But sometimes God likes to be a practical joker. Once you're around 0.18 micron, things like noise, IR drop, crosstalk and other SI issues can haunt you. And it turns out that the only way you can accurately simulate these effects is (you guessed it) through painful, slow transistor-level Spice decks. Ugh.

Thank God, for the near-Spice guys. If you're willing to be 1 percent to 5 percent off from a true Spice sim, the near-Spice guys will give you a 100x speed-up. Epic pretty much owned this niche throughout the '90s. They were the "hot technology find" of DAC '94. Synopsys acquired Epic in 1997 for $440 million. Most of the original Epic team left Synopsys within two years.

Now, there's a new near-Spice company, Nassda, that's trying to steal this niche from Synopsys Epic. "The Epic tools are getting pretty old when run against new designs," wrote John Szetela of AMD. "Nassda looks very good if you just want a super Spice."

"We looked at HSIM by Nassda, and to gain any significant speed advantage on a PLL circuit, we had to sacrifice so much accuracy that it was useless," reported Todd Moyer of Pixelworks. "We went with TimeMill by Synopsys, even though it was harder to use."

"We have been using the Nassda HSIM simulator, and it works better than PowerMill," wrote Michael Fliesler of AMD. "It uses the Spice deck directly. It doesn't require fiddling with a config file each time to run different simulations, and it seems to run 3x or more faster. We like it!"

"Nassda's HSIM is still the high-capacity circuit simulator to beat. Their tool is an absolute requirement when designing with big on-chip memories," said Mike Carter of Mosaid. "Synopsys' NanoSim is also attractive because of its integration with VCS. There's room for both tools in companies like ours, and we own both."

The irony here is twofold. First, no matter what, after all these years you're still going to be doing Spice or near-Spice runs. Second, Nassda is mostly ex-Epic employees. So it'll even be the same people selling you the software to do these near-Spice runs. That is, on two levels, the more things change, the more they stay the same.

John Cooley runs the E-mail Synopsys Users Group (ESNUG), is a Contract ASIC Designer and loves hearing from engineers at "jcooley@world.std.com" or (508) 429-4357.