GHz-Bandwidth Twin-Coil Magnetic Current Sensors for Compact Switching Circuits

Accurate measurement of current switching transients in SiC and GaN power converters requires current sensors with bandwidths exceeding 100 MHz, along with high immunity, sensitivity, isolation, and usability. Magnetic coils are typically the least invasive type of sensor but can be challenging to design and may be unsuitable in high EMI environments. This paper explores the use of coreless twin-coil magnetic current sensors in compact power circuits with complex magnetic fields. A design method is presented to achieve the required bandwidth, immunity, and signal-to-noise ratio (SNR), guided by 2D gain and immunity plots to optimise orientation relative to adjacent currents. Equations for gain and bandwidth as functions of geometry are experimentally verified using a vector network analyser. The method is validated in two scenarios: individual gate current sensing on adjacent, parallel-connected power devices, and power loop current sensing on a 30 mm wide PCB trace with a closely spaced return path on an adjacent layer. The gate sensor achieves an SNR above 10, a 660 MHz bandwidth, and closely matches current sense resistor measurements. The power loop current sensor has similar accuracy to a commercial Rogowski coil. These results demonstrate removable high bandwidth AC current sensors that minimally impact compact, optimised circuits, and show promise for application in power modules.