Programmable Gain and Bandwidth Op-Amp Using Controllable Input Stage Tail Current

Abstract

This paper presents a novel technique to design a programmable open-loop DC gain and bandwidth single-ended output CMOS (complementary metal oxide semiconductor) opamp (operational amplifier) using a serial digital interface. The circuit topology allows for the programming of the differential input stage tail current. With this variable tail current, a controllable open-loop DC gain and frequency response is created that can be controlled from a host digital processor. The op-amp circuit has a rail-to-rail output where the first stage of the op-amp consists of differential input and folded-cascode circuits that are compensated using a negative Miller capacitor, and the second stage is a class-AB amplifier compensated by a conventional Miller capacitor. The op-amp has been designed using a $0.35\ \mu \mathrm{m}$ CMOS technology, its operation simulated using the Cadence Spectre simulator and operates on a single-rail +3.3V power supply.