A novel pH sensor using differential ISFET current mode read-out circuit

Abstract

This paper presents a novel differential current mode read-out circuit for the Ion Sensitive Field Effect Transistor (ISFET), as a pH sensor. It uses six Operational Floating Current Conveyors (OFCC), and provides linear sensitivity to pH over a wide range (pH values 2-12). Moreover, it provides an output current that is linearly related to the differential voltage between the ISFET and the Reference Field Effect Transistor (REFET) sensors. The proposed read-out circuit uses only one type of active element (i.e. an OFCC) that makes this circuit easier to be both integrated and fabricated using a conventional CMOS process. Our experimental and simulation results demonstrate that the read-out circuit works reliably and can be a suitable sensor read-out circuit for lab on chip biomedical applications. The read-out circuit connected with the system composed of the ISFET and REFET sensors also reduces the impact of the parameter fluctuations and environment conditions on the performance of the ISFET sensor.