Bi-stable chiral nematic liquid crystal display and driving method for the same

• US 20060279501A1
• Filed: 08/22/2005
• Published: 12/14/2006
• Est. Priority Date: 06/08/2005
• Status: Abandoned Application

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Lu, Chih-Chiang, Kung, Chen-Pang, Chang, Chung-Yi, Liao, Chi-Chang
• Application Number:
  US11/207,818
• Publication Number:
  US 20060279501A1
• Time in Patent Office: Days
• US Class Current: 345/94
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0486 Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals

Abstract

The present invention provides a bi-stable chiral nematic liquid crystal display and a driving method for the same. Each pixel of the liquid crystal display includes at least a transistor as a switch element to switch a column voltage to the pixel and a capacitor for storing a voltage of the pixel. The method for driving the bi-stable chiral nematic liquid crystal display is to divide each frame to be updated into a plurality of sub-frames. During a period of each sub-frame, the bi-stable chiral nematic liquid crystal is driven to a corresponding state in accordance with a respective driving condition.

Claims

1. A method for driving a bi-stable chiral nematic liquid crystal display, by which each frame of said liquid crystal display is divided into a first sub-frame, a second sub-frame and a third sub-frame, said method comprising:

driving said first sub-frame to activate bi-stable chiral nematic liquid crystal to homeotropic states to eliminate memory information of pixels;

driving said second sub-frame to write updated information in said pixels; and

driving said third sub-frame to zero down applied voltages of said pixels such that said bi-stable chiral nematic liquid crystal stays at states corresponding to write in said updated information.

2. The method as defined in claim 1, wherein the step for driving said first sub-frame includes simultaneously driving the whole of said first sub-frame.

3. The method as defined in claim 1, wherein the step for driving said third sub-frame includes simultaneously driving the whole of said third sub-frame.

4. The method as defined in claim 1, wherein the step for driving said second sub-frame includes sequentially writing in the updated information by scanning said second sub-frame.

5. The method as defined in claim 1, wherein the step for driving said third sub-frame includes zeroing down the applied voltages of said pixels by scanning said second sub-frame.

6. The method as defined in claim 1, wherein the write-in updated information of said second sub-frame is a one-bit data.

7. The method as defined in claim 1, wherein the write-in updated information of said second sub-frame is multi-bit data.

12. The method as defined in claim 1, further comprising performing an inversion function to keep the same updated information to write in said pixels by inversing writing-in bits or changing driving voltages.

14. The method as defined in claim 1, wherein bi-stable chiral nematic liquid crystal includes cholesterol liquid crystal molecules.

8. A method for driving a bi-stable chiral nematic liquid crystal display, by which each frame of said liquid crystal display is divided into a first sub-frame and a second sub-frame, said method comprising:

driving said first sub-frame to write updated information in pixels; and

driving said second sub-frame to zero down applied voltages of said pixels such that bi-stable chiral nematic liquid crystal stays at states corresponding to write in said updated information.

9. The method as defined in claim 8, wherein the step for driving said first sub-frame includes sequentially writing in the updated information by scanning said first sub-frame.

10. The method as defined in claim 8, wherein the step for driving said second sub-frame includes zeroing down the applied voltages of said pixels by scanning said second sub-frame.

11. The method as defined in claim 8, wherein the step for driving said second sub-frame includes simultaneously driving the whole of said second sub-frame.

13. The method as defined in claim 8, further comprising performing an inversion function to keep the same updated information to write in said pixels by inversing writing-in bits or changing driving voltages.

15. The method as defined in claim 8, wherein bi-stable chiral nematic liquid crystal includes cholesterol liquid crystal molecules.

16. A bi-stable chiral nematic liquid crystal display device, comprising:

a first substrate having a first surface;

a plurality of row electrodes and a plurality of column electrodes formed on said first surface of said substrate in a matrix form;

a second substrate having a second surface opposite to said first surface;

a common electrode formed on said second surface of said second substrate such that said common electrode is opposite to said row electrodes and said column electrodes;

a bi-stable chiral nematic liquid crystal layer sealed between said first substrate and said second substrate, wherein a portion of said bi-stable chiral nematic liquid crystal layer corresponding to an intersection of each said row electrode and each said column electrode forms a pixel, said pixel forms a pixel capacitor, and one end of said pixel capacitor is connected to said common electrode and the other end of said pixel capacitor forms a pixel electrode;

a plurality of scan lines formed on said first surface of said first substrate, each of said scan lines corresponds to a row of said row electrodes;

a plurality of data lines formed on said first surface of said first substrate, each of said data lines corresponds to a column of said column electrodes;

at least one switch element formed on an intersection of each said row electrode and each said column electrode to serve as a drive switch of said corresponding pixel, said switch element including a conducting path and a control terminal for controlling electrical conductivity of said conducting path, said control terminal connected to one said scan line corresponding thereto, said conducting path including a first terminal and a second terminal, said first terminal connected to one said data line and said second terminal connected to one said pixel electrode;

a scan line driver for providing at least a scan line signal to each said scan line;

a data line driver for providing at least a data signal to each said data line; and

a graphic controller for storing and processing graphic information, said graphic controller sending said graphic information to said data line driver and controlling said data line driver to output at least one voltage signal, simultaneously sending a control signal to control said scan line driver to send a scan signal, and at the same time, sending another control signal to a voltage source to control said voltage source to output a voltage to determine an applied voltage of each said pixel;

wherein each frame of said display is divided into a first sub-frame, a second sub-frame and a third sub-frame, said applied voltage of each said pixel of said first sub-frame and said third sub-frame is a constant voltage, and said applied voltage of each said pixel of said second sub-frame is determined by writing in said graphic information, said constant voltages of said first sub-frame and said second sub-frame are provided by said voltage source, and said applied voltage of each said pixel of said second sub-frame is provided by said data line driver.

17. The device as defined in claim 16, further comprising a plurality of capacitor elements formed on said first surface of said first substrate, each said capacitor element corresponding to one said pixel, one end of said capacitor element connected to one said pixel electrode corresponding thereto.

20. The device as defined in claim 16, wherein said switch element includes a transistor.

22. The device as defined in claim 16, wherein said bi-stable chiral nematic liquid crystal layer includes cholesterol liquid crystal molecules.

24. The device as defined in claim 16, wherein said voltage source provides respective voltages to said data line driver, said scan line driver and said common electrode.

26. The device as defined in claim. 16, wherein further comprises a voltage selector connected to an output terminal of said data line driver and said voltage source that serve as voltage input and connected to said data line that serve as voltage output, said selector selects an input voltage and conducts to said data lines depending on a control signal inputted via a control pin.

28. The device as defined in claim 26, wherein said control signal via said control pin is provided by said graphic controller.

18. A bi-stable chiral nematic liquid crystal display, comprising:

a first substrate having a first surface;

a plurality of row electrodes and a plurality of column electrodes formed on said first surface of said first substrate in a matrix form;

a second substrate having a second surface opposite to said first surface;

a common electrode formed on said second surface of said second substrate such that said common electrode is opposite to said row electrodes and said column electrodes;

a bi-stable chiral nematic liquid crystal layer sealed between said first substrate and said second substrate, wherein a portion of said liquid crystal layer corresponding to an intersection of each said row electrode and each said column electrode forms a pixel, said pixel forms a pixel capacitor, one end of said pixel capacitor is connected to said common electrode and the other end of said pixel capacitor forms a pixel electrode;

a plurality of scan lines formed on said first surface of said first substrate, each said scan line corresponding to a row of said row electrodes;

a plurality of data lines formed on said first surface of said first substrate, each said data line corresponding to a column of said column electrodes;

at least a switch element formed on the intersection of each said row electrode and each said column electrode to serve as a switch element of said pixel, said switch element including a conductance path and a control terminal for controlling electrical conductance of said conductance path, said control terminal connected to one said scan line corresponding thereto, said conductance path including a first terminal and a second terminal, said first terminal connected to one said data line and said second terminal connected to one said pixel electrode;

a scan line driver for providing at least a scan signal to each said scan line;

a data line driver for providing at least a data signal to each said data line; and

a graphic controller for storing and processing graphic information, said graphic controller sending the graphic information to said data line driver to control said data line driver to output a voltage signal, simultaneously sending a control signal to said scan line driver such that said scan line driver outputs a scan signal, and at the same time, sending another control signal to a voltage source such that said voltage source outputs a voltage to determine the applied voltage of each said pixel;

wherein said frame of said display is divided into a first sub-frame and a second sub-frame, the applied voltage of each said pixel of said second sub-frame is a constant voltage, and the applied voltage of each said first pixel is determined by writing in the graphic information, the constant voltage of said second sub-frame is provided by said voltage source, and the applied voltage of each said pixel of said first sub-frame is provided by said data signal driver.

19. The device as defined in claim 18, further comprising a plurality of capacitor elements formed on said first surface of said first substrate, each said capacitor element corresponding to one said pixel, one end of said capacitor element connected to one said pixel electrode corresponding thereto.

21. The device as defined in claim 18, wherein said switch element includes a transistor.

23. The device as defined in claim 18, wherein said bi-stable chiral nematic liquid crystal layer includes cholesterol liquid crystal molecules.

25. The device as defined in claim 18, wherein said voltage source provides respective voltages to said data line driver, said scan line driver and said common electrode.

27. The device as defined in claim 18, wherein further comprises a voltage selector connected to an output terminal of said data line driver and said voltage source that serve as voltage input and connected to said data line that serve as voltage output, said selector selects an input voltage and conducts to said data lines depending on a control signal inputted via a control pin.

29. The device as defined in claim 27, wherein said control signal via said control pin is provided by said graphic controller.