[SI-LIST] Re: Convergence problem after inserting detailed connector model
- From: "Beal, Weston" <weston_beal@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 20 Feb 2004 16:22:18 -0800
Wow! I think I'll save this email for posterity's sake. Scott admitted to
being not as smart as he sounds! :) I think he's pretty smart anyway.
On your last comment about formalizing the passivity correction, there was a
paper delivered at DesignCon 2004 about this. I just read through it quickly,
but it looks OK to me. It appears to be a more formalized Whack-a-Mole process.
7-WA1 Making S-parameter Data Suitable for SPICE Modeling
Jan De Geest, Ph.D., FCI CDC
Stefaan Sercu, Ph.D., FCI CDC
Craig Clewell, FCI CDC
Jim Nadolny, FCI CDC
Later,
Weston
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Scott McMorrow
Sent: Friday, February 20, 2004 2:59 PM
To: michael.mirmak@xxxxxxxxx
Cc: Raymond.Anderson@xxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Convergence problem after inserting detailed
connector model
Michael and Ray,
First of all, I am not as smart as I sometimes sound. I had a good
friend of mine, Rob Hinz, develop the code for passivity checking and
passivity correction based upon some of my simple thoughts on the
subject . We use what we call the "Wack a Mole" method for correction
of non-passive s-parameters. You can imagine from that name what we
might do.
You will want to compute the minimum real eigenvalue of Identity matrix
- Smatrix * Smatrix' on the complex data.
In matlab this is done as follows
mineigv = min(real(eig(eye(size(S))-S*S')))
The matrix is passive the value is positive real
THe matrix is conditionally passive if the value is zero
The matrix is non-passive if the value is negative.
The original reference is:
R. A. Rohrer, "Lumped network passivity criteria," IEEE Trans. Circuit Theory,
vol.
CT-15, no. 1, pp24-29, March 1968
At this time, no one has developed a mathematiclly rigorous method for
passivity correction that I am aware of.
regards,
scott
Mirmak, Michael wrote:
>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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--
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
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