Model for Estimating Radiated Emissions from a Printed Circuit Board with Attached Cables Due to Voltage-Driven Sources

Todd H. Hubing, Missouri University of Science and Technology
Hwan-Woo Shim

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Common-mode currents induced on cables attached to printed circuit boards (PCBs) can be a significant source of unintentional radiated emissions. This paper develops a model for estimating the amount of common-mode cable current that can be induced by the signal voltage on microstrip trace structures or heatsinks on a PCB. The model employs static electric field solvers or closed-form expressions to estimate the effective self-capacitances of the board, trace, and/or heatsink. These capacitances are then used to determine the amplitude of an equivalent common-mode voltage source that drives the attached cables. The model shows that these voltage-driven common-mode cable currents are relatively independent of the cable parameters and the trace or heatsink location when the PCB is small relative to the cable length and to a wavelength.