Measurement of PCB-Related Commutation-Loop Inductance Using a Vector Network Analyzer

The stray inductance in the commutation loop is cause of oscillations that affect the efficiency of a power converter and are source of electromagnetic noise. Since the advent of Wide Band-Gap (WBG) power devices made possible generating steeper current and voltage transition, these high-speed switching is exacerbating the phenomenon. Commercial components are characterized by the manufacturers and datasheets are often reporting the value of the stray inductance for a given package. Unfortunately this is not enough, since the Printed Circuit Board (PCB) introduces the main part of the commutation loop inductance. This paper proposes to use Vector Network Analyzer (VNA) measurements to characterize the impedance of a bare PCB trace. The presented method has proved to be reliable in comparing different PCB designs to determine the best one.