| 摘要 |
PROBLEM TO BE SOLVED: To improve stable filter characteristics in a piezoelectric filter device where first and second piezoelectric filters, using the double wave of a thickness vertical oscillation mode, are electrically connected via a relay capacity. SOLUTION: In a piezoelectric filter device 1, first and second piezoelectric filters are connected electrically via a relay capacity 4. At setting of the thickness of piezoelectric substrates 5, 15 in the filter 2, 3 to T1, T2, distances between main surfaces 5a, 15b and ground electrodes 6, 16 of the filters 2, 3 to be respective ta1, ta2, and distances between the main surfaces 5a, 15b and the ground electrode 16 of the filters 2, 3 to be respective tb1, tb2, tb1-ta1 ranges from 0 to 0.1T1 and tb2-ta2 ranges from 0 to 0.1T2, or tb1-ta1 ranges from -0.1T1 to 0, and tb2-ta2 ranges from -0.1T2 to 0.
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