A CMOS ISFET interface circuit for water quality monitoring

A new CMOS ISFET readout circuit is presented in this paper. The interface circuits is based on VI converter like design plus a grounded ISFET device biased in the triode region together with a source follower in a self-biasing configuration. The major advantage of this design is the elimination of body effect in the ISFET sensing element, thus reducing extra temperature dependent effect on modulating the threshold parameter, which permits simpler temperature compensation implementation. This circuit has been demonstrated experimentally a linear response of the output with respect to the pH value of the solution. Compared to the prior-art circuits, the proposed circuit is simple and minimizes the use of identically design component pair in matching perspective. This leads to robust as well as insensitive circuit structure, and hence it is very suitable for the environmental water monitoring application.