DESIGN TOOLS: Analog analysis tool works with flow

Santa Cruz, Calif. — Startup Gradient Design Automation Inc. claimed an industry first last year with FireBolt, a 3-D thermal analysis tool for digital ICs. This week, the company will launch CircuitFire, which is said to be the first 3-D thermal analysis tool for analog and mixed-signal ICs that's integrated directly into the design flow.

CircuitFire builds a detailed thermal model and computes temperatures across a die, detecting possible circuit failures due to thermal gradients. It presents text reports and a visual 3-D floor plan, and back-annotates thermal data to Spice simulators. The tool incorporates package characteristics, ambient temperature and package-to-chip connections.

CircuitFire uses the same underlying engine as FireBolt, but is geared to smaller circuit sizes and offers integration with Spice simulators, said Rajit Chandra, Gradient president and chief executive officer. While FireBolt is still under evaluation, CircuitFire is ready to ship today and is in use at AMI Semiconductor Inc.

“Digital circuits are huge and complex, so it's not surprising that [FireBolt] is taking longer,” Chandra said. “Analog designers have been aware of temperature variations and thermal effects on circuits for a long time.”

However, the need for 3-D thermal analysis is no less acute in the analog world, Chandra said. “In circuit analysis, parametric failure is an even bigger concern than in digital design,” he said. “Even a 4° gradient across some circuit elements, such as bandgap reference circuits, can cause circuits to mal- function.”

Yet analog and mixed-signal applications can see gradients of 100°C in some applications, Chandra said, compared with 50° or less for digital. That's because high-powered transistors are often deployed to run circuits or trigger devices such as automobile airbags. Moreover, ambient temperature variations can be huge, he pointed out.

In addition to parametric failure, temperature gradients can cause reliability problems because of electromigration or bias temperature instability, he said. Finally, thermal gradients can increase leakage current “exponentially,” raising a severe problem for mobile applications, he said.

While FireBolt tackles large digital designs–handling up to 15 million instances, according to Gradient–CircuitFire is a device-level tool that can handle from 50,000 to 80,000 instances. Chandra noted that it can also analyze hierarchical designs and can work at a block, cell or transistor level.

Inputs to CircuitFire include a LEF, DEF or GDSII format layout file; technology data; package data; and power data from a circuit simulator. CircuitFire then annotates temperature changes back to the circuit simulator so it can modify its power estimates. CircuitFire outputs text reports showing device temperature, wire temperature and updated power. A visual floor plan with contours shows what's going on inside the die.

Accuracy is “very close,” Chandra said, coming within 1°C of measured data in one benchmark. CircuitFire can run a hierarchical design with 30,000 transistors, covering all metal layers, in a “matter of minutes,” he said.

CircuitFire today works with Cadence Design Systems physical design tools, as well as the Spectre simulator from Cadence and the Eldo simulator from Mentor Graphics. CircuitFire is available now starting at $75,000 per year.

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