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Thinking outside the data sheet

In Critical Link’s inaugural blog post, way back in February 2013, our topic was “Is DSP Dead?” (By the way, the answer was and is, “No, it isn’t.”) In that post, we gave a shout out to Gene Frantz, the father of DSP, on the occasion of his retirement from TI.  While Gene retired from TI, he didn’t retire-retire. I met with him recently at his new company, Octavo Systems, and he mentioned a paper he had written, along with Chau Mai and Ivan Garcia, nearly a decade ago. Published by and still available from TI, Push Performance and Power Beyond the Data Sheet addressed the “need to find new ways to satisfy our continuing demand for more performance and to achieve that performance at a lower power level.”

Three years later, EE Times revisited the paper in a two part article.  Part One gives a quick overview of the paper, noting that it covers how developers can boldly go beyond the specifications that are promised in an IC data sheet to get the performance and power you need for your products. In Part Two, Gene and Ivan expand on their original work.

With the caveat that, once you do go beyond what’s vouched for in the IC manufacturer’s spec, the warranty no longer applies, Gene and Ivan go into quite a bit of detail on how to go about things.

Using Gene’s baby, a DSP, as their IC example, the key points covered include:

  • Clock speed:  Look at the fine points of those specs to figure out where there’s some play with respect to your specific application. The example they use is that if a “device is rated to run for a case temperature as high as 85ºC at, say, 1.2 V, the manufacturer must rate this device to run at 360 MHz at most.” But if you app doesn’t need to work at temps above 25ºC, you can boost the clockspeed to nearly 500 MHz.
  • Tweaking the performance, power budget:  While you always need to account for the worst case scenario, i.e., max power consumption, Gene and Ivan suggest playing with other conditions. Rather than design for worst case across all conditions, there may be ways you can juggle things (e.g., going with a lower voltage requirement) to meet your needs without blowing your power budget.
  • Performance vs. reliability: Exercise judgement and caution here, and seriously manage temperature and operating voltage limits so that you won’t be damaging the device. That said, there may be tradeoffs you want to take, upping the performance while accepting a failure rate that you can live with.

Gene and Ivan also cover design considerations, and end by emphasizing the importance of assessing the risk associated with each tradeoff you make.

That said,  sometimes to hit the requirements you need, you just have to think outside the data sheet.