03 October 2011

App Note 45 part 1

"Measurement and control circuit collection: Diapers and designs on the night shift." 24 pages.

This app note is another classic. It is the first with a rating system; here the circuits are rated by how long they took to complete, measured by the number of feedings that his infant son required. "I decided to introduce Michael to the glories of late night circuit hacking... We loaded up on formula, diapers, and bottles and went into the lab." The number of bottles is shown in each figure.

The selection of circuits here is very interesting. I believe that Jim took a leave of absence from Linear Tech after his son was born, and that the circuits here represent his own interests, rather than the the requirements of customers or the assignments of his bosses ("the Captains of this corporation", as he called them in App Note 25). Thus, we have a collection of circuits that captured Jim's imagination in some way: low-noise amplifiers, thermometers, a hygroscope, a barometer, oscillators, V-to-F converters, a pulse generator, and a fluorescent-lamp power supply. Many of these circuits are improvements of circuits from previous app notes. It's always fun to go back to previous designs and see if you can improve them!

Figures 2 and 4 show extremely low-noise amplifiers using chopper stabilization. Figure 2 is especially noteworthy, with only 40 nV of noise in a 10-Hz bandwidth. Figure 6 is a 20-MHz cable driver, using current feedback (for the original circuits see App Note 21 Figures 6 and 11, the latter for the current-feedback gain stage and the former for the JFET front end). Figure 8 is a simple, programmable current source. Figure 10 is a floating current-loop transmitter (an improved version of App Note 11, Figures 10 and 11).

The next few circuits are instrumentation projects (some of which, I imagine, turned up in his art projects; for example, see the cover of his 1995 book). Figures 11 and 13 are thermometers (a previous version appeared in App Note 7 Figure 2). Figure 15 is a battery-powered hygroscope (a previous version appeared in App Note 3 Figure 8). Figure 16 is a barometer using a low-cost sensor, and Figure 17 is a battery-powered cosmic-ray detector.

I'll cover the second half of the app note (starting with the oscillator in Figure 18) next time.


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