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.