[SI-LIST] Re: Agilent TDR Normalization Questions
- From: "Jeremy Plunkett" <jeremy@xxxxxxxxxxxx>
- To: cpad@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 29 Jun 2005 16:18:13 -0700
Chris,
The minimum available rise time after normalization varies with the time
scale setting. Try zooming in the horizontal scale prior to normalization
and you should be able to get risetimes down to 10ps single ended.
Jeremy
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Chris Padilla (cpad)
Sent: Wednesday, June 29, 2005 2:03 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Agilent TDR Normalization Questions
I've read the Help files included with my 86100B w/ 54754A TDR module and I
follow what happens when one Normalizes to the end of cable and/or test
fixture so I understand that. There is an IFT and FIR filters being used
and then FFT'ing back.
I did a little check, however, and have some seemingly strange results that
I hope someone here can explain.
I find that as long as I am using decent high-quality cables, the
Normalization routine will degrade (increase) the ristime of the step from
~30 ps (unnormalized step) to ~65 ps: a factor of ~2+. I tried this for
several different cable I had laying around and they are all about the same
as far as Normalization goes. Expectedly, the normalized step is cleaned up
of some higher-frequency content wiggles at the top of the step.
Next, I decided to Normalize to the end of the TDR module or put another
way, I didn't add any cable or test fixtures to the TDR module...I just
screwed my Cal Standards right to the 3.5 mm SMA on the TDR module.
Guess what? I got the same ~2x increase of risetime as if I had some cable
and/or test fixtures attached!
Anyone have an explanation for this? Seems to me that as long as I use
those "decent high-quality cables", all the Normalization adjustments happen
INSIDE the TDR module!? What am I missing here...this doesn't seem right.
My next questions regards even using Normalization in the first place.
I often see a lot of TDR plots (with TDA Systems logo on them! ;o) ) that
don't appear to have been normalized. It is probably for good reason since
Normalization appears to chop the bandwidth of the scope right in half. I
have been learning to use I-Connect and I'm confused whether or not I should
be using the Normalization routine on my scope.
Thanks,
Chris Padilla
Cisco Systems
San Jose, CA
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