Current Measurement of GaN HEMTs Without Insertion Impedance and Unaffected by Magnetic Field Noise Using Two Optical Probe Electric Current Sensors

This paper proposes a current measurement method that precisely utilizes an ultra-low invasive current probe for high-speed switching GaN power devices. A conventional current measurement method using the Optical probe Electric Current Sensor (OpECS) offers advantages including a compact sensor head, a maximum bandwidth of 150 MHz, and no additional insertion impedance. However, it suffers from distorted current measurements due to background magnetic field noise. To address this issue, a new current measurement method employing two OpECSs is proposed. One OpECS measures the magnetic field generated by the target current, while the other detects the background magnetic field noise. The unwanted noise is then canceled by subtracting the two signals. The validity of the proposed method is demonstrated through double-pulse tests of GaN HEMTs, measuring overshoot currents during turn-on switching transitions at 200V, 4A and 400V, 8 A.