FreeLists / si-list / [SI-LIST] Re: Differential pair impedance

[Pat Diao <Pat_Diao@xxxxxxxx>]

In a differential pair, compared against Differential Impedance, most times
we refer Single-ended Impedance as the Characteristic Impedance of one of
the single lines.  Now we have the following definition of Single-Ended
Impedance.  Any relationship between these two, or just another case of
mis-used terms.

Pat


>   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)



Pat Diao, Ph.D.
Manager - Package Thermal, Electrical 
and Mechanical Engineering and Development
ASAT Inc.
Fremont, CA


-----Original Message-----
From: Abe Riazi [mailto:ARIAZI@xxxxxxxxxxx]
Sent: Saturday, September 28, 2002 9:41 AM
To: si-list@xxxxxxxxxxxxx
Subject: [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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