[SI-LIST] Re: Questions on losses of transmission line
- From: "Jian X. Zheng" <jian@xxxxxxxxxx>
- To: <tlzhang@xxxxxxxxxxxx>, <howie03@xxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
- Date: Tue, 25 Nov 2003 11:51:31 -0800
Dear Mr. Zhang:
I think both dielectrics and the metallics are in a single system. They are
related and inseparable even you can calculate the losses based upon the
field inside them individually. They are really dependent upon each other.
1. There is an old question: Is the power on a coupled line carried in the
couple line (assuming PEC without field penetration into the wire) or
carried by the field surrounding it?
For a circuit person, the P = 1/2 * V * conjugate(I). It looks like the
power is carried by the current on the wires. For a field person, the P =
1/2 * integration( E X conjugate(H) ) over the cross-section. Since there is
no field inside the PEC wires, it looks like the power is carried by the
field surronding the wires instead of the wires. From what I can see, they
are just 2 different interpretations only. It is an inseparable system.
Without the wires, you can not have the same field. With the wires, if the
surrounding is different, you may not be able to transmitt the power.
2. Another similar situation is the L and C per unit length on a TEM
transmission line. v = 1 / sqrt( L * C ). In some sense, if we reduce either
L or C, will be able to increase v. However, for a TEM transmission line,
when the dielectrics it is in is fixed, it is impossible to increase the v
even we can change the L or C. The situation is that L and C are related.
They are in the same system and they are not separable.
Best regards,
----------------------------------------------------------------------------
---------
Jian-X. Zheng, Ph.D., Zeland Software, Inc.
48834 Kato Road, 103A, Fremont, CA 94538
Tel: 510-623-7162, Fax: 510-623-7135
E-mail: jian@xxxxxxxxxx, web: www.zeland.com
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--------
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Tonglong Zhang
> Sent: Tuesday, November 25, 2003 11:18 AM
> To: howie03@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Questions on losses of transmission line
>
>
> 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
> P.O. Box 57013=20
> Irvine, CA 92619-7013=20
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> Cel: (949)2938941=20
> Fax: (949)4500237=20
>
>
>
> -----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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