The design of a chemical interface circuit for water quality monitoring

Abstract

ISFETs have played an eminent role in society, particularly being utilized in specially designed interface circuits for adaptation in various useful applications of which includes water quality monitoring through pH sensing. With ISFETs as the main driving force, there is often a need to be able to increase the pH sensing range as well as to take into account any discrepancies in output readings, particularly through temperature effects. In the search for better understanding, an interface circuit utilizing ISFET was specially designed, with the entire operation based solely using analog devices, bypassing the use of digital devices like microcontrollers for instance. In this design, the use of a novel temperature compensation element was included, together with that of a modified folded cascode operational amplifier, providing an insight on the process details. The implementation of a flipped voltage follower in the output stage of the operational amplifier was investigated as well, paving the way for the ease of outputting results desired from the interface circuit.