Abstract
Electronic nose (E-Nose) is one of the applications for surface acoustic wave (SAW) sensors. In general, the SAW sensor consists of a passive element (LiNbO3 and IDTs) and an oscillator circuit. A SAW sensor array is formed to construct the odor patterns for gas recognition. The injection current through the substrate seriously affect the performance of the SAW sensors. If the number of the SAW sensors increases, more injection current would raise the output noise level of the SAW sensors. This will affect the sensitivity of the SAW sensor because the frequency change from the SAW sensor is very small at sensing low concentration gas. In the previous works, asynchronous types SAW sensor array system have been developed to implement a portable E-Nose to reduce the interference between sensors. However, the data acquired from the asynchronous type SAW sensor array system is not continuous, thus it is not suitable for further analysis. In contrast, synchronous type SAW sensor array system has the advantage of data integrity. In this paper, we focus on the design of low substrate noise synchronous type SAW sensor array system. We used deep N-Well to separate the substrates of NMOS transistors to reduce the injection noise from the substrates between sensors. The system was implemented by an application-specific integrated circuit (ASIC) that converted the analog sensor signal into digital. The proposed circuit has been fabricated by TSMC 0.18μm 1P6M CMOS process technology. The chip operated at 1V supply voltage for digital circuits and 1.8V for analog circuits, respectively.