| 摘要 |
PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter with an excellent characteristic that can attain balanced operation under various impedance values. SOLUTION: In a 3-electrode type interdigital electrode 15 where a 1st interdigital electrode 11 is placed on a piezoelectric substrate 10 and 2nd and 3rd interdigital electrodes 12, 13 are placed at both sides in a surface wave propagation direction, and a reflector electrode 14 is placed at both sides of the electrode 15, the 1st interdigital electrode 11 is split around its middle, electrode fingers 11a, 11b are connected to balance input terminals 16a, 16b of a package, one electrode finger of the 2nd and 3rd interdigital electrodes 12, 13 is connected to an earth terminal 18 of the package, the other is connected to an unbalanced output terminal 17, and splitting the 1st interdigital electrode 11 around its mid-position can increase the impedance of the balanced input terminals 16a, 16b by a multiple of 4 in comparison with that before the splitting.
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