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> 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-foun
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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