1. An operational amplifier (opamp) comprising: an input stage of the opamp including a differential device pair coupled to a tail device and configured to be responsive to a differential input signal for conducting a first current; an output stage of the opamp including a class AB interface stage circuit and a pair of output devices connected to the class AB interface stage circuit; and a first bias circuit coupled to an input of the class AB interface stage circuit, wherein the first bias circuit is configured to provide a first input signal to the class AB interface stage circuit such that an output device of the pair of output devices comprises a substantially constant transconductance, and wherein the first bias circuit comprises a current generating portion, a first current mirror and a second current mirror.