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power distribution network impedance measurement

Question asked by e4411a on Aug 6, 2008
I am looking to measure the impedance of the power distribution network on a PC mother board using the PNA-L network analyzer.We are using a ggb prober with the necessary calibration structures for doing a full 2 port cal till the probe tip end. The probe is CS-11 and has a 800micrometer pitch
We are following the application note 5989-5935EN that talks about the measurement of very low impedances. I have also attached the application note for your ready reference.

What is the lowest possible impedance value that can be measured using the 2 port method? The frequency range of 300 kHz to 2 GHz. Also what would be the accuracy of the impedance measurement?
How do we arrive at the accuracy of the measurement ?
There is a mention of the Power distribution network analyzer P4800 from ultimetrix. What does this box do?

How do we correlate the uncertainty calculator with the accuracy of measurements? Could you please explain this with the help of an example?

There is a formula given in the app note for calculating the impedance on page 13.

Under what conditions is the formula valid? When I do a 2 port cal with an ecal module and connect a thru between the cables, how do I interpret the results of the S21 data as they do not seem to match with the formula above.