Method and implementation of gain-bandwidth product (GWB) tuning are disclosed. In an embodiment an operational amplifier (opamp) includes 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 and 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, wherein a first constant gm bias circuit is coupled to an input terminal of the class AB interface stage circuit.