MOUNTAIN VIEW, Calif. Synopsys Inc. this week will roll out what it calls the first tool to combine static-timing and crosstalk-analysis. PrimeTime-Signal Integrity, an add-on for the company's widely used PrimeTime static-timing analyzer, addresses a problem that's become increasingly severe for very deep-submicron designs, but has received relatively little tool support thus far.
Since crosstalk is calculated after routing, PrimeTime-SI is aimed at systems houses that use customer-owned tooling (COT), or at ASIC or semiconductor manufacturers. But the information gleaned from PrimeTime-SI can be used throughout the design flow, and brought to front-end designers as individual blocks are placed and routed, Synopsys said.
At 0.18 micron and below, signal-integrity issues like crosstalk and voltage drop are starting to affect tapeouts, said Rajiv Maheshwary, director of static-timing analysis at Synopsys (Mountain View, Calif.). "Signal-integrity closure is becoming the next big issue that people will look at," he said.
Maheshwary noted that Synopsys' tool development approach is to build an analysis foundation first, and then move on to implementation. That means crosstalk-aware synthesis is coming next. "You can expect that in the very near term, Physical Compiler Synopsys' synthesis and placement tool will evolve to take on signal-integrity effects for prevention and repair," he said.
Wire-to-wire capacitance has a profound impact on delays at 0.18 micron and below, but Maheshwary said chip designers today aren't doing much about it. "What people are using today, if at all, has been Spice," Maheshwary said.
Synopsys decided a standalone crosstalk analyzer was the wrong way to go, he said. "A standalone tool doesn't work because of long run-times, complex flows and the requirement of expertise that ASIC designers don't really have," he said. "By having an integrated solution, we can enable crosstalk analysis throughout the design flow."
No special expertise is needed to use the tool, Maheshwary said. "What we've done with PrimeTime-SI is extend a couple of PrimeTime commands with a couple of attributes, and that's it. The cost of adoption will be very low."
Synopsys worked with STMicroelectronics to develop PrimeTime-SI, leveraging ST's experience and some algorithmic techniques.
The input to PrimeTime-SI is a Standard Parasitic Delay Format (SPEF) file along with a listing of coupling capacitors, which is derived from a post-route resistance-capacitance extraction. Maheshwary noted that the add-on uses the same constraints, libraries, scripts and commands as PrimeTime. There are two additional commands for PrimeTime-SI, as well as some user control options.
The output consists of reports that show the signal-timing deviation, in terms of speedup or slowdown, of nets due to crosstalk. There's also a graphical debugging environment that depicts "victim" and "aggressor" nets. PrimeTime-SI produces an incremental Standard Delay Format (SDF) file that takes crosstalk effects into account.
Synopsys said that PrimeTime-SI runs more quickly than other crosstalk-analysis techniques. In one Synopsys benchmark, a 1.3 million-gate design with 23,000 top-level coupled nets, and up to 2,500 aggressors per net, ran in five hours on a 400-MHz SparcOS5 workstation. Actual run-time speeds, Maheshwary said, are highly design dependent. As for accuracy, Maheshwary said that customers are seeing results within 5 to 10 percent of Spice.
In a posting that appeared in the recent Synopsys Users Group (SNUG) report, a designer from Cisco Systems complained that Synopsys' approach to crosstalk will force a move away from SDF files. "We will have to move to something like SPEF files and depend on PrimeTime models to calculate the timing," the designer wrote.
That's basically true, said Maheshwary. "To get an accurate delay calculation requires parasitic data. SDF is no longer cutting it," he said. "As customers start doing more COT-style designs, absolutely, SPEF is what people will be using."
Maheshwary said Synopsys will offer other PrimeTime add-ons in the future, covering problems such as noise and voltage drop. But crosstalk is the "biggest pain we see" and thus the highest priority, he said.
PrimeTime-SI will be available in June as an add-on to PrimeTime. Pricing for a one-year TSL license starts at $34,000.