[Ideas For Design]
A Look Back At 40 Years Of Ideas For Design
Though many facets of design execution have changed significantly over time, numerous core ideas for design remain timeless.
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.
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