Switching amplifiers

A controller for controlling a switching amplifier to modulate voltages at first and second output nodes so as to drive a load connected between said first and second output nodes with a differential drive signal based on an input signal, wherein:

• the controller is configured to control the switching amplifier to selectively operate in at least a first mode or a second mode, wherein in each of the first and second modes, the first and second output nodes are modulated between switching voltages with a controlled duty-cycle and at least one of the switching voltages is different in the first and second modes;
• the controller is configured to control the mode based on the amplitude of the input signal such that the switching amplifier can dynamically change between the first and second modes;
• the controller is configured such that in operation in the first mode a common-mode voltage applied to the first and second output nodes has a first steady-state value and in operation in the second mode a common-mode voltage applied to the first and second output nodes has a second steady-state value, different to the first steady-state value;
• and
• for a change in mode between the first and second modes, the controller is configured to operate in a transitional period before and/or after the change in mode wherein, during the transitional period, the common-mode voltage applied to the first and second output nodes is ramped over time so that any step change in common-mode voltage on the change in mode is less than the difference between the first and second steady-state values.