A class-D amplifier or switching amplifier is an electronic amplifier where all power devices (usually MOSFETs) are operated as binary switches. They are either fully on or fully off. Ideally, zero time is spent transitioning between those two states.
Output stages such as those used in pulse generators are examples of class D amplifiers. However, the term mostly applies to power amplifiers intended to reproduce signals with a bandwidth well below the switching frequency.
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