Purpose of low pass filter on LTC2054 Amplifier

Hello all,

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,

cheers!

  • 0
    •  Analog Employees 
    on Apr 24, 2018 8:46 AM

    Hi,

    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.

    Cheers!

    Kaung