| 摘要 |
PROBLEM TO BE SOLVED: To provide an effective sprious suppressing means in a ladder type piezoelectric filter. SOLUTION: In the ladder type piezoelectric filter, with which a plurality of resonators composed of rectangular piezoelectric elements to be operated in a contour vibrating mode are serially and parallel combined, the characteristics of respective resonators are controlled so that a mountain (m) of a secondary sub-resonance frequency Fa of parallel branch resonators P1 and P2 can be almost matched with a valley (n) of a secondary sub-resonance frequency Fa of serial branch resonators S1 and S2. Thus, the output of each of secondary sub-resonance frequencies is canceled, a spriousγbased on such a secondary sub-resonance frequency is remarkably reduced and filter characteristics are improved.
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