[SI-LIST] Re: Cascading differential 2-Port Networks

Bob,

The main problem is that the transformation in text books from S-parameters to 
T-parameters is defined for 2x2 matrices.  I don't know what the transformation 
is for a 4x4 matrix, but I'm sure it can be done.  Assuming you find out how to 
do it, then just use mixed-mode like you would a standard S-parameter block, 
except now it is a 4x4 matrix instead of 2x2.  Since the mixed-mode and 4-port 
S-parameters are related by a simple linear transformation, all the math 
carries over.

Start with the mixed-mode S-matrix, convert to T-parameters, multiply the 
matrices, and convert back to S-matrix.  You now have a mixed-mode matrix that 
reflects two cascaded mixed-mode matrices.  Upper-left quadrant is still 
differential parameters, Lower-right quadrant is still common-mode parameters, 
and the other two quadrants are still mode-conversion parameters.

Again, this assumes that a transformation from 4x4 S-parameters to 4x4 
T-parameters can be computed.

A good technical reference is:

Bockelman & Eisenstadt; "Combined Differential and Common-Mode Scattering 
Parameters: Theory and Simulation"; IEEE Trans. MTT; July 1995; pp. 1530-1539.

It doesn't talk about T-parameters, but it does talk about how mixed-mode 
S-parameters can be treated just like any other 4x4 s-parameter matrix (as long 
as you interpret it correctly as I stated above).

From: "Bob Welte" <welte@xxxxxxxxxx>
> 
> Hello to All
> I have run into an interesting problem.
> I am trying to put together a simple modeling environment of our 2.5Gb/s
> high speed digital channel using S-parameters.  Because it is a
> differential environment, I will be using mixed-mode S-parameters.  While I
> understand the concept of converting "S" into "T" parameters and using the
> chain-scattering-matrix to cascade the 2 ports of a channel, I do not know
> what to do when the channel is differential, and you begin with mixed-mode
> S-parameters.
> Can anyone offer a reference, or perhaps share some knowledge?
> 
> Bob Welte
> IBM Microelectronics

--
Daniel
ZZZ-dgun-ZZZ-@xxxxxxxxxxxxxxx
(remove the Z-'s to reply--they're what I do when I read spam)

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