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

摘要

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.