| CPC H03H 9/6483 (2013.01) [H03H 9/145 (2013.01); H03H 9/25 (2013.01); H03H 9/725 (2013.01)] | 11 Claims |
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1. A filter comprising:
a support substrate;
a piezoelectric layer provided on the support substrate;
one or more series resonators connected in series between an input terminal and an output terminal, wherein each of the one or more series resonators has a plurality of first electrode fingers provided on the piezoelectric layer and having a first average pitch;
one or more parallel resonators having one end connected to a path between the input terminal and the output terminal and another end connected to a ground, wherein each of the one or more parallel resonators has a plurality of second electrode fingers provided on the piezoelectric layer and having a second average pitch more than a maximum first average pitch;
another resonator having one end connected to the path, wherein the another resonator has a plurality of third electrode fingers provided on the piezoelectric layer and having a third average pitch less than or equal to an intermediate value that is half a sum of the maximum first average pitch and a minimum second average pitch; and
an inductor having one end connected to another end of the another resonator and another end connected to the ground, and having an inductance more than a maximum inductance connected between the one or more parallel resonators and the ground,
wherein when the maximum first average pitch is Dsmax and a minimum first average pitch which is different from the maximum first average pitch is Dsmin, (Dsmax−Dsmin)/(Dsmax+Dsmin) is 0.005 or less.
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