[Ideas For Design]
Who Actually Designs Reference Designs?
These gems sure come in handy when you're sitting at your bench and scratching your head. But who came up with them in the first place?
It’s fair to say there are really two kinds of reference designs. One is developed by chip companies that want a permanent foothold in an original device manufacturer’s high-volume platform in a consumer market. The other is produced by a chip company’s Web-based or downloadable PC tool that lets ordinary bench engineers mix and match ICs, simulate circuits, and obtain bills-of-materials (BOMs) and sometimes actual circuit board reference designs.
When it comes to the latter, I always wondered if the chip company can really afford to wring all the possible design permutations out of its tools. Also, are those designs bulletproof? The answer turns out to be yes—within reason. More on that later.
Both kinds of reference design are worth looking at because they represent an inflection point in the way design engineering is evolving—as in where the jobs are. You can find exceptions, of course. But generally, for high-volume products, the elements that are designed in the United States come from chip companies and show up in the first kind of reference designs. Later, I’ll describe the other kinds of U.S. designs. What characterizes many of the companies that employ the engineers that develop them is that they buy through distributors. Their engineers use the second kind of reference designs.
WHY DO WE NEED HELP? Why create reference designs at all? Did schools stop teaching calculus? Did colleges drop too many basic semiconductor physics prerequisites? Let’s not go down that road. Without even looking at designers’ skill sets, as operating voltages on the circuits themselves have followed feature sizes, signal levels have fallen so low relative to noise. Frequencies and conversion rates also have edged up. And, yes, those old analog engineers have retired. Today, there is a need for reference designs of both kinds.
In the first kind, the chip company creates a complete subsystem, fine-tuned on the basis of its parts, in the hopes that its specs, along with its executives’ relationships with the customer established on many golf courses over many years, along with its sales force’s pencil-whipping of pricing over the duration of the contract, will beat out the reference design created by its competitor. In that case, it’s a good bet that the design has been thoroughly wrung out in the lab.
What about the second kind of reference design? The thought occurred to me when I was interviewing Linear Technology’s Bob Dobkin for another story in this issue, collecting his reminiscences about Ideas for Design he’d seen and contributed over the years. “What IFDs don’t you like?” I asked. “Ones that don’t work!” he thundered! (Yes, people do send us “dry-labbed” IFDs. And no, we don’t actually breadboard them all ourselves. Perhaps we need a “Caveat Lector” statement.)
So that was on my mind when National Semiconductor wanted to show me a new extension of its Webench Tools (see the figure). There are versions of Webench for op amps, audio amps, data converters, power supplies, filters, and more. This new version deals with matching amplifiers and data converters to sensors. (To find the Webench Sensor Designer tool, go to www.national.com/sensors.)
This is a classic instance of the second kind of reference design environment. In industrial applications, there’s pressure and temperature sensing, optical measurements, HVAC control, gas/chemical monitoring, valve positioning weigh scales, flow sensing, and so forth. Then there’s medical applications in the hospital and for patients when they are out of the hospital.
The tool matches specific bridge pressure sensors, photodetector sensors, and thermocouple sensors with appropriate National op amps and compatible 8-, 10-, 12-, 14-, and 16-bit analog-todigital converters (ADCs). The sensors are all the most popular devices that National’s applications engineers were familiar with from their experience with customers.
To do this right, you need more than a few basic canned circuits and Spice models. There are a couple of ways to configure a bridge measurement signal path—it’s an accuracy/cost tradeoff—and you’d make different amplifier and ADC selections depending on which you chose. Then there are 12 different ways to configure the signal path for thermocouple circuits!
The Webench sensor tool will rapidly do these designs, including excitation and power supply, in the low- to mid-volume industrial/medical applications space. It also will provide circuit analyses, BOMs, and (through the distributor) a complete reference design for a few hundred dollars.
“So,” I asked Howard Joseph, the guy at National who directed the designers and apps engineers that created this instance of Webench, “Who designs the reference designs—specifically, the boards? Is there an EDA tool that just churns them out, or is there a lab somewhere where people make measurements and try to break them?”
The reassuring answer was that it’s the latter. No dry-labbing. How can National afford to do that? It’s the disti thing. Aggregated, all of National’s smaller customers are tremendously important. Through the distributor network, this sort of effort is supported. At National, and I am sure at other chip companies, even the onesie-twosie reference boards are getting significant personal attention.
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