The bottom is that transition time is a filter and as usual it depends on what
TDR is to be used for. Yes, if there is high system SNR at high frequencies,
transition time may not as limiting as black and white. It is more about the
benefits and drawbacks of the analysis put around the intended use. TDR is
powerful tool but also easy to misuse, especially if the original data is
sampled in the frequency domain.
... Rich Mellitz
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Alfred P. Neves
Sent: Wednesday, March 09, 2016 10:51 AM
To: si-list <si-list@xxxxxxxxxxxxx>
Cc: hzyltgg@xxxxxxxxx; Tom Dagostino <tom@xxxxxxxxxxxxxxxxx>; Samaan, Samie
<samie.samaan@xxxxxxxxx>; gmanikandan20@xxxxxxxxx; Josiah Bartlett
<josiah.bartlett@xxxxxxxxxxxxx>; Istvan Novak <istvan.novak@xxxxxxxxxxx>
Subject: [SI-LIST] Re: TDR Rise time
WRT, Tektronix (Josiah Bartlett), and SiSoft folks co-authored a 2014 DesignCon
paper entitled: “ Cracking the Code of 32 Gbpsec Differential Vias with
Advanced Time Domain Methods”.
We benchmarked time domain transform of S-parameter to Tektronix 80E10 TDR,
comparing the response from our Whisker time domain resolving circuit on the
Channel Modeling Platform, CMP-28.
The circuit incorporates small time domain stubs consistent for spatially
resolving 8psec and 22psec rise time pulses. We learned that time domain
transform from the VNA to TDR correspondence is not trivial and that 50-70GHz
correspondence is really challenging. This analysis was used to benchmark the
measurement approaches for resolving VIA features (pads, antipads, …).
One of the problems is that many structures resonate with a fast TDR, so
although you have the rise time performance, the structure itself masks the
classic TDR bumps, such that you have to correspond the resonance to the VNA
data and analyze the 1/4 and 1/2 wavelength resonances from TDR resonance to
nulls in the S-parameters. We tried to minimize the resonance in the Whisker
benchmarking circuit.
The paper is available on the WRT website.
- Al Neves
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technologist
Office: 503-679-2429
www.wildrivertech.com <http://www.wildrivertech.com/>
2015 Best In Design&Test Finalist
On Mar 9, 2016, at 5:28 AM, Istvan Novak <istvan.novak@xxxxxxxxxxx> wrote:
The quoted approximation formula is usable as long as the 'correction'
due to the probe and cable rise time degradation is not much bigger
than the signal rise time. And when we want to use it for spatial
resolution purposes, we need to keep in mind that it is valid at the
DUT input; what happens as we move along the DUT may strongly depend
on the DUT itself (its losses, dispersion, numbr and magnitude of
discontinuities, etc).
Regards,
Istvan Novak
Oracle
On 3/9/2016 7:40 AM, 黄涛 wrote:
Hi folks,
I would like to take this question to confirm the spatial resolution
with system BW.The spatial resolution is up to system risetime.If the
we consider the BW of cable and probe ,thespatial resolution will be
degradation than instrumen specification.the system rise time is
determined by Tsys^2=Tsignal^2+Tcable^2+Tprobe^2
T(10~90)*BW=0.35 Or T(20~80)*BW=0.4 for calculate device or system
performanc.
Am I right?
2016å¹´3月5日星期å…，Tom Dagostino <tom@xxxxxxxxxxxxxxxxx
<mailto:tom@xxxxxxxxxxxxxxxxx>> 写é“：
Samie------------------------------------------------------------------
There are two ways in improving the SNR of any TDR based analysis.
The first is averaging as you suggest. The second is sample
density. For example if the time window of interest is 1 nsec,
having 5000 samples in that timeframe will have more energy than 500
samples. This improves the signal to noise ratio.
Regards,
Tom Dagostino
971-279-5325
tom@xxxxxxxxxxxxxxxxx <javascript:;>
Teraspeed Labs
9999 SW Wilshire Street
Suite 102
Portland, OR 97225
-----Original Message-----
From: Samaan, Samie [mailto:samie.samaan@xxxxxxxxx ;<javascript:;>]
Sent: Thursday, March 03, 2016 5:01 PM
To: Tom Dagostino; gmanikandan20@xxxxxxxxx <javascript:;>;
'Bartlett, Josiah'
Cc: si-list@xxxxxxxxxxxxx <javascript:;>
Subject: RE: [SI-LIST] Re: TDR Rise time
Hi Tom,
You are correct. Averaging would not improve the BW. But what I
meant was that if the SNR is high enough, then even if the energy
content at a certain frequency is low (slow rise-time), a
deconvolution would yield the correct system transfer function.
Best regards
Samie Samaan
-----Original Message-----
From: Tom Dagostino [mailto:tom@xxxxxxxxxxxxxxxxx ;<javascript:;>]
Sent: Thursday, March 03, 2016 4:27 PM
To: Samaan, Samie; gmanikandan20@xxxxxxxxx <javascript:;>;
'Bartlett, Josiah'
Cc: si-list@xxxxxxxxxxxxx <javascript:;>
Subject: RE: [SI-LIST] Re: TDR Rise time
Hi Samie
Averaging will not improve the bandwidth, it will only improve the SNR.
Tom Dagostino
971-279-5325
tom@xxxxxxxxxxxxxxxxx <javascript:;>
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <javascript:;> [mailto:
si-list-bounce@xxxxxxxxxxxxx <javascript:;>] On Behalf Of Samaan,
Samie
Sent: Thursday, March 03, 2016 4:04 PM
To: gmanikandan20@xxxxxxxxx <javascript:;>; Bartlett, Josiah
Cc: si-list@xxxxxxxxxxxxx <javascript:;>
Subject: [SI-LIST] Re: TDR Rise time
The formula is saying that if you were to perform a Fourier
transform on the TDR step, then its 3-db down frequency content is
~0.35/(10-90% Rise-time).
If the data rate is 28 Gb/s, then one Unit Interval is about 36 ps.
So, if you want to probe a channel (or a system) which is supposed
to handle 36-ps pulses, then you'd want to hit it with a TDR step
that has a lot of energy at the 14 Ghz Nyquist. That would mean a
DTR rise-time of > "0.35/14 = 25 ps". But that is barely enough, so
personally, I would hit such a system with a TDR of at least 10 ps,
so I have a lot more energy in my region of interest.
I reality, if you can de-convolve the incident signal out of the
result (output), then you can use a slower rise-time, but in order
to avoid having to know the exact shape and frequency content of
your incident wave, use a much faster rise than the formula gives
you at Nyquist, and make your life simple...if you can afford such a
TDR :-)
To dig deeper, if you average the TDR signal a lot, and your Signal
to noise ratio is very high, then you can use a TDR rise/fall slower
than 25ps...But then again, why go into all that if you can afford a
TDR which is much faster than 25 ps!
Best Regards
Samie Samaan
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <javascript:;> [mailto:
si-list-bounce@xxxxxxxxxxxxx <javascript:;>] On Behalf Of Mani
Sent: Thursday, March 03, 2016 3:44 PM
To: Bartlett, Josiah
Cc: si-list@xxxxxxxxxxxxx <javascript:;>
Subject: [SI-LIST] Re: TDR Rise time
Hi
Thank you all. I understand the theory behind TDR. But I am confused
about calculating the rise time to be used for simulation.
In the formula 0.35/BW. what is the bandwidth here? is it the data
Nyquist frequency?
Lets say the data rate is 28Gbps, how to calculate rise time based
on 10%-90% calculation and how does it change for 20%-80%?
Regards
Dan
On Thu, Mar 3, 2016 at 3:40 PM, Bartlett, Josiah <
josiah.bartlett@xxxxxxxxxxxxx <javascript:;>> wrote:
Dan,time.
http://www.tek.com/document/fact-sheet/tdr-impedance-measurements-f
oun dation-signal-integrity has some basics of TDR calculations and
applications that you may be interested in.
Best wishes,
Josiah Bartlett
Principal Engineer- High Performance Probes
Phone: 503.627.2946
www.tektronix.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <javascript:;>
[mailto:si-list-bounce@xxxxxxxxxxxxx ;<javascript:;>] On Behalf Of
Mani
Sent: Thursday, March 03, 2016 3:20 PM
To: si-list@xxxxxxxxxxxxx <javascript:;>
Subject: [SI-LIST] TDR Rise time
Hi,
Can I get help in understanding TDR rise time calculation? I came
across 10% to 90% calculation and 20% to 80% as well. Just wanted
to know what is the difference between them and how to calculate
the TDR rise
Thanks for the help.Subject field
Regards
Dan
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