From: Degerstrom, Michael J. ([email protected])
Date: Tue Sep 05 2000 - 19:15:06 PDT
I assumed that George meant that for high speed you have to
match either transmitter or receiver impedance. From that
impedance you must then work with your pcb constraints to
get the lowest loss conductor that will be practical to
fabricate, assemble, route and so on.
Mike
_______________________________________________________________
Mike Degerstrom Email: [email protected]
Mayo Clinic
200 1st Street SW
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_______________________________________________________________
> -----Original Message-----
> From: ytang [mailto:[email protected]]
> Sent: Friday, September 01, 2000 6:57 PM
> To: 'C Deibele'; [email protected]; [email protected]
> Subject: RE: [SI-LIST] : "skin effect/depth calculation results"
>
>
> The discussion is rather hot.
> I would say,
> the impedance of a transmission line is affected only by the structure
> confining electric field, it doesn't matter with what it is
> connected to.
> The circuit nearby may change the impedance a little by
> interfering with its
> electric field.
>
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]]On Behalf Of C Deibele
> > Sent: Friday, September 01, 2000 4:32 PM
> > To: [email protected]; [email protected]
> > Subject: Re: [SI-LIST] : "skin effect/depth calculation results"
> >
> >
> > [email protected] wrote:
> > >
> > > This is great from a theoretical stand point. But in reality,
> > > the trace impedance, Zo, is fixed at a certain range by either
> > > the driver or receiver. You will need to make the widest
> > > possible trace while keeping the same impedance. This brings
> > > us back to the original discussion.
> > >
> > > George Tang
> > >
> >
> > I disagree completely, George. What in the world are you
> > talking
> > about?? I do not know how one can make a constant impedance
> > by
> > varying line widths. You certainly know that impedance is a
> > distributed quantity. Varying line widths varies the
> > impedance.
> > How then, can one make the widest possible trace while
> > keeping
> > the same impedance constant?
> >
> > It is clear from the most basic funamentals of
> > transmissionline
> > theory, see Pozar for example, that one only one geometry
> > will
> > enjoy the least transmission attenuation. The driver and
> > receiver
> > are irrelevant to that standpoint.
> >
> > The driver and receiver may dictate a range of impedances
> > that can
> > be used. but other than that, one can easily transverse
> > from the saddle
> > point of the least attenuation.
> >
> > For example, George, in coax, the best impedance is 77
> > ohms. That is
> > to say, 77 ohms has the least copper attenuation. so, are
> > you
> > saying that the driver and the receiver change this
> > intrinsic property
> > of physics?
> >
> > Your point George, is equivalent to saying that the source
> > and
> > driver dynamically change Maxwell's Equations, which I am
> > certain you will
> > agree must satisfy Maxwell's Equations.
> >
> > In fact, probably the only time one may disregard
> > the simulations I presented are for wavelengths much longer
> > than the geometry in question. And in these circumstances,
> > then skin depth is of importance.
> >
> > I think Pozar goes through the coax example in Chapter 2....
> >
> > I hope everyone was on their toes...I made a mistake in my
> > text. The text is only valid for the coax case of a >>
> > delta.
> >
> > For the point of Bill Owsley, you are correct, but I think
> > we are concerned for the case of "ALL THINGS BEING EQUAL".
> > So, if for the original problem, given a certain trace
> > width,
> > does it help to reduce copper loss if one widens the trace
> > or thickens the trace? I can imagine that the effect of
> > surface
> > roughness might be reduced if the trace would be thickened.
> >
> >
> > Craig Deibele
> >
> >
> > --
> > Craig Deibele, PhD, PE
> > Fermilab--Beams Division
> > PO Box 500 MS 341
> > Batavia IL 60510
> >
> > my opinions only....not of the gov't...nor of the lab...
> >
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