Synthesis of wideband bulk acoustic wave coupled resonator filter combined with lumped components

• Published in: International journal of circuit theory and applications Vol. 50; no. 6; pp. 1907 - 1921
• Main Authors: Li, Qingwen, Li, Xiuping, Xie, Yuqiang, Cao, Zheyan, Dong, Jiarui
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.06.2022
• Subjects: Acoustic coupling; Acoustic waves; Broadband; bulk acoustic wave; Chebyshev approximation; coupled resonator filter; filter synthesis; Finite element method; Inductors; Narrowband; Prototypes; Resonators; Simulation; Synthesis; wideband filter
• ISSN: 0098-9886; 1097-007X
• DOI: 10.1002/cta.3267

Summary A novel wideband bulk acoustic wave (BAW) coupled resonator filter (CRF) combined with external lumped inductors and capacitors is proposed. The filter synthesis method based on the Butterworth–van Dyke (BVD) model of CRF (CRF‐BVD) is also presented. To improve the synthesis accuracy, the CRF‐BVD model is modified and the CRF configuration with a single rather than the traditional multiple coupling layer is adopted in this paper. By establishing equivalence relationships between the modified CRF‐BVD model and the filter prototype synthesis network, exact CRF dimensions are solved through a set of equations without any further parameters tuning. The proposed method exhibits a maximum 37.4% (FBW) for a Chebyshev filter with 9.4‐dB return loss, which overcomes the narrowband limitation of regular BAW filters with FBW below 5%. To demonstrate the synthesis procedure, an n77 band filter with 3.723‐GHz center frequency and 24.2% FBW is designed and simulated. Good agreements are obtained among the simulation results of the prototype synthesis network, the modified CRF‐BVD model, and the co‐simulations of physical model based on the finite element method (FEM) and the CMOS 130‐nm technology. A wideband BAW CRF is proposed by introducing external inductors and capacitors, which exhibits a maximum 37.4% FBW with 9.4‐dB return loss. A synthesis method for wideband CRF design is also developed. Though the synthesis method, exact CRF dimensions can be solved through a set of equations without any further parameters tuning. A n77 band filter is designed and simulated to verify the proposed CRF and synthesis method.