12 September 2011

App Note 35 part 1

"Step down switching regulators." 32 pages.

This app note is another great work that will take several days to cover. Again, I want to start by talking about some of the instrumentation. One measurement that is worthy of note is Figure 30, showing a 500-volt square wave! As the caption says,"DANGER! Lethal potentials present..."

However, the best measurement is clearly Figure 34, that shows a 115-volt sine wave, its distortion products, and its frequency spectrum all in one shot.

Jim teases us, but gives away no secrets, in the footnote:

Test equipment aficionados may wish to consider how this picture was taken. Hint: Double exposure techniques were not used. This photograph is a real time, simultaneous display of frequency and time domain information.

How did he do that? I assume he's using his trusty Tektronix 556 with a vertical-amplifier plug-in in one bay (perhaps a 1A2 or 1A4), and a spectrum-analyzer plug-in in the other bay (perhaps the 1L5 50Hz-to-1MHz spectrum analyzer). As for the distortion products, perhaps a HP 339A Distortion Analyzer?

This picture actually pretty funny at present. Tektronix is currently touting their new "Scope Revolution", the "world's first and only" mixed-domain oscilloscope (which they call the MDO4000) that has a built-in spectrum analyzer. Their ad copy says,"See both time and frequency domains in one glance. View the RF spectrum at any point in time to see how it changes." Take a look at http://www.scoperevolution.com/ and then take another look at Figure 34. Jim Williams beat them to the punch 22 years ago with technology from the 1960s.

(OK, OK, I admit that the MDO4000 does a lot more than I suggest above (for one thing, there is no logic analyzer here, nor would Jim use one, and the MDO4000 time-correlation functions are really cool); however, the superficial similarities are striking. And hilarious.)

I once heard that Tektronix offered Jim a brand new oscilloscope of his choosing, anything he wanted, if he promised to stop using vintage instruments in his app notes. No deal.


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