A High-Bandwidth and Low-Inductive Sensor for Measuring the Commutation Current of WBG Devices

Measuring the commutation current is a major challenge in the characterization of wide bandgap semiconductor devices. Commercial solutions such as coaxial shunts are not suitable for measuring very fast switching transients in the nanosecond range, as they appear in GaN applications. Therefore, new solutions are currently being researched, with both inductive and resistive sensors being considered. After a brief review of existing approaches, this paper presents a novel concept for a shunt resistor that meets the requirements of a very high bandwidth above 1 GHz and an parasitic inductance below 100 pH. These characteristics are realized via discrete thin film resistors, which are integrated into a coaxial connector on a regular multi-layer board. The solution presented is ready to use and has the advantage of a simple structure that can be easily adopted and is very cost effective. The characteristics are analyzed by simulation and validated by frequency domain measurements of several prototypes with different resistor configurations.