[SI-LIST] Re: S-parameter to SPICE
- From: Ege Engin <engin@xxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Sat, 07 Dec 2002 16:58:08 +0100
Hello,
Let me summarize the 2 methods that I know to get SPICE models from
S-parameters:
1) Convert the S-parameters to a Y-Matrix. This matrix can implemented
in SPICE by means of voltage controlled current sources defined for
discrete frequencies. (The code at CERN 's2spice' seems to do this).
2) Or interpolate the Y-matrix by a rational polynomial approximation.
(Spice Model Generator of ADS does this)
In the first method, simulation in time-domain can be performed by using
FFT and convolution. In the second method, the simulator performs
recursive convolution.
The second method is similar to reduced order modeling procedures (Pade
approximations, AWE, etc.). Important criteria for these procedures are
to preserve stability and passivity. Does anybody know, if passivity and
stability are considered in the Spice Model Generator of ADS, Sigrity
BroadBand Spice, EMWonder, etc?
Ege
"Hassan O. Ali" schrieb:
>
> Mick,
>
> Your question has a lot of "catch phrases" that one has to be aware of
> before giving you a "correct" answer.
>
> "DC-20GHz":
>
> Would you be able to obtain S-parameter values at DC? By extrapolation,
> right? How do you then define a phase of a DC (non-oscillating) signal?
> Besides, aren't S-parameters a linear wave phenomenon that implies
> wave-like propagation?
>
> I think, requiring the SPICE model to be valid at DC is quite a tall
> order unless you have a priori knowledge of how the structure behaves at
> DC. That wouldn't be the case with "complex structures" (another catch
> phrase).
>
> "Complex structures":
>
> How complex? Is it by its many ports? Is it by its irregular S-parameter
> characteristics? Is it by its radiative and coupling effects? Is it
> non-linear?
>
> Here this: if your structure is indeed "complex", getting a SPICE model
> for it may also be a very complex matter and may even be impossible or
> impractical. You see, when you represent a structure by its S-parameters
> or a SPICE model, you assume it to be a "covered" black-box. That is it
> won't interact with the rest of the circuit in any manner other than
> through its defined ports and with the wave propagating in its dominant
> (quasi-TEM) mode.
>
> But that can simply be not true for "complex structures". In reality the
> structure is "uncovered" hence subject to interacting with other circuit
> structures through ways other than the ports, and may involve more than
> one mode of wave propagation. That is even more true at higher
> frequencies of your interest.
>
> If your structure has irregular S-parameters, with resonances everywhere
> (for example), you may also have difficulty creating a SPICE model for
> such a broad frequency band other than using the method used by Ansoft's
> Fullwave SPICE.
>
> My 2 cent's worth.
>
> Hassan.
>
> "Zhou, Xingling (Mick)" wrote:
> >
> > Hello,
> >
> > Did anybody successfully generate broadband (DC-20GHz) SPICE model from S
> > matrix for complex structures using the SPICE generator in ADS ? Or any
> > other alternatives. I know Ansoft fullwave SPICE does the work.
> > Unfortunately, some circuit simulators do not support the frequency
> > dependent lookup table sources. We can definitely use [S] directly, but some
> > users still prefer SPICE models. Any experience to share ?
> >
> > Thanks,
> >
> > Xingling(Mick) Zhou, PhD
> > Signal Integrity Technologist
> > Agere Systems
> >
> > Tel: 610-712-7462
> > Fax: 610-712-4081
>
> --
> Hassan O. Ali Email: hassan@xxxxxxxx
> 12-2159 Elmira Drive Tel/Fax: (613) 721-9047
> Ottawa, Ontario
> CANADA K2C 1H3 WWW: http://www.glcom.com/hassan
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