What is Class D?

A Class-D amplifier, or switching amplifier, is an electronic amplifier in which the amplifying devices (typically MOSFETs) function as electronic switches, rather than linear gain devices as in other types of amplifiers. These amplifiers operate by rapidly switching between the supply rails, with a modulator using techniques such as pulse width modulation, pulse density modulation, or related methods to encode the audio input into a pulse train. The audio is then passed through a low-pass filter into the loudspeaker, while the high-frequency pulses (which can reach up to 6 MHz) are blocked. Since the output transistor pairs are never conducting simultaneously, there is no alternate path for current flow other than through the low-pass filter and loudspeaker, allowing efficiency to exceed 90%.