[SI-LIST] Re: Agilent TDR Normalization Questions

In my vague memory, you can display normalized or un-normalized waveform
on screen.  Then, if you only display normalized waveform on screen, I
guess the normalized algorithm (DSP ?) will tune the rising time to
65ps. =20

You work for Cisco, you should be able to get the answer from Agilent
very easily.

As a hardware Engineer, I really want to see what the signal looks like
with another equipment, and not to be fooled by some software package.

I attended the gigalab's class.  I heard the instructor said at the
model, the rising time is about 35ps, at the end of cable, it could be
65ps.  Cable did attenuate the edge rate.  I just wonder if we can put a
chart of data, saying edge rate vs. cable length, of course, the setup
has to be good to eliminate operator's mistake.

Regards,
Joseph Wang


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Chris Padilla (cpad)
Sent: Wednesday, June 29, 2005 2:14 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Agilent TDR Normalization Questions

Length of the cable appears irrelevant.  I just click the little
"risetime" icon on the scope screen to get the 20-80% tr.


Chris

-----Original Message-----
From: Joseph Wang [mailto:JYWANG@xxxxxxxxxx]=3D20
Sent: Wednesday, June 29, 2005 2:11 PM
To: Chris Padilla (cpad); si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Agilent TDR Normalization Questions

Have you tried to use different length of cables?  Could you share
results to us all?  And how do you measure the rise time?  With TDT or
another sampling scope, or 40GS/s real time scope?

Regards,
Joseph Wang


-----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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