| 摘要 |
PROBLEM TO BE SOLVED: To attain a desired passband width without employing an inductor in an electric filter. SOLUTION: The electric filter having a piezoelectric resonator 10 obtaining a signal having a predetermined resonance frequency by a bulk wave propagating through a piezoelectric film 15 is arranged to satisfy a relation k<SP>2</SP>>(BP/0.6f), where k<SP>2</SP>is the square of effective electromechanical coupling coefficient of the piezoelectric resonator 10, BP is the passband width of the electric filter, and f is the central frequency of the objective passband of the electric filter. A desired passband width can be attained even if an inductor is not formed. COPYRIGHT: (C)2005,JPO&NCIPI
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