A 4.6 µW, 133-VPP Common-Mode Interference-Tolerant Biopotential Amplifier for Two-Electrode Recording System in 110-nm CMOS

Abstract

This article presents a biopotential recording ana- log front-end (AFE) specifically tailored for a two-electrode measurement system, capable of capturing small biopotential signals while tolerating a large common-mode interference (CMI) over 130 V PP. By leveraging the Miller e ffect, the proposed CMI-Follower provides a significantly low common-mode input impedance ( ZIN-CM-C), achieving large CMI tolerance without additional noise contribution. The low ZIN-CM-C enables the isolated chip-ground (Chip-GND) to precisely track the cou- pled CMI, significantly reducing the Chip-GND referred input CMI. Furthermore, the proposed CMI-Follower features inher- ently a large total common-mode rejection ratio (T-CMRR) without relying on power-hungry techniques. A noise-e fficient common-mode adaptive current-reuse operational transconduc- tance amplifier (CMA-CR-OTA) is also introduced to extend the input common-mode range (ICMR), featuring a linear amplification of biopotential signals in the presence of residual CMI exceeding 400 mV PP, which can be caused by unexpected large parasitic capacitance (CGND) between Chip-GND and Earth- ground (Earth-GND). Fabricated in a 110-nm CMOS process, the prototype AFE consumes 4 .6 µW per channel from 1 to 1.5-V supplies. The CMI-Follower accounts for only 17% of the total power consumption, while supporting CMI tolerance over 130 V PP. Experimental results demonstrate that the proposed AFE successfully captures small biopotential signals such as elec-