Use of chopper-notch modulator in chopper amplifiers for replica images cancellation

A method for cancelling the replica image limiting the chopper stabilization technique is presented. The modulation of the 1/f noise at the chopping frequency and its multiple are conventionally reduced by a low-pass filter and, possibly by a notch filter. The method presented here combines the second chopper and the notch filter by using a simple SC circuit that enables cancelling the replica images. The method just requires a simple local loop for reducing the amplified offset to a reasonable level and this is obtained with a simple modification of the amplifier used in the chopper scheme. Simulation results show the expected benefits.