Transflective liquid crystal display with gamma harmonization

• US 20070263144A1
• Filed: 05/10/2006
• Published: 11/15/2007
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: AU Optronics Corporation
• Original Assignee: AU Optronics Corporation
• Inventors: Lin, Ching-Huan, Chang, Chih-Ming, Su, Jenn-Jia
• Granted Patent: US 7,683,988 B2
• Time in Patent Office: Days
• US Class Current: 349/114
• 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 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

In a transflective liquid crystal display having a transmission area and the reflection area, the transmissive electrode is connected to a switching element to control the liquid crystal layer in the transmission area, and the reflective electrode is connected to the switching element via a separate capacitor to control the liquid crystal layer in the reflection area. The separate capacitor is used to shift the reflectance in the reflection area toward a higher voltage end in order to avoid the reflectance inversion problem. In addition, an adjustment capacitor is connected between the reflective electrode and a different common line. The adjustment capacitor is used to reduce or eliminate the discrepancy between the gamma curve associated with the transmittance and the gamma curve associated with the reflectance.

Claims

1. A method for improving viewing quality of a liquid crystal display panel, the display panel comprising a liquid crystal layer having a first side and an opposing second side, and a common electrode disposed on the first side of the liquid crystal layer, wherein the common electrode is operatively applied with a common voltage, and wherein the display panel has a plurality of pixels, and at least some of the pixels have a first area and a second area, the first area comprising a first electrode disposed on the second side of the liquid crystal layer, the second area comprising a second electrode disposed on the second side of the liquid crystal layer adjacent to the first electrode, wherein the first electrode is operatively applied with a first voltage to achieve a first optical transmissivity through the liquid crystal layer in the first area as a function of the first voltage, and the second electrode is operatively applied with a second voltage to achieve a second optical transmissivity through the liquid crystal layer in the second area as a function of the second voltage, wherein the first optical transmissivity has a lower transmissivity section and a higher transmissivity section, and the second transmissivity has a lower transmissivity section and a higher transmissivity section, said method comprising:

adjusting the second voltage relative to the first voltage for substantially matching the higher transmissivity section of the second optical transmissivity to the higher transmissivity section of the first optical transmissivity, leaving a discrepancy between the lower transmissivity section of the second optical transmissivity and the lower transmissivity section of the first optical transmissivity; and

providing a voltage different from the common voltage to the second electrode via a charge storage device so as to reduce the discrepancy between the lower transmissivity section of the second optical transmissivity and the lower transmissivity section of the first optical transmissivity.

2. The method of claim 1, wherein the first electrode comprises a transmissive electrode and the second electrode comprises a reflective electrode.

3. The method of claim 2, wherein the first optical transmissivity is equal to the transmittance of the liquid crystal layer through the transmissive electrode in the first area and the second optical transmissivity is equal to the reflectance of the liquid crystal layer reflected from the reflective electrode in the second area.

4. The method of claim 2, wherein the first voltage is a data signal.

5. The method of claim 4, wherein the second area comprises a charge storage capacitor having a first end electrically connected to the data signal and a second end operatively connected to the reflective electrode, and the second voltage is a voltage signal at the second end of the charge capacitor.

6. A method to improve viewing quality of a liquid crystal display, the liquid crystal display comprising:

a plurality of data lines for conveying a data signal;

a plurality of gate lines for providing a driving signal; and

a plurality of pixels, wherein each pixel has a switching unit to admit the data signal from a data line responsive to the driving signal from a gate line, and wherein each pixel has a first liquid crystal capacitor and a second liquid crystal capacitor, wherein a first end of the first capacitor is coupled to the switching unit, said method comprising;

in said each pixel

electrically connecting a coupling capacitor between the switching unit and a first end of the second liquid crystal capacitor;

applying a first common voltage signal to a second end of the first liquid crystal capacitor and a second end of the second liquid crystal capacitor; and

electrically connecting an adjustment capacitor between the first end of the second liquid crystal capacitor and a second common voltage signal.

7. The method of claim 6, further comprising:

electrically connecting a storage capacitor in parallel to the first liquid crystal capacitor.

8. The method of claim 6, further comprising:

electrically connecting a storage capacitor in parallel to the second liquid crystal capacitor.

9. The method of claim 6, further comprising:

operatively connecting an additional switching unit between the adjustment capacitor and a voltage source so as to allow the voltage source to provide the second common voltage signal to the adjustment capacitor via the additional switching unit responsive to the driving signal from the gate line.

10. The method of claim 9, further comprising:

electrically connecting a further capacitor to additional switching unit for stabilizing a voltage at the second common electrode.

11. A liquid crystal display, comprising:

a plurality of data lines for conveying a data signal;

a plurality of gate lines for providing a driving signal; and

a plurality of pixels, each pixel comprising;

a switching unit, responsive to the driving signal from a gate line, for admitting the data signal from a data line;

a first common electrode for providing a first common voltage signal;

a second common electrode for providing a second common voltage signal;

a pixel electrode, electrically connected to the switching unit, for driving a liquid crystal layer within the pixel based on the admitted data signal and the first common voltage signal;

a first liquid crystal capacitor having a first end electrically connected to the first common electrode, and a second end electrically connected to the pixel electrode;

an coupling capacitor having a first end and a second end, wherein the first end is electrically connected to the pixel electrode;

an adjustment capacitor having a first end electrically connected to the second common electrode and a second end connected to the second end of the coupling capacitor; and

a second liquid crystal capacitor having a first end electrically connected to the first common electrode, and a second end electrically connected to the second end of the coupling capacitor, for driving the liquid crystal layer based on the admitted data signal, the first common voltage signal and the second common voltage signal.

12. The liquid crystal display of claim 11, further comprising

a storage capacitor connected in parallel to the first liquid crystal capacitor in said each pixel.

13. The liquid crystal display of claim 11, further comprising

a storage capacitor connected in parallel to the second liquid crystal capacitor in said each pixel.

14. The liquid crystal display of claim 11, wherein, in said each pixel,

the first liquid crystal capacitor has two electrode ends, each of which is made of substantially transparent material, and

the second liquid crystal capacitor has a first electrode end made of substantially transparent material and a second electrode end made of a reflective material.

15. The liquid crystal display of claim 11, wherein, in said each pixel,

the second liquid crystal capacitor has two electrode ends, each of which is made of substantially transparent material, and

the first liquid crystal capacitor has a first electrode end made of substantially transparent material and a second electrode end made of a reflective material.

16. The liquid crystal display of claim 11, further comprising:

a voltage source for providing the second common voltage signal; and

an additional switching unit, responsive to the driving signal from said gate line, for electrically connecting the second common electrode in said each pixel to the voltage source.

17. The liquid crystal display of claim 16, further comprising

a further capacitor electrically connected to the second common electrode in said each pixel for stabilizing a voltage at the second common electrode.

18. The liquid crystal display of claim 17, wherein the further capacitor has a first end electrically connected to the second common electrode and a second end electrically connected to the first common electrode.

19. The liquid crystal display of claim 16, wherein each of the first and second common voltage signals is a constant voltage signal or an AC voltage signal.

20. The liquid crystal display of claim 16, wherein the first common voltage signal and the second common voltage signal are AC signals 180 degrees out of phase with each other.

21. The liquid crystal display of claim 16, wherein the first common voltage signal and the second common voltage signal are AC signals in phase with each other.

22. The liquid crystal display of claim 16, wherein the second common voltage signal comprises a constant voltage signal.

23. The liquid crystal display of claim 11, wherein the first end of the first liquid crystal capacitor comprises a first transparent electrode and the second end of the first liquid crystal capacitor comprises a second transparent electrode, and wherein the first end of the second liquid crystal capacitor comprises a transparent electrode and the second end of the second liquid crystal capacitor comprises a reflective electrode.

24. The liquid crystal display of claim 23, further comprising:

a voltage source for providing the second common voltage signal;

an additional switching unit, responsive to the driving signal from said gate line, for electrically connecting the second common electrode in said each pixel to the voltage source; and

a further capacitor electrically connected to the second common electrode for stabilizing a voltage at the second common electrode.