Chemical field-effect transistor with constant-voltage constant-current drain-source readout circuit

Response of Chemical Field-Effect Transistor (CHEMFET) electrochemical sensors are taken from the output of a readout interface circuit that maintains constant drain-source voltage and current levels. We employ the readout circuit for the purpose of supervised learning training data collection. Sample solutions are prepared by keeping the main ion concentration constant while the activity of an interfering ion varied based on the fixed interference method. Results show that the voltage response demonstrates linear relationship to the ion concentration within the detection limit. However, noise in the form of abrupt and random changes in DC levels reduces correlation and increases mean square error between similarly repeated measurements. We find that referencing the voltage response to the sensor response in DIW prior to measurement greatly improves the repeatability. The process of approximating ionic concentration level is achieved up to 80% recognition by feeding the readout circuit output to a neural network post-processing stage.