Patent ID: 6466106
Filing Date: 2002-10-15
Classification: H03H

Abstract:
A piezoelectric filter device which operates by using a second harmonic wave of a thickness-extension vibration mode comprising:a first piezoelectric filter and a second piezoelectric filter electrically connected to each other; a relay capacitor interposed between said first piezoelectric filter and said second piezoelectric filter, the first and second piezoelectric filters being polarized in their thickness directions, each of the first and second piezoelectric filters including: a pair of mutually opposing piezoelectric substrate plates each having a first main surface and a second main surface; a ground electrode provided between the piezoelectric substrate plates; an input electrode provided on the first main surface of one of the piezoelectric substrate plates such that said input electrode is opposite to one portion of the ground electrode with said one of the piezoelectric substrate plates partially interposed between said input electrode and said ground electrode; an output electrode provided on the second main surface of the other piezoelectric substrate plate such that said output electrode is opposite to the ground electrode in a portion other than said one portion thereof, with said other of the piezoelectric substrate plates partially interposed between said output electrode and said ground electrode; wherein a distance between the first main surface of the first piezoelectric filter and the adjacent ground electrode is ta1, a distance between the second main surface of the first filter and the adjacent ground electrode is tb1, a distance between the second main surface of the second piezoelectric filter and the adjacent ground electrode is ta2, a distance between the first main surface of the second piezoelectric filter and the adjacent ground electrode is tb2, the thicknesses of the piezoelectric substrate plates of the first and second piezoelectric filters are T1 and T2, respectively, such that 01âˆ’ta1&lE;0.1Ã—T1, 02âˆ’ta2&lE;0.1Ã—T2, or âˆ’0.1Ã—T1&lE;tb1âˆ’ta1<0, âˆ’0.1Ã—T2&lE;tb2âˆ’ta2<0.