Patent ID: 6208224
Filing Date: 2001-03-27
Classification: H03H

Abstract:
A surface acoustic wave filter having a ladder type circuit configuration, comprising:an input terminal;an output terminal;at least one series arm;a plurality of parallel arms;a plurality of series resonators included in the at least one series arm located between the input and output terminals; anda plurality of parallel resonators included in the plurality of parallel arms, respectively, located between the at least one series arm and a reference potential; whereinsaid series resonators and parallel resonators each include a one-port surface acoustic wave resonator, the parallel resonators are arranged alternately with the series resonators along a direction extending from the input terminal toward the output terminal, and a resonant frequency of at least one of the parallel resonators is different from resonant frequencies of the others of the plurality of parallel resonators;first, second, and third of said parallel arms are arranged along the direction extending from the input terminal toward the output terminal, in that order, and the resonant frequency of the parallel resonator included in the second parallel arm is different from the resonant frequencies of the parallel resonators included in the first and third parallel arms, such that if f1 represents the resonant frequency of the parallel resonator included in the second arm, and f2 represents the resonant frequency of at least one of the parallel resonators included in the first and third arms, the following formula (1) is satisfied:f2>f1>0.99.times.f2 formula (1).