Bandwidth-enhanced Feed-forward Amplifier with Shared Class-AB Gain and Compensation Paths

An analysis of the inherent trade-offs of the existing feed-forward architectures for wideband applications is presented. A current-reused, class-AB, feed-forward compensated operational amplifier (opamp) capable of driving large capacitive loads is proposed. The architecture is based on sharing a single output stage between the gain and the compensation paths using AC-coupling between them, while retaining the inherent class-AB operation of the output stage. The bandwidth of the opamp is enhanced by boosting the transconductance of the compensation path using a pre-amplifier. The opamp is shown to support a load capacitance of 10 pF while maintaining >40 dB baseband gain over a frequency range of 100 MHz while maintaining a phase-margin in excess of 60° in a standard 65 nm bulk-CMOS technology.