[SI-LIST] Re: Even mode, common mode, and mode conversion

  • From: sainath@xxxxxxxxxxxxx (Sainath Nimmagadda)
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Mon, 25 Feb 2002 11:17:54 -0800

Arpad,

This two T-lines vs one T-line mode distinction is confusing to me.
What makes the two T-lines support even or odd kind of modes? and the one
T-line support the TEM kind of modes?
Is it not possible to have TEM kind of mode propagation in a two T-line
system?
How would you define a MODE when it is meant even or odd mode ? and when it
is meant TEM mode?

Thanks,
Sainath

----- Original Message -----
From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Monday, February 25, 2002 10:26 AM
Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion


>
> What may be confusing to some is that the word "mode" is used
> in different ways in different contexts, both involving
> transmission lines.
>
> So far most responses mentioned the even or odd mode, where
> the signals of ***two*** T-lines go either in the same or the
> opposite direction.
>
> The other usage of this word involves only one T-line (or
> wave guide or optical fiber) and describes how the electro
> magnetic waves propagate inside that line, one of the most
> familiar mode being the TEM (Transverse Electro Magnetic)
> mode.  Don't confuse the two meanings of the word MODE!
>
> Arpad Muranyi
> Intel Corporation
> =================================================================
>
> -----Original Message-----
> From: Dima Smolyansky [mailto:Dima@xxxxxxxxxxxxxx]
> Sent: Monday, February 25, 2002 9:54 AM
> To: doug@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
>
>
>
> Doug:
>
> The distinction is subtle, and the two mode impedances are defined as :
> - Differential mode impedance is impedance between two traces when the
> traces are driven with differential stimulus
> - Odd mode impedance is impedance of one of the traces when the traces are
> driven with differential stimulus
>
> In practical terms, if you need to measure odd mode impedance with TDR
> oscilloscope, you would simply drive the trace pair differentially and
> measure one channel only (no waveform math). If you need to measure
> differential mode impedance, you would drive the trace pair differentially
> and subtract your voltage waveforms on the two channels, or add the
> impedance waveforms, depending on how your scope operates. If your traces
> are symmetric, then the differential impedance is simply twice the odd
mode.
>
> We have an FAQ entry on our web site at
> http://www.tdasystems.com/faq/faqTDR.htm#even_odd_modes.
>
> Thanks,
>
> ===================
> Dima Smolyansky
> 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: "Doug Brooks" <doug@xxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Sent: Monday, February 25, 2002 9:31 AM
> Subject: [SI-LIST] Even mode, common mode, and mode conversion
>
>
> >
> > Gurus,
> >
> > I've been following the thread on mode conversion and suspect I am not
the
> > only one with this question. Can someone explain, in layman's terms:
> >
> > The distinction between even mode and common mode?
> >         between odd mode and differential MODE (not to be confused with
> > differential traces)
> >
> > And does the existence of differential traces add any complications to
> > these distinctions?
> >
> > Thanks for bringing the dummies along with you!
> >
> > Doug Brooks
> >
> >
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