RE: [SI-LIST] : "skin effect/depth calculation results"

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From: ytang (ytang@axonphotonics.com)
Date: Fri Sep 01 2000 - 16:57:18 PDT


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: owner-si-list@silab.eng.sun.com
> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of C Deibele
> Sent: Friday, September 01, 2000 4:32 PM
> To: George_Tang@Dell.com; si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : "skin effect/depth calculation results"
>
>
> George_Tang@Dell.com 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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