[SI-LIST] Re: tips of using TDR probe
- From: "Han, Guobing" <han.guobing@xxxxxxxxx>
- To: "tom@xxxxxxxxxxxxxxxxx" <tom@xxxxxxxxxxxxxxxxx>
- Date: Mon, 26 Jan 2015 10:55:56 +0800
Hello Tom,
Agree with you, to be sure not to probe in a middle of a trace to make the
probe point closer.
As for the leading trace length, I think 3~4inch is acceptable if the Df is
very little, else 0.5~2inch is acceptable.
BTW, I think that directly probe at the via pad is not recommended. :)
Thanks,
Robin
2015-01-26 10:17 GMT+08:00 Tom Dagostino <tom@xxxxxxxxxxxxxxxxx>:
> Robin
>
>
>
> There are practical limits to the location for TDR probing. You should
> not probe in the middle of a trace, you will get reflections off both sides
> of the insertion point causing a confusing display that will be hard to
> interpret. Likewise probing at the DUT with 5 inches of trace from a
> connector or whatever will give you hard to interpret data. Pick the best
> point that you can, preferably at the end of the trace leading up to the
> DUT. If there are connectors leading up to the final trace and DUT then
> disconnect the other boards or cables and probe at the connector. I.e.,
> don't try to TDR through more trace than you have to .
>
>
>
> Tom Dagostino
>
>
>
> Teraspeed Labs
>
> 9999 SW Wilshire Street
>
> Suite 102
>
> Portland, OR 97225
>
>
>
> tom@xxxxxxxxxxxxxxxxx
>
> www.teraspeedlabs.com
>
>
>
> 971-279-5325 office
>
> 503-430-1065 cell
>
>
>
> *From:* Han, Guobing [mailto:han.guobing@xxxxxxxxx]
> *Sent:* Sunday, January 25, 2015 5:36 PM
> *To:* Chen, Sherman
> *Cc:* tom@xxxxxxxxxxxxxxxxx; Charles.Grasso@xxxxxxxxxxxx;
> heidi_barnes@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> *Subject:* Re: [SI-LIST] Re: tips of using TDR probe
>
>
>
> Hello Sherman and Tom,
>
>
>
> I am afraid that I can't agree with point 1 to launch the step at the
> closest location to the DUT, which will make the peeling effect worse.
>
> To be simplifed, the first reflection point is the probe, the second one
> is the input point of DUT, the third is the second refection point of DUT.
>
> If the delay between probe and input point of DUT is too short, such as
> 1~5ps, the come and back reflection of input point of DUT will superimpose
> to the second and later refection point of DUT. Thus, make the peeling
> effect worse.
>
>
>
> So, my point is just opposite of yours, it's not recommended to launch the
> step at the closest location to the DUT by a probe.
>
>
>
>
>
> Thanks,
>
> Robin
>
>
>
>
>
>
>
> 2015-01-22 23:45 GMT+08:00 Chen, Sherman <sherman.chen@xxxxxxx>:
>
> Tom,
>
> Agree with you on all you said.
> My point is:
> a. launch the step at the closest location to the UUT thus to reduce the
> peeling effect.
> b. reduce the preceding peak or dips as much as could. Better to be even
> with Z0.
> Then you will obtain quite accurate impedance profile of UUT.
> We taught our JDM this method and they applied it in measuring vias. The
> results are pretty good.
>
> Best Regards,
>
> Sherman Chen
> Signal Integrity
> EMC Global Hardware Engineering
> Tel: +86 21 60951100-3329
>
>
>
>
> --
>
> Thanks,
> - Robin (Han, Guobing)
> TEL: 86-21-61094805
> MSN: han_guobing@xxxxxxxxxxx
>
--
Thanks,
- Robin (Han, Guobing)
TEL: 86-21-61094805
MSN: han_guobing@xxxxxxxxxxx
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