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Date: | Thu, 27 Mar 1997 16:34:55 -0500 |
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Thanks John,
It obvious from the ratio of s/d the magnitudes of
the units don't matter as long as the units are the same,
but upon what are the units based -
inches, mils, millimeters...?
I assume that since we are dealing with wire it's mils?
John Nieznanski wrote:
> >From "High Speed Digital Design - A Handbook of Black Magic",
> by Howard Johnson and Martin Graham, 1993, Prentice-Hall, p. 186,
>
> Zo = 120 * ln (2s/d)
> --------
> sqrt(er)
>
> where, d = diameter of conductor
> s = separation between wire centers (s > d)
> er = effective relative permittivity
>
> For widely separated wires, use er = 1.
>
> For wire pairs with the insulation touching,
> use the er of the insulating material.
>
> Also, propagation delay (ps/in): 85 * sqrt(er)
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