Predicting the Impact of Magnetic Components Used for EMI Suppression on the Base-Band of a Power Amplifier

Class-D audio amplifiers are switching circuits that produce serious Electromagnetic (EM) emissions and disturb the surrounding electronics. In order to reduce these emissions, electromagnetic compatibility (EMC) filters with ferrite beads are used. However, ferrite beads contain magnetic materials that have a nonlinear behavior. Thus, they have an unfavorable impact on the system audio quality. The common ferrite bead models do not take into account nonlinear phenomena. Thus, to predict the impact on the signal quality, this paper models the ferrite bead using the Jiles-Atherton magnetic material theory. The presented model provides the designers with a tool to quantify the effect of EMC filters on the total harmonic distortion (THD) of audio amplifiers. The simulated and measured results show that the tested ferrite bead have a negative effect on the audio signal for a wide range of amplitudes and can increase the THD up to 37 dB. Finally, this paper highlights the impact of the magnetic material type on the audio distortion by simulating the same component with different types of materials.