Ultralow-Power Inverter-Based Delta-Sigma Modulator for Wearable Applications

This paper introduces and experimentally validates a switched-capacitor inverter-based second-order 3-tap FIR single-bit Delta-Sigma Modulator (Delta Sigma M) designed for nanowatt-level analog-to-digital conversion in wearable healthcare devices. The focus is on applications with energy harvesters, emphasizing continuous monitoring of chronic conditions and closed-loop drug-delivery systems. The design methodology addresses ultralow-power considerations at both architectural and transistor levels, tackling challenges like process variations without relying on complex digital calibration techniques. Experimental results from prototypes, implemented on a standard 180-nm CMOS process, reveal a peak SINAD of 77.8 dB and SNR of 79.4 dB, with a power consumption of 71.5 nW at a 900-mV supply. Measurements across nine chip samples are consistent, demonstrating low DC offset, with low temperature drift and live sensitivity. The outcomes confirm the modulator suitability for energy-harvested wearable systems.