High CMRR current-feedback operational amplifier

Despite excellent high frequency and high speed performance, current-feedback operational amplifiers (CFOAs) generally exhibit poor common-mode rejection properties, which limits their utility. In this paper the authors analyse the conventional (CFOA) in terms of common-mode rejection ratio (CMRR) performance, and, having identified the mechanism primarily responsible for the CMRR, they present a modified CFOA input stage circuit design by introducing a combination of a bootstrapping technique and folded cascode transistors. Simulation results of this new CFOA architecture indicate that the amplifier has significantly improved both CMRR and gain accuracy. Other key characteristics are also improved, with the notable exception of slew rate, which is reduced as a consequence of the new topology.