Improved two-probe approach for in-circuit measurement based on three-port network pre-calibration

In high-speed electrical designs, the in-circuit characteristics of the components are usually obtained from in-circuit measurements as the references for designers. The two-probe approach (TPA) is one of in-circuit measurement approaches by adopting the inductive coupling effects of the current probes, and it gains good accuracy below 30MHz. In this paper, we propose an improved two-probe approach (ITPA) by introducing network parameters. Rather than modeling the measurement setup using equivalent circuits in the TPA, the proposed ITPA models it by using a three-port network, and pre-calibrates it before real measurements. By comparing the results measured from ITPA with those from the impedance analyzer (IA), it is proven that, the ITPA extends the highest measurement frequency to 100MHz from 30MHz (with the TPA), while maintaining allowable accuracy; besides, the ITPA avoids the trial-error pre-calibrations required in the TPA.