本論文介紹應用於數位電視頻帶(UHF 470-710 MHz)之平衡-不平衡轉換器(Balun)。因應數位電視分佈於較低頻帶的需求，傳統馬群(Marchand)平衡-不平衡轉換器因為其四分之波長耦合線，有電路面積過大的問題。本論文提出利用傳統馬群平衡-不平衡轉換器架構，將原本電路結構之開路端變成短路端，使耦合線長度由 縮短成 ，應用於較低輸出阻抗轉換時，仍能得到良好之電氣響應。同時利用一個於開路端聯接到地的電容器，找出開路與短路架構兩者之間控制頻寬的機制，則在本文中也有詳細的探討。在之後章節裡進一步提出微小化，並適用於窄頻操作，且達成各種實數輸出阻抗轉換之平衡-不平衡轉換器，但其對輸出阻抗的改變是較為敏感的。引入阻抗中心並以放大器設計觀點為例，提出能在一段實數輸出阻抗範圍下，中心頻率皆不隨之飄移之電路架構，且頻寬具有可調性，耦合線長度更可縮短至 。最終，提出符合單面電路板的佈局方法，可做為實現全平面電路的另外一種選擇。本論文設計之平衡-不平衡轉換器，其平衡端大小差皆在0.5dB，相位差皆在5度之內。所有的量測與模擬結果皆在FR4基板上實現，均有良好的一致性。 Baluns designed for digital TV( UHF 470-710MHz ) applications will be presented in this thesis. Conventional Marchand baluns employ coupled lines. These structures occupy large circuit areas, especially for lower frequency applications (ex .DVB-T). In this thesis, we replaced conventional Marchand baluns open-terminal to short, the required coupled-line lengths of this balun structure can be made as short as . This balun is suitable for low impedance-transforming ratio . At open-terminal, with a series capacitor to ground, we can find how to control bandwidth by using the optimal value of the capacitor. The miniature, narrow band, wide impedance-transforming ratio balun is realized by using one series capacitor at unbalanced port, but it is sensitive to output impedance. In terms of the center of impedance and amplifier design, circuit structures insensitive to output impedance are presented. This balun bandwidth is controllable, and the required coupled-line lengths of this balun structure can be made as short as . Finally, the fabrication on single printed circuit broad is presented, and it supplied another choice. Both baluns achieved 0.5 dB amplitude balance and phase balance. All circuits are fabricated on FR4 substrate, and are in good agreement with simulation.
