U.S. patent application number 16/126444 was filed with the patent office on 2019-03-14 for display optimization techniques for micro-led devices and arrays.
The applicant listed for this patent is VueReal Inc.. Invention is credited to Gholamreza Chaji.
Application Number | 20190080645 16/126444 |
Document ID | / |
Family ID | 65441676 |
Filed Date | 2019-03-14 |
![](/patent/app/20190080645/US20190080645A1-20190314-D00000.png)
![](/patent/app/20190080645/US20190080645A1-20190314-D00001.png)
![](/patent/app/20190080645/US20190080645A1-20190314-D00002.png)
![](/patent/app/20190080645/US20190080645A1-20190314-D00003.png)
![](/patent/app/20190080645/US20190080645A1-20190314-D00004.png)
![](/patent/app/20190080645/US20190080645A1-20190314-D00005.png)
United States Patent
Application |
20190080645 |
Kind Code |
A1 |
Chaji; Gholamreza |
March 14, 2019 |
DISPLAY OPTIMIZATION TECHNIQUES FOR MICRO-LED DEVICES AND
ARRAYS
Abstract
Systems and methods to achieve desired color accuracy, power
consumption, and gamma correction in an array of pixels of a
micro-LED display. The method and system provides an array of
pixels, wherein each pixel comprising a plurality of sub-pixels
arranged in a matrix and a driving circuitry configured to provide
an individual emission control signal to each sub-pixel of each
pixel in the array of pixels to independently control a emission
time and a duty cycle of each sub-pixel.
Inventors: |
Chaji; Gholamreza;
(Waterloo, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VueReal Inc. |
Waterloo |
|
CA |
|
|
Family ID: |
65441676 |
Appl. No.: |
16/126444 |
Filed: |
September 10, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62556608 |
Sep 11, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2933/0041 20130101;
H01L 33/502 20130101; G09G 3/2014 20130101; G09G 2300/0452
20130101; G09G 3/2003 20130101; G09G 2310/0264 20130101; H05B 45/37
20200101; H01L 22/24 20130101; H01L 25/0753 20130101; G09G 3/32
20130101 |
International
Class: |
G09G 3/32 20060101
G09G003/32; H05B 33/08 20060101 H05B033/08; G09G 3/20 20060101
G09G003/20 |
Claims
1. A display device comprising: an array of pixels, wherein each
pixel comprising a plurality of sub-pixels arranged in a matrix;
and a driving circuitry configured to provide an individual
emission control signal to each sub-pixel of each pixel in the
array of pixels to independently control a emission time and a duty
cycle of each sub-pixel.
2. The display device as claimed in claim 1, wherein a first
emission control signal is provided concurrently to each sub-pixel
of a first color in at least one row of pixels, a second emission
control signal is provided concurrently to each sub-pixel of a
second color in at least the one row of pixels, and a third
emission control signal is provided concurrently to each sub-pixel
of a third color in at least the row of pixels.
3. The display device as claimed in claim 2, wherein the first
color is red, the second color is green, and the third color is
blue.
4. The display device as claimed in claim 2, wherein a fourth
emission control signal is provided to each sub-pixel of a fourth
color in the array of pixels, wherein the fourth color is one of
cyan, white, and yellow.
5. The display device as claimed in claim 1, wherein the emission
control signal is a pulse-width-modulation (PWM) signal.
6. The display device as claimed in claim 1, wherein each pixel and
sub-pixel is a micro-light emitting device (LED).
7. The display device as claimed in claim 2, wherein the first,
second and third emission control signals are enabled at a same
time or a different time during a frame time.
8. The display device as claimed in claim 6, wherein the first,
second and third emission control signals are turned on and off
multiple times at different duty cycle during the frame time.
9. The display device as claimed in claim 1, wherein the emission
time or the duty cycle for each sub-pixel is dynamically adjusted
to tune the display device color and optimize power
consumption.
10. The display device of claim 1, wherein a frame data is
evaluated to find the optimized duty cycle and the emission
time.
11. The display device of claim 1, wherein an optimization
algorithm is employed to calculate a global or a local optimized
value for the duty cycle or the emission time for each
sub-pixel.
12. The display device as claimed in claim 9 , wherein the duty
cycle is optimized for two range of grayscales to achieve the
lowest power consumption.
13. A method for controlling a pixel circuit of an array of pixel
circuits of a display device, the pixel circuit comprising a
plurality of subpixels, the method comprising: providing an
individual emission control signal to each sub-pixel of each pixel
in the array of pixel circuits independently to control an emission
time and a duty cycle of the sub-pixels.
14. The method as claimed in claim 13, wherein the emission time or
the duty cycle for each sub-pixel is dynamically adjusted to tune
the display device color and optimize power consumption.
15. The method as claimed in claim 13, wherein a frame data is
evaluated to find the optimized duty cycle and the emission
time.
16. The method as claimed in claim 13, wherein an optimization
algorithm is employed to calculate a global or a local optimized
value for the duty cycle or the emission time for each
sub-pixel.
17. The method as claimed in claim 13 , wherein the duty cycle is
optimized for two range of grayscales to achieve the lowest power
consumption.
18. The method as claimed in claim 13, wherein the emission control
signal is a pulse-width-modulation (PWM) signal.
19. The method as claimed in claim 13, wherein each pixel and
sub-pixel is a micro-light emitting device (LED).
20. The method as claimed in claim 13, further comprising:
providing a first emission control signal concurrently to each
sub-pixel of a first color in at least one row of pixels; providing
a second emission control signal concurrently to each sub-pixel of
a second color in at least the one row of pixels; and providing a
third emission control signal concurrently to each sub-pixel of a
third color in at least the row of pixels.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/556,608, filed Sep. 11, 2017, which is hereby
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present disclosure relates generally to micro LED
displays and, more particularly, to a micro LED display system and
method for improving dynamic range, power consumption and color and
gamma correction of the micro LED display.
SUMMARY
[0003] Briefly stated, technologies are generally described herein
to achieve desired color accuracy, power consumption, and gamma
correction in an array of pixels of a micro-LED display. Using the
technologies described herein, either the duty cycles or the
emission times of sub-pixels arranged in a matrix for each pixel of
the micro-LED display may be adjusted to tune the display color
without affecting the gamma.
[0004] According to one embodiment, a display device may be
provided. The display device may include an array of pixels,
wherein each pixel may comprising a plurality of subpixels arranged
in a matrix. The display device may also include a driving
circuitry configured to provide an individual emission control
signal to each sub-pixel of each pixel in the array of pixels to
independently control a emission time and a duty cycle of each
sub-pixel.
[0005] According to other embodiment, a method for controlling a
pixel circuit of an array of pixel circuits of a display device
comprising a plurality of subpixels may include providing an
individual emission control signal to each sub-pixel of each pixel
in the array of pixel circuits independently to control an emission
time and a duty cycle of the sub-pixels.
[0006] The foregoing summary is illustrative only and is not
intended to be in any way limiting. In addition to the illustrative
aspects, embodiments, and features described above, further
aspects, embodiments, and features will become apparent by
reference to the drawings and the following detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The foregoing and additional aspects and embodiments of the
present disclosure will be apparent to those of ordinary skill in
the art in view of the detailed description of various embodiments
and/or aspects, which is made with reference to the drawings, a
brief description of which is provided next.
[0008] FIG. 1a is a circuit diagram showing individual emission
(EM) control signal for sub-pixel elements.
[0009] FIG. 1b is a timing diagram illustrating an example of three
different emission time created by three individual EM signal.
[0010] FIG. 1c is a timing diagram illustrating an example of
controlling the emission time of each sub-pixel.
[0011] FIG. 2a-2b diagrammatic illustrations of a power optimized
display driving scheme.
[0012] While the present disclosure is susceptible to various
modifications and alternative forms, specific embodiments or
implementations have been shown by way of example in the drawings
and will be described in detail herein. It should be understood,
however, that the disclosure is not intended to be limited to the
particular forms disclosed. Rather, the disclosure is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of an invention as defined by the appended
claims.
DETAILED DESCRIPTION
Color Share and Gamma Adjustment
[0013] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs.
[0014] As used in the specification and claims, the singular forms
"a", "an" and "the" include plural references unless the context
clearly dictates otherwise.
[0015] The term "comprising" as used herein will be understood to
mean that the list following is non-exhaustive and may or may not
include any other additional suitable items, for example one or
more further feature(s), component(s) and/or element(s) as
appropriate.
[0016] In this description, the term "sub-pixel" and "micro device"
are used interchangeably. However, it is clear to one skill in the
art that the embodiments described here are independent of the
device size. Each pixel and sub-pixel used in the description is a
light emitting micro-device (Micro-LED).
[0017] Micro-LEDs, in general, tend to have a nonlinear
current-luminance efficiency (Cd/A) as a function of the drive
current. This characteristic may often includes a peak of
efficiency at a certain current level. A display module may
consists an array (active or passive) of pixels. Each pixel itself
may comprised of multiple sub-pixels (RGB, RGBW, RGBY, or other
combination of color elements, e.g. blue with light conversion). In
order to get a target "white-point" (W.sub.x,y), it may be required
to mix certain ratios of the color elements. For instance, for
given Red (R.sub.x,y), Green (G.sub.x,y), and Blue (B.sub.x,y)
elements, one can use share factors to create the wanted color
based on the sum of all the sets, such as
K.sub.R.R.sub.x,y+K.sub.G.G.sub.x,y+K.sub.B.B.sub.x,y=W.sub.x,y
(1)
[0018] where Ki's are the share factors for the tri-color set and
x,y are two color coordinates that specify a point on a CIE
chromaticity diagram, which represents the mapping of human color
perception in terms of the two CIE parameters x and y.
[0019] In some applications, it may be required to drive the
micro-LEDs at the current level corresponding to the peak
efficiency. In this scenario, the desired output luminance level
may be achieved using modulation techniques, e.g. Pulse Width
Modulation (PWM). Accordingly, a duty-cycle of the emission (EM)
control signal will determine the luminance level. However, in
order to achieve the desired white-point, one cannot apply the same
duty cycle to each of the color elements. The duty-cycle refers to
the total amount of time a pulse is `on` over the duration of the
cycle/frame.
[0020] FIG. 1a is a circuit diagram showing individual EM signals
for sub-pixel elements. The driving circuitry 100 includes a
plurality of emission control signals (102, 104, 106) and a
plurality of data lines (108, 110, 112) extending to a pixel 120
having a plurality of sub-pixels elements (114, 116 and 118).
[0021] As shown in FIG. 1a, instead of providing combined emission
control for each pixel 120, a driving circuitry 100 consisting of
three individual EM control signals EM.sub.R 102, EM.sub.G 104, and
EM.sub.B 106 for each subpixel (R 114, G 116, B 118) may be
provided to facilitate proportional contribution of color elements.
The driving circuitry 100 may be configured to provide an
individual emission control signal to each sub-pixel of each pixel
in the array of pixels to independently control a emission time and
a duty cycle of the sub-pixels.
[0022] By controlling emission control signals EM.sub.R 102,
EM.sub.G 104 and EM.sub.B 106 of sub-pixels rather than pixels, a
desired luminance may be achieved. Thus, a first emission control
signal e.g. EM.sub.R 102 is provided concurrently to each sub-pixel
of a first color in at least one row of pixels, a second emission
control signal e.g. EM.sub.G 104 is provided concurrently to each
sub-pixel of a second color in at least the one row of pixels, and
a third emission control signal e.g. EM.sub.B 106 is provided
concurrently to each sub-pixel of a third color in at least the row
of pixels. The first color may be provided as red, the second color
may be provided as green, and the third color may be provided as
blue.
[0023] In one embodiment, a fourth emission control signal may be
provided to each sub-pixel of a fourth color in at least one row of
pixels in the array of pixels, wherein the fourth color is one of
cyan, white, and yellow. The emission control signal may be a
pulse-width-modulation (PWM) signal.
[0024] FIG. 1b is a timing diagram illustrating an example of three
different emission time created by three individual EM signals
EM.sub.R 102, EM.sub.G 104 and EM.sub.B 106. Here, a frame may
start with a off time due to programing or other requirement. Then,
the three EM control signals 102, 104, 106 of subpixels are
enabled. In one case, all three emission signals may be enabled at
the same time, or they may be enabled at different time during a
frame time 120. In an example as demonstrated in FIG. 1b, the first
color (e.g. red) has longer emission time 126 to operate at its
peak efficiency and meeting display requirements. The second color
(e.g. green) has a shorter emission time 124 and the third color
(e.g. blue) can have a different emission time 122 as well. Despite
simplicity, the main challenge with this approach can be the color
mixing.
[0025] To address this challenge, each emission is turned on and
off multiple times at different duty cycle during the frame time
120 as demonstrated in FIG. 1 c. FIG. 1 c is a timing diagram
illustrating an example of controlling the emission time of each
sub-pixel. As shown in Fig lc, different duty cycles 132, 134, and
136 are used for controlling the emission time of each subpixels.
Moreover, there can be black frame before or after a combination of
few toggles.
[0026] Either the duty cycles 132, 134, 136 or the emission times
122, 124, 126 as demonstrated in FIG. 1b and FIG. 1c can be
adjusted to tune the display color without affecting the gamma. For
example, if for some application, the display needs to have a white
point more towards red, the red emission time 122 (or red duty
cycle 136) can be increased to provide more red light.
[0027] For illustrative purposes, only one pixel 120 is explicitly
shown in the FIG. 1a. It is understood that it is not limited to a
particular number of rows and columns of pixels. For example, a
display system can be implemented with a display screen with a
number of rows and columns of pixels commonly available in displays
for mobile devices, monitor-based devices, and/or
projection-devices. In a multichannel or color display, a number of
different types of pixels, each responsible for reproducing color
of a particular channel or color such as red, green, or blue, will
be present in the display. Pixels of this kind may also be referred
to as "subpixels" as a group of them collectively provide a desired
color at a particular row and column of the display, which group of
subpixels may collectively also be referred to as a "pixel".
Power Optimization and Dynamic Range Enhancement
[0028] Displays configured to display a video feed of moving images
typically refresh the display at a regular frequency for each frame
of the video feed being displayed. Displays incorporating an active
matrix can allow individual pixel circuits to be programmed with
display information during a program phase and then emit light
according to the display information during an emission phase.
Thus, displays operate with a duty cycle characterized by the
relative durations of the program phase and the emission phase. In
addition, the displays operate with a frequency that is
characterized by the refresh rate of the display. The refresh rate
of the display can also be influenced by the frame rate of the
video stream. In such displays, the display can be darkened during
program phases while the pixel circuits are receiving programming
information. Thus, in some displays, the display is repeatedly
darkened and brightened at the refresh rate of the display. A
viewer of the display can undesirably perceive that the display is
flickering depending on the frequency of the refresh rate.
[0029] A frame defines the time period that includes a programming
cycle or phase during which each and every pixel in the display
system is programmed with a programming voltage indicative of a
brightness and a driving or emission cycle or phase during which
each light emitting device in each pixel is turned on to emit light
at a brightness commensurate with the programming voltage stored in
a storage element. A frame is thus one of many still images that
compose a complete moving picture displayed on the display
system.
[0030] There are at least two schemes for programming and driving
the pixels: row-by-row, or frame-by-frame. In row-by-row
programming, a row of pixels is programmed and then driven before
the next row of pixels is programmed and driven. In frame-by-frame
programming, all rows of pixels in the display system are
programmed first, and all of the pixels are driven at the same
time. Either scheme can employ a blanking time at the beginning or
end of each frame during which the pixels are not emitting any
light.
[0031] For emissive displays, the current of the emissive device is
controlled by the pixel circuit to create different grayscales
during each frame cycle. In one case, the amount of the current is
controlled. The main challenge with this method is that the some
emissive devices (e.g. micro-LEDs) have efficiency curves that
drops at lower current and higher current densities. Another method
is to control the duration of the current applied to the pixel for
each grayscale. There are several issues associated with this
approach. However, the main one is the timing. The high resolution
and high frame rate displays cannot accommodate the timing needed
for this approach.
[0032] In one embodiment, the frame timing is adjusted so that the
emissive device is working on optimized current density most of the
time. For example, if the display is working mainly at a specific
brightness, the duty cycles 132, 134, 136 or emission times 122,
124, 126 as shown in FIGs. lb and 1 c can be adjusted so that the
emissive device current density is optimized for such brightness.
For example, the red emissive device optimized current density can
be J.sub.r-opt. If the red pixel is on during the entire frame time
at such current density, the display can produce brightness
B.sub.r-full. If the major red brightness is B.sub.r-mj, the
emissive time 122 can be calculated as
T.sub.f*B.sub.r-full/B.sub.r-mj where T.sub.f is the frame time.
Similarly, one can calculate the duty cycle 132 for red.
[0033] In another embodiment, one method to find the major
brightness, is to use the peak brightness and the applications. For
example, videos are mainly running at 30% of peak brightness.
[0034] In yet another embodiment, another method to find the
optimize duty cycles 132, 134, 136 and emission times 122, 124, 126
is to evaluate the frame data to find the optimized duty cycle. In
one case, the major brightness is calculated for the frame to find
the proper value for the duty cycles or emission times. In another
method, an optimization algorithm is run to find a global or a
local optimized value for the duty cycles or the emission times.
The same method can be used for multiple frames instead of one
frame.
[0035] In another method, the frame can be divided into several sub
frame and the emission times or the duty cycles that are optimized
for each sub frames for a power consumption of different ranges of
gray scales. These optimization can be done similar to the one done
for a single sub frame.
[0036] FIG. 2a-2b depicts two examples of power optimized display
driving scheme. A panel driving scheme comprises plurality of
sub-frame cycles in which at least one gray-scale level may be
optimized to achieve lower power consumption.
[0037] In the driving scheme of FIG. 2a, a panel driving scheme
200a comprises a frame having a plurality of sub-frame cycles such
as low grayscale emission time 222l and no emission 208l for low
grayscale subframe 206l and high grayscale emission time 222h and
no emission 208h for high grayscale subframe 206h during a frame
time 220. As illustrated in FIG. 2a, the emission time 222l, 222h
optimization for both low and high grayscale ranges is used. Every
row of the display array is accessed only twice during each frame
time 220 to refresh the pixel contents within that row according to
the optimized video data. The row access interval may be separated
by one or more row times. Accordingly, in this driving scheme, the
memory buffer depth requirement may be limited to the number of
rows between two consecutive access intervals.
[0038] In the driving scheme 200b of FIG. 2b, the duty cycle
optimization is used. Here, the duty cycle 232l and 232h is
optimized for two range of grayscales (e.g. low and high) to
achieve the lowest power consumption.
[0039] According to some examples, a display device may be
provided. The display device may comprising an array of pixels,
wherein each pixel comprising a plurality of subpixels arranged in
a matrix and a driving circuitry configured to provide an
individual emission control signal to each sub-pixel of each pixel
in the array of pixels to independently control a emission time and
a duty cycle of each sub-pixel.
[0040] According to another embodiments, the display may further
include a first emission control signal may be provided
concurrently to each sub-pixel of a first color in at least one row
of pixels, a second emission control signal may be provided
concurrently to each sub-pixel of a second color in at least the
one row of pixels, and a third emission control signal may be
provided concurrently to each sub-pixel of a third color in at
least the row of pixels. The first color may be red, the second
color may be green, and the third color may be blue.
[0041] Another to some embodiments, the display may further
comprising a fourth emission control signal may be provided to each
sub-pixel of a fourth color in the array of pixels, wherein the
fourth color is one of cyan, white, and yellow.
[0042] According to further embodiments, the emission control
signal may be a pulse-width-modulation (PWM) signal and each pixel
and sub-pixel may be a micro-light emitting device (LED).
[0043] According to yet further embodiments, the first, second and
third emission control signals may enabled at a same time or a
different time during a frame time. The first, second and third
emission control signals may turned on and off multiple times at
different duty cycle during the frame time.
[0044] According to further examples, the emission time or the duty
cycle for each sub-pixel may dynamically adjusted to tune the
display device color and optimize power consumption.
[0045] According to some embodiments, a frame data may be evaluated
to find the optimized duty cycle and the emission time. An
optimization algorithm may employed to calculate a global or a
local optimized value for the duty cycle or the emission time for
each sub-pixel. The duty cycle may be optimized for two range of
grayscales to achieve the lowest power consumption.
[0046] According to other embodiments, a method for controlling a
pixel circuit of an array of pixel circuits of a display device,
the pixel circuit comprising a plurality of subpixels may include
providing an individual emission control signal to each sub-pixel
of each pixel in the array of pixel circuits independently to
control an emission time and a duty cycle of the sub-pixels.
[0047] According to some embodiments, the emission time or the duty
cycle for each sub-pixel may dynamically adjusted to tune the
display device color and optimize power consumption.
[0048] According to another embodiments, a frame data may evaluated
to find the optimized duty cycle and the emission time. an
optimization algorithm may be employed to calculate a global or a
local optimized value for the duty cycle or the emission time for
each sub-pixel. The duty cycle may optimized for two range of
grayscales to achieve the lowest power consumption.
[0049] According to yet other embodiments, the emission control
signal may be a pulse-width-modulation (PWM) signal. Each pixel and
sub-pixel is a micro-light emitting device (LED).
[0050] According to some other embodiments, the method may further
comprising providing a first emission control signal concurrently
to each sub-pixel of a first color in at least one row of pixels,
providing a second emission control signal concurrently to each
sub-pixel of a second color in at least the one row of pixels; and
providing a third emission control signal concurrently to each
sub-pixel of a third color in at least the row of pixels.
[0051] While particular embodiments and applications of the present
invention have been illustrated and described, it is to be
understood that the invention is not limited to the precise
construction and compositions disclosed herein and that various
modifications, changes, and variations can be apparent from the
foregoing descriptions without departing from the spirit and scope
of the invention as defined in the appended claims.
* * * * *