Imbalance Difference Model for Common-Mode Radiation From Printed Circuit Boards

The differential-mode signals in printed circuit board (PCB) traces are unlikely to produce significant amounts of radiated emissions directly; however these signals mayinduce common-mode currents on attached cables, enclosures, or heat sinks that result in radiated electromagnetic (EM) interference. Full-wave EM modeling can be performed in order to determine the level of radiated emissions produced by a PCB, but this modeling is computationally demanding and does not provide the physical insight necessary to explain how differential signals induce common-mode currents on distant objects. This paper describes a model for determining the common-mode currents on cables attached to a PCB that is based on the concept of imbalance difference. The imbalance difference model is derived from research that shows that changes in geometrical imbalance cause differential-to common-mode conversion. This paper applies an imbalance difference model to PCB structures and compares the resulting equivalent source configurations to those obtained with traditional voltage-and current-driven models, as well as full-structure simulations.