[[alternative]]Design and Analysis on a Novel Read-out Circuit of Ion-Sensitive Field Effect Transistor

碩士機電工程學系[[abstract]]近來，微機電技術崛起使得ISFET元件逐漸受到重視，為配合其應用，讀取電路研究也是重要關鍵。本論文主要目的在於改良離子感測場效電晶體(Ion-Sensitive Field-Effect Transistor, ISFET)之氣體感測電路，其研究流程由感測原理、系統晶片架構、讀取電路設計與模擬分析、晶片佈局，文中皆有詳細的敘述。本設計是採用TSMC 0.35μm 2P4M製程環境進行設計與模擬。 論文中，首先設計一個具有輸出回授作用之軌對軌(Rail-to-Rail)運算放大器，並利用此軌對軌運算放大器，組合成為一種可應用於離子感測場效電晶體之氣體感測電路，此離子感測場效電晶體的閘極端對外連接至感測結構，其餘部分則包含於電路中。欲偵測氣體濃度時，將感測薄膜塗佈於結構上，當氣體濃度發生變化，經由讀取電路可轉換成為電壓變化並進行訊號讀取的動作，但傳統的ISFET讀取電路很容易受到共模雜訊影響，使輸出值不穩定而影響準確度。 本文利用開關切換將讀取電路工作狀態分為感測階段(Sensing Phase)和重置階段(Reset Phase)，再於後端接上相關性雙取樣(Correlated Double Sampling, CDS)電路將不同階段之訊號讀出，最後利用減法電路將兩訊號互相扣除，即可得到穩定的輸出電壓。 經由此改良式ISFET讀取電路，可降低環境溫度對輸出值的影響程度，電壓變異量由74.2μV降低至16.6μV，並使輸出呈現線性狀態，有利於訊號讀取。對於定電流不穩定對輸出值的影響，抵抗力更是優異，電壓變異量由7.74mV降低至4.2μV，使輸出穩定度大幅增加。[[abstract]]Recently, because of the rise of MEMS, ISFET becomes more important. Read-out circuit of ISFET is the key for its application. The objective of this thesis is how to improve the efficacy of ion-sensitive field-effect transistor (ISFET) gas read-out circuit. All of the research process such as sensing theory, architecture of the system chip, read-out circuit design and simulation and layout of the system chip are included in the thesis. The layout design and the circuit simulation are used the SPICE model of TSMC 0.35μm 2P4M 3.3V process. First, we design a rail-to-rail operation amplifier with output feedback. Then several rail-to-rail operation amplifiers combine to form a novel ISFET read-out circuit which can apply to gas sensing. The gate of ISFET extended to sensor structure, and the other parts of ISFET included in the read-out circuit. In order to detect gas concentrations, the sensor structure is coated with the sensing film. The variation of gas concentrations can be converted into voltage variation by the read-out circuit and then the signal can be read easily. However, traditional ISFET read-out circuit is very susceptible to common mode noise impact, which will cause output value instability and in turn affect the accuracy. In this thesis, the read-out circuit is divided into sensing phase and reset phase. Then we connect the back-end with correlated double sampling circuit, so as to read different phases of the output. Finally, the two signals deducted each other by subtraction circuit, and we can obtain the steady output voltage. It reduces the condition impact of temperature on the output through the novel ISFET read-out circuit. The voltage variation decrease from 74.2μV to 16.6μV, and change output into linear state that helps signal to read. Additionally, the circuit towards the current instability in the resistibility is excellent and so that it increases the output stability. The voltage variation decreases from 7.74mV to 4.2μV