Obstacles and Mitigations for an Accurate Low Impedance, Low Frequency Measurement

The two-port shunt configuration is often heralded as the gold standard for low-impedance measurements. However, this measurement method is not without its own issues. The shunt configuration inherently creates a ground loop between the measurement device's reference plane and the reference of the device under test (DUT). Additionally, probes often must be oriented in such a way that allows inductive coupling to occur. This work uses microprobes to measure the shunt impedance of a non-ideal short to explore the limitations of this measurement method in terms of both frequency and impedance. It highlights the importance of ground loop isolation and common-mode rejection ratio (CMRR) as well as limitations resulting from the mutual inductance between probes. The conclusions of these experimental measurements aim to find a path to further optimize shunt impedance measurements for power distribution networks (PDNs) as the industry points towards further lowering PDN impedance to meet increased current demands.