An Ultra-Low-Power Biopotential Acquisition Analog Front-End Chip for Wearable Devices

Abstract

A 0.8-V, 1.2-μW biopotential analog front-end (AFE) IC is presented for wearable sensing. The front end combines a dynamically biased, chopper-stabilized capacitively coupled instrumentation amplifier (CCIA) with a dual-time-scale electrode dc-offset (EDO) management path. In steady state, a low-leakage DC servo loop (DSL) preserves sub-Hz baseline restoration and > 1 GΩ input impedance at 10 Hz; after an abrupt EDO disturbance, an event-triggered fast-recovery path temporarily increases the low-frequency discharge conductance and then returns to the low-leakage state. The 0.18-μm CMOS core occupies 0.35 mm², provides 60- to 100-dB programmable gain, and consumes 1.2 μW from 0.8 V. Without trimming, calibration codes, or postmeasurement mismatch compensation, the measured input-referred integrated noise is 0.98 μVrms over 0.5–100 Hz, with CMRR > 125 dB, PSRR > 98 dB at 10 Hz, and > 1 GΩ input impedance at 10 Hz under the calibrated balanced bench fixture. New quantitative robustness validation shows postlayout PVT ranges of 121.8–127.9 dB for CMRR, 94.6–101.0 dB for PSRR, 0.93–1.07 μVrms for input-referred noise, and 53–82 ms for fast-recovery time; 200-run mismatch Monte Carlo analysis gives CMRR = 126.4 ± 2.7 dB, PSRR = 99.1 ± 2.1 dB, and input-referred offset = 0.08 ± 0.34 mV. For the representative EDO-step emulation, the fast-recovery mode returns to the sustained linear region in approximately 60–70 ms, whereas the DSL-only response remains unsettled at the 300-ms observation limit.