A Rail-to-Rail class AB amplifier design with an offset cancellation for LCD source drivers

Abstract

Increasing demands of LCD panel with high color depth and resolution makes it hard to design a buffer with such resolution. Since buffer design determines the speed, resolution, voltage swing and power dissipation of LCD drivers. But the resolution of the buffer amplifier depends upon settling time, low offset voltage and slew rate. Generally the methods used to reduce offset voltage are output offset storage technique and input offset storage technique. In this paper a complementary amplifier which has Rail-to-Rail feature with offset cancellation technique to enhance high resolution Liquid Crystal Display (LCD) drivers is implemented. The dual complementary differential pairs are divided into main and auxiliary trans-conductance amplifiers to obtain Rail-to-Rail input-output swing and an offset cancelling ability. The offset cancellation and charge conservation, which is used to reduce the dynamic power consumption, are to be operated in the same time slot so that the driving period does not need to increase. The implemented buffer exhibits a very high DC gain with good phase margin. The offset voltage is considerably reduced thereby reducing crossover distortion. The implemented buffer is stable and is providing Rail-to-Rail output swing.