Display device with reduced flickering
An LCD device is provided with an image signal modifier to reduce wire frame flickering. The image signal modifier monitors image signals and outputs modified image signals to a data driver for application to data lines and pixels in the LCD device. The image signal modifier retrieves modified signals from a set of predetermined modified signal values stored a lookup table. The image signal modifier performs calculations to interpolate between the predetermined modified signal values. The predetermined modified signal values are predetermined empirically as modified signal values that reduce wire frame flickering.
1. A method of driving a display device, the method comprising:
determining a previous image's gray signal g N−1 corresponding to an (N−1)th frame;
determining a current image's gray signal g N corresponding to an Nth frame;
selecting a modified signal g′ N from a set of predetermined modified signal values by using g N−1 and g N , wherein each of the predetermined modified signal values is selectable for a range of g N−1 and g N ; and
applying the modified signal g′ N to data lines in the display device to elongate a falling time of liquid crystal molecules, wherein g′ N is larger than or equal to g N when g N <g N−1 .
2. The method of claim 1 further comprising setting g′ N equal to g N if a difference between g N and g N−1 is less than a threshold value.
3. The method of claim 1 , wherein each predetermined modified signal value in the set has a first predefined most-significant-bit value for the g N−1 and a second predefined most-significant-bit value for the g N .
4. The method of claim 1 further comprising calculating the modified signal value g′ N .
5. The method of claim 4 , wherein the calculating of the modified signal value g′ N comprises:
mapping a grid on a plot having g N as a first axis and g N−1 as a second axis, wherein the grid has blocks that span a range of g N and a range of g N−1 ;
selecting a block defined by four corners;
determining modified signal values for the four corners; and
interpolating the modified signal values for the four corners to determine coordinates for points inside the block.
6. The method of claim 5 , wherein the modified signal value g′ N is determined using the formula
g
N
′
=
f
+
p
×
g
N
[
y
-
1
:
0
]
/
2
y
-
q
×
g
N
-
1
[
y
-
1
:
0
]
/
2
y
+
r
×
g
N
[
y
-
1
:
0
]
×
g
N
-
1
[
y
-
1
:
0
]
/
2
2
y
,
where
f
(
g
N
[
x
+
y
-
1
:
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,
g
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)
=
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g
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2
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g
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;
p
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g
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=
f
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;
q
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g
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g
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+
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;
and
r
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-
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,
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:
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+
1
)
wherein x represents a bit number of the most significant bit and y represents the bit number of the least significant bit.
7. The method of claim 6 further comprising storing the values of f, p, q, and r in a memory, wherein the f is stored as unsigned 8-bit data and p, q and r are stored as signed 8-bit data.
8. The method of claim 5 , wherein each of the previous image's gray signal g N−1 , the current image's gray signal g N , and the modified signal g′ N is an 8-bit signal with three most significant bits and five least significant bits.
9. A method of driving a display device, the method comprising:
determining a previous image's gray signal g N−1 corresponding to an (N−1)th frame;
determining a current image's gray signal g N corresponding to an Nth frame;
selecting a modified signal g′N from a set of predetermined modified signal values by using g N−1 and g N , such that g′ N is larger than or equal to g N when g N <g N−1 ; and
applying the modified signal g′ N to data lines in the display device to elongate a falling time of liquid crystal molecules.
10. A display device comprising:
a display panel having pixels defined by data lines and gate lines;
an image signal modifier for receiving a previous image's gray signal g N−1 from a frame memory and a current image's gray signal g N from a signal receiver, and selecting a modified signal g′ N from a set of predetermined modified signal values by using g N−1 and g N , wherein each of the predetermined modified signal values is selectable for a range of g N and g N−1 ; and
a data driver for applying the modified signal g′ N to the data lines to elongate a falling time of liquid crystal molecules, wherein g′ N is larger than or equal to g N when g N <g N−1 .
11. The display device of claim 10 , wherein the image signal modifier accesses the set of predetermined modified signal values from a look-up table.
12. The display device of claim 10 , wherein the selected modified signal g′N is greater than the current image's gray signal g N .
13. The display device of claim 10 , wherein the image signal modifier sets g′N equal to gN if a difference between gN and g N−1 is less than a threshold value.
14. The display device of claim 10 , wherein each predetermined modified signal value in the set has a first predefined most-significant-bit value for the g N−1 and a second predefined most-significant-bit value for the g N .
15. The display device of claim 10 , wherein each of the previous image's gray signal g N−1 , the current image's gray signal g N , and the modified signal g′ N is an 8-bit signal with three most significant bits and five least significant bits.
16. The display device of claim 10 further comprising a frame memory for storing the previous image's gray signal g N−1 .
17. The display device of claim 10 further comprising a signal controller that feeds control signals to the data driver, wherein the image signal modifier is part of the signal controller.
18. The display device of claim 10 , wherein the display device is a vertical alignment (VA) liquid crystal display device.
19. The display device of claim 10 , wherein the display device is a patterned vertical alignment (PVA) liquid crystal display device.