Every op-amp has error. We all know that. So logically, the more op-amp used, the less accuracy we will have, right?
In the circuit ,there are 2 parts: first is the current to voltage converter, second is the voltage amplifier. So let start by assuming that the current through LED as detector is -1 nA, variable resistor is 10 kOhm, so the final output should be 10V.
But I wonder: does that really need for the second op-amp? I mean, if we replace 1MOhm resistor with 10Mohm resistor (so that we wont need the second Voltage amplifier part) we will get the same value, and because fewer elements are used, the accuracy is better. Is that correct?
Also, I tried to read a lot but I still don't understand. The capacitor here acts as a filter or in order to stablize? What if we don't have capacitor?