Electromagnetic Radiation Mechanism Analysis and Field Strength Prediction of an Elementary Digital Inverter with Cables

In this paper, common mode (CM) and differential mode (DM) far-field radiation models of a typical digital inverter with cables are built up to predict electromagnetic field strength and analyze field characteristics. The CM current model and its analyses are based on the imbalance difference method. It is found out that the voltage between the drain and the source electrodes of upper transistor is the key equivalent source of electromagnetic interference (EMI). Far-field radiation strength of the digital inverter in free space is predicted by using the asymmetrical antenna radiation method and current loop radiation method. The accuracy of these methods is verified by the CST electromagnetic simulation results in the frequency range from 1 MHz to 400 MHz. Furthermore, the radiation models are improved by using the mirror method, which enables to include the reflection effect of the metal ground plane at the electromagnetic compatibility (EMC) test site. Both the results of measurements in a semi-anechoic chamber and the simulation results confirm the proposed electromagnetic radiation prediction method.