A Coupled Transmission-Line-Based Measurement Technique for Currents in Switch-Mode Converters

Power integrity issues arise at gigahertz (GHz)-range in compact systems integrating fast-switching power devices, such as gallium nitride high-electron mobility transistors. GHz-range current measurement techniques must be used in switch-mode converters to assess those issues. State-of-the-art techniques are insufficient due to the inherent limitations of the high-impedance probe in a pick-up coil or the impractical dimensions of the probing apparatus for current-surface probes. This article proposes a novel compact coupled transmission-line-based measurement technique that takes advantage of mutual inductance, allowing the measurement of currents in the GHz-range. A thorough analytical formulation shows that its measurement distortion can be predicted at up to multiple GHz and that the probing pad can be placed at any convenient location on the substrate without affecting the measurement distortion. Measurements with the proposed structure validated with a resistive shunt show that the current in a switch-mode converter can be characterized at up to 1.95 GHz with less than 3-dB measurement distortion, which represents more than 4-dB reduction in amplitude distortion with respect to a resistive shunt technique.