High-Bandwidth Current Shunt With Extremely Low Stray Magnetic Field Based on Thin-Film Resistors

The use of wide bandgap (WBG) devices introduces higher frequency components into power electronics due to increased switching speeds. To achieve reliable measurement of these high-frequency components in power electronics, high-bandwidth voltage and current probes are essential. While 1 GHz bandwidth voltage probes are commercially available, current probes are typically limited to below 200 MHz. A resistive current sensor, often called a current shunt, converts magnetic field measurement into electric potential measurement, enabling us to use well-established gigahertz-level voltage probes. The overall structure must have an extremely low level of stray magnetic field to minimize parasitic inductance and hence to increase the measurement bandwidth. This article proposes a novel coaxial structure based on thin-film resistors for current shunts. ANSYS Q3D and high-frequency structure simulator (HFSS) simulations demonstrate that this structure effectively cancels magnetic fields along various axes, leading to nearly nonexistent stray fields outside the structure and significantly minimizing parasitic inductance. Experimental results from a prototype with a bandwidth of up to 2.063 GHz validate the proposed design.