Longitudinally coupled resonator type elastic wave filter

Abstract

Provided is a longitudinally coupled resonator type elastic wave filter in which electric power resistance and weather resistance are unlikely to be degraded. In a longitudinally coupled resonator type elastic wave filter 1: first to third IDT electrodes 3-5 are provided on a piezoelectric substrate 2; the first to third IDT electrodes 3-5 each have a plurality of first electrode fingers 13, 23, 33, respectively, and each have a plurality of second electrode fingers 14, 24, 34, respectively; the IDT electrodes 3-5 have narrow pitch electrode finger sections each having a pitch between electrode fingers that is narrower than that of the remaining electrode finger sections; in the first to third IDT electrodes 3-5, an intersection region A has a center region B, and first and second edge regions C1, C2 provided outward of the center region B in a direction in which the first and second electrode fingers 13, 14 are extended; and in the remaining electrode finger sections other than the narrow pitch electrode finger sections, the first electrode fingers 13, 23, 33 and the second electrode fingers 14, 24, 34 have large width sections 15, 16, 25, 26, 35, 36 having large widths in the first or second edge region C1, C2.

Description

technical field [0001] The present invention relates to a longitudinally coupled resonator-type elastic wave filter having narrow-pitch electrode fingers. Background technique [0002] Conventionally, the ripple caused by the transverse mode has been suppressed by utilizing the piston mode. For example, Patent Document 1 below discloses a longitudinally coupled resonator type elastic wave filter using a piston mode. In the longitudinally coupled resonator type elastic wave filter described in Patent Document 1, the intersecting region of the IDT electrodes has a central region and first and second edge regions provided on both sides of the central region in the direction in which electrode fingers extend. The first electrode finger has a wider portion in the second edge region than the rest of the electrode finger. The second electrode refers to having a wide portion in the first IDT electrode. [0003] However, in an IDT electrode having narrow-pitch electrode fingers, t...

AI Technical Summary

Problems solved by technology

[0003] However, in an IDT electrode having narrow-pitch electrode fingers, the distance between the electrode fingers becomes narrower in the narrow-pitch electrode fingers than in the remaining electrode fingers, and the elastic wave propagation velocity changes in the elastic wave propagation direction.

In the structure where the length and width of the electrode region are fixed, it is effective for one elastic wave propagation speed, but it is not effective for the part where the elastic wave propagation speed is different. Therefore, in the IDT electrode with narrow-pitch electrode fingers case, the ripple caused by the transverse mode cannot be sufficiently suppressed

Images