[SI-LIST] Re: Differential pair impedance

Brandon Kemp Wrote:
>
>  I had a trouble
> finding a definition of differential Z in my old textbook ("Analysis of
> Multiconductor Transmission Lines", Paul), although it is a good and
fairly
> thorough book.  Instead of doing a full literature search at the library,
I
> went through the derivation myself.  I've included it with an explanation
> for correlation with Innoveda's XFX Transmission Line Parameters.
>
> (See attached file: derivation.doc)
>
> Brandon Kemp
> EMC/SI Engineer
> Lexmark International, Inc.
>

Hi:

As indicated by "derivation.doc", the XFX generated
Transmission Line Parameters (.tlp) file does not directly output the
differential line impedance ( Z_diff  ) but provides
the odd and even mode impedances ( Z_odd and Z_even).

The following relation is valid for a symmetrical pair:

Z_diff = 2 * Z_odd

Sometimes, it is also desirable to calculate the single ended  impedance
 ( Z_se )  which is obtainable via:

Z_se = (2 * Z_even * Z_odd) / (Z_odd + Z_even)

Best Regards,

Abe Riazi
ServerWorks









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