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What-If tools for everyone

Posted: 16 Mar 2006 ?? ?Print Version ?Bookmark and Share

Keywords:richard goering? PCBSI analysis tools? design software? AS/SIST tool suite? PCB model generator?

As a manager running AMP Inc.'s SI consulting business, Stan Harris was surprised by the high prices of commercial PCBSI analysis tools. Today, Harris is CEO of startup What-If Design Software LLC, which is rolling out its AS/SIST tool suite over the Internet for $695.

AS/SIST is billed as a comprehensive tool set that includes a PCB model generator, IBIS model translator, interconnect-system editor, spice simulator, waveform analyzer, pulse-train generator and eye-diagram analyzer. It aims to provide an iterative, what-if analysis that engineers can run before PCB layout begins.

Keeping its costs down by using the Internet for sales and support, the company is able to offer a low price tag for capabilities that might cost thousands of dollars elsewhere, Harris said. "Our approach is to establish a market for highly affordable, high-quality SI simulation software that average engineers will use as a tool during the design process," Harris said. "We like to think of AS/SIST as everyone's tool."

Harris said he helped found What-If Design Software after taking an early retirement from AMP, where he ran the SI consulting unit and convinced AMP to go into the software business before Tyco International took over the company.

Harris said that What-If was able to hire "world-class individuals" to develop key parts of the AS/SIST software, including the Spice engine, 2D field solver and schematic-capture capability.

While there's a huge potential market for AS/SIST, there are also some challenges, Harris noted. One, perhaps surprisingly, is the low price. "We have to overcome the 'you get what you pay for' attitude," Harris said. "People look at $695 for industrial-grade software and say it can't be very goodbut in fact, it's high-quality stuff."

AS/SIST doesn't have all the features of high-priced SI packages. It doesn't offer interfaces to PCB layout tools, which are costly to develop, Harris said. It doesn't provide a 3D field solver. On the other hand, it allows for rapid "what-if" analyses that can be run by engineers without extensive SI knowledge. Harris said the software has been validated against 2.5Gbps differential serial-data-rate data paths and 15ps rise time systems. It doesn't place limits on board size and can run a multiboard analysis, given connector models.

To use AS/SIST, designers create a board cross-section with a stackup editor. A sub-stackup editor lets users specify ground planes, dielectric layers, conductors and signal-path elements. The tool's PCB model generator then uses a 2D field solver to create a resistance, inductance, capacitance and conductance model of the design.

The user provides driver and receiver models in IBIS format. AS/SIST has an IBIS model generator that can convert the models into Spice-compatible subcircuits. The AS/SIST interconnect-system editor lets users schematically capture all models, subcircuits, discrete components, measurement points and parameters necessary for Spice circuit generation. A topology checker verifies connectivity before a Spice circuit is generated.

Users then run the AS/SIST Spice simulator, which has been enhanced with extensions that permit modeling of multiconductor transmission lines with frequency dependencies. Results are provided in a waveform viewer that, said Harris, appears much like an oscilloscope. The viewer helps users pinpoint such problems as crosstalk, noise, overshoot and undershoot. If a problem is found, the user can generate a new PCB model and run the simulation.

AS/SIST also provides a pulse-train generator that can provide long, contiguous data sequences, and uses waveform shaping to accentuate failure modes or model system performance. It offers edge-parameter shaping, differential-pulse generation, jitter injection, arbitrary sequences and piecewise-linear voltage sources. An eye-diagram analyzer helps users interpret the results.

Finally, a utility called AS/SIST Bridge provides routines that allow users to transfer and view data in Matlab. This opens the door to a more extensive mathematical analysis.

While some SI packages are used after layout, AS/SIST is best used before PCB layout, Harris said. "It actually tells you how to lay the board out."

- Richard Goering
EE Times

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