以多重耦合線實現單端至平衡帶通濾波器之分析與設計

Analysis and Design of Single-to-Balanced Multicoupled Line Bandpass Filters

蔡謹隆(Chin-lung Tsai)

指導教授 ： 林祐生

國立中央大學/資訊電機學院/電機工程學系/博士(2011年)

摘要

手持行動無線裝置被廣泛的使用在日常生活中。因此，輕薄短小是一個非常重要的趨勢。要達到此目的，所有的電子零件必須朝向多功能、高效能與低成本的方向邁進。在射頻收發模組中，帶通濾波器、單端至平衡轉換器與匹配電路是非常重要的元件並且佔用較多的電路面積。本論文提出兩種電路架構，同時整合上述三種電路功能，有效的降低整體的電路面積與元件數量。
在本論文中所提出的第一個設計電路，主要是由多重耦合線與負載電容所組成。藉由導入負載電容，耦合線電氣長度可小於二十四分之一波長，達到電路小型化的目的。再加上多重耦合線接地位置的設計，使得此電路同時具備帶通濾波器、單端至平衡轉換器與匹配電路的特性。藉由濾波器階數的增加，此電路可以輕易提升外頻選擇度。藉由圖示轉換法來分析多重耦合線，使得設計流程與分析過程可以較有效率且直觀。為了要驗證所提出的電路架構與設計流程，不同的設計規格如阻抗轉換、濾波器階數、中心頻寬與中心頻將會一一舉例，並且最後用低溫陶瓷共燒技術來實現電路，達到電路小型化的目的。俱備二階帶通濾波器響應的電路將實現在 2.0 mm × 1.2 mm (2012) 的晶片上，而俱備三階帶通濾波器響應的電路將實現在 2.6 mm × 1.2 mm (2612) 的晶片上。除此之外，由量測板所產生的高頻側傳輸零點可透過耦合量的控制來調整傳輸零點的位置，進而提升外頻選擇度。
在本論文中所提出的第二個設計電路，也是由多重耦合線與負載電容所組成。本電路藉由電磁耦合效應所產生的兩個傳輸零點可以有效控制零點位置。另外，非相鄰耦合線的影響與隨頻率而變化的導納反轉器也在本論文中有詳細的探討。藉由導入負載電容，耦合線電氣長度可小於二十九分之一波長，此電路架構最後也是以低溫陶瓷共燒技術來達到電路小型化的目的。所舉出的兩個設計例子證明零點可以有效且彈性的控制。
本論文所提出的兩種電路架構具備高整合度、高選擇度、精簡的電路架構以及小尺寸等特性。隨著射頻收發模組小型化與多工化的趨勢，本論文所提出來的單端至平衡帶通濾波器將非常適合運用在現今的手持行動無線裝置上。

關鍵字

低溫共燒陶瓷技術 ； 多重耦合線 ； 傳輸零點 ； 單端至平衡帶通濾波器

並列摘要

Nowadays portable wireless communication devices are being widely adopted into daily life, with ever-greater demands on more functionalities, higher performance, and
lower cost in smaller and lighter formats. Especially, the demand for high-performance and miniaturized passive components such as filters, baluns, and matching circuits continues to grow since these passive components usually dominate the circuit area of RF transceiver. In this study, we proposed two kinds of single-to-balanced multicoupled line bandpass filters that integrated above three functions in a simple circuit. In this way, one can reduce the circuit area as well as component count effectively.
The first design is composed of a multicoupled line of electric length as small as λg/24 along with shunt capacitors loaded at suitable positions. By a proper design of ground terminations for the multicoupled line, the proposed filter is simultaneously equipped with the functionality of a bandpass filter, a balun, and an impedance transformer. The bandpass characteristic can be easily developed to higher order for better selectivity. The graph-transformation method for coupled-line analysis is adopted to make the design procedure efficient and intuitive. To validate the design procedure and feasibility of proposed filter for mobile applications, several design examples with different filter order, impedance transformation ratio, fractional bandwidth and center frequency have been implemented in chip type by using the low temperature co-fired ceramic technology (LTCC). The second-order design is realized in a chip size of 2.0 mm × 1.2 mm (2012), while the third-order one is realized in a chip size of 2.6 mm × 1.2 mm (2612). Moreover, an additional transmission zero in the upper stopband can be achieved and controlled flexibly by adjusting the outer printed circuit board layout with minimum effect on passband performance.
The second design is also composed of multicoupled line with loaded capacitors. Besides, the cross-coupled effect is introduced to create two transmission zeros that can be located independently in either the upper or lower stopband. The effect of non-adjacent line coupling on the filter response is properly addressed, and an efficient way to compensate it is proposed. Also, the issue of a frequency-dependent J-inverter in bandpass filter design is well treated. The proposed filter can be implemented using the LTCC process to achieve very compact circuit size, in which the combline line length is as small as λg/29. Two design examples implemented in LTCC demonstrate the controllability of transmission zeros, good selectivity, and compactness.
The proposed multi-functional bandpass filters have the advantages of compact size, high integration level, good selectivity, and simple circuit topology. With the increasing demands on highly integrated, multifunctional, miniaturized, and high-performance RF front-end modules, we believe that the proposed single-to-balanced bandpass filters are highly suitable for modern mobile communication applications.

並列關鍵字

Transmission zero ； Multicoupled line ； Single-to-balanced bandpass filter ； Low-temperature co-fired ceramic(LTCC)

參考文獻

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