Design of Efficient White LED Driver

在今日隨著手持式消費性電子產品的快速成長，對功率積體電路設計者而言，減少產品的功率損耗與提高電源效率已經成為一個相當重要的研究主題。本篇論文中詳細討論一個高效率的白光LED驅動電路的設計與實現，所設計的白光LED驅動電路中包括交換電容式的電壓轉換器、高供應電源排斥比的低壓降線性電壓穩壓器以及亮度調整電路。由於交換電容式的電壓轉換器具有三種分數型式的電壓放大增益，用於將輸入電壓放大至輸出端，即使電池電壓已經低於所設計的輸出電壓時，LED仍然可以正常工作，因此電池的使用時間可以被延長。另外，在交換電容式的電壓轉換器設計中，一個時脈訊號放大技術被應用在降低開關切換過程中的電荷損耗上，高供應電源排斥比的低壓降線性電壓穩壓器能夠提供良好的電源雜訊抑制能力，當具高漣波電壓的交換電容式電壓轉換器輸出做為低壓降線性電壓穩壓器的供應電源時，白光LED驅動器的輸出電壓可以輕易地達到穩壓效果並且將漣波電壓明顯地降低。亮度調整電路則是藉由設定外部電阻以及控制訊號，達到調整每個白光LED上的順向電流，因此即可呈現亮度明暗。 整個白光LED驅動器的電路設計是透過台積電2P4M 0.35μｍ 5V的CMOS製程進行模擬，此白光LED驅動器提供每個白光LED以並聯方式連接，每個白光LED的最大額定電流為20mA在其順向電壓為3.6V時。連接的LED數量可依照不同的應用而改變，最多可同時並聯五個白光LED於驅動電路上。As the fast growing of today’s portable consumer electronics, the reduction of power consumption or improvement of power efficiency has become an important subject for the power IC designer. This thesis presents the design and implementation of efficient white LED driver. This white LED driver includes a switched-capacitor voltage converter, high PSRR low dropout linear regulator and a brightness control circuit. Since the switched-capacitor contains three types of fractional gain to boost the supply voltage, the lifetime of battery can be extended. Moreover, a technique of clock boosting is utilized to alleviate the charge loss in the duration of switching for the switched-capacitor circuit and then the power efficiency can be improved. The high PSRR low dropout linear regulator is designed to inhibit the noise from the output of switched-capacitor voltage converter and regulate the output voltage of white LED driver. Therefore, the output ripple voltage can be reduced significantly. The brightness control circuit is used to adjust the forward current of each LED by setting the external resistors and control signal. The overall circuits included in the white LED driver are simulated by tsmc 2P4M 0.35μm 5V CMOS process. The white LED driver provides the topology of parallel connection for each LED, which has the maximum current rating 20mA at its forward voltage 3.6V. The amount of connected LEDs is flexible for different applications and the maximum is five.Acknowledgement Chinese Abstract English Abstract Table of Contents I List of Figures IV List of Tables VIII Chapter 1 Introduction 1 1.1 Background 1 1.2 Motivation 3 1.3 Research Goals and Contribution 5 1.4 Thesis Organization 6 Chapter 2 Fundamental of LDO and SC Voltage Converter 7 2.1 Principle of Operation 7 2.1.1 Low Dropout Linear Regulator 7 2.1.2 Switched-Capacitor Voltage Converter 8 2.2 Specifications and Definitions of LDO 10 2.2.1 Dropout Voltage 10 2.2.2 Ground Current and Quiescent Current 11 2.2.3 Topologies of LDO 12 2.2.4 Efficiency 14 2.2.5 Load Regulation 15 2.2.6 Line Regulation 16 2.2.7 Frequency Response 16 2.2.8 Transient Response 19 2.2.9 Power Supply Rejection Ratio 21 2.2.10 Stable Range of ESR 21 2.3 Fractional Gain Switched-Capacitor Architecture 22 2.3.1 MOS Switch 24 2.4 Power Dissipation 26 2.4.1 Conduction Loss 26 2.4.2 Dynamic Power Loss 29 Chapter 3 Design of High PSRR Low Dropout Voltage Regulator 31 3.1 Motivation 31 3.2 Architecture 32 3.2.1 Definition of PSRR 33 3.2.2 PSRR of the LDO 34 3.3 Control Loop Design 35 3.4 Bias Circuit 38 3.5 Error Amplifier Circuit 39 3.5.1 Proposed OTA Topology 40 3.6 Analog Driver Circuit 44 3.7 Bandgap Voltage Reference 46 3.7.1 Conventional Bandgap Reference 47 3.7.2 Proposed Bandgap Reference 49 3.8 Simulation Results 53 3.8.1 Static State Performance 53 3.8.2 Dynamic State Performance 56 3.8.3 High Frequency Performance 57 3.9 Summary 60 Chapter 4 Design of Efficient Switched-Capacitor Voltage Converter 61 4.1 Motivation 61 4.2 Architecture 62 4.3 Switched Capacitor Array 63 4.4 Comparator Circuit 67 4.5 Oscillator Circuit 70 4.6 Encoder Circuit 72 4.7 Controller Circuit 74 4.8 Non-Overlapping Clock Generation Circuit 75 4.9 Gate Driver Circuit 76 4.10 Simulation Results 82 4.11 Summary 86 Chapter 5 Design of White LED Driver 87 5.1 Architecture 87 5.2 Brightness Control Circuit 88 5.3 Simulation Results 90 5.4 Summary 95 Chapter 6 Conclusion and Future Works 96 6.1 Conclusion 96 6.2 Future Works 96 Reference 9