A Motion-Artifact-Tolerant Biopotential-Recording IC With a Digital-Assisted Loop

This paper proposes a motion-artifact-tolerant multi-channel biopotential-recording IC. A simple counter-based digital-assisted loop (DAL), implemented entirely with digital circuits, is proposed to track motion artifacts. The DAL effectively tracks motion artifacts without signal loss for amplitudes up to 120 mV with a 10 Hz bandwidth and can accommodate even larger motion artifacts, up to 240 mV, with a 5 Hz bandwidth, demonstrating its robustness across various conditions and motion artifact ranges. The IC includes four analog front-end (AFE) channels, and they share the following programmable gain amplifier (PGA) and analog-to-digital converter (ADC) in a time-multiplexed manner. It supports a programmable gain from 20 dB to 54 dB. Furthermore, the chopper with an analog DC-servo loop (DSL) is added to cancel out electrode DC offsets (EDO) and achieve a low noise level by removing the 1/f noise. The proposed IC fabricated in a 0.18-$\mu$m CMOS technology process achieves an input-referred noise (IRN) of 0.71 $\mu$V${}_{\textrm{rms}}$ over a bandwidth of 0.5 to 500 Hz and a signal-to-noise-and-distortion ratio (SNDR) of 63.34 dB. It consumes 5.74 $\mu$W of power and occupies an area of 0.40 mm${}^{\textrm{2}}$ per channel. As a result, the proposed IC can record various biopotential signals thanks to its artifact-tolerant and low-noise characteristics.