Design and Implementation of Multiple-Supply Reconfigurable Switched-Capacitor DC-DC Step-Down Regulator

切換電容式降壓電路非常適合應用在各種不同的電子系統中，因為具有體積小、卻能提供高能量密度的特性，且隨著電子產品的成長而需求大幅提升，切換電容式降壓電路朝向快速、低成本且提高轉換效率的設計趨勢，非常適合應用在由電池供應電壓的穿戴式裝置中。 本論文利用0.18m CMOS標準邏輯製程設計多供應電壓之可重組切換電容式直流降壓穩壓器，內含520pF的切換電容，且可內建於晶片中之降壓穩壓器電路。降壓器使用切換式電容降壓器設計，並透過PFM(Pulse Frequency Modulation)的機制來維持電壓穩定。由於切換式電容降壓器具有可變之轉換倍率，因此具有高轉換效率，且PFM的穩壓機制可以使輸出的穩定電壓有較大的電壓範圍和較好的負載調節度，同時利用並聯4組相同的降壓器改善輸出的漣波電壓。一般文獻都是輸入電壓或是輸出電壓為可變範圍，而本論文設計的切換電容式降壓電路更有彈性，其輸入電壓和輸出電壓皆為可變電壓範圍，降壓器供應電壓可為2.5V~3V，輸出電壓可穩壓在0.8V~1.3V。 此電路在供應電壓為3V，輸出電壓為1V時，能產生最大輸出電流為31mA，當電路在供應電壓為2.8V，輸出電壓為1.2V及輸出5.5mA電流時，有最大功率轉換效率70%，另外因為各文獻電路之規格與製程等皆不相同，若將此電路的輸出電流針對時脈及切換電容定義為正規化輸出電流，此電路可以得到最大的正規化輸出電流。Switch-capacitor (SC) step-down converter circuits are good for applications of different electronic systems, because it has the characteristics of high energy density on a small chip size. As the rapid growth of electronic products, the trend of SC step-down circuits is high-speed, low-cost and enhancement of power conversion efficiency. It is a good candidate for applications in battery powered wearable devices. In this thesis, a multiple-supply reconfigurable switched-capacitor DC-DC step-down regulator with 520pF flying capacitance built in the chip was designed using the 0.18μm CMOS standard logic process. The step-down converter is based on the SC topology with Pulse Frequency Modulation (PFM) to regulate the output voltage. The proposed SC circuit with PFM has variable conversion ratios to achieve high conversion efficiency, large output voltage range and good load regulation. Besides, the 4 parallel step-down SC branches reduce the output ripples. The SC step-down regulators reported so far have either the input or output voltages varied in a specific range. Here, the SC step-down regulator were designed more flexible with both input and output voltages varied in a specific range. The supply voltage range can be 2.5V to 3V, while the output voltage is regulated to 0.8V and up to 1.3V. This circuit can generate maximum output current 31mA with output voltage of 1V at supply voltage of 3V. When it is operated at 2.8V for output voltage of 1.2V and output current of 5.5mA, the maximum power conversion efficiency reaches 70%. Because the specifications and processes of the circuits in literature are different, if the normalized output current is defined as the output current divided by the clock frequency and flying capacitance, we can get the highest normalized output current.致謝 i 摘要 ii Abstract iii 目錄 iv 圖目錄 vi 表目錄 viii 第一章 序論 1 1.1前言 1 1.2電壓源產生電路介紹 1 1.3研究動機 2 1.5論文大綱 2 第二章 直流降壓電路介紹 3 2.1 直流降壓器種類 3 2.1.1 降壓轉換器 4 2.1.2 低壓降線性穩壓器 4 2.1.3 切換電容式降壓器 5 2.1.4 降壓器特性比較 6 2.2 切換電容式降壓器相關發展 6 2.2.1 電路架構 6 2.2.2 製程技術 9 2.3 穩壓機制介紹 10 2.3.1脈衝頻率調變(Pulse Frequency Modulation) 10 2.3.2脈衝寬度調變(Pulse Width Modulation) 12 2.3.3低壓降穩壓機制(LDO) 13 2.4 切換電容式降壓器規格介紹 14 2.4.1 輸入電壓(Input Voltage) 14 2.4.2 輸出電壓連波(Output Ripple) 14 2.4.3 切換比例(Conversion Ratio) 14 2.4.4 轉換效率(Efficiency) 14 2.4.5 切換頻率(Switch Frequency) 16 2.4.6 最大負載電流(Maximum Loading Current) 16 2.4.7 飛跨電容(Flying Capacitor) 17 2.4.8 線性調節率(Line Regulation) 17 2.4.9 負載調節率(Load Regulation) 17 2.4.10 暫態響應(Transient Response) 18 2.5切換電容式降壓電路轉換效率分析 19 第三章 多供應電壓之可重組切換電容式降壓穩壓器 24 3.1 降壓器的切換設計 24 3.2 電路架構 26 3.2.1 切換電容式降壓器 (SC DC-DC Converter) 27 3.2.2 PFM穩壓電路 32 3.2.3 降壓比例選擇電路(Select) 38 3.2.4 MUX+Buffer 40 第四章 電路模擬結果與佈局 43 4.1非重疊時脈產生器模擬 43 4.2負載電流及效率 44 4.3電路佈局 54 4.4整體電路效能與比較 56 4.5量測規劃 57 第五章 結論與未來工作 58 5.1結論 58 5.2未來工作 58 參考文獻 5