Design Of Potentiostat For Gas Sensor

Long term exposure to hazardous gas fumes in diesel and gasoline equipments or in coal mines may hurt the health of human being. Amperometric electrochemical sensor can track and detect the gases. Its reaction mechanisam is to convert gas concentration signal to electrical signal. The sensor and other peripheral circuits form a potentiostat which accomplish the pre-amplifing of the electrical signal. If the gas sensor interface circuit can be realized to be low-cost, low-power, high detecting current, and etc, it can be applied to more specific environments to detect various gases, and then the application of gas sensor will be everywhere.This thesis gives detail analysis of the electrochemical cell and electrode before referring to potentiostat, not only gives the theoretical analysis of electrode’s equivalent electrical modeling, but also presents a practical model of three-electrode electrochemical cell. Theories of potentiostat and ways of realizing potentiostats are presented and compared in this thesis. Basic realization of the applied TIA structure potentiostat is presented as well. This thesis also focuses on analysis and deduction of feedback-type of class AB control loop applied to the output stages for the control amplifier.Recent in-vivo electrochemical sensor can measure the small redox (reduction and oxidation) current of several nAs to hundreds of μAs. The control amplifier of the potentiostat should be a low power amplifier with high current drive ability to monitor gases with high concentration. In addition, the large-signal settling time of the potentiostat to charge/discharege the double layer capacitors can be reduced to a large extent if the maximum output current of the control amplifier is high enough. Based on SMIC0.13μm RF process, this thesis has realized a potentiostat with maximum push/pull current of20mA and maximum detection current of1.5mA. The total current consumption is135μA with3.3V supply voltage.