Dynamic drive methods and apparatus for a bistable liquid crystal display

• US 6,154,190 A
• Filed: 05/07/1997
• Issued: 11/28/2000
• Est. Priority Date: 02/17/1995
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Huang, Xiao-Yang, Zhu, Yang-Ming, Yang, Deng-Ke
• Primary Examiner(s): BRIER, JEFFERY A
• Application Number:
  US08/852,319
• Time in Patent Office: 1,301 Days
• Field of Search: 345/94, 345/97, 345/87, 345/89, 345/208, 345/96, 345/99, 345/95, 349/33, 349/96, 349/177, 349/86, 349/169, 349/168, 349/141
• US Class Current: 345/94
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• 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 2310/0205 Simultaneous scanning of several lines in flat panels
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/0209 Crosstalk reduction, i.e. to reduce direct or indirect influences of signals directed to a certain pixel of the displayed image on other pixels of said image, inclusive of influences affecting pixels in different frames or fields or sub-images which constitute a same image, e.g. left and right images of a stereoscopic display
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
• CPC Class Codes: G09G 3/3681 suitable for passive matrices only

Abstract

A flat-panel liquid crystal display. The display includes a flat sheet of bistable chiral nematic liquid crystal material activated by a drive circuit that individually controls the display state of multiple picture elements. The driver circuitry activates the liquid crystal domains with various drive schemes which have any number of different phases to attain various addressing sequence times. At the end of each drive scheme, the texture of the liquid crystal material is allowed to provide either focal conic or twisted planar end states across the two-dimensional array of picture elements. Each drive scheme employs at least a preparation phase and a selection phase to predispose the liquid crystal material to one of the end states.

Claims

1. A method of addressing a bistable chiral nematic liquid crystal material disposed between electrodes arranged on opposed sides of said liquid crystal and adapted to selectively apply an electric field through said liquid crystal material, said method comprising the steps of:

energizing said electrodes to establish a preparation voltage across said liquid crystal during a preparation phase;

energizing said electrodes to establish a post-preparation voltage across said liquid crystal during a post-preparation phase;

energizing said electrodes to establish a selection voltage across said liquid crystal during a selection phase for selecting a selection state which evolves into one of two final display states for said liquid crystal; and

energizing said electrodes to establish an evolution voltage across said liquid crystal during an evolution phase and creating an evolution state which changes to one of two final display states after completion of the addressing method, wherein said final display states remain indefinitely until said energizing steps are repeated.

2. The method according to claim 1 wherein after said evolution phase, the evolution voltage to said electrodes is reduced to allow said liquid crystal to exhibit one of its final display states.

3. The method according to claim 1 wherein after said evolution phase, the voltage to said electrodes is removed to allow said liquid crystal to exhibit one of its final display states.

4. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal and said preparation voltage is of a magnitude, and said preparation phase is of a duration sufficient to homeotropically align said liquid crystal material.

5. The method according to claim 4 wherein said preparation phase is up to about 40 ms in duration.

6. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal and the magnitude of said selection voltage is selected to either maintain said liquid crystal in a homeotropic texture or to permit said liquid crystal to initiate a transition to a transient twisted planar texture.

7. The method according to claim 1 wherein said selection phase is about 0.2 ms in duration.

8. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal and said selection voltage is of a magnitude sufficient to establish one of a focal conic or a twisted planar final display state.

9. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal and said evolution voltage is of a magnitude, and said evolution phase is of a duration effective to maintain liquid crystal that is in a homeotropic texture in said homeotropic texture, and to allow liquid crystal in a transient twisted planar texture to evolve to a focal conic texture during said evolution phase, and wherein said evolution voltage is the same for obtaining either final display state.

10. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal and said evolution voltage is of a magnitude, and said evolution phase is of a duration effective to allow liquid crystal in a transient twisted planar texture to relax to a focal conic texture, and to allow liquid crystal in a homeotropic texture to remain in the homeotropic texture during the evolution phase and afterward to a reflecting twisted planar texture.

11. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal and said preparation phase includes modulating said preparation voltage on and off to shorten the duration of said preparation phase.

12. The method according to claim 1 wherein said liquid crystal is a chiral nematic liquid crystal having a pitch length in said twisted planar texture effective to reflect light in the visible spectrum.

13. The method according to claim 1 wherein said liquid crystal is a chiral nematic crystal material and the magnitude of said post-preparation voltage is of a magnitude to relax said liquid crystal material from a homeotropic texture to a transient planar texture, wherein said post-preparation phase is of a duration about 0.2 ms.

14. The method according to claim 1 further comprising the step of energizing said electrodes to establish an after-selection voltage across said liquid crystal during an after-selection phase after said selection phase to adjust the polar angle of the liquid crystal material.

15. The method according to claim 14 wherein said liquid crystal material is a chiral nematic and wherein said selection voltage places said liquid crystal material in one of a homeotropic or a transient planar texture.

16. The method according to claim 1 wherein said step of energizing said electrodes includes the step of time modulating said electrodes during said selection phase to cause said liquid crystal material to exhibit gray scale properties.

17. The method according to claim 1 wherein said step of energizing said electrodes includes the step of amplitude modulating said electrodes during said selection phase to cause said liquid crystal material to exhibit gray scale properties.

18. A method for displaying information comprising the steps of:

a) providing a layer of bistable liquid crystal material and arranging electrodes on opposed sides of the liquid crystal material to form an array of display elements;

b) coupling the electrodes to a drive circuit for energizing the electrodes to selectively activate the display elements of the array to one of a first and a second final display state; and

c) addressing selected display elements of the array by sequentially energizing the liquid crystal material at a selected display element location with a preparation signal during a preparation phase, reducing the preparation signal to a post-preparation signal during a post-preparation phase, adjusting the post-preparation signal to a selection signal for selecting a desired final display state during a selection phase, changing the selection signal across the display element to an evolution signal during an evolution phase which creates a state which can change to one of two final display states for each display element after completion of the addressing step, wherein said final display state remains indefinitely until said addressing steps are repeated.

19. The method of claim 18 wherein the first final display state is a twisted planar texture of the liquid crystal material and the second final display state is a focal conic texture of the liquid crystal material.

20. The method of claim 18 further comprising the step of providing a layer of chiral nematic liquid crystal material having a pitch length effective to reflect light in the visible spectrum, and wherein said evolution voltage is the same for obtaining either final display state.

21. The method of claim 18 further comprising the step of arranging said electrodes on one side of the liquid crystal layer in generally parallel rows and electrodes on an opposite side of the liquid crystal layer in generally parallel columns substantially orthogonal to said rows, whereby said display elements are defined by the points on said rows and columns at which said rows and columns would intersect when in the same plane, and further wherein a plurality of rows of display elements are simultaneously in said preparation phase.

22. The method according to claim 18 further comprising the step of arranging said electrodes on one side of the liquid crystal layer in generally parallel rows and electrodes on an opposite side of the liquid crystal layer in generally parallel columns substantially orthogonal to said rows, whereby said display elements are defined by the points on said rows and columns at which said rows and columns would intersect when in the same plane, and further wherein a plurality of rows of display elements are simultaneously in said evolution phase.

23. The method of claim 18 wherein the step of addressing further includes the step of applying an after-selection signal prior to said evolution signal across the display element.

24. The method of claim 23 wherein said after-selection signal includes the step of adjusting a polar angle of the liquid crystal material to hasten attainment of the final display state.

25. The method according to claim 18 wherein said step of addressing said display elements during said selection phase includes the step of time modulating said selection voltage to cause said liquid crystal material to exhibit gray scale properties.

26. The method according to claim 18 wherein said step of addressing said display elements during said selection phase includes the step of a multitude modulating said selection voltage to cause said liquid crystal material to exhibit gray scale properties.

27. A display apparatus comprising:

a) a layer of bistable liquid crystal material;

b) multiple electrodes spaced on opposite sides of the liquid crystal layer for applying selected activation voltages across multiple picture elements of the liquid crystal layer; and

c) control electronics for sequentially setting a display state of multiple picture elements of the liquid crystal layer comprising circuitry for;

i) applying a preparation signal across a selected picture element during a preparation phase;

ii) applying a post-preparation across said selected picture element during a post-preparation phase;

iii) applying a selection signal across said selected picture element during a selection phase to select a selection state which evolves into one of two final display states; and

iv) applying an evolution signal across said selected picture element during an evolution phase and creating an evolution state which changes to one of two final display states after completion of the applying steps, wherein said final display state remains indefinitely until said energizing steps are repeated.

28. The apparatus of claim 27 wherein the control electronics comprises circuitry for applying bipolar preparation, post-preparation, selection and evolution signals to the multiple picture elements and wherein said evolution voltage is the same for obtaining either final display state.

29. The apparatus of claim 27 wherein electrodes on one side of the liquid crystal layer are arranged in generally parallel rows and electrodes on an opposite side of the liquid crystal layer are arranged in generally parallel columns substantially orthogonal to said rows and said picture elements are defined by the points on said rows and columns at which said rows and columns would intersect when in the same plane, wherein when the control electronics applies a voltage signal to a row electrode, all picture elements in that row are electrically connected to the same voltage signal and when the control electronics applies a voltage signal to a column electrode, all picture elements in that column are connected to the same voltage signal.

30. The apparatus of claim 27 wherein the control electronics includes a timer to control the timer durations of the preparation, post-preparation, selection and evolution signals.

31. The apparatus of claim 29 wherein the control electronics includes circuitry for applying said preparation and said evolution signals to a plurality of rows of said picture elements.

32. The apparatus of claim 29 wherein said control electronics includes circuitry for simultaneously applying said selection signal to a plurality of rows of said picture elements.

33. The apparatus of claim 27, wherein said control electronics circuitry pre-disposes said layer of bistable chiral nematic liquid crystal material to a state different than said predetermined final display state during said selection phase.

34. The apparatus of claim 27, wherein said control electronics applies an after-selection signal across said selected picture element during an after-selection phase to hasten attainment of said display state.

35. The apparatus of claim 34, wherein said control electronics further comprises circuitry for applying said after-selection signal to the multiple picture elements and a timer to control the duration of said after-selection signal.

36. The apparatus of claim 27, wherein said control electronics time modulates application of said selection signal so that said predetermined final display state exhibits gray scale properties.

37. The apparatus of claim 27, wherein said control electronics amplitude modulates application of said selection signal so that said predetermined final display state exhibits gray scale properties.

38. A method of addressing a bistable liquid crystal material disposed between electrodes arranged on opposed sides of said liquid crystal and adapted to selectively apply an electric field through said liquid crystal material, said method comprising the steps of:

energizing said electrodes to establish a preparation voltage across said liquid crystal material during a preparation phase;

energizing said electrodes to establish a selection voltage across said liquid crystal material during a selection phase for selecting one of two final display states for said liquid crystal; and

permitting said liquid crystal to exhibit the final display state without further energizing said electrodes, wherein at least one of the final display states is different than a preparation state of the liquid crystal material during said selection phase and creating a state which changes to one of two final display states after completion of the addressing method, wherein said final display state remains indefinitely until said energizing steps are repeated.

39. The method of claim 38 wherein said bistable liquid crystal material is chiral nematic.

40. The method of claim 39 wherein said chiral nematic liquid crystal material has a pitch length effective to reflect light in the visible spectrum.

41. The method of claim 38 wherein said step of establishing said preparation voltage causes said liquid crystal material to exhibit a focal conic texture.

42. The method of claim 38 wherein said step of establishing said selection voltage causes said liquid crystal material to exhibit one of a focal conic texture or a homeotropic texture.

43. The method of claim 38 wherein said step of permitting includes the step of removing said selection voltage from a cross said electrodes and allowing said liquid crystal material to exhibit one of its final display states, wherein said selection voltage causes said liquid crystal material to attain one of a focal conic texture or a homeotropic texture and said removing step causes said liquid crystal material that is in a focal conic texture to remain in the focal conic texture and causes said liquid crystal material that is in a homeotropic texture to exhibit a planar texture.

44. A method for displaying information comprising the steps of:

a) providing a layer of bistable liquid crystal material and arranging electrodes on opposed sides of the liquid crystal material to form an array of display elements;

b) coupling the electrodes to a drive circuit for energizing the electrodes to selectively activate the display elements of the array to one of a first and a second final display state; and

c) addressing selected display elements of the array by sequentially energizing the liquid crystal material at a selected display element location with a preparation signal during a preparation phase, providing a selection signal for selecting a desired final display state during a selection phase, and then allowing the display element to exhibit the desired final display state without further energizing said electrodes and creating a state which can change to one of two final display states after completion of the addressing steps, wherein said final display state remains indefinitely until said addressing steps are repeated.

45. The method of claim 44 wherein the first final display state is a twisted planar texture of the liquid crystal material and the second final display state is a focal conic texture of the liquid crystal material and further comprising the step of providing a layer of chiral nematic liquid crystal material having a pitch length effective to reflect light in the visible spectrum.

46. The method of claim 44 further comprising the step of arranging said electrodes on one side of the liquid crystal layer in generally parallel rows and electrodes on an opposite side of the liquid crystal layer in generally parallel columns substantially orthogonal to said rows, whereby said display elements are defined by the points on said rows and columns at which said rows and columns would intersect when in the same plane, and further wherein a plurality of rows of display elements are simultaneously in said preparation phase.

47. The method according to claim 44 further comprising the step of arranging said electrodes on one side of the liquid crystal layer in generally parallel rows and electrodes on an opposite side of the liquid crystal layer in generally parallel columns substantially orthogonal to said rows, whereby said display elements are defined by the points on said rows and columns at which said rows and columns would intersect when in the same plane, and further wherein a plurality of rows of display elements are simultaneously in said evolution phase.

48. A display apparatus comprising:

a) a layer of bistable liquid crystal material;

b) multiple electrodes spaced on opposite sides of the liquid crystal layer for applying selected activation voltages across multiple picture elements of the liquid crystal layer; and

c) control electronics for sequentially setting a display state of multiple picture elements of the liquid crystal layer comprising circuitry for;

i) applying a preparation signal across a selected picture element during a preparation phase to cause the liquid crystal layer to exhibit a preparation texture; and

ii) applying a selection signal across said selected picture element during a selection phase to select a predetermined final display state wherein at least one of the predetermined final display states is different than the preparation texture of the liquid crystal material during said selection phase and creating a state which can change to one of two final display states after completion of the addressing method without further energizing said selected picture element, wherein said final display state remains indefinitely until said applying steps are repeated.

49. The apparatus of claim 48 wherein the control electronics comprises circuitry for applying bipolar preparation and selection signals to the multiple picture elements.

50. The apparatus of claim 48 wherein electrodes on one side of the liquid crystal layer are arranged in generally parallel rows and electrodes on an opposite side of the liquid crystal layer are arranged in generally parallel columns substantially orthogonal to said rows and said picture elements are defined by the points on said rows and columns at which said rows and columns would intersect when in the same plane, wherein when the control electronics applies a voltage signal to a row electrode, all picture elements in that row are electrically connected to the same voltage signal and when the control electronics applies a voltage signal to a column electrode, all picture elements in that column are connected to the same voltage signal.

51. The apparatus of claim 48 wherein said control electronics includes circuitry for simultaneously applying said selection signal to a plurality of rows of said picture elements.

52. The apparatus of claim 48, wherein said control electronics circuitry pre-disposes said layer of bistable chiral nematic liquid crystal material to a state different than said predetermined final display state during said selection phase.