Impact of Pseudo-Random Modulation on Measured Conducted EMI

This paper demonstrates that using conventional frequency scanning methods for the evaluation of conducted electromagnetic interference generated by DC/DC converters can give misleading results when pseudo-random modulation is used as part of the converter control scheme. The paper therefore proposes that the resolution bandwidth of the super heterodyne EMI test receiver used for measurements and the dwell time should be adjusted to match the control parameters of the random modulation scheme. The use of different values for resolution bandwidth and dwell time is demonstrated and measurements for random and fixed modulation schemes are compared.