Rakesh wrote on Oct 23rd, 2017, 1:36pm:Can you explain this "If you put the chopper in the loop than the chopping frequency is amplified by the open loop amplifier, so chopping might work at a higher frequency".
No, because I did not formulated it well, and it is not true
. As the picture in jdp's next post explains it the chopping frequency can be higher if the chopper is outside the loop. Note, that you have to have a filter which removes the upconverted flicker noise and offset. So the system bandwidth is always smaller than the chopping bandwidth. The higher is your chopping frequency the harder to filter it out, unless you do not use a switched cap notch filter which puts the the notch exactly at the chopping frequency, but if I remember it good it will introduce some phase shift creating some stability problems to solve. Such a filter should be in your loop, otherwise the low frequency "noise" will appear again at the input of your amplifier.
I guess the main reason why I have bad feelings with chopping outside the loop is because in that case the core amplifier's gain is reduced by its offset, which is one of the things you wanted to avoid. If the chopping is outside of the loop, only the resistor mismatch will be removed.