Methods for addressing electrophoretic displays

• US 6,531,997 B1
• Filed: 04/28/2000
• Issued: 03/11/2003
• Est. Priority Date: 04/30/1999
• Status: Expired due to Term

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: E Ink Holdings Incorporated
• Inventors: Drzaic, Paul S, Gates, Holly G, Albert, Jonathan D., Comiskey, Barrett, Kazlas, Peter T.
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Kovalick, Vincent E.
• Application Number:
  US09/561,424
• Time in Patent Office: 1,047 Days
• Field of Search: 345/87, 345/95, 345/97, 345/107, 345/210, 204/606, 315/169.3, 359/296-299, 349/35
• US Class Current: 345/107
• CPC Class Codes: G02F 1/167 by electrophoresis
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• 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 2320/0204 Compensation of DC component across the pixels in flat panels
• 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

Abstract

Novel addressing schemes for controlling bistable electronically addressable displays include the use of addressing signals with additional signals having opposite polarity and equal integrated signal strength, and addressing schemes that minimize the number of state changes that a display element undergoes. In one embodiment, pre-pulses are employed to apply a pre-stress to an display element that is equal and opposite to the electrical stress applied in addressing the element. In another embodiment, the addressing signal is followed by a post-stressing pulse. Methods for minimizing the number of display elements that must change state to change the image displayed include the determination of a set of elements that must be deactivated and a set of elements that must be activated to change the image depicted by a display. Alternatively, only the elements forming one image are deactivated before the elements forming a different image are activated.

Claims

1. A method for addressing a bistable display element having first and second display states differing in at least one optical property, the method comprising:

(a) applying to the display element a first addressing signal effective to change the display state of the display element; and

(b) thereafter applying to the display element a second addressing signal which does not change the display state of the display element

the algebraic sum of the integral of the first addressing signal with respect to time and the integral of the second addressing signal with respect to time having an absolute value less than about 1 Volt-second.

2. A method according to claim 1 wherein the display element is an electrophoretic display element.

3. A method according to claim 2 wherein the display element is an encapsulated electrophoretic display element.

4. A method according to claim 2 wherein the display element comprises an electrophoretic medium comprising a liquid and at least one particle disposed within the liquid and capable of moving therethrough on application of an electric field to the medium.

5. A method according to claim 4 wherein the display element has a viewing surface and the liquid has a optical property differing from that of the at least one particle, the display element being in its first display state when the at least one particle lies adjacent its viewing surface and being in its second display state when the at least one particle is spaced from its viewing surface so that the liquid lies adjacent the viewing surface.

6. A method according to claim 4 wherein the display element has a viewing surface and the liquid has disposed therein at least one first particle having a first optical property and a first electrophoretic mobility and at least one second particle having a second optical property different from the first optical property and a second electrophoretic mobility different from the first electrophoretic mobility, the display element being in its first display state when the at least one first particle lies adjacent its viewing surface and being in its second display state when the at least one second particle lies adjacent its viewing surface.

7. A method according to claim 1 wherein the absolute value of the algebraic sum is less than about 0.1 Volt-second.

8. A method according to claim 1 wherein the first and second addressing signals are of opposite polarity.

9. A method according to claim 1 wherein the first and second addressing signals have different amplitudes and different durations.

10. A method according to claim 9 wherein the second addressing signal has an amplitude not greater than about one-fifth of the amplitude of the first addressing signal and a duration at least about five times the duration of the first addressing signal.

11. A method according to claim 10 wherein the second addressing signal has an amplitude not greater than about one-tenth of the amplitude of the first addressing signal and a duration at least about ten times the duration of the first addressing signal.

12. A method according to claim 1 wherein, in step (a), a plurality of first addressing pulses are applied to the display element.

13. A method according to claim 1 wherein, in step (b), a plurality of second addressing pulses are applied to the display element.

14. A method according to claim 1 wherein a predetermined time is allowed to elapse after step (a) and before step (b).

15. A method of addressing a bistable display, this display comprising a set of display elements each having first and second display states differing in at least one optical property, the method comprising:

(a) causing the display to display a first image in which a first subset of display elements are in their first display state and the complement of the first subset of display elements are in their second display state;

(b) applying to the first subset of display elements, but not to the complement of the first subset, a first addressing signal, thereby causing the first subset to assume their second display state; and

(c) applying to a second subset of display elements, different from said first subset, but not to the complement of the second subset, a second addressing signal, thereby causing the second subset to assume their first display state and the display to display a second image, different from the first image, the second image being formed by the second subset of display elements being in their first display state and the complement of the second subset being in their second display state.

16. A method according to claim 15 wherein the display elements are electrophoretic display elements.

17. A method according to claim 16 wherein the display elements are encapsulated electrophoretic display elements.

18. A method according to claim 16 wherein the display element comprises an electrophoretic medium comprising a liquid and at least one particle disposed within the liquid and capable of moving therethrough on application of an electric field to the medium.

19. A method according to claim 18 wherein the display element has a viewing surface and the liquid has a optical property differing from that of the at least one particle, the display element being in its first display state when the at least one particle lies adjacent its viewing surface and being in its second display state when the at least one particle is spaced from its viewing surface so that the liquid lies adjacent the viewing surface.

20. A method according to claim 18 wherein the display element has a viewing surface and the liquid has disposed therein at least one first particle having a first optical property and a first electrophoretic mobility and at least one second particle having a second optical property different from the first optical property and a second electrophoretic mobility different from the first electrophoretic mobility, the display element being in its first display state when the at least one first particle lies adjacent its viewing surface and being in its second display state when the at least one second particle lies adjacent its viewing surface.

21. A method according to claim 15 further comprising, prior to step (a), causing all the display elements of the set to assume their second display state, and thereafter applying to the first subset of display elements, but not to the complement of the first subset, a third addressing signal, thereby causing the first subset of display elements to assume their first display state.

22. A method according to claim 21 wherein all the display elements of the set are caused to assume their second display state by applying to all the display elements a pre-blanking signal sufficient to cause every display element to assume its first display state, and thereafter applying to all the display elements a blanking signal sufficient to cause every display element to assume its second display state.

23. A method according to claim 22 wherein the algebraic sum of the integral of the pre-blanking signal with respect to time and the integral of the blanking signal with respect to time is substantially zero.

24. A method according to claim 15 wherein the algebraic sum of the integral of the first addressing signal with respect to time and the integral of the second addressing signal with respect to time is substantially zero.

25. A method according to claim 24 wherein the absolute value of the algebraic sum is less than about 10 Volt-seconds.

26. A method according to claim 25 wherein the absolute value of the algebraic sum is less than about 1 Volt-second.

27. A method according to claim 26 wherein the absolute value of the algebraic sum is less than about 0.1 Volt-second.

28. A method according to claim 15 wherein a plurality of first addressing pulses are applied to the first subset of display elements.

29. A method according to claim 15 wherein a plurality of second addressing pulses are applied to the second subset of display elements.

30. A method according to claim 15 wherein said display has on one side thereof a common electrode extending across all the display elements of the set, and on the opposed side thereof a plurality of discrete electrodes, one of the discrete electrodes being associated with each display element of the set, and wherein the first addressing signal is provided by setting the common electrode to a first voltage and the discrete electrodes associated with the first subset of display elements to a second voltage different from the first voltage, while the second addressing signal is provided by setting the common electrode to the second voltage and the discrete electrodes associated with the second subset of display elements to the first voltage.

31. A method according to claim, 30 further comprising, prior to step (a), causing all the display elements of the set to assume their second display state, and thereafter applying to the first subset of display elements, but not to the complement of the first subset, a third addressing signal, thereby causing the first subset of display elements to assume their first display state.

32. A method according to claim 31 wherein all the display elements of the set are caused to assume their second display state by applying to all the display elements a pre-blanking signal sufficient to cause every display element to assume its first display state, and thereafter applying to all the display elements a blanking signal sufficient to cause every display element to assume its second display state.

33. A method according to claim 32 wherein the pre-blanking signal is provided by setting the common electrode to the second voltage and all the discrete electrodes to the first voltage, while the blanking signal is provided by setting the common electrode to the first voltage and all the discrete electrodes to the second voltage.

34. A method of addressing a bistable display, this display comprising a set of display elements each having first and second display states differing in at least one optical property, the method comprising:

(a) selecting a first subset of display elements that represent a first image, and applying to the first subset a first addressing signal, thereby causing the first subset to assume their first display state and the display to display the first image;

(b) selecting a second subset of display elements that represent a second image different from the first image and thereby defining four classes of display elements, namely a first class which are members of both the first and second subsets, a second class which are members of the first subset but not members of the second subset, a third class which are not members of the first subset but are members of the second subset, and a fourth class which are not members of either the first or the second subset, and applying to the second class a second addressing signal, thereby setting the second class to their second display state, and applying to the third class a third addressing signal, thereby setting the third class to their first display state, and causing the display to display the second image,

and wherein the display has on one side thereof a common electrode extending across all the display elements of the set, and on the opposed side thereof a plurality of discrete electrodes, one of the discrete electrodes being associated with each display element of the set, the common electrode being kept at a substantially constant first voltage during steps (a) and (b).

35. A method according to claim 34 wherein the discrete electrodes associated with at least one of the first and fourth classes of display elements are kept at substantially the constant first voltage during steps (a) and (b).

36. A method according to claim 35 wherein the discrete electrodes associated with both the first and fourth classes of display elements are kept at substantially the constant first voltage during steps (a) an (b).

37. A method according to claim 35 wherein the second addressing signal is provided by setting the discrete electrodes associated with the second class of display elements to a second voltage substantially equal to the first voltage plus a predetermined difference, and the third addressing signal is provided by setting the discrete electrodes associated with the third class of display elements to a third voltage substantially equal to the first voltage minus the predetermined difference.

38. A method according to claim 37 wherein the second and third addressing signals are each preceded by a pre-addressing signal, this pre-addressing signal being provided by setting the discrete electrodes associated with the second class of display elements to substantially the third voltage and the discrete electrodes associated with the third class of display elements to substantially the second voltage.

39. A method of addressing a bistable display comprising a set of display elements each having first and second display states differing in at least one optical property, the display having on one side thereof a common electrode extending across all the display elements of the set, and on the opposed side thereof a plurality of discrete electrodes, one of the discrete electrodes being associated with each display element of the set, the method comprising:

(a) selecting a first subset of display elements that represent a first image;

(b) selecting a second subset of display elements that represent a second image different from the first image and thereby defining four classes of display elements, namely a first class which are members of both the first and second subsets, a second class which are members of the first subset but not members of the second subset, a third class which are not members of the first subset but are members of the second subset, and a fourth class which are not members of either the first or the second subset,

(c) bringing the display to a state in which the first and classes of display elements are in their first display state and the third and fourth classes are in their second display state, thereby causing the first image to be displayed; and

(d) applying a first voltage to the common electrode for a first period and a different second voltage to the common electrode for a second period, while maintaining the discrete electrodes associated with at least one of the first and fourth classes of display elements at substantially the same voltages as the common electrode, and maintaining the discrete electrodes associated with one of the second and third classes of display elements substantially at the first voltage while maintaining the discrete electrodes associated with the other of the second and third classes substantially at the second voltage,

thereby causing the first and third classes of display elements to be in their first display state and the second and fourth classes of display elements to be in their second display state, so that the display displays the second image.

40. A method according to claim 39 wherein, in step (d) the discrete electrodes associated with both the first and fourth classes of display elements are maintained at substantially the same voltage as the common electrode.

41. A method according to claim 39 wherein the first and second periods are substantially equal in duration.

42. A method according to claim 39 wherein the common electrode is subjected to a plurality of cycles each comprising a first period in which the first voltage is applied and a second period in which the second voltage is applied, and wherein the discrete electrodes associated with one of the second and third classes of display elements are maintained substantially at the first voltage and the discrete electrodes associated with the other of the second and third classes are maintained substantially at the second voltage throughout the plurality of cycles.

43. A bistable display element having first and second display states differing in at least one optical property;

and

a signal control module arranged to apply at least first and second addressing signals to the display element, the first addressing signal changing the display state of the element and the second addressing signal not substantially changing the display state of the element, the algebraic sum of the integral of the first addressing signal with respect to time and the integral of the second addressing signal with respect to time having an absolute value less than about 1 Volt-second.