Prediction of noise reduction effect of ferrite beads on electromagnetic emission from a digital PCB

To reduce power supply noise such as power bounce and GND bounce, ferrite beads are usually inserted between the power supply and V_cc terminal of an IC by trial and error. An analytical approach on noise reduction effect of ferrite beads has not been established yet, referring to the catalog data on ferrite beads. In this paper, the noise reduction effect of ferrite beads on electromagnetic interference (EMI) is analytically discussed. Resonance characteristics of a digital circuit with ferrite beads are calculated and noise reduction effects are predicted in this paper. Near field EMI spectra are predicted and are compared with measured results. With respect to peak level of EMI spectra, predicted results coincide with measured results within an error of 4 dB