So we are trying to detect very low levels of UV light using the circuit below. One of the problems I am having is that the response time for the output at "signal" is as long as 1-2 seconds. If we pulse our light at 10 Hz the output is 1.8 V but if we have the LED on constantly we are getting 5V. I assume this is becuase when we pulse the signal the output hasn't had time to rise yet.
From the research I have done so far it looks like a smaller capacitor is needed but with so much gain do I also need an op amp with a higher GBP? The AD820 has a GBP of 1.8MHz. Is there a simple calculation for what C45 should be or is the only one F = 1/2.pi.C.R?
Any advice/suggested reading material would be much appreicated.