Elastic wave filter device

Abstract

A 5-IDT type longitudinally-coupled resonator type elastic wave filter device with narrowly-pitched electrode finger sections improves steepness of the filter characteristics. It is a 5-IDT type longitudinally-coupled resonator type elastic wave filter device (1) having first through a fifth IDTs (11a-11e) wherein, when the total numbers of the electrode fingers provided at the narrowly-pitched electrode finger sections in a first region (R1) and a fourth region (R4) are denoted respectively as Nx, and the total numbers of the electrode fingers provided at the narrowly-pitched electrode finger sections in a second region (R2) and a third region (R3) are denoted respectively as Ny, the average value of the cycles of the electrode fingers is set greater for the narrowly-pitched electrode finger sections in the regions with the greater total numbers between the total numbers Nx of the electrode fingers and the total numbers Ny of the electrode fingers than the narrowly-pitched electrode finger sections in the regions with the smaller total numbers, and cycles of the electrode fingers are set narrower for the IDT electrodes that are included in the regions with the greater total numbers out of the first, the third, and the fifth IDT electrodes (11a, 11c, 11e) than the IDT electrodes that are included in the regions with the smaller total numbers of electrode fingers, except at the parts where the narrowly-pitched electrode finger sections are provided.

Description

technical field [0001] The present invention relates to an elastic wave filter device such as an RF band filter used in a mobile phone, and more specifically, to a longitudinally coupled resonator type elastic wave filter device having first to fifth IDT electrodes. Background technique [0002] In the band filter, it is strongly required to increase the steepness of the filter characteristic in the region between the pass band and the stop domain. Patent Document 1 below discloses a surface acoustic wave filter device capable of enhancing the steepness of filter characteristics. In the surface acoustic wave filter device described in Patent Document 1, acoustic wave resonators are connected in series or in parallel to a 3IDT type longitudinally coupled resonator type surface acoustic wave filter unit. By controlling the position of the resonant frequency or the antiresonant frequency of the elastic wave resonators connected in series or in parallel, the steepness of the fi...

AI Technical Summary

Problems solved by technology

However, the steepness of the filter characteristics is still not high enough, and it is necessary to seek further improvement

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