Two-Stage Operational Amplifier Design by Using Direct and Indirect Feedback Compensations

This paper states the stability requirements of the amplifier system, and then presents, and summarizes, the classic two stage CMOS Op-Amp design by employing several popular frequency compensation techniques including traditional Miller compensation, nulling resistor, voltage buffer, and current buffer. The advantages and disadvantages of all these compensation strategies are evaluated based on a standard performance which has a 70dB DC gain, a 60◦ phase margin, a 25MHz gain bandwidth, and a slew rate of 20 V/us requirements. All the designs and simulation results are based on a 180mm 1.8 V standard TSMC CMOS technology. Ultimately, the traditional Miller compensated Op-Amp (a single compensation capacitor amplifier) cannot meet all the requirements but all other techniques could with also a boost of performance in various aspects.