[SI-LIST] Re: Using standard scope and single ended pulse to estimate differential impedance
- From: "Kevin G. Rhoads" <kgrhoads@xxxxxxxxxxxx>
- To: alfred1520list <alfred1520list@xxxxxxxxx>
- Date: Fri, 05 Mar 2010 23:49:06 +0000
If you are driving but one side, then you effectively excite BOTH the
differential (+v/-v) and the common mode (+v/+v) to get the single-ended
(+2v/0) --
Since your excitation is a superposition of the two states (differential,
a.k.a.,
perfectly anti-symmetric voltages and common mode, a.k.a., perfectly symmetric
voltages) your responses will also be a superposition of the responses to those
two states.
If you properly can account for that, then you can properly measure differential
with single-ended excitations. Normally you account for such by measuring
in such a way as to distinguish the responses directly. You, on the other
hand, are distinguishing the responses INDIRECTLY.
That is valid, with the caveat that precision errors and noise will combine
in the calculated results. But if the raw measurements are sufficiently
precise and of high enough S/N, then the calculated results can meet
requirements.
So, your method is sound. Whether your implemmentation suffices to your needs
is hard to say from a distance.
Sincerely
Kevin
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