New ISFET interface circuits with noise reduction capability

In this paper three different noise reduction techniques for Ion Sensitive Field Effect Transistor (ISFET) readout configuration and their comparison is presented. The proposed circuit configurations are immune to the noise generated from the ISFET sensory system and particularly to the low frequency pH dependent 1/f electrochemical noise. The methods used under these studies are- Compensation of noise by differential techniques (Implemented in LabVIEW environment and with OPAMP based circuit) and compensation by Wheatstone bridge method. Here two identical commercial ISFET sensors from Microsens were used. The statistical and frequency analysis of the data generated by the proposed methods were compared for different pH value ranging from pH-2 to pH 10 under room temperature, and it is found that the interface circuits are able to compensate the noise to a great extent.