Drive schemes for gray scale bistable cholesteric reflective displays

A method of addressing a bistable cholesteric liquid crystal material having incremental reflectance properties disposed between opposed substrates, wherein one substrate has a first plurality of electrodes deposited thereon facing the other substrate which has a second plurality of electrodes deposited thereon, the intersections of the first and second plurality of electrodes forming a plurality of pixels, the method comprising the steps of:

• selecting first and second characteristic voltage values, wherein one of said characteristic voltage values drive the material to a minimum reflectance and the other of said characteristic voltage values drives the materials to a maximum reflectance;
• energizing the first and second plurality of electrodes to drive all the liquid crystal material to one of the maximum and minimum reflectances;
• and
• energizing the first and second plurality of electrodes to obtain a pixel voltage waveform so as to switch the liquid crystal material to a corresponding incremental reflectance somewhere between the reflectance obtained by application of said first and second characteristic voltage values, wherein application of a portion of said pixel voltage waveform to at least one of said plurality of electrodes is varied to vary said pixel voltage waveform between said first and second characteristic voltages to obtain a corresponding incremental reflectance of the liquid crystal material, wherein obtaining said pixel voltage waveform includes time modulating application of said portion of said pixel voltage waveform in the form of a single bi-level pulse having a first voltage level for a first variable period of time and a second voltage level, different than said first voltage level, for a second variable period of time, wherein the sum of said first and second variable periods of time are equal to a set time period.