High-Bandwidth Differential Voltage Probe for Accurate Switching Characterization of WBG Devices

For a more secure, anti-interference characterization of high-speed wide-bandgap (WBG) power devices, there is a growing need for galvanically isolated measurement methods with higher bandwidth and wider dynamic range. Among these techniques, the differential sensing method has gained attention due to its simplicity, cost-effectiveness, wide dynamic range, and floating measurement capability. Nevertheless, the limited bandwidth of the differential method remains a significant obstacle for characterizing ultrafast switching transients of WBG devices. This article highlights the significant bandwidth limitations encountered in the front-end high-voltage attenuation of the differential method, i.e., the parasitic effects of capacitive networks and the overlooked high-frequency transmission line effects. To address these limitations, the concept of transmission line voltage divider (TL-VD) is introduced, enabling the extension of the operating frequency range of the front-end high-voltage attenuation into the GHz level. To achieve this, four underlying matching principles regarding resistance, capacitance, inductance, and wave impedance are established, which are further simplified to three decoupled, mutually independent, and easily implementable matching objectives of resistance, wave impedance, and transmission line length. These contributions collectively result in the successful development of a ±2.0-kV differential voltage sensing system (DVSS) with an ultrahigh measurement bandwidth of 1.3 GHz and a common-mode rejection ratio of 48 dB at 100 MHz. The experimental comparisons with state-of-the-art commercial galvanically isolated products in both the frequency and time domains confirm the superior performance of the developed TL-VD-based DVSS.