In the final installment of this blog series, Benjamin Dannan, Heidi Barnes, and Steve Sandler discuss how to calculate the minimum CMRR with a PDN impedance measurement using a 2-port probe, demonstrating how is possible to measure a sub-40 µΩ impedance using a 2-port probe when using an isolator that has sufficient CMRR using two different VNAs, the Bode 100 and E5061B. Achieving sub-40 µΩ impedance measurements is challenging, but completely realistic with the proper test equipment.