Ferrite bead effect on Class-D amplifier audio quality

Abstract

This paper studies the effect of ferrite beads on the audio quality of Class-D audio amplifiers. This latter is a switching circuit which creates high frequency harmonics. Generally, a filter is used at the amplifier output for the sake of electromagnetic compatibility (EMC). So often, in integrated solutions, this filter contains ferrite beads which are magnetic components and present nonlinear behavior. Time domain measurements and their equivalence in frequency domain are presented. Total Harmonic Distortion (THD) measurements according to the audio signal frequency and amplitude are exposed and discussed. It is shown that ferrite beads introduce up to 30 dB of additional THD which prove the negative effect of the ferrite bead on the amplifier audio quality.