[SI-LIST] Re: Antwort: Re: Diff line

  • From: "Dima Smolyansky" <Dima@xxxxxxxxxxxxxx>
  • To: "Andreas Lenkisch" <Andreas_Lenkisch@xxxxxxxxxx>,"silist" <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 15 Feb 2002 10:22:05 -0800

Andreas:

Even mode return loss specifically is related to even mode impedance
mismatches and reflections. Even mode is primarily responsible for the
interaction between the trace and the ground plane (vs. odd mode, which is
primarily responsible for the interaction between the lines in differential
pair). As a result, a discontinuity in the trace path will result in
increased reflections for the even mode, whereas it may have only minor
effect on the odd mode. Conversely, a skew between the lines will have
little effect on the even mode reflections, whereas it will have a major
impact on the odd mode reflections. I tend to look at the even mode
discontinuities as "single-ended" discontinuities, whereas I refer to the
odd mode discontinuities as "differential" discontinuities.

Thanks,

===================
Dima Smolyansky
Time Domain Analysis (TDA) Systems, Inc.
11140 SW Barbur Blvd., Suite 100
Portland, OR 97219
(503) 246-2272
(503) 246-2282 (fax)
(503) 804-7171 (mobile)
www.tdasystems.com


----- Original Message -----
From: "Scott McMorrow" <scott@xxxxxxxxxxxxxxxx>
To: "Andreas Lenkisch" <Andreas_Lenkisch@xxxxxxxxxx>; "silist"
<si-list@xxxxxxxxxxxxx>
Sent: Friday, February 15, 2002 9:48 AM
Subject: [SI-LIST] Re: Antwort: Re: Diff line


>
> Andreas,
>
> Return loss arises from reflections.  S11 is an indication of how much
> reflected energy is returned in the system.  Anything that causes
> increased impedance mismatch, causes reflection and higher return loss.
>
> I don't know any one book where all this information can be found.  But
> the following are my favorites:
>
> Microwave Engineering, Pozar
> Digital Signal Integrity, Brian Young
>
>
> regards,
>
> scott
>
>
>
> Andreas Lenkisch wrote:
>
> >Scott,
> >
> >from where the even mode return losses do arise?, may yoe recommend me
some
> >literature .
> >
> >regards
> >Andreas
> >
> >Andreas Lenkisch
> >Product Manager Backplanes
> >Schroff GmbH
> >Langenalber Strasse 96-100
> >D-75334 Straubenhardt
> >Germany
> >Ph.:     ++49 7082 794 674
> >FAX.:   ++49 7082 794 133
> >mobile: ++49 175 59 43 544
> >e-mail: andreas_lenkisch@xxxxxxxxxx
> >Internet: www.schroff.de
> >
> >
> >
> >
> >
> >                      Scott McMorrow
> >                      <scott@vasthorizo         An:
zanella_fabrizio@xxxxxxx
> >                      ns.com>                   Kopie:
"'pikeda@xxxxxxxxxxx'" <pikeda@xxxxxxxxxxx>,
> >                      Gesendet von:             si-list@xxxxxxxxxxxxx
> >                      si-list-bounce@fr         Thema:   [SI-LIST] Re:
Diff line
> >                      eelists.org
> >
> >
> >                      15.02.2002 04:16
> >                      Bitte antworten
> >                      an scott
> >
> >
> >
> >
> >
> >
> >
> >All,
> >
> >Both loosely coupled and tightly coupled differential pair designs work
> >as all authors have previously stated.  The following is a list of some
> >of the general differences between the two types of edge-coupled
> >differential pairs:
> >
> >Loosely coupled
> >    better impedance control
> >    less sensitivity to manufacturing variations
> >    lower track density
> >    lower even mode return loss
> >    lower insertion loss
> >    less impedance variation at 2mm connector transitions
> >    less impedance variation at BGA escapes transitions
> >    less impedance variation at via transitions
> >
> >Tightly coupled
> >    worse impedance control
> >    greater sensitivity to manufacturing variations
> >    higher track density
> >    higher even mode return loss
> >    higher insertion loss
> >    greater impedance variation at 2mm connector transitions
> >    greater impedance variation at BGA escape transitions
> >    greater impedance variation at via transitions
> >
> >As with all things in interconnect engineering, there are tradeoffs. At
> >3.125 Gbps and above, it's the impedance mismatches that get you into
> >trouble, especially near connectors, vias and device escapes.  It is
> >extremely easy to create unwanted resonances which will cause unexpected
> >losses at the strangest frequences, some easily within the frequency
> >spectrum of data streams.
> >
> >For high speed circuits where trace density is not an issue, I always
> >choose to use loosely coupled differential pair conductors, where
> >impedance control is much more precise, and resonances caused by
> >impedance mismatch can more easily be reduced.
> >
> >
> >regards,
> >
> >scott
> >
> >
> >--
> >Scott McMorrow
> >Principal Engineer
> >SiQual Interconnect Engineering
> >18735 SW Boones Ferry Road
> >Tualatin, OR  97062-3090
> >(503) 885-1231
> >http://www.siqual.com
> >
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> --
> Scott McMorrow
> Principal Engineer
> SiQual Interconnect Engineering
> 18735 SW Boones Ferry Road
> Tualatin, OR  97062-3090
> (503) 885-1231
> http://www.siqual.com
>
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