Transflective liquid crystal display with partially shifted reflectivity curve

• US 7,768,604 B2
• Filed: 09/20/2005
• Issued: 08/03/2010
• Est. Priority Date: 09/20/2005
• Status: Active Grant

• Current Assignee: Optronic Sciences LLC
• Original Assignee: AU Optronics Corporation
• Inventors: Lin, Ching-Huan, Chang, Chih-Ming
• Primary Examiner(s): Nelms; David
• Assistant Examiner(s): Nguyen; Lauren
• Application Number:
  US11/230,393
• Publication Number:
  US 20070064182A1
• Time in Patent Office: 1,778 Days
• Field of Search: 349/114, 349/48
• US Class Current: 349/114
• CPC Class Codes: G02F 1/133514 Colour filters
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 1/134345 Subdivided pixels, e.g. for grey scale or redundancy
• CPC Class Codes: G02F 1/13624 having more than one switching element per pixel

Abstract

A transflective liquid crystal display having a plurality of pixels, each pixel having a plurality of color sub-pixels. Each sub-pixel comprises a reflective electrode, a transmissive electrode connected to a secondary reflective electrode. The transmissive electrode is associated with a color filter, while one only of the reflective electrode and the secondary reflective electrode is associated with a color filter. The transmissive electrode is associated with a first charge storage capacitance. The reflective electrode is associated with a second charge storage capacitance which is adjustable depending on the operating states of the liquid crystal display.

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 comprising a plurality of color sub-pixels, each color sub-pixels adapted for displaying a single color, each sub-pixel comprising a transmissive electrode and a first reflective electrode, the transmissive electrode disposed adjacent to the second side for allowing light entering the sub-pixel from the second side to be transmitted through the transmissive electrode and the liquid crystal layer and then through the first side, the first reflective electrode disposed adjacent to the second side spaced from the transmissive electrode for allowing a part of light entering the sub-pixel from the first side through the liquid crystal layer to be reflected by the first reflective electrode through the liquid crystal layer back to the first side, and wherein the liquid crystal display is operable in a first voltage mode and in a second voltage mode for controlling optical behavior of the liquid crystal layer, said method comprising the steps of:

electrically connecting at least one second reflective electrode to the transmissive electrode, the second reflective electrode disposed adjacent to the second side spaced from the first reflective electrode, allowing a further part of the light entering the sub-pixel from the first side through the liquid crystal layer to be reflected by the second reflective electrode through the liquid crystal layer back to the first side;

operating the first reflective electrode at the first voltage mode; and

operating the transmissive electrode and said at least one second reflective electrode at the second voltage mode.

2. The method of claim 1, wherein the liquid crystal layer comprises a first layer section associated with the transmissive electrode and a second layer associated with the first reflective and the second reflective electrodes, and the first layer section has a first thickness and the second layer section has a second thickness substantially equal to the first thickness.

3. The method of claim 1, wherein the liquid crystal layer comprises a first layer section associated with the transmissive electrode and a second layer associated with the first reflective and the second reflective electrodes, and the first layer section has a first thickness and the second layer section has a second thickness smaller than the first thickness.

4. The method of claim 1, wherein the liquid crystal layer comprises a first layer section associated with the transmissive electrode and a second layer associated with the first reflective and the second reflective electrodes, and the first layer section has a first thickness and the second layer section has a second thickness substantially equal to half of the first thickness.

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

disposing a color filter on the first side for filtering the light transmitted through the transmissive electrode and for filtering at least a portion of the further part of light reflected by the second reflective electrode.

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

disposing a color filter on the first side for filtering the light transmitted through the transmissive electrode and for filtering at least a portion of the light reflected by the first reflective electrode.

7. The method of claim 1, wherein the transflective liquid crystal display comprises a plurality of data lines, said method further comprising:

electrically connecting the transmissive electrode to a ground via a first capacitor, and to one of the data lines via a first switching element for achieving the first voltage mode; and

electrically connecting the first reflective electrode to the ground via a second capacitor, to said one of the data lines via a second switching element, and to a refresh capacitor through a third switching element for achieving the second voltage mode.

8. The method of claim 7, wherein the transflective liquid crystal further comprises a plurality of gate lines, and wherein the third switching element comprises a first switching end connected to the first reflective electrode and a second switching end connected to the refresh capacitor, and the second switching end is further connected to the ground via a fourth switching element, and wherein the first switching element, the second switching element and the fourth switching element are configured to close (“

ON”

) by a signal in one of the gate lines, and the third switching element is configured to close (“

ON”

) by a signal in another one of the gate lines.

9. The method of claim 1, wherein the transflective liquid crystal display has a plurality of data lines, said method further comprising:

electrically connecting the transmissive electrode to a ground via a first capacitor, and to one of the data lines via a first switching element for achieving the first voltage mode; and

electrically connecting the first reflective electrode;

to the ground via a refresh capacitor,

to the ground via a third switching element and a second capacitor, and

to the ground via a fourth switching element, and wherein the second capacitor is electrically connected to said one of the data lines via a second switching element for achieving the second voltage mode.

10. The method of claim 9, wherein the transflective liquid crystal further comprises a plurality of gate lines, and wherein the first switching element, the second switching element and the fourth switching element are configured to close (“

ON”

) by a signal in one of the gate lines, and the third switching element is configured to close (“

ON”

) by a signal in another one of the gate lines.

11. A liquid crystal display device having an array of pixels, each pixel comprising a plurality of color sub-pixels, each color sub-pixel adapted for display a single color, the liquid crystal operable in a first state and in a second state, said display device comprising:

a first substrate having a common electrode;

a second substrate having a plurality of gate lines, a plurality of data lines and a plurality of common lines;

the data lines and the gate lines arranged in different directions, and

a liquid crystal layer disposed between the first and second substrates, wherein each of at least some of the pixels is associated with a data line, a first gate line and a second gate line, each color sub-pixel comprising;

a first sub-pixel area and a second sub-pixel area, the first sub-pixel area having a transmissive electrode and at least one first reflective electrode electrically connected to the data line through a first switching element, the second sub-pixel area having a second reflective electrode electrically connected to the data line through a second switching element, wherein

when the liquid crystal display is operated in the first state, the first and second switching elements are closed (“

ON”

) and a first voltage potential between the transmissive electrode and the common electrode is substantially equal to a second voltage potential between the second reflective electrode and the common electrode, and

when the liquid crystal display is operated in the second state, the first and second switching elements are open (“

OFF”

).

12. The display device of claim 11, wherein the second reflective electrode is electrically connected to a charge refresh capacitor through a third switching element such that when the liquid crystal display is operated in the first state, the third switching element is open (“

OFF”

) and when the liquid crystal display is operated in the second state, the third switching element is closed (“

ON”

).

13. The display device of claim 12, wherein the first switching element has a control end electrically connected to the first gate line, the second switching element has a control end electrically connected to the first gate line, and the third switching element has a control end electrically connected to the second gate line for causing the respective switching element to close or to open.

14. The display device of claim 12, wherein the third switching element is electrically connected to the refresh capacitor at one capacitor end, and said one capacitor end is further connected to one of the common lines through a fourth switching element, wherein the fourth switching element is closed (“

ON”

) before the third switching element is closed (“

ON”

) and the fourth switching element is open (“

OFF”

) when the third switching element is closed (“

ON”

).

15. The display device of claim 14, each of the first, second and fourth switching elements having a control end electrically connected to the first gate line.

16. The display device of claim 14, wherein each of the first, second, third and fourth switching element has a control end and each switching element comprises a thin-film transistor and the control end is the gate of the corresponding thin-film transistor.

17. The display device of claim 11, wherein the common electrode is electrically connected to one of the common lines.

18. The display device of claim 11, wherein said pixel comprises a color filter for filtering light transmitted through the transmissive electrode and for filtering light reflected by the first reflective electrode.

19. The display device of claim 11, wherein said pixel comprises a color filter for filtering light transmitted through the transmissive electrode and for filtering light reflected by the second reflective electrode.

20. A liquid crystal display device having an array of pixels, each pixel comprising a plurality of color sub-pixels, each color sub-pixel adapted for display a single color, the liquid crystal display device operable in a first state and in a second state, said display device comprising:

a first substrate having a common electrode;

a second substrate having a plurality of gate lines, including a gate-line n and a gate-line n+1, a plurality of data lines including a data line m, and a plurality of common lines;

the data lines and the gate lines arranged in different directions;

a liquid crystal layer disposed between the first and second substrates, wherein one of the color sub-pixels is associated with the data line m, the gate line n and the gate line n+1, said color sub-pixels comprising;

a first sub-pixel area having a transmissive electrode and at least one first reflective electrode electrically connected to the data line m through a first switching element, and

a second sub-pixel area having a second reflective electrode electrically connected to the data line m through a second switching element, the second sub-pixel area having a refresh capacitor having a first end and a second end, the second end electrically connected to one of the common lines, the second reflective electrode further connected to the first end of the charge refresh capacitor through a third switching element, each of the first and second switching elements having a control end electrically connected to the gate line n, the third switching element having a control end electrically connected to the gate line n+1, wherein

when the liquid crystal display is operated in the first state, the first and second switching elements are closed (“

ON”

) and the third switching element is open (“

OFF”

), such that a first voltage potential between the transmissive electrode and the common electrode is substantially equal to a second voltage potential between the second reflective electrode and the common electrode, the transmissive electrode and the refresh capacitor having an electric charge associated therewith, and

when the liquid crystal display is operated in the second state, the first and second switching elements are open (“

OFF”

) and the third switching element is closed (“

ON”

) so as to cause a redistribution of the electric charge associated with the second pixel electrode and the refresh capacitor.

21. The display device of claim 20, wherein said pixel further comprises a fourth switching element and wherein the first end of the refresh capacitor is further connected to a common line through the fourth switching element, the fourth switching element having a control end electrically connected to the gate line n, wherein the fourth switching element is closed (“

ON”

) before the third switching element is closed (“

ON”

) and the fourth switching element is open (“

OFF”

) when the switching third element is closed (“

ON”

).

22. The display device of claim 21, wherein the common electrode is made from a transmissive material, electrically connected to one of the common lines.

23. The display device of claim 20, wherein said pixel comprises a color filter for filtering light transmitted through the transmissive electrode and for filtering light reflected by the first reflective electrode.

24. The display device of claim 20, wherein said pixel comprises a color filter for filtering light transmitted through the transmissive electrode and for filtering light reflected by the second reflective electrode.