Compact CMOS Class-AB Output Stage With Robust Behavior Against PVT Variations

A compact CMOS class-AB output stage with static control of the quiescent current, suited to be included in low-voltage low-power operational amplifiers, is presented. The principle of operation is based on a floating DC voltage level shifter, automatically tuned by a replica circuit and able to keep constant the quiescent current of the output stage. The tuning criterion established in the control section includes a static feedback loop, thus not imposing any frequency limitation on the main output stage. The overall operational amplifier, designed in 180 nm CMOS technology to operate with a 1.8 V supply, presents a supply current of 37.6 μA with a variation of only ±3.3% among all the process-voltage-temperature (PVT) corners considered.

keywords: class AB output stage, operational amplifier, PVT variations, replica circuit, static tuning