Calibrated Contactless Impedance Measurements with DC Bias Currents

Fast switching semiconductors in power electronic devices require the knowledge of the high frequency behaviour of the implemented system components. Impedance probes can be used to examine the HF properties of those devices in situ and without galvanic contact. However in systems under operation, DC or low frequency currents will lead to saturation effects in the impedance probe's core resulting in a degradation of the coupling between the probe and the system under test. In this paper the influence of DC bias currents on contactless impedance measurements is examined and different solution attempts are presented.