LCD device with improved optical performance

• US 20060284811A1
• Filed: 06/15/2005
• Published: 12/21/2006
• Est. Priority Date: 06/15/2005
• Status: Active Grant

• Current Assignee: AU Optronics Corporation
• Original Assignee: AU Optronics Corporation
• Inventors: Huang, Hsueh-Ying
• Granted Patent: US 7,652,649 B2
• Time in Patent Office: Days
• US Class Current: 345/92
• CPC Class Codes: G02F 1/136213 Storage capacitors associated with the pixel electrode
• CPC Class Codes: G02F 2203/09 transflective
• CPC Class Codes: G02F 2203/21 Thermal instability, i.e. DC drift, of an optical modulator; Arrangements or methods for the reduction thereof
• CPC Class Codes: G09G 2300/0443 with several sub-pixels for the same colour in a pixel, not specifically used to display gradations G09G3/364 takes precedence
• CPC Class Codes: G09G 2300/0456 with a reflective area and a transmissive area combined in one pixel, such as in transflectance pixels
• CPC Class Codes: G09G 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors

Abstract

In an LCD pixel, the pixel voltage is usually reduced after a gate line signal has passed. To compensate for this voltage reduction, the voltage applied to the charge storage capacitor in the pixel is increased from Vcom to Vcom1 after the gate line signal has passed. Voltage adjustment can be achieved by using two switching elements connected to the second end of the charge storage capacitor. One is activated by the gate line signal so that the applied voltage is equal to Vcom, and the other is activated by the next gate line signal so that the applied is increased to Vcom1. In a transflective LCD panel or a color LCD panel, each pixel is divided into two or three sub-pixels, each sub-pixel having a separate charge storage capacitor, a similar Vcom change is applied to each of the charge storage capacitors in the pixel.

Claims

1. A method to reduce a drop in a voltage potential in a liquid crystal display having a plurality of gate lines for providing gate line signals and a plurality of data lines for providing data signals, the liquid crystal display having a plurality of pixels arranged in a plurality of pixel rows, each pixel having

a first electrode,

a second electrode, and

a liquid crystal layer segment disposed between the first and second electrodes, the first electrode electrically connected to a first voltage and the second electrode electrically connected to a data line through a switching element for receiving a data signal during a gate line signal so as to achieve the voltage potential across the liquid crystal layer segment, the pixel further comprising a charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end of the charge storage capacitor electrically connected to the second electrode, said method comprising the steps of:

applying a second voltage to the second capacitor end of the charge storage capacitor during the gate line signal; and

applying a third voltage to the second capacitor end of the charge storage capacitor after the gate line signal has passed, wherein the third voltage in at least some of the plurality of pixels is greater than the second voltage.

2. The method of claim 1, wherein each of the pixel rows has a first side and an opposing second side and said some of the plurality of pixels are located on the first side, and some other of the plurality of pixels are located on the second side, and wherein the second voltage is substantially equal to the first voltage.

3. The method of claim 2, wherein the third voltage in said some other pixels is substantially equal to the second voltage.

4. The method of claim 2, wherein the third voltage in said some other pixels is also greater than the second voltage.

5. The method of claim 2, wherein the third voltage in said some other pixels is different from the third voltage in said some pixels.

6. The method of claim 1, wherein the plurality of pixel rows include a pixel row m and an adjacent pixel row m+1, and the plurality of gate lines include a gate line m for driving the pixel row m and a gate line m for driving the pixel row m+1 and wherein

the gate line signal is provided to the gate line m for driving the pixel row m,

a next gate line signal is provided to the gate line m+1 for driving the pixel row m+1, and

the third voltage is applied to the second capacitor end of the charge storage capacitor during the next gate line signal.

7. The method of claim 6, wherein each pixel further comprises a further charge storage capacitor, the further charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the second electrode, the second capacitor end electrically connected to the gate line m+1.

8. The method of claim 4, wherein the third voltage varies with temperature of the liquid crystal display.

9. The method of claim 2, wherein the liquid crystal display is a transflective display and each pixel has a transmission sub-pixel and a reflective sub-pixel, the second electrode comprising a transmissive electrode in the transmission sub-pixel, the reflective sub-pixel having a third electrode electrically connected to the data line through another switching element for receiving the data signal during the gate line signal, the reflective sub-pixel further comprising a further charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the third electrode, said method further comprising the step of:

applying the third voltage to the second capacitor end of the further charge storage capacitor.

10. The method of claim 2, wherein the liquid crystal display is a color display and each pixel has a first color sub-pixel, a second color sub-pixel and a third color sub-pixel, and wherein the second electrode comprises a first sub-electrode in the first color sub-pixel, a second sub-electrode in the second color sub-pixel and a third sub-electrode in the third color sub-pixel, the first sub-electrode electrically connected to the first end of the charge storage capacitor, wherein

the second color sub-pixel further comprises a second charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the second sub-electrode, and

the third color sub-pixel further comprises a third charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the third sub-electrode, said method further comprising the step of:

applying the third voltage to the second capacitor end of the second charge storage capacitor and the second capacitor end of the third charge storage capacitor.

11. A liquid crystal display having a plurality of pixels arranged in a plurality of pixel rows, a plurality of gate lines for providing gate line signals and a plurality of data lines for providing data signals to the plurality of pixels, each pixel having

a switching element;

a first electrode,

a second electrode,

a liquid crystal layer segment disposed between the first and second electrodes, the first electrode electrically connected to a first voltage and the second electrode electrically connected to a data line through the switching element for receiving a data signal during a gate line signal, and

a charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the second electrode, said liquid crystal display comprising;

a voltage source connected to the second capacitor end of the charge storage capacitor so as to apply the first voltage to the charge storage capacitor during the gate line signal and to apply a second voltage to the charge storage capacitor after the gate line signal has passed, wherein the second voltage in at least some of the plurality of pixels is greater than the second voltage.

12. The liquid crystal display of claim 11, wherein each of the pixel rows has a first side and an opposing second side, and said some of the plurality of pixels are located on the first side and some other of the plurality of pixels are located on the second side.

13. The liquid crystal display of claim 12, wherein the second voltage in said some other pixels is substantially equal to the first voltage.

14. The liquid crystal display of claim 12, wherein the second voltage in said some other pixels is also greater than the first voltage.

15. The liquid crystal display of claim 12, wherein the second voltage in said some pixels is different from the second voltage in said some other pixels.

16. The liquid crystal display of claim 11, wherein the plurality of pixel rows include a pixel row m and an adjacent pixel row m+1 and the plurality of gate lines include a gate line m for driving the pixel row m and a gate line m for driving the pixel row m+1 and wherein

the gate line signal is provided to the gate line m for driving the pixel row m,

a next gate line signal is provided to the gate line m+1 for driving the pixel row m+1, and

the second voltage is applied to the second capacitor end of the charge storage capacitor during the next gate line signal.

17. The liquid crystal display of claim 16, wherein each pixel further comprises a further storage capacitor, the further charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the second electrode, the second capacitor end electrically connected to the gate line m+1.

18. The liquid crystal display of claim 14, further comprising a temperature sensor operatively connected to the voltage source, the temperature sensor adapted to sense a temperature of the liquid crystal display for providing a signal indicative of the sensed temperature, so as to change the second voltage at least based on the sensed temperature.

19. The liquid crystal of claim 12, wherein each pixel has a transmission sub-pixel and a reflective sub-pixel, and wherein

the second electrode comprises a transmissive electrode in the transmission sub-pixel, and

the reflective sub-pixel comprises a third electrode electrically connected to the data line through another switching element for receiving the data signal during the gate line signal, the reflective sub-pixel further comprising a further charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the third electrode, and wherein the second voltage is also applied to the second capacitor end of the further charge storage capacitor.

20. The liquid crystal display of claim 12, wherein each pixel has a first color sub-pixel, a second color sub-pixel and a third color sub-pixel, and wherein the second electrode comprises a first sub-electrode in the first color sub-pixel, a second sub-electrode in the second color sub-pixel and a third sub-electrode in the third color sub-pixel, the first sub-electrode electrically connected to the first end of the charge storage capacitor, wherein

the second color sub-pixel further comprises a second charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the second sub-electrode, and

the third color sub-pixel further comprises a third charge storage capacitor having a first capacitor end and a second capacitor end, the first capacitor end electrically connected to the third sub-electrode, and wherein the second voltage is also applied to the second capacitor end of the second charge storage capacitor and the second capacitor end of the third charge storage capacitor.