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Low current source

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Gyro:

--- Quote ---Couple that with one of those fA or pA input bias current opamps and you should be good to go, no?
--- End quote ---

LMC662, cheap and 3fA typ. at room temperature.

Benta:

--- Quote from: welterde on June 11, 2020, 09:01:43 pm ---
Shouldn't something like 2N4392 (can be had for around 3EUR from mouser) work quite reasonably?
Specified leakage at V_DS = 20V is 0.1nA max at ambient temperature.

Couple that with one of those fA or pA input bias current opamps and you should be good to go, no?

--- End quote ---

So a transistor that has a drain-source leakage current of 0.1 nA should be "reasonable" for a 10...100 pA current source?

'Das glaube ich nicht, Tim...'

Marco:
The options I see :
Opamp based high compliance current source. TIA in reverse, chicken and egg probem ... can't test the current source at AC without a superior TIA and vice versa

A modulated voltage source with a resistor (or capacitor). This is effectively a low compliance current source. The resistor or capacitor will have a lesser/different AC impedance than a photodiode or similar device, AC response will fall off differently. It's okay, but just be aware of the way it's different from the real deal.

The real deal will be the proof in the pudding ... and unfortunately you'll have to optimize with imperfect information, no helping it.

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