**From:** Doug (*dmckean@gte.net*)

**Date:** Fri Jun 09 2000 - 09:35:55 PDT

**Next message:**Doug Brooks: "Re: [SI-LIST] : just starting"**Previous message:**Barry Ma: "RE: [SI-LIST] : Upper limit of interplane capacitance"**In reply to:**Larry Miller: "RE: [SI-LIST] : Upper limit of interplane capacitance"**Next in thread:**Barry Ma: "RE: [SI-LIST] : Upper limit of interplane capacitance"

*> Larry Miller wrote:
*

*>
*

*> Dr Howie Johnson did an article on this sometime back.
*

*>
*

*> Here is an excerpt. See what you think:
*

What would people expect the characteristic impedance

to be of a 4" x 6" x 4mil FR-4 structure?

Parallel plates are just two dimensional transmission

lines with L and C being in units of H/area and F/area.

The equations pop out pretty much the same as a one

dimensional transmission line, i.e.

vprop = 1/sqrt(LC)

Z0 = sqrt(L/C)

In fact, there's some pretty neat derivations

for parallel plates such as

Z0 = sqrt(mu/epsilon)*d/w

d = distance of separation

w = width

ignoring fringing effects.

Just was wondering if anyone has done any

research into correlating pure theory

versus reality.

- Doug McKean

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**Next message:**Doug Brooks: "Re: [SI-LIST] : just starting"**Previous message:**Barry Ma: "RE: [SI-LIST] : Upper limit of interplane capacitance"**In reply to:**Larry Miller: "RE: [SI-LIST] : Upper limit of interplane capacitance"**Next in thread:**Barry Ma: "RE: [SI-LIST] : Upper limit of interplane capacitance"

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