A1 . 8 - G Input-Impedance 0.15-μV Input-Referred- Ripple Chopper Amplifier With Local Positive Feedback and SAR-Assisted

Abstract

This article presents a chopper-stabilized multipath current-feedback instrumentation amplifier (CFIA) that can also be reconfigured to a general-purpose operational amplifier (OPA). By utilizing a local positive feedback loop (LPFL), both the CFIA and the OPA benefit from gain-independent impedance boosting while retaining the merits of chopping, i.e., low noise and low offset. In addition, the chopping-induced ripple, one of the main issues of conventional chopper amplifiers, is suppressed by a passive high-pass filter with the S AR-assisted offset calibration. The prototype IC is implemented in a 0.18- μm CMOS process and draws 1.07-mA current from a 5-V supply. The chopper CFIA exhibits the minimal input impedance of 1.8 G  and the maximum input referred ripple of 0.15 μV (ten samples for both tests). These correspond to at least 1.13× and 1.3× improvements on the state-of-the-art IAs, res pectively. The CFIA and the OPA also achieve excellent power efficiency (the highest GBW/I SUPPLY), competitive input offset (4 and 2 μV), and input noise density (39 and 20 nV/ √ Hz).