Patent ID: 7623009
Filing Date: 2009-11-24
Classification: H03H

Abstract:
1. A boundary acoustic wave filter device comprising: a piezoelectric substrate; a dielectric film disposed on the piezoelectric substrate; at least one longitudinally coupled resonator boundary acoustic wave filter including a plurality of IDTs disposed along a boundary between the piezoelectric substrate and the dielectric film; and at least two one-terminal-pair boundary acoustic wave resonators each having an IDT located at the boundary between the piezoelectric substrate and the dielectric film; wherein at least one of the at least two one-terminal-pair boundary acoustic wave resonators defines a serially connected boundary acoustic wave resonator connected in series to the longitudinally coupled resonator boundary acoustic wave filter; at least another of the at least two one-terminal-pair boundary acoustic wave resonators defines a parallel-connected boundary acoustic wave resonator connected in parallel to the longitudinally coupled resonator boundary acoustic wave filter; an anti-resonant frequency of the serially connected boundary acoustic wave resonator is located in a higher frequency range than a passband of the longitudinally coupled resonator boundary acoustic wave filter; a resonant frequency of the parallel-connected boundary acoustic wave resonator is equal to or higher than the anti-resonant frequency of the serially connected boundary acoustic wave resonator; the piezoelectric substrate is a single-crystal-LiNbO a terminal impedance of the at least one longitudinally coupled resonator boundary acoustic wave filter in the passband is inductive.