Synthesis tool enables mixed-signal core design

Synthesis tool enables mixed-signal core design
By Stephan Ohr, EE Times
November 15, 1999 (5:32 p.m. EST)
URL: http://www.eetimes.com/story/OEG19991115S0007

SCOTTS VALLEY, Calif. — Antrim Design Systems Inc. promises to bring mixed-signal block design into the digital ASIC design flow this week when it announces Antrim-MSS, billed as the first commercial tool set for synthesizing mixed-signal ICs. Antrim says the tool set will enable the rapid creation of mixed-signal intellectual property (IP).

Providing an analog synthesis tool is a step forward in the automation of analog design-a process that may take the next five years, said Gary Smith, senior EDA industry analyst at Dataquest. "Once you have a 'flow' that automates analog design, the analog world will explode. Antrim understands the market is big-once it all gets done," said Smith.

Getting it all done will require a design flow for analog that encompasses synthesis, placement and test, Smith said. "There are a number of tools that perform analog and mixed-signal simulation — that look at a circuit to say, 'Yeah, it works.' Then wh at do you do?"

Whereas RTL synthesis is independent of the fabrication process, the performance of analog and mixed-signal ICs is highly dependent on process variations. Any EDA tool that proposes to synthesize analog and mixed-signal circuits — and Antrim's tool has been anticipated for months — is thus seen as a breakthrough.

The foundation of Antrim's synthesis technology is a behavioral-model library that includes characterization data drawn from actual silicon. In operation, the Antrim-MSS compiler works in combination with the Antrim-A/MS simulator and Antrim-ACT model characterization tool. It examines circuit topol- ogies and culls usable silicon-based models from a library of working parts.

The tool thus enables the capture and reuse of an expert analog designer's knowledge for the creation of IP. Antrim believes the methodology will reduce the design cycle for a mixed-signal IC from months to weeks.

Indeed, Antrim's corporate mission keys on top-down analog and mixed-signal IC design. Founded in early 1997 with approximately $11 million from such sources as Brentwood Venture Capital, the company boasts a formidable roster of analog experts, including veterans of HSpice pioneer Meta-Software, PSpice pioneer Microsim and the Epic Design Technologies subsidiary of Synopsys. Analog tool developer Georges Gielen of the Catholic University of Leuven (Belgium) serves on Antrim's board. The company's previous offerings were in simulation, characterization and model development; the long-awaited new products support analog IP packaging and IP synthesis.

'The best vision'

"Antrim has the best vision of any of the companies I've talked to," said Smith. Most other analog EDA companies are concentrating on point solutions, such as process migration tools, he said; very few are focused on automating the entire design flow for analog and mixed-signal .

Analog circuit synthesis, as developed by researchers at Carnegie-Mellon University (Pittsburgh) and the University of Cincinnati, allows analog design to proceed top-down from a digital design language such as VHDL or Verilog.

But the actual creation of an analog IC depends on a tool that early EDA developers would have called a silicon compiler: In operation, the Carnegie-Mellon synthesis approach examines the topology of an analog circuit and searches a library of preexisting cells for devices that match that topology.

Recent university research efforts have concentrated on streamlining the search trees and harnessing multiple computers to the effort. But critics note that the approach takes many hours, even days, to compile even a simple op amp circuit.

Antrim improves on that method of building circuits by initiating a "guided search," said Mike Demler, the company's director of engineering. Analog and mixed-signal synthesis, like its digital counterpart, depends on a library of circ uit functions. "The big question is what to put in the library," said Demler.

It is important to create an optimized model to drive the compiler, and the Antrim compiler depends on a library of working circuits. "Why not keep the analog and mixed-signal knowledge you already possess?" Demler asks. "Don't ask the machine to design an op amp if a designer has already done that."

Antrim-MSS analyzes simulation output from Antrim-A/MS and characterization models. It then synthesizes new versions of an existing mixed-signal circuit. Thus, Antrim-MSS encourages the reuse of mixed-signal IP in new projects. The inability to reuse existing analog IP has been a key stumbling block in the automation of mixed-signal design, Demler said.

Like Carnegie-Mellon's synthesis system, the Antrim compiler uses an intelligent search engine. Unlike previous compilers, the Antrim search engine incorporates large-signal behaviors — such as min/max frequency and power consumption — that cannot be readily desc ribed with small-signal simulation techniques.

Go to the library

"The library is key," said Smith of Dataquest. He cited the early custom circuit libraries developed by AMI and LSI Logic as the foundation for developments in digital circuit synthesis. He believes analog circuit libraries will play the same role. "These days everybody's got a phase-locked loop, but what else? Until the library is established, we don't know if this [analog synthesis] is going to work," he said.

In operating the Antrim synthesizer tool, the user develops a "synthesis plan" — a top-level view of the circuit that sets performance expectations-to guide the synthesizer toward the desired end result, Demler said. Representing a "blueprint" for the synthesis of mixed-signal IP, it requires inputs from expert mixed-signal IC designers using MSS and ACT plan development tools.

The plan represents a programmed series of steps for circuit partitioning, model selection, sizing and optimization. Its design pa rameters are specifications that serve as optimization variables. The plan will also include steps for process retargeting.

The plan depends on a synthesis library, which includes Simulation models in Verilog-A/MS. Represented are library functions, parameterized to users' performance specifications; a model circuit with optimized performance; netlists of mixed-signal functions; and test harnesses and characterization plans for the completed circuit.

The synthesis tool set extracts and tweaks a new behavioral model from the synthesis library. It includes optimizers (a tool kit of algorithms for sizing of design parameters), the Antrim-AMS simulator (for trying out sized netlists) and Antrim-ACT (for test harnesses and circuit characterization). The Antrim-MSS Command Interpreter, also in the tool set, is based on extensions to the Perl scripting language. The command interpreter executes the synthesis plan, building a circuit.

Because it depends on the personal input of experts, synthesis is far from a pushbutton operation. But where working models can be culled from an existing library, much of the manual labor involved in IP creation can be eliminated. The most difficult part is keeping accurate models in the library. While Perl is used as the command and interface language, Verilog-AMS is used for modeling; indeed, this is among the first commercial implementations of Verilog-A/MS.

"A good designer will pick this [model development language] up in a short period of time," said Leslie Spruiell, Antrim's vice president of marketing. But a "starter library" with many basic functions in Verilog-A/MS will ship with the first release of the product, due in the first quarter, Spruiell said.

Dataquest's Smith is excited about Antrim's efforts, but he doesn't underestimate the work ahead for the company and the industry at large.

"Yes, we're going to automate analog design," he said, "but it'll be 2004 to 2006 before we get there."