Liquid crystal print bar having a single backplane electrode

Claim 1

Apparatus for projecting data on a photoreceptor surface including: drive means for moving the photoreceptor surface, a linear, optical writing station arranged transversely to the direction of travel of the photoreceptor surface including an array of liquid crystal pads mounted adjacent to the photoreceptor surface, said liquid crystal pads being arranged along two parallel lines with the location of the liquid crystal pads of the second line being staggered relative to the location of the liquid crystal pads of the first line, said array extending over a linear extent equivalent to the width of said photoreceptor surface onto which data is to be projected, an array of thin film transistors supported on a substrate and connected to the array of liquid crystal pads for electrically driving said pads, a source of light for projecting light onto said liquid crystal pads, means to focus said light onto the photoreceptor surface from the liquid crystal pads, a first means electrically connected to the liquid crystal pads for initially energizing the pads to prevent the passage of light therethrough, a second means electrically connected to the pads for selectively de-energizing said first means to permit the passage of light through selected liquid crystal pads, and multiplexing means electrically connected to the array of thin film transistors for selective pulsing of said array of liquid crystal pads whereby said photoreceptor surface is selectively exposed by light from said light source wherein the improvement comprises: a single backplane electrode disposed near the liquid crystal pads.