Driving methods and circuit for bi-stable displays

Abstract

The disclosure is directed toward driving methods and a driving circuit which are particularly suitable for bi-stable displays. In certain embodiments, methods provide the fastest and most pleasing appearance to the desired image while maintaining the optimal image quality over the life expectancy of an electrophoretic display device.

1 . A driving method for a multi-pixel electrophoretic display comprising:
 recording driving pulses applied to individual pixels of the multi-pixel electrophoretic display; and   periodically applying a corrective waveform such that the driving pulses applied to all of the individual pixels are substantially equalized over a period of time.   
   
   
       2 . The driving method of  claim 1  wherein the recording of the driving pulses applied to the individual pixels is selected from the group consisting of: a number of times a driving pulse is applied to the individual pixels, a number of resets to a particular color state for the individual pixels, a number of resets to two or more color states for the individual pixels and a relative DC imbalance in applied driving pulses among the individual pixels. 
   
   
       3 . The driving method of  claim 1  wherein the corrective waveform comprises applying a driving voltage across the multi-pixel electrophoretic display such that a net vector magnitude of the driving pulses over the period of time are substantially equalized for all the individual pixels. 
   
   
       4 . The driving method of  claim 2  wherein the individual pixels are considered substantially equalized when differences in the number of driving pulses among all the individual pixels is less than or equal to 20% over the period of time. 
   
   
       5 . The driving method of  claim 1  wherein the driving pulses includes a duration in a range of about 50 milliseconds to 500 milliseconds. 
   
   
       6 . The driving method of  claim 2  further comprising applying the corrective waveform to at least those individual pixels receiving a lower number of driving pulses than other individual pixels such that all individual pixels are substantially equalized in the number of driving pulses over the period of time. 
   
   
       7 . The driving method of  claim 1  further comprising waiting for a predetermined amount of time before applying the corrective waveform to at least a portion of the individual pixels. 
   
   
       8 . The driving method of  claim 1  further comprising determining whether a sufficient period of inactivity has elapsed for the multi-pixel display before applying the corrective waveform to the individual pixels. 
   
   
       9 . The driving method of  claim 1  wherein the corrective waveform includes a duration of less than 350 milliseconds. 
   
   
       10 . The driving method of  claim 2  wherein a duration of the corrective waveform is substantially equal to a cumulative duration of driving pulses applied to a given pixel. 
   
   
       11 . The driving method of  claim 2  wherein the corrective waveform includes an opposite polarity from the driving pulses applied to a given pixel. 
   
   
       12 . A driving method for a multi-pixel electrophoretic display comprising:
 applying driving pulses to a given pixel;   applying, over a period of time, a cumulative number of resets to a first color state and a cumulative number of resets to a second color state that are substantially equal over the period of time.   
   
   
       13 . The driving method of  claim 12  further comprising applying a corrective waveform to the given pixel to correct for a DC imbalance relative to other individual pixels of the multi-pixel electrophoretic display. 
   
   
       14 . The driving method of  claim 12  wherein the driving pulses are provided in a multi-pulse driving frame having a duration in a range of about 200 milliseconds to 1500 milliseconds. 
   
   
       15 . A driving method for a multi-pixel electrophoretic display comprising:
 applying driving pulses to individual pixels of the multi-pixel electrophoretic display;   applying, over a period of time, a cumulative number of resets to all color states that is substantially equalized for all individual pixels.   
   
   
       16 . The driving method of  claim 15  further comprising applying a corrective waveform for correcting DC imbalances among the individual pixels. 
   
   
       17 . The driving method of  claim 15  method further comprising applying driving pulses to the individual pixels such that all of the individual pixels are reset to a given color state after the individual pixels have been substantially equalized. 
   
   
       18 . A system for driving a multi-pixel electrophoretic display comprising:
 a microcontroller operatively coupled to the multi-pixel electrophoretic display, the microcontroller including;   a memory for recording parameters associated with driving pulses applied to individual pixels of the multi-pixel electrophoretic display; and,   a set of logical instructions which when performed by the microcontroller causes the microcontroller to;   determine from the recorded parameters which individual pixels require application of a corrective waveform; and,   apply the corrective waveform to the individual pixels determined by the microcontroller.   
   
   
       19 . The system according to  claim 18  wherein the set of logical instructions further comprises logical instructions which when performed by the microcontroller causes the microcontroller to wait a predetermined amount of time before applying the corrective waveform. 
   
   
       20 . The system according to  claim 18  wherein the corrective waveform substantially equalizes a number of driving pulses applied to all individual pixels over a period of time. 
   
   
       21 . The system according to  claim 18  wherein the corrective waveform resets the individual pixels to a given color state. 
   
   
       22 . The system according to  claim 18  wherein the corrective waveform resets the individual pixels to two or more color states. 
   
   
       23 . The system according to  claim 18  wherein the corrective waveform resets all individual pixels such that a cumulative number of resets to all color states are substantially equalized. 
   
   
       24 . The system according to  claim 18  wherein the corrective waveform corrects for DC imbalances among the individual pixels. 
   
   
       25 . The system according to  claim 18  wherein the corrective waveform substantially equalizes a net magnitude of driving pulses for all the individual pixels over the period of time. 
   
   
       26 . The system according to  claim 18  wherein the corrective waveform is provided to obtain a DC imbalance of less than 90 volt·sec over a duration of about 60 minutes.