( ESNUG 412 Item 13 ) ------------------------------------------- [05/22/03]
Subject: ( SNUG 03 #22 ) NanoSim, Nassda HSIM, Avanti HSPICE, Spectre, Eldo
> I've only used NanoSim & Mentor MachTA. MachTA has gotten better but I
> think that NanoSim seems more polished. As a circuit designer, I usually
> need more accuracy than speed & NanoSim has a way of designating accuracy
> but still speeds up the other parts of top level simulations that makes it
> very useful. Avanti HSPICE and Cadence Spectre seem to have similar
> accuracy and usually have results that correspond well. Spectre has
> issues with accepting other inputs like SPICE netlists. Mentor Eldo does
> not correspond as well and isn't used as much due to accuracy questions.
>
> The Synopsys EPIC RailMill tool is hard to run. It needs an expert user
> to get any results that are useful. Cadence Analog Artist doesn't seem to
> be easy to script for repeatable characterizations.
>
> - Amanda Reddy
> Micron
From: Greg Berger <greg.berger=engineer group=primarion thought lawn>
Hi, John,
We're presently using Nassda's HSIM (v2.0) for full-chip verification on
mixed-signal designs. All in all, we are quite pleased with Nassda's HSIM.
Using HSIM has allowed us to implement a true top-level simulation approach
for most of our mixed signal applications. However, anyone interested in
this type of tool should test both NanoSim and HSIM on their own data
though. The specifics of your foundries & circuits could swing either way.
Previously we had used Mentor's Mach-TA and Eldo-Mach (which is Eldo with a
Mach module for speeding up CMOS simulation). Before buying HSIM, we did
evaluations of NanoSim vs. HSIM vs. Mach. As we have more than one design
flow, we used both Eldo and Spectre as the benchmark to compare against,
depending on the foundry and technology of interest. We found that there
were many cases in the CMOS world where we just couldn't get the right
answer using Mach-TA. Until very recently, any low or zero Vt devices
wouldn't work at all. We couldn't get our PLL circuits to lock, despite
help from the AEs. We had to perform all of the top-level SPICE simulations
by pre-locking the PLL output. Mach is table based for speed, but this
limits the level of accuracy for the model. Mach is pretty much able to
simulate Avanti HSPICE or Eldo formatted netlists, but not Spectre native
format. In a Cadence environment, you have to go through a convoluted
path to bring up Eldo (and thus Eldo-Mach) in the Analog Artist environment.
When we started looking at NanoSim and HSIM, both didn't run the Eldo
netlists well but did not support Spectre netlists correctly. Both Nassda
and Synopsys have really been pushing on this though and have full Spectre
netlist support now. NanoSim converged on the CMOS PLL circuits very
quickly. However, we had to slow down the simulation to increase the
accuracy, in order to get the right answer. HSIM was slightly slower than
NanoSim, but converged on the answer we expected quite rapidly. Either
simulator can be used quite effectively for CMOS circuits in an HSPICE or
Eldo environment. The clincher for us to go to Nassda HSIM was that we got
excellent speed up on SiGe BiCMOS simulations in HSIM, including the bipolar
devices. We just couldn't get the right answer in NanoSim for both Bipolar
and CMOS ADCs. There are still some cases where neither HSIM nor NanoSim
can match the accuracy of Spectre or Eldo though, and considering the cost
of large-scale simulators, they won't be replacing Spectre/Eldo/HSPICE any
time soon.
In terms of features, both HSIM and NanoSim had around the same support for
Verilog-A. NanoSim does have the benefit of supporting a co-simulation
environment with VCS. Hopefully HSIM will have a similar capability soon.
As for Cadence-Celestry, I know of no one who has actually gotten a look at
Ultra-Sim. It just isn't playing in the big leagues right now.
Avanti-HSPICE (Synopsys) vs. Cadence Spectre vs. Mentor Eldo:
HSPICE is the Dracula of circuit simulation. It's a "standard" waiting to
be replaced. We don't use it any more. Pretty much anything you can do (of
value) in HSPICE can be done better in Eldo. Eldo out-converges both HSPICE
and Spectre and can run larger circuits in general. If you are primarily in
a Cadence environment though, stick with Spectre. You could glue Eldo in
just like you can glue in HSPICE or HSIM or NanoSim, but there isn't much
value added in doing so. If you design in Mentor's front-end go with Eldo
though. The big kicker here is to make sure your foundry supports your
simulator. It's a pain to convert between formats due to differences in how
the standard models are interpreted. The offshore fabs can support Spectre,
Eldo, or HSPICE model formats directly, albeit poorly in many cases.
However, smaller fabs as well as large American fabs tend to have more
robust full custom design kits that are centered around the Cadence tools.
We are starting to see less foundry supplied design kits with HSPICE support
(although more than we see with Eldo support). All of the main spice type
simulators don't seem to have much innovation any more, and they all pretty
much can do what you need for circuit of up to a few thousand devices.
In general, for full custom design a foundry has to support the Cadence
framework. We've tried to go with alternates for full-custom, but it just
isn't worth it as you are pretty much on your own. There are better tools
out there for full custom, but Cadence has far better integration.
- Greg Berger
Primarion, Inc. Tempe, AZ
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