LTE通訊系統用戶端之可重構濾波器設計

Design of Reconfigurable Filters at UEs of LTE Communication Systems

蔡涵昀(Han-Yun Tsai)

指導教授 ： 吳瑞北教授

國立臺灣大學/電機資訊學院/電信工程學研究所/博士(2018年)

https://doi.org/10.6342/NTU201803099

摘要

本論文主要研究可重構濾波器的設計，包含使用微帶線共振器以及聲波共振器。第一部份為固定比例頻寬之可重構濾波器，利用可調之外部品質因子維持通帶內反射損耗的響應，使用一具有接地傳輸線段負載之網式雙模共振器及兩組可調式電容來實現，固定比例頻寬是利用具有接地傳輸線段負載之網式雙模濾波器的特性來達成，一組可變電容做為調整濾波器之中心頻率，另一組則接於饋入傳輸線段之ㄧ端，維持外部品質因子以調整通帶內的反射損耗。基於此設計概念，論文中所提之固定比例頻寬可重構濾波器，在可調頻率範圍中，可以使反射損耗皆維持在20dB，且插入損耗小於2.9dB，可改善一般可重構濾波器，反射損耗與插入損耗會隨著中心頻率下降而變差的情況。
第二部分為使用薄膜聲波共振器設計可重構濾波器，分別使用一般高機電耦合係數之薄膜聲波共振器與可調式薄膜聲波共振器。本論文中所提之薄膜聲波濾波器皆使用微波濾波器的耦合理論進行設計，將薄膜聲波共振器串聯一電感之電路簡化為並聯RLC電路模型且作為濾波器的共振器，中心頻率、耦合係數以及外部品質因子的調整，皆使用可調式電容進行設計。為了增加可重構濾波器的可調範圍，使用具有高機電耦合係數之薄膜聲波共振器以及具有高品質因子之可調式電容。基於此設計概念，此可重構濾波器使用機電耦合係數為26% 的薄膜聲波共振器以及品質因子為150的可調式電容，在插入損耗小於4dB的情況下可以達到8.2% 的可調範圍。
由於外加之可變電容，會使可重構濾波器的頻率降低時，插入損耗隨之增加，使用可調式薄膜共振器可有效改善此情況，可調式薄膜聲波共振器本身的可調機制即可用來調整可重構濾波器的中心頻率，不須再額外加入可調式電容，故可重構濾波器之可調範圍便由可調式薄膜共振器決定，在與使用高機電耦合係數薄膜共振器設計之可重構濾波器相同規格下，使用可調式薄膜共振器設計之可重構濾波器的可調範圍為10%，而插入損耗則小於2.24dB。

關鍵字

可重構濾波器 ； 可調式濾波器 ； 雙模共振器 ； 網式共振器 ； 可調式外部品質因子 ； 可變電容 ； 聲波共振器 ； 薄膜聲波共振器 ； 可調式薄膜聲波共振器 ； 高機電耦合係數 ； 高品質因子之可調式電容

並列摘要

This dissertation focuses on the research of reconfigurable filters using microstrip resonators and acoustic wave resonators. The first part is the constant fractional bandwidth (CFBW) reconfigurable filter with frequency invariant passband characteristics using tunable external quality factors. A grounded-stub loaded net-type dual-mode resonator and two sets of varactors for tuning both the center frequency and the return loss level are used to design the reconfigurable filter. The design is featured with the net-type dual-mode filter of a short grounded-stub so that the CFBW property can be assured. In addition to conventional design, a pair of varactors is added at the ends of feeding transmission lines to keep the external quality factors constant while tuning. From the design concept, the return losses of reconfigurable CFBW filter with tunable external quality factor maintain at 20dB and the insertion losses are below 2.9dB over the entire frequency tuning range. The design can improve the return loss and insertion loss of reconfigurable filters when the center frequency decreases.
The second part is the reconfigurable filters using film bulk acoustic resonators (FBARs), including high electromechanical coupling coefficient (kt2) FBARs and tunable FBARs. The FBAR resonator and a series inductor are first represented by a simplified parallel RLC circuit model. The reconfigurable FBAR filters are then designed by applying the general coupled resonator filter theory, with tunable capacitors to adjust center frequencies, coupling coefficients and external quality factors. To increase the tuning ranges of reconfigurable filters, high kt2 FBARs and variable capacitors with high quality factor are used. In the presented reconfigurable filters using high kt2 FBARs, the tuning range is about 8.2% with < 4dB insertion loss by using high-Q digital capacitors of Q = 150. For deceasing the losses of extra tunable capacitors for tuning the center frequency, tunable FBARs are used to design the reconfigurable filters. By the mechanism of tunable FBARs, the center frequency of reconfigurable filters is tuning by TFBARs, not extra tunable capacitors. The tuning range of reconfigurable filters is determined by tunable FBARs. In same specification, the tuning range of reconfigurable filters using tunable FBARs is about 10% and the insertion loss is below 2.24dB.

並列關鍵字

Reconfigurable filter ； Tunable filter ； Dual mode resonator ； Net-type resonator ； Tunable external quality factor ； Varactor ； Acoustic wave resonator ； Film bulk acoustic resonator (FBAR) ； Tunable film bulk acoustic resonator (TFBAR) ； High electromechanical coupling coefficient ； High-Q digital capacitors

參考文獻

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