A High Linearity Detection Circuit with Constant Detection Voltage for Resistive Gas Sensor

In this paper, we present the design of a high linearity detection circuit with constant detection voltage for resistive gas sensor. The detection circuit is designed using a resistance to frequency structure, which can keep the voltage across the sensor constant, thus avoiding the non-ohmic feature and improving the detection accuracy. Furthermore, a PWM wave is used as output and the low-level time of the output frequency is strictly proportional to the resistance of the gas sensor, which makes the circuit highly linear. This chip was fabricated by SMIC 180nm complementary metal-oxide- semiconductor technology. Test results show that the circuit does ensure that the voltage across the sensor remains constant (1V) and also has an excellent linearity from 1kΩ to 10MΩ. Experimental results combined with the resistive MEMS gas sensor show that the system has a good detection effect in a wide gas concentration range (0ppm-300ppm), and can even detect a gas concentration change of 0.1 ppm at a low concentration. The maximum power consumption of this circuit is only 4.6mW at a 1.8V power supply and the chip area is 0.8 × 0.6 mm
²
.