在現今科技發達的年代，出現了各式各樣的可攜式電子產品，而可攜式最不可缺少的元件即是供應電量的電池，此元件決定了產品的續航能力，而改善輸出電壓對輸入電壓的轉換效率，不將只是提高電池的壽命，也將會節省成本，達到節能的目的。電池的供應電壓會隨著使用的時間，而有所下降直到一定的電壓值，這也代表著轉換器的輸入電壓將有可能高於、等於或是低於輸出電壓，為了滿足以上的條件，勢必需要設計一個可升降壓的切換式直流-直流轉換器，而高效率亦是所追求的目標。
傳統的升降壓轉換器架構通常是反馳式轉換器、反向升降壓轉換器、SEPIC或是升壓電路後端另外再銜接降壓電路，以上幾種架構較為複雜、低效率且電路佔用的面積較大，且前面所提的第二個架構輸出與輸入的極性相反。本報告中所設計的四開關升降壓轉換器所強調的是提高效率，降低外部元件數目及精簡電路面積。相較於前面所提到的幾種電路，本設計除了一次就能執行升降壓的動作、輸出電壓並無反相、與SEPIC相比還可減少一個電感的使用，是一個較為精簡的電路。
本報告中的晶片是經由國家晶片系統設計中心所提供的製程服務所完成，使用台灣積體電路公司0.35μm 2P4M 5V混合訊號製程，以40 S/B封裝，尺寸為1.38 x 1.80 mm2。設計的輸入電壓為2.5V至5.0V，輸出電壓為3.3V，供應負載電流範圍為60 ~ 300 mA，切換頻率為1 MHz。

With the rapid progress of semiconductor technology, all kinds of electronic products, especially portable electronics, appear in the market day by day. The most indispensable component for portable products is the battery that supplies energy, and determines the service life of the product. The supply voltage of the battery will drop gradually with time, which means the input voltage supplying by battery can be higher than, equal to, or lower than the desired voltage. Therefore, a DC-DC converter is required to convert the time-varying battery voltage to a fixed desired output voltage. Moreover, it would be better to have a high-efficiency buck-boost converter that can either step up or step down the battery voltage to a desired voltage.
The conventional buck-boost converters include flyback, inverting buck-boost, SEPIC, boost circuit with back end connects a buck circuit, etc. The above mentioned structures are either more complicated, more chip/PCB area, or having poor efficiency. Especially the inverting buck-boost architecture, the polarity of its output voltage is reversed. A four-switch buck-boost DC-DC converter was designed and presented in this thesis. The presented converter improves the efficiency, reduces the external component and chip/PCB area, compared with the above mentioned prototypes.
The input voltage range of the presented converter is 2.5~5.0V, its output voltage is set to 3.3V, load current range is 60~300 mA and switching frequency is 1 MHz. The chip was implemented by Taiwan Semiconductor Manufacturing Company (TSMC) 0.35μm 2P4M 5V mixed-signal polycide process, patronized by National Chip Implementation Center (CIC). The die area of the chip is 1.38 ×1.80 mm2, with 40 S/B package.

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