[SI-LIST] Re: TDR equipments -- comments or reviews
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: "'Scott McMorrow'" <scott@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 4 Nov 2010 08:45:06 -0700
I have evaluated 2 and 4-port S-parameter models generated with the LeCroy
Sparq. The models did not have reciprocity and passivity violations in the
frequency band up to 40 GHz. The conversion of the original Touchstone
models into rational and broad-band SPICE macro-models was seamless and the
macro-models matched the original data with high accuracy (RMS error below
0.01 - it typically indicates that the models are causal and have high
overall quality). TDR/TDT responses computed from the Touchstone models
matched well the original TDR/TDT responses of the test fixtures. I wish
there were more such high-quality models - it would make our analysis tasks
much easier :-)
Best regards,
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Scott McMorrow
Sent: Thursday, November 04, 2010 7:37 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: TDR equipments -- comments or reviews
I'd like to follow on and add to Jeff's good comments.
I had the opportunity back in February to evaluate the LeCroy Sparq and
compare it to 20 and 40 GHz VNA measurements on our PLRD and other test
boards we've designed. Having worked with the Tek and Agilent boxes in
the past, I was, of course, skeptical. Quite frankly, I was surprised
and extremely impressed. The early alpha unit that I was able to
evaluate, with Peter Pupalaikis of LeCroy at my side in my office
(home), had prototype issues but was still able to faithfully resolve
differential 4-port measurements that matched VNA measurements, with
extremely low error and high dynamic range. I measured multiple
resonant and non-resonant structures and found that it was quite easy to
measure pretty much anything (insertion loss, return loss, crosstalk)
from 0 to 35 GHz with a measurement range of 0 dB to -60 dB. Return
loss peaks and nulls were sharp, clear and dead on when compared to the
VNA results.
regards,
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
TeraspeedR is the registered service mark of
Teraspeed Consulting Group LLC
On 11/4/2010 10:06 AM, Loyer, Jeff wrote:
> I find the Tek equipment much more intuitive than the Agilent. I usually
can get what I need out of the Agilent, but it takes much longer. And,
sometimes I haven't been able to get what I want, but I'll leave open the
possibility I'm missing something that a more experienced user can find
and/or my equipment is out of date. I know others have echoed my feelings;
I look forward to seeing comments from folks who have had positive
experiences w/ the Agilent and/or Sparq and have reasons for preferring
them.
>
> I've witnessed it proven that the Tek can provide very accurate 2-port
S-parameters using IConnect, see
>
http://www.tek.com/products/oscilloscopes/sampling/interconnect_analysis/cus
tomer_papers/vna_tdr_correlation.pdf
> I expect these results could also be replicated on the Agilent and/or
Sparq. Of course, there's going to be a difference in the dynamic range
between the TDR and VNA, so don't expect to measure massively lossy systems
with a TDR.
>
> The Tek provides differential excitation; the Agilent performs
single-ended measurements and derives the differential response from those
(Sparq too?). Theoretically nothing wrong with that - that's what VNA's do
also. But, on the practical side, I've been able to use Tek's differential
probes (P80318) to measure SDD21 of actual traces on product boards. This
wouldn't be practical if I couldn't take advantage of the purely
differential signaling to preclude the need for ground connections.
> Some caveats:
> * I measured extremely long traces to minimize the effect of launch
discontinuities on the results
> * I used traces close to the top and backdrilled vias so their effects
were minimal
> * I wouldn't want to quote my results very precisely, especially after
about 10GHz
> * Don't try this with cruddy cables - the skew has to be in the sub
picosecond range
> But, the measurements were enough to clearly discern the SDD21 difference
between "bad" and "good" boards.
>
> The P80318 probes are also nice for quick differential impedance
measurements since you don't need a ground connection; it would only work
with the Tek.
>
> Also, you didn't mention how many ports you're hoping to measure, though
you imply>2 since you're getting a separate sampler. As Cherry's paper
(link above) demonstrates, TDR/TDT works just fine for 2-port measurements.
If you're going above 2 ports, you have a completely different beast to
wrestle: femtoseconds of skew will influence your measurements. For some
limited cases or coarse measurements, I've been able to make the Tek work
for>2 ports, but wouldn't want to push it too far. I haven't heard of a
calibration scheme from Tek to accommodate this; I've crafted my own but it
takes a lot of effort. Perhaps Agilent or Sparq do better here. 4-port
VNAs have calibration algorithms to solve the problem.
>
> I think folks would find risetimes of about 15 ps out of both the Agilent
and Tek; PicoSecond Pulse labs has modules if you need faster, and I think
the Sparq is faster.
>
> Of course, this is purely opinion, and I'd probably be loyal to the
Agilent or Sparq if I'd used them more.
>
> My $0.02...
>
> Jeff Loyer
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Dan
> Sent: Tuesday, November 02, 2010 3:15 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] TDR equipments -- comments or reviews
>
> Hi all,
> I am planning to buy TDR equipments. I have shortlisted two equipments,
one
> from Agilent and anther Tektronix, along with the mainframe. Can anybody
let
> me know your comments or reviews about these equipment and your advice or
> idea to buy this?
>
> I am also planning to do s-parameter extraction from the TDR measurement.
So
> i need to TDT also. So i am adding a samping module.
>
> Agilent:
> mainframe: 86100C (option202 for extarcting s-parameter touchstone)
> TDR: 54754A (can anyone tell me the achievable rise time or frequency in
> this module)
> Sampling module: 86112A
>
> Tektronix:
> mainframe: DSA8200 (80SSPAR Iconnect for s-parameter extraction)
> TDR: 80E04 (can anyone tell me the achievable rise time or frequency in
this
> module)
> Sampling module for TDT: 80E03
>
> Is TEK better than Agilent. Is TEK's Iconnect outperforms Agilent's option
> 202 in the mainframe to extract s-parameter touchstone?
>
> Thank You for your time.
>
> DAN
>
>
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