[SI-LIST] Re: Spectre S-parameter based modeling- Stability issues

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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