A differential circuit is described having first, second, third and fourth devices, each device having a control terminal and first and second terminals. The first and second devices are arranged to receive a differential input signal at their respective control terminals and each drive an end of a load in communication with a second terminal of the first and second devices. The third and fourth devices are in communication, via their first terminals, with the second terminal of a respective one of the first and second devices and with a respective one of the first and second input signals via their control terminals. The third and fourth devices each have second terminals biased with an impedance arranged so that variations in load current requirements are accommodated by the third and fourth devices and current through the first and second devices is substantially constant.