Distributed attenuators

Jul 10, 2019 23 Replies

Did something like that at Nijmegen in the late 1990's. The lasers involved worked at wavelengths too low for PMT's so I stuck a wideband variable gai n amplifier onto a photo-diode

Stuck two fast Burr-Brown VGAs in series to get fast forward gain, and two cheap slow Linear Technology parts in series to do the DC feeback to keep t he average long-term output at 0V.

Decoupling the rails well enough to keep the whole mess stable was demandin g, but I designed it onto a printed circuit board in one hit.

I used a Texas Isntruments CMOS-input op-amp to monitor the average output, and the data sheet failed to mention that it had an input capacitance of a bout 15pF which I hadn't compensated, so the board oscillated (rather slowl y) when I first turned it on. A 3.3pF compensation capacitor fixed that, bu t stuck out like a sore thumb on surface mount board.

I hadn't been fond of Texas Instrument before that , and that didn't make m e any fonder.

Bill Sloman, Sydney

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I think Phil said in another thread that he's using an avalanche photodiode for this. Not sure if that's true anymore.

George H.

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Which garden did you find that in? I ended up using the DG3257 for similar specs (5.5 ? / 3 pF), and TI has since released the TMUX1511, but more variety sure would be nice.

As very much a C++ (D) person myself, I can really recommend Julia for that sort of work. Fast, concise, and amazing amount of cutting-edge algorithm research is available in library form on GitHub.

? David

I'm using the 1511, yeah.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com

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