WO1995006307B1

WO1995006307B1 - Electrophoretic display having reduced writing time

Info

Publication number: WO1995006307B1
Application number: PCT/US1994/009217
Authority: WO
Filing date: 1994-08-15
Publication date: 1995-04-13

Abstract

An electrophoretic display (10) is provided which enables an image to be displayed by selectively energizing intersecting grid (16) and cathode (14) lines each indicative of a pixel and varying the bias between the lines to cause suspended pigment particles to migrate to an anode (20) and away from the energized pixels. Selected intersections of grid (16) and cathode (14) lines indicative of pixels are energized with a set of voltages during a fixed time interval, thereby causing an image to be displayed thereon. The time interval selected is less than the time required to completely remove the pigment particles from the pixels and the image is sequentially enhanced by rewriting at least some of the pixels with the set of voltages at least once. This permits a readable image to be produced much more rapidly and also provides incrementally darker pixels in the image as additional pigment particles are moved from selected intersections during subsequent energizing intervals.

Claims

AMENDED CLAIMS[received by the International Bureau on 7 March 1995 (07.03.95); original claims 1-3, 7-9, 12 and 15 amended; remaining claims unchanged (4 pages)]

1. Apparatus for driving an electrophoretic display in a write mode, said display is of the type having a plurality of electrically conductive grid lines insulated from a plurality of electrically conductive cathode lines with said grid and cathode lines intersecting one another to provide an X-Y matrix, and said display having an anode electrode and an insulating fluid containing particles of at least one color pigment in suspension disposed between said anode electrode and said lines, said display providing an image by selectively accessing pixels defined by said intersecting grid and cathode lines and varying a bias between said lines to cause said particles to migrate to said anode for each selected pixel, the improvement in connection therewith comprising: means for energizing said selected pixels with a set of voltages for a fixed time interval, thereby causing said image to be displayed thereon, wherein said fixed time interval is less than a time required to completely remove said pigment particles from said selected pixels and wherein said energizing means sequentially enhances said image by rewriting at least some of said selected pixels with said set of voltages, at least one time, said means for energizing comprising a pulse generator for providing pulses which energize said selected pixels for said fixed time interval.

2. The apparatus according to claim 1, wherein said display provides a given number of grey scale levels and said energizing means takes a given number of times to write a darkest pixel, said given number of times to write being equal to said given number of grey scale levels.

3. The apparatus according to claim 1, wherein said display provides a given number of desired pixel shades and said fixed time interval is equal to the time needed to completely remove said pigment particles from said selected pixels divided by said given number of pixel shades desired for the display.

4. The apparatus according to claim 1, wherein said energizing means includes electric field applying means coupled to electrodes associated with said cathode and grid lines.

5. The apparatus according to claim 1, further including keyboard means coupled to said energizing means operative to generate alphanumeric characters for presenting X-Y data to said display.

6. The apparatus according to claim 1, wherein said energizing means includes microprocessor means for selecting pixels of said image to be written and re-written.

7. A method of providing grey scale capability for an electrophoretic information display of the type employing an insulating fluid containing particles of at least one color pigment in suspension disposed between an anode electrode and intersecting electrically conductive grid and cathode lines, each intersecting grid and cathode line defining a pixel, wherein each of said pixels is fully written by applying a potential thereto and thereby removing pigment particles therefrom, comprising the steps of: energizing selected pixels with a pulse generator for a fixed interval of time less than that required to completely remove said particles therefrom, thereby causing an image of a first shade, formed by said selected pixels, to be displayed; and energizing at least some of said selected pixels a second time for said fixed interval, thereby causing a portion of said image to be of a second shade darker than said first shade of said image to be displayed.

8. The method of claim 7, further including the step of selecting the duration of said interval by dividing a minimum time needed to completely remove pigment particles from said selected pixels by a given number of shades to be displayed.

9. The method of claim 7, further including sequentially energizing a number of said at least some of said selected pixels to incrementally darker other portions of said image until said number of said at least some of said selected pixels have all of said pigment particles removed therefrom.

10. The method of claim 7, further including the step of generating alphanumeric characters for presenting X-Y data to said display.

11. The method of claim 10, wherein said characters are generated by a keyboard during said generating step.

12. An apparatus for operating an electrophoretic information display with grey scale capability, said display being of the type having a plurality of pixel areas each accessible by an X-Y addressing format and each indicative of a given display content at that associated display area, comprising: means comprising a pulse generator for sequentially applying an electric field across selected pixel areas during a series of equal successive time intervals, each of said time intervals being less than a time necessary to completely remove pigment particles associated with said selected pixel areas therefrom, wherein incrementally darker pixels are provided after each of said successive time intervals until all of said pigment particles are removed from at least one of said selected pixel areas, wherein a grey scale image is obtained by applying said electric field only to said pixel areas which are not of a desired shade after a previous time interval.

13. The apparatus according to claim 12, wherein said energizing means includes means for driving X lines associated with said display and means for driving Y lines associated with said display with intersections between X and Y lines indicative of said pixel areas.

14. The apparatus according to claim 12, wherein said display is of the type employing X lines deposited on a glass substrate and fabricated from indium tin oxide (ITO) at a thickness such that said line pattern is transparent and having insulated therefrom a Y line pattern also fabricated from ITO with the intersection at each X and Y line associated with a particle well and indicative of a pixel area for said display.

15. The apparatus according to claim 12, further including microprocessor means for determining a number of said successive time intervals during which said electric field is to be applied to each of said pixels.