Transflective liquid crystal display with gamma harmonization

• US 7,868,976 B2
• Filed: 01/07/2010
• Issued: 01/11/2011
• 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
• Primary Examiner(s): Qi; Mike
• Application Number:
  US12/655,870
• Publication Number:
  US 20100141858A1
• Time in Patent Office: 369 Days
• Field of Search: 349/114, 349/38, 349/39, 345/80, 345/90
• 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 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 liquid crystal 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 to the first end of the second liquid crystal capacitor and providing a second common voltage signal to the first end of the second liquid crystal capacitor via the adjustment capacitor.

2. The method of claim 1, further comprising:

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

3. A method according to claim 1, further comprising:

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

4. A method according to claim 1, further comprising:

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

5. A method according to claim 4, further comprising:

electrically connecting a further capacitor to the additional switching unit.

6. A method according to claim 4, wherein each of the first and second common voltage signals is a constant voltage signal or an AC voltage signal.

7. A method according to claim 4, wherein the first common voltage signal and the second common voltage signal are AC signals 180 degrees out of phase with each other.

8. A method according to claim 4, wherein the first common voltage signal and the second common voltage signal are AC signals in phase with each other.

9. A method according to claim 4, wherein the second common voltage signal comprises a constant voltage signal.

10. A method according to claim 1, wherein

the first liquid crystal capacitor comprises

a first capacitor electrode on the first end and a second capacitor electrode on the second end, each of the first capacitor electrode and the second capacitor electrode is made of a substantially transparent material, and

the second liquid crystal capacitor comprises

a first capacitor electrode on the first end, the first capacitor electrode made of a substantially reflective material, and

a second capacitor electrode on the second end, the second capacitor electrode made of a substantially transparent material.

11. A method according to claim 1, wherein

the second liquid crystal capacitor comprises

a first capacitor electrode on the first end and a second capacitor electrode on the second end, each of the first capacitor electrode and the second capacitor electrode is made of a substantially transparent material, and

the first liquid crystal capacitor comprises

a first capacitor electrode on the first end, the first capacitor electrode made of a substantially transparent material, and

a second capacitor electrode on the second end, the second capacitor electrode made of a substantially reflective material.