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Doug McKean wrote:
>
> Anyone have a general equation for calculating the
> characteristic impedence for a twisted pair?
>
>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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