Ye Olde (new) Transimpedance Amplifier

Thread Starter

KL7AJ

Joined Nov 4, 2008
2,225
http://www.electronicdesign.com/analog/whats-all-transimpedance-amplifier-stuff-anyhow-part-1

I've been reintroducing myself to the transimpedance amplifier, for use in a couple of specialized RF applications. It's really an intriguing concept....and somewhat counterintuitive. I first learned about these while working with photomultipliers at Hipas Observatory, under the "guruship" of UCLA's Dr. Ralph Wuerker, (now deceased) who taught me everything I know about optics.

If I might amend the great Pease's comments a tad. The reason all the input current has to go through the feedback resistor isn't so much a direct result of the opamp's high gain (though that is important), it's rather the result if the input IMPEDANCE being nearly infinite. There IS only one possible current path, and that is through the feedback resistor. I think this slight modification makes the circuit easier to understand.

(P.S.....I don't think I've ever been able to improve on anything else The Great Pease has ever uttered. ) :)

RIP both of you guys. I wonder what you're doing in that great laboratory in the sky these days?

Eric
 

Bordodynov

Joined May 20, 2015
2,643
In this circuit, you can add two bipolar transistors (into the drain), and make cascode circuits. This makes sense if the capacity of the photodiode is small.
 

Thread Starter

KL7AJ

Joined Nov 4, 2008
2,225
In this circuit, you can add two bipolar transistors (into the drain), and make cascode circuits. This makes sense if the capacity of the photodiode is small.
Yes indeed! I've also become "re-enamored" with the cascode topology. Stay tuned!
Eric
 
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