Saw Gas Sensor Signal Detection Circuit Design And Optimization

Sensor technology is developing very fast and has been applied to military and our daily life right now, so developing novel sensor has been the main direction of sensor research. SAW sensor has been one of the research focuses and could be used in environment and chemical monitor areas due to its advantages, such as the low cost, high accuracy and resolution, small volume and easy integrated.Tested gas makes dynamics property of medium in the SAW transmission path change as the sensitive film adsorbs gas, and then the resonant frequency of SAW devices will be changed consequently. Accompanying signal detection circuit detects the frequency change, and the relative characteristics of the tested gas are obtained. Also the characteristic of the detection circuit influence the detection precision and accuracy and other technical indicators in the sensor system. So the design of detection circuit is an important procedure in the gas SAW. Signal detection circuit applying to the gas SAW was designed, and the relative properties of the circuit were tested in this work.Aiming at the double-resonance SAW devices the detection circuit based on frequency detection mean was designed. Firstly, resonator-based oscillator circuit was designed, and the oscillator circuit generates stable oscillation and outputs frequency associated with the resonator frequency signals. Then, the mixer circuit was designed. After mixing the output signal from the oscillator circuit of the resonator coated with a sensitive film and the output signal from the reference oscillator circuit of the resonator without a sensitive film, difference frequency signal was obtained. Through the shaping circuit, mixing signal was changed to be convenient for the data processing based on single-chip computer. Finally, by producing the printed circuit board and welding parts, the finished board was obtained according to the design. Closed chamber, which is used to protect the sensitive unit and detect the gas according to the actual situation.The test of performance and practical application was also introduced. In the performance of testing, the output signal of oscillator and mixer circuit in the detection circuit was detected in this work. The relative performance of the detection circuit was analyzed from the detection data. The stability of the detection circuit was also tested, which indicated that the circuit performs well. In order to detect the practical application of the detection circuit, we test the gas sensitivity. DKAP was coated on the sensing channel as sensing film to test the gas sensitivity of DMMP, and then measured the output signal from the detection circuit. The result indicated that the detection circuit has a good performance in the practical application and could meet the requirement of application.