Nascentric intros Fast Spice simulator for digital, AMS, analog designs

By Michael Santarini, Senior Editor -- 2/5/2008

EDA start-up Nascentric Inc has introduced a new Fast SPICE simulation tool for analog, mixed-signal, and custom digital designs that claims true Spice accuracy while running 10x faster than other commercial Fast Spice simulators.

The company’s first Fast Spice tool, AuSim, was targeted at designers doing full custom digital designs (mainly memory and processor designs). But now the company has released a new tool that replaces AuSim called OmegaSim, which is suited for everything from custom digital to full blown analog design. Its president and CEO, Rahm Shastry, said the company named it OmegaSim because “Omega’s the last character in the Greek alphabet and OmegaSim is the last Fast Spice tool you’ll ever need.”

If Fast Spice is Greek to you, or you think Fast Spice seems to be oxymoronic, you are not alone. The EDA industry first started introducing Fast Spice tools about 10 years ago as an alternative to lethargic Spice simulators. Spice is traditionally the most accurate form of simulation in the EDA space, but it is extremely slow and for the most part is only suitable for relatively small circuits or small chunks of a large design.

Because digital designs -- especially custom digital ICs like memory or CPUs -- tend to be huge, Spice is very cumbersome to use. Likewise in mixed-signal designs, designers must simulate analog blocks with digital blocks. To do this, they need to connect Spice simulation with digital simulators (Verilog or VHDL simulators), but Spice slows the combined simulation to a crawl. So EDA companies came up with Fast Spice tools, which allow designers to simulate larger blocks many times faster than Spice. But in order to get that speed up, the tools had to compromise on accuracy a bit. Many Fast Spice tools let users adjust accuracy versus performance to suit given tasks. Still many argue that Fast Spice still isn’t fast enough.

Shastry said that’s where OmegaSim will step in. He said that OmegaSim is a superset of AuSim and expands the tools coverage to mixed signal and analog. “It offers the best of both worlds,” said Shastry. “It has the digital speed and the analog accuracy.”

Shastry noted the company has 10 patents in the digital Fast Spice domain and has extended those patents and concept to analog with OmegaSim.

Like AuSim, OmegaSim uses a patented current based Spice model and engine. Essentially, the tool quickly classifies particular elements in a design, groups them, and then assigns each group to a simulation engine that Nascentric optimized for a particular operation.

“Each of the engines is focused on what it does best,” said Shastry. “The transistor engine is pretty complex but we don’t need the same complexity for interconnect because interconnect is only RLC [resistance, inductance, capacitance]. That means the interconnect engine can be much simpler and interconnect can simulate really fast and accurately, the same goes for SRAM bit cells, which go to an SRAM engine.”

On top of that approach, OmegaSim’s engines are multi-threaded, which speeds up the simulation further.

Users can run OmegaSim in two modes: digital or analog. The digital mode has a submode for verification or analysis. In digital mode running on a single thread, the tool will run typically 10x faster than other commercial Fast Spice simulators, claimed Shastry. On a multithread platform, such as an Intel CoreDuo, the tool can run 2x faster. In digital verification mode, the tool will run between 2 to 4% accuracy of Spice, while in digital analysis mode, the tool will run anywhere from 2 to 1% accuracy of Spice.

“In analog mode we have the same accuracy as Spice, but are 10 to 15 times faster than analog other Fast Spice simulators,” said Shastry.

Shastry said the tool doesn’t do frequency domain analysis, thus it isn’t well suited for RF designs.

Nascentric licenses its tools under a unique thread-based licensing model. It costs $1,200 per thread per month (thread month) or $12,000 per thread per year (thread year) for the digital-only version. The company offers the mixed digital analog for an extra $500 per thread month or $5,000 thread year.

Shastry noted that Nascentric is doing pretty well despite a tough environment in which many of the larger EDA companies tend to throw in their Fast Spice tools for free in bundle deals. Shastry said that customers get what they pay for (or don’t pay for) in many cases. Nascentric, according to Shastry, has landed some big customers. Shastry wouldn’t name the company as user, but Intel Capital is a chief investor it Nascentric.

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