Low-Distortion, Low-Noise Composite Operational Amplifier

摘要

A composite operational amplifier is presented that is optimized for building low frequency (≤100 kHz) signal paths with very low distortion and noise. It consists of a cascade of two monolithic operational amplifiers and additional RC components for frequency compensation. The open-loop response is designed for conditional stability, such that a very large gain-bandwidth product at signal frequencies can be achieved. This leads to very good distortion performance in the audio frequency range. A numerical optimization procedure is introduced that is used to derive the frequency compensation, based on specific stability criteria. Monte Carlo simulation results are presented that estimate the worst case deviation from the nominal stability margins. Measurement results confirm the predicted high gain-bandwidth product (10 GHz at 100 kHz) and excellent distortion performance (< — 180 dB). Furthermore application notes considering various implementation issues such as large-signal stability are given. Applications for the new composite operational amplifier include, e.g., audio frequency distortion measurement equipment.