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Phil H MMIC as TIA

Phil,

Have you ever considered using a darlington-type MMIC, like a Mini-Circuits part, as a fast photodiode TIA? Apart from scant specs, and no Spice model, and ghastly DC behavior, it ought to work. They are cheap, stable, and super fast. Conventional opamp-type TIAs run out of speed low, and commercial ROSA-type things are mostly useless for DC-coupled applications.

As you note in your book, dumping the PD current into a grounded resistor and voltage-amplifying the result, is fast, easy, and noisy. A MMIC is sort of a TIA, a bunch of negative gain and a feedback resistor.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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jlarkin
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Sure thing. We've discussed that in these hallowed halls a few times--you just dump the DC photocurrent into the input and AC couple the output. The input of a quiet amp usually looks like about 30 ohms at 100-200 K, so you can get into the shot noise limit with a few hundred microamps of photocurrent.

There's no bootstrap or TIA action, so you get whatever bandwidth the RC rolloff gives you, but for simple fast stuff when there's lots of light, it's a definite win.

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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Phil Hobbs

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