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

  • From: sainath@xxxxxxxxxxxxx (Sainath Nimmagadda)
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 26 Feb 2002 14:05:42 -0800

Aubrey,

Cool. Microwave guys worry about their modes and SI guys worry about their
modes.

Having background in both microwave and SI, I was trying to get at what is
fundamentally common to these two seemingly different types of modes. Once I
get that, these different mode types, descriptions and semantics are mere
spices to give personality to those subjects ...and, of course, job
securities - as some one already pointed out.

Thanks,
Sainath


----- Original Message -----
From: <Aubrey_Sparkman@xxxxxxxx>
To: <sainath@xxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Tuesday, February 26, 2002 1:04 PM
Subject: RE: [SI-LIST] Re: Even mode, common mode, and mode conversion


> Sainath,
> Perhaps I can help.  Seems like there are two different types of modes
being
> confused here.
>
> Type 1)
> Any single transmission line will propagate the TEM mode up to it's
cut-off
> frequency, then you get other modes like TE11, TM11, etc which means one
of
> the cross-sectional dimensions is greater than 1/2 wavelength (if memory
> serves, microwave experts feel free to correct me) but you should
> investigate waveguides if you want to understand all these different types
> of modes.  I haven't seen this type of modes be relevant to SI engineers
in
> the past.  Perhaps the hi speed serial links will change that.  Most of
our
> chip-to-chip signals (on the same PCB) signal each other using TEM mode.
>
> Type 2)
> SI engineers talk about odd and even modes when a pair of signals are
either
> in phase or 180 degrees out of phase. The pair of odd mode signals see a
> differential impedance and SI engineers call that differential signaling.
> The noise that disturbs the pair is usually "in phase" and we hope for
good
> common mode rejection; the differential receiver sees no difference.  If
you
> consider the odd mode pair having an "a" signal and a "b" signal, the "a"
> signal will see the odd mode impedance when the pair of signals are 180
> degrees out of phase.  The "a" signal will see the even mode impedance
when
> the pair of signals are in phase.
>
> Hope this helps.
>
> Aubrey Sparkman
> Signal Integrity
> Aubrey_Sparkman@xxxxxxxx
> (512) 723-3592
>
>
>
> -----Original Message-----
> From: sainath@xxxxxxxxxxxxx [mailto:sainath@xxxxxxxxxxxxx]
> Sent: Tuesday, February 26, 2002 1:31 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
>
>
>
> Steve,
>
> I better leave my three questions at that with all those 'refer to's.
> My attention is turned to the statement: "A system doesn't really support
> modes, it has modes."
> Again, is it Paul's book that I should refer to?
>
> Thanks,
> Sainath
>
> ----- Original Message -----
> From: "Steve Corey" <steve@xxxxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Sent: Tuesday, February 26, 2002 10:48 AM
> Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
>
>
> >
> > Sainath -- I'll see what I can do without getting too embroiled in the
> > details:
> >
> > 1. What makes the two T-lines support even or odd kind of modes? and the
> > one T-line support the TEM kind of modes?
> >
> > For the first part of #1, I would refer to the book by Paul.  A system
> > doesn't really support modes, it has modes.  Sometimes in analysis we
> > break down voltages and currents into the system modes to simplify
> > analysis.  If you come up with a good answer to the first part of #1,
> > you will understand that the even and odd are also TEM modes in the same
> > way that a single line has a TEM mode.
> >
> > 2.  Is it not possible to have TEM kind of mode propagation in a two
> > T-line system?
> >
> > Yes, as you will see in my previous post.
> >
> > 3.  How would you define a MODE when it is meant even or odd mode ? and
> > when it is meant TEM mode?
> >
> > For the first part of #3, you can refer to Paul's book for a rigorous
> > mathematical definition.  You can also refer to Eric Bogatin's post to
> > this thread for what may be a more intuitive definition.  For the second
> > part of the question, refer to my earlier post for a short definition,
> > or to Paul's book or any E/M book that covers waveguides for a longhand
> > definition.
> >
> >
> >  > >
> >  > >
> >
> >
> >
> > Sainath Nimmagadda wrote:
> >
> > > Steve,
> > >
> > > I suppose your message was to address my questions to Arpad.
> > > There are 3 questions and I'm not clear which one is addressed.
> > > Is it possible to say few simple words about each question separately?
> > >
> > > Thanks,
> > > Sainath
> > >
> > > ----- Original Message -----
> > > From: "Steve Corey" <steve@xxxxxxxxxxxxxx>
> > > To: <si-list@xxxxxxxxxxxxx>
> > > Sent: Tuesday, February 26, 2002 7:20 AM
> > > Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
> > >
> > >
> > >
> > >>Sainath -- I will give you the short answer, and refer you to the
texts
> > >>for the long answer.  The even and odd modes are TEM modes, or at
least
> > >>quasi-TEM.  TEM vs. higher order modes describes the field
distribution
> > >>across a single transmission line or waveguide structure.  Quasi-TEM
is
> > >>a basic assumption of the transmission line theory on which we rely,
> > >>including characteristic impedance and RLGC matrices.  It requires
that
> > >>to first order, no field has a component in the direction of
> > >>propagation.  I usually rely on "Analysis of Multiconductor
Transmission
> > >>Lines" by Clayton R. Paul when I have questions of this sort.
> > >>
> > >>The higher order modes are significant to transmission line theory for
> > >>the most part in that we try to make sure they don't exist, since they
> > >>each propagate with their own velocities and make a mess of our nice
> > >>clean square waves.  Any E/M text with a waveguide section will
describe
> > >>the physics behind this.
> > >>
> > >>On the other hand, all TEM modes propagate.  Analysis of the different
> > >>TEM modes supported on a multiconductor transmission line structure is
> > >>from my perspective more of a mathematical tool for breaking down a
> > >>system into its most basic components.  In the case of even/odd, this
> > >>has a very practical application in differential signaling, but once
we
> > >>step outside of the symmetric coupled two-line regime, the math gets
> > >>pretty complicated to try and define signaling schemes which coincide
> > >>with any particular modes.
> > >>
> > >>So-called "full-wave" analysis, which essentially means "non-TEM
> > >>analysis" for our purposes, is necessary for situations where we can't
> > >>count on quasi-TEM assumptions.  These situations occur when we step
> > >>outside of the strict geometries of uniform transmission lines, or
into
> > >>certain loss regimes.  Again, I would refer you to the book by Clayton
> > >>R. Paul.
> > >>
> > >>   -- Steve
> > >>
> > >>-------------------------------------------
> > >>Steven D. Corey, Ph.D.
> > >>Time Domain Analysis Systems, Inc.
> > >>"The Interconnect Modeling Company."
> > >>http://www.tdasystems.com
> > >>
> > >>email: steve@xxxxxxxxxxxxxx
> > >>phone: (503) 246-2272
> > >>fax:   (503) 246-2282
> > >>-------------------------------------------
> > >>
> > >>
> > >>Muranyi, Arpad wrote:
> > >>
> > >>
> > >>>To all,
> > >>>
> > >>>Sainath addressed his question to me, but I am going on vacation
> > >>>and don't have the time to answer it.  Could someone please
> > >>>give him a good explanation to his questions?  Thanks,
> > >>>
> > >>>Arpad
> > >>>=================================================================
> > >>>
> > >>>-----Original Message-----
> > >>>From: sainath@xxxxxxxxxxxxx [mailto:sainath@xxxxxxxxxxxxx]
> > >>>Sent: Monday, February 25, 2002 11:18 AM
> > >>>To: si-list@xxxxxxxxxxxxx
> > >>>Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
> > >>>
> > >>>
> > >>>
> > >>>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
> > >>>>=================================================================
> > >>>>
> > >>>>
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> >
> >
> > --
> > -------------------------------------------
> > Steven D. Corey, Ph.D.
> > Time Domain Analysis Systems, Inc.
> > "The Interconnect Modeling Company."
> > http://www.tdasystems.com
> >
> > email: steve@xxxxxxxxxxxxxx
> > phone: (503) 246-2272
> > fax:   (503) 246-2282
> > -------------------------------------------
> >
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