電子鼻系統主要分為三個部分，依序為氣體感測器、介面電路與訊號處理。其中表面聲波感測器為常見電子鼻系統感測器。本論文中所提到的表面聲波感測器包含了表面聲波感測元件以及提供其相位與增益的震盪電路。單一顆表面聲波感測器，可以經由量測其輸出頻率變化量感測有無氣體通入。我們在表面聲波感測器上旋佈高分子化學薄膜，可以增加感測器對於特定氣體感測的靈敏度，將旋佈不同高分子薄膜的感測器組成氣體感測器陣列可以做為氣體辨識使用。
當表面聲波感測器同時起震的時候，基底注入電流頻率成份增加，因此表面聲波感測器經由基底電流產生互相干擾的現象。當互相干擾的情形愈來愈嚴重時，將會影響表面聲波感測器的靈敏度，因為干擾會造成表面聲波感測器的中心頻率產生飄動，而當頻率飄動量過大時，感測器與氣體的反應量將會被雜訊值所掩蓋。本論文著重於降低感測器之間的雜訊，使用Deep N-well將NMOS的基底分開，藉此降低震盪器經由基底產生干擾，經由量測結果可以得到雜訊約有5db的下降量。
一般而言，表面聲波感測器陣列介面電路是採用非連續式的架構，雖然可以降低感測器之間的干擾情形，但是會有資料量不連續的缺點，對於後端的資料處理也比較麻煩。相反的，連續式的架構擁有資料完整的特性，但是介面電路的雜訊處理就變得很重要。本論文針對類比式低雜訊連續式表面聲波感測器介面電路做設計，其中包含了頻率混波器，低通濾波器、類比多工器以及週期計數電路，因為通道之間的切換為雜訊主要的來源，因此我們設計了低雜訊的類比多工器，並且提出了間隔切換的想法來降低通道之間的干擾。最後因為考慮到之後資料的處理，我們將輸出訊號處理成數位訊號。本論文使用TSMC 0.18μm 1P6M製成來實現整個系統，數位電路我們採用1V的電壓，而類比電路的部份我們使用1.8V的電壓。
晶片我們分兩個部份做量測，首先我們先使用理想的訊號作為輸入，量測電路的一些基本特性；接著我們再使用表面聲波感測器作為訊號輸入。最後表面聲波感測器震盪電路輸出中心頻率為113.76MHz，輸出功率為-1.7419dbm，且在1MHz時的相位雜訊為-123.2316dbc/Hz。頻率混波器的輸出誤差經由量測的到的結果都在1%以下，且輸出的頻率範圍可以從0.002Hz~1.9MHz。我們對類比多工器的輸出做傅立葉轉換，得到間隔輸出的結果確實可以降低通道之間的雜訊，且輸出的duty cycle rate範圍在47%~53%之間。最後我們將類比訊號轉換成數位的形式做輸出，便於後端做訊號處理。

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.

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