Acoustic wave filter and multiplexer
An acoustic wave filter includes a first filter circuit on a first path and an additional circuit connected to the first path. The first filter circuit includes a series arm resonator and a longitudinally coupled resonator. The longitudinally coupled resonator includes a first acoustic wave resonator and a first reflector. The additional circuit includes a second acoustic wave resonator on the opposite side of the first acoustic wave resonator with respect to the first reflector. The second acoustic wave resonator includes a first end connected to the first path through a second path and a second end connected to ground. The series arm resonator is connected to a portion of the first path between a connection node at which the second acoustic wave resonator is connected to the first path and the longitudinally coupled resonator.
1 . An acoustic wave filter comprising:
a first filter circuit on a first path that connects a first terminal to a second terminal; and
an additional circuit connected to the first path; wherein
the first filter circuit includes:
one or more series arm resonators; and
a longitudinally coupled resonator connected to a predetermined series arm resonator of the one or more series arm resonators;
the longitudinally coupled resonator includes:
a first acoustic wave resonator; and
a first reflector in a propagation direction of an acoustic wave excited by the first acoustic wave resonator with respect to the first acoustic wave resonator;
the additional circuit includes a second acoustic wave resonator on an opposite side of the first acoustic wave resonator with respect to the first reflector in the propagation direction of the acoustic wave;
the second acoustic wave resonator includes a first end connected to the first path through a second path that is different from the first path and a second end connected to ground;
the predetermined series arm resonator is connected to a portion of the first path between a connection node at which the second acoustic wave resonator is connected to the first path and the longitudinally coupled resonator;
the first acoustic wave resonator and the second acoustic wave resonator each include an IDT electrode; and
the IDT electrode of the first acoustic wave resonator is at least partly overlapped with the IDT electrode of the second acoustic wave resonator in the propagation direction of the acoustic wave.
2 . The acoustic wave filter according to claim 1 , wherein
the IDT electrode of the second acoustic wave resonator includes a plurality of comb electrodes that face each other; and
a comb electrode of the plurality of comb electrodes is connected to a portion of the first path located on an opposite side of the longitudinally coupled resonator with respect to the predetermined series arm resonator through the second path, and another comb electrode thereof is connected to the ground.
3 . The acoustic wave filter according to claim 1 , wherein the additional circuit includes a second reflector on an opposite side of the first reflector with respect to the second acoustic wave resonator in the propagation direction of the acoustic wave.
4 . The acoustic wave filter according to claim 1 , wherein the additional circuit includes a reactor on the second path.
5 . The acoustic wave filter according to claim 1 , wherein
the additional circuit includes a plurality of the second acoustic wave resonators; and
the plurality of the second acoustic wave resonators are on the opposite side of the first acoustic wave resonator with respect to the first reflector in the propagation direction of the acoustic wave.
6 . The acoustic wave filter according to claim 1 , wherein
the additional circuit includes a plurality of the second acoustic wave resonators; and
the plurality of the second acoustic wave resonators are provided at respective outer side portions of the longitudinally coupled resonator in the propagation direction of the acoustic wave.
7 . The acoustic wave filter according to claim 1 , wherein
the longitudinally coupled resonator includes a plurality of the first acoustic wave resonators connected in parallel; and
the additional circuit is between the plurality of the first acoustic wave resonators in the propagation direction of the acoustic wave.
8 . The acoustic wave filter according to claim 1 , wherein the first filter circuit further includes another resonator that is different from the one or more series arm resonators.
9 . The acoustic wave filter according to claim 1 , wherein
the additional circuit includes a plurality of the second acoustic wave resonators;
the second acoustic wave resonator of the plurality of the second acoustic wave resonators includes a first end connected to a portion of the first path on a side of the first terminal and a second end connected to the ground; and
the other second acoustic wave resonator that is different from the second acoustic wave resonator includes a first end connected to a portion of the first path on a side of the second terminal and a second end connected to the ground.
10 . A multiplexer comprising:
the austic wave filter of claim 1 ; and
a second filter circuit that is different from the acoustic wave filter; wherein
the acoustic wave filter and the second filter circuit are connected to a common terminal; and
on the first path, the connection node at which the second acoustic wave resonator is connected to the first path is closer to the common terminal than a connection node at which the predetermined series arm resonator is connected to the first path.
11 . The multiplexer according to claim 10 , wherein the additional circuit and the first filter circuit of the acoustic wave filter have opposite signal phases in a pass band of the second filter circuit.
12 . The multiplexer according to claim 10 , wherein
the IDT electrode of the second acoustic wave resonator includes a plurality of comb electrodes that face each other; and
a comb electrode of the plurality of comb electrodes is connected to a portion of the first path located on an opposite side of the longitudinally coupled resonator with respect to the predetermined series arm resonator through the second path, and another comb electrode thereof is connected to the ground.
13 . The multiplexer according to claim 10 , wherein the additional circuit includes a second reflector on an opposite side of the first reflector with respect to the second acoustic wave resonator in the propagation direction of the acoustic wave.
14 . The multiplexer according to claim 10 , wherein the additional circuit includes a reactor on the second path.
15 . The multiplexer according to claim 10 , wherein
the additional circuit includes a plurality of the second acoustic wave resonators; and
the plurality of the second acoustic wave resonators are on the opposite side of the first acoustic wave resonator with respect to the first reflector in the propagation direction of the acoustic wave.
16 . The multiplexer according to claim 10 , wherein
the additional circuit includes a plurality of the second acoustic wave resonators; and
the plurality of the second acoustic wave resonators are provided at respective outer side portions of the longitudinally coupled resonator in the propagation direction of the acoustic wave.
17 . The multiplexer according to claim 10 , wherein
the longitudinally coupled resonator includes a plurality of the first acoustic wave resonators connected in parallel; and
the additional circuit is between the plurality of the first acoustic wave resonators in the propagation direction of the acoustic wave.
18 . The multiplexer according to claim 10 , wherein the first filter circuit further includes another resonator that is different from the one or more series arm resonators.