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.