Acoustic wave filter device, radio-frequency front-end circuit, and communication apparatus
A filter includes a series-arm resonator connected on a path connecting input/output terminals, and first and second parallel-arm resonators connected between the same node on the path and ground. A resonant frequency of the second parallel-arm resonator is higher than a resonant frequency of the first parallel-arm resonator, and an anti-resonant frequency of the second parallel-arm resonator is higher than an anti-resonant frequency of the first parallel-arm resonator. Each of the first and second parallel-arm resonators includes an acoustic wave resonator including an IDT electrode. The IDT electrode in the second parallel-arm resonator has a higher duty ratio than the IDT electrode in the first parallel-arm resonator, where the duty ratio is the ratio of the width to the pitch of electrode fingers.
1. an acoustic wave filter device comprising:
a series-arm resonant circuit connected on a path connecting a first input/output terminal and a second input/output terminal; and
a first parallel-arm resonator and a second parallel-arm resonator connected between a node on the path and ground; wherein,
a resonant frequency of the second parallel-arm resonator is higher than a resonant frequency of the first parallel-arm resonator;
an anti-resonant frequency of the second parallel-arm resonator is higher than an anti-resonant frequency of the first parallel-arm resonator;
each of the first parallel-arm resonator and the second parallel-arm resonator includes an acoustic wave resonator including an IDT electrode; and
the IDT electrode in the second parallel-arm resonator has a duty ratio that is higher than a duty ratio of the IDT electrode in the first parallel-arm resonator, the duty ratio being a ratio of a width of a plurality of electrode fingers to a pitch of the plurality of electrode fingers included in the corresponding IDT electrode.
2. The acoustic wave filter device according to claim 1 , wherein
the series-arm resonant circuit includes an acoustic wave resonator including an IDT electrode; and
the duty ratio of the IDT electrode in the first parallel-arm resonator is lower than a duty ratio of the IDT electrode in the series-arm resonant circuit.
3. The acoustic wave filter device according to claim 1 , wherein the first parallel-arm resonator and the second parallel-arm resonator are connected in parallel.
4. The acoustic wave filter device according to claim 3 , further comprising:
an impedance element and a switch element that are connected in parallel and that are connected in series with at least one of the first parallel-arm resonator and the second parallel-arm resonator.
5. The acoustic wave filter device according to claim 4 , wherein the impedance element and the switch element that are connected in parallel are connected in series with only the second parallel-arm resonator of the first and second parallel-arm resonators.
6. The acoustic wave filter device according to claim 4 , wherein the impedance element and the switch element that are connected in parallel are connected in series with only the first parallel-arm resonator of the first and second parallel-arm resonators.
7. The acoustic wave filter device according to claim 4 , wherein the impedance element and the switch element that are connected in parallel are connected in series with a circuit including the first parallel-arm resonator and the second parallel-arm resonator connected in parallel.
8. The acoustic wave filter device according to claim 3 , further comprising:
an impedance element and a switch element that are connected in parallel and that are connected in series with only the first parallel-arm resonator of the first and second parallel-arm resonators; and
another impedance element and another switch element that are connected in parallel and that are connected in series with only the second parallel-arm resonator of the first and second parallel-arm resonators.
9. The acoustic wave filter device according to claim 1 , wherein the first parallel-arm resonator and the second parallel-arm resonator are connected in series.
10. The acoustic wave filter device according to claim 1 , wherein the first parallel-arm resonator and the second parallel-arm resonator are connected in series; and
the acoustic wave filter device further includes a switch element connected in parallel to one of the first parallel-arm resonator and the second parallel-arm resonator.
11. The acoustic wave filter device according to claim 1 ,
wherein the IDT electrode in the second parallel-arm resonator has a lower aspect ratio than the IDT electrode in the first parallel-arm resonator, the aspect ratio being a ratio of an overlap width of the plurality of electrode fingers to a number of pairs of electrode fingers in the corresponding IDT electrode.
12. The acoustic wave filter device according to claim 1 , wherein
the series-arm resonant circuit is a series-arm resonator including one or more acoustic wave resonators; and
the series-arm resonant circuit, the first parallel-arm resonator, and the second parallel-arm resonator define a ladder filter structure.
13. The acoustic wave filter device according to claim 1 , wherein the series-arm resonant circuit is a longitudinally coupled resonator including a plurality of acoustic wave resonators.
14. A radio-frequency front-end circuit comprising:
the acoustic wave filter device according to claim 1 ; and
an amplifier circuit connected to the acoustic wave filter device.
15. The radio-frequency front-end circuit according to claim 14 , wherein
the series-arm resonant circuit includes an acoustic wave resonator including an IDT electrode; and
the duty ratio of the IDT electrode in the first parallel-arm resonator is lower than a duty ratio of the IDT electrode in the series-arm resonant circuit.
16. The radio-frequency front-end circuit according to claim 14 , wherein the first parallel-arm resonator and the second parallel-arm resonator are connected in parallel.
17. The radio-frequency front-end circuit according to claim 16 , further comprising:
an impedance element and a switch element that are connected in parallel and that are connected in series with at least one of the first parallel-arm resonator and the second parallel-arm resonator.
18. The radio-frequency front-end circuit according to claim 17 , wherein the impedance element and the switch element that are connected in parallel are connected in series with only the second parallel-arm resonator of the first and second parallel-arm resonators.
19. The radio-frequency front-end circuit according to claim 17 , wherein the impedance element and the switch element that are connected in parallel are connected in series with only the first parallel-arm resonator of the first and second parallel-arm resonators.
20. A communication apparatus comprising:
an RF signal processing circuit that processes a radio-frequency signal transmitted or received by an antenna element; and
the radio-frequency front-end circuit according to claim 14 that transmits the radio-frequency signal between the antenna element and the RF signal processing circuit.