A Portable CMOS Based pH Sensor

This paper demonstrates a portable pH sensing system which converts pH to a digital readout. The system consists of a CMOS ISFET pH sensor with discrete analog to digital conversion and display modules. The front end sensor was fabricated in standard 0.5 μm CMOS technology and an easy to use Arduino microcontroller is used as the computing device. Measurement results have reasonable agreements with the simulations. The average sensitivity in simulation is 46 mV/pH and it is 42 mV/pH based on experimentally extracted capacitance parameters. The design uses a differential ISFET readout circuit with 12 μW of power consumption at 2 V and 80 μW of power consumption at 5 V. The portable sensor implemented is 10cm × 16cm, while the main ISFET front end readout occupies a chip area of 0.0093 mm
²
. This portable device is suitable for environmental and biomedical applications.