| 摘要 |
PROBLEM TO BE SOLVED: To improve the degree of balance inter balanced ends of an elastic surface wave filter of longitudinal coupled resonance type with a balanced- unbalanced conversion function and with almost four times difference between an input impedance to an output impedance. SOLUTION: In an elastic surface wave filter 1 of longitudinal coupled resonance type, first and second elastic surface wave filters 5 and 6 having a plurality of IDT 5a-5c and 6a-6c along the direction of a propagation of surface waves on a piezoelectric board 2 is equipped, each first end of the filters 5 and 6 is connected to a unbalanced signal end 3, each second end of the filters 5 and 6 is connected respectively through grounds ore directly to become balanced signal ends 7 and 8, so that the conversion function is obtained, and in the filters 5 and 6, a duty of electrode arms of narrow pitch electrode arms part are different inter the filters 5 and 6.
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