A rail-to-rail unity gain buffer amplifier for low-cost high resolution TFT LCD panels

A structural rail-to-rail high voltage CMOS buffer amplifier for driving gamma correction reference voltage of TFT LCD panels is presented. It operates from a single supply and only consumes 0.5 mA at 18 V power supply voltage. The circuit is designed for 8-bit or 10-bit high resolution TFT LCD panels. The buffer has high slew rate, 0.5 mA static current and 1 kohm resistive and capacitive load driving capability. Also, it offers wide supply range, offset voltages below 50 mV at 5 mA constant output current, and below 2.5 mV input referred offset voltage. To achieve wide-swing input and output dynamic range, current mirrored n-channel differential amplifier, p-channel differential amplifier, a class-AB push-pull output stage and an input level detector using hysteresis comparator are applied. The complete circuit is realized in a high voltage 0.18 um 18 V CMOS process technology for display driver IC and the area measures only 0.056 mm². The circuit operates at supply voltages from 8 V to 18 V.