
structures, including to different pixel emitter circuits, pixel
sensor circuits, and/or pixel photon flux integrator circuits.
[0097] The FIG. 5 embodiment is a voltage sensing circuit. Line L1
supplies voltage to both power transistor T2 and sensor S1. The
dark resistance of sensor S1 is extremely high and sensor capacitor
C2 receives very little charge through S 1 when the pixel is off.
During the frame time when OLED or other emissive device or diode
D1 (such as an OLED) is in the on state and a photo flux is
received by S1 the conductivity of S1 significantly increases and
allows charge to flow into sensor capacitor C2 causing a voltage to
appear across C2 with respect to ground. (Note that the combination
of Sensor SI and sensor capacitor C2 in the context of the rest of
the circuit are operative to form a photon flux integrator device.)
This voltage is proportional to the photon flux level emitted by
D1. In order to read the voltage on C2, sensor TFT transistor T3 is
turned on by applying a voltage to line L2 (this occurs when the
row is enabled). The voltage of sensor capacitor C2 is subsequently
applied to the plus terminal of an operational amplifier (op amp)
OA1 or equivalent amplifier circuit. The negative terminal of the
operational amplifier OA1 is coupled to a reference node such as
ground G2. This voltage is amplified by the ratio of resistor R2
(in the voltage sensing amplifier to the line resistance of L4
which is coupled to the positive input of operational amplifier
OA1. For example, if the line resistance of line L4 is 3K ohms and
the resistance of resistor R2 is 3 Mohms, the voltage on capacitor
C2 is amplified by 30 dB (1000 times), which voltage appears at
node P4. The amplified voltage is sent to a sample and hold circuit
for further processing.
[0098] Another embodiment is shown by FIG. 6. In this embodiment,
when a voltage, for example, 10 volts, is applied to the plus
terminal of charge amplifier CA1, line L4 quickly also ramps up to
10 volts. A resistor R1 is coupled between the negative input
terminal of the charge amplifier and its output at note P3, and
capacitor C3 is connected in parallel across resistor R3. The
voltage appearing at node P3 is an offset voltage determined by the
characteristics of charge amplifier CA1 and any leakage current on
L4. This leakage current typically may arise from the fact that in
a multi-row display each row will have a transistor T3 attached to
line L4 and although the T3s is every row except the row that is
enabled will be in the off state there still is an off state
current leakage associated with each T3. Capacitor C2 is charged up
to the voltage on the plus, terminal of CA1 when T3 is turned on.
Any charge flowing into C2 reduces by the same amount the charge
across C3 and the voltage rises on node P3. Resistor R1 may usually
be a large resistance that allows the reduced charge on C3 to be
restored for the next reading. In practice a reading of P3 is
advantageously made prior to turning on transistor T3 in order to
measure the offset voltage. Then another reading is made after T3
is turned on and the first reading is subtracted from the second
reading to give a value for the amount of charge that flowed into
C2. Therefore, as in the embodiment of the circuit of FIG. 5, the
photon flux from D1 causes charge to move from C2 to ground during
the frame duration. When line L2 is again selected for the next
frame, the charge on C2 is read by the charge amp circuit.
[0099] The column drive unit 238 works in conjunction with line
buffer 236 and row select unit 240 too sequentially select and
sends pixel signals to each subsequent row of the display. The
operation of column drive unit 238 and row select unit 240 are
generally known in the art and not described in further detail
here.
[0100] A sensor 294 is positioned or disposed within or adjacent to
pixel 292 so that it can receive at least a portion all of the
light, photons, or other radiation that may emanate from pixel 292
when the pixel is driven by the column drive circuitry at a level
what causes it to emanate. The sensor 294 may also be responsive to
ambient light or radiation levels. Sensor 294 may be any type of
sensor that undergoes a measurable change in physical or electrical
characteristic in response to different levels of the incident
light or radiation.
[0101] Sensor 294 therefore generates an electrical signal, in the
form of a photo current that is a measure of, or otherwise
indicative of, the incident photon flux on the sensor during the
period of the frame time of the measurement. In one embodiment of
the invention, the sensor measures the integrated photon flux over
a defined period time. In at least one embodiment of the invention,
the defined period of time is the frame period. It is noted that
most displays operate at a frame rate of at least 60 Hz so that the
content (such as a image) displayed does not appear to flicker to a
human observer. A frame rate of 60 Hz corresponds to a frame time
or period of substantially 16.7 ms. Other displays operate at
higher frequencies to further reduce the possible flickering. A
frame rate of 100 Hz corresponds to a frame time or period of
substantially 10 ms.
[0102] The invention is not limited to any particular frame rate,
and is applicable to non-interlaced and interlaced display types.
Furthermore, while much of the description indicated that the photo
flux is integrated for a period of exactly or substantially the
display frame time, there is no reason why the photon flux
integration need extend for the full frame time so long as the time
is long enough to provide an integrated photon flux of sufficient
magnitude in absolute terms and relative to the noise, and so the
positive and negative contributions to random noise cancel within
required margins. It is anticipated that photon flux integration
times on the order of between at least one-quarter of a frame time
and one frame time may readily be used, and that photon flux
integration times as short as about one-tenth of a frame time (e.g.
1.67 ms) may also be used as this still provides a gain of 333
times as compared to the typical 5 .mu.s instantaneous time for
measurement in the prior-art as explained in the previous example.
Even a photon flux integration time of between one one-hundredth
and one-tenth of a frame time may provide satisfactory performance.
Typically the integration time will be one frame time so that a
single set of control and timing signals may be used for the pixel
write operations and integrated photon flux sensor read operations.
It is anticipated that even time frames as short as the row address
times may be practical with the use of noise canceling
circuitry.
[0103] It is noted that most displays operate at a frame rate of at
least 60 Hz so that the content (such as a image) displayed does
not appear to flicker to a human observer. A frame rate of 60 Hz
corresponds to a frame time or period of substantially 16.7 ms.
Other displays operate at higher frequencies to further reduce the
possible flickering. A frame rate of 100 Hz corresponds to a frame
time or period of substantially 10 ms. The invention is not limited
to any particular frame rate, and is applicable to non-interlaced
and interlaced display types.
[0104] If photon flux is measured in photons/second/meter-squared,
then the sensor is integrating or counting the total number of
photons intercepted over the sensor area during that time period so
that sensor is acting as a photon counter and not as an
instantaneous detector of photons, electrons, or other energy or
particle. The integration over time permits the acquisition of a
single magnitude sufficient to overcome instantaneous noise that
may be present and of a signal that is relatively stable from frame
to frame assuming that there are no changes in the display pixels
or the electronics that drive the display pixels.
[0105] It will be appreciated that each pixel (really each subpixel
when implemented in a tri-color RGB color display) within each
display row has an associated separate sensor 294, and that each
sensor 294 generates and communicates a sensor output signal 207 to
off-display glass electronics. In one embodiment this sensor output
signal is a voltage (Vs), but in other embodiments the sensor
output signal is a current (Is). Additional signal processing
structures or circuits may be provided either within the pixels or
subpixels, display, or in off-display glass processing circuitry to
convert from one signal type to another and/or to derive a
different signal from the raw sensor signal. In order to simplify
the discussion, this description is limited to the manner in which
the sensor signal 207 from a single particular sensor is processed
through the drive and control electronics 204 to achieve the
desired operation and display uniformity. In reality each pixel
(and sub-pixel) has a sensor that generates and communicates a
sensor output signal 207 to off-display electronics so that a
pix-by-pixel (and subpixel-by-subpixel) measurement and feedback
based correction can be made. In a separate portion of this
description, the calibration and operational procedures will
described the manner in which pixel sensor data is used to correct
display nonuniformity.
[0106] Sensor output signals 207 (one for each column in the
display) are simultaneously captured by Sample and Hold Z101,
processed by analog-to-digital (A/D) converter 270 and MUX 270a to
convert the normally parallel analog signals 207 into serial
digital signals or value Vs 276. This digital sensor signal 276 is
received by a signal comparison unit 260 that is responsible for
comparing the measured pixel integrated photon flux (as indicated
by the sensor output signal 276) with a reference pixel integrated
photon flux value 251 that corresponds to the expected pixel gray
level stored in calibration memory 250. It will be appreciated that
signal levels may be scaled or otherwise processed so that the
comparison unit 260 compares signals having the same scale or range
so that precise and accurate differences can be computed. The
difference between the reference value and the sensed value for
that particular pixel is referred to as the difference or delta
gray scale .DELTA..sub.GS amount and is sent to Pixel Deviation
Memory Z102.
[0107] The reference voltage stored in calibration memory 250 may
be generated in any number of different ways. In one embodiment the
values placed in calibration memory 250 are generated at the
manufacturing point where the active-matrix back plane has been
completed before the OLED materials are deployed over the back
plane. At this point the active-matrix is fully exposed to ambient
luminance. Therefore, the display may be sequentially exposed to
calibrated gray levels and each sensor scanned as though in normal
operation with the measured sensor values being electronically
stored and later introduced into calibration memory 250. Another
embodiment uses a procedure in which display manufacture is
completed, which includes adjusting the Gray Level Logic block Z103
to produce the desired color mixing and luminance uniformity using
practices well known in the industry. When the display is first
booted up or turned on it may enter a calibration mode where it is
assumed that the first sensor values are correct since the display
has no aging history. These first values are stored in the
calibration memory and subsequently used to maintain the initial
condition of the display.
[0108] The Pixel Deviation Memory Z102 contains the status of all
pixels with reference to the initial conditions, or to initial
calibration in manufacturing. It is the purpose of the Gray Level
logic functional block Z103 to produce the correct digital voltages
that will faithfully reproduce the image data on the display.
Procedures for accomplishing this are well known in the display
industry and therefore not described in further detail here.
[0109] In embodiments of the present invention the decisions made
by the Gray level logic function are modified by the data stored in
the Pixel Deviation Memory. In one embodiment, for example, if the
data in the Pixel Deviation memory indicates that pixel has
degraded by two gray levels, then the Gray level Logic function
adds two levels of gray scale to the normal digital voltage level
determined for the image data. Another embodiment would be to
subtract two levels of gray from all the other pixels and thus
maintain color balance, but decrease the dynamic range of the
display. Another embodiment use an approach wherein the on time of
the degraded pixel is increased in order to increase its perceived
luminance by two gray levels. Other embodiments involve spatial
and/or temporal dithering using techniques will known in the
industry.
[0110] Embodiments of the invention provide for performing the
calibration at any time either automatically according to some
rule, policy or schedule, or manually by the user. Automatic
calibration is preferred. Two particular schemes are to perform the
calibration every frame, at some integral number of frames interval
where that interval can be any number, a power-on, at power-down,
at some elapsed time interval (e.g. every 1 hour) or according to
any other scheme. It will be appreciated that the user is not aware
that the calibration is occurring and there is no or substantially
no loss or overhead associated with the calibration once the
structures for performing the calibration are in place. Operations
such as additional write operations to memory and/or additional
switching or logic operations represent the only additional
activity, but these are inconsequential compared to the other
operations that occur.
[0111] These and the other circuits described herein may be
implemented as integrated circuits either on the same substrate as
the display (e.g. the display glass) or on separate substrates off
the display. In general the control system elements may
advantageously be provided off of the display substrate. In
particular embodiments of the inventive control system and circuits
provide the sample and hold circuits Z101, analog-to-digital
converter circuits 270, multiplexer 270a, comparator circuits 260,
calibration memory 250 and pixel deviation logic Z102a and pixel
deviation memory Z102b. The display controller Z104, gray level
logic Z103, and image A/D converter 209 may also advantageously be
implemented as one or more integrated circuits off of the display
substrate. Embodiments of the pixel circuits described in detail
hereinafter are implemented as structures for each pixel on the
display glass or substrate.
2. Exemplary Pixel Device Structures and Circuits
[0112] One aspect of the invention provides a conversion from a
high impedance to a low impedance. The conversion from high
impedance to low impedance occurs at least in part because of the
structure, configuration, and/or operation of the sensor capacitor.
The sensor operation of charging or discharging the sensor
capacitor C2 is a high impedance operation since the sensor has
gig-ohms of resistance. During this charging or discharging time,
the sensor line is isolated from the high impedance by sensor
transistor T3. During the read time sensor transistor T3 is opened
connecting the sensor capacitor C2 (which had been isolated from
sensor line L4) to the sensor line L4.
[0113] Impedance between the sensor capacitor C2 and the sensor
line L4 is only the resistance of the sensor line, which would
normally be only about 3 Kohms for typical implementations. The
impedance difference is therefore on the order of one million to
one (10.sup.6:1). Interference from noise results in nano-amps of
current flow which in a gig ohm impedance system amounts to noise
that is on the order of volts, but in a kilo-ohm impedance system
amounts to micro-volts. Since it is the long length of the sensor
line L4 in a typical display implementation that picks up the noise
interference, a measurement should preferably not be made when the
sensor line is connected to a high impedance system. When the
sensor S1 is isolated by sensor TFT T3 any noise affecting the
sensor S1 has to be picked up by the extremely short lines of the
pixel circuitry; therefore, very little if any noise affects the
charging or discharging of the sensor capacitor. These switching
and impedance characteristics contribute to the successful
operation of the pixel and sensor circuits.
[0114] Two exemplary pixel with sensor circuits are now described
that may be used with the inventive display, display control system
and method, and sensor readout circuits and methods. Although
particular pixel emitter, sensor, and circuit topologies are
described relative to these two embodiments, it will be appreciated
that the invention is not limited to only these particular circuits
or device structures and that variations in the design and the
particular electrical circuit devices may be modified, such as by
changing the types of control devices to be other than particular
transistors, TFT, diodes, or the like and substituting any
two-terminal or three-terminal control or switching means. While
the transistors are indicated as being TFT type transistors, the
invention is not limited to only TFT type transistors. Furthermore,
other alterations to pixel circuit topology, such as by adding
additional circuitry may be made without departing from the spirit
and scope of the invention. The type of emissive device may also be
modified to be other than an OLED emitter and for example any
active emitter may be used including but not limited to inorganic
photon emitting devices or structures; and the characteristics of
the sensor may be modified so that in addition to photoresistive or
photoconductive devices, any sensor device that undergoes a change
in response to incident photon flux may be substituted
[0115] One of the advantages of both of the circuits described
relative to the embodiments in FIG. 7 and FIG. 8 are that they
provide a high-impedance to low-impedance conversion system for an
active matrix emission feedback stabilized flat panel display, such
as an OLED display. The circuits of FIG. 7 and FIG. 8 provide this
by isolating the off display glass or substrate circuitry (such as
voltage comparator amplifier VC1 and switching transistor TFT T4)
from the high impedance of sensor S1 in the pixel during the photon
flux integration operation, which occurs during the frame time. The
design of the circuits prevents noise on sensor line L4 that would
result if sensor line L4 was connected to a high impedance
source.
[0116] In this regard, it is well known that a conducting line
connected to a high impedance will pick up electromagnetic
interference from the environment. This is easily demonstrated by
observing the behavior of a volt meter with the plus and minus
leads open in the air. The voltage will continually range from plus
a few volts to minus a few volts due to radio and TV interference.
Since S1 has a resistance in the gig-ohm range and higher, it acts
like an open circuit to sensor line L4 if L4 is connected directly
to sensor S1 without benefit of sensor capacitor C2. During the
photon flux integration time sensor TFT T3 is turned off. While
power supply line L1 is not isolated from sensor S1 in this pixel
circuit configuration, noise on power supply line L1 does not
affect the operation of the pixel or the display since power TFT T2
is operating in the saturation mode and therefore changes of
voltage (even on the order of volts) across power TFT T2 due to
noise does not change the current through T2, and therefore the
emission of photons from pixel diode emitters D1 for all pixels in
the display remains stable.
[0117] Furthermore, any noise picked up by power supply line L1
fluctuates around zero volts (that is on average it has
substantially equivalent positive and negative fluctuations about
zero volts) during the frame time when sensor capacitor C2 is
charging through sensor S1; therefore, the noise cancels out and
the voltage on sensor capacitor C2 after the frame time is complete
is due only to the discharge rate of sensor SI when photons are
intercepted. During the row address time when the voltage on line
selection voltage line L2 goes high and turns on drive TFT T1 and
sensor TFT T3, the voltage on sensor capacitor C2 is read by the
voltage comparison amplifier VC1 at its sensor input on P1. This
sensor input at P1 is compared with a reference voltage at P2 on
its other input to generate a difference or error voltage at output
P3. Noise does not interfere during the reading of the voltage
present on sensor capacitor C2, because the current induced by
noise is in the nanoampere range and at most may cause slight
changes in the charge on capacitor C2, but since virtually no
current goes though the high impedance no voltage results from the
low level of noise interference.
[0118] One of the primary differences between the circuits of the
embodiments of FIG. 7 and FIG. 8, is that in the FIG. 7 circuit
embodiment, the voltage on sensor capacitor C2 at the beginning of
the frame is zero volts and provided by turning on grounding TFT T4
at the end of the read time during the row address time. The
voltage on the other side of sensor capacitor C2 is at the line L1
voltage which is the supply voltage to power transistor T2, which
may for example be at +10 volts. As sensor S1 in combination with
sensor capacitor C2 integrates the photon flux from OLED D1 over
the frame time, the voltage at the point P5 between C2 and T3 rises
toward the supply voltage on L1 (e.g. toward +10 volts). The more
photons received by sensor S1 and integrated by the combination of
sensor S1 and sensor capacitor C2, then the closer the voltage
between sensor capacitor C2 and sensor transistor T3 comes to the
supply voltage on line L1. While this circuit has many advantages
over conventional circuits and methods, a possible drawback of this
particular embodiment of the circuit in an actual implementation is
that the supply voltage on line L2 may possibly fluctuate a small
amount due to the number of pixels and the level of OLED emission
from each pixel being supplied by L1. Since this can be any
combination of pixels and emission levels the voltage reading on
sensor capacitor C2 may theoretically have some slight ambiguity
but this ambiguity may generally be small and performance still an
improvement over conventional circuits and methods.
[0119] The circuit 380 described by FIG. 8 on the other hand is
referenced to ground and to the voltage of Vcap 355 that is fed or
communicated to sensor capacitor C2 327 through the sensor TFT T3
330 and TFT T4 340 transistors during the address time.
[0120] Although the two circuits have a somewhat different
structure and operation, they have certain features in common. In
each of the circuits, an emissive device (such as an OLED diode)
coupled to ground is driven by a controlled current source (such as
a TFT transistor T2). The pixel data value in the form of a voltage
is applied to the control terminal (TFT gate) so that the pixel
emission (number of photons) is related to its intended integrated
photon flux. Recall that a sensor S1 324 and a capacitor C2 327 are
coupled as a photon flux integrator device 339 (along with
supporting circuitry) with the pixel emissive element (OLED diode)
so that a representative and measurable number of the photons
emitted from the emitter are incident on the sensor and the
combination of the sensor and capacitor generates a photon count.
The sensor S1 and capacitor C2 combination integrates or counts the
total number of photons it has collected during a defined period
(in one embodiment the display frame time of 16.7 milliseconds).
This integrated photon flux is a useful measure because it provides
greater repeatability and immunity from noise than any
instantaneous measure, provides a larger signal amplitude, and the
integrated nature of the photon flux may likely be more
representative of the integrated photon flux perceived by a human
observer owing to the relatively slow response and latency of the
human visual system.
[0121] A reference integrated photon flux has been established, and
the sensor signal is then communicated to the control system and
used with the reference to adjust the data signal that is applied
to the control device during the next calibration period (such as
the next frame) so that the actual pixel integrated photon flux
(effectively photons emitted by the OLED diode or other emitter)
matches the desired integrated photon flux (number of photons
identified during calibration).
[0122] Having now described some of common aspects of the pixel
circuit structure and operation, attention is now directed to a
more detailed description of the two embodiments illustrated in
FIG. 7 and FIG. 8.
[0123] An embodiment of an active matrix display pixel with
emitter, sensor, photon flux integration, and control components is
now described relative to FIG. 7. A pixel diode drive transistor T1
310 is coupled to a image voltage line L3 301 at its drain
(D.sub.T1) terminal 311, to a first terminal 315 of storage
capacitor C1 314 and to the gate terminal (G.sub.T2) 323 of a power
control transistor TFT T2 320 at its source (S.sub.T1) terminal
312, and to a line selection voltage line L2 302 at its gate
(G.sub.T1) or control terminal 313. Power TFT transistor T2 320 is
coupled to power supply voltage line L1 301 at its drain terminal
321, and this drain terminal is also coupled to a first terminal
325 of sensor S1 324 and to a first terminal 328 of sensor
capacitor C2 327 at a common node. A second terminal 316 of storage
capacitor C1 324 is coupled to the source terminal 322 of power TFT
T2 320 and to the input terminal 337 of emitter (OLED diode) 336.
The output terminal 337 of OLED emitter 336 is coupled to ground
305. A second terminal 326 of sensor SI 324 is coupled to the
second terminal 329 of sensor capacitor C2 327. A calibration read
voltage (Vcal) is measured or read at node P5 334 defined by the
connection of sensor S1 output at 326 and the sensor capacitor
terminal 329 as described hereinafter. This node P5 is also coupled
to the source terminal 331 of sensor TFT T3 330. Sensor TFT T3 330
is also coupled at its source terminal 332 to sensor line L4 304
which provides an input signal at an input port P1 351 of voltage
comparator VC1 350. Voltage comparator 350 receives a reference
voltage at a second input port 352 and generates a difference or
error signal P3 353 computed as the difference between the P1 351
and P2 352 inputs. In this embodiment, the sensor output that is
applied as an input to the voltage comparator VC1 350 is also
applied at a common node 351 as the drain terminal 341 input of
grounding TFT T4 340. The source terminal 342 of TFT T4 340 is
coupled to ground 306, and receives a control signal 344 at its
gate terminal 343. These transistors provide switching to connect
pixel elements at times and to isolate other pixel elements at the
same or different times so that tight management, control, and or
measurement of small voltages, currents, charges, and/or photon
counts may be precisely and accurately accomplished. Note that the
sense of source and drain terminals of the TFT may be reversed
depending upon the n- or p-type of material used for the TFT
transistors.
[0124] While certain elements of the circuit described cooperate
and contribute to operation of the pixel emitter, the pixel photon
flux integrator, and the measurement and calibration operation,
some approximate categories may be developed to assist the reader
in understanding aspects of the invention; however, these
categorizations are should not be applied to limit the scope of the
invention as elements of the circuit described contribute to more
than one category at some times and not at all at other times as
described in detail in this specification. With this in mind, drive
TFT T1, storage capacitor C1, power control TFT T2 and diode D1 may
contribute primarily to operation of the OLED diode emitter; sensor
S1, sensor capacitor C2, and sensor TFT T3 contribute primarily to
the operation of determining or generating an integrated photon
flux measurement; and voltage comparator VC1 and grounding TFT T4
in this embodiment contribute primarily to reading the integrated
photon flux measurement and determining a difference between that
measurement and a reference so that a correction may be applied to
adjust the pixel emitter luminance as indicated by the measured
integrated photon flux.
[0125] Having described the general topology and connectivity of
the circuit elements in FIG. 7, attention is now focused on its
operation so that additional aspects and advantages of the
invention will be better appreciated. A power source voltage
(V.sub.PS) typically in the range of 10 to 15 volts is applied to
line L1 301, which serves as the power source for both OLED D1 336
and the charging source for sensor capacitor C2 327. The invention
is not limited to any particular range and higher and lower
voltages may be used consistent with device characteristics. At the
same time, a line selection voltage (V.sub.LS) is applied to line
L2 302 causing data drive TFT T1 301 to turn on. Also at the same
time an image voltage (V.sub.IM) representing the image to be
displayed and referred to as the image voltage is applied to line
L3 303, and due to the fact that data drive TFT T1 301 is turned on
(or conducting), this image voltage (V.sub.IM) is delivered by TFT
T1 to the gate G.sub.T2 323 of power control TFT T2 320 and storage
capacitor C1 314. This causes a device current (I.sub.D1) to be
delivered by TFT T2 320 to OLED D1 336 and a specific light
emission level is emitted from OLED D1 336 that is calculated to be
the proper light emission (E.sub.CALC) required by the image. When
the display is new and freshly adjusted by the manufacturer the
image voltages will produce the correct pixel/OLED emission values.
In one embodiment, sensor S1 324 is physically located in contact
with the semiconductor anode side of the OLED D1 336 for optimum
optical coupling so that sensor S1 collects or intercepts at least
a portion of the light emitted by OLED during its emission, and
preferably as much of the emitted photons as possible so as to
improve integrated photon count and signal strength. In terms of
luminance, in this embodiment sensor S1 receives the same or
substantially the same luminance as the OLED pixel emits, because
the flux density striking the pixel (the sensor portion of the
pixel) is the same as the flux density emitted by the pixel (the
emitter portion of the pixel) as a whole because the portions are
preferably (but not necessarily) in contact. (Other embodiments
provide the sensor S1 to be physically located near the OLED so
that it collects or intercepts enough light to provide useful
sensor signals but not in contact with the anode side of the OLED
D1.) In one embodiment, the sensor S1 is a photoresistive (or
photoconductive) sensor in which the resistance decreases (or
conductivity increases) with increasing photon flux density emitted
by the OLED emitter.
[0126] During the frame duration (T.sub.FR), which at 60 frames per
second (fps) is 16.7 ms, the light emitted from OLED D1 336
impinges on sensor S1 324 and causes a resistance (R.sub.S1) 347
component of the sensor S1 324 to decrease in proportion to the
intensity of the light (photon) emission. During the display frame
time, sensor capacitor C2 327 is being discharged through sensor S1
324. The frame duration and the average resistance (R.sub.ave) 348
of sensor S1 during the frame time determine the amount of charge
discharged by sensor capacitor C2. The amount of charge discharged
by sensor capacitor C2 is an important parameter because it
controls or determines the voltage (V.sub.CAL) on the node P5
connected between sensor capacitor C2 and sensor TFT T3. This read
calibration voltage will be the read value sent to the circuit or
other logic that determines the correction that is used to
calibrate and maintain the uniformity and color balance of the
display during normal operation. (Different embodiments of the
invention provide different read circuits which are described
elsewhere in this specification.) It is important to note that the
higher the voltage measured at the node P5 between sensor capacitor
C2 and sensor TFT T3, the greater amount of photon flux (pixel
luminance) that was detected or intercepted by sensor S1. This
happens because the lower the resistance of S1, the closer (or the
smaller the difference) the voltage at the node P5 between sensor
capacitor C2 and sensor TFT T3 comes to the supply voltage on
L1.
[0127] With reference to FIG. 8, there is illustrated a second
embodiment of the present invention. Like numbered elements in this
specification have the same or similar operation unless such
differences are described. There are many similarities between the
two circuits and the entire topology and connectivity of elements
is not repeated here. In this embodiment sensor capacitor C2 327 is
first charged to a predetermined voltage as it was in the first
embodiment of FIG. 7 using the power line, but in this embodiment
sensor capacitor C2 327 is charged through the sensor line by TFT
T4 340 and a capacitor charging voltage source (Vcap) 355, such as
for example to +10 volts (or to any other voltage value). (Recall
that the FIG. 7 embodiment does not utilize a capacitor charging
voltage Vcap in this manner and note that the TFT T4 transistor is
operable to interact between the P1 input of the voltage comparator
350 and Vcap 355 rather than between the P1 input and ground
306.)
[0128] During the frame time (for example, a frame time of about
16.7 ms for a 60 frame/sec (fps) system), light or photons from the
OLED D1 causes the resistance of sensor S1 324 to decrease and
accelerate the discharge of sensor capacitor C2 327 to ground. As
compared with the FIG. 7 embodiment, in this FIG. 8 embodiment the
voltage on sensor capacitor C2 336 moves towards the ground voltage
at G1 305 (or other voltage) instead of moving towards the positive
supply voltage as in the FIG. 7 embodiment. Therefore, the greater
the photon flux emission from OLED D1, the lower the resistance of
sensor S1, the greater the current during the frame time discharge,
and the lower the voltage remaining on sensor capacitor C2 when
sensor capacitor C2 is measured during the read time. This FIG. 8
embodiment therefore has advantages over the FIG. 7 embodiment,
because the charge voltage may be better controlled on the sensor
line L4 than it is on the supply voltage line L1, but both
embodiments are useful and have significant advantages over
conventional circuits and methods. In general for an actual
implementation, the voltage on supply voltage line L1 varies
according to the amount of current being delivered by line L1 and
the row being measured. For many display architectures, the higher
the row number the further away the row will be from the line L1
power supply and more current times resistance (I*R) voltage drop
in the line to that row. By comparison, because the sensor line L4
in this embodiment only delivers current when a reading or
measurement is being made, or when sensor capacitor C2 is being
re-charged, the voltage is highly stable and not subject to
possible variations as the supply voltage line may be so
subject.
[0129] These and the other circuits described herein may be
implemented as integrated circuits either on the same substrate as
the display (e.g. the display glass) or on separate substrates off
the display.
3. Embodiment of Calibration of the Sensors and Circuit
[0130] The sensors may be calibrated during manufacturing before
the display is completed (pre-manufacture calibration) or after
manufacturing has been complete (or at selected stages in between
these two times). The first embodiment of calibration is the
calibration during manufacturing. FIG. 9 is an illustration showing
an embodiment of the calibration flow chart for pre-manufacturing
calibration. The point of calibration is after the active-matrix
and sensor circuitry has been completed, but before the OLED
structure has been deposited on the active-matrix back plane. At
this point the completed active matrix back plane is inserted into
a test fixture that connects all the display inputs except the L1
supply voltage to a display control board which drives the
active-matrix backplane in an identical fashion as it will be in
full operation as a display. There need be no connection to L1
since there is no OLED D1 yet integrated with the back plane. This
calibration process is described relative to the second embodiment
of the pixel circuitry illustrated and described relative to FIG.
8, where capacitor C2 is charged through the sensor line and
Vcap.
[0131] First (Step 801), the active-matrix backplane (am backplane)
is loaded into the test fixture which is connected to the display
control system, such as for example the control system illustrated
in FIG. 4.
[0132] Second (Step 802), the am backplane is uniformly illuminated
with a calibrated laboratory uniform light source at a luminance
equal to gray scale luminance 1. (This step may be performed with
the backplane uniformly illuminated with a light source at a
luminance equal to gray scale luminance of a different level, such
as another low level illumination so long as the level is known and
the calibration procedure takes this different level into account,
but this approach is not preferred.)
[0133] Third (Step 803), the display controller Z104 sends a select
row 1 to Row Select 240 to turn on all the T3 transistors in row 1
of the display.
[0134] Fourth (Step 804), since the third step (Step 803) turned on
all the transistor T3s in row 1, and charge flows from the sensor
line L4 into capacitor C2 charging it to a voltage, such as for
example, charging it to 10 volts.
[0135] Fifth (Step 805), when capacitor C2 charges, the current is
sensed by operational amplifier (OP amp) to generate VC1 and the
value is sampled and held by Z101 for each pixel in row 1.
[0136] Sixth (Step 806), the sampled and held voltages are
digitized and multiplexed (MUX) to a serial data stream by A/D
Converter 207 and MUX, 207a. The sequence of the D/A and MUX may be
interchanged with no affect on performance.
[0137] Seventh (Step 807), the display controller Z104 directs the
serial data stream to be stored as the zero line to Calibration
Memory (Cal Mem) 250. This is referred to as the zero line because
this data is on sensors that have not had the full frame time to
photon flux integrate the gray level.
[0138] Next (Step 808), Steps 803 through Steps 807 are repeated
for all rows in the display to be calibrated (usually every row)
until all rows in the frame have been sampled. At this point the
first gray level of emission for the first row has been integrated
by S1 and C2 for the full frame time.
[0139] After all rows have been calibrated for the gray level 1
value, the next step (Step 809) repeats Steps 803 though Step 807
for the next gray level to be calibrated, usually gray level 2 in
the preferred embodiment. The sample and held values determined
from Step 806 are the proper values for the first gray level and
are stored in Step 807 to the first row values for gray level
1.
[0140] In a final step (Step 810), each of the first nine steps
(Step 801 through Step 809) are repeated until all gray levels have
been sampled and stored to Calibration Memory (Cal Mem) 205. Note
that in one embodiment, the last or highest gray level (e.g. gray
level 256 for an 8-bit system) may be or is run for two frames
since the gray level values recorded at the beginning of the
256.sup.th frame are for the 255.sup.th gray level and this assures
that the final value is stored in the Calibration Memory 250.
[0141] The second embodiment for calibration (post-manufacture
calibration), calibrates the completed manufactured display, such
as for example when the display is first powered on, booted-up, or
otherwise initialized or used for the first time. This calibration
system assumes that the manufacturer adjusted the display in the
usual manner prior to shipment for sale to the display user or OEM
manufacturer of another device. Therefore the voltages used to
operate the display have been put into a gamma table or other
look-up table as is the usual practice in the industry. This means
that the first sensor values measured are automatically calibrated.
This embodiment takes advantage of the manufacturer's calibration.
Details of this post-manufacture calibration are described with
reference to the embodiment illustrated in FIG. 10.
[0142] First (Step 831), the analog image Data function logic block
208 sends first gray level 1 image voltage for the first pixel
(pixel 1) in the first row (row 1) to image A/D converter 209 where
the analog voltage is digitized to a gray level 1 digital value.
(Where the gray level image values are already in digital form this
analog-to-digital conversion is not necessary.)
[0143] Second (Step 832), this digitized gray level 1 voltage value
is sent or otherwise communicated to gray level logic function
block Z103.
[0144] Third (Step 833), gray level logic function block Z103
combines information from (i) the manufacturer's (or an otherwise
generated or available) gamma table Z103b and from (ii) a pixel
deviation memory Z102 within a pixel deviation logic block, but
since there are no values yet stored or only default values stored
in the pixel deviation memory there is no change to the
manufacturer's value determined by the gamma table. (The pixel
deviation logic block and the pixel deviation memory and its stored
values are described in greater detail herein below.)
[0145] Fourth (Step 834), the digital gray level 1 voltage is sent
to Display Controller function logic block Z104.
[0146] Fifth (Step 835), Display Controller function logic block
Z104 relays the digital gray level 1 voltage value to display first
column driver (column driver 1) in function logic block 238.
[0147] Sixth (Step 836), Step 831 through Step 835 are repeated for
all the pixels in the first row until all the pixels data in row 1
have been loaded into a line buffer in column driver 238.
[0148] Seventh (Step 837), on command from Display Controller Z104,
the row 1 pixel data is downloaded to a series of digital-to-analog
converters (DACs) at the head of each column, where each digital
pixel voltage is converted to an analog voltage and loaded onto the
line L3s for each column of pixels.
[0149] Eighth (Step 838), display controller Z104, after waiting
for the analog voltages on the column lines L3 to stabilize, sends
a select row 1 signal to the Row Select function logic block
240.
[0150] Ninth (Step 839), the row select function logic block 240
puts a high voltage on line L2 and turns on all the gates to all
the transistor T1 in row 1, causing the display voltage on line L3
to flow into capacitor C1 where it is held when the voltage on line
L2 goes low; and at the same time transistor T3 is turned on
causing charge to flow into capacitor C2 from sensor line L4.
[0151] Tenth (Step 840), the movement of charge into capacitor C2
causes a voltage to be sampled and held in function logic block
Z101, and a value for each individual sensor S1 in row one is
read.
[0152] Eleventh (Step 841), the sample and held voltages are
digitized and multiplexed (or multiplexed and then digitized) to a
serial data stream by A/D Converter 207 and multiplexer (MUX)
207a.
[0153] Twelfth (Step 842), Display Controller Z104 directs the
serial sensor data stream to be stored in row 1 of Calibration
Memory (Cal Mem) 250 for gray level zero.
[0154] Thirteenth (Step 843), Step 836 through Step 843 are
repeated until all rows in the frame have been sampled and stored
for gray level 0.
[0155] Fourteenth (Step 844), Step 831 through Step 843 are
repeated for gray level 2. The sensor values read on this frame are
for the previous gray level 1 and are stored in calibration memory
(Cal Mem 250) as the values for the first gray level or gray level
1.
[0156] Fifteenth (Step 845), Steps 831 through Step 844 are
repeated until all gray levels have been sampled and saved to the
calibration memory Cal Mem 250. Note that as in the pre-manufacture
calibration procedure, the last gray level is run for two frames so
that the final value is stored in calibration memory Cal Mem
250.
[0157] The Pixel Deviation memory has been referred to in the above
calibration procedures. In one embodiment, the Pixel Deviation
memory stores data or other information that indicates changes,
differences, history, aging or other data or information relevant
to display operation and calibration. There are many methods to use
the data such as aging data stored in Pixel Deviation Memory
Z102.
[0158] In one embodiment, for example, the voltage can be raised
for the aged pixels that have undergone a decrease in luminance to
bring them back to the correct luminations. One possible drawback
in some embodiments may be that voltage head room has to be built
into the column drivers in Column Drivers 238 to fully utilize this
type of correction or compensation. In another embodiment, another
way to use the data in Pixel Deviation Memory is implemented to
reduce the number of gray levels for the less aged (or less
degraded) pixels. Yet another method is to use a 9-bit gray scale
in a nominally 8-bit system allowing the highest gray level to
increase beyond gray level 256 so that an aged pixel can be
effectively be driven to level 257 (or other required gray level
value) so that it will emit a luminance at the luminance level
specified for a gray level 256. Therefore, all the image gray
levels for that pixel would be bumped up by one (or an appropriate
number) level of gray. Another method uses spatial dithering, a
well know gray scale method, to increase the effective number of
gray levels without increasing the number of bits in the logic.
Alternately, temporal dithering which is known for conventional
displays may be used, or combinations of spatial and temporal
dithering can be used. These different methods or techniques and
the structures associated with such methods may be used alone or in
any combination with each other or with other techniques.
4. Embodiment of the Sensor Read Circuit and Method
[0159] FIG. 5 shows an exemplary embodiment of a voltage sensing
amplifier read circuit. When the row is selected by Row Select 240
the voltage goes high on line L2 turning on transistor T3 allowing
voltage on capacitor C2 to transfer to the plus terminal on
operational amplifier OA1. This voltage is amplified according to
the ratio of resistance R2 to the resistance (R.sub.L4)of line L4.
Typically the resistance R.sub.L4 of L4 is on the order of several
kilo-ohms (.apprxeq.1.sup.3 ohms). Therefore, if resistance R2 is
several megohms (.apprxeq.10.sup.6 ohms) the amplification factor
is 30 dB or 1000 to 1. Therefore, a one-millivolt reading on
capacitor C2 would show up on pin or node P4 as one-volt and be
sent to the sample and hold function block Z101. One possible
drawback to this circuit is that any parasitic capacitance on line
L4 may reduce the voltage on capacitor C2 during the read time.
Therefore this circuit is best used for a display with a low number
of rows and therefore a relatively low resolution display, but in
any event even with this possible limitation, performance relative
to conventional circuits and methods is improved and this potential
constraint is only pointed out so that the virtues of a second
embodiment may be appreciated to the fullest.
[0160] The second embodiment of the read circuit is shown in FIG. 6
and is termed a charge amp/transimpedance amplifier. It gets its
name from the fact that the charge required to re-charge capacitor
C2 to the full voltage is measured by this circuit and that the
input of the circuit (the negative input on charge amplifier CA1)
is in the Gig-ohms range or higher and the output at pin or node P3
is almost zero ohms. In fact the node at P3 may sometimes be viewed
as a virtual ground.
[0161] Operation of this embodiment of the circuit is now described
with reference to FIG. 6. A voltage is placed on the plus input pin
of first charge amplifier CA1, for example, 10 volts (or other
established value). Since initially there is no voltage on the
negative input pin, 10 volts instantly appears on pin P3 and is
transferred to the negative input pin by C3. Subsequently, the now
10 volts appearing on the negative pin is subtracted from the 10
volts on the positive input pin of the first charge amplifier CA1,
causing the voltage on pin P3 to become zero (or substantially
zero), but the 10 volts on the negative pin remains, because if the
voltage on the negative input pin decays by an amount of voltage
(such as by a volt, for example) then this voltage difference (a
volt) shows up on pin P3 thereby boosting the voltage on the
negative pin back up to 10 volts (or other established value). This
is similar to how a charge pump works.
[0162] When the circuit settles, there is 10 volts (or other
established value) on both the input pin to charge amplifier CA1
and zero volts on pin P3. Node or pin P3 may almost never be
exactly 0 volts for a couple of reasons. First of all, the family
of operational amplifiers to which charge amplifier CA1 belongs may
typically have an offset voltage, because the pair of internal
transistors that make up the operational transistor may not usually
be exactly alike in characteristics or performance and the
difference shows up a the offset voltage. Another reason that the
voltage on P3 is not zero is that L4 is connected to all the T3
transistors in the column. This may for example, be as high as
one-thousand T3 transistors for a high resolution display having
1000 rows, and an even greater number for larger and/or higher
resolution displays. Each of these T3s may typically have a current
leakage on the order of several pico-amps (10.sup.-12 amps) that
tends to lower the voltage on the negative pin of the charge
amplifiers CA1 causing a voltage to appear at pin P3 on top of the
afore described offset voltage. In operation, the voltage on pin P3
is sampled before the voltage on L2 goes high, in order to
determine the voltage caused by the offset voltage and the leakage
current on line L4. Pin P3 is advantageously again sampled after
the voltages on line L2 goes high and the two voltage subtracted
(using logic functions common in the industry) to generate a
difference voltage. The difference between the two readings is a
measure of the charge moving into capacitor C2 to bring line L4 and
capacitor C2 up to the 10 volts (or other established value) as
used in the example.
[0163] One advantage of this embodiment is that the reading of
charge by a voltage change on pin P3 is independent (or
substantially independent) of the capacitance on line L4. The first
charge amplifier CA1 keeps line L4 charged to the voltage on its
plus (+) input pin. If one electron is removed from L4 then one
electron moves out of capacitor C3 to replace it, and any movement
of electrons from capacitor C2 cause the voltage to decrease on the
negative input pin of charge amplifier CA1 with a corresponding
voltage change on pin P3. In one embodiment, the value of the C3
capacitance is selected to be on the same order as the C2
capacitance; therefore, if capacitor C2 has a capacitance of about
a picofarad then C3 should also be selected to have a capacitance
of about a picofarad, but they need not have identical values. The
charge amplifier may be a typical operational amplifier as used in
the industry. The size of the charge amplifier (its power rating)
is determined by taking into account the leakage on line L4. If for
example the leakage of one-thousand T3 transistors is a several
nano-amps, then charge amplifier CA1 is advantageously able to
supply several nano-amps, and preferable this amount with some
safety margin. Embodiments of the invention provide safety margins
of a factor of two or three times the leakage current, but lesser
or greater safety margins may be implemented.
[0164] The discussion has focused on the inventive sensor circuit
and its operation. It will be appreciated that any photoconductive
(or photoresistive) material may be used for the sensor, including
for example any of amorphous silicon, poly-silicon, cadmium
selenide, or other photoconductive or photoresistive materials that
are know in the art or to be developed in the future. It will also
be appreciated that a poly-silicon based sensor may provide for an
inherently more stabile operation than an amorphous silicon based
sensor, the use of poly-silicon also has inherently greater
production costs for a display because the flat panel display
manufacturing infrastructure is well established for amorphous
silicon, but would need to be rebuilt for poly-silicon at costs
measured in the billions of dollars. Therefore the inventive
system, structure, and method that permit use of amorphous silicon
materials through its calibration and feedback stabilization and
control provide distinct advantages. Issues associated with the
differences between crystalline silicon (x-Si), poly-silicon (p-Si)
and amorphous silicon (a-Si) are described elsewhere in this
specification.
5. Embodiment of Method of Operation the Display Device and
System
[0165] Having described many features of the inventive system and
device and calibration methods and techniques related thereto,
further attention is directed to aspects of operation of the
display. Attention is focused on embodiments that use the read
circuit of the FIG. 6 embodiment, and the pixel circuit of the FIG.
8 embodiment with VC1 and T4 being replaced with charge amplifier
CA1 in FIG. 6. It will be apparent to those workers having ordinary
skill in the art in light of the description provided here that
other combinations of the different embodiments already described
may be utilized for the display device and system.
[0166] An embodiment of a system and method for operating a display
and display system is now described with reference to the
flow-chart diagram of FIG. 11. This sequence of steps is exemplary,
including optional steps, and it will be apparent that some
reordering of steps may be made, and that other steps may be
performed in parallel, without deviating from the spirit and scope
of the invention.
[0167] First (Step 851), the analog image Data function logic block
208 sends the image voltage for the first pixel in the first row
(pixel 1, row 1) to the image A/D Converter 209 where the image
analog voltage is converted to a digital number representing the
image gray level, which, in an 8-bit gray level system, is a number
between 0 and 255. For a gray level system supporting a different
number of bits of pixel gray level data, the digital number will
correspond to that range or to a lesser range if fewer than all
possible levels are actually utilized. An 8-bit gray level system
with 256 levels for each color channel will be assumed for purposes
of this description, but this in no way limits the invention. (Note
that performing this procedure or any of the other procedures
beginning with the first pixel of the first row and then subsequent
pixels of the first row and then all the other rows makes logical
sense, but neither this procedure requires this starting point or
sequence, and in reality so long as the logic is designed to
calibrate and/or operate each pixel in the described manner, any
ordering may be used.)
[0168] Second (Step 852), this image gray level value between 0 and
255 is sent to the gray level logic function block Z103.
[0169] Third (Step 853), gray level logic function block Z103
converts the gray level number for the first pixel in the first row
(pixel 1, row 1) into a digital voltage to be applied to the pixel
to cause the OLED D1 to emit a photon flux at a level of luminance
to equal the image gray level input to the display system at the
first step. This voltage is determined using information in the
manufacturer's gamma table and the information from the Pixel
Deviation Memory Z102. Initially when the display is new there is
no deviation data in Pixel Deviation Memory or the values stored
there are default values so that these values will not really
change the manufacturer's gamma table values, but as the display
ages pixel deviation values are built up in the Pixel Deviation
Memory Z102.
[0170] Fourth (Step 854), the digital voltage for the first pixel
of the first row (pixel 1, row 1) is sent to Display Controller
Z104.
[0171] Fifth (Step 855), Display Controller Z104 relays or
otherwise communicates a digital voltage for the first pixel in the
first row (pixel 1, row 1) to a line buffer in Column Driver 238.
Line buffers for displays are known in the art and not described
here in greater detail. The pixel voltage for the first pixel in
the first row (pixel 1, row 1) is loaded into the line buffer at
the first column position (column position 1).
[0172] Sixth (Step 856), Step 851 through Step 855 are repeated for
all the pixels in the row until all the pixels in the row have
voltages loaded into the line buffer of Column Driver 238.
[0173] Seventh (Step 857), on command from the Display Controller
Z104, the first row (row 1) pixel data is downloaded to a series of
parallel DACs (one for each column in the display) which convert
the digital pixel voltages to analog voltage applied to all the L3
(one for each column).
[0174] Eighth (Step 858), Display controller Z104, after waiting
for the voltage placed on L3 to settle sufficiently, sends a select
row 1 signal to Row Select logic block 240.
[0175] Ninth (Step 859), Row Select logic block 240 places a high
voltage on line L2 for row 1, therefore turning on all T1
transistors in the first row and causing the voltages applied to
the line L3s to be transferred to the C1 capacitors in all the
pixels in the first row. This in turn, causes the power TFT
transistor T2 to supply current to the D1 OLED diodes in the first
row. At the same or substantially the same time, all the sensor
TFTs T3 are turned on causing charge to flow into capacitor C2
until capacitor C2 is at the re-charge voltage, for example, the
10V exemplary value described in the earlier example.
[0176] Tenth (Step 860), the movement of charge into capacitor C2
causes a voltage to be sampled and held in function logic block
Z101 for each pixel in the row. Eleventh (Step 861), the sampled
and held voltages are digitized and multiplexed to a serial data
stream (the order of digitizing and multiplexing can be reversed
without loss of performance) by A/D Converter 207 and multiplexer
MUX 207a.
[0177] Twelfth (Step 862), Display Controller Z104 directs the
serial sensor data and a stream of calibration data from
Calibration Memory (Cal Mem) 250 to meet at Comparator 260 so that
a comparison of the serial sensor data and the calibration data for
the pixels can be generated.
[0178] Thirteenth (Step 863), comparator 250 subtracts (or
generates a difference between) the sensor data from the
calibration data and sends the result to Pixel Deviation Memory
Z102 for the first row (row 1) where the data is stored according
to pixel number and row (or any other scheme) and by gray level
established for the pixel in the first step (Step 851) that is a
digital number representing the image gray level.
[0179] Fourteenth (Step 864), Step 856 through Step 863 are
repeated for all rows until all rows in the frame have been down
loaded and deviations (if any) have been determined and stored in
Pixel Deviation Memory.
[0180] Fifteenth (Step 865), Step 851 through Step 864 are repeated
for each frame (or for any designated frame according to an
established plan of operation). While one embodiment performs the
procedure for each frame, this is not necessary as pixels do not
normally age or otherwise change at this rate. Alternatives may
include repeating the procedure at any predetermined number of
frames, at device power-on, after a clock determined period of time
of operation, in response to an automatically or manually generated
signal, or other event. In one embodiment, the procedure is
repeated for every frame as once the circuits and methods have been
established, there is no cost in performing the procedure for every
frame.
6. Embodiment of a Display System
[0181] FIG. 12 is an illustration showing an embodiment of a
display system according to aspects of the present invention. A
display screen 602 having a plurality of emissive pixels 603 of the
type already described arranged in an array is held or mounted
within a housing 604 such as a monitor frame, cabinet, or other
device, and displays an image 605 or other two dimensional graphic.
(Note that one-dimensional displays may also be fabricated using
the features of the invention but although possibly useful are less
interesting.)
[0182] Circuits and devices that are formed on the display
substrate (often glass or polymeric material) are referred to as
on-glass circuits and devices while those that are not formed on
the display substrate are referred to as off-glass circuits and
devices. The pixels including the pixel emitters D1, sensors S1,
sensor capacitors C2, and other elements formed within each of the
display pixels are formed on-glass. Other elements may be formed
off glass according to conventional display design principles. The
on-glass circuits and devices connect to the off-glass circuits and
elements such as display drive and control electronics 606 over an
interface 608. These display drive and control electronics 606 may
be mounted within or without the monitor housing 604 but may
usually be housed within so that a user may simply plug in one or
more (analog or digital) video or image sources (such as for
example, a DVD player 610, a computer 612, a video or digital
camera 614, or memory card 616) and have the image or video
displayed. Alternatively or in addition, the display system 600 may
include image generators within the system, such as a TV tuner or
receiver 618 or other internal generator. Of course there may be
various other wired or wireless interfaces for sending data to the
system 600 for display. A switching device SW 620 may be provided
to manually or automatically select which of the sources are to be
displayed, and multiple sources may be simultaneously displayed
such as by using picture-in-picture technology. The system may also
support various forms of image processing and enhancement.
[0183] This is only one example of the application of the display
technology to imaging applications and it will be appreciated that
although a primary application of the technology is to flat-panel
displays, the inventive technology may be applied to displays
having curved surfaces as well. There are an endless variety of
display applications for which the inventive technology may be
applied. We list several by way of example but not limitation; they
include: any information appliance, a television monitor, a CD
player, a DVD player, a computer monitor, a computer system, an
automobile instrument panel, an aircraft instrument display panel,
a video game, a cellular telephone, a personal data assistant
(PDA), a telephone, a graphics system, a printing system, a
scoreboard system, document and image scanners, an entertainment
system, a domestic or home appliance, a copy machine, a global
positioning system navigation display, a dynamic art display
device, a digital or video camera, and any combinations of
these.
7. Exemplary Embodiments having Particular Combinations of
Features
[0184] Various structures, devices, systems, architectures,
methods, procedures, and computer programs have been described in
this specification and illustrated in the figures. It will be
appreciated in light of the description that the invention provides
many different features and elements that can be utilized
separately or in various combinations. This section of the
description sets forth some particular embodiments that have or
require particular combinations of features and elements of the
invention. The combinations set forth are merely exemplary, and any
of the features and elements described in this section or in the
specification as a whole may be used separately or in combination.
It will also be appreciated that the section headers and
sub-headers set forth in the detailed description are merely
intended to serve as a guide to the reader and that different
aspects, features, and elements of the invention are set forth
throughout the specification.
[0185] In one aspect the invention provides a system and method for
a long-life luminance feedback stabilized display panel. In a first
embodiment, the invention provides a stabilized feedback display
system comprising: a display device having a plurality of emissive
picture elements (pixels) each formed from at least one electronic
circuit device; a display driver circuit receiving a raw input
image signal from an external image source and applying a corrected
image signal the display; a display luminance detector generating
at least one display device luminance value; and a processing logic
unit receiving the at least one display device luminance value and
communicating information to the display driver circuit, the
display driver circuit using this communicated information to
generate a transformation for generating the corrected image signal
from the raw input image signal.
[0186] In second particular embodiment of this system, each of the
picture elements comprises: a sample and hold circuit; a current
source controlled by the sample and hold circuit; a photon emission
device supplied by the current source; and a luminance detection
device disposed within a separation distance from the photon
emission device for detecting photons emitted by the photon
emission device.
[0187] In a third embodiment, each of the picture elements
comprises: a photon emitter; and a photon flux integrator disposed
within the pixel to intercept a flux of photons from the photon
emitter during a specified time, to undergo an electrical property
change in response to the photons intercepted, to integrate or
count the number of photons intercepted during the time, and to
generate a signal indicative of a the total integrated photon flux
during the specified time. In a fourth embodiment, the photon flux
integrator comprises: a sensor formed of a photo device that
exhibits changing or variable properties in response to a changing
or variable photon flux; a charge storage device adapted to store
or release charges; and a control circuit that directs charges to
or removes charges from the charge storage device in response to
the change in resistance or conductance of the sensor. In a fifth
embodiment, the charge storage device comprises a capacitor. In a
sixth embodiment, the control circuit includes a transistor. In a
seventh embodiment, the photo device comprises a photo sensitive
resistor that changes its resistance or conductance with changes of
photon flux impinging on its surface. In an eighth embodiment,
photo device comprises a photo diode the leakage of which increases
or decreases with variations of photon flux impingent on its
surface. In a ninth embodiment, the photo diode leakage comprises
one or more of voltage leakage, current leakage, or charge leakage.
In a tenth embodiment, the photo device comprises a phototransistor
the current of which increases or decreases with variations of
photon flux impingent on the phototransistor surface.
[0188] In another embodiment of the system, the luminance detector
comprises a photon flux integrator. In another embodiment of the
system, the picture element (pixel) comprises a particular photon
flux integrator that integrates a photon flux emitted by the photon
emission device within the same pixel as the photon flux
integrator. In another embodiment of the system, each photon flux
integrator comprises: an isolation switching device for isolating a
first circuit node from a second circuit node and having an output
port (node); a photosensitive unit having an input coupled to the
isolation switching device output port (node) and an output
connected with a voltage reference node; and a charge storage
device having a first electrode coupled with a first port of the
isolation switch and a second electrode coupled with the voltage
reference node. In another embodiment of the system, the charge
storage device comprises a capacitor. In another embodiment of the
system, the isolation switch comprises a transistor. In another
embodiment of the system, the isolation switch is formed on a
substrate as a thin film transistor (TFT). In another embodiment of
the system, the thin film transistor is constructed from amorphous
silicon. In another embodiment of the system, the thin film
transistor is constructed from polysilicon. In another embodiment
of the system, the thin film transistor is constructed from cadmium
selenide. In another embodiment of the system, the thin film
transistor is constructed from any semiconductor material.
[0189] In another embodiment of the system, the thin film
transistor comprises a channel defined in a material, and the
material is selected from the set of materials consisting of: an
amorphous silicon channel, a poly-silicon channel, a cadmium
selenide channel, a gallium arsenide channel, and a channel formed
or defined in any other semiconducting material.
[0190] In another embodiment of the system, the display device
comprises multiple picture elements arranged in a planar array. In
another embodiment of the system, the multiple individual picture
elements are addressed by column and row. In another embodiment of
the system, the specified time is equal to or less than the row
address time. In another embodiment of the system, the specified
time is between 0.01 (1 percent) of the row address time and the
row address time. In another embodiment of the system, the
specified time is between 0.1 (10 percent) of the row address time
and the row address time. In another embodiment of the system, the
specified time is equal to or less than the frame time. In another
embodiment of the system, the specified time is greater than 0.01
of the row address time and less than or equal to the frame time.
In another embodiment of the system, the specified time is equal to
multiple frame times.
[0191] In another embodiment of the system, the display emissive
device is an organic light emitting diode (OLED). In another
embodiment of the system, the organic light emitting diode (OLED)
is a small molecule OLED. In another embodiment of the system, the
organic light emitting diode (OLED) is a polymer OLED (PLED). In
another embodiment of the system, the organic light emitting diode
(OLED) is a phosphorescent OLED (PHOLED). In another embodiment of
the system, the organic light emitting diode (OLED) is constructed
from any organic material in any combination of single or multiple
layers of organic materials and electrodes. In another embodiment
of the system, the organic light emitting diode (OLED) is a active
matrix OLED. In another embodiment of the system, the display
emissive device is an electroluminescent device. In another
embodiment of the system, the display emissive device is a plasma
emission device. In another embodiment of the system, the display
emissive device is any controllable photon emissive device. In
another embodiment of the system, the active matrix is constructed
from amorphous silicon. In another embodiment of the system, the
active matrix is constructed from poly silicon. In another
embodiment of the system, the active matrix is constructed from
cadmium selenide. In another embodiment of the system, the active
matrix is constructed from any type of semiconductor material.
[0192] In another aspect, the invention provides a method for
stabilizing a display system comprising: providing a display device
having a plurality of emissive picture elements (pixels) each
formed from at least one electronic circuit device; receiving a raw
input image signal by a display driver circuit from an external
image source and applying a corrected image signal to the display;
detecting a display luminance and generating at least one display
device luminance value; and receiving the at least one display
device luminance value by a processing logic unit and communicating
information to the display driver circuit, and using this
communicated information to generate a transformation for
generating the corrected image signal from the raw input image
signal.
[0193] In another aspect the invention provides a method for
operating and individually controlling the luminance of each pixel
in an emissive active-matrix display device. In one embodiment of
this method, the invention provides a method for controlling the
luminance of a picture element (pixel) in a display device, the
method comprising: storing a transformation between a digital image
gray level value and a display drive signal that generates a
luminance from a pixel corresponding to the digital gray level
value; identifying a target gray level value for a particular
pixel; generating a display drive signal corresponding to the
identified target gray level based on the stored transformation and
driving the particular pixel with the drive signal during a first
display frame; measuring a parameter representative of an actual
measured luminance of the particular pixel at the end of the first
display time; determining a difference between the identified
target luminance and the actual measured luminance for the
particular pixel; modifying the stored transformation for the
particular pixel based on the determined difference; and storing
and using the modified transformation for generating the display
drive signal for the particular pixel during a frame time following
the first frame time.
[0194] In another embodiment of this method, the first display
frame is any display frame designated by software programming or by
the display user or by a combination of the programming and the
user. In another embodiment of this method, the frame time
following the first frame is any subsequent frame time. In another
embodiment of this method, the first display frame is any display
frame designated by software programming or by the display user or
by a combination of the programming and the user. In another
embodiment of this method, the first display time may be either a
single continuous period of time or comprised of a plurality of
discontinuous periods of time, and wherein either of the continuous
period of time and the discontinuous periods of time may occur
during a single frame time or over multiple frame times. In another
embodiment of this method, storing and/or the using of the modified
transformation for generating the display drive signal for the
particular pixel is applied at any subsequent portion of a single
frame or at different frames. In another embodiment of this method,
the storing and/or the using of the modified transformation for
generating the display drive signal for the particular pixel may be
either at single continuous period of time or comprised of a
plurality of discontinuous periods of time, and wherein either of
the continuous period of time and the discontinuous periods of time
may occur during a single frame time or over multiple frame times.
In another embodiment of this method, the storing and/or the using
of the modified transformation for generating the display drive
signal for the particular pixel may be either at single continuous
period of time or comprised of a plurality of discontinuous periods
of time, and wherein either of the continuous period of time and
the discontinuous periods of time may occur during a single frame
time or over multiple frame times.
[0195] In another embodiment of this method, the stored
transformation comprises a transformation stored in a gray level
logic functional block of a display system. In another embodiment
of this method, the stored transformation comprises a
transformation stored in a gamma table for a display device. In
another embodiment of this method, the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a voltage
measurement corresponding to a number of electrons accumulated or
released from a charge storage device. In another embodiment of
this method, the measured parameter representative of an actual
measured luminance of the particular pixel at the end of the first
display time comprises a current measurement corresponding to a
number of electrons accumulated or released from a charge storage
device. In another embodiment of this method, the measured
parameter representative of an actual measured luminance of the
particular pixel at the end of the first display time comprises a
charge measurement corresponding to a number of electrons
accumulated or released from a charge storage device. In another
embodiment of this method, the charge storage device comprises a
capacitor. In another embodiment of this method, the electrons are
accumulated or released in proportion to a resistivity or
conductivity of a sensor element having a resistivity or
conductivity that changes in response to a flux of photons incident
on the sensor. In another embodiment of this method, the proportion
is a direct proportion.
[0196] In another embodiment of this method, the frame time
following the first frame time is the next subsequent frame time.
In another embodiment of this method, the frame time following the
first frame time is any subsequent frame time. In another
embodiment of this method, the frame time following the first frame
time is a next display device power on time. In another embodiment
of this method, the frame time following the first frame time is a
frame time at a predetermined or dynamically determined time
interval. In another embodiment of this method, a different
transformation is stored for each pixel in the display device. In
another embodiment of this method, a different transformation is
stored for each different gray level that may be displayed for each
separately addressable pixel in the display device. In another
embodiment of this method, the first display time is the duration
of time a pixel is turned on in the display. In another embodiment
of this method, the display time is substantially any time between
8 milliseconds and 36 milliseconds. In another embodiment of this
method, the display time is substantially any time between 10
milliseconds and 20 milliseconds. In another embodiment of this
method, the portion of the frame time comprises substantially the
row address time. In another embodiment of the method, the
specified time is equal to or less than the row address time. In
another embodiment of the method, the portion of the frame time is
between 0.01 (1 percent) of the row address time and the row
address time. In another embodiment of the method, the portion of
the frame time is between 0.1 (10 percent) of the row address time
and the row address time. In another embodiment of the method, the
portion of the frame time is equal to or less than the frame time.
In another embodiment of the method, the portion of the frame time
is greater than 0.01 of the row address time and less than or equal
to the frame time. In another embodiment of the method, the portion
of the frame time is equal to multiple frame times. In another
embodiment of the method, the portion of the frame time comprises a
time between the row address time and the frame time.
[0197] In another embodiment of the method, the measuring of a
parameter representative of an actual measured luminance of the
particular pixel at the end of the first display time comprises
measuring a voltage stored on a capacitor that has either been
charged toward or discharged from a known voltage and the amount of
charging or discharging is proportional to a photon flux emitted
from the emitter within the particular pixel onto a sensor within
the same particular pixel.
[0198] In another embodiment of the method, the steps of
identifying, generating, measuring, determining, modifying, and
using are repeated for every pixel in the display. In another
embodiment of the method, the determining of a difference between
the identified target luminance and the actual measured luminance
for the particular pixel is based on a reference integrated photon
flux on the particular pixel sensor determined during a display
calibration procedure performed during manufacture or when
initially used. In another embodiment of the method, the method
further comprising a display calibration procedure that determines
and stores an initial transformation for every pixel and every gray
level the display may be commanded to display.
[0199] In another aspect the invention provides a control system
for controlling the luminance of a picture element (pixel) in a
display device, the control system comprising: a stored pixel gray
level to display pixel drive signal transformation for each pixel
and each gray level the pixel may be commanded to display, the
stored transformation based on performance characteristics of the
display pixels during a prior display frame time period; a display
drive signal generator responsive to a control that receives a
command to display a particular gray level for a particular pixel
location and generates a drive signal to the particular pixel using
the stored transformation during a first frame time; a luminance
measurement circuit for each separate pixel in the display for
measuring parameters representative of an actual measured
luminances of each of the plurality of particular pixels at the end
of the first display time; a comparator circuit for determining a
difference between the identified target luminance and the actual
measured luminance for the particular pixel; transformation update
logic for modifying the stored transformation for each particular
pixel based on the determined difference during a portion of a
first frame time; and using the modified transformation for
generating the display drive signal for the particular pixel during
a portion of a second frame time following the first frame
time.
[0200] In another embodiment of the control system, the stored
transformation comprises a transformation stored in a gray level
logic functional block of a display system. In another embodiment
of the control system, the stored transformation comprises a
transformation stored in a gamma table for a display device. In
another embodiment of the control, system, the luminance
measurement circuit measures a parameter representative of an
actual measured luminance of the particular pixel at the end of the
first display time and comprises a voltage measurement
corresponding to a number of electrons accumulated or released from
a charge storage device separately for each pixel of the display.
In another embodiment of the control system, the charge storage
device comprises a capacitor. In another embodiment of the control
system, the electrons are accumulated or released in proportion to
a resistivity or conductivity of a sensor element having a
resistivity or conductivity that changes in response to a flux of
photons incident on the sensor. In another embodiment of the
control system, the proportion is a direct proportion. In another
embodiment of the control system, the second frame time following
the first frame time is a portion of the next subsequent frame
time. In another embodiment of the control system, the portion of a
second frame time following the portion of the first frame time is
a portion of time in any one or plurality of subsequent frame
times. In another embodiment of the control system, the frame time
following the first frame time is a next display device power on
time. In another embodiment of the control system, the frame time
following the first frame time is a frame time at a predetermined
or dynamically determined time interval. In another embodiment of
the control system, a different transformation is stored for each
pixel in the display device. In another embodiment of the control
system, a different transformation is stored for each different
gray level that may be displayed for each separately addressable
pixel in the display device. In another embodiment of the control
system, the first display time is the duration of time a pixel is
turned on in the display.
[0201] In another embodiment of the control system, the display
time is substantially any time between 8 milliseconds and 36
milliseconds. In another embodiment of the control system, the
display time is substantially any time between 10 milliseconds and
20 milliseconds. In another embodiment of the control system, the
portion of the frame time comprises substantially the row address
time. In another embodiment of the control system, the portion of
the frame time comprises a time between the row address time and
the frame time. In another embodiment of this control system, the
portion of the frame time comprises substantially the row address
time. In another embodiment of the control system, the portion of
the frame time is equal to or less than the row address time. In
another embodiment of the control system, the portion of the frame
time is between 0.01 (1 percent) of the row address time and the
row address time. In another embodiment of the control system, the
portion of the frame time is between 0.1 (10 percent) of the row
address time and the row address time. In another embodiment of the
control system, the portion of the frame time is equal to or less
than the frame time. In another embodiment of the control system,
the portion of the frame time is greater than 0.01 of the row
address time and less than or equal to the frame time. In another
embodiment of the control system, the portion of the frame time is
equal to multiple frame times. In another embodiment of the control
system and method, the portion of the frame time comprises a time
between 0.01 of the row address time and the frame time.
[0202] In another embodiment of the control system, the measuring
of a parameter representative of an actual measured luminance of
the particular pixel at the end of the first display time comprises
measuring a voltage stored on a capacitor that has either been
charged toward or discharged from a known voltage and the amount of
charging or discharging is proportional to a photon flux emitted
from the emitter within the particular pixel onto a sensor within
the same particular pixel.
[0203] In another embodiment of the control system, the steps of
identifying, generating, measuring, determining, modifying, and
using are repeated for every pixel in the display. In another
embodiment of the control system, the determining of a difference
between the identified target luminance and the actual measured
luminance for the particular pixel is based on a reference
integrated photon flux on the particular pixel sensor determined
during a display calibration procedure performed during manufacture
or when initially used. In another embodiment of the control
system, the control system further comprises a display calibration
procedure that determines and stores an initial transformation for
every pixel and every gray level the display may be commanded to
display. In another embodiment of the control system, the measured
parameter representative of an actual measured luminance of the
particular pixel at the end of the first display time comprises a
current measurement corresponding to a number of electrons
accumulated or released from a charge storage device. In another
embodiment of the control system, the measured parameter
representative of an actual measured luminance of the particular
pixel at the end of the first display time comprises a charge
measurement corresponding to a number of electrons accumulated or
released from a charge storage device. In another embodiment of the
control system, the first display frame is any display frame
designated by software programming or by the display user or by a
combination of the programming and the user. In another embodiment
of the control system, the frame time following the first frame is
any subsequent frame time. In another embodiment of the control
system, the first display frame is any display frame designated by
software programming or by the display user or by a combination of
the programming and the user. In another embodiment of the control
system, the first display time may be either a single continuous
period of time or comprised of a plurality of discontinuous periods
of time, and wherein either of the continuous period of time and
the discontinuous periods of time may occur during a single frame
time or over multiple frame times.
[0204] In another embodiment of the control system, the storing
and/or the using of the modified transformation for generating the
display drive signal for the particular pixel is applied at any
subsequent portion of a single frame or at different frames. In
another embodiment of the control system, the storing and/or the
using of the modified transformation for generating the display
drive signal for the particular pixel may be either at single
continuous period of time or comprised of a plurality of
discontinuous periods of time, and wherein either of the continuous
period of time and the discontinuous periods of time may occur
during a single frame time or over multiple frame times. In another
embodiment of the control system, the storing and/or the using of
the modified transformation for generating the display drive signal
for the particular pixel may be either at single continuous period
of time or comprised of a plurality of discontinuous periods of
time, and wherein either of the continuous period of time and the
discontinuous periods of time may occur during a single frame time
or over multiple frame times.
[0205] In another aspect the invention provides a feedback control
system and method for operating a high performance stabilized
active matrix emissive display. In one embodiment of this method,
the invention provides a system for operating an active-matrix OLED
display device or other emissive display device having a plurality
of pixels, the system comprising: a gray level logic coupled to an
external source of digital image data, the gray level logic
including a transformation for transforming a first representation
of an image pixel gray level value to a second representation of
the same image gray level pixel value; a display controller
operable to receive inputs from the gray level logic and to
communicate image and control signals to display matrix row select
and column drive circuits, the row select and column drivers
operable to cause an image to be displayed during a frame time for
a plurality of pixels; each of the plurality of pixels including a
pixel photon flux emitter and a pixel photon flux receptor that
integrates at least a portion of the emitted photon flux from the
emitter during a portion of the pixel display frame time and
generates an output signal indicative of the integrated photon
flux; a calibration memory storing a calibration value for each
pixel and each pixel value that may be displayed by the pixel; a
comparator receiving the output signals from each of the plurality
of pixels and the calibration memory and comparing the received
output signals with a like plurality of corresponding signals from
the calibration memory to compute a difference signal for each
pixel; and a pixel deviation logic receiving difference signals
from the comparator and directing a change in the gray level logic
transformation for at least pixel locations and pixel gray level
values that have a difference between the calibration and the
measured values.
[0206] In another embodiment of this system, the pixel deviation
logic includes a pixel deviation memory for storing a deviations
between a calibrated pixel luminance value and a measured pixel
luminance value. In another embodiment of this system, the
calibration values are voltage values and the output signals
indicative of the integrated photon flux are voltages, and the
comparator is a voltage comparison circuit. In another embodiment
of this system, the calibration values are current values and the
output signals indicative of the integrated photon flux are
currents, and the comparator is a current based charge
amp/impedance transformation circuit. In another embodiment of this
system, the calibration values are charge values and the output
signals indicative of the integrated photon flux are charges, and
the comparator is a charge based comparison circuit. In another
embodiment of this system, the calibration values are voltage
values and the output signals indicative of the integrated photon
flux are charges, and the comparator is a voltage comparison
circuit.
[0207] In another embodiment of this system, the output signal
indicative of the integrated photon flux are analog signals, and
the system further comprising: a sample and hold circuit for
sampling an analog signal as a voltage representing a per pixel
integrated photon flux during the portion of the pixel display
frame time and holding that sampled signal for conversion to a
digital value; an analog to digital converter converting the
sampled and held analog signals to digital values; and a
multiplexer coupled to the analog-to-digital converter and
receiving digital values and communicating them to the comparator
according to a predetermined format and order.
[0208] In another embodiment of this system, the output signal
indicative of the integrated photon flux are analog signals, and
the system further comprising: a sample and hold circuit for
sampling an analog signal as a voltage representing a per pixel
integrated photon flux during the portion of the pixel display
frame time and holding that sampled signal; a multiplexer coupled
to the sample and hold circuit and receiving the sampled and held
analog values; and an analog to digital converter converting the
sampled and held analog signals received from the multiplexer and
converting the analog values to digital values and communicating
them to the comparator according to a predetermined format and
order.
[0209] In another embodiment of this system, the system further
comprising the external source of digital image data. In another
embodiment of this system, the external source of digital image
data comprises either a source of digital image data, or the
combination of an analog image data and a image analog-to-digital
converter.
[0210] In another embodiment of this system, the portion of the
frame time comprises the row address time or a shorter period of
time. In another embodiment of this system, the portion of the
frame time comprises substantially the entire frame time. In
another embodiment of this system, the portion of the frame time
comprises at least 50 percent of the entire frame time. In another
embodiment of this system, the portion of the frame time comprises
at least between 90 percent and 100 percent of the entire frame
time. In another embodiment of this system, the portion of the
frame time comprises at least 1 millisecond. In another embodiment
of the control system, the portion of the frame time comprises
substantially the row address time. In another embodiment of the
control system, the portion of the frame time comprises a time
between the row address time and the frame time. In another
embodiment of this control system, the portion of the frame time
comprises substantially the row address time. In another embodiment
of the control system, the portion of the frame time is equal to or
less than the row address time. In another embodiment of the
control system, the portion of the frame time is between 0.01 (1
percent) of the row address time and the row address time. In
another embodiment of the control system, the portion of the frame
time is between 0.1 (10 percent) of the row address time and the
row address time. In another embodiment of the control system, the
portion of the frame time is equal to or less than the frame time.
In another embodiment of the control system, the portion of the
frame time is greater than 0.01 of the row address time and less
than or equal to the frame time. In another embodiment of the
control system, the portion of the frame time is equal to multiple
frame times. In another embodiment of the control system, the
portion of the frame time comprises a time between 0.01 of the row
address time and the frame time.
[0211] In another embodiment, the invention provides a method for
operating an active-matrix display device having a plurality of
pixels, the method comprising: storing a calibration value for each
pixel and each gray level value that may be displayed by each of
the pixels in a calibration memory; storing a transformation in a
transformation memory for transforming first representations of an
image pixel gray level values to second representations of the same
image gray level pixel values for each pixel and each gray level
that may be displayed by each of the pixels in the display;
receiving first gray level representations of image pixel gray
level values for a plurality of pixels from an external source;
transforming the first gray level representations to an equivalent
number of second gray level representations for each pixel in
accordance with the stored transformation; generating image data
and control signals for driving pixel elements in a matrix display
device during a present display frame time in accordance with the
second representation of the image gray level pixel value;
generating an integrated photon flux signal for each of the
plurality of pixels in the display indicative of the integrated
photon flux on each of the plurality of pixels in the display
during a portion of the present display frame time; comparing the
plurality of integrated photon flux signals for a commanded gray
level and with the calibration values for the same gray level for
each pixel on a pixel-by-pixel basis and generating a plurality of
comparison results indicating a difference between the commanded
gray level and the measured gray level; and identifying any
deviation for each pixel based on the comparison results and
directing a change in the stored transformation to be applied
during a subsequent display flame time for at least pixel locations
and pixel gray level values that have a difference between the
calibration and the measured values.
[0212] In one embodiment of this method, the step of identifying
any deviation includes storing pixel deviations between a
calibrated pixel luminance value and a measured pixel luminance
value in a pixel deviation memory.
[0213] In one embodiment of this method, the calibration values are
voltage values and the integrated photon flux values are voltages,
and the comparison includes a comparison of voltages. In one
embodiment of this method, the calibration values are current
values and the integrated photon flux values are currents, and the
comparison includes a comparison of currents. In one embodiment of
this method, the calibration values are charge values and the
integrated photon flux values are charges, and the comparison
includes a comparison of charges.
[0214] In one embodiment of this method, the integrated photon flux
values are analog signals, and the method further comprising:
sampling an analog signal as a voltage representing a per pixel
integrated photon flux during the portion of the pixel display
frame time and holding that sampled signal for conversion to a
digital value; and converting the analog sampled signal to a
digital signal.
[0215] In one embodiment of this method, the integrated photon flux
values are analog signals, and the method further comprising:
sampling an analog signal as a charge representing a per pixel
integrated photon flux during the portion of the pixel display
frame time and holding that sampled signal for conversion to a
digital value; and converting the analog sampled signal to a
digital signal.
[0216] In one embodiment of this method, the integrated photon flux
values are analog signals, and the method further comprising:
sampling an analog signal as a current representing a per pixel
integrated photon flux during the portion of the pixel display
frame time and holding that sampled signal for conversion to a
digital value; and converting the analog sampled signal to a
digital signal.
[0217] In one embodiment of this method, the method further
comprising generating the first gray level representations of image
pixel gray level values for a plurality of pixels. In one
embodiment of this method, the digital image data comprises either
a digital image data, or an analog image data that is converted to
a digital data by an image analog-to-digital converter. In one
embodiment of this method, the portion of the frame time comprises
a time less than or equal to the row address time.
[0218] In one embodiment of this method, the portion of the frame
time comprises substantially the entire frame time. In one
embodiment of this method, the portion of the frame time comprises
at least 50 percent of the entire frame time. In one embodiment of
this method, the portion of the frame time comprises at least
between 90 percent and 100 percent of the entire frame time. In one
embodiment of this method, the portion of the frame time comprises
at least 1 millisecond. In another embodiment of the method, the
portion of the frame time comprises a time between the row address
time and the frame time. In another embodiment of this method, the
portion of the frame time comprises substantially the row address
time in another embodiment of the method, the portion of the frame
time is equal to or less than the row address time. In another
embodiment of the method, the portion of the frame time is between
0.01 (1 percent) of the row address time and the row address time.
In another embodiment of the method, the portion of the frame time
is between 0.1 (10 percent) of the row address time and the row
address time. In another embodiment of the method, the portion of
the frame time is equal to or less than the frame time. In another
embodiment of the method, the portion of the frame time is greater
than 0.01 of the row address time and less than or equal to the
frame time. In another embodiment of the method, the portion of the
frame time is equal to multiple frame times. In another embodiment
of the method, the portion of the frame time comprises a time
between 0.01 of the row address time and the frame time.
[0219] In another embodiment of the method, the subsequent display
frame time is the next display time following the present display
frame time. In another embodiment of the method, the subsequent
display frame time is any display frame time following the present
display frame time. In another embodiment of the method, the
subsequent display frame time is a frame time at display
initialization or power-on. In another embodiment of the method,
the image data and control signals include display matrix row and
column control and drive signals operable to cause an image to be
displayed during a frame time for a plurality of pixels.
[0220] In another embodiment of the method, the pixels include at
least one thin film transistor constructed from amorphous silicon.
In another embodiment of the method, the pixels include at least
one thin film transistor constructed from polysilicon. In another
embodiment of the method, the pixels include at least one thin film
transistor constructed from cadmium selenide. In another embodiment
of the method, the pixels include at least one thin film transistor
constructed from semiconductor material.
[0221] In another embodiment of the method, the portion of the
present display frame time is equal to or less than the row address
time. In another embodiment of the method, the portion of the
present display frame time is equal to or less than the frame time.
In another embodiment of the method, the portion of the present
display frame time is equal to multiple frame times. In one
embodiment of this method, the portion of the frame time comprises
substantially the entire frame time. In one embodiment of this
method, the portion of the frame time comprises at least 50 percent
of the entire frame time. In one embodiment of this method, the
portion of the frame time comprises at least between 90 percent and
100 percent of the entire frame time. In one embodiment of this
method, the portion of the frame time comprises at least 1
millisecond. In another embodiment of the method, the portion of
the frame time comprises a time between the row address time and
the frame time. In another embodiment of this method, the portion
of the frame time comprises substantially the row address time. In
another embodiment of the method, the portion of the frame time is
equal to or less than the row address time. In another embodiment
of the method, the portion of the frame time is between 0.01 (1
percent) of the row address time and the row address time. In
another embodiment of the method, the portion of the frame time is
between 0.1 (10 percent) of the row address time and the row
address time. In another embodiment of the method, the portion of
the frame time is equal to or less than the frame time. In another
embodiment of the method, the portion of the frame time is greater
than 0.01 of the row address time and less than or equal to the
frame time. In another embodiment of the method, the portion of the
frame time is equal to multiple frame times. In another embodiment
of the method, the portion of the frame time comprises a time
between 0.01 of the row address time and the frame time.
[0222] In another embodiment of the method, the display device is
an organic light emitting diode (OLED) pixel display device. In
another embodiment of the method, the organic light emitting diode
(OLED) is a small molecule OLED. In another embodiment of the
method, the organic light emitting diode (OLED) is a polymer OLED
(PLED). In another embodiment of the method, the organic light
emitting diode (OLED) is a phosphorescent OLED (PHOLED). In another
embodiment of the method, the organic light emitting diode (OLED)
is constructed from any organic material in any combination of
single or multiple layers of organic materials and electrodes. In
another embodiment of the method, the organic light emitting diode
(OLED) is a active matrix OLED. In another embodiment of the
method, the display device is an electroluminescent device. In
another embodiment of the method, the display device is an plasma
emission device. In another embodiment of the method, the display
device is any controllable photon emissive device. In another
embodiment of the method, the active matrix display device is
constructed from amorphous silicon. In another embodiment of the
method, the active matrix display device is constructed from
poly-silicon. In another embodiment of the method, the active
matrix display device is constructed from cadmium selenide. In
another embodiment of the method, the active matrix display device
is constructed from any type of semiconductor material.
[0223] In another aspect the invention provides an active-matrix
display and pixel structure for feedback stabilized flat panel
display. In one embodiment the invention provides an emissive pixel
device having an integrated luminance sensor, the pixel device
comprising: a light emitting device; a drive circuit generating a
current to drive the light emitting device to a predetermined
luminance corresponding to an image voltage and applying the drive
current to the light emitting device during a frame time; a photo
sensor that exhibits a change in electrical characteristic in
response to a change in incident photon flux disposed near the
light emitting device to intercept a measurable photon flux when
the light emitting device is in an emitting state; a charge storage
device coupled with the sensor for accumulating or releasing
charges and exhibiting a capacitance charge and voltage
proportional to the charge at a time; and a control circuit or
other control means for controlling the charging and discharging of
the charge storage device in response to changes in the electrical
characteristics of the sensor during at least a portion of the
frame time.
[0224] In one embodiment of this device, the device further
comprising: a voltage reading circuit for measuring the voltage
across the charge storage device at the end of the at least a
portion of a display frame time, the measured voltage being an
indication of a measured luminance of the pixel during the portion
of the frame time.
[0225] In another embodiment of the device, the device further
comprising: a current reading circuit for measuring the current
from the charge storage device at the end of the at least a portion
of a display frame time, the measured current being an indication
of a measured luminance of the pixel during the portion of the
frame time.
[0226] In another embodiment of the device, the device further
comprising: a charge reading circuit for measuring the charge on
the charge storage device at the end of the at least a portion of a
display frame time, the measured charge being an indication of a
measured luminance of the pixel during the portion of the frame
time.
[0227] In another embodiment of these devices, the device further
comprising a feedback control circuit for applying a correction to
the pixel drive circuit during a subsequent frame time so that the
measured luminance during the subsequent frame time will have a
smaller variation from the reference luminance than during the
frame time of the measurement.
[0228] In one embodiment of the device, the voltage across the
charge storage device represents an integrated photon flux during
the portion of the frame time over which the control circuit
permitted charging or discharging or the charge storage device. In
another embodiment of the device, the voltage reading circuit
further comprising a voltage comparator circuit that receives the
voltage across the charge storage device and a reference voltage
corresponding to a target luminance and generates a difference
signal representing the difference between the target luminance and
the measured luminance. In another embodiment of the device, the
current reading circuit further comprising a current comparator
circuit that receives the current from the charge storage device
and a reference current corresponding to a target luminance and
generates a difference signal representing the difference between
the target luminance and the measured luminance. In another
embodiment of the device, the charge reading circuit further
comprising a charge comparator circuit that receives the charge on
the charge storage device and a reference charge corresponding to a
target luminance and generates a difference signal representing the
difference between the target luminance and the measured luminance.
In another embodiment of the device, the read circuit is configured
as a charge amp/transimpedance amplifier having a charge amplifier
circuit. In another embodiment of the device, the charge
amp/transimpedance amplifier measures the charge required to
re-charge the storage capacitor to the full charge voltage, and
that an inverting (-) input of the charge amplifier circuit has a
resistance that is at least one Gig-ohm and the output of the
charge amplifier circuit has a resistance that is between about 0
ohms and 100 ohms. In another embodiment of the device, the
resistance of the output of the charge amplifier circuit is a
resistance that is substantially between 0 ohms and 10 ohms. In
another embodiment of the device, the control circuit comprises at
least one transistor. In another embodiment of the device, the
charge storage device comprises at least one capacitor. In another
embodiment of the device, the charge storage device comprises
multiple capacitors. In another embodiment of the device, the
sensor device comprises a photoresistive or photoconductive device
having a resistivity or conductivity that varies according to the
number of photons incident on it. In another embodiment of the
device, the light emitting device emits photons. In another
embodiment of the device, the light emitting device comprises a
light emitting diode. In another embodiment of the device, the
light emitting device comprises an organic light emitting diode. In
another embodiment of the device, the light emitting device
comprises an inorganic light emitting diode. In another embodiment
of the device, the light emitting device is one of a plurality of
light emitting devices arranged as a two-dimensional array arranged
as rows and columns. In another embodiment of the device, the light
emitting device comprises a light emitting diode.
[0229] In another embodiment of the device, the light emitting
device comprises an organic light emitting diode. In another
embodiment of the device, the organic light emitting diode (OLED)
is a small molecule OLED. In another embodiment of the device, the
organic light emitting diode (OLED) is a polymer OLED (PLED). In
another embodiment of the device, the organic light emitting diode
(OLED) is a phosphorescent OLED (PHOLED). In another embodiment of
the device, the organic light emitting diode (OLED) is constructed
from any organic material in any combination of single or multiple
layers of organic materials and electrodes. In another embodiment
of the device, the organic light emitting diode (OLED) is a active
matrix OLED. In another embodiment of the device, the display
device is an electroluminescent device. In another embodiment of
the device, the display device is an plasma emission device. In
another embodiment of the device, the display device is any
controllable photon emissive device.
[0230] In another embodiment of the device, the active matrix
display device is constructed from amorphous silicon. In another
embodiment of the device, the active matrix display device is
constructed from poly-silicon. In another embodiment of the device,
the active matrix display device is constructed from cadmium
selenide. In another embodiment of the device, the active matrix
display device is constructed from any type of semiconductor
material.
[0231] In another embodiment of the device, the photo sensor
element includes a resistive component and the resistance changes
in proportion to the photon flux incident upon it. In another
embodiment of the device, the photo sensor element includes
photodiode exhibiting a change of resistance and/or conductance in
response to photon flux incident upon it. In another embodiment of
the device, the photo sensor element includes phototransistor
exhibiting a change of resistance and/or conductance in response to
photon flux incident upon it. In another embodiment of the device,
the photo sensor intercepts photons emitted by the light emitting
device and converts them to charge carriers making the material of
the sensor a better current conductor and thus having lower
electrical resistance. In another embodiment of the device, the
lower resistance of the photo sensor drains a charge stored on a
capacitor coupled in parallel across a two-terminal resistive
component of the sensor. In another embodiment of the device, the
pixel circuit includes a photon flux count integrator comprising
the sensor having a resistive component and a capacitor. In another
embodiment of the device, the amount of drained charge is
proportional to the number of photons incident on the sensor during
a portion of the frame time and the voltage on the capacitor at the
end of the portion of the frame time is an indicator of the photons
counted or integrated during the portion of the frame time.
[0232] In another embodiment of the device, a particular luminance
level produces a photocurrent in the sensor, and the magnitude of
the photocurrent serves as an indication of the luminance (photon
flux through the sensor). In another embodiment of the device, the
photocurrent is proportional to the luminance. In another
embodiment of the device, the photocurrent is directly proportional
to the luminance. In another embodiment of the device, the photo
responsive element is disposed within the same pixel as the light
emitting diode. In another embodiment of the device, the photo
responsive element is integrated with the light emitting diode so
that all or substantially all the photon flux emitted by the light
emitting diode is incident on the photo responsive element. In
another embodiment of the device, the photo responsive element has
a surface or layer that is physically located in contact with a
semiconductor anode side of the light emitting device.
[0233] In another embodiment of the device, the portion of the
frame time comprises the row address time or less. In another
embodiment of the device, the portion of the frame time comprises
substantially the entire frame time. In another embodiment of the
device, the portion of the frame time comprises at least 50 percent
of the entire frame time. In another embodiment of the device, the
portion of the frame time comprises at least between 90 percent and
100 percent of the entire frame time. In another embodiment of the
device, the portion of the frame time comprises at least 1
millisecond. In another embodiment of the device, the portion of
the frame time is equal to or less than the row address time. In
another embodiment of the device, the portion of the frame time
comprises a time between the row address time and the frame time.
In another embodiment of this device, the portion of the frame time
comprises substantially the row address time. In another embodiment
of the device, the portion of the frame time is equal to or less
than the row address time. In another embodiment of the device, the
portion of the frame time is between 0.01 (1 percent) of the row
address time and the row address time. In another embodiment of the
device, the portion of the frame time is between 0.1 (10 percent)
of the row address time and the row address time. In another
embodiment of the device, the portion of the frame time is equal to
or less than the frame time. In another embodiment of the device,
the portion of the frame time is greater than 0.01 of the row
address time and less than or equal to the frame time. In another
embodiment of the device, the portion of the frame time is equal to
multiple frame times. In another embodiment of the device, the
portion of the frame time comprises a time between 0.01 of the row
address time and the frame time.
[0234] In another aspect, the invention provides a method of
operating an emissive pixel device having an integrated luminance
sensor, the method comprising: generating a current to drive a
light emitting device to a predetermined luminance corresponding to
an image voltage and applying the drive current to the light
emitting device during a frame time; a charge storage device
coupled with the sensor for accumulating or releasing charges and
exhibiting a capacitance charge and voltage proportional to the
charge at a time; exposing a photo sensor that exhibits a change in
electrical characteristic in response to a change in incident
photon flux to photons emitted by the light emitting device during
the frame time; accumulating (charge) or draining (discharge)
charges to or from a charge storage device coupled with the sensor,
the sensor including a component that controls the rate of
accumulation or release of charges during the frame time; measuring
the voltage arising from the charges present on the charge storage
device at the end of a portion of the frame time, the measured
voltage being an indication of an actual luminance during the
portion of the frame time; comparing the luminance related measured
voltage with a reference target luminance for the pixel emitter
image voltage and pixel emitter drive current to generate a
difference value; and applying the difference value as a feedback
input to a correction circuit that modifies the image voltage and
drive current for the same pixel during a subsequent frame
time.
[0235] In one embodiment of the method, the light emitting device
comprises an inorganic light emitting diode. In one embodiment of
the method, the light emitting device comprises an organic light
emitting diode (OLED). In one embodiment of the method, the organic
light emitting diode (OLED) is a small molecule OLED. In one
embodiment of the method, the organic light emitting diode (OLED)
is a polymer OLED (PLED). In one embodiment of the method, the
organic light emitting diode (OLED) is a phosphorescent OLED
(PHOLED). In one embodiment of the method, the organic light
emitting diode (OLED) is constructed from any organic material in
any combination of single or multiple layers of organic materials
and electrodes. In one embodiment of the method, the organic light
emitting diode (OLED) is a active matrix OLED. In one embodiment of
the method, the display emissive device is an electroluminescent
device. In one embodiment of the method, the display emissive
device is an plasma emission device. In one embodiment of the
method, the display emissive device is any controllable photon
emissive device.
[0236] In one embodiment of the method, the active matrix is
constructed from amorphous silicon. In one embodiment of the
method, the active matrix is constructed from poly silicon. In one
embodiment of the method, the active matrix is constructed from
cadmium selenide. In one embodiment of the method, the active
matrix is constructed from any type of semiconductor material.
[0237] In one embodiment of the method, the photo sensor intercepts
photons emitted by the light emitting device and converts them to
charge carriers making the material of the sensor a better current
conductor and thus having lower electrical resistance. In one
embodiment of the method, the amount of accumulated or drained
charge is proportional to the number of photons incident on the
sensor during a portion of the frame time and the voltage on the
capacitor at the end of the portion of the frame time is an
indicator of the photons counted or integrated during the portion
of the frame time. In one embodiment of the method, a particular
luminance level produces a photocurrent in the sensor, and the
magnitude of the photocurrent serves as an indication of the
luminance (photon flux through the sensor). In one embodiment of
the method, the photo sensor element is disposed within the same
pixel as the light emitting diode.
[0238] In one embodiment of the method, the portion of the frame
time comprises the row address time or less. In one embodiment of
the method, the portion of the frame time comprises substantially
the entire frame time. In one embodiment of the method, the portion
of the frame time comprises at least 50 percent of the entire frame
time. In one embodiment of the method, the portion of the frame
time comprises at least between 90 percent and 100 percent of the
entire frame time. In one embodiment of the method, the portion of
the frame time comprises at least 1 millisecond. In one embodiment
of the method, the portion of the frame time is equal to or less
than the row address time.
[0239] In another embodiment of the method, the portion of the
frame time comprises a time between the row address time and the
frame time. In another embodiment of this method, the portion of
the frame time comprises substantially the row address time. In
another embodiment of the method, the portion of the frame time is
equal to or less than the row address time. In another embodiment
of the method, the portion of the frame time is between 0.01 (1
percent) of the row address time and the row address time. In
another embodiment of the method, the portion of the frame time is
between 0.1 (10 percent) of the row address time and the row
address time. In another embodiment of the method, the portion of
the frame time is equal to or less than the frame time. In another
embodiment of the method, the portion of the frame time is greater
than 0.01 of the row address time and less than or equal to the
frame time. In another embodiment of the method, the portion of the
frame time is equal to multiple frame times. In another embodiment
of the method, the portion of the frame time comprises a time
between 0.01 of the row address time and the frame time.
[0240] In another aspect the invention provides a device and method
for operating a self-calibrating emissive pixel. In one embodiment
the invention provides an emissive pixel device and a method for
operating a self-calibrating pixel, the method comprising:
establishing a sensor capacitor at a predetermined starting
voltage; delivering a current to a photon emitting device to cause
photons to be emitted at a predetermined target photon emission
level; exposing a sensor device, having electrical properties that
varies according to a photon flux on the sensor device, to the
emitted photon emission during at least a portion of a display
frame time; permitting the sensor capacitor to either charge or
discharge from the predetermined starting voltage through the
sensor device so that the portion of the frame time and the average
resistance of the sensor during the portion of the frame time
determine the amount of charge on the sensor capacitor; measuring
the voltage or charge remaining on the sensor capacitor at the end
of a portion of the frame time as an indication of the integrated
photon flux and pixel luminance during the portion of the frame
time used for measurement; and modifying the image voltage and
current to be applied to the same pixel and gray level during a
subsequent display frame time using the measured sensor capacitor
voltage as a feedback parameter.
[0241] In one embodiment of this method, the sensor comprises a
photoresistive device. In one embodiment of this method, the sensor
comprises a photoconductive device. In one embodiment of this
method, the sensor comprises at least one of a photodiode, a
photoresistor, a photoconductor, and a phototransistor. In one
embodiment of this method, the sensor comprises a phototransistor.
In one embodiment of this method, the sensor comprises a
photodiode. In one embodiment of this method, the established
capacitor starting voltage is established by charging the sensor
capacitor to a predetermined charging voltage. In one embodiment of
this method, the established capacitor starting voltage is
established at substantially zero volts. In one embodiment of this
method, the predetermined capacitor starting voltage is a non-zero
voltage having a voltage magnitude. In one embodiment of this
method, for a sensor capacitor that was charged to a non-zero
predetermined starting voltage and then permitted to discharge, the
difference voltage remaining across the sensor capacitor is an
indication of total photon integrated flux during the portion of
the frame time.
[0242] In one embodiment of this method, for a sensor capacitor
that was uncharged at substantially zero volts or charged at a
different voltage and then permitted to charge during the portion
of the frame integration time, the difference of the starting
voltage and the ending voltage across the sensor capacitor is an
indication of total photon integrated flux during the portion of
the frame time.
[0243] In one embodiment of this method, the step of modifying the
image voltage and current to be applied to the same pixel and gray
level during a subsequent display frame further comprises comparing
the measured sensor capacitor voltage with a reference calibration
voltage stored in a memory and generating a correction using the
difference between these voltages.
[0244] In one embodiment of this method, the method is performed
substantially in parallel for each pixel of a two-dimensional
active-matrix pixel array.
[0245] In one embodiment of this method, the current delivered is
delivered by applying a voltage to a control device that delivers a
current corresponding to that voltage to the photon emitting device
to cause photons to be emitted at a predetermined target photon
emission level.
[0246] In one embodiment of this method, the portion of the frame
time comprises the row address time or less. In one embodiment of
this method, the portion of the frame time comprises substantially
the entire frame time. In one embodiment of this method, the
portion of the frame time comprises at least 50 percent of the
entire frame time. In one embodiment of this method, the portion of
the frame time comprises at least between 90 percent and 100
percent of the entire frame time. In one embodiment of this method,
the portion of the frame time comprises at least 1 millisecond. In
one embodiment of this method, the portion of the frame time is
equal to or less than the row address time. In another embodiment
of the method, the portion of the frame time is between 0.01 (1
percent) of the row address time and the row address time. In
another embodiment of the method, the portion of the frame time is
between 0.1 (10 percent) of the row address time and the row
address time. In another embodiment of the method, the portion of
the frame time is equal to or less than the frame time. In another
embodiment of the method, the portion of the frame time is greater
than 0.01 of the row address time and less than or equal to the
frame time. In another embodiment of the method, the portion of the
frame time is equal to multiple frame times. In another embodiment
of the method, the portion of the frame time comprises a time
between 0.01 of the row address time and the frame time.
[0247] In one embodiment of the method, the method further
comprising charging a sensor coupled capacitor to a first
predetermined voltage through a sensor line by a transistor and
capacitor charging voltage source prior to an integration frame
time. In one embodiment of the method, a capacitor charge voltage
is applied over a sensor line and the sensor line only delivers
current when a measurement is being made of the sensor capacitor
voltage or when sensor capacitor is being recharged and the voltage
is highly stable and not subject to variation.
[0248] In another aspect the invention provides high-performance
emissive display device for computers, information appliances, and
entertainment systems. In one embodiment the invention provides an
information appliance comprising: a flat panel or other display
device comprising a plurality of active-matrix pixels arranged as a
two-dimensional array, each pixel including an organic light
emitting diode emitter, an emitter drive circuit receiving an input
image data for each pixel and generating a pixel drive signal
intended to produce a corresponding target pixel luminance during a
frame time, and an emitter luminance sensor and measurement circuit
that measures an electrical parameter indicative of the actual
luminance of each pixel over a portion of a measurement display
frame time; and a display logic subsystem coupled to the flat panel
display device and receiving the pixel luminance related electrical
parameter for each pixel and generating a correction to be applied
during a frame time subsequent to the measurement display frame
time to the input image data for each pixel based on a difference
between the target pixel luminance and the measured pixel
luminance.
[0249] In one embodiment, the information appliance further
comprises at least one of: a television monitor, a television
receiver, a CD player, a DVD player, a computer monitor or display,
a computer system, an automobile instrument panel, an aircraft
instrument display panel, a video game, a cellular telephone, a
personal data assistant (PDA), a telephone, a graphics system, a
printing system, a scoreboard system, an entertainment system, a
domestic or home appliance, a copy machine, a global positioning
system navigation display, a dynamic art display device, a camera,
and any combinations thereof.
[0250] In one embodiment of this information appliance, each of the
pixels comprises: a light emitting device; a drive circuit
generating a current to drive the light emitting device to a
predetermined luminance corresponding to an image voltage and
applying the drive current to the light emitting device during a
frame time; a photo sensor that exhibits a change in electrical
characteristic in response to a change in incident photon flux
disposed near the light emitting device to intercept a measurable
photon flux when the light emitting device is in an emitting state;
a charge storage device coupled with the sensor for accumulating or
releasing charges and exhibiting a capacitance charge and voltage
proportional to the charge at a time; a control circuit controlling
the charging and discharging of the charge storage device in
response to changes in the electrical characteristics of the sensor
during at least a portion of the frame time; a voltage reading
circuit for measuring the voltage across the charge storage device
at the end of the at least a portion of a display frame time, the
measured voltage being an indication of a measured luminance of the
pixel during the portion of the frame time; and a feedback control
circuit for applying a correction to the pixel drive circuit during
a subsequent frame time so that the measured luminance during the
subsequent frame time will have a smaller variation from the
reference luminance than during the frame time of the
measurement.
[0251] In another embodiment, the invention provides a method of
operating a display device of the type having a plurality of
active-matrix pixels arranged as a two-dimensional array, each
pixel including a light emitting diode emitter and an emitter drive
circuit receiving an input image data for each pixel and generating
a pixel drive signal intended to produce a corresponding target
pixel luminance during each frame display time; the method
characterized in that the method further includes: measuring a
voltage indicative of a photon flux intercepted by an emitter
luminance measurement circuit during at least a portion of a first
frame time; and comparing the measured voltage corresponding to a
measured luminance with a reference voltage corresponding to a
reference luminance to generate a difference signal and using the
difference signal to modify the input image data for each pixel
during a subsequent frame display time so that the pixel luminance
during the subsequent display frame time will more nearly equal the
reference luminance.
[0252] In one embodiment of this method, the portion of the frame
time comprises the row address time or less. In one embodiment of
this method, the portion of the frame display time comprises
substantially the entire frame time. In one embodiment of this
method, the portion of the frame display time comprises at least 50
percent of the entire frame time. In one embodiment of this method,
the portion of the frame display time comprises at least between 90
percent and 100 percent of the entire frame time. In one embodiment
of this method, the portion of the frame display time comprises at
least 1 millisecond. In one embodiment of this method, the portion
of the frame time is equal to or less than the row address time. In
another embodiment of the method, the portion of the frame time is
between 0.01 (1 percent) of the row address time and the row
address time. In another embodiment of the method, the portion of
the frame time is between 0.1 (10 percent) of the row address time
and the row address time. In another embodiment of the method, the
portion of the frame time is equal to or less than the frame time.
In another embodiment of the method, the portion of the frame time
is greater than 0.01 of the row address time and less than or equal
to the frame time. In another embodiment of the method, the portion
of the frame time is equal to multiple frame times. In another
embodiment of the method, the portion of the frame time comprises a
time between 0.01 of the row address time and the frame time.
[0253] In one embodiment of the method, the subsequent frame
display time is a frame display immediately following the first
display time. In one embodiment of the method, the subsequent frame
display time is a frame display a predetermined number of display
frames following the first frame display time for which the
luminance measurement was made, and wherein the predetermined
number of frames is any integer number of frames N. In one
embodiment of the method, the subsequent frame display time is a
frame display at the occurrence of a predetermined or dynamically
determined event.
[0254] In one embodiment of the method, the occurrence of a
predetermined or dynamically determined event is selected from a
display initialization event, a display power-on event, a display
time of operation event, a user initiated event, any automatic
policy or rule based event, and combinations of these.
[0255] In one embodiment of the method, the display device
comprises a flat panel display device that is a component in an
overall system and wherein the system is selected from the set of
systems consisting of: any information appliance, a television
monitor, a CD player, a DVD player, a computer monitor, a computer
system, an automobile instrument panel, an aircraft instrument
display panel, a video game, a cellular telephone, a personal data
assistant (PDA), a telephone, a graphics system, a printing system,
a scoreboard system, an entertainment system, a domestic or home
appliance, a copy machine, a global positioning system navigation
display, a dynamic art display device, a camera, and any
combinations thereof.
[0256] In one embodiment of the appliance and method, the light
emitting device comprises an organic light emitting diode (OLED).
In one embodiment of the appliance and method, the organic light
emitting diode (OLED) is a small molecule OLED. In one embodiment
of the appliance and method, the organic light emitting diode
(OLED) is a polymer OLED (PLED). In one embodiment of the appliance
and method, the organic light emitting diode (OLED) is a
phosphorescent OLED (PHOLED). In one embodiment of the appliance
and method, the organic light emitting diode (OLED) is constructed
from any organic material in any combination of single or multiple
layers of organic materials and electrodes. In one embodiment of
the appliance and method, the organic light emitting diode (OLED)
is a active matrix OLED. In one embodiment of the appliance and
method, the light emitting device is an electroluminescent device.
In one embodiment of the appliance and method, the light emitting
device is a plasma emission device. In one embodiment of the
appliance and method, the light emitting device is any controllable
photon emissive device.
[0257] In one embodiment of the appliance and method, the display
device is constructed from amorphous silicon. In one embodiment of
the appliance and method, the display device is constructed from
poly silicon. In one embodiment of the appliance and method, the
display device is constructed from cadmium selenide. In one
embodiment of the appliance and method, the display device is
constructed from any type of semiconductor material.
[0258] In another aspect, the invention provides an integrated
circuit. In one embodiment, the integrated circuit comprises: a
sample and hold circuit receiving an analog voltage signals
characterizing integrated photon flux and luminance measurements
from a plurality of display pixels; an analog-to-digital converter
receiving the sampled and held analog voltage signal and converting
the analog signal to a digital signal; a calibration value memory
for storing a reference value for each pixel and for each gray
level value the pixel may be required to display; at least one
comparator receiving at least one of the converted digital signal
value indicating a particular measured pixel luminance and at least
one reference signal value indicating a reference luminance for the
same pixel and generating a difference signal indicating a
deviation of the measured pixel luminance from the reference pixel
luminance; and a pixel deviation logic including a pixel deviation
memory for storing an indication of the deviation for the pixel. In
another embodiment of the integrated circuit, the pixel deviation
memory and the calibration value memory are logically defined
within a common physical memory. In another embodiment of the
integrated circuit, the pixel deviation memory and the calibration
value memory are defined within different physical memories.
[0259] Having described several methods in considerable detail it
will be appreciated that these descriptions include optional
device, apparatus, system, and methodological steps (features) that
may be combined so that fewer than the recited number of features
may be implemented to achieve the same or substantially same
result. It will also be appreciated that the order of the steps in
method claims may be modified in many instances to achieve the same
or substantially the same results and that the connectivity of
circuits and devices may often be modified while still achieving
the performance of the invention.
[0260] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention.
* * * * *