[SI-LIST] Re: Spectre S-parameter based modeling- Stability issues
- From: "bratfest" <bratfest@xxxxxxxxxxxxxx>
- To: <erdinih@xxxxxxxxx>, <thamiral@xxxxxxxxx>
- Date: Sun, 3 Dec 2006 13:15:53 -0600
Just because a simulator can solve a problem does not mean that the model is
correct.
Models for passive systems need to be passive... and as far as I can tell,
all models should be causal...
The solution technique of the simulation engine is irrelevant to the
"correctness" of the original model.
This being said... the Zabinski post is 100% on target...
BR
Gus
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Ihsan Erdin
Sent: Sunday, December 03, 2006 9:31 AM
To: thamiral@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Spectre S-parameter based modeling- Stability issues
Taha,
The passivity issue is a direct result of integration techniques employed by
the time domain circuit simulators (SPICE, ELDO, Spectre, etc.), which are
essentially nonlinear differential equation solvers.
In the frequency domain solution of the MNA matrix, there's no time stepping
algorithm, hence no passivity or stability problems. All you need to do a
cyclic convolution of the output with the spectrum of the input pulse and
FFT the data into the time domain. One can easily do this with less than a
50 line long MATLAB script.
Regards
Ihsan
On 12/3/06, Taha Amiralli <thamiral@xxxxxxxxx> wrote:
> It is likely that applying an inverse DFT, on a freq response obtained
> by non-passive and non-causal matrices, could result in an unstable
> time response.
> I would say that the best approach to this problem would be to try and
> enforce passivity/causality on the S-parameter matrices as suggested
> by Madhu and endorsed by Patrick. I would assume that the a simple
> check of the accuracy of the vector fitted data would be accomplished
> by comparing the freq response of both the vector fit data and the
> original data. This would help circumvent the second point brought up by
Patrick.
>
> I am however curious, if these interconnects are Power lines, why is
> it that one would require a transient/freq analysis :) Its not like
> there are timing issues that need to be maintained at each branch in the
power line node...
> Yes there could be the issue of finding out how long it takes power to
> appear at some obscure end of the device before letting the reset
> circuitry pull the device out of reset, but cant that be done via
> theoretical calculations with a bit of extra delay as insuarance?
>
> Sincerely,
>
> -------------------
> Taha Amiralli
> thamiral [A] uwo [D] ca
> thamiral [A] gmail [D] com
>
> MESc Candidate 2007, Computer Engineering The University Of Western
> Ontario
>
> BESc, BSc. 2005,
> Computer Engineering & Computer Science The University Of Western
> Ontario
> ---------------------------------------------------------------
>
>
>
>
> On 12/2/06, Ihsan Erdin <erdinih@xxxxxxxxx> wrote:
> >
> > Madhusudanan,
> > If you're dealing with the power planes there's a good chance the
> > port loads are linear (decoupling caps and their parasitics, etc.)
> > Then why bother with the time domain simulations and painful data
> > constraintment? Just use a linear frequency domain simulator and get
> > the time domain results by DFT in a straightforward manner.
> >
> > Regards
> >
> > Ihsan
> >
> > On 12/2/06, Madhusudanan K Sampath <mkeezhve@xxxxxx> wrote:
> > >
> > > Hi All,
> > > I am using n-port component in spectre to perform time domain
> > > simulation using touchstone s-parameter files for power planes
> > > which are obtained from measurement/full wave tools. In many
> > > cases, the simulation explodes due
> > to
> > > stability reasons. What are the possible causes of this and how
> > > can one solve this issue. I think Spectre n-port component uses
> > > convolution methods to perform time domain simulation from
> > > frequency domain s-parameter data and hence are prone to
> > > convergence issues. If so how does it enforce
> > passivity
> > > in the model. I verified the s-parameter matrix for eigenvalues
> > > and it proves the data is not passive. I would like to compensate
> > > for passivity and then re-try the time domain simulation. There
> > > are quite a few
> > interesting
> > > passivity enforcements techniques in literature by Dr. B.
> > > Gustavsen and
> > Dr
> > > S.G. Talocia . However they are applied on the rational functions
> > > which are obtained by vector fitting the data. My question is if
> > > I vector fit the data, enforce the passivity using these
> > > techniques and then
> > calculate the
> > > S-parameter matrix for each frequency point from the passive
> > > rational function model. Will spectre give stable results with this
new data ?
> > >
> > > Please share your ideas and views on this. Thanks in advance.
> > >
> > > Madhu
> > >
> > >
> > >
> > >
> > >
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