Power analysis and optimal design of op amps for oversampled converters

Abstract

In this paper, we address three issues related to the design of op amps for oversampled converters: the theoretical minimum-power bound for an ideal op amp, the best op amp choice in terms of power dissipation, and the best design strategy to reduce power dissipation. To be able to do so, we develop a model that captures the dynamics of the integrator inside the modulator. Based on this model, power dissipation for various op amp topologies is computed and compared with each other. We show that class-A op amps can consume one to six times the current consumed by an idealized class-AB op amp, though the savings for practical class-AB op amps is likely to be lower. For high-resolution applications, class-A topologies are most optimal, while for lower resolution lower power applications, class-AB op amps may be more suitable. We further demonstrate a design strategy with the help of an example that can be used to minimize the power dissipation for class-A op amps.