RE: [SI-LIST] : Focusing on Parasitic Parameters

Andrew Ingraham (Andrew.Ingraham@digital.com)
Sun, 29 Nov 1998 23:26:21 -0500

> ... Perhaps one conclusion implied by your
>email is following:
>
> It is simpler to quantify parasitic via capacitance than via
>inductance.

This is certainly true. It is easy to determine capacitance as a static
problem and typically it doesn't change much from its value at 0Hz.

Determining inductance, on the other hand, requires you to define a
closed loop. You will get different answers depending on how you choose
the loop that includes your via. The inductive effect of the via may be
imagined as being partly in series with the signal trace, partly in
series with its return path, since the return current may need to spread
out when reaching the via, to find enough capacitance to flow from one
plane to another. It's an interesting 3D problem that doesn't easily
shoe-horn into a simple 1D solution.

Regards,
Andy

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