Drive schemes for gray scale bistable cholesteric reflective displays utilizing variable frequency pulses

• US 7,023,409 B2
• Filed: 02/09/2001
• Issued: 04/04/2006
• Est. Priority Date: 02/09/2001
• Status: Expired due to Term

• Current Assignee: Kent Displays Incorporated
• Original Assignee: Kent Displays Incorporated
• Inventors: Huang, Xiao-Yang, Ernst, Todd, Blackson, Chris
• Primary Examiner(s): Shankar, Vijay
• Application Number:
  US09/780,737
• Publication Number:
  US 20020109661A1
• Time in Patent Office: 1,880 Days
• Field of Search: 345/691, 345/690, 345/692, 345/693, 345 87-101, 345103-107, 345/204, 345/212
• US Class Current: 345/87
• 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 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2081 with combination of amplitude modulation and time modulation space and time error diffusion G09G3/2066
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals

Abstract

A method of addressing a bistable liquid crystal material having incremental reflectance properties disposed between opposed substrates is disclosed. One substrate has a first plurality of electrodes deposited thereon facing a second substrate which has a second plurality of electrodes disposed thereon. The intersection of the first and second plurality of electrodes forms a plurality of pixels. The addressing method includes applying a predetermined number of pulses to the first plurality of electrodes, and applying a like number of the predetermined number of pulses to the second plurality of electrodes. Each of the predetermined number of pulses has a different frequency, wherein the predetermined number of pulses are applied in a set time period.

Claims

1. A method of addressing a bistable cholesteric liquid crystal material having incremental reflectance properties disposed between opposed substrates, wherein one substrate has a first plurality of electrodes deposited thereon facing the other substrate which has a second plurality of electrodes disposed thereon, the intersection of the first and second plurality of electrodes forming a plurality of pixels, the addressing method comprising:

applying a predetermined number of pulses to the first plurality of electrodes within a set period of time, each said pulse applied to the first electrodes having a different duration drive period within said set period of time;

applying said predetermined number of pulses to the second plurality of electrodes, which is the same number of pulses as applied to said first plurality of electrodes, within said set period of time, each said pulse applied to the second electrodes also having said different duration drive periods within said set period of time; and

selectively associating one of two amplitude values with at least one of said predetermined number of pulses applied to the electrodes to generate a desired incremental reflectance the each of the pixels, wherein said desired incremental reflectance is determined by which one of said amplitude values is associated with which one of said different duration drive periods.

2. The method according to claim 1, further comprising:

preparing said liquid crystal material by applying a preparation pulse to the first and second plurality of electrodes, prior to said applying steps.

3. The method according to claim 1, wherein each of said different drive duration periods are applied to the first and second plurality of electrodes at the same time.

4. The method according to claim 1, wherein the number of said predetermined number of pulses correspond to a different number of said desired incremental reflectances.

5. The method according to claim 1, wherein a number of said desired incremental reflectances at each pixel is equal to two raised to the number of said predetermined number of pulses less one, or less a constant value.

6. The method according to claim 1, wherein said pulses are bipolar.

7. The method according to claim 1, wherein said pulses are unipolar.

8. The method according to claim 1, wherein the number of said predetermined number of pulses is equal to a number of said desired incremental reflectances.

9. The method according to claim 8, wherein said number of said desired incremental reflectances corresponds to said number of drive periods, each said drive period having a different length of time than all other said drive periods.

10. The method according to claim 1, wherein said number of said predetermined number of pulses is equal to an exponent number applied to two, wherein the exponent number corresponds to a number of pulses, plus one, or plus a constant value.

11. The method according to claim 10, wherein said exponent number of pulses corresponds to said different duration drive periods, each said different duration drive period having a different length of time, and wherein the additional pulse corresponds to a preparation pulse.

12. The method according to claim 11, wherein the shortest drive period is about half the duration of the next longest drive period.

13. The method according to claim 11, wherein each drive period is at least either about twice as long in duration as the next shortest drive period or about half as short in duration as the next longest drive period.

14. A liquid crystal display, comprising:

a pair of opposed substrates having disposed therebetween a cholesteric liquid crystal material, one of said substrates having a first plurality of electrodes disposed thereon facing the other of said substrates which has a second plurality of electrodes, wherein the intersection of said first and second plurality of electrodes form a plurality of pixels; and

a drive circuit that applies a predetermined number of pulses to said first plurality of electrodes and said predetermined number of pulses to said second plurality of electrodes, which is the same number of pulses as applied to said first plurality of electrodes, within a set period of time, each of said predetermined number of pulses having a different duration drive period within said set period of time, said drive circuit associating one of two amplitude values with at least one of said predetermined number of pulses to generate a desired incremental reflectance for each of the pixels which is determined by which one of said amplitude values is associated with which one of said different duration drive periods.

15. The liquid crystal display according to claim 14, wherein said driver circuit applies each of said different duration drive periods to said first and second plurality of electrodes at the same time.

16. The liquid crystal display according to claim 14, wherein the number of said predetermined number of pulses correspond to a different number of incremental reflectances.

17. The liquid crystal display according to claim 14, wherein the number of said predetermined number of pulses is equal to a number of incremental reflectances.