原创 Learn about the engineering desk-to-bench ratio

In the second and last company I worked at - a company started by a lawyer, not an engineer - the desks were all in an office environment and the lab was some distance away. This induced a kind of occupational schizophrenia, so in time I moved to the spacious lab and rarely visited my desk. This had the added advantage that few were in the lab and interaction with others in the form of distractions was reduced.

At Tek, Paul was one of my fellow college-student friends who went to MIT during the school year. He spent what seemed like inordinate amounts of time thinking through a design plan before he ever started building it. For resistors with values that were broadly optimal, he would select them so that their color codes had pleasing color combinations when next to each other on the circuit-board. Yet for an undergrad student, he was rigorous. Tek would involve “summer students” in design work and although it was not expected that they would be as productive as full-time, fully-qualified engineers, productive work did ensue from them.

Remembering those early days, I always intended to write a book (and recently did; Transistor Amplifiers at www.innovatia.com) that assumes only pre-calculus mathematics yet develops s-domain circuit theory (bypassing the Laplace transform) so that zealous, rigorous high-school students can become engineers with high-school math. Jim Williams of Linear Technology Corp. took psychology in college and probably did not think in the s-domain. His thinking was experimentally-oriented and done at the bench. Some good engineers operate this way, but in the end, theoretical depth has advantages if it can be related to actual circuits. The best engineers have depth across the full spectrum, from desk to bench. A few of them, however, operate like Jim Williams did.

Some engineers think that with enough intuitive circuits understanding and insight, it is possible to bypass all that math and still achieve the substantial designs. They do this by developing keen qualitative insights to design based on what in math would be the polarity of derivatives. Change this resistor value a little, and the gain changes hugely, or not at all. With a qualitative database of knowledge, even measurement instruments can be designed. When I was still in my teens at Tek, one of the business-unit managers, Jerry Shannon, liked to help technicians struggling upward. He would go over to final test and calibration and take some of the better technicians into engineering. Some of them worked out passably, but there were times of excitement. Roger S. was one of them. He designed the TM500 FG502 10 MHz function generator. It went into pilot production, but it had problems with the sine shaper. In an intensive burst, he put 71 modifications into the design - a huge number for a product already sent to production. Jim G. was another technician, an older, even-keeled guy with more experience. He ran into trouble with the DM502 DMM in the usual place DMMs run into trouble: around zero-scale. I remember that the modifications, which were one or two - not 71 - were based on intuitive, qualitative reasoning, sufficiently in-depth to achieve a workable design. As I look back at Tek circuit diagrams from that era of the ‘60s and ‘70s, it is amazing that so much equipment others depended on for their own design work was designed with intuitively-placed patches and ad hoc modifications.

In the design groups at Tek that produced the highest-performance products, there were people with significant depth at both theory and practice. One that comes to mind is Barrie Gilbert, still going strong in his 70s at Analog Devices. Barrie is an IEEE fellow and has a good intuitive sense of circuitry at the bench. Yet if you read some of his IEEE papers, he has more theoretical depth than many engineers. The oscilloscope wideband vertical amplifier designers also fell into this category - people like Carl Battjes, Thor Hallen, Val Garutz, John Addis, Bob Ross, Art Metz and Jim Woo. And for the fastest ‘scopes, the time-base was also a challenge to which Bruce Hofer, later the analog founder of Audio Precision, Inc. brought penetratingly new circuit ideas, one of which I used for the time-base design of a (slower) portable ‘scope.

My desk/bench ratio has been increasing with time, and I am becoming more like Paul Magerl. It is easier to change a circuit in a computer file or on paper than on a prototype board, especially if the change is extensive. However, if you are a younger engineer, do not expect to be as proficient at this as you will be later if you keep learning electronics. A lower desk/bench ratio is expected of less experienced engineers. As you work with actual circuits, you encounter some of the subtleties that are deeper than you have descended to at present. These subtler, unexpected behaviors of circuits can at first be frustrating, even overwhelming, as though the gods are being fickle in capriciously tweaking the physical laws as you try to master them. But don’t give up; the physical universe has a rational and trustworthy underpinning. It all makes simple sense when the causes of unwanted behaviors are discovered. Persistence can turn a feeling of resignation into one of curiosity, in how the circuit could possibly behave differently than you really think it should. This leads to a hunt for causes in an exploratory frame of mind. It is a quest for discovery of false assumptions in thinking about the circuit. And this leads to fabulous new insights, one of the personal rewards we as engineers are privileged to experience.

The perplexities arising out of bench work are a driver for deeper study into electronics. Sometimes a sophomoric view of engineering can develop which arrests further progress in gaining proficiency. This is the attitude that familiarity is the same as understanding. (My “Seemingly Simple Circuits” series on the Planet Analog website is in part intended to dispel this obstructive mental habit.) Circuits that become familiar often - almost always - have deeper subtleties that are not obvious to the novice who does not know that they are even there. Do not assume that all the important concepts - even basic ones that have continual application - are covered in formal education. A graduate degree in E.E. is no guarantee that you’ve descended below SCUBA depth.

As years of improvement as an engineer occur, you reach a point where not much that is new comes along -- though this is never nothing! The more you think you’ve mastered electronics, the keener you are to find what you have missed. An engineer friend of mine who worked at Keithley on precision DMMs, Gary Bergstrom, sometimes ends his emails to me about technical matters with “What have I missed?” At this level of proficiency, the desk/bench ratio increases and maximizes productivity. It is quite satisfying to achieve the ability to design a complicated circuit or system, take the time to think it through carefully, and then build it and have it work almost, if not exactly, as planned. Eventually, the desk/bench ratio is necessarily maximized as failing eyesight and weakening motor skills leave one in the position of doing solely theoretical work.

Dennis Feucht

Electronics Engineer