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PSRR: The Real Story about Closed- and Open-Loop Class-D Amplifiers

Abstract : As open- and closed-loop Class-D amplifiers increasingly become the preferred choice of consumer-audio electronics designers, a different way of looking at the effects of power-supply ripple is needed to adequately capture the performance of the amplifier. Today's audio designers are increasingly focused on reducing system cost, shrinking form factors and delivering high-quality audio, all of which require high supply-noise rejection architectures. Unfortunately, the power-supply rejection ratio (PSRR) measurement does not accurately capture the performance of Class-D bridge-tied load (BTL) amplifiers.

In this article, we discuss the traditional PSRR specification and measurement technique, and explain why it fails to adequately capture the supply-rejection capability of the amplifier. We then describe an alternate way to look at the effects of power supply ripple on the amplifier's audio performance.

About the Authors
Yang Boon Quek is an Applications Engineer for the High-Performance Analog group at Texas Instruments, responsible for application support of TI's audio power amplifiers for customers in China, Taiwan, Singapore and Malaysia.
Michael Firth is the Product Marketing Manager for the Display and Consumer audio products in the High-Performance Analog group at Texas Instruments.

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