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.
