Balanced Photodiode? (Phil Hobbs)

Oct 28, 2009 3 Replies

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Tim Williams 16 years ago

Hey Phil, think there would there be any value in this?

Put two photodiodes in series. The node between them is like a voltage divider, so run it to a FET op-amp. Now, one photodiode is the input, and the other is servoed with an LED to match the current, which is what the op-amp is for. It also doubles as an logarithmic converter, so you get log(light) is an output voltage.

Seems to me you were recently asking about stupid-low-current CCS's, maybe this was already suggested... if not, you read it here first, it's in the public domain, you can't patent it! :-)

Tim

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Phil Hobbs 16 years ago

Tim,

The difficulty with this is that it doubles the shot noise power. I could have done that with a BJT with no degeneration, which is more or less how it turned out at very low photocurrent and high frequency. Adding the diode degeneration makes the sink current sub-Poissonian, which helps with the SNR.

BTW patent examiners never read USENET, so your idea isn't as safe as you think. ;)

Thanks

Phil Hobbs

Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net

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Joerg 16 years ago

It doesn't matter what they read, and some of them don't seem to read much anyhow considering what gets patented these days. What matters is how clever counsel on the side of an accused "infringer" is. Any lawyer worth his salt should manage to operate an Internet search engine :-)

Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.

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MooseFET 16 years ago

.. which is why I called the diodes "SeQQnsing eleQQments" (without the Qs) and not photo diodes in the patent application. The search engines only look for words not ideas.

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