Ultra‐Minimally Invasive Current Measurement in Fast Switching GaN Devices Using Optical Probe Current Sensor

ABSTRACT Previously, the authors have proposed a contactless probe‐type current sensor with low insertion impedance. In this paper, the insertion impedance of the proposed current sensor at high frequencies is clarified. Then, we measured the actual high‐speed switching current flowing through a GaN device and compared the measured waveforms with those of a coaxial‐type shunt resistor. Comparison of the measured waveforms showed that the coaxial shunt resistor exhibited ringing in the waveform due to the effect of insertion impedance, but the proposed current sensor exhibited less ringing, indicating that the measurement is minimally invasive to the circuit under test.