Suppose I have photodiode with a Dark Current of 5 pA and that using the NEP of that photodiode at some frequency \$\lambda\$ I determined that the smallest signal I could detect was of 1 pA.
First of all, does it make sense that my signal is smaller than the Dark Current?, my understanding is that they are additive, so when I have no signal I would see Dark Current \$\pm\$ Noise, but that would always be smaller than 6 pA, thus when I get 6 pA I know I had a real signal.
Now, assuming this is the case, what should I do with my ADC in order to have all my bits carrying information from the signal?.
Again, my understanding is that if I have, for example, 16 bits, and the Dark Current uses 8 of those, then there are only 8 for my signal.
Should I set the ADC to ignore signals smaller than 6 pA?, 11 pA?.
Signal theory is really not my area and I am not sure where to start learning it.