Measuring ultra-low impedance is a common requirement for assuring power integrity. This means measuring 1 milliohm to 2 milliohm voltage regulator modules (VRMs) and power distribution networks (PDNs). Today, it is common to see 500 uOhm power rails, however more recently the bleeding edge is below 100 uOhm. Measuring 100 uOhm is a significant challenge, even using the venerable 2-port shunt-thru measurement that has served as the staple of ultra-low impedance measurement. The dynamic range of the 100 uOhm, 2-port, measurement is 108dB. An impedance dip to 30 uOhm reduces this to 118 dB. Explore below to tackle this fundamental problem.
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