Development of Economical ASIC for PCS for water Quality Monitoring

In this paper, the design of an ASIC is presented that implement a low-cost system for the supervision of water quality in urban areas or rivers. Photo catalytic sensor (PCS) estimates the parameter biological oxygen demand (BOD) which is generally used to estimate quality of water. The system proposed in this paper involves a simple potentiometric approach that provides a correlation in the input–output signals of low-cost sensors. This approach which is more users friendly and fast in operation is obtained by modeling and optimization of sensor for water quality monitoring. This is to overcome several drawbacks generally found in the previous flow injection analysis method of determining chemical oxygen demand (COD)-like complex designing, nonlinearity and long computation time. The system constitutes a significant cost reduction in the supervision of water quality monitoring. The main reason of employing a readout circuit to PCS circuitry, is the fact that the fluctuation of O2 influences the threshold voltage, which is internal parameter of the FET and can manifest itself as a voltage signal at output but as a function of the trans-conductance gain. The trans-conductance is a passive parameter and in order to derive voltage or current signal from its fluctuations the sensor has to be attached to readout circuit. This circuit provides high sensitivity to the changes in percentage of O2 in the solution. In this design simple potentiometric approach with few passive components are used to build a readout circuit. The paper focuses on the electronic implementation of the readout system for the PCS which optimize the circuit performance and increases reliability.