LIGHTING A CHOLESTERIC LIQUID CRYSTAL DISPLAY APPARATUS

摘要

A display apparatus comprises a cholesteric liquid crystal display device having cells comprising a layer of cholesteric liquid crystal material and an electrode arrangement capable of providing independent driving of a plurality of pixels across the layer of cholesteric liquid crystal material. A drive circuit generates drive signals supplied to the pixels to drive them into states reflectances in accordance with an image signal. The drive signals may have a waveform shaped to drive the respective pixels into the homeotropic state and the planar state alternately within successive drive periods for respective periods of time which are varied to provide an average reflectance as perceived by a viewer in accordance with the image signal. A light source illuminates the display device and is supplied with power by a power circuit. The power circuit supplies either: a) DC power, or b) AC power at a supply frequency FS in accordance with the equation |2FS-FH|>=FT where FH is the frequency at which the pixels are driven into the planar state. This reduces the perception of flicker in a displayed image and FT is the flicker fusion threshold.