單級晶格型聲波濾波器的參數合成與衍生多級設計

Abstract

本論文研究聲波濾波器設計，針對晶格型組合架構分別利用解析解以及數值解兩種方法，萃取出單級晶格型聲波共振器等效電路參數。並依照此方法，針對基於YX 〖42〗^°切角的鉭酸鋰(機電耦合係數約6%)，使濾波器之S參數頻率響應盡量滿足系統規格。 針對單級晶格型聲波濾波器，本文除了數值解外還提供兩種方法進行設計，一種為以傳統濾波器合成理論得到解析解，以理想Chebyshev響應推導出LC共振器的LC值，在通帶具小比例頻寬(FBW)或低回波損耗(RL)時，LC共振器可以近似到聲波共振器之等效電路模型，即BVD模型的近似公式;另一種為參數化分析，用此方法得到通帶最佳的設計曲線，提供設計者規格與設計參數的關係和通帶最佳設計規格的限制。 針對晶格型衍生多級設計，本研究進一步使用數值最佳化方法，設計二級、三級晶格型以及修正晶格型組合架構，在給定特定聲波共振器特性以及材料限制下，使設計之濾波器頻率響應盡可能滿足系統規格。設計結果與參考文獻相比，階梯型與傳統晶格型比例頻寬可設計的極限皆在5%左右;修正型的晶格型組合架構則頻寬可以不受機電耦合係數的限制，且在回波損耗10 dB以上的要求下，最大能設計出約35%的頻寬。最後，以三級晶格型架構實際應用在5G頻段，設計的頻寬範圍落在1.9%-5.1%，可滿足通帶回波損耗10 dB以上的要求，也有良好的帶外性能。

In this thesis, the equivalent circuit parameters of the primary lattice type acoustic resonator are extracted for the lattice combination architecture by using both analytical and numerical solutions. Based on this method, the S-parameter frequency response of the filter is made to meet the system specifications as much as possible for the lithium tantalum based on the YX 〖42〗^° cut angle (electromechanical coupling coefficient of about 6%). For single-stage lattice acoustic wave filter, this thesis provides two methods for design in addition to numerical solution. One is to obtain the analytical solution by traditional filter synthesis theory and derive the LC value of LC resonator by ideal Chebyshev response, when the passband has a small fractional bandwidth (FBW) or low return loss (RL), i.e., the approximation formula of the BVD model. Another method is parametric analysis, which is used to obtain the optimal design curve for the passband, providing the designer with the relationship between the specifications and design parameters and the limits of the optimal design specifications for the passband. For the extended multi-stage design, the study further uses the numerical optimization method to design two- and three-stage lattices and a modified lattice configuration to make the designed filter frequency response meet the system specifications as much as possible given the specific acoustic resonator characteristics and material constraints. Compared with the results in the literature, the bandwidth of the ladder type and the conventional lattice type can be designed with a limit of about 5%; the bandwidth of the modified lattice configuration is not limited by the electromechanical coupling coefficient, and the maximum bandwidth can be designed with a return loss of 10 dB or more. Finally, with a three-stage lattice-type for practical application in the 5G band, the designed bandwidth range from 1.9% to 5.1%, which can meet the requirement of passband return loss of more than 10 dB and also has good out-of-band performance.