Transflective liquid crystal display

• US 7,567,312 B2
• Filed: 07/25/2007
• Issued: 07/28/2009
• Est. Priority Date: 06/07/2005
• Status: Active Grant

• Current Assignee: AU Optronics Corporation
• Original Assignee: AU Optronics Corporation
• Inventors: Lin, Ching-Huan, Tsai, Ching-Yu
• Primary Examiner(s): Nelms; David
• Assistant Examiner(s): Vu; Phu
• Application Number:
  US11/881,191
• Publication Number:
  US 20070268418A1
• Time in Patent Office: 734 Days
• Field of Search: 349 38- 39, 349/48
• US Class Current: 349/48
• 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 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 3/3659 the addressing of the pixel involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependant on signal of two data electrodes

Abstract

A transflective liquid crystal display having a plurality of pixels, each pixel having a plurality of color sub-pixels, each sub-pixel having a transmission area associated with a first charge storage capacitance and a reflection area associated with a second storage capacitance. In the sub-pixel, a data line, a first gate line, a second gate line and a common line are used to control the operational voltage on the liquid crystal layer associated with the sub-pixel. The first and second gate lines are separately set at a first state and a second state. The ratio of the first charge storage capacitance to the second charge storage capacitance can be controlled according to the states of the gate lines. The second charge storage capacitance is provided by two capacitors connected in parallel through a switching element which can be open or closed according to the states of the gate lines.

Claims

1. A method for improving viewing quality of a transflective liquid crystal display having a first side, an opposing second side, and a liquid crystal layer disposed between the first and second sides, the display comprising a plurality of pixels, at least some of the pixels including a plurality of sub-pixels, each sub-pixel comprising a transmission area and a reflection area, wherein the transmission area comprises a transmissive electrode disposed adjacent to the second side, allowing light entering the sub-pixel from the second side to be transmitted through the transmissive electrode, and the liquid crystal layer and then to the first side, and the reflection area comprises a reflective electrode disposed adjacent to the second side spaced from the transmissive electrode, allowing light entering the sub-pixel from the first side through the liquid crystal layer to be reflected by the reflective electrode back through the liquid crystal layer and then to the first side, and wherein the liquid crystal display is operable in a first state and in a second state for controlling optical behavior of the liquid crystal layer for viewing, said method comprising the steps of:

providing a first charge storage capacitance in the transmission area;

providing a second charge storage capacitance in the reflection area, the second charge storage capacitance having a relative capacitance value compared to the first charge storage capacitance; and

controlling at least one of the first charge storage capacitance and the second charge storage capacitance such that the relative capacitance value when the liquid crystal display is operated in the first state is different from the relative capacitance value when the liquid crystal display is operated in the second state.

2. The method of claim 1, further comprising the step of:

coupling a third charge storage capacitance to the second charge storage capacitance for increasing the relative capacitance value when the liquid crystal display is operated in the second state.

3. The method of claim 2, wherein the reflective electrode has a voltage potential across the liquid crystal layer in the reflective area and wherein said coupling decreases the voltage potential when the liquid crystal display is operated in the second state.

4. The method of claim 2, further comprising the step of:

coupling the third charge storage capacitance to a switching element such that

the switching element keeps the second charge storage capacitance electrically uncoupled from the third charge storage capacitance when the liquid crystal display is operated in the first stage, and

the switching element is caused to electrically connect the second charge storage capacitance to the third charge storage capacitance in parallel so as to increase the relative capacitance value when the liquid crystal display is operated in the second state.

5. The method of claim 4, further comprising:

coupling the switching element to a gate line, wherein the gate line has a first voltage level when the liquid crystal display is operated in a first state and the gate line has a different second voltage level for causing the switching element to electrically connect the second charge storage capacitance to the third charge storage capacitance in parallel so as to increase the relative capacitance value when the liquid crystal display is operated in the second state.

6. The method of claim 1, further comprising the step of:

coupling a third charge storage capacitance to the first charge storage capacitance for decreasing the relative capacitance value when the liquid crystal display is operated in the second state.

7. The method of claim 6, wherein the transmissive electrode has a voltage potential across the liquid crystal layer in the transmissive area and wherein said coupling decreases the voltage potential when the liquid crystal display is operated in the second state.

8. The method of claim 6, further comprising the step of:

coupling the third charge storage capacitance to a switching element such that

the switching element keeps the first charge storage capacitance electrically uncoupled from the third charge storage capacitance when the liquid crystal display is operated in the first stage, and

the switching element is caused to electrically connect the first charge storage capacitance to the third charge storage capacitance in parallel so as to decrease the relative capacitance value when the liquid crystal display is operated in the second state.

9. The method of claim 8, further comprising:

coupling the switching element to a gate line, wherein the gate line has a first voltage level when the liquid crystal display is operated in a first state and the gate line has a different second voltage level for causing the switching element to electrically connect the first charge storage capacitance to the third charge storage capacitance in parallel so as to decrease the relative capacitance value when the liquid crystal display is operated in the second state.

10. A liquid crystal display having a first side and a second side, comprising:

a plurality of pixels;

a liquid crystal layer disposed between the first and second sides, wherein at least some of the pixels include a plurality of sub-pixels, each sub-pixel comprising a transmission area and a reflection area, wherein the transmission area comprises a transmissive electrode disposed adjacent to the second side, allowing light entering the sub-pixel from the second side to be transmitted through the transmissive electrode, and the liquid crystal layer and then to the first side, and the reflection area comprises a reflective electrode disposed adjacent to the second side spaced from the transmissive electrode, allowing light entering the sub-pixel from the first side through the liquid crystal layer to be reflected by the reflective electrode back through the liquid crystal layer and then to the first side, and wherein the liquid crystal display is operable in a first state and in a second state for controlling optical behavior of the liquid crystal layer for viewing;

a first charge storage capacitance coupled to the transmissive electrode;

a second charge storage capacitance coupled to the reflective electrode, the second charge storage capacitance having a relative capacitance value compared to the first charge storage capacitance; and

a switching element coupled to at least one of the first charge storage capacitance and the second charge storage capacitance such that the relative capacitance value when the liquid crystal display is operated in the first state is different from the relative capacitance value when the liquid crystal display is operated in the second state.

11. The liquid crystal display of claim 10, further comprising:

a third charge storage capacitance coupled to the second charge storage capacitance in parallel for increasing the relative capacitance value when the liquid crystal display is operated in the second state.

12. The liquid crystal display of claim 11, wherein

the reflective electrode is coupled to a data line for providing a voltage potential on the reflective electrode across the liquid crystal layer in the reflective area,

the third charge storage capacitance is coupled to the switching element, and

the switching element is coupled to a gate line, wherein the gate line has first voltage level when the liquid crystal display is operated in the first state for keeping the second charge storage capacitance uncoupled from the third charge storage capacitance, and

the gate line has a different second voltage level when the liquid crystal display is operated in the second state for electrically connecting the second charge storage capacitance to the third charge storage capacitance in parallel so as to increase the relative capacitance value and to decrease the voltage potential on the reflective electrode.

13. The liquid crystal display of claim 10, further comprising:

a third charge storage capacitance coupled to the first charge storage capacitance in parallel for decreasing the relative capacitance value when the liquid crystal display is operated in the second state.

14. The liquid crystal display of claim 13, wherein

the reflective electrode is coupled to a data line for providing a voltage potential on the transmissive electrode across the liquid crystal layer in the reflective area,

the third charge storage capacitance is coupled to the switching element, and

the switching element is coupled to a gate line, wherein

the gate line has a first voltage level when the liquid crystal display is operated in the first state for keeping the first charge storage capacitance uncoupled from the third charge storage capacitance, and

the gate line has a different second voltage level when the liquid crystal display is operated in the second state for electrically connecting the first charge storage capacitance to the third charge storage capacitance in parallel so as to decrease the relative capacitance value and the voltage potential on the transmissive electrode.