Circuit Simulation - the current state of play

Summary: In the handful of articles published to date on this site on the subject of circuit simulation, we've visited - briefly, at least - each of the three generations of circuit simulation stretching from the early 1970s to today. Nassda bought HSIM to market in 2001, and while there's been undoubted evolution in circuit simulation during the last few years, there's still significant opportunity for innovation to advance the state of the art still further. Before we look at where these trail-blazing advances will come, let's just take a moment to review the current state of play in the circuit simulation market.

In the handful of articles published to date on this site on the subject of circuit simulation, we’ve visited - briefly, at least - the following:

Nassda bought HSIM to market in 2001, and while there’s been undoubted evolution in circuit simulation during the last few years, there’s still significant opportunity for innovation to advance the state of the art still further. Before we look at where these trail-blazing advances will come, let’s just take a moment to review the current state of play in the circuit simulation market.

“Regular” SPICE
We’ve already seen that a more modern implementation of the well-proven circuit simulation algorithms can result in a leaner and cleaner product. Cadence’s SPECTRE had for a while a significant performance and capacity advantage over HSPICE; however, these advantages are rarely sustainable in the long term, and HSPICE has already clawed back much, if not all, of the ground it had lost. Berkeley Design Automation (not to be confused with UC Berkeley) offers another implementation, adding some new algorithms that afford faster DC convergence and speed transient simulation.

You can change your “regular” SPICE simulator on a whim, of course, but that’s an incredibly risky proposition. Validation, characterization and qualification of a new SPICE simulator is a several person-year project; netlist syntax and semantics, configuration and control options, models and the interaction with simulator core, even output formats must be rigorously and exhaustively checked and compared. There are two other costs that are rarely considered beforehand, and which always bite hard.

Maintaining two copies of models, libraries, etc, for the period of transition is a grotesquely under-estimated cost. For a fairly lengthy duration you’ll be developing and qualifying components for two simulators, striving for compatibility between the two.
Your current simulator has bugs. Many bugs. Some of them you even know about and have long-established workarounds to deal with them. Your newer simulator also has bugs. Probably more of them, since it is less mature. Certainly different bugs. Identifying the common core capabilities that, bug free, work identically across the two simulators is hard, and may reduce the subset of capabilities to less than a designer needs. Incompatibilities result, and resolving these differences during design diverts scarce and precious resources from the critical job in hand.

For these reasons, SPICE is a very “sticky” tool. Once in broad use, replacing it - and all the infrastructure that’s been set up to feed the beast - is far from trivial. I’m not saying never change your simulator, or never give one of the newer simulators a chance. Just be careful in how you move from a successful evaluation to a broad deployment, and consider deeply all the implications and the ramifications before you negotiate that VPA.

Fast-SPICE
There’s plenty going on in the Fast-SPICE world as well. Synopsys may have the vast majority of this market sewn up, and be hoping that the XA option (an HSPICE solver engine bolted onto - or should that be into?) their Fast-SPICE offerings will defend against some of the more outlandish (and somewhat specious) claims from some competitors. There are - well, were - a few plucky little startups licking their lips at this opportunity, but Mentor has picked up ADiT and Magma has picked up ACAD, and to be frank their success as standalone enterprises hadn’t been stellar. Maybe with a bigger organization behind them things will be different. Infinisim remains in stealth mode at the time of writing, and it’s been a few years, so expect something from them soon.

Recommended and reference reading

The SPICE Book, by Andrei Vladimirescu

Inside Spice: Overcoming the Obstacles of Circuit Simulation, by Ron Kielkowski

Electronic Circuit & System Simulation Methods, by Larry Pillagi

Circuit Simulation Methods and Algorithms, by Jan Ogrodzki

Computer Methods for Circuit Analysis and Design, by Jirí Vlach