Methods for driving color electrophoretic displays

Abstract

An electrophoretic medium includes a fluid, a first, light scattering particle (typically white) and second, third and fourth particles having three subtractive primary colors (typically magenta, cyan and yellow); at least two of these colored particles being non-light scattering. The first and second particles bear polymer coatings such that the electric field required to separate an aggregate formed by the third and the fourth particles is greater than that required to separate an aggregate formed from any other two types of particles. Methods for driving the medium to produce white, black, magenta, cyan, yellow, red, green and blue colors are also described.

1 . A method for addressing a color electrophoretic display having at least one pixel, the method comprising:
 applying an addressing pulse to drive the pixel to a first optical state;   leaving the pixel undriven for a period of time, thereby permitting the pixel to assume a second optical state different from the first optical state;   applying to the pixel a refresh pulse which substantially restores the pixel to the first optical state, the refresh pulse being of a shorter duration than the addressing pulse; and   applying a second addressing pulse after application of the refresh pulse to drive the pixel to a third optical state,   wherein the impulse applied by the second addressing pulse is the sum of (a) the impulse needed to drive the pixel from the first to the third optical state; and (b) an impulse equal in magnitude but opposite in polarity to the algebraic sum of the refresh pulses applied to the pixel between the first and second addressing pulses.   
     
     
         2 . The method of  claim 1 , wherein the color electrophoretic display includes four sets of particles and each set of particles has a different optical property. 
     
     
         3 . The method of  claim 2 , wherein the one of the sets of particles comprises a reflective white particle and the other three sets of particles each comprise a different subtractive color. 
     
     
         4 . A color electrophoretic display comprising a layer of electrophoretic media, an outer viewing surface, and a shuttering filter between the layer of electrophoretic media and the outer viewing surface, wherein the shuttering filter is configured to transition between an opaque and light-transmissive state and obscure the layer of electrophoretic media during transition between images displayed by the display. 
     
     
         5 . The color electrophoretic display of  claim 4 , wherein the shuttering filter comprises an electrochromic medium. 
     
     
         6 . A color electrophoretic display comprising a layer of electrophoretic media, a controller, and a bezel surrounding the layer of electrophoretic media, the bezel including one or more light elements, wherein the controller is configured to synchronize operation of the one or more light elements with a transition between images displayed by the display. 
     
     
         7 . The color electrophoretic display of  claim 6 , wherein the controller is configured to illuminate the one or more light elements during the transition between images displayed by the display. 
     
     
         8 . The color electrophoretic display of  claim 6 , wherein the controller is configured to switch off the one or more light elements during the transition between images displayed by the display. 
     
     
         9 . The color electrophoretic display of  claim 6 , wherein the controller is configured to intermittently illuminate the one or more light elements during transition between images displayed by the display. 
     
     
         10 . The color electrophoretic display of  claim 6 , wherein the one or more light elements is provided in the form of a scrolling marquee. 
     
     
         11 . A method for addressing a color electrophoretic display comprising a plurality of pixels arranged in a plurality of rows and a plurality of columns, a plurality of row electrodes each associated with one of the plurality of rows, a plurality of column electrodes each associated with one of the plurality of columns, and drive means arranged to select each of the row electrodes in turn and to apply to the column electrodes during the selection of any given row electrode voltages chosen so as to address the pixels in the row associated with the selected row electrode and write one row of a desired image on to the display, the method comprising:
 writing a first image to the display;   receiving data representing a second image to be written to the display;   comparing the first and second images and dividing the rows of the display into a first set, in which at least one pixel of the row differs between the first and second images, and a second set, in which no pixel of the row differs between the first and second images; and   writing the second image by sequentially selecting only the row electrodes associated with the first set of rows, and applying voltages to the column electrodes to write only the first set of rows, thereby forming the second image on the display.   
     
     
         12 . The method of  claim 11 , wherein the color electrophoretic display includes four sets of particles and each set of particles has a different optical property. 
     
     
         13 . The method of  claim 12 , wherein the one of the sets of particles comprises a reflective white particle and the other three sets of particles each comprise a different subtractive color.