[SI-LIST] Re: Spectre S-parameter based modeling- Stability issues
- From: "Ihsan Erdin" <erdinih@xxxxxxxxx>
- To: thamiral@xxxxxxxxx
- Date: Sun, 3 Dec 2006 10:30:57 -0500
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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