A 115.2-dB Dynamic-Range Two-Step Direct-Conversion Front-End With Mismatch Error Shaping for Noninvasive Biomedical Devices

This article presents a two-step direct-conversion front-end (Direct-FE) for noninvasive wearable biomedical devices. In the first step, a delta modulator ( $\Delta $ M) with embedded gain is used to implement coarse quantization, while in the second step, a discrete-time sigma delta modulator (DT- $\Sigma \Delta $ M) is used to realize fine quantization. DC-coupled differential difference amplifier (DDA) with resistor-based digital-to-analog converter (RDAC) is adopted as the input stage. Mismatch error shaping (MES) with reduced silicon area is utilized to suppress the mismatch error of the RDAC. The prototype has been implemented in 0.18- $\mu $ m BCD process and achieves a peak input range of $7.64~{\mathrm {V}_{\mathrm {pp}}}$ , an input-referred-noise (IRN) of $1.59~\mu \mathrm {V}_{\mathrm {RMS}}$ , a corresponding dynamic range (DR) of 115.2 dB, while consuming 2.4-mW power. The real physiological signals recording demonstrates its potential capability for wearable bio-potential acquisition, boosting the wearable and fitness application areas.