A Low-Power adaptive biasing CMOS Operational Amplifier with enhanced DC-Gain

A new circuit topology for a low-voltage low-power class AB amplifier is presented. The circuit uses adaptive bias to have a better efficiency in driving high capacitive loads. Indeed, being the amplifier bias current dependent on the applied input signal, its slew rate strongly improves so enabling the op-amp to deal with large input signals. Differently than the typical adaptive biased amplifier, we introduce a positive feedback at the input stage to enhance the op-amp DC gain up to 90dB. The circuit has been designed in a 0.5mum CMOS technology. Simulation results are shown. The circuit presents a quiescent supply current of only 10muA. It is able to settle in 1mus with 0.1% of error for a 0.4V input voltage step and 10pF of load capacitance