[SI-LIST] Re: Preparing S-Parameters for Simulation
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: amolak_badesha@xxxxxxxxxxx
- Date: Wed, 25 Feb 2009 16:08:05 -0500
Amolak
Is there documentation on how those causality/passivity corrections are
performed? Any way to compare the before and after results?
regards,
Scott
amolak_badesha@xxxxxxxxxxx wrote:
> Hi Yuriy and Timothy,
>
> The reason typical Spice tools have tough time with S-parameter models is
> because they do not have comprehensive causality and passivity
> checks/corrections built into the tool. However, there are Spice tools
> available now (like Agilent ADS), that can accurately simulate S-parameters
> directly in Time-domain. This is done with built-in causality/passivity
> corrections.
>
> For many customers, converting S-parameters models to broadband spice models
> is an extra step which can be avoided if the Time-domain Spice tools do the
> model "correction" directly. Also, there is a question of the fidelity of the
> broadband spice model - the accuracy depends on how complicated the channel
> response is and how many poles/zeros are used.
>
> Regards,
>
> Amolak S. Badesha
> Agilent EEsof EDA
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Yuriy Shlepnev
> Sent: Wednesday, February 25, 2009 7:15 AM
> To: 'Timothy Coyle'; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Preparing S-Parameters for Simulation
>
> Hi Timothy,
>
> Though, this topic was discussed here multiple times, I think it worth to
> revisit it from time to time, considering the recent developments in this
> area. Here are my takes on it.
>
> First of all, you have to distinguish two S-parameters use cases during the
> system-level analysis.
> S-parameters may be used directly in discrete or tabulated form with
> possible interpolation in frequency domain and with some IFFT or convolution
> algorithms in time domain.
> Alternatively, S-parameters can be converted into rational compact
> macro-model both for frequency and time-domain analysis. The rational
> macro-models usually provide superior accuracy and performance both in time
> and frequency domain analyses and ideally should be used as the models of
> multiport structures (in form of broad-band SPICE models for instance)
> whenever possible instead of the Touchstone tabulated models.
>
> Considering setting the bandwidth for electromagnetic analysis, the low
> frequency should be below the transition to skin-effect (lower MHz for PCBs)
> to allow safe extrapolation to DC. Note, that this is not possible with
> tools that use SIBC to simulate the skin-effect. Typically, the high
> frequency should be defined by the required resolution in time-domain
> (1/2tr). Though that may be not possible due to propagating high-order modes
> and this frequency may be set to a smaller value if your solver builds
> rational compact macro-model with the delay extraction - it technically
> provides the extrapolation. The resolution and spacing are very important
> for IFFT and convolution algorithms and were discussed here before, but not
> that important to build rational macro-models, as soon as there are 3-4
> frequency points for each resonance.
>
> Considering the quality analysis and restoration, I would recommend to study
> this paper:
> P. Triverio, S. Grivet-Talocia, M.S. Nakhla, F.G. Canavero, R. Achar,
> Stability, causality, and passivity in electrical interconnect models, IEEE
> Trans. on Adv. Pack., v. 30, N4, p. 795-808.
> The best way to compare the original and "restored" S-parameters is to plot
> and compare them in frequency domain (phase and magnitude). The original and
> restored S-parameters are typically almost identical in case of small
> violations and visually different in case of large violations. The data
> should be discarded in the later case as rightly pointed out in the cited
> paper.
>
> Considering the quality of S-parameters from the electromagnetic analysis,
> violation of reciprocity and passivity are relatively rare (only in case of
> algorithm failure). Properties of S-parameters due to geometric symmetry can
> be violated with non-symmetric meshing. The causality is often the issue due
> to non-causal models of dielectrics and conductors used in some
> electromagnetic analysis tools. This is not a problem for narrow-band
> microwave applications, but a problem for the broad-band digital
> application. Causality of such S-parameters can be restored by building the
> rational macro-model, but it does not actually improve the quality of the
> model and the model typically has to be discarded and rebuilt with the
> broad-band causal models both for dielectrics and conductors.
>
> Best regards,
> Yuriy Shlepnev
> www.simberian.com
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Timothy Coyle
> Sent: Tuesday, February 24, 2009 9:52 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Preparing S-Parameters for Simulation
>
> Hi,
> I am working on a tutorial for the next issue of XrossTalk Magazine about
> getting S-Parameter models ready for simulation. I see a lot of S-Parameter
> models from lab measurements and simulation tools that have a lot of quality
> issues (causality and passivity) and have to do a lot of clean up to make
> them suitable for simulation. I have my own bag of tricks I use as well as
> some good books on S-Parameter theory and application notes but I would like
> to hear from other people what their approaches are or some good resources.
>
>
>
> For some particular specifics review the list below:
>
> . What considerations should go into setting up a simulation tool to
> extract an S-Parameter model? (bandwidth to be used, number of points,
> importance of linear spacing of points, starting at DC, etc)
>
> . A lot of tools will automatically "fix" causal and passivity
> issues or enforce them. What's the pros and cons for this? What do engineers
> need to look out for when they do this?
>
> . What's the best way to clean up a lab measured S-Parameter model
> with poor resolution?
>
> . What type of quality checks should you perform on an S-Parameter
> model before simulating? (what do you look for in the S21 plots, do you use
> smith charts, ect?)
>
>
>
> Thanks for any and all suggestions and links.
>
>
>
> Best,
>
>
>
> Timothy Coyle
>
> Editor In Chief
>
> XrossTalk Magazine
>
> 405 Western Ave #430
>
> South Portland, ME 04106
>
> Tel: 617.297.2566
>
> Fax: 207.510.8099
>
> Email: tim@xxxxxxxxxxxxxxxx
>
> http://www.xrosstalkmag.com <http://www.xrosstalkmag.com/>
>
>
>
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