Patent ID: 6608428
Filing Date: 2003-08-19
Classification: H03H

Abstract:
A longitudinally coupled multi-mode piezoelectric filter utilizing a piezoelectric stiffened effect, comprising:a multilayer piezoelectric element, the multilayer piezoelectric element including: at least four excitation electrodes arranged substantially parallel to one another, and a plurality of piezoelectric layers each provided between adjacent ones of said at least four excitation electrodes and polarized in a direction that is substantially perpendicular to or substantially parallel to the excitation electrodes, wherein the multilayer piezoelectric element has first and second end surfaces opposing each other in the direction that is substantially perpendicular to the excitation electrodes; a ground electrode provided on an outer surface of the multilayer piezoelectric element and electrically connected to a first group defined by at least two of the at least four excitation electrodes, the at least two of the excitation electrodes of the first group being selectively arranged in the direction in which the piezoelectric layers are provided; an input electrode provided on the outer surface of the multilayer piezoelectric element and electrically connected to a second group defined by at least one of the at least four excitation electrodes, the at least one of the excitation electrodes of the second group being arranged toward the first end surface and being other than the excitation electrodes of the first group; and an output electrode provided on the outer surface of the multilayer piezoelectric element and electrically connected to a third group defined by at least one of the excitation electrodes, the at least one of the excitation electrodes of the third group being arranged toward the second end surface and being other than the excitation electrodes of the first group; wherein an input signal applied between the input electrode and the ground electrode causes vibration of different order modes to be excited and coupled, such that an output signal is extracted between the output electrode and the ground electrode.