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XA offers better simulation accuracy

Posted: 01 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:XA simulation technology? Spice simulation accuracy?

Promising a new approach to fast SPICE simulation, Synopsys Inc. has introduced Discovery AMS 2007, a group of solutions that includes the XA simulation technology option for the NanoSim and HSim fast Spice simulators. The new release also promises tighter integration with the digital VCS verification simulator and a unified mixed-signal debugging environment.

Discovery AMS includes NanoSim, Synopsys' original fast Spice simulator; HSim, a fast Spice simulator that Synopsys acquired along with Nassda Corp.; HSPICE, a full Spice simulator; and VCS, a digital Verilog simulator. Discovery AMS is not a bundle; customers can pick the components they want. XA is an option for either HSim or NanoSim.

XA promises a new level of performance and accuracy for fast Spice simulation, along with user control over performance and accuracy through one of seven "modes." It also eliminates the setup and tuning requirements of today's fast Spice simulators, Synopsys said.

XA was built on top of a full Spice engine. Synopsys expects most of XA's usage to be in modes three to six. Here, said Ying, performance is about five times faster than typical fast Spice simulation and 50 times faster than Spice, with only a 1 percent loss in accuracy compared with full Spice.

According to a comparison by Synopsys, a switching regulator that took 24hrs to simulate in Spice and 4.1hrs in fast Spice ran in 48mins using XA. A charge pump that took 13hrs in Spice and four hours in fast Spice simulations ran in 3mins using XA.

A PLL that Spice couldn't handle ran in 24 days in fast Spice and 2.5 days in XA. These comparisons used modes four and five, Ying said.

Moreover, said Ying, traditional fast Spice requires setup commands and configuration files, none of which exist in XA. "You can get to within 1 percent of Spice accuracy almost effortlessly," he said. "You may be able to tune fast Spice to that level of accuracy, but it will take a lot of effort and a lot of commands."

XA is a full-fledged simulator, but Synopsys is not selling it as a standalone product. That's because it doesn't have all the capabilities designers have come to expect from fast Spice products, Ying said. For example, it lacks the IR drop and electromagnetic simulation capabilities of HSim and the cosimulation capabilities of NanoSim.

XA performs some simulations much faster than Spice.

XA is also not a replacement for HSpice. XA runs only in the time domain, Ying noted. XA uses the HSpice model evaluation engine, however, and runs HSpice netlists, he said.

Two technologiespartitioning and multirate designgive XA an edge in fast Spice mode. Fast Spice simulators generally partition designs so they don't have to solve the matrix for the entire design. XA provides a "dynamic" partitioning approach that recognizes the mode of operation for the circuit and decides how to partition it on the fly.

Synopsys literature states that XA is particularly well-suited for non-ideal power supplies, PLL lock times and switched capacitor circuits. But despite its broad range of uses, "I wouldn't guarantee 50x performance across the board," Ying said.

Also with Discovery AMS 2007, HSim and NanoSim are more tightly integrated with VCS. Previously, said Ying, the integration was through the Verilog programming language interface. With the new release, it's a direct kernel-based integration, resulting in one process and one executable. The two advantages are performance and flexibility, Ying said.

Finally, while previous releases of Discovery AMS had separate analog and digital waveform displays, the new release has a single debugging environment so users don't have to switch back and forth.

Discovery AMS 2007.03 is available immediately. The NanoSim, HSim and XA options start at $75,000.

- Richard Goering
EE Times

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