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

The use of wide bandgap 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 1GHz bandwidth voltage probes are commercially available, current probes are typically limited to below 200MHz. A resistive current sensor, often called a current shunt, converts magnetic field measurement into electric potential measurement, enabling us to use well-established GHz-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 paper proposes a novel coaxial structure based on thin-film resistors for current shunts. ANSYS Q3D and 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 2.063GHz validate the proposed design.