[SI-LIST] Re: Spectre S-parameter based modeling- Stability issues
- From: "Ihsan Erdin" <erdinih@xxxxxxxxx>
- To: thamiral@xxxxxxxxx
- Date: Mon, 4 Dec 2006 21:19:36 -0500
Taha,
Spectre (or any circuit simulator that uses a time evolution
technique) fails because its iterative algorithm builds the error in
the S-parameter data at every time step. If the data is unstable the
result shoots to the sky, if non-passive, it oscillates. The
convolution they mention is an intermediate step to get the
s-parameter data into the admittance matrix. Keep in mind that the
original frequency domain data can't be directly included in the
simulator's time domain algorithm. The data is first approximated in a
rational form and then expanded in decaying exponentials, which saves
storage and computational time by recursive convolution. But the end
result is still obtained by marching in the time, hence the passivity
requirements.
For the analysis of power delivery systems, I don't really see a big
incentive to use a transient simulator as long as the linear load
assumption holds. This applies to most practical cases. Usually the
frequency domain solution will give enough information for the
decoupling efficiency etc. A time domain response may be desired just
to see the peak-to-peak noise level but then one can easily get it
through IFFT as you put it.
Regards
Ihsan
On 12/4/06, Taha Amiralli <thamiral@xxxxxxxxx> wrote:
> Ihsan,
> Your comments are definitely correct. No matter how bad the S-parameter
> matrices are, with respect to passivity/causality, you will still get a
> frequency response and thus, an IFFT should do the trick.
>
> The thing is that I have read that spectre does use convolution when
> computing the time domain response from S-parameter matrices. So I guess the
> question then becomes, why would spectre fail to compute the transient
> response of a non passive S-parameter dataset, as is the case with Madhu?
>
> Bratfest,
>
> I definitely did not consider all those options... but I am still not sure
> why a transient response would be required... If the design is lets say an
> Integrated circuit, with lots of different loads, wouldn't it suffice to
> just find out what the max power levels required are and provide a power
> supply that is suited to the task? I guess I am still unsure of how a
> transient analysis would apply since the loading conditions are different
> depending on what the integrated circuit is doing at a certain moment in
> time.
>
> Thanks,
>
> Sincerely,
>
> Taha
>
>
>
> On 12/3/06, Dmitriev-Zdorov, Vladimir <vladimir_dmitriev-zdorov@xxxxxxxxxx>
> wrote:
> >
> >
> > Hi Madhu,
> >
> > We do have a tool that can solve the problem you describe, unless your
> > original touchstone files are of an extremely bad quality (in terms of
> > resolution, causality, passivity etc.) For example, if instead of having
> > L2 norm of the matrix below one, it reaches 1.1...1.5, it is possible to
> > make the model passive without changing the dependences too much.
> > However, if the norm goes up to hundreds, this is less likely.
> >
> > Anyway, we may produce either passive/causal/smooth data in a form of
> > the touchstone file, re-sampled with sufficient resolution, or, in a
> > form of an equivalent SPICE-compatible circuit, whichever you prefer.
> >
> > Please contact off-line for more technical details.
> >
> > Vladimir
> >
> >
> >
> > ------------------------------
> >
> > Msg: #5 in digest
> > Date: Sat, 02 Dec 2006 00:16:01 -0500
> > From: Madhusudanan K Sampath <mkeezhve@xxxxxx>
> > Subject: [SI-LIST] Spectre S-parameter based modeling- Stability issues
> >
> > Hi All,=20
> > 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 ?=20
> >
> > Please share your ideas and views on this. Thanks in advance.=20
> >
> > Madhu=20
> >
> > =20
> >
> >
> >
> >
> > ------------------------------
> >
> > End of si-list Digest V6 #422
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>
> --
> -------------------
> 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
> ---------------------------------------------------------------
>
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