After Electronic Design
asked me to contribute
something to this special
issue, all kinds of possibilities
ran through my
mind. After all, it had been
40 years since my first ED
article, which was itself an
Idea for Design (IFD), “Gated Amplifier Uses FET in
Feedback Loop,” in the Jan. 4, 1968 issue.
So, what’s an IFD? The snappy answer is that it’s
one of Electronic Design’s most popular editorial features.
But more germane is the fact that the IFD distills
the “what, why, and how” of an EE design challenge,
summarizing an example solution into a one- or
two-page writeup, often
ready to be applied just
as described. Typically,
they aren’t heavily theoretical,
though they are
often long on practicality.
So, what to do and
what to say became big
questions.
HITTING THE BOOKS
I began with a “stimulation
by observation,” a
review of my huge collection
of various IFD
tear sheets accumulated
over the years (not all
of which have been
adequately catalogued, I
hate to admit). In addition
to this IFD rat’s nest,
the review also included
more formal sources.
I had three of the four
published
400 Ideas for
Design
books (References
1-4). Then, I also found
the very first of this series online, via AbeBooks
(www.abebooks.com), and snapped up a copy. The
series began in 1961, and these four hardbound
books span four- to five-year periods from 1961 to
1979. Later on, there were smaller “Best of Issue”
IFD magazine supplements (References 5-7). All of
these are recommended reading, should you be able
to find them.
Should it matter how a design was done in the
1970s or 1980s, versus an approach today? Yes!
First, there is the adage of being ignorant of history’s
mistakes, thus condemning one to repeat them. But
what is so useful about a historical review of designs
lies in extracting the optimization and evolution
towards maturity.
Keep in mind that many of these published IFDs
are also what I call the “timeless” variety (see the
figure). The timelessness comes from the inclusion
of a basic principle that will generally continue to be
useful, even if the specific parts shown in its execution
might become obsolete.
For example, take families of op-amp precision
rectifiers, of which there are many IFD examples
over the years. Each time a newer, faster op amp
appears, another variant shows up. Computer programs
can also fall into the timeless category of IFD.
The mathematical routines will remain valid even if
executed within another host program. So, these IFD
principles can continue to be valuable, even though
exact design details may change.
THE IFD EVOLUTION
A strong impression that I came way with after
reviewing a couple of decades worth of IFDs is
how much (and how many) things have changed, in
terms of how designs are physically executed. This
wouldn’t always show up within an IFD, but it does
offer perspective on where we are and perhaps about
where we’re going. Today, we have evolved into
different ways of doing many engineering tasks and
using different parts to build our electronic assemblies.
A lot of this is good, but some of it is not.
For example, there’s greater use of computers and
advanced prototypes. We have much more powerful
computers to aid us in executing our designs faster
and with greater efficiency. But some engineers seem
to feel that a successful Spice run alone validates
a circuit design. In the long run, a well-executed
breadboard/prototype is the only real proof of circuit
design validity. The higher the frequency of operation,
the truer this becomes.
Fortunately, many IC vendors now routinely offer
evaluation boards that use high-frequency techniques
like ground planes, controlled transmission lines, and
low inductance bypassing, as well as surface-mount
(SMD) components and other factors. This really
does help control the undesired parasitics and speeds
the design cycle. Of course, another part of the design
process aided immensely by the more powerful computer
is the printed-circuit-board (PCB) design.
Additionally, there are more IC components, with
much broader capability. To take op amps as one
familiar point of reference, we’ve come from Bob
Widlar’s 1965 709 to a vast array of parts with
hundreds of megahertz of bandwidth and outputs of
a hundred milliamps today. Switched-mode video
amps make a gated amplifier no more complicated
than wiring up a logic control pin—or, from a general
functionality point, a wide array of parts that run
rail-rail (input and/or output) and feature low (or very
low) current consumption.
Yet considering all IC types, a radical revolution
in packaging has happened since the old TO-99 can
originals. For the most part, this broader availability
of packages is also good. In some cases, though, it
does impact performance.
For instance, low-power op amps are noisier and
have less bandwidth—a design fact of life. Another
con during the design cycle is that it complicates
breadboarding, since tiny SMD parts are extremely
difficult to handle manually. Yet this in itself is a
two-edged sword, as it tends to force the prototype
into a PCB layout, which is that much closer to the
end item—and thus more real-to-life.