[SI-LIST] Re: Convergence problem after inserting detailed connector model
- From: "Mirmak, Michael" <michael.mirmak@xxxxxxxxx>
- To: <Raymond.Anderson@xxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 20 Feb 2004 14:10:16 -0800
To echo Raymond (forgive the questions from the matrix-impaired):
Scott,
If I have an 8-port S-parameter measurement (S11, S28, etc.), from a
Touchstone or CITI file for example, would the given equation apply to
the complex data or just to eh magnitudes?
More specifically, taking the equation literally, my eigenvalues are
calculated as:
Identity matrix (8x8) - Smatrix * Smatrix'
Where Smatrix is an 8x8 matrix of complex S-parameter values, Smatrix'
is its transpose, and the identity matrix is just that, an 8x8 matrix
filled with zeros on the off-diagonals and ones on the diagonals. Is it
still correct to say that a complex result from that calculation, if
having a negative real part, indicates non-passivity?
More specifically still, I get an 8x8 matrix result of "eigenvalues"
from your equation. However, if I request eigenvalues from Matlab using
the same 8x8 Smatrix, I get a result which is 8x1 only. Why the
difference?
Thanks!
- MM
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Raymond Anderson
Sent: Friday, February 20, 2004 12:26 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Convergence problem after inserting detailed
connector model
Scott McMorrow wrote:
>
>One way to check this is to run the model in the frequency domain and=20
>compute the eigenvalues of the S-parameters at each frequency point=20
>with I - S*S'. If there are any negative eigenvalues then the matrix=20
>is not passive. Dr Liu has had some experience with this, since his=20
>software will simulate with standard SPICE models and with=20
>s-parameters. He has found that not only can s-parameters be=20
>non-passive, but also that lumped element models with coupling can be=20
>non-passive. The culprit is usually mutual L. A simple test for this=20
>in a multi-section connector model is to comment out all K elements,=20
>re-run the simulation and see if it is stable. If the simulation is=20
>stable then it is most likely non-passive. More formally it should be=20
>run through an eigenvalue check, which Dr Liu reports to me that he has
>done on a number of occasions. In that case, the model is bad and
needs=20
>to go back to the developer.
> =20
>
Does anyone have any pointers to papers, books, or other info on how to
compute the eigenvalues of the s-parameters as described above. i.e.,
are
there any tools available or published matlab or whatever code available
to
automate the process?
-Ray Anderson
Sun Microsystems Inc.
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