由於手持式無線通訊電子產品需求量的增加，為了延長電子產品使用的時間，最直接的方式就是降低操作電壓，使系統達到低功率消耗。而且為了減少電池在電子產品中所占的體積和重量，太陽能將成為另一種提供能源的方式，由於太陽能電池所能供應的電壓約為0.5伏特，因此我們以藍芽( Bluetooth )做為參考規範，設計一個操作在0.5伏特高斯頻移鍵控( GFSK )的解調器。
在這個研究當中包含了兩個部分，一個是將訊號拉到軌對軌( rail to rail )的限幅放大器( Limiting Amplifier )，另一個則是用延遲鎖相迴路為架構的解調器。限幅放大器主要的目地是提供足夠的增益，讓類比的信號轉換成數位信號，為了避免電路本身的雜訊影響訊號，也會對這一個部分進行分析。而解調方面則是將拉到軌對軌的數位信號延遲一段固定的時間，之後將延遲的信號對原來的信號去做取樣，藉由判斷相位的超前和落後，來達到解調的目的。而延遲鎖相迴路( DLL )就是利用回授的方式準確的鎖定我們所需要的延遲時間( 1/3MHz )。
由於大部分電路都是偏數位方面的電路，比較適合操作在較低的工作電壓，此外，數位電路並不消耗直流電流，可以進一步減低功率的消耗。晶片的製作採用台積電0.18um 1P6M 製程來實現，晶片面積為1.54mm2，在此設計當中，選擇以3 MHz作為居中頻率( Intermediate Frequency, IF )，在0.5伏特的操作電壓下，功率消耗為0.2mW。

1 Introduction 1
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Test Circuit for Bulk Input Structure 3
2.1 Low Voltage Operational Amplifier . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Simulation and Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 FSK Receiver Architecture 11
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Receiver Radio Architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1 Heterodyne Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.2 Homodyne Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.3 Low-IF Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3 System Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4 Limiting Amplifier 21
4.1 Limiting Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.1.1 Gain Stage Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1.2 Offset Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.3 Common Mode Feedback . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1.4 Noise Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5 FSK Demodulator 33
5.1 FSK Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2 FSK Demodulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2.1 Differentiator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2.2 PLL type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.2.3 Quadrature Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.2.4 Zero-crossing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.2.5 DLL type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.3 DLL type FSK Demodulator . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3.1 Phase Frequency Detector . . . . . . . . . . . . . . . . . . . . . . . . 41
5.3.2 Charge Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.3.3 Voltage Controlled Delay Line . . . . . . . . . . . . . . . . . . . . . . 45
5.3.4 LO Shift Compensation . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.4 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6 Measurement Result 50
6.1 Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.1.1 SNR to BER Measurement . . . . . . . . . . . . . . . . . . . . . . . . 52
6.1.2 Noise of the Limiter . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.1.3 Performance Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 55
7 Conclusion 56
7.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

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