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Class D Amplifiers: Fundamentals of operation and recent developments

Posted: 23 Aug 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Class D amplifier? audio amplifier? audio systems?

Most audio system design engineers are well aware of the power-efficiency advantages of Class D amplifiers over linear audio-amplifier classes such as Class A, B, and AB. In linear amplifiers such as Class AB, significant amounts of power are lost due to biasing elements and the linear operation of the output transistors. Because the transistors of a Class D amplifier are simply used as switches to steer current through the load, minimal power is lost due to the output stage. Any power losses associated with a Class D amplifier are primarily attributed to output transistor on-resistances, switching losses, and quiescent current overhead. Most power lost in an amplifier is dissipated as heat. Because heatsink requirements can be greatly reduced or eliminated in Class D amplifiers, they are ideal for compact high-power applications.

In the past, the power-efficiency advantage of classical PWM-based Class D amplifiers has been overshadowed by external filter component cost, EMI/EMC compliance, and poor THD+N performance when compared to linear amplifiers. However, most current-generation Class D amplifiers utilize advanced modulation and feedback techniques to mitigate these issues.

A Class D amplifier's high efficiency makes it ideal for portable and compact high-power applications.

Traditional Class D amplifiers require an external lowpass filter to extract the audio signal from the PWM output waveform. Many modern Class D amplifiers, however, utilize advanced modulation techniques that, in various applications, both eliminate the need for external filtering and reduce EMI. This article discusses the advantages of Class D filters and the recent improvements that can not only reduce board space, but can also significantly reduce the cost of many portable/compact systems.

Please view the PDF document for more information.

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