Design of Multi-Channel Gas Sensor Circuit with Large Dynamic Range and High-Precision

In order to realize a multi-channel exhalation detection device with large dynamic range and high precision, a well designed signal processing and sampling circuit is essential for gas sensors. In this paper, a particular circuit is designed to meet above requirement. The proposed circuit uses a constant current source to achieve linear transformation of resistance value and output voltage, and uses a voltage follower for impedance transformation to minimize the impact of the AD acquisition on the front-end circuit. Since the gas sensor can be regarded as a variable resistor, the proposed circuit is tested with variable resistors varying from 10k$\Omega$ to 50M$\Omega$, over three orders of magnitude. In order to increase the sensitivity of the gas sensors, it is need to heat the sensor. Then a multi-channel heating circuit is designed with independent adjustable heating current in each channel, which can be controlled with multi-channel PWM signal from the MCU. With simulation and experiment, the performance of the proposed circuit has been verified to be excellent. Furthermore, the circuit has the advantage of being used in various fields.