Driving methods and circuit for bi-stable displays

A method for driving a display device which comprises a plurality of pixels each of which is sandwiched between a common electrode common to all pixels and a pixel electrode, and is capable of displaying a first color or a second color, the method comprising applying a driving sequence which comprises:

• a) for a first time period, applying no voltage potential to the common electrode, applying a first voltage potential to pixel electrodes corresponding to a first group of pixels, and applying no voltage potential to pixel electrodes corresponding to a second group of pixels of the second color, to cause the display device to display a onetime image of the first color with a background of the second color;
• b) for a second time period, applying no voltage potential to the common electrode, applying no voltage potential to the pixel electrodes corresponding to the first group of pixels, and applying a second voltage potential to the pixel electrodes corresponding to the second group of pixels, to clear the onetime image created in step (a);
• and
• c) for a third time period, applying a third voltage potential to the common electrode, and applying no voltage potential to the pixel electrodes corresponding to the first and second groups of pixels;
• wherein time lengths of the first, second and third time periods are equal, and the driving sequence is DC balanced;
• and
• wherein the driving sequence display a onetime password image used in a smartcard application, and the driving sequences reset the plurality of pixels to clear the onetime password image.