An AC-Coupled Instrumentation Amplifier Achieving 110-dB CMRR at 50 Hz With Chopped Pseudoresistors and Successive-Approximation-Based Capacitor Trimming

High common-mode rejection ratio (CMRR) with concurrent electrode offset rejection is essential for physiological signal acquisitions. This article presents a CMRR enhancement technique for ac-coupled instrumentation amplifiers (ACIAs), where the mismatch of passive components limits the CMRR performance primarily. A modified chopping structure is proposed to mitigate the mismatch effect of the pseudoresistors, and a successive-approximation based capacitor trimming loop is exploited. Fabricated in a 0.18-μm CMOS technology, the ACIA draws 2.3 μA from a 1.2-V supply and exhibits 3.2-μV _rms input-referred noise over 0.5-400 Hz. The measured prototypes achieve >110-dB CMRR at 50/60 Hz without any off-chip tuning.