A Delta-Based SAR ROIC for Low-Voltage Wide-Input-Range Gas Sensor Readout

Abstract

This letter presents a delta-conversion successive approximation register (SAR)-based readout integrated circuit (ROIC) for low-power gas sensing with large sensor output swings. Instead of digitizing the absolute sensor output, the proposed architecture converts only the intersample difference using back-switching-based residue generation. It compresses the effective conversion range by generating the intersample residue inside the capacitor digital-to-analog converter, enabling low-voltage operation while directly sampling the full sensor output. The SAR conversion is further limited to a small least significant bit range, reducing comparison cycles and switching activity. A 10 bit prototype was fabricated in a 0.18 μm CMOS process and operates at 1.2 V. The proposed ROIC consumes 89.3 μW, achieving a 57.5% reduction compared to a conventional full-range SAR analog-to-digital converter, while reducing comparator power from 70% to 2.8%. The measured results show a maximum reconstruction error of 1.2 mV, relative error below 0.09%. These results demonstrate accurate signal reconstruction with improved energy efficiency for low-power gas monitoring systems.