[SI-LIST] Re: TDR questions
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: "joel@xxxxxxxxxx" <joel@xxxxxxxxxx>, SI-List <si-list@xxxxxxxxxxxxx>
- Date: Wed, 2 May 2012 14:21:15 +0000
In my experience, the standard TEK and Agilent TDR's put out a risetime at the
head of about 20 ps, even though 40 ps is cited (not quite sure why). With
quality cables, I get very good S-parameters up to 20GHz, which should be
sufficient for your SATA signals.
If you go with the TEK 80E04, you might consider buying extension cables that
will allow you to move your TDR heads out of the mainframe and close to your
work, with correspondingly shorter cables. The higher bandwidth heads (80e08,
etc.) already separate the TDR head from the mainframe.
In general, you'll get finer spatial resolution than you really need; you might
need to apply filters to determine if that discontinuity you can see at 30ps
risetime really "means anything" at your actual risetimes.
I personally haven't done much w/ LeCroy's units, but I would look into them
also if you're thinking of purchasing a TDR for this kind of characterization.
Between TEK and Agilent, I find the TEK much more intuitive.
I believe your biggest challenge will be to get 4-port measurements (S-params
for a differential signal). It will be extremely challenging to get all 4 of
your channels calibrated precisely. I believe LeCroy has done more work in
this direction than other TDR vendors.
Perhaps a 4-port VNA might not be much more expensive and would get results in
a faster manner.
Finally, remember that your instrument settings, cables, and probing fixtures
will have as much to do with quality measurements as which unit you use. Study
their effects carefully for your particular application.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Joel Brown
Sent: Tuesday, May 01, 2012 9:33 AM
To: SI-List
Subject: [SI-LIST] TDR questions
I am considering renting a TDR to characterize a SATA 6 GB/S signal path
including cables, connectors, boards, etc.
I also would use the TDR to derive an s-parameter model that I could use for
simulation to see what the resulting eye diagram would look like.
I have done some simulation already using s-parameter models for some parts of
the path but i don't have models for everything.
I know that TDR has a resolution based on rise time of the pulse.
The units I am looking at range from 15 to 40 ps with price scaling accordingly.
I am not sure if the resolution would be good enough to generate useful data
for smaller structures such as vias and connectors.
I also wonder if the rise time of the TDR is faster than the actual SATA signal
then it would be good enough.
Is there perhaps a better approach than using a TDR?
Thanks
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