Re: [SI-LIST] : 20H Revisited

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From: Sainath Nimmagadda (sainath@lsil.com)
Date: Thu Jan 13 2000 - 11:45:09 PST


Thank you Ray and Michael, for quickly picking up my comment and clarifying. For people who do not know that fields and SI are two sides of the same coin, I was
afraid Michael's 'side note' might mislead them that they are not related subjects. Hence the comment.

Sainath

Michael Vrbanac wrote:

> Sainath,
>
> Everything to do with SI is ultimately a field problem. (T-line work & crosstalk, are
> easy examples.) It isn't always convenient to handle SI that way, though. Let me
> explain.
>
> Most engineers aren't specialists in field issues although they may know something
> about them. Since most of the issues SI folks deal with appear in the time domain,
> many times it is easier to stay in that domain (i.e. keep the problem as simple as
> possible and still get the job done!) Also, SI folks need to speak the "language"
> of the design engineer who is working in the time domain.
>
> The field simulators that we use for SI are designed to relieve us from having to
> directly deal with field theory and make our jobs much easier (thank goodness!).
> The "bad news" is that we might begin to lose touch with our field theory skills
> because the simulator is supposed to do that for us (and that can create even
> larger issues.) The "good news" is, in the near term, we become more effective
> in producing meaningful results which, of course, results in products entering the
> market which then translates into a steady paycheck for the SI engineer!
>
> Michael E. Vrbanac
>
> Sainath Nimmagadda wrote:
>
> > Interesting! What SI issues have to do with fields anyway.
> >
> > Sainath
> >
> > Michael Vrbanac wrote:
> >
> > > D.C.
> > >
> > > re: change in orientation of the fringing fields
> > > Yes. That's a very good point.
> > >
> > > re: Vss plane being cut back instead
> > > In the original application of the 20H rule, it probably wouldn't have mattered.
> > > In later applications (and alterations) other than the original, it might have mattered.
> > >
> > > As as side note:
> > > The original 20H rule came out of a "field" problem being solved. From
> > > that standpoint, it might have actually been true to some extent to have
> > > called it a "screwy SI rule" because it really wasn't an SI problem to begin
> > > with. Knowledgeable folks dealing with SI issues would never have
> > > classified the original use as an SI issue. Subsequent uses of the 20H rule
> > > may indeed have blurred the lines a bit.
> > >
> > > Michael E. Vrbanac
> > >
> > > "D. C. Sessions" wrote:
> > >
> > > > Keeping in mind that There Is No Ground, what happens if
> > > > the Vss plane is the one cut back?
> > > >
> > > > As an alternate consideration, note that the stepback would
> > > > change the orientation of the fringing fields, which would
> > > > interact with the enclosure to potentially limit net radiation.
> > > >
> > > > --
> > > > D. C. Sessions
> > > > dc.sessions@vlsi.com
> > > >
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