Ferrite bead effect on Class-D amplifier audio quality

Kevin El Haddad (1) , Roberto Mrad (2, 3, 4) , Florent Morel (4) , Gaël Pillonnet (2) , Christian Vollaire (3) , Angelo Nagari (1)

1 STMicroelectronics
2 INL - CSH - INL - Conception de Systèmes Hétérogènes
3 MIS - Ampère, Département Méthodes pour l'Ingénierie des Systèmes
4 EE - Ampère, Département Energie Electrique

This paper studies the effect of ferrite beads on the audio quality of Class-D audio amplifiers. This latter is a switch-ing circuit which creates high frequency harmonics. Generally, a filter is used at the amplifier output for the sake of electro-magnetic 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.

Mots clés: Harmonics distortion; Audio fre-quency band; Magnetic material; Ferrite bead

Domaines: Sciences de l'ingénieur [physics]; Acoustique [physics.class-ph]; Electromagnétisme; Micro et nanotechnologies/Microélectronique; Traitement du signal et de l'image [eess.SP]

Kevin El Haddad, Roberto Mrad, Florent Morel, Gaël Pillonnet, Christian Vollaire, et al.. Ferrite bead effect on Class-D amplifier audio quality. 17th IEEE MELECON, Apr 2014, Beyrouth, Lebanon. ⟨10.1109/MELCON.2014.6820510⟩. ⟨hal-01103584⟩