[SI-LIST] Questions on losses of transmission line
- From: "Tonglong Zhang" <tlzhang@xxxxxxxxxxxx>
- To: howie03@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 25 Nov 2003 11:18:02 -0800
Gurus,
Regarding transmission line losses, have a few questions.
1)EM enery are in both the dielectric in between the line and its =
reference
plans and inside the line (rapidly decrease due to skin effect for high
frequency). Is this correct?
2) what is the percentage of energy travel inside the conductive trace =
vs.
inside the dielectric material?
3) dielectric loss only effect the EM energy in the dielectric, not the =
EM
energy inside the conductive trace. Metal loss only affect EM energy =
inside
the metal, not the EM energy in the dielectric. Right?
Thanks
Tonglong Zhang=20
Staff Engineer=20
IC Packaging Engineering=20
Broadcom Corporation=20
16215 Alton Parkway=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On
Behalf Of Dr. Howard Johnson
Sent: Tuesday, November 25, 2003 10:50 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: TDR and line losses
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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