U.S. patent application number 12/774760 was filed with the patent office on 2010-11-11 for apparatus and drive method for display light source.
Invention is credited to Chen-Jean Chou.
Application Number | 20100283719 12/774760 |
Document ID | / |
Family ID | 42771511 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100283719 |
Kind Code |
A1 |
Chou; Chen-Jean |
November 11, 2010 |
Apparatus and drive method for display light source
Abstract
A display device comprising a backlight and a light valve array,
such as an array of liquid crystal (LC) cells, and a method for
operating such display device are provided. The display and the
method operate to reduce the intensity of the light source of the
backlight during the period when the light valve (LC cell) is in
the transition from a dark state to a bright state, and to increase
the intensity during the period when the light valve (LC cell) is
near or mostly completing its transition. As light transmission is
ineffective in the dark or transitional state of the light valve,
lighting power efficiency is improved by delivering the light
mostly in the final state of the light valve.
Inventors: |
Chou; Chen-Jean; (New City,
NY) |
Correspondence
Address: |
CHEN-JEAN CHOU
21 RIDGEFIELD ROAD
NEW CITY
NY
10956
US
|
Family ID: |
42771511 |
Appl. No.: |
12/774760 |
Filed: |
May 6, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61176887 |
May 9, 2009 |
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Current U.S.
Class: |
345/102 |
Current CPC
Class: |
G09G 3/3648 20130101;
G09G 2320/0646 20130101; G09G 3/3406 20130101 |
Class at
Publication: |
345/102 |
International
Class: |
G09G 3/36 20060101
G09G003/36 |
Claims
1. A display device comprising: a plurality of light emitting
elements; wherein the response time of said light emitting elements
is T2; a light modulator comprising a plurality of light valves
modulating light directed thereto; wherein the relaxation time from
the fully charged state to the fully relaxed state of said light
valve is T1, and wherein T1 is substantially greater than T2; a
control circuit performing recurring operations on said light
emitting elements and said light valves; said operations comprising
setting the light valves according to an image information to
display image; said operations comprising: 3) applying image signal
to a light valve according to the image data for displaying image;
4a) a delay period after operation 3); 4b) after said delay period,
applying the control signal that sets at least a light emitting
element that illuminates said light valve in 3) to a bright state;
wherein the response time of the light valve in response to said
operation 3) is T3; said delay period is at least one-twentieth of
T3.
2. The device according to claim 1 wherein said control signals for
setting said light emitting element to a bright state set the light
emitting element to an intensity substantially higher than the
average light output of the light emitting element averaged over a
period of one or more operation cycles.
3. The device according to claim 1 wherein the duration of
operation 4a) is longer than operation 4b).
4. The device according to claim 1 wherein said operations further
comprise: 1) applying the control signals for setting a light
emitting element to off or a dimming state; wherein said operation
1) precedes operation 3).
5. The device according to claim 4 wherein said operations further
comprises 2) applying a control signal that sets a light valve
illuminated by said light emitting element to a relaxed state.
6. The device according to claim 5 wherein in an operation cycle,
said operation 2) precedes said operation 1) by a small fraction of
T1; or said operation 1) precedes said operation 2); or said
operation 1) leads and overlaps operation 2); wherein a small
fraction of T1 is less than 30% of T1.
7. The device according to claim 5 wherein in an image refreshing
operation cycle, operation 2) precedes operation 3).
8. The device according to claim 1 wherein said plurality of light
valves and said light emitting elements are arranged separately in
plurality of groups; wherein the groups of light valves are
operated in coordination with the groups of light emitting elements
in a manner that said operation 3) operates on a group of light
valves, setting the light valves according to image data, and said
operation 4b) operates on a group of light emitting elements
illuminating said group of light valves to a bright level after the
delay period of 4a).
9. The device according to claim 5 wherein said operation step 1)
sets all said light emitting elements to off or a dimming state,
and wherein said operation 2) sets all Light valves to a relaxed
state; wherein in an operation cycle, said operation 1) precedes or
overlaps said operation 2), and said operation 2) precedes said
operation 3).
10. The device according to claim 5 wherein a group of said light
valves are arranged to connect to a first common electrode, and
wherein said operation 2), setting a light valve to a relaxed
state, is effectuated on said group of Light valves by applying a
control voltage to said first common electrode.
11. The device according to claim 10 wherein said common electrode
connects to all light valves of the display, wherein said operation
2) operates on all light valves by applying a voltage to said
common electrode, setting all light valves to the relaxed
state.
12. The device according to claim 1 wherein a group of said light
emitting elements is arranged to connected to a second common
electrode, wherein said operation 1) is effectuated on the group of
light emitting elements by applying a control voltage to the second
common electrode.
13. The device according to claim 5 wherein the relaxed state of a
light valve corresponds to a state where the voltage applied on the
light valve is zero or near neutral.
14. The device according to claim 5 wherein said plurality of light
valves form array of cells; said control circuit comprising at
least a data driver circuit for delivering image data to said light
valves, and at least a scan driver circuit for selecting light
valve cells to receive the image data according to a control
timing; wherein said scan driver comprising a plurality of output
terminals each connecting to a plurality of light valve cells via a
scan electrode; wherein said scan driver further comprises a
recurring discharge operation; said discharge operation enabling a
selected group of said scan driver terminals at a time so that all
light valves connected to said group of scan driver output
terminals are enabled at the same time to receive data from said
data driver during such discharge operation.
15. The device according to claim 14 wherein said data driver
operates to set a discharging voltage to its data output terminals
for the period when said scan driver performs said discharging
selection; said discharging voltage setting the light vales to a
relaxed state.
16. The device according to claim 1 wherein said operations further
comprises 5) applying a control signal for setting a light valve to
a charged or over-charged state.
17. The display device according to claim 16 wherein said charged
or over-charged state of the light valve corresponds to a voltage
near or higher than the voltage for operating said light valve for
displaying a full range of gray scale.
18. The device according to claim 16 wherein said charged or
over-charged state of the light valve corresponds to a dark state
of said light valve.
19. The device according to claim 16 wherein said operation 5)
precedes said operation 3).
20. The device according to claim 19 further comprising an
operation 7) applying a control signal that sets a light emitting
element to off or a dark state.
21. The device according to claim 20 wherein said operation 7)
precedes operation 4b).
22. The device according to claim 1 wherein in said operation 4b),
said control circuit applies the control signals for setting said
light emitting element to a bright state according to a scaling
relation with the average or maximum image brightness in the area
illuminated by said light emitting element, wherein said scaling
relation provides a brightness setting that increases with
increasing average or maximum image brightness in said area for at
least part of the brightness range.
23. The device according to claim 1 wherein a said light valve is a
liquid crystal (LC) cell or a MEMS cell.
24. The device according to claim 5 wherein said relaxed state of
said light valve corresponds to a bright state at which the LC cell
allows the light to pass to the viewing side.
25. A method of operating a display device; said device comprising:
a plurality of light emitting elements; a plurality of light valves
modulating light output from said light emitting elements; said
method comprising recurring operations of: 3) applying image signal
to a light valve for displaying an image; 4a) a delay period after
operation 3); 4b) after said delay period, applying a control
signal that sets at least a light emitting element that illuminates
said light valve of 3) to a bright state; wherein the response time
of the light valve in response to said operation 3) is T3; said
delay period is at least a significant fraction of T3.
26. The method according to claim 25 wherein said operations
further comprise: 1) applying the control signals that sets a light
emitting element to off or a dimming state; wherein said operation
1) precedes operation 3).
27. The method according to claim 25 wherein said control circuit
performs recurring operations on said light emitting elements and
said light valves; said operations further comprising 2) applying a
control signal that sets a light valve in the area illuminated by
said light emitting element to a relaxed state.
28. A circuit for operating a light valve and a light emitting
element in coordination, said circuit performing recurring
operations of: applying a SELECT signal for enabling said light
valve to receive an image data; providing a delay time; after said
delay time, applying a lighting control signal for enabling power
for driving said light emitting element; wherein said delay time is
substantially greater than zero.
29. The circuit according to claim 28 wherein said delay time is at
least a significant fraction of the response time of said light
valve in response to receiving said image data.
30. The circuit according to claim 28 wherein said operations
further comprise a step of applying a control signal for setting
said light valve to a charged or over-charged state.
31. The circuit according to claim 30 wherein said charged or
over-charged state of the light valve corresponds to a voltage
setting near or higher than the voltage that sets said light valve
to the lowest gray scale.
32. The circuit according to claim 30 wherein said charged or
over-charged state of the light valve corresponds to a dark state
of said light valve.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority of U.S. Provisional
Patent Application No. 61/176,887, filed on May 9, 2009, which is
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an image display apparatus
and a drive method to operate the display apparatus. The display
apparatus comprises a light source and a light modulator that
modulates the light from the light source to produce images. The
display apparatus further comprises a control means for operating
the light source and the light modulator. The control means
operates the light source and the light modulator in coordination,
and in such a manner that reduces the power of the light source
during the transition of the light valves from a dark state to a
bright state and increases the light power when the light valves
are approaching the final state of the transition, thereby saving
the lighting power. Furthermore, the light source comprises light
emitting elements with response time substantially faster than the
relaxation time of the light modulator, and is operated in such a
manner that eliminates the adverse effects from switching the light
modulator.
[0004] 2. Description of the Prior Art
[0005] A liquid crystal (LC) cell is a light valve that modulates
light directed thereto. A liquid crystal display (LCD) produces
images by modulating light with a plurality of spatially
distributed liquid crystal cells. As in other light valves such as
MEMS, such modulation controls the amount of light delivered to the
viewer.
[0006] Using the LC display (LCD) as an example, the images are
displayed by setting the liquid crystal cells to various gray
levels according to the spatial distribution of the brightness and
color in the images. Each cell represents a spatial and color point
in the image. Accordingly, in displaying motion pictures, the LC
cells are set in such a manner that the light directed thereto is
modulated to replicate the temporal and spatial image in brightness
and color.
[0007] A light valve changes states in response to a setting
voltage by re-arranging its structure according to the applied
voltage. For example, an LC cell changes its molecular alignment
according to the applied voltage. Such change of state requires a
period of time to settle to the final state. During the transition,
the cell does not provide the full optical property as defined by
the final state. Accordingly, when an LC cell is reset to a bright
state from a dark state, the cell remains dark or partially dark
until the later stage of the transition. Consequently, if the light
intensity is kept constantly high, the light and the lighting power
is not utilized efficiently as the cell is inhibiting the light
transmission in a significant portion of time.
[0008] In a situation when an LC cell is set to a dark state from a
bright state, the optical transmission of the cell remains high at
the early stage of the transition from the initial state to the
final state. Accordingly, the light continues to be transmitted in
a cell where the cell is set dark. Therefore, extra light is light
is consumed.
[0009] In the conventional display, the illuminating light is not
reduced when a light valve (such as an LC cell) is in the
transition from a dark state to a bright or in the opposite
direction. The present invention provides a display apparatus and
method to reduce the consumption of unnecessary lighting power
during the period that a light valve, such as an LC cell, is in the
transition and only partially performing the optical property of a
designated state. Lighting power is provided when the light valve
has substantially conformed to the optical property of the
designated state.
[0010] In this specification, a preferred embodiment of the light
valve is a liquid crystal (LC) cell for the purpose of
illustration.
SUMMARY OF THE INVENTION
[0011] The present invention provides a display apparatus
comprising a light source and a plurality of light valves, wherein
the response time of the light source is faster than the response
of the light valves. A preferred embodiment of such light source is
a plurality of light emitting diodes (LED). A preferred embodiment
of the light valves is an array of liquid crystal (LC) cells. The
light source may comprise multiple lighting elements wherein each
lighting element may be switched independently. The light source
may also be constructed in a way that the lighting elements are
arranged in groups, where all elements in one group is switched on
and off together. The display device displays images according to
input image signals. The present invention further comprises a
control device controlling the output light intensity of the light
source and the transmission of the LC cells in synchronism.
[0012] In a preferred embodiment of the present invention, the
display apparatus is operated in a manner that in refreshing the
image data of a light valve, the lighting elements illuminating
said light valve are set to provide light output in a fraction of
the refreshing cycle and after a delay period. A preferred
embodiment of the delay period is a significant fraction of the
response time of the light valve. A 5 percent or more of the
response time is a significant fraction.
[0013] The present invention provides a method for operating the
display apparatus in a manner that the light is turned on or
increased following a delay period after setting the image data to
a light valve illuminated by the light source.
[0014] The present invention further provides a display apparatus
and a method for operating the apparatus wherein the method of
operation comprises setting the illuminating light to dark prior to
setting the light valve to represent an image point, a delay period
following said setting of the light valve, and setting said
illuminating light to a bright level after the delay period.
[0015] The present invention further comprises the apparatus and
method of operation to operate the apparatus according to the
previous paragraph wherein the operation further comprises setting
the illuminating light to a dark level, and an operation of setting
the light valve to a relaxed state; wherein in a preferred
embodiment the relaxed state corresponds to a bright state of the
light valve.
[0016] In a preferred embodiment, the LC cells are constructed in
an orientation that the relaxed state corresponds to the bright
state that allows the highest degree of transmission of light to
the viewing side.
[0017] Furthermore, the present invention provides a display
apparatus with LC cells operated in a manner that a cell of the
display is first set to a relaxed state, thereafter set to the
state to replicate the image. In an operation of setting a LC cell
to the relaxed state, a control signal enabling the writing of data
is applied to a group of cells for receiving the input data; such
enabling operation may be performed by applying a select signal to
the scan electrode connected to the cells thereby turning on a
transistor in a pixel circuit that connects to the data electrode.
In an alternative embodiment, said group of LC comprises the entire
cells of the display.
[0018] In coordination with setting the LC cells to the relaxed
state, the light source illuminating such cells is operated in
synchronous with the dynamic change of state of the cells so that
the illumination is reduced (dark) when the cells are in the
transition from a dark state to a bright level, or during the
operation of setting a group of cells to the relaxed state. The
duration of this light-extinguishing period is a fraction of a
frame time which is the time for refreshing (updating data for) a
full image frame. The operation time for applying the control
signals for setting the cells to the relaxed state is approximately
the same as that of addressing image data to a single display line.
A preferred embodiment is to group the display lines in such a
manner that all lines in a group are set to the relaxed state
simultaneously. Accordingly, the added operation time for setting
to the relaxed state is less than a small fraction of a frame time
As the illumination is turned off for the cells being set to the
relaxed state or in the transition from a dark to a bright level,
the change of state of the LC cells that deviates from the image is
not visible and does not produce any disturbing artifact.
Accordingly, power efficiency is improved, and a longer time may be
allowed for the cell to approach and settle to the relaxed state
without introducing adverse effect to image quality.
[0019] The present invention further provides an apparatus
comprising LC cells and LED elements, and an operation method
thereof to set the LC cells to replicate the input image after
setting the LC cells to the relaxed state. The LED light source is
then turned on to provide distributed illumination as defined by
the input image signal.
[0020] The present invention provides a display apparatus
comprising LC cells and an operation method thereof wherein the
illuminating light is reduced during setting the LC cells, and when
the LC cell is pre-set to a relaxed state. Accordingly, since the
illumination light source is extinguished when the LC cells are in
the transition, the leak of light during the transition of cell is
eliminated, thereby improving the contrast ratio and eliminating
flicker.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIGS. 1a, 1 b, and 1c are illustrations of a LC cell
response in a conventional LC display.
[0022] FIGS. 2a, 2b and 2c are schematic diagrams of a preferred
embodiment of the present invention.
[0023] FIG. 2d is a schematic diagram of a preferred embodiment of
the present invention.
[0024] FIG. 3 is a schematic diagram of a preferred embodiment of
the present invention.
[0025] FIG. 4 is a schematic diagram of a preferred embodiment of
the present invention.
[0026] FIG. 5 is a schematic diagram of a preferred operation of
the present invention.
[0027] FIG. 6 is schematic diagram of a preferred embodiment of the
present invention.
[0028] FIG. 7 is a schematic diagram of a preferred embodiment of
the present invention.
[0029] FIGS. 8a, 8b, 8c are schematic diagrams illustrating a
preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] A light valve is a device that modulates the light directed
thereto according to a control signal. Examples of light valve
include passive and active liquid crystal cell, and MEMS cell. For
the purpose of illustration, the liquid crystal (LC) cell is used
as the preferred embodiment for the light valve hereinafter in this
description.
[0031] A typical LC cell comprises at least two electrodes where a
voltage is applied to set the state of the LC cell. The state of
the LC cell is determined by the arrangement of LC molecules in
combination with other optical components such as the polarizer
films integrated as part of the LC cell. The applied voltage sets
the optical transmission of the LC cell via changing the alignment
of the LC molecules.
[0032] Accordingly, in operating a liquid crystal (LC) cell, a
voltage is applied to an LC cell on the two electrodes where the
liquid crystal is filled between the two electrodes. The LC is
switched between the relaxed state and an energized (i.e., charged)
state by the applied voltage across the two electrodes, and may be
set to any state between the fully relaxed state and the fully
charged state according to the applied voltage. In a fully relaxed
LC state, the control voltage, as well as the electrical field
between the electrodes, is nearly zero and the LC material is
relaxed and aligned to the boundary surfaces mostly according to
its internal molecular forces, with little or no influence from the
externally applied electrical force. In a charged state of an LC
cell, an applied voltage and its associated electrical field causes
the LC material to have preferential alignment in the direction of
the electrical field according to the strength of the electrical
field, thereby changing the optical property of the LC cell.
Accordingly, different degree of light modulation by an LC cell is
effectuated by the applied voltage, thereby modulating the amount
of passing light.
[0033] A control signal, typically an applied voltage, causes a
light valve to change from its current state to a final state. The
response time is the measure of time for the light valve to
substantially complete such change of state in response to an
applied voltage. For example, in a common practice, the time for
completing 90 percent of the transition of such change of state is
considered as the response time.
[0034] In this specification, a significant fraction of a response
time (T3) refers to a substantially measurable fraction of T3. In
practice, a 5% or more of the response time is a significant
fraction in this specification. As described in subsequent
paragraphs, a longer delay produces more significant effect in
reducing the power consumption.
[0035] In this description, a light modulator is a device that
modulates the light directed thereto from a light source, according
to a control signal. A light modulator may be a single cell or
comprises a plurality of cells, wherein each said cell operates to
modulate the light directed thereto according to a control signal.
A preferred embodiment of a light modulator comprises light valves
or optical components that modify the direction, intensity, or both
of the light directed thereto. The liquid crystal display (LCD)
array is the preferred embodiment hereinafter for the purpose of
illustration in this description.
[0036] The alignment of LC molecules and the optical properties of
an LC cell are influenced by the electrical field induced by an
applied voltage. In the absence of an applied voltage and the
associated electrical field, the LC orientation is mostly aligned
according to the structures on the surface surrounding the LC cell.
In operating an LC cell in a display device, the control signal
(typically a voltage for LC cell) and the voltage applied on the LC
electrodes change with time according to input image signal. An
increasing control voltage causes more charge accumulation on the
LC cell and a stronger electrical field, and a decreasing control
voltage causes discharging and lowering electrical field. In a
preferred embodiment, a stronger electrical field causes the LC to
align more preferentially along the direction of the electrical
field, and a decreasing electrical field allows the LC to relax
more towards its alignment with surface structures. Accordingly,
the increase in magnitude of the applied voltage relates to a
charging or energizing process, and decrease of voltage relates to
the relaxation of the LC.
[0037] The response of an LC cell (and other light valves) is
substantially slower in relaxation than in energizing. For example,
a liquid crystal (LC) cell responds to a zero voltage that sets the
cell to a charge neutral state (relaxed state) in about 10 to 30
millisecond; same LC cell responds to a voltage that energizes (or
charges) the cell in about 5 milliseconds or less.
[0038] During the transition from the initial state to the final
state of the LC cell, the optical property of the LC cell changes
with the time. For example, for a control signal that sets an
initially dark LC cell to a bright state, the LC cell switches from
dark to bright in a time frame close to the response time.
Accordingly, in the early stage after applying such control signal,
this LC cell remains mostly in a state of low optical transmission
and the light utilization is ineffective. Consequently, the
lighting power is mostly wasted during the transition of an LC cell
from a dark state to a bright state.
[0039] Preferred embodiments of the present invention are herein
described using light emitting diodes (LED) as light source, and
liquid crystal display (LCD) cells as illustration. Examples of
constructing a display apparatus comprising array of LCD cells and
LED light source are found in U.S. patent application Ser. No.
11/754,268 and U.S. Pat. No. 5,408,109, and examples of using
organic light emitting diode to form active matrix display devices
are found in U.S. Pat. No. 5,684,365, U.S. Pat. No. 6,157,356, and
U.S. Provisional Patent Application No. 61/176,887, all of which
are hereby incorporated by reference.
[0040] A preferred embodiment of the present invention uses an
illuminating light source that switches in a fractional time of
that of switching the LC cells. An example of such preferred
embodiment is using LED as the light source and LCD cells as the
light valves. The LED response time (T2) is on the order of 200
micro seconds, and the typical LC response time (T1) is a few
milliseconds.
[0041] FIGS. 1a-1c illustrate a typical transition of the optical
transmission of a preferred embodiment of the LC cell in response
to an abrupt increase of the voltage applied to the electrodes of
the LC cell. In this preferred embodiment, an applied voltage
higher in magnitude (i.e., stronger electrical field) results in a
lower optical transmission, and the bright LC state corresponds to
V=0. FIG. 1a provides the change of applied control voltage with
time. An abrupt voltage change from V0 to V1 occurs at the time t0.
FIG. 1b illustrates the change of optical transmission of the LC
cell after the voltage change. The initial state of the LC cell has
an optical transmission indicated by 110. The optical transmission
increases with time after the voltage change at t0, and approaches
its final optical transmission 111 with increasing time. The final
equilibrium state 111 may take a substantially long time to reach.
In practice, a preferred definition of the response time is taken
as the time to reach 90 percent of the total transition, i.e. the
level 112 at t1. The difference between 111 and 112 is 10 percent
of the total change of optical transmission from 110 to 111. A
preferred definition of the response time is T3=t1-t0.
[0042] In a conventional display system, the light source remains
on during the period when the light valve (LC cell) is changing
from a dark state to a bright state, i.e., between t0 and t1. As
illustrated in FIG. 1c, the light source remains at an intensity
level of 102 in the time between t0 and t1. Since the LC cell
remains in a state of low optical transmission in this time, the
light transmission is inhibited and does not produce any desired
lighting effect for the image. The lighting energy indicated by the
area 103 is consumed without producing useful effect. Consequently,
the utilization of the light is not effective, and the lighting
power is wasted.
[0043] In a display system where the LC cells are set to a dark
state each time when an image is refreshed, the LC cells are driven
from a dark state to a brighter state each time the image is
refreshed. As described above, significant lighting power in such
system is consumed while LC cells are in the dark states, resulting
in low brightness and low power efficiency. An example of such
system is a display system using the overdrive scheme and with an
intermediate black frame.
[0044] The present invention provides an apparatus comprising a
light source and a light valve such as an LC cell, and a method for
operating such display system. According to this method, the
lighting power is kept low or off during the period when the LC
cell is in the transition from an initial state to a final state.
The lighting power is turned on or increased when the LC cell is
near the completion or in the late stage of the transition after
setting the LC state. FIG. 2 provides an illustration of a
preferred embodiment of the present invention. As in FIG. 2a, at t0
a control signal is applied to an LC cell to set the LC cell to a
state according to the applied signal V1. An example of the control
signal is the data signal of image data refreshing that sets each
of the LC cells to a state according to the image data. The
response of the LC cell is illustrated in FIG. 2b. A preferred
embodiment for setting the light intensity is provided in FIG. 2c,
wherein the light intensity is set to low or off between t0 and t1,
and the light intensity is set to bright at t1 and maintain to be
bright for a period after t1. A delay period T=t1-t0 is provided
between setting the LC cell at t0 and setting the light intensity
to bright at t1.
[0045] A schematic drawing of a preferred embodiment of the
apparatus for the operation described above is provided in FIG. 4.
FIG. 4 is a side view of a display panel, wherein 403 is an
illuminating light source such as an LED, 405 is a group of a
plurality of LC cells (light valves), and 404 is an LC cell
illuminated by the light source 403. In an example where the LC
cells are arranged in rows and columns, 404 represents a row of LC
cells, and 405 represents a section of the LC rows. In a preferred
embodiment, the light source comprises a plurality of lighting
element as illustrated by 401 in FIG. 4, and the light valves (LC
cells) 402 comprise a plurality of groups of 405. The data
electrodes are connected to the plurality of LC cells, such as the
column electrodes in a typical LC display array, and the control
circuit comprises circuit controlling the LC cells image data
setting and circuit for setting the intensity of LED 403.
[0046] Accordingly, the present invention provides an apparatus
comprising a light source; a plurality of light valves modulating
light output from said light source; a data electrode for applying
data voltages to said light valves; a control circuit performing
recurring operations on said light emitting elements and said light
valves; said operations comprising:
[0047] 3) applying image signal to a light valve according to the
image data for displaying image;
[0048] 4a) a delay period after operation 3);
[0049] 4b) after said delay period, applying the control signal
that sets at least a light emitting element that illuminates said
light valve of 3) to a bright state;
[0050] wherein the response time of the light valve in response to
said operation 3) is T3;
[0051] Said delay period is a significant fraction of T3 or at
least one-twentieth of T3. Since the light power is not used
effectively when the LC is in the transition, a longer delay time,
i.e., a larger fraction of the response time when the situation
allows, is a preferred embodiment of the present invention.
[0052] In a preferred embodiment, the light valves are LC
cells.
[0053] In a preferred embodiment, applying the image data to set
the LC cells and applying signals to set the LED intensity operate
in coordination in a group-by-group or section-by-section manner.
In a preferred embodiment where the LC cells are in rows and
columns, a group of LC cells correspond to a section of rows of LC
cells. Such a section of rows of LC cells is represented by 405 in
FIG. 4 where the drawing shows a side view of a display panel. In a
first period, the image data are applied (i.e., addressed) to the
LC cells row by row sequentially in the section. After the
completion of the addressing of said section, and after a delay
period, a control signal is applied to the LED to turn on the LED
light to illuminate the section of the LC cells. Such operation
proceeds section by section and scans through the whole display
panel. In another embodiment, the section by section operation is
controlled in a manner that the addressing the image proceeds line
by line continuously, and the LED lighting element are turned on
after the full section of LC cells under its illumination has
completed the image data setting.
[0054] FIG. 2d further provides a preferred embodiment of the
operation of the present invention wherein the light intensity is
set to a level 206 which is substantially higher than the average
intensity 102, and is operated in a short duration T4 substantially
shorter than the time for displaying one image frame. An example of
the preferred embodiment is to set the light intensity 206 to 3
times or higher than the average intensity 102 in a duration of 1/5
of a frame time. For example, in a display system where the image
is refreshed at 120 frames per second, each frame is displayed for
a duration of 1/120 second or .about.8.3 milliseconds. The
operation of the short duration pulse of high intensity
illumination may be performed to set the intensity at 3 times
higher than the light level of 102 in 1.7 ms in the later stage of
a frame period when the LC transition is near its completion.
[0055] FIG. 3 provides a preferred embodiment of the operation
sequence of the present invention, wherein 312 is the time period
during which an operation is performed to apply image signal to a
light valve 404 (in FIG. 4) according to the image data for the
image point at the location of 404 for displaying the image, and a
delay period 314 after the operation 312 is provided; and wherein,
after said delay period 314, in the time period 317, an operation
is performed to apply the control signal that sets at least a light
emitting element 403 that illuminates said light valve 404 to a
bright state.
[0056] The efficiency of light power may also be improved by
reducing the light intensity in a gradual manner during the period
when an LC cell is in the transition. FIG. 5 illustrates a
preferred embodiment of the operation wherein the light intensity
is reduced at or slightly before applying the control signal at t0
to set the LC cell state. The light intensity is increased at the
time t4 in a later stage of the LC transition after setting the LC
state at t0. In this operation, the signals controlling the light
intensity does not have to be an abrupt change. Either a gradual
change or an abrupt change will operate to achieve the improvement
of lighting power efficiency.
[0057] The present invention further provides a display apparatus
according to the previous paragraphs wherein in said operation 4b),
said control circuit applies the control signals for setting said
light emitting element to a brightness level according to a scaled
brightness level. In a preferred embodiment, said scaled brightness
level relates to the average or maximum image brightness in the
area illuminated by said light emitting element with a scaling
relation. In a preferred embodiment, the scaling relation is an
increasing function with increasing average or maximum image
brightness in said area in at least part of the gray scale range
(i.e., part of the range from full dark 0 to full bright 255.) For
example, such a scaling relation applies in the range from gray
level 100 to gray level 200. In another preferred embodiment, said
scaled brightness is in proportion to the average or maximum image
brightness in the area illuminated by said light emitting element.
The proportionality need not to be linearly proportional.
[0058] The present invention further provides a drive method to
operate a display apparatus comprising an illuminating light source
and a plurality of light valves modulating light from said light
source in a manner that before addressing or refreshing the light
valves with new image data, the light valves are set to a charged
or over-charged state. The present invention further provides a
circuit as the control circuit to perform such operations. Such
control circuit operates to deliver a voltage to charge the light
valve (LC cell) according to a timing sequence.
[0059] The present invention further provides a display apparatus
and the operation method according to FIG. 3 and the previous
description of paragraph 52, wherein the method further comprises
an operation of 5) applying a control signal for setting an LC cell
to a charged or over-charged state prior to setting the cell to
display image data. FIG. 6 provides a schematic drawing of a
preferred embodiment of the operation of the display apparatus,
wherein 610 indicates the time period of the operation 5) applying
a control signal for setting an LC cell to a charged or
over-charged state prior to setting the cell to display image data.
The operation 610 precedes operation 312 which corresponds to
operation 3) applying image signal to a light valve according to
the image data for displaying image. In a preferred embodiment of
the LC cell, the charged or over-charged state corresponds to a
dark state. For an LC cell, this corresponds to low or no optical
transmission for the LC cell.
[0060] The present invention further provides a drive method to
operate a display apparatus comprising an illuminating light source
and a plurality of light valves modulating light from said light
source in a manner that before addressing or refreshing the light
valves with new image data, the light source is set to a dimming
state and the light valves are set to a discharged state. The
present invention further provides a circuit as the control circuit
to perform such operations.
[0061] Accordingly, the present invention further comprises 1)
setting a light emitting element to off or a dimming state. An
illustration of the operation is provided in FIG. 7 wherein 711
indicates the operation timing for operation 1). A dimming state of
a light source corresponds to a light source setting where the
light output is near the minimum of the dynamic range of the light
output in an operation. For example, a setting to turn an LED off
may set the LED to the lowest light level of its operation range
where the light output is nearly, but not completely, extinguished.
A dimming state in such example represents a setting near the
lowest lighting level of the LED.
[0062] Furthermore, the present invention further comprises an
operation 2) applying a control signal for setting a light valve
illuminated by said light emitting element of the previous
paragraph to a relaxed state; wherein in an operation cycle, said
operation 1) precedes, or overlaps said operation 2). In another
preferred embodiment, said operation 2) may lead said operation 1)
by a small fraction of the response time. A preferred embodiment of
a small fraction of T1 is less than 30% of T1. Since the light
valve responds slower than the lighting element in the present
invention, the light valve has not changed substantially in the
time within a small fraction of the response time. Therefore, the
light transmission has not changed substantially in such period. A
preferred embodiment of operation 2) is illustrated in FIG. 7
wherein 710 indicates the operation timing of operation 2).
[0063] FIG. 8a provides a schematic drawing of the 3-dimensional
illustration of a preferred embodiment of a display apparatus of
the present invention, wherein the apparatus comprises an array of
LC cells 820, and the light source 821 illuminating the LCD array
820. The arrangement of the light source may be a single lighting
element, one or more planner light sources, one or more lighting
tubes, or an array of lighting elements such as LEDs shown as 822
in FIG. 8b. Preferred embodiment of a planar light source includes
a light diffuser or a luminescent layer coupled with a light
source. It is construed that the present invention is not limited
by the type, shape, or the arrangement of the light source and
lighting elements.
[0064] FIG. 8c provides a schematic drawing of the circuit diagram
of a preferred embodiment of present invention, wherein the scan
driver circuits 832 provides multiple scanning signals for the
selection of cells in the LCD array 831 to receive data, the data
driver 833 delivers image data to LCD array 831, LED driver circuit
836 provides drive current to the LED light source 835, and the
control circuit 837 operates to process image data and provide
synchronized control signals to the LCD and LED drivers. In one
preferred embodiment, the LED driver 836 is constructed to have
drivers distributed in the LED array wherein each driver output
control an LED or a set of LED in series. Register or memory may
also be integrated in the driver to maintain a drive current for a
prolonged period of time. In another preferred embodiment, the LED
driver 836 is constructed in rows and columns, to address the LED
array with drive signals, wherein, each element of LED array is
connected to a local driver circuit that responds to the drive
signal and sets the LED driver current. In response to the control
signals generated by the controller 837, the LED driver 836
increases or decrease drive current to the LED, thereby increasing
or decreasing the light output of the LED lighting elements. In
response to the controller signals for the LCD array, the LCD
driver 832 selects the LCD cells to receive the data input, thereby
increasing or decreasing the light transmission of the selected LCD
cells according to the data signals.
[0065] A preferred scan driver 832 comprises a plurality of
outputs. The cells of LCD array 831 are arranged in scan groups
wherein all cells in one scan group are connected to the same
output terminal of the scan driver 832, and are selected
simultaneously to receive the data. A preferred scan group is a row
of cells in the array. Without limiting the generality of a scan
group, in the following description, a row indicates a scan group
that is connected to the full set of data driver outputs.
Therefore, different rows of cells must be selected at different
time for receiving different image data of their own. For this
reason, a scan (or row) driver used in a conventional LCD display
operates to select one scan group (or one row) at a time, and
operates sequentially.
[0066] In a preferred embodiment of the present invention, the
driver circuit 832 further incorporates a function that operates to
select a plurality of rows of the LCD cell array simultaneously by
a control signal. The driver circuit 832 in another embodiment of
the present invention further incorporates a function that operates
to select all rows of the LCD cell array simultaneously. In yet
another preferred embodiment of the present invention, the scan
driver incorporates a function to set all the selected rows of
cells simultaneously to a state that corresponds to a relaxed state
of the LC cell. The driver circuit 832 may be a single integrate
circuit (IC) that has sufficient output terminals to connect to and
control the LCD rows as described, or an assembly of multiple
driver ICs each one having the full function as described above and
operating on the LCD lines connected to its output terminals
independently according to its control signal.
[0067] In the present invention, the control circuit 837 provides a
synchronized timing control to drive the LED 835 and LCD 831. FIG.
3 provides a timing diagram of a preferred embodiment of the
synchronized drive of LED and LCD. The time axis indicates the
direction of the time.
[0068] A preferred embodiment of the control means is a control
circuit comprising a programmed integrated circuit (IC) or a
plurality of integrated circuit elements. The program comprises
executable instructions to perform the operations provided in this
invention. Such control circuit is typically assembled on a printed
circuit board.
[0069] A preferred embodiment of the LCD display is structured so
that the relaxed state of the LCD cells corresponds to a bright
state. In a relaxed state, the electrical field between the two
electrodes is nearly zero, and the LC is aligned to the surfaces
according to the molecular forces and the surface structures. A
preferred embodiment is structured so that the directions of LC
alignment at the light entering surface (i.e., the back side of the
LC cell) and at the light exiting surface (the front side of the LC
cell) are different by an angle; the orientations of the polarizer
at the entering surface and the orientation of the polarizer at the
existing surface are different by a similar angle. Accordingly,
highest amount of light passes from the back side to the viewing
side when LC is in the relaxed state. Furthermore, the transition
of the LC material from a relaxed state to a charged (i.e.,
energized) state is substantially faster than the transition in the
opposite direction. In such typical embodiment, a relaxed state of
LC cell corresponds to the bright state. The description herein
illustrates the present invention using such embodiment.
Furthermore, in a preferred embodiment of the LC cell, the charged
state corresponds to a dark state.
[0070] Since the lighting element is turned off or dimmed during
the delay period, the duration of light output is shortened.
Accordingly, the light intensity is increased during the lighting
period. A preferred embodiment here is to set a substantially
higher light intensity during the lighting period than in the
situation of the constant light source. An example of the preferred
embodiment is to set the light intensity in reverse proportion to
the duration during which the light source is turned on.
[0071] As described herein above, the operation of the display
device may continue in a subsequent cycle for another input image
data, which may be different from the previous input image data or
repeating the same data, with all the operations and variations
described above included or partially included in such subsequent
operation cycle.
[0072] In a preferred embodiment, the operations or parts of the
operations are programmed into an integrated circuit (IC). Such IC
comprises the circuit for performing such operations and may also
include circuits for peripheral operations such as input and
output, and image processing. The control circuit comprises said
integrated circuit and is typically fabricated on a printed circuit
board with other circuitry, or completely integrated in one IC. In
further detail, such control circuit comprises at least a timing
management or generating circuitry and control signal circuitry to
provide clock and control signals to operate the light emitting
element and the LC cells according to the sequences described
herein above. Such circuit may be constructed by programming a
logic array, or by designing or converting to an application
specific IC.
[0073] Furthermore, the present invention comprises a control
circuit comprising scan driver circuit to enable the selection of
all LCD lines in a group, as illustrated by area 405 of FIG. 4. A
scan driver is so constructed and assembled with the display
apparatus to operate to select all lines corresponding to the cells
in area 405. Furthermore, a data driver is constructed and
assembled in the display to deliver a data signal synchronously
with the scan driver to set all data lines to a voltage state
corresponding to the charged state, or the relaxed state of the LC
cells, according to the operations.
[0074] A typical liquid crystal display comprises scan electrodes
for selection and data electrodes for delivering image data to the
LC cells. Each LC cell comprises a thin-film transistor (TFT)
having a gate terminal and a data terminal (drain terminal of the
TFT). A plurality of LC cells, typically a row of LC cells, are
connected via the gate terminals to a scan electrode. Applying a
SELECT signal on a scan electrode selects all cells connected
thereto to receive image data from the data electrode.
[0075] The present invention further provides a control circuit
comprising the scan driver described above, and a data driver
circuit for delivering image data to its data output terminals
according to the input image signal; wherein during said
discharging operation, output terminals of said data driver are set
to a discharge voltage according to a control signal.
[0076] A control circuit is provided in the present invention that
operates a recurring function comprising:
[0077] 3) applying image signal to a light valve according to the
image data for displaying image;
[0078] 4a) a delay period after operation 3);
[0079] 4b) after said delay period, applying the control signal
that sets at least a light emitting element that illuminates said
light valve of 3) to a bright state.
[0080] A preferred embodiment of the control circuit of the
previous paragraph comprises a scan driver circuit, a data driver
circuit, and a lighting control circuit, wherein the circuits
operate to
[0081] a) setting image data at the output terminals of the data
driver circuit according to the input image data;
[0082] b) enabling a scan driver terminal that select a group of LC
cells connected to said scan driver terminal to receive the image
data;
[0083] c) allowing a delay period;
[0084] d) applying a signal via the lighting control circuit to set
the light intensity to a light level according to the image.
[0085] The present invention further provides the control circuit
of the previous paragraph further comprising an operation of 5)
setting a group of LC cells to charged or over-charged state. A
preferred embodiment of such operation in the control circuit is a
circuit function of setting the data driver output terminals to a
charging voltage corresponding to said charged state, and enabling
a scan output terminal or a section of scan driver output terminals
to select a subset of LC cells that corresponds to a row or a
section of rows to receive the charging voltage.
[0086] The present invention further provides a control circuit
according to the previous paragraph further operating a function of
setting an LC cells to the relaxed state, and setting the light
emitting elements that illuminates said LC cell to off or a dimming
state. A preferred embodiment of such circuit function is to
provide in the circuit the operation of
[0087] 1) setting all data output terminals to a discharging or
neutral voltage;
[0088] 2) enabling a scan output terminals or a section of scan
driver terminals to select a row or a section of rows connected to
the scan driver terminals to receive said discharging or neutral
voltage.
[0089] In a preferred embodiment, a scan driver terminal is
connected to a row of LC cells, and a section of scan driver
terminals connects to a section of rows.
[0090] A preferred embodiment of the scan driver circuit in the
present invention comprises a plurality of output terminals for
operating a liquid crystal display, wherein each output terminal
operates to deliver a SELECT signal cyclically according to a
control timing to enable the liquid crystal cells connected thereto
to receive image data, and to inhibit data transfer to said cells
when said SELECT signal is not present; wherein said scan driver
further comprises a cyclic discharge operation according to a
control signal; said discharge operation operating on a section of
or all scan output terminals at the same time.
[0091] A preferred discharge operation comprises applying a
discharge signal at said section of or all scan output terminals
simultaneous. A preferred discharge signal is a signal the select
all cells connected thereto to receive a discharge data voltage
from the data electrodes. Such a signal is preferably the same as
the SELECT signal. The scan driver described here may be
constructed in an integrated circuit on silicon.
[0092] It is construed that the scope of present invention is not
limited by the above structural illustration. Furthermore, a single
control circuit IC may comprise multiple control programs to
control both rows and columns, or comprises both LED control
programs and the image processing of data for LCD control.
Furthermore, it is construed that the present invention is not
limited by the type, shape, or the arrangement of the light source,
lighting elements, and the LC cells. The applicability of the
principle of the present invention is not limited by such
variations. Examples of variations include: the arrangement of LCD
cell elements being arranged in a non-orthogonal arrangement; the
LED elements being arranged with multiple colors or comprising
multiple LEDs in one unit; the LED elements being arranged on one
side of the display and illuminates on the LCD cells via a light
guide.
[0093] Various structures may be used to achieve the function of
the circuit operation and timing scheme of the display disclosed in
the present invention. Specific preferred embodiments of its
construction were provided in this description to illustrate the
driving scheme, operation principles, and functional definition of
the driver, of this invention. The application of the principles of
the present invention, however, is not limited by such examples. It
is conceivable that various types of circuit implementation and
cell assembly may be used to construct such display operate under
the principles of the present invention. All such variations are
embraced by the present invention.
[0094] Although various embodiments utilizing the principles of the
present invention have been shown and described in detail, it is
perceivable those skilled in the art can readily devise many other
variances, modifications, and extensions that still incorporate the
principles disclosed in the present invention. The scope of the
present invention embraces all such variances, and shall not be
construed as limited by the number of elements, specific
arrangement of groups as to rows and column, and specific circuit
embodiment to achieve the architecture and functional definition of
the present invention.
* * * * *