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

This article presents a biopotential recording analog 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 VPP. By leveraging the Miller effect, the proposed CMI-Follower provides a significantly low common-mode input impedance ( <tex-math notation="LaTeX">ZIN-CM-C</tex-math> ), achieving large CMI tolerance without additional noise contribution. The low <tex-math notation="LaTeX">ZIN-CM-C</tex-math> enables the isolated chip-ground (Chip-GND) to precisely track the coupled CMI, significantly reducing the Chip-GND referred input CMI. Furthermore, the proposed CMI-Follower features inherently a large total common-mode rejection ratio (T-CMRR) without relying on power-hungry techniques. A noise-efficient common-mode adaptive current-reuse operational transconductance 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 mVPP, which can be caused by unexpected large parasitic capacitance ( <tex-math notation="LaTeX">CGND</tex-math> ) between Chip-GND and Earth-ground (Earth-GND). Fabricated in a 110-nm CMOS process, the prototype AFE consumes <tex-math notation="LaTeX">4.6~μ</tex-math> W 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 130VPP. Experimental results demonstrate that the proposed AFE successfully captures small biopotential signals such as electrocardiograms (ECGs) and electroencephalograms (EEGs), even in a real-environment condition with 76-VPP CMI, thanks to its low input-referred noise (IRN) of <tex-math notation="LaTeX">0.43~μ</tex-math> Vrms (0.5–100Hz). The prototype AFE also achieves 90.5-dB and 102-dB T-CMRR with 5% and 30% dry-electrode impedance mismatches, respectively.