28 October 2014

Some History of Bandgap References

I am finally giving this talk on the East Coast in an open-to-the-public venue. It's not about Jim Williams, but it does mention Bob Widlar (and [spoiler] it includes my favorite Bob Widlar story). If you're in the neighborhood, please come!

Some History of Bandgap References
Electrical Engineering Seminar Series
Harvard School of Engineering and Applied Sciences
3pm, Friday, 31 October 2014
Maxwell Dworkin G125


Bob Widlar designed the first commercial bandgap voltage reference and introduced it with an elaborate ruse in 1969. The National Semiconductor LM109 was more than a simple reference, it was a feature-packed integrated circuit that jump-started the category of three-terminal voltage regulators. Over the next few years, the LM109 was followed up by the National LM113 current shunt, the LM199 temperature-controlled buried zener, and ground-breaking products from Analog Devices, Precision Monolithics, Linear Technology, and others. This talk discusses the history and design of voltage regulators, references, and current sources from the 1960s to present day.

12 January 2014

James K. Roberge

Another giant of analog circuit design has left us: It is with great sadness that I report that James K. Roberge passed away on Friday.

A short obituary from the Boston Globe is here.

Professor Roberge and I taught MIT 6.331 "Advanced Circuit Techniques" together this past term (Roberge describes this course in "Propagation of the Race (of Analog Circuit Designers)", Chapter 10 of Jim Williams's first book). Here's a picture that I snapped of him during the last lecture on December 11, 2013. I'm sorry for the terrible cell-phone quality, but I didn't know it'd be the last time I'd see him. He was born to teach, he was happiest when teaching, and this is how I'll remember him (teaching circuits, and here, discussing the Pade approximate for a time delay in active filter design).

I'm at a loss for words.

Update. Two more (better) pictures of Professor Roberge: Here's a photo from earlier in the Fall term of 6.331 (late October) where he was discussing voltage-reference circuits, and the calibration thereof (photo courtesy of Zhen Li).

Here's a photo from the end of the Spring term, of his famous "Train Lecture" in 6.302, where he uses the speed control of a model train (a Lionel O-gauge engine, his favorite) as a vehicle to discuss motor instrumentation, phase-lock loops, and feedback compensation (photo courtesy of Prof. David Trumper).

I had a work-related conversation with a friend and colleague last night, and I said, "I wish I could ask Jim" only three times.

06 January 2014

The History of "Analog", part 1

When did the word "analog" obtain its present meaning?

I've been researching some topics in the history of electronics, and as I was digging around, it crossed my mind that the word "analog" has an interesting history itself. Its definition and use changed several times during the twentieth century. In the 1989 print edition of the Oxford English Dictionary, the only engineering use of the word analog (of course, they spelt it "analogue") was as an adjective before the word "computer":
ANALOGUE --- (adjective) analogue computer, a computer which operates with numbers represented by some physically measurable quantity, such as weight, length, voltage, etc.
The 2013 on-line edition has a much improved and expanded entry for the word, which includes
ANALOGUE --- (adjective) typically contrasted with digital... 1c. of signals or data: represented by a continuously variable physical quantity, such as voltage, spatial position, etc.
However, in the context of circuit design and signal processing, I prefer the definition
ANALOG --- (adjective) in signals, continuous in amplitude and time; in circuit design, circuits that operate on these signals using continuous quantities
as opposed to
DIGITAL --- (adjective) in signals, quantized in amplitude and discrete in time; in circuit design, circuits that operate on discrete-time signals using quantized (usually binary) representations.
I don't insist these definitions are exhaustive or complete(1), but they draw a line in the sand for the starting point in this archaeological dig.

So, when did the meaning of "analog" change from "scale model" to its modern definition? I plan to find out. One interesting way to trace the evolution of the word is to find when it became commonly accepted enough to appear in the titles of publications, rather than in the text, where its meaning could be easily defined with a footnote or parenthetical phrase(2).

I've been digging around a little bit, and I've found some interesting things, and about which I have many comments, which I will share over the next few posts.


Can't wait? Here are some early findings: The first published articles to use the word "analog" (as a noun) in the title were a pair of papers by H. H. Skilling of Stanford University in 1931:
[1] H. H. Skilling, "An electric analog of friction for solution of mechanical systems such as the torsional-vibration damper," Transactions of the American Institute of Electrical Engineers, vol. 50, no. 3, pp. 1155-1158, Sep. 1931.

[2] H. H. Skilling, "Electric analogs for diffi cult problems," Electrical Engineering, vol. 50, no. 11, pp. 862-865, Nov. 1931.
The first published article to use the word "analog" as an adjective in the title was published in 1948:
[3] E. L. Harder and G. D. McCann, "A large-scale general-purpose electric analog computer," Transactions of the American Institute of Electrical Engineers, vol. 67, no. 1, pp. 664-673, Jan. 1948.
The first book(3) to use the word "analog" in the title was the classic text by Korn and Korn in 1952:
[4] Granino A. Korn and Theresa M. Korn, Electronic Analog Computers. New York: McGraw-Hill, 1952.
Analog Devices, Inc. was founded in 1965, see:
[5] Walt Jung, "Op amp history," in Op Amp Applications, Walter G. Jung, Ed. Norwood, Mass.: Analog Devices, 2002, ch. H, p. H.35.
[6] Dan Sheingold, "Editor's notes: Analog dialectic," Analog Dialogue, vol. 30, no. 3, p. 1, 1996.
The first books to use the words "analog" and "circuit" in the title were published in 1972:
[7] Alan B. Grebene, Analog Integrated Circuit Design. New York: Van Nostrand Reinhold, 1972.
[8] Jacob Millman and Christos C. Halkias, Integrated Electronics: Analog and Digital Circuits and Systems. New York: McGraw-Hill, 1972.
If you have additional (or contradictory!) information, please leave a comment.

  1. For example, switched-capacitor filters are continuous in amplitude and discrete in time, and asynchronous digital systems do exist.
  2. This approach has the added bonus of being easier to research, given modern searchable databases, so it makes a good starting point (but just a starting point).
  3. I define "book" to mean published by a major publishing house for public distribution. Technical reports, computer manuals, and theses don't count.

01 January 2014

Top Five Posts 2013

A year ago, I declared the "Top Five Most Popular Posts in 2012". A year before that, I declared the "Top Five Most Popular Posts in 2011" with an incomplete year of data. Therefore, following the tradition, I do declare:

The Top Five Most Popular Posts in 2013
  1. Best App Notes Page (2012 rank: #1)
  2. Not really a "post" in the strictest sense of the word, but this page received the most traffic in 2012. It continues to be updated as I continue to read...
  3. Scope Sunday 13 (2012 rank: #2)
  4. Photos from my trip to the Computer History Museum to see the opening night of Jim's Linear Technology laboratory bench on display (with my business card in the mess).
  5. Vintage Scopes are Better, part 2
  6. The second part of a five-part series. See below for part one.
  7. Vintage Scopes are Better, part 1 (2012 rank: #3)
  8. The first part of my five-part series on why vintage analog oscilloscopes are better than modern digital ones, with plenty of quotes from Jim. See also part two, part three, part four, and part five.
  9. My Favorite Widlar Story (2012 rank: #6)
  10. A retelling of the three-terminal-voltage-regulator prank. My second-favorite Bob Widlar story is the one about the sheep.

Some of the stats don't make sense (part two above part one?), so I suspect that Blogger suffered some kind of soft reset sometime during the year. Nonetheless, I charge forward with the only data I have. Also, I note that all of these posts are from 2011 and 2012, which is further evidence of my falling down on the job here. I hope that I will produce more interesting posts in the coming months.