臺灣博碩士論文加值系統

本論文的研究目的在於如何利用MOSFET之特性設計一個穩定的獨立微定電流源，且此電流源能同時滿足直流與交流的微電流輸出，為達成此目的，我們將MOSFET操作於較特殊的區域，即弱反轉區，當MOSFET操作於弱反轉區時，其工作電流可達數nA至數十nA，且因消耗功率低，故非常適合應用於低電壓工作環境的電路裡。此外，為了我們可以輸出交流型態的定電流，我們也在電流源電路中加入一個方波產生器以達成此目的；此外，因MOS操作於弱反轉區時需要微小且穩定的閘級-源級電壓，所以我們在此電流源電路中加入一電壓穩定電路，即能隙電壓源（bandgap reference），能隙電壓源能提供與電壓源和溫度無關的參考電壓，相當適合應用於本電路。而在第二部分，本論文提出了一套系統電路可以將微定電流源加以應用，此系統電路即阻抗量測電路，而在不同放大倍率下，阻抗之量測範圍可由150Ω至25MΩ，操作頻率最多可達50KHz。最後在本論文中提出利用此系統電路所達成之人體皮膚濕度量測系統，從文獻可得知在操作頻率為1KHz之情況下，人體皮膚阻抗隨著濕度變化約在100Ω～50KΩ/cm2之間，利用此特性我們就可以測量出皮膚阻抗，進一步得知皮膚之濕度關係。

The research purpose of this thesis lies in how to utilize the characteristics of the MOSFET to design a steady independent current source. And this current can satisfy the direct nano-current and the autonative nano-current at the same time. In order to reach this purpose, we operate the MOSFET in a specific region, namely the weak inversion region. When the MOSFET operates in the weak inversion region, its operating current can often reach several nA. It is extremely suitable for the low-voltage working conditions’ electric circuit, since it consumes a lower power. Furthermore, we’ve added a square wave generator into the current circuit to provide the constant current source circuit’s AC current output; In addition, for the MOS been operating in a weak inversion region needs a small and a steady gate-source voltage, we added an bandgap reference circuit, which can offer stable reference voltage that would not be affected by the power supply or the temperature. In the second part of this study, we constructed a system circuit that can be used to advantage the constant current source we’ve made in the previous section, called impedance measurement system circuit. And under the different enlargement percentage, the impedance range could be from 150Ω to 25MΩ, and the operating frequency can reach 50KHz at most. We constructed a system circuit in order to measure the human skin moistness in the last section. According to early research, under 1KHz operating frequency situation, the variety of the human skin impedance is between 100Ω to 50KΩ/cm2. With this specialty, we could measure the human skin’s impedance and find out the relation of the skin’s humidity.

中文摘要-------------------------------------------------------------------------------I
英文摘要------------------------------------------------------------------------------II
誌謝-----------------------------------------------------------------------------------III
目錄----------------------------------------------------------------------------------IV
圖目錄-------------------------------------------------------------------------------VI
表目錄--------------------------------------------------------------------------------X

第一章　緒論

1.1 研究背景------------------------------------------------------------------------1
1.2 研究動機------------------------------------------------------------------------1
1.3 定電流源架構------------------------------------------------------------------2
1.4 阻抗量測系統電路架構------------------------------------------------------4
1.5 論文架構說明------------------------------------------------------------------7
1.6 實驗設計流程------------------------------------------------------------------8

第二章　微小定電流源設計與系統應用考量


2.1.1 電流源電路簡介-------------------------------------------------------------9

2.1.2 電流源電路架構及工作原理----------------------------------------------9
2.1.3 弱反轉區(Weak Inversion)介紹----------------------------------------12

2.2 系統應用考量----------------------------------------------------------------14

2.2.1 振盪源簡介-----------------------------------------------------------------15
2.2.2 方波訊號產生器-----------------------------------------------------------15
2.2.3 單穩態複振電路-----------------------------------------------------------18
2.2.4 電壓穩定考慮--------------------------------------------------------------21
2.2.5 能隙參考電壓（Bandgap Reference）-----------------------------25

第三章　微定電流源應用於阻抗量測系統各子電路設計

3.1 阻抗量測系統電路系統簡介----------------------------------------------33
3.1.1 比較器電路簡介-----------------------------------------------------------33

3.1.2 比較器電路架構-----------------------------------------------------------34
3.1.3 兩級開迴路比較器的設計-----------------------------------------------38
3.1.4 比較器輸入級部份的設計-----------------------------------------------40
3.1.5 比較器輸出級部份的設計-----------------------------------------------46
3.1.6 比較器之偏移電壓--------------------------------------------------------49
3.1.7 兩級比較器模擬輸出圖形-----------------------------------------------54

3.2 運算放大器設計-------------------------------------------------------------56

3.2.1 運算放大器簡介-----------------------------------------------------------56
3.2.2 折疊式運算放大器(Folded-Cascode Amplifier)設計-------------59
3.2.3 折疊式運算放大器模擬輸出圖形--------------------------------------65
3.2.4 運算放大器輸出級設計--------------------------------------------------66

3.3 精密二極體整流電路--------------------------------------------------------69

3.4 脈波寬度調變電路-----------------------------------------------------------72

第四章　阻抗量測系統各子電路量測與結果討論

4.1 微定電流源電路實現與量測-----------------------------------------------75
4.2 阻抗量測電路實現與量測結果--------------------------------------------81
4.3 皮膚濕度感測電路-----------------------------------------------------------89
4.4 顯示電路-----------------------------------------------------------------------91

第五章　結論與未來展望-------------------------------------------------------93

參考文獻----------------------------------------------------------------------------94

附錄
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