A method of operating a power amplifier supplying power to an antenna, supplying switched power to the power amplifier comprises in a first mode of operation via a driver circuit and one or more switches to switch the supply of power to the power amplifier on and off periodically; and calibrating the power amplifier in a second mode of operation. The calibrating comprises supplying voltage to the power amplifier via the same driver circuit and one or more switches for a calibration pulse duration longer than the on/off period. A power supply and an RF front end comprising the power supply are also disclosed.