A 0.01-mm2 0.83-V Input Range SAR-Based Bridge-to-Digital Converter

Abstract

This letter presents a compact buffer-less 12-bit output SAR-based bridge-to-digital converter. Eliminating the sample-and-hold circuit substantially simplifies the sensor front-end by providing a high-impedance input stage. The binary weighted digital-to-analog converter (DAC) is replaced with a switched-capacitor DAC which is driven by an error-feedback modulator. This alleviates mismatch issues and provides area and power savings when used with a Wheatstone bridge as a read-out. The converter has a wide input range of 830 mV making it suitable for gas sensor applications. It is realized in 65-nm CMOS, occupies 0.01 mm2 area, and consumes 6.2 $\mu \text{A}$ with a 45 ms conversion time. It achieves 9.1 ENOB for a DC input and a Walden FoM of 0.65 nJ/conv-step.