From: Sainath Nimmagadda ([email protected])
Date: Wed Mar 14 2001 - 18:19:06 PST
Dear Howard,
Please see below:
Howard Johnson wrote:
> Dear Itzhak Hirshtal and Brian Young,
>
> The difficulties with approximating the inductance
> of a via are even worse than you
> may have suspected. Both approximations are flawed whether
> you use +1 or -3/4, (or, as I have also seen, -1).
>
> The issue of the exact constant (1, -3/4, or something
> else) depends critically on your assumption about
> the path of returning signal current. (Current always
> makes a loop; when signal current traverses the via,
> a returning signal current flows SOMEWHERE in
> the opposite direction.). It is a principle
> of Maxwell's equations that high-speed returning signal
> current will flow in whatever path produces the
> least overall inductance.
My question is on this last statement. I like to understand which
Maxwell's equation suggests this and how? Thanks.
Sainath
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