Novel frame buffer pixel circuits for liquid-crystal-on-silicon microdisplays

A 32 × 16 liquid-crystal-on-silicon (LCOS) backplane with novel frame buffer pixels is designed and fabricated using the AMI Semiconductor´s 0.5-μm double-poly triple-metal CMOS process. The three novel pixel circuits described herein increase the brightness of an XGA LCOS microdisplay by at least 36% without sacrificing image contrast ratio. The increase of brightness is attributed to maximizing overall image view time, allowing an image to be displayed at full contrast while the next image is buffered onto the backplane. The new circuits achieve this by removing charge sharing and charge inducement problems shown in previously proposed frame buffer pixel circuits. Voltages on the pixel electrodes measured through rail-to-rail operational amplifiers with negative feedback vary from 0 to 4.25 V (6-V power source). All data voltage levels remain constant over a frame time with less than 1% drop, thus ensuring maximum contrast ratio. Modeling and experimental measurement on the fabricated chip show that these pixel circuits outperform all others to date based on storage time, data storage level, and potential for highest contrast ratio with maximum brightness.