隨著晶片整合度的提升，功率的消耗問題也越來越嚴重。在諸多節能技術當中，可變電壓技術越來越受到矚目，搭配可變頻率操作，不僅在動態功率消耗得到大幅的降低，連靜態功率消耗和漏電消耗都能得到節省。在可變電壓頻率系統中，除了系統本身必須能夠適應變壓變頻的操作和軟體排程的支援，同時必須有一個可以動態輸出可變電壓的電壓產生器。
與傳統穩壓器比較，電壓產生器除了本身必須具備高效能之外，同時必須具備快速的動態反應速度，特別是電壓追蹤的特性。此外，除了要能抵抗對於系統元件和寄生元件的變異量，更要能夠適應大範圍操作條件的要求。
在這次的研究報告中，我們是採用數位電路的方式去實現可變電壓產生器的控制電路。相較於類比控制，數位控制具備強大的運算功能，能夠實現複雜的控制演算法，不需要額外的電路補償元件，而且數位訊號操作沒有類比電路操作飽和的問題，同時對於切換雜訊的干擾也比較輕微，不過使用數位方式實現要面臨的會是較多的功率消耗。
對於設計的可變電壓器，我們希望能夠具備幾項特性:在穩定狀態時電壓器的切換頻率是定頻操作，主要是定頻操作在頻譜上的雜訊底層值較低，諧波(harmonic)表現是可以選擇的，這對於電磁干擾(EMI)設計的複雜度能大幅降低。穩定精準的靜態輸出，對於系統的變異量要能夠動態調整，接近電壓器物理限制的快速動態反應。
為了達到設計目標，在系統設計上，採用多種模式控制完成動態電壓輸出，在穩壓操作是採用傳統等比、積分、微分控制器，此類控制器除了具備等比積分基本特性，微分控制可以降低反應不及的問題，同時因為控制參數少在硬體實現具備優勢，對於控制器整合度高。在電壓追蹤操作，是採用開迴路的控制方式，利用電感電壓的斜率變化和電容電荷變化量的需求，可以求得理論上最佳的控制法則，但是如果考量到系統元件(如: 輸入電源、輸出負載和電感電容元件) 的變異和元件寄生效應，最佳化的控制方式是無法達成的，為了讓控制能得到有效地提升，在這裡採用觀察輸出變化和對應的控制脈衝變化，去求得有效的控制變化量，然後再去調整控制器裡原有的控制變數。值得一提的是這樣的動態調整機制不需要額外的偵測電路，所需要的訊息都可以在原本的控制迴路裡面得到。控制器可以藉由學習的方式去調整控制器參數，從量測值得知，最差的情況可以由41%的工作表現提升到83%的工作表現。同樣的調整機制也可以用在調整等比、積分、微分控制器，在這類的調整主要是針對系統操作條件(輸入電源)的變異，相較一般穩壓控制由一組控制參數去做反應，從量測值推算，系統頻寬的差異可以由最大100%變到最差只有20%。
在電路實現方面，查找表(look-up table)取代需要高速操作的運算子，另外應用數位抖動的特性發展預測抖動調變，由偵測輸出斜率變化的方式，去決定最低兩位元的控制碼，這樣的方式可以有效的去消除數位實現產生的量化誤差。在介面電路實現部份，主要是類比數位轉換器(ADC)和數位脈衝調變器(DPWM)，在我們的應用裡，線性震盪器用來將電壓轉換成頻率，為了配合預測內插的方式，名為接力式(relay-race) 計數器用以支援。具備類似同時運算的能力，等效上來說可以增加類比數位轉換器的輸出量，更重要的是可以在額定時間內獲得更多相關的資訊。接力式計數器由幾個位元數少的計數器所組成，一旦當計數器的計數量為其飽和數值，會有一個指示信號觸發下一個計數器，而目前工作的計數器會在一段時間延遲後重置工作，靜置的計數器可以使用在下一個需要觸發的程序，
這樣的配置可以降低計數單元的複雜度，同時降低電路觸發所需要的功率消耗達原本所需的70%。數位脈衝調變器是採用計數器為基礎的架構，根據所接收到的控制脈衝指令決定所需要的延遲，在這裡是用連續除頻(/2)的方式完成。
除了數位控制迴路，為了讓直流轉換器控制效能提升，在轉換器本身增加了電流偵測器，藉由觀察功率電晶體上的電流變化，判別連續導通模式(CCM)和非連續導通模式(DCM)的操作邊界，以及時修正數位控制器所得到的脈衝寬度，同時保護功率電晶體免於大電流或電壓擾動等物理傷害。
除了電磁元件電感、電容之外，整個系統均被整合在單晶片之中，並使用了0.18μm標準CMOS製程，功率切換元件是採用3.3伏的元件，電壓產生器的切換頻率是1MHz，控制器所需最高頻率為32MHz，由量測值推算現性控制部份的單位增益頻寬約為50KHz，藉由動態調整機制，電壓產生器都能大致維持系統設計的頻寬表現，同樣在動態調整機制的協助之下，電壓追蹤的動態表現約為25μs/V，而在沒有電流限制的情況下，最佳電壓追蹤可以達16μs/V，數位控制電路部份幾乎可以由合成的方式完成，控制器部分的電流消耗在最佳操作條件下約為100μA，電壓產生器的最佳效能在0.35W的輸出可以量到96%，數位控制器包含類比數位轉換器和數位脈衝調變器面積約為0.09mm2，在不含測試電路，控制器電路包含類比保護電路占整體有效面積約15%。

1 SOC Power Management 1
1.1 Power Management for High Efficiency Processor . . . . . . . . . . . . . . . . . . 2
1.2 Overviews of Dynamic Output Switching Converter . . . . . . . . . . . . . . . . . 3
1.3 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Digitally Controlled Switching Type DC-DC Converter 5
2.1 Buck Converter Basic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Buck Converter and Characteristic . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Buck Converter Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Buck Converter with Digital Control Overview . . . . . . . . . . . . . . . . . . . 9
2.3 Design Issues for Digital Controller . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.1 Quantization Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.2 Digital Time Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.3 Digital Dither Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Buck Converter Control Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4.1 Voltage Mode Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4.2 Current Mode Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.3 Advanced Control Techniques . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.4 Discrete Control Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5 Peripheral Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.5.1 Digital Pulse Width Modulator . . . . . . . . . . . . . . . . . . . . . . . . 34
2.5.2 Analog-to-Digital Converter . . . . . . . . . . . . . . . . . . . . . . . . . 35
3 System Design for Dynamic Output Digitally Controlled Power Converter 36
3.1 Previous Works for DVS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Current Profile in Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.1 Evaluation of Current Signal for Buck Control . . . . . . . . . . . . . . . 37
3.2.2 Practical Issues for Current Sensing . . . . . . . . . . . . . . . . . . . . . 41
3.3 Optimum Operation Points for Switching Power-MOS . . . . . . . . . . . . . . . 43
3.4 Mixed Signal Simulation Environment . . . . . . . . . . . . . . . . . . . . . . . . 44
4 Digital Controller for Dynamic Output Power Converter 47
4.1 System Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 Transient-Triggered System Adaption . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3 Indirect Current Slop Control with Adaptive Parameter Assignment . . . . . . . . 54
4.4 Operation Sequence under Physical Limitation . . . . . . . . . . . . . . . . . . . 62
5 Digital Controller Realization of Dynamic Output Power Converter 65
5.1 Linear and Nonlinear Control Combination . . . . . . . . . . . . . . . . . . . . . 66
5.2 PID-Like Control Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.3 FSM-Based Predictive Dither Modulation . . . . . . . . . . . . . . . . . . . . . . 77
5.4 Relay-Race-Counter Based A/D Converter . . . . . . . . . . . . . . . . . . . . . . 82
5.5 Digital Pulse Width Modulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6 Experimental Results 88
7 Conclusion and Future Work 100
7.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.2 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

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