A pixel scale digital to analog converter for liquid crystal on VLSI displays

Abstract

A pixel scale digital to analog converter and driver for liquid crystal (LC) cells is presented. The circuit is a highly compact CMOS logic gate that sums pulse density modulation (p.d.m.) signals. Low pass filtering of the p.d.m. signal is done by the liquid crystal material. The circuit is suitable to build large arrays of converters as for example in display applications. It is applicable in liquid crystal on VLSI displays where gray scale data are stored and converted at each pixel site. Advantages over the commonly used active matrix technology is the removal of all analog circuitry, no need for refresh reduced interconnect complexity, no capacitive loading of analog lines and the ability to build larger scale or smart displays that combine storage, drive, and processing circuitry. Experimental results from a CMOS implementation are presented.