Dynamically biased full-swing operation amplifier for an active matrix liquid crystal display driver

摘要

A versatile amplifier circuit for driving a TFT LCD panel is disclosed. The amplifier circuit of the present comprises consists of a complementary input stage, biasing switches, and a rail-to-rail output stage. A signal-transfer switch determines which of two differential amplifiers in the input stage will drive the output stage of the amplifier. A biasing signal precharges a capacitor between the gates of output stage. The rail-to-rail output stage utilizes the precharged capacitor to maintain a voltage required to operate the output stage properly. A polarity signal is used to control the signal-transfer switch. The polarity signal specifies if a lower half of the input stage or an upper half of the input stage is used to drive the output stage of the amplifier circuit. A non-active transistor is kept turned-on above the threshold voltage for quick switching of the output driver. In one embodiment, a coupling capacitor is used between output stage transistors is for this purpose. This capacitor maintains the voltage necessary to keep the non-active transistor turned-on and flowing with a minimum current, and prevents the non-active transistor from being turned off. This simple scheme allows the amplifier circuit of the present invention to operate rapidly and in rail-to-rail range.