[SI-LIST] Re: TDR and line losses
- From: "Dr. Howard Johnson" <howie03@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 25 Nov 2003 10:49:45 -0800
The article to which Mr. Smolyansky refers,
"Characteristic impedance of lossy line",
appeared in my regular EDN column on 10/3/2002.
The article is posted at http:\\sigcon.com, under
"archives",
see the alphabetical index , or go here:
http://www.sigcon.com/Pubs/edn/LossyLine.htm
Figure 1 in the article illustrates, for a hypothetical,
150-micron (6-mil), 50? FR-4 stripline, the relative
influence of skin-effect and dielectric losses on the
characteristic impedance of a lossy transmission line. The
chart depicts the characteristic impedance of a trace with
only skin-effect and dc-resistive losses (assuming a perfect
dielectric), a trace with only dielectric losses (assuming
zero resistance), and a combination of both.
Figure 2 shows how line losses affect the shape of the TDR
response.
Similar figures appear on pp. 204-205 of my latest book,
"High-Speed Signal Propagation", ISBN 0-13-084408-X, along
with a great deal of additional explanatory text.
Best regards,
Dr. Howard Johnson, Signal Consulting Inc.,
tel +1 509-997-0505, howiej@xxxxxxxxxx
http:\\sigcon.com -- High-Speed Digital Design articles,
books, tools, and seminars
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Dima
Smolyansky
Sent: Friday, November 21, 2003 2:22 PM
To: Suresh.Subramaniam@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: TDR and line losses
Suresh,
The upward slope of the TDR trace is indicative of losses.
However, the
losses will need to be quite substantial for the upward
"creep" to be
clearly visible. In other words; your transmission trace
(TDT) will show
even fairly small losses through rise time amplitude
degradation; however,
when you begin to see the "creep" in the reflection (TDR),
that will show up
as large rise time and amplitude degradation in TDT.
Also, Howard Johnson did an article once, where he played
with skin effect
and dielectric loss, and showed how they affect different
portion of the TDT
waveform. You can do the same in IConnect's lossy line model
by varying the
skin effect and dielectric loss parameters independently,
and evaluating
their effect on the TDT (or TDR) waveform.
Thanks,
-Dima
----- Original Message -----
From: "Suresh Subramaniam" <Suresh.Subramaniam@xxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Friday, November 21, 2003 2:00 PM
Subject: [SI-LIST] TDR and line losses
>
> If I TDR (rise time 26ps) a long lossy transmission line,
should I expect
> the impedance profile to gradually creep up to a higher
value (assuming I
> start out with a 50 Ohm impedance?). In other words, how
does the TDR
> take into account the effect of losses?
>
> Thanks
> Suresh
>
>
>
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