Proposed is a bias circuit for a transistor in a C class amplifier. The bias circuit comprises: a class AB amplifier bias voltage generating means adapted to generate a bias voltage at an output terminal; and a transistor connected between the output terminal and a first reference voltage, the control terminal of the transistor being connected to a second reference voltage via a switch. Closure of the switch connects the second reference voltage to the control terminal of the transistor to cause a shift in the bias voltage generated by the class AB amplifier bias voltage generating means to achieve a predetermined class C bias voltage at the output terminal.