Featured Engineer

Interview with Dr. Kent Lundberg

Dr. Kent Lundberg

Dr. Kent Lundberg - Independent Consultant, Amateur Historian, Bibliomaniac, and Visiting Prof. at Olin College of Engineering

How did you get into electronics/ engineering and when did you start?

Like many engineers, I started taking stuff apart at an early age (toys, radios, clocks, TV sets). One of my favorite recurring projects was to delicately reassemble a clock without the case, and get it working again (until somebody bumped it and it all fell apart or shorted out; my mother hated that). When my parents finally (tried to) put a stop to it, I was lucky enough to live down the street from a retired jack-of-all-trades (electrician, plumber, carpenter) with a big junk pile (and a few old TV sets) who let me come over to his house and take stuff apart there. Later, he taught me how to really put things back together, and finally, how to build new stuff. My father finally broke down and bought me my own voltmeter and soldering iron when I was nine, and a computer (a Commodore PET) when I was eleven.

In high school, I devoured all the math and science courses. Oddly, I went to college thinking I wanted to be a physicist. I didn’t realize until my junior year at M.I.T. that I really wanted to be an electrical engineer, and an analog-circuit designer at that.

How did the “Reading Jim Williams” blog get started?

Jim Williams of Linear Technology was one of the greatest living designers and most prolific authors on the topic of analog circuits. I considered him a role model and friend. After he died unexpectedly last summer, I vowed to reread all of his books and application notes. I’ve been posting commentary on this blog as I read. It’s been very interesting (and also quite educational).

What are your favorite hardware tools that you use?

My HP 3562A dynamic signal analyzer is an indispensible tool for control-systems and analog-circuits work. Being able to hook it up and get a Bode plot or a Nyquist diagram is a beautiful thing.

Like Jim Williams, I am a rabid fan of vintage oscilloscopes. They truly don’t make them like they used to. My favorite is the Tektronix 7104, a completely analog scope with a 1-GHz bandwidth. Although I rarely actually need that much analog bandwidth, the instrument is a work of art. The dual-beam Tektronix 556 is also very capable, flexible, and immovable. Jim got me hooked on oscilloscope collecting, and now I own dozens of vintage and classic Tektronix scopes from an early Tek 511A to several Tek 547s and Tek 7104s.

What is on your bookshelf?

I have several thousand books on my bookshelves, as well as piled on the floor, stacked up in closets, and boxed up in the basement, attic, and garage. I am an insatiable book collector. I have complete sets of the MIT Rad-Lab books, the Bell Labs series, the National Nuclear Energy Series, original control engineering books from the 1940s, as well as books on analog computing, circuit design, technology history, math, and general science. Most interesting, perhaps, are the books stacked up on the floor around my desk (that is, the ones that I’m currently reading and referencing for my classes and various projects).

  • Jim Williams, Analog Circuit Design: Art, Science, and Personalities
  • Jim Williams, The Art and Science of Analog Circuit Design
  • Franklin, Powell, and Emami-Naeini, Feedback Control of Dynamic Systems
  • Walter Evans, Control-System Dynamics
  • Barry Klein, Electronic Music Circuits
  • Hal Chamberlin, Musical Applications of Microprocessors
  • Thomas Lee, The Design of CMOS Radio-Frequency Integrated Circuits
  • Thomas Lee, Planar Microwave Engineering
  • Alan Grebene, Bipolar and MOS Analog Integrated Circuit Design.
  • James Roberge, Operational Amplifiers: Theory and Practice
  • Richard Thornton, et al., Multistage Transistor Circuits
  • Lawrence Huelsman, Active and Passive Analog Filter Design
  • Paul Nahin, When Least is Best
  • James Burke, Connections
  • Leslie Lamport, LaTeX: A Document Preparation System

What are your favorite software tools that you use?

I spend a lot of time writing, so LaTeX (and XCircuit for figures) is at the top of the list. For control-systems simulations, Matlab is king. For circuit-design work, LTspice and Eagle.

What kinds of consulting projects do you work on?

I have three primary areas of expertise: control-system design, analog-circuit design, and seminar teaching. I enjoy all three. I thrive on the challenge of a tough controls project. I revel in getting a recalcitrant circuit design to finally work in the lab. And I love teaching: I teach a wide variety of courses for industry on feedback systems, filter design, low-level transistor circuits, and instrumentation.

What is the hardest/trickiest bug you have ever fixed?

Well, it might not be the trickiest bug, but the most recent round of “high fives” in the lab was the result of some successful hardware hacking without a schematic. We were testing an extremely sensitive low-noise amplifier, but we couldn’t get a small enough signal from the UHF signal generator. Even with the output amplitude at the minimum setting, 60 dB of attenuators in-line with the coax, and judicious RF shielding, the parasitic coupling from the generator to the input stage was still too high. So I opened up the signal generator and traced the output microstrip. There were two unlabeled chips on the line, but both of them had bias-tee inductors on the microstrip, which implied they were the power amplifiers. By removing the inductors, I depowered the amplifiers and reduced the output power by 45 dB. This reduction was enough to quell the parasitic coupling and allow us to complete our noise-floor measurements. “No user-serviceable part inside,” my ass!

Do you have any tricks up your sleeve?

Due to my background in control systems, I find feedback loops in everything. This approach has served me well. Feedback is the most useful and important tool in engineering. Every system that you encounter as an engineer — every system that you use, design, buy, or fix — uses feedback in some form, either intentionally or unintentionally, either explicitly or implicitly. Understanding a little feedback theory is key to understanding the things that you can do to create, build, repair, and improve systems that exploit feedback. One of my colleagues once said that “feedback is so fundamentally important that analog engineers who don’t understand it should be legally barred from circuit design,” and I agree!

What’s this “historian” gig?

I was Associate Editor for History of IEEE Control Systems Magazine for eight years. I find the history of science and technology to be entertaining and educational. It is interesting to see how previous generations of engineers, working in (or even before!) the days of vacuum tubes and analog computers, invented the tricks and techniques that we now take for granted. Also, some of the “big names” were amazing and intriguing characters. Everybody knows the crazy stories about Heaviside and Widlar, but Routh, Nyquist, Bode, Darlington, and Cauer (and many others) were all interesting men.

What are you currently working on?

As I write this, the Spring term just started, so I’m neck-deep in teaching two classes, Controls (my favorite!) and an elective called “Circuits for Electronic Music”. It’s going to be a great term.

Circuits for Electronic Music?

The market for analog synthesizers has surged in the past decade, but really, I’m always exploring new ways to get students excited about circuit design. Teaching a class on circuits and systems for music synthesis is just a thinly veiled excuse to teach topics in linear-systems theory, analog circuit design, frequency modulation, oscillators, filters, waveform shapers, and op-amp applications. Plus, we get to build effects pedals, listen to music, make some noise, and discuss the history of music synthesis. I have an enthusiastic class of engaged students, and it’s a lot of fun.

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