The Goldilocks TDR



Those that know me, know that I like things that, on a scale of one to ten, go to eleven.  For the youngsters out there, see Spinal Tap, 1984.  But is there such a thing as turning it up too high?  I receive, and answer, a lot of questions about measuring with a time domain reflectometer (TDR). 


How much bandwidth do I need?

How fast should the edge be?

How to I connect it to the DUT?


It pains me to say this, but there is such a thing as turning the TDR up too high and it is also easy not to have enough.  I addressed this briefly in my book, Power Integrity. If there is a “too high,” and a “not high enough,” there must also be a “just-right,” or Goldilocks, setting. Using measurements, and a smattering of math, the Goldilocks setting answers will be clear.  In the words of the infinitely wise Eric Bogatin, “it depends” will define these settings, which will change on a case-by-case basis. 


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