A 1.74.12 mm3 Fully Integrated pH Sensor for Implantable Applications using Differential Sensing and Drift-Compensation

Abstract

This paper presents a $1.7 \times 4.1 \times 2$ mm3 pH sensor that is a fully integrated, stand-alone and implantable system. Instead of a bulky cm size Ag/AgCl electrode, we use a mm-size integrated platinum electrode, and differential sensing using ISFET and REFET pair to compensate for unstable fluid potential. We also propose a drift compensation technique in which the leakage from the source and drain through the gate oxide is canceled, reducing drift $> 100 \times $.