I would like to see a current decay from a photodiode with a high dynamic range. By saying "high dynamic range", I mean it decayed from about 1uA down to 100pA or 10pA. I tried with a linear preamplifier SR570 that had different transimpedance gains. The measurement circuit is shown below:
My crude idea was to measure the initial fast and high current with low gain, then the later slow and low current with high gain (unavoidably I would get initial overload plateau with this high gain measurement), and somehow stitch them together to have a full picture. The example measurement results are shown below:
However, I am not sure how to stitch them together. There is obviously some time delay between these two transients. For this specific case, the DC input impedance of the amplifier is 100 Ohm with 1e5 V/A gain, and 10kOhm with 1e7 V/A gain. The bandwidth is 20kHz and 2kHz for this two gains respectively. So it is not surprising to see a time delay. There may be other artifacts. Can anyone suggest any solution?