[SI-LIST] Re: HSPICE S-paramter questions
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: "Pratt, Gary" <gary_pratt@xxxxxxxxxxx>
- Date: Thu, 17 Mar 2005 12:19:28 -0500
Gary
Yes, I am quite aware that ELDO can run unencrypted HSPICE models and
models encrypted in the ELDO format. As for encrypted ELDO models,
being a very small consulting company, I generally do not have the
"juice" to arrange for ELDO models from a silicon vendor. But I would be
interested in what silicon vendors currently provide ELDO encrypted
models, for those customers I deal with that have ELDO available.
regards,
scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
Pratt, Gary wrote:
>Scott,
>
>Please note, Eldo doesn't require "Eldo models" (as strange as that may
>sound). It is perfectly happy with either unencrypted HSPICE models, or
>HSPICE Models encrypted in Eldo format. Encryption is the only problem
>here. Not model (or netlist syntax) compatibility.
>
>Do let me know when you run into a vendor who does not provide
>eldo-encrypted models. I can help with that. Most silicon vendors are
>interested in being eda-vendor neutral, when they can.
>
>Gary
>
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Scott McMorrow
>Sent: Thursday, March 17, 2005 10:18 AM
>To: Dmitriev-Zdorov, Vladimir
>Cc: ray.anderson@xxxxxxxxxx; silist
>Subject: [SI-LIST] Re: HSPICE S-paramter questions
>
>Vladmir,
>Your points are well taken. However, there are several issues.
>
>1.) At least one 3rd party solution using Hspice recursive convolution
>is extremely fast. Extraction times are equivalent to yours, as are the
>extraction times of passivity corrected models.
>
>2) ELDO does not work with encrypted HSPICE models, which makes it an
>unacceptable solution for most simulations with complex Silicon.
>
>I have followed the progress of your s-parameter modeling approach and
>am impressed. But, it still does not solve the basic problem of
>simulation of real circuits in real systems with real silicon models.
>Ray does have the advantage of being at a silicon company where he can
>use ELDO models for the silicon. But, even he will have issues if he
>wants to simulate the interoperability of their silicon with that of
>other vendors, when the other vendors' models are in encrypted HSPICE.
>
>Your software is generally good if:
>
> * the user is simulating with IBIS models. (in which case the
> accuracy is extremely limited)
> * the user is simulating pure passive interconnect. (a good
> application of your software for passive characterizations.
> *
>
> * the user has ELDO models of the silicon available.
>
>Whenever accurate models of the silicon are required, HSPICE must be
>used. It may not be the technically superior product, but it is the VHS
>to your Betamax.
>
>
>
>best regards,
>
>scott
>
>
>
>Scott McMorrow
>Teraspeed Consulting Group LLC
>121 North River Drive
>Narragansett, RI 02882
>(401) 284-1827 Business
>(401) 284-1840 Fax
>
>http://www.teraspeed.com
>
>Teraspeed(r) is the registered service mark of Teraspeed Consulting
>Group LLC
>
>
>
>Dmitriev-Zdorov, Vladimir wrote:
>
>
>
>>Hi Ray,
>>
>>
>>
>>So far you consider only two alternatives: using S-model based on
>>touchstone file or the n-port "circuit" model whose frequency response
>>
>>
>
>
>
>>approximates the touchstone data. Both have their own limitations.
>>E.g. direct use the tabulated data (touchstone) for transient
>>simulation leads to convolution-based approach that is slow
>>(super-linear by complexity) and often inaccurate. Possible trade-off
>>between accuracy and performance normally is not successful.
>>
>>The equivalent n-port models (sub-circuits) produced by the
>>third-party model tools are good from those points but they add a
>>large amount of the circuit components (and sometimes internal nodes)
>>that slow down simulation from the other end. Such models are also not
>>
>>
>
>
>
>>free from accuracy issues. Although they do not suffer from inaccuracy
>>
>>
>
>
>
>>inherent for convolution, they develop LTE (local truncation error),
>>as any other circuits with LC elements or LAPLACE-type controlled
>>circuits.
>>
>>When solving transient for a long enough with models that have sharp
>>resonances, such errors become considerable and/or force using smaller
>>
>>
>
>
>
>>step. Even worse, the step selection mechanism cannot correctly
>>predict how much this error will accumulate over time.
>>
>>
>>
>>There is a simulator (ELDO) that utilizes a third solution, free from
>>above limitations. In addition, it does not need third party
>>conversion tools and makes everything by itself, including passivity
>>enforcement. For re-use purpose, it generates the compact model in the
>>
>>
>
>
>
>>intermediate format that is neither touchstone nor circuit. Such
>>S-model does not generate convolution-specific error or LTE. On
>>average, it is 5-7 times faster (per step) than the corresponding
>>equivalent circuit.
>>
>>
>>
>>Example. Given the 158-port touchstone file of 214MB size (fully
>>populated S-matrix) it took 5 minutes to convert it into such
>>intermediate format (however 30 minutes if with passivity
>>enforcement). Then, simulation with 10,000 output points takes 3
>>minutes. The user should not care about conversion: if needed it is
>>performed automatically on the initialization stage. The converted
>>model is stored and made re-usable. During re-simulation, the
>>converted model is loaded in seconds.
>>
>>With the equivalent circuit, built from the same converted model, it
>>takes about 25 min for the simulator only to parse and check errors in
>>
>>
>
>
>
>>the subcircuit, before any simulation starts. This time cannot be
>>avoided if simulated repeatedly. Solution itself takes about 15
>>
>>
>minutes.
>
>
>>Convolution-based approach (also available in ELDO) fails on that
>>model. Not because of poor implementation but due to inherent
>>
>>
>problems.
>
>
>>
>>
>>Vladimir
>>
>>
>>
>>
>>
>>-----Original Message-----
>>
>>From: si-list-bounce@xxxxxxxxxxxxx
>>[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Ray Anderson
>>
>>Sent: Wednesday, March 16, 2005 11:57 AM
>>
>>To: si-list@xxxxxxxxxxxxx
>>
>>Cc: scott@xxxxxxxxxxxxx
>>
>>Subject: [SI-LIST] Re: HSPICE S-paramter questions
>>
>>
>>
>>Scott-
>>
>>
>>
>>I agree with you completely regarding the speed issue. Another factor
>>to consider is stability/passivity. S-parameters originating from
>>measurements (and quite often from simulation/extraction) can exhibit
>>stability/passivity issues. I do not believe the S element checks
>>and/or corrects these issues. Most of the available s-parameter to
>>n-port model tools available have passivity enforcement capability
>>such that the synthesized n-port model is guaranteed passive. Some of
>>the tools also have the capability of regenerating a passivity
>>enforced set of s-parameters from the original input data set. This is
>>
>>
>
>
>
>>accomplished by "nudging" the problematic parameters until passivity
>>is achieved. In most cases the response of the resulting data set is
>>acceptably close to the original (but not passive) data set.
>>
>>
>>
>>-Ray
>>
>>
>>
>>
>>
>>Scott McMorrow wrote:
>>
>>
>>
>>
>>
>>>Ray,
>>>
>>>
>>>The other reason for using these other tools is speed. For example,
>>>
>>>
>>>after conversion of a Xilinx differential s-parameter model to a
>>>
>>>
>>>Laplace pole-zero model, I typically see a 20X speed up in performance
>>>
>>>
>>>when compared to the Spice s-element simluations. If you are doing
>>>
>>>
>>>only one simulation, then the translation time dominates. But if you
>>>
>>>
>>>are doing multiple trace length, connector type, backplane sweeps in
>>>
>>>
>>>simulation, then the performance advantages of the Laplace pole-zero
>>>
>>>
>>>model is significant, with no decrease in accuracy.
>>>
>>>
>>>scott
>>>
>>>
>>
>>
>>--
>>
>>Raymond Anderson
>>
>>Senior Signal Integrity Staff Engineer
>>
>>Product Technology Dept.
>>
>>Package Engineering Group
>>
>>Xilinx Inc.
>>
>>
>>
>>
>>
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