Feb 23, 2023

What are the differences between Class AB power amps and Class D power amps?

Class AB and Class D are two different types of amplifier topologies, with distinct advantages and disadvantages.

Class AB Amplifier

A Class AB amplifier is a linear amplifier that uses transistors to amplify an analog audio signal. It has two transistors in its output stage, and each one conducts for half of the waveform cycle. When the input signal is low, one transistor is off, and the other is conducting a small current to maintain a small output voltage. When the input signal is high, both transistors conduct, and the output voltage rises. Class AB amplifiers are more power-efficient than Class A amplifiers, but not as efficient as Class D amplifiers.

Class D Amplifier

A Class D amplifier is a switching amplifier that uses pulse-width modulation (PWM) to convert a digital audio signal into an analog output. The input signal is first digitized, then processed by a modulator to generate a high-frequency pulse train. This pulse train is used to switch a high-frequency power MOSFET or transistor on and off, creating a square wave with a variable duty cycle that matches the input signal. The square wave is then low-pass filtered to remove the high-frequency components, resulting in an analog output signal. Class D amplifiers are much more efficient than Class AB amplifiers, but they can introduce distortion and noise due to the switching process.

In summary, Class AB amplifiers are linear amplifiers that are more power-efficient than Class A amplifiers, but not as efficient as Class D amplifiers. Class D amplifiers are switching amplifiers that are very efficient but can introduce distortion and noise. The choice between the two depends on the application, power requirements, and desired sound quality.