[SI-LIST] Re: Help Explaining Microstrip
- From: "Kihong Joshua Kim" <joshuakh@xxxxxxxxx>
- To: Istvan.Novak@xxxxxxx
- Date: Fri, 19 Oct 2007 10:36:06 -0400
It is interesting discussion!
I have added some questions to try to digest it by myself:
- Does Oersted force apply on to electrons? Probably not electrons
maybe current.
- Does Oersted force apply on to current to change their path in electron
gas in any conductors? or the media that carries the current?
Cheers-
Kihong J Kim
On 10/19/07, istvan novak <Istvan.Novak@xxxxxxx> wrote:
>
> Ihsan,
>
> I am not sure I would call the return current fictitious, at least not
> when we do speak about signal current at the same time. What do we do
> then when we have the hypothetical case of a floating symmetrical
> differential wire pair, where 'signal wire' and 'return wire' look and
> behave the same?
>
> Respectfully,
>
> Istvan Novak
> SUN Microsystems
>
> Ihsan Erdin wrote:
>
> >Paul,
> >
> >Unlike the trace current which is forced by the source, return current
> >is a fictitious entity which mainly serves for pedagogical purposes.
> >In this regard, it is not correct to treat the signal-reference
> >conductor system like a differential structure in which the current is
> >forced with opposite polarities in both lines. A microstrip -or in a
> >broader sense- any transmission line is a waveguide that entraps the
> >EM energy between the reference and the signal conductor and directs
> >it along the line axis. What we call "line characteristic impedance"
> >is indeed nothing but the "wave impedance" in EM theory. The current
> >flows on the signal conductor only, thus supporting the transverse
> >electric and magnetic field components. All SI (and EMI) issues like
> >crosstalk, discontinuity effects, etc. can be rigorously explained
> >with the medium and field interaction. This, however, requires a
> >considerable grasp of EM and microwave theory. The "return current"
> >phenomenon is a short cut way of explaining SI issues to people who
> >may have little exposure to EM theory.
> >
> >Regards
> >
> >Ihsan
> >
> >On 10/17/07, Paul Levin <levinpa@xxxxxxxxxxxxx> wrote:
> >
> >
> >>Dear SI-LIST'ers,
> >>
> >>I'm working on a presentation to explain transmission line to
> >>non-engineers and I
> >>find myself stumbling over some of the basics. (There's nothing like
> >>explaining
> >>something to bring out all of the glitches in what you were sure you
> >>understood!)
> >>I'm hoping that one of you may be able to supply the missing link.
> >>
> >>Nearly two hundred years ago Oersted and Ampere figured out that if you
> >>have
> >>two conductors carrying current in the same direction, they would would
> >>to pull
> >>in close to each other whereas if you had two conductors carrying
> >>current in
> >>opposite directions, they would want to separate.
> >>
> >>If one were to apply just these observations to microstrip, you would
> >>expect to
> >>see all of the trace current bunched on the side away from the ground
> >>plane and
> >>the return plane current in two bunches to either side of the trace and
> >>as far away
> >>from the trace as possible, if not on the bottom.
> >>
> >>Of course, this is almost exactly opposite from what we know happens.
> >>
> >>What is the force that overcomes Oersted and Ampere and causes the trace
> and
> >>return currents to be so heavily attracted to each other?
> >>
> >>Thank you in advance.
> >>
> >>Regards,
> >>
> >>Paul Levin
> >>Senior Principal Engineer
> >>Xyratex
> >>
> >>
> >>
> >>
>
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