An amplifier for amplifying radio frequency signals comprising: a signal splitter configured to split an input radio frequency signal into two or more signals; and two or more switching power amplifiers. Each of the switching power amplifiers is configured to amplify a respective signal of the two or more signals using an active device and output a respective amplified signal at a respective output terminal of the switching power amplifier when the switching power amplifier is activated. Each of the two or more switching power amplifiers has a different maximum output power. The amplifier further comprises: an output node connected to each of the output terminals of the switching power amplifiers to combine the amplified signals and output a combined amplified signal; and control circuitry configured to issue control signal to control bias voltages provided to a gate of each of the active devices of the switching power amplifier to selectively activate and deactivate the active devices.