Transflective liquid crystal display with gamma harmonization

• US 7,683,988 B2
• Filed: 05/10/2006
• Issued: 03/23/2010
• 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, ZHI QIANG
• Application Number:
  US11/432,157
• Publication Number:
  US 20070263144A1
• Time in Patent Office: 1,413 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 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 terminal and a second terminal, wherein the first terminal 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 terminal 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 terminal 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.

2. The liquid crystal display of claim 1, further comprising

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

3. The liquid crystal display of claim 1, further comprising

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

4. The liquid crystal display of claim 1, 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.

5. The liquid crystal display of claim 1, 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.

6. The liquid crystal display of claim 1, 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.

7. The liquid crystal display of claim 6, 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.

8. The liquid crystal display of claim 7, 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.

9. The liquid crystal display of claim 6, wherein each of the first and second common voltage signals is a constant voltage signal or an alternating current voltage signal.

10. The liquid crystal display of claim 6, wherein the first common voltage signal and the second common voltage signal are alternating current signals 180 degrees out of phase with each other.

11. The liquid crystal display of claim 6, wherein the first common voltage signal and the second common voltage signal are alternating current signals in phase with each other.

12. The liquid crystal display of claim 6, wherein the second common voltage signal comprises a constant voltage signal.

13. The liquid crystal display of claim 1, 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.

14. The liquid crystal display of claim 13, 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.