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Simulators >> Circuit Simulators >> True (and fast) Spice simulation
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Message started by Godfrey on Oct 2^nd, 2005, 8:28am

Title: True (and fast) Spice simulation
Post by Godfrey on Oct 2^nd, 2005, 8:28am

Im simulating a large analog chip at present and getting a little weary of trying to get this running using a combination of models/HDL's. Even when it does start running, Im not comfortable that the results are meaningful due to the number of approximations and compromises I have to make. Simulating the pieces is fine, but combining these into an accurate system level simulation is driving me nuts.

I really need spice level simulation throughout. Anyone done an evaluation of true fast spice simulators?

By 'true' I mean that the simulation is accurate in both time and voltage/current axes. I see a lot of claims about tools such as HSIM, but these are a bit misleading since hierarchical tools such as this only appear to work well where there is significant repetition in the design. In large chips which are predominantly analogue, such tools really dont deliver.

I guess the holy grail of simulation would be full chip simulation at spice accuracy with short simulation times. Obviously CAD vendors have been chasing this goal for many years and maybe it will never happen, but which simulators are the closest to this ideal?

From press reports it sounds like Avanti's Star-SimXT is the first in line. Experiences on this subject anyone?

Title: Re: True (and fast) Spice simulation
Post by byang on Oct 2^nd, 2005, 12:10pm

Godfrey,

I have quite some experience with fast-Spice tools. Could you e-mail me at

baolin_yang@yahoo.com ?

I would like to discuss your need with you in private.

Best Regards,

Baolin

Title: Re: True (and fast) Spice simulation
Post by rf-design on Oct 2^nd, 2005, 3:28pm

Godfrey,

the feature of HSIM to simulate a number of parallel connected identical subcircuits only once and then divide the current by the number of instances is a small feature. This HSIM implementation is simply the replication of the simulation technique long time ago in practice to simulate memory circuits. The advantage is now that the netlist reader and matrix stamp engine doing the work now. Also if there are different initial states the reader handels that properly.

The other advantage of HSIM is that it support true hiearchical tolerance setting. So you can have circuit type depending settings. That improve the speed a little bit. If you use the same accuracy as spice for all node voltages and currents HSIM is slower than the industry standard. So comparing only the speed of the full chip simulation and cover all possible mailfunction (parametric, functional, missconnection, misinterpretation,...) you have to use many levels of simulation descriptions. At each level you can improve level of confidence. So describing that with tools or languages:

Matlab+Simulink+VerilogA+HSIM+Spectre

I share the view that also full chip spice is needed to verify special interaction effects. But the key is to minimize the number of these simulations and indication to run redesign loops through higher levels.

For future design with sticked CPU powers there is the need for parallel processing spice with multirate/multiresolution simulation. That does not exist in research either.

Title: Re: True (and fast) Spice simulation
Post by jbdavid on Oct 17^th, 2005, 1:46am

In my experience, it hard to beat the simplicitiy of using AMS-Designer from Cadence..
for each simulation you have a choice between Spectre and Ultrasim solvers for the transistor level part of this,
This is REALLY nice, as the SAME TESTBENCH can be used for the High level HDL sim, and one that puts LARGE blocks of circuits into ultra-sim..
I've also used the Accelerated MOS evaluation of the spectre solver and gotten significant speed ups that way. The spectre solver (in AMSD) also has (had?) a PMR option that allowed for the Multirate partitioning to be done, but I didn't have time to play much with that over the last couple of years..

When you couple the Ease of use, with the ease of licensing, (with an MMSIM license you get 6 tokens each equivalent to 1 spectre.. you need checkout only 1 for spectre, 2 for spectreRF, 3 (I think) for AMSD, 6, for Ultrasim, and 9 for AMS-Ultra ) so you can run spectre sims in parallel or AMS-Ultra sims with the same tokens..
Seems a lot more cost effective, at least for my designs, than buying spectre and another vendor's fast spice simulator..
Of course you need to be satisfied it will do the job you need it to.. Thats what an evaluation license is for..
Jonathan