A CMOS Conductometric Circuit For Chemical Sensing Using Nanowire Sensor Arrays

Abstract

In this thesis, a readout circuit for conductometric electrochemical sensor array is designed and implemented. It is designed to work with the output range of a Carbon Nanotube Chemiresistive Sensor Array. The sensor arrays are designed to measure the Volatile Organic Compounds (VOCs) in the environment. The circuit reads out the outputs of the sixteen conductometric sensor arrays and calculates the change in conductance during the interaction with the chemicals present in the environment. A constant voltage is applied to the sensor arrays and when the sensor detects the VOCs, it changes the conductance and a change in current through the sensor arrays is observed. This change in current is measured by the readout circuit and the conductance can be found out. The conductometric circuit consist a 16:1 analog multiplexer, trans-impedance amplifier (TIA), and a microcontroller to control and process the signals.For the CMOS IC implementation, the conductometric circuit is designed and fabricated in 0.35 um CMOS process. The design and analysis of the individual circuit components including the analog multiplexer and operational amplifier are presented in this work. The op amp achieves 118.1 dB gain and 59.79 degree phase margin. The circuit gives a linear dc response for the resistance variation range of 10 KΩ to 100 KΩ.