Patent ID: 6822536
Filing Date: 2004-11-23
Classification: H03H

Abstract:
A longitudinally coupled multi-mode piezoelectric bulk wave filter device comprising:first and second multi-mode piezoelectric bulk wave filters which are designed so that vibration modes of different orders of harmonic waves are excited and coupled to provide an output signal between an output electrode and an ground electrode when an input signal is input between an input electrode and the ground electrode; and a casing substrate on which the first and second longitudinally coupled multi-mode piezoelectric bulk wave filters are disposed on a surface thereof, wherein each of the first and second multi-mode piezoelectric bulk wave filters includes: at least four exciting electrodes extending substantially parallel to each other; and a laminated piezoelectric body having a plurality of piezoelectric layers arranged between the exciting electrodes and polarized in a direction that is substantially perpendicular to or substantially parallel to the exciting electrodes and having first and second end surfaces facing in a direction that is substantially perpendicular to the plurality of the piezoelectric layers and first through fourth side surfaces connecting the first and second end surfaces; wherein the input electrode is disposed on at least one of the first through fourth side surfaces of the laminated piezoelectric body closer to the first end surface; the output electrode is disposed on at least one of the first through fourth side surfaces of the laminated piezoelectric body closer to the second end surface; the ground electrode is disposed on at least one of the first through fourth side surfaces of the laminated piezoelectric body; the at least four exciting electrodes includes a first group which is connected to the input electrode, a second group which is connected to the output electrode, and a third group which is connected to the ground electrode; the first and second multi-mode piezoelectric bulk wave filters are cascaded and arranged so that distance between the ground electrodes of the first and second multi-mode piezoelectric bulk wave filters is smaller than the distance between the input electrodes of the first and second multi-mode piezoelectric bulk wave filters and the distance between the output electrodes of the first and second multi-mode piezoelectric bulk wave filters.