Re: [SI-LIST] : differential impedance calculations

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From: Brad Underwood ([email protected])
Date: Wed Nov 01 2000 - 14:39:49 PST

The equation z in your drawing is for the characteristic impedance of
the line in the geometries of the board you described with the
variables. This is without the effects of coupling from the other trace.
You need to calculated the odd and even mode impedances based on the
coupling factor of the other trace.


Brad Underwood
Metera Networks

Gary Peterson wrote:
> I seem to recall Dr. Howard Johnson mentioning that impedance calculation
> formulas made assumptions (since closed-form solutions aren't possible).
> Can someone comment on assumptions made for the equation for differential
> impedance shown below? Seems to me that as traces get closer together, the
> single ended impedance would be affected. When I calculate single-point
> values for differential impedance using Hyperlynx LineSim, I do see the
> single-ended impedance change when the spacing between the pair gets small.
> Thanks,
> Gary Peterson
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