Acoustic Wave Coupled Resonator Filter Research Articles

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

SummaryA 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.

Bulk acoustic wave-coupled resonator filters: Concept, design, and application

Bulk-acoustic-wave-coupled resonator filters is an emerging technology that is capable of meeting increasingly ambitious demands of wireless applications by addressing performance, chip size, and die cost. This article outlines the fundamental design principles of these filters. A major consideration of filter design is the choice of the coupling structure between the two vertically stacked resonators. This can be either a multilayer Bragg coupler or a novel structure using a single layer of a very low acoustic impedance material. It is demonstrated how spurious modes are related to the dispersion diagram and how they affect the passband characteristics. For the suppression of these spurious modes suitable edge termination techniques are discussed. Based on optimized coupler performance and known parasitic effects, we analyze circuit design methods for microwave filters and duplexers with specific passband, roll-off, and wideband responses. We show as example a miniature 2.0 × 1.6 mm2 Universal Mobile Telecommunication System (UMTS) Band1 duplexer fabricated using the coupler resonator technology. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. © 2011 Wiley Periodicals, Inc.

Analysis Technique for Asymmetrically Coupled Resonator Structures

Asymmetrical acoustically coupled structures are present in several acoustic applications. Specifically when they are used in filter design, some configurations provide unexplored and special response characteristics with high selectivity and relatively wide bandwidths. The relationships between geometries, configurations, and response specifications do not rely on a direct link. In this work, a novel approach to the analysis of these structures is presented as well as a model of an asymmetrical bulk acoustic wave coupled resonator filter obtained from the analysis presented.

Closed-Form Expressions for the Design of BAW CRF Acoustic Inverters

A bulk acoustic wave coupled resonator filter is a device in which two thin film bulk acoustic wave resonators are stacked on top of each other separated by a set of passive layers which control the degree of acoustic interaction between resonators contributing to the conformation of the radiofrequency passband response. The set of passive layers implements an impedance inverter which has to fulfill the desired coupling value. The variation of the acoustic lengths of the coupling layers gives the degree of freedom to implement the desired inverter. In this work, a set of closed-form expressions are provided to obtain the coupling layers thicknesses without any time-consuming optimization procedure. The provided solution gives an explanation to the underlying fundamentals that take place in a successful optimization procedure.