[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

Teraspeed® 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 equipment is out of date.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/customer_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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