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The True Value of Virtual Test Software Virtual testing of mixed-signal designs requires an initial investment of time and money, but down the line it can pay off in big time-to-volume dividends. by Craig Siegel

In traditional mixed-signal IC development, the test department must wait for silicon before it can begin developing functional tests. This cumbersome serial design-then-test process, though, is falling under scrutiny from semiconductor companies that develop high-volume commercial ICs.

The demand for mixed-signal ICs is increasing. The number of mixed-signal chips needed for multimedia applications alone is expected to grow from 45 million units in 1996 to 229 million units by 2001. At the same time, product shelf life is shrinking from years to months and long development cycles can't be tolerated. So what can semiconductor companies do to cut development time and still maintain device quality?

One answer is virtual test (otherwise known as virtual prototyping or test simulation). As soon as a preliminary device design is completed, engineers can use a behavioral simulation model of the device, along with a model of the complete test environment, to start functional test development without waiting for silicon. That method can shorten the overall development cycle by weeks or months, thereby reducing time to volume. That can be critical where commercial ICs are concerned, for their profit comes early, before the price curve declines.

But what's the cost of virtual test and what value do you receive from your investment? The cost of implementing virtual test can, at first, seem prohibitive. First, you need all the software pieces: an ATE software emulator, simulation models of the test instrumentation and interface connections, and a behavioral-level mixed-signal simulator. Most semiconductor companies use some simulation in their mixed-signal design process, so they may have most--if not all--of the necessary software. If not, they must purchase what they need.

Since virtual test makes use of high-level, behavioral simulation models in conjunction with top-down design techniques, implementing top-down design can also add cost. Many companies that produce high-volume commercial ICs have already implemented top-down design for complex devices or they plan to. But if you don't use the techniques, adopting the methodology will require some initial outlay of time and manpower. At a minimum, design and test engineers must learn how to create high-level simulation models of devices in development.

Finally comes the cost of training personnel to use the simulation tools. Test engineers must have proper training in simulation and modeling to make the process work effectively.

So before implementing virtual test, examine the true cost--it's more than just purchasing software. Don't fail, though, to examine the value and benefits. Market demands are causing development windows to shrink, and devices are becoming more complex--putting increasing pressure on both design and test. Virtual test can help designers meet or even exceed objectives and add to the bottom line.

For one, giving test engineers a head start with virtual test can cut four to six weeks or more off of total development time, allowing the company to ship early, when the price is high. One semiconductor manufacturer estimates that cutting just four weeks off the development cycle can be worth hundreds of thousands of dollars.

Virtual test yields time savings not just because testing is under way by the time silicon is ready. Providing the design to test engineers before it's finalized allows them to catch design errors early on, alerting designers before spinning silicon. That precaution saves direct money as well as time.

Consider also that tester time is very expensive. Using virtual test to start development of functional tests off-line reduces the time on the tester needed for development and maximizes the time available for its true purpose: functional testing.

Clearly, the benefits far outweigh the costs. As competition for the mixed-signal market heats up, companies will need to use all the tools at their disposal. So instead of asking yourself if you can afford to implement virtual test, perhaps the more important question is this: Can you afford not to?

Craig Siegel is marketing program manager for Analogy, Inc. in Beaverton, Ore. He's currently responsible for the company's simulation-for-test products and has 11 years' experience with simulation software engineering and marketing.

Editor's note: For more on virtual test, see "A Virtual Test Revolution," p. 32.

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integrated system design  December 1998