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Several questions about precision amps for photodiodes

Question asked by tmissach on Dec 17, 2011
Latest reply on Jan 5, 2012 by OliverSedlacek

Hello,

I have several photodiode-specific questions. My application is a position detector based on a lateral effect diode. For me it is very important to have nearly zero offset und strong liniarity over wide temperature ranges used in a low frequency range < 10 kHz. The measured current is between 100 nA and 500 µA.

 

At the moment I use auto zero / zero drift operational amplifiers (AD8638) and the lateral effect diode is reverse biased to improve linearity. But there are some additional noise in the signal. I guess it comes from the auto-zero-chopper (typ. 1.2µVpp). Is there any other applicable solution having nearly zero offset (ideally <5 µV and zero drift) without chopping and dual supply operation (ideally SOT-23)? Which OPV could you recommend for the use as a outputbuffer in combination with secound order butterworth to eliminate unwanted noise >10 kHz and to drive the cable capacitance of a 25 m shilded signal cable with a 10 mA load?

 

How should I handle the tradeoff between a low input bias current at one and the offset voltage at the other side in general? Is it in the case of a in photovoltaic-mode connected photodiode better to use amps with extreme low input bias current or with extreme low offset voltage if a zero output-offset is important? Because Eout=(-Isignal-Ibias)*R+Vos… Is this right?

Regards, Thomas

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