Methods and apparatus for driving electro-optic displays

Abstract

Waveforms for driving electro-optic displays, especially bistable electro-optic displays, are modified by one or more of insertion of at least one balanced pulse pair into a base waveform; excision of at least one balanced pulse pair from the base waveform; and insertion of at least one period of zero voltage into the base waveform. Such modifications permit fine control of gray levels.

1 . A method for driving an electro-optic display having at least one pixel capable of achieving at least three different gray levels including two extreme optical states, the method comprising:
 applying a modified base waveform to the pixel to drive the pixel to a selected gray level,   wherein the base waveform comprises at least one reset pulse to drive the pixel to, or close to, one of the extreme optical states, and a set pulse to drive the pixel from the selected extreme optical state to a gray level different from the selected extreme optical state,   wherein the modified base waveform includes a modification to the base waveform of at least one of the following:   (a) insertion of at least one balanced pulse pair into the base waveform;   (b) excision of at least one balanced pulse pair from the base waveform; and   (c) insertion of at least one period of zero voltage into the base waveform,   where “balanced pulse pair” denotes a sequence of two pulses of opposite polarity such that the total impulse of the balanced pulse pair is essentially zero.   
     
     
         2 . The method of  claim 1 , wherein the base waveform is modified by insertion of at least one balanced pulse pair or excision of at least one balanced pulse pair. 
     
     
         3 . The method according to  claim 2 , wherein the two pulses of the balanced pulse pair are each of constant voltage but of opposite polarity and are equal in duration. 
     
     
         4 . The method according to  claim 2 , wherein the period in the base waveform occupied by each excised balanced pulse pair is replaced by a period of zero voltage. 
     
     
         5 . The method according to  claim 2 , wherein at least one balanced pulse pair is excised from the base waveform, elements of the base waveform are shifted in time to occupy the period formerly occupied by each excised balanced pulse pair, and a period of zero voltage is inserted at a point in time different from the point in time formerly occupied by each excised balanced pulse pair. 
     
     
         6 . The method according to  claim 1 , wherein the base waveform comprises, in succession, a first reset pulse sufficient to drive the pixel to, or close to, one of the extreme optical states, a second reset pulse sufficient to drive the pixel to, or close to, the other extreme optical state, and the set pulse. 
     
     
         7 . The method according to  claim 1 , where a voltage of 0, +V, or −V is applied to the pixel, wherein V is a predetermined drive voltage. 
     
     
         8 . The method according to  claim 1 , wherein the total number of inserted balanced pulse pairs, excised balanced pulse pairs, and inserted periods of zero voltage does not exceed six pairs. 
     
     
         9 . The method according to  claim 8 , wherein the total number of inserted balanced pulse pairs, excised balanced pulse pairs, and inserted periods of zero voltage does not exceed four pairs. 
     
     
         10 . The method according to  claim 9 , wherein the total number of inserted balanced pulse pairs, excised balanced pulse pairs, and inserted periods of zero voltage does not exceed two pairs. 
     
     
         11 . The method according to  claim 1 , wherein the modified base waveform is DC balanced. 
     
     
         12 . The method according to  claim 1 , wherein the display comprises a rotating bichromal member or an electrochromic medium. 
     
     
         13 . The method according to  claim 1 , wherein the display comprises an electrophoretic electro-optic medium comprising a plurality of electrically charged particles in a fluid, the electrically charged particles being capable of moving through the fluid on application of an electric field to the medium. 
     
     
         14 . The method according to  claim 13 , wherein the fluid is gaseous. 
     
     
         15 . The method according to  claim 13 , wherein the charged particles and the fluid are confined within a plurality of capsules or microcells. 
     
     
         16 . A display controller, application specific integrated circuit, or software code adapted to carry out the method according to  claim 1 .