[SI-LIST] Re: HSPICE S-paramter questions
- From: "Pratt, Gary" <gary_pratt@xxxxxxxxxxx>
- To: <scott@xxxxxxxxxxxxx>, "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- Date: Thu, 17 Mar 2005 11:43:49 -0500
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. =20
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
=20
-----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. =20
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,
>
> =20
>
> So far you consider only two alternatives: using S-model based on=20
> 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=20
> simulation leads to convolution-based approach that is slow=20
> (super-linear by complexity) and often inaccurate. Possible trade-off=20
> between accuracy and performance normally is not successful.
>
> The equivalent n-port models (sub-circuits) produced by the=20
> third-party model tools are good from those points but they add a=20
> large amount of the circuit components (and sometimes internal nodes)=20
> 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),=20
> as any other circuits with LC elements or LAPLACE-type controlled=20
> circuits.
>
> When solving transient for a long enough with models that have sharp=20
> resonances, such errors become considerable and/or force using smaller
> step. Even worse, the step selection mechanism cannot correctly=20
> predict how much this error will accumulate over time.
>
> =20
>
> There is a simulator (ELDO) that utilizes a third solution, free from=20
> above limitations. In addition, it does not need third party=20
> conversion tools and makes everything by itself, including passivity=20
> enforcement. For re-use purpose, it generates the compact model in the
> intermediate format that is neither touchstone nor circuit. Such=20
> S-model does not generate convolution-specific error or LTE. On=20
> average, it is 5-7 times faster (per step) than the corresponding=20
> equivalent circuit.
>
> =20
>
> Example. Given the 158-port touchstone file of 214MB size (fully=20
> populated S-matrix) it took 5 minutes to convert it into such=20
> intermediate format (however 30 minutes if with passivity=20
> enforcement). Then, simulation with 10,000 output points takes 3=20
> minutes. The user should not care about conversion: if needed it is=20
> performed automatically on the initialization stage. The converted=20
> model is stored and made re-usable. During re-simulation, the=20
> converted model is loaded in seconds.
>
> With the equivalent circuit, built from the same converted model, it=20
> takes about 25 min for the simulator only to parse and check errors in
> the subcircuit, before any simulation starts. This time cannot be=20
> avoided if simulated repeatedly. Solution itself takes about 15
minutes.
>
> Convolution-based approach (also available in ELDO) fails on that=20
> model. Not because of poor implementation but due to inherent
problems.
>
> =20
>
> Vladimir
>
> =20
>
> =20
>
> -----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
>
> =20
>
> Scott-
>
> =20
>
> I agree with you completely regarding the speed issue. Another factor=20
> to consider is stability/passivity. S-parameters originating from=20
> measurements (and quite often from simulation/extraction) can exhibit=20
> stability/passivity issues. I do not believe the S element checks=20
> and/or corrects these issues. Most of the available s-parameter to=20
> n-port model tools available have passivity enforcement capability=20
> such that the synthesized n-port model is guaranteed passive. Some of=20
> the tools also have the capability of regenerating a passivity=20
> enforced set of s-parameters from the original input data set. This is
> accomplished by "nudging" the problematic parameters until passivity=20
> is achieved. In most cases the response of the resulting data set is=20
> acceptably close to the original (but not passive) data set.
>
> =20
>
> -Ray
>
> =20
>
> =20
>
> Scott McMorrow wrote:
>
> =20
>
>>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
>
>>=20
>
>>
>
>>=20
>
>>
>
> =20
>
> --
>
> Raymond Anderson
>
> Senior Signal Integrity Staff Engineer
>
> Product Technology Dept.
>
> Package Engineering Group
>
> Xilinx Inc.
>
> =20
>
> =20
>
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