Auto Correction Feedback for Ripple Suppression in a Chopper Amplifier

This paper proposes a local feedback, named Auto Correction Feedback (ACFB), for a chopper amplifier to suppress its offset related ripple. It nulls out the amplifier's initial offset in DC domain which would otherwise become modulated ripple at the chopper amplifier's output, instead of filtering the ripple with a post filter. The proposed ACFB has been implemented as a stand alone chopper operational amplifier fabricated in 0.64 mm ² die area with a 0.35 μm standard CMOS process. It achieves 10 μV maximum input offset voltage and 95 nV/rt(Hz) input voltage noise spectrum density flat down to 0.1 Hz, with a 1.8-5.5 V supply voltage range and 13 μA supply current dissipation. When configured in unity-gain, the typical magnitude of the input referred ripple at the chopping frequency is 9.4 μVrms, as a result of 45 dB ripple attenuation obtained by the ACFB. The analysis, the simulation, and the measurement prove there is no noise penalty due to the addition of ACFB.