I am working on a design using the LTC2054 op-amp, I am planning on using this device to amplify a photodiode, on page 16 of the datasheet for the 2054, they list and example circuit for exactly this purpose, which consists of what looks basically to be a standard low pass active filter (With a very slight modification to the feedback path), they state that this configuration should have a bandwidth of 10Hz, which upon simulation, it does. So I cannot seem to figure out why there is a ~8kHz low pass on the filter on the output of what is basically a 10Hz low pass active filter.
Any insight would be helpful,
One reason could be to attenuate higher frequency noise by another 20dB. As you may have guessed, the 10Hz filter rolls off at 20dB/dec. By adding an extra low pas filter at the output of amplifier, the overall system will have -40dB/dec roll off starting from ~8kHz and adding the extra -20dB/dec outside the loop does not impact stability
Hope it helps.