Patent ID: 11929737
Assignee: MURATA MANUFACTURING CO., LTD.
Field: Basic communication processes (Electrical engineering)
Classification: CPC H | IPC H

Claim 2:
3. A band pass acoustic wave filter having a pass band and an attenuation band on at least one of a lower-frequency side and a higher-frequency side than the pass band, the acoustic wave filter comprising:
a first input/output terminal and a second input/output terminal;
at least one serial arm resonance circuit on a path connecting the first input/output terminal and the second input/output terminal; and
at least one parallel arm resonance circuit between a respective node on the path and a ground; wherein
any serial arm resonance circuit of the at least one serial arm resonance circuit includes a serial arm resonator on the path;
any parallel arm resonance circuit of the at least one parallel arm resonance circuit includes a parallel arm resonator between the respective node and the ground;
each of the at least one serial arm resonator and the at least one parallel arm resonator includes at least one acoustic wave resonator including an IDT (InterDigital Transducer) electrode provided on a substrate having piezoelectricity;
the IDT electrode includes a pair of comb-shaped electrodes each including a plurality of electrode fingers extending in a direction intersecting with an acoustic wave propagation direction and in parallel or substantially in parallel to one another, and bulbar electrodes connecting ends of electrode fingers of the plurality of electrode fingers to each other;
where, among the plurality of electrode fingers:
a first electrode finger which is not connected to the busbar electrodes is defined as a first withdrawal electrode,
a second electrode finger having a maximum electrode finger width, and including an electrode finger width two or more times an average electrode finger width of the plurality of electrode fingers excluding the second electrode finger is defined as a second withdrawal electrode, and
a third electrode finger connected to a same one of the busbar electrodes as adjacent electrode fingers on both adjacent sides of the third electrode finger in the acoustic wave propagation direction is defined as a third withdrawal electrode;

a parallel arm resonator included in a first parallel arm resonance circuit of the at least one parallel arm resonance circuit includes at least one of the first withdrawal electrode, the second withdrawal electrode, and the third withdrawal electrode;
an anti-resonant frequency of the first parallel arm resonance circuit is on the higher-frequency side than the pass band; and
a resonant frequency of a first serial arm resonance circuit of the at least one serial arm resonance circuit is on a lower-frequency side than the anti-resonant frequency of the first parallel arm resonance circuit.