Ultralow-Power Inverter-Based Delta-Sigma Modulator for Wearable Applications
Alessandro Catania, Francesco Gagliardi, Massimo Piotto, Paolo Bruschi, Michele Dei
Abstract
This paper introduces and experimentally validates a switched-capacitor inverter-based second-order 3-tap FIR single-bit Delta-Sigma Modulator (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \Sigma $ </tex-math></inline-formula>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.