Methods for driving electro-optic displays

• US 20050024353A1
• Filed: 06/29/2004
• Published: 02/03/2005
• Est. Priority Date: 11/20/2001
• Status: Active Grant

• Current Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Original Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Inventors: Knaian, Ara N., Zehner, Robert W., Amundson, Karl R., Zion, Benjamin
• Granted Patent: US 7,528,822 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/08 Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
• CPC Class Codes: G09G 2310/02 Addressing, scanning or driving the display screen or processing steps related thereto
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2310/063 Waveforms for resetting the whole screen at once
• CPC Class Codes: G09G 2310/065 Waveforms comprising zero voltage phase or pause
• CPC Class Codes: G09G 2310/068 Application of pulses of alternating polarity prior to the drive pulse in electrophoretic displays
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/04 Maintaining the quality of display appearance
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2018 : by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/344 : based on particles moving in a fluid or in a gas, e.g. electrophoretic devices electrophoretic devices per se G02F1/167
• CPC Class Codes: G09G 3/38 : using electrochromic devices

Abstract

An electro-optic display, having at least one pixel capable of achieving any one of at least four different gray levels including two extreme optical states, is driven by displaying a first image on the display, and rewriting the display to display a second image thereon, wherein, during the rewriting of the display, any pixel which has undergone a number of transitions exceeding a predetermined value without touching an extreme optical state, is driven to at least one extreme optical state before driving that pixel to its final optical state in the second image.

Claims

1. A method for driving an electro-optic display having at least one pixel capable of achieving any one of at least four different gray levels including two extreme optical states, the method comprising:

displaying a first image on the display; and

rewriting the display to display a second image thereon,

wherein, during the rewriting of the display any pixel which has undergone a number of transitions exceeding a predetermined value, the predetermined value being at least one, without touching an extreme optical state, is driven to at least one extreme optical state before driving that pixel to its final optical state in the second image.

2. A method according to claim 1 wherein the rewriting of the display is effected such that, once a pixel has been driven from one extreme optical state towards the opposed extreme optical state by a pulse of one polarity, the pixel does not receive a pulse of the opposed polarity until it has reached the opposed extreme optical state.

3. A method according to claim 1 wherein said predetermined value is not greater than N/2, where N is the total number of gray levels capable of being displayed by a pixel.

4. A method according to claim 1 wherein the rewriting of the display is effected by applying to the or each pixel any one or more of voltages −

V, 0 and +V.

5. A method according to claim 1 wherein the rewriting of the display is effected such that, for any series of transitions undergone by a pixel, the integral of the applied voltage with time is bounded.

6. A method according to claim 1 wherein the rewriting of the display is effected such that the impulse applied to a pixel during a transition depends only upon the initial and final gray levels of that transition.

7. A method according to claim 1 wherein, for at least one transition undergone by the at least one pixel from a gray level R2 to a gray level R1, there is applied to the pixel a sequence of impulses of the form:

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2)

where “

IP(Rx)”

represents the relevant value from an impulse potential matrix having one value for each gray level, and TM(R1,R2) represents the relevant value from a transition matrix having one value for each R1/R2 combination.

8. A method according to claim 7 wherein for all transitions in which the initial and final gray levels are different, the sequence of impulses of the form:

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2).

9. A method according to claim 7 wherein, in the

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2)

sequence, the final TM(R1,R2) section occupies more than one half of the maximum update time.

10. A method according to claim 1 wherein the rewriting of the display is effected such that a transition to a given gray level is always effected by a final pulse of the same polarity.

11. A method according to claim 10 wherein gray levels other than the two extreme optical states are approached from the direction of the nearer extreme optical state.

12. A method according to claim 7 wherein the TM(R1,R2) values are chosen such that the sign of each value is dependent only upon R1.

13. A method according to claim 12 wherein the TM(R1,R2) values are chosen to be positive for one or more light gray levels and negative for one or more dark gray levels so that gray levels other than the two extreme optical states are approached from the direction of the nearer extreme optical state.

14. A method according to claim 7 wherein the at least one transition further comprises an additional pair of pulses of the form [+y][−

y], where y is an impulse value, which may be either negative or positive, the [+y] and [−

y] pulses being inserted into the

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2)

sequence.

15. A method according to claim 14 wherein the at least one transition further comprises a second additional pair of pulses of the form [+z][−

z], where z is an impulse value different from y and may be either negative or positive, the [+z] and [−

z] pulses being inserted into the

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2)

sequence.

16. A method according to claim 7 wherein the at least one transition further comprises a period when no voltage is applied to the pixel.

17. A method according to claim 16 wherein the period when no voltage is applied to the pixel occurs between two elements of the

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2)

sequence.

18. A method according to claim 16 wherein the period when no voltage is applied to the pixel occurs between at an intermediate point within a single element of the

−

TM(R1,R2) IP(R1)−

IP(R2) TM(R1,R2)

sequence.

19. A method according to claim 16 wherein the at least one transition comprise at least two periods when no voltage is applied to the pixel.

20. A method according to claim 7 wherein the display comprises a plurality of pixels divided into a plurality of groups, and the transition is effected by (a) selecting each of the plurality of groups of pixels in succession and applying to each of the pixels in the selected group either a drive voltage or a non-drive voltage, the scanning of all the groups of pixels being completed in a first frame period;

(b) repeating the scanning of the groups of pixels during a second frame period; and

(c) interrupting the scanning of the groups of pixels during a pause period between the first and second frame periods, this pause period being not longer than the first or second frame period.

21. A method according to claim 1 wherein the electro-optic display comprises an electrochromic or rotating bichromal member electro-optic medium.

22. A method according to claim 1 wherein the electro-optic display comprises an encapsulated electrophoretic medium.

23. A method according to claim 1 wherein the electro-optic display comprises a microcell electrophoretic medium.

24. A method for driving an electro-optic display having a plurality of pixels divided into a plurality of groups, the method comprising:

(a) selecting each of the plurality of groups of pixels in succession and applying to each of the pixels in the selected group either a drive voltage or a non-drive voltage, the scanning of all the groups of pixels being completed in a first frame period;

(b) repeating the scanning of the groups of pixels during a second frame period; and

(c) interrupting the scanning of the groups of pixels during a pause period between the first and second frame periods, this pause period being not longer than the first or second frame period.

25. A method according to claim 24 wherein the first and second frame periods are equal in length.

26. A method according to claim 25 wherein the length of the pause period is a sub-multiple of the length of one of the first and second frame periods.

27. A method according to claim 24 wherein the method comprises scanning the groups of pixels during at least first, second and third frame periods, and interrupting the scanning of the groups of pixels during at least first and second pause periods between successive frame periods.

28. A method according to claim 27 wherein the first, second and third frame periods are substantially equal in length, and the total length of the pause periods is equal to one frame period or one frame period minus one pause period.

29. A method according to claim 24 wherein the pixels are arranged in a matrix having a plurality of rows and a plurality of columns with each pixel defined by the intersection of a given row and a given column, and wherein each group of pixels comprises one row or one column of the matrix.

30. A method according to claim 24 wherein the scanning of the display is effected such that, for any series of transitions undergone by a pixel, the integral of the applied voltage with time is bounded.

31. A method according to claim 24 wherein the electro-optic display comprises an electrochromic or rotating bichromal member electro-optic medium.

32. A method according to claim 24 wherein the electro-optic display comprises an encapsulated electrophoretic medium.

33. A method according to claim 24 wherein the electro-optic display comprises a microcell electrophoretic medium.

34. A method for driving an electro-optic display having a plurality of pixels, the pixels being driven with a pulse width modulated waveform capable of applying a plurality of differing impulses to each pixel, the method comprising:

(a) storing data indicating whether application of a given impulse to a pixel will produce a gray level higher or lower than a desired gray level;

(b) detecting when two adjacent pixels are both required to be in the same gray level; and

(c) adjusting the impulses applied to the two pixels so that one pixel is below the desired gray level, while the other pixel is above the desired gray level.

35. A method according to claim 34 wherein the pixels are divided into two groups such that each pixel has at least one neighbor of the opposite group, and different drive schemes are used for the two groups.

36. A method according to claim 34 wherein the electro-optic display comprises an electrochromic or rotating bichromal member electro-optic medium.

37. A method according to claim 34 wherein the electro-optic display comprises an encapsulated electrophoretic medium.

38. A method according to claim 34 wherein the electro-optic display comprises a microcell electrophoretic medium.