Power analysis and optimal design of opamps for oversampled converters

In this paper, we address three issues related to the design of opamps for oversampled converters: the theoretical minimum-power bound for an ideal opamp, the best opamp 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 opamp topologies is computed and compared with each other. We show that class-A opamps can consume one to six times the current consumed by an idealized class-AB opamp, though the savings for practical class-AB opamps is likely to be lower. For high-resolution applications, class-A topologies are most optimal, while for lower resolution lower power applications, class-AB opamps 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 opamps.