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

TLDR: A modified chopping structure is proposed to mitigate the mismatch effect of the pseudoresistors, and a successive-approximation based capacitor trimming loop is exploited to enhance the CMRR performance primarily.

Abstract: 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- $\mu \text{m}$ CMOS technology, the ACIA draws $2.3~\mu \text{A}$ from a 1.2-V supply and exhibits 3.2- $\mu \text{V}\mathrm {_{rms}}$ input-referred noise over 0.5–400 Hz. The measured prototypes achieve > 110-dB CMRR at 50/60 Hz without any off-chip tuning.