Hi Scott, Thanks for your reply. I would not discuss the silicon model related issues, this is not my area. Just a short note about passivity: * the user is simulating pure passive interconnect. (a good application of your software for passive characterizations. There is no requirement that the interconnect model is passive. It can be active and non-reciprocal. The only requirement is that the model is linear and stationary, i.e. everything described as a touchstone. BTW, ELDO supports slightly extended touchstone, where you can define normalizing impedance individually for each port. Useful feature when we need to put interconnect and power distribution models together. Just a short question. 1.) At least one 3rd party solution using Hspice recursive convolution is extremely fast. Do you mean that it is HSPICE that performs recursive convolution? Regards, Vladimir -----Original Message----- From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx] Sent: Thursday, March 17, 2005 9:18 AM To: Dmitriev-Zdorov, Vladimir Cc: ray.anderson@xxxxxxxxxx; silist Subject: 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 <mailto: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. 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