New method to design feedback amplifier employing two-stage CMOS op amp

Abstract

A new method to design feedback amplifier employing two-stage CMOS op amp is proposed. It is shown that although the open-loop phase margin of around 65 degrees is suitable for op amp connected as unity-gain amplifier (100% feedback), such is not the case when amplifier’s feedback factor of is less than 100%. In the proposed design method, the open-loop phase margin requirement is replaced by closed-loop bandwidth and quality factor of feedback amplifier such that a better control of the responses of the amplifier is achieved. Comparison of simulation results of feedback amplifiers obtained from the traditional method and the proposed method is given. It is demonstrated that the inverting amplifier obtained from the proposed method consumes somewhat less power than the one obtained from the traditional design, which employs the op amp with 65 degrees phase margin, while having comparable gain, bandwidth, transient and noise performances.