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 mm² 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.