Characterization of EMI-Reducing Spread-Spectrum Techniques for Class-D Audio Amplifiers

Audio amplifiers for portable devices need to be
power efficient, therefore Class-D amplifiers are used. These
amplifiers employ a switching output stage, so that they generally
produce a significant amount of EMI. Filtering these frequency
components usually is not an option since the amplifiers have to
be small and lightweight. A reduction of EMI can be achieved by
using spread-spectrum techniques that distribute the emissions
over a wider frequency range. Unfortunately spread-spectrum
techniques can impact the audio performance. This work presents
a test setup for a Class-D prototype to evaluate different spread-spectrum
methods by measurement or even by listening to the
audio output. Using this setup several spread-spectrum methods
are compared in terms of EMI-reduction and audio performance.