Filter apparatus, multiplexer, radio-frequency front end circuit, and communication apparatus
A filter includes a series arm resonant circuit connected between input/output terminals, and a parallel arm resonant circuit connected between a node on a path connecting the input/output terminals and ground. The series arm resonant circuit includes a series arm resonator having a band width ratio wider than the band width ratio of the parallel arm resonant circuit and a capacitor connected to the series arm resonator.
1. A filter apparatus comprising:
a series arm resonant circuit connected between a first input/output terminal and a second input/output terminal; and
a parallel arm resonant circuit connected to a node on a path connecting the first input/output terminal to the second input/output terminal and ground; wherein
when a value calculated by dividing a frequency difference between an anti-resonant frequency at a lowest frequency side, among one or more anti-resonant frequencies of a resonant circuit, and a resonant frequency at the lowest frequency side, among one or more resonant frequencies of the resonant circuit, by the resonant frequency, is defined as a band width ratio of the resonant circuit, and a value calculated by dividing a frequency difference between an anti-resonant frequency of a resonator and a resonant frequency of the resonator by the resonant frequency is defined as a band width ratio of the resonator;
the series arm resonant circuit includes:
a first series arm resonator having a band width ratio higher than the band width ratio of the parallel arm resonant circuit; and
a first capacitor connected to the first series arm resonator.
2. The filter apparatus according to claim 1 , wherein the band width ratio of the series arm resonant circuit is equal or substantially equal to the band width ratio of the parallel arm resonant circuit.
3. The filter apparatus according to claim 1 , wherein the first series arm resonator is an acoustic wave resonator including an IDT electrode including a plurality of electrode fingers provided on a substrate at least partially having piezoelectricity.
4. The filter apparatus according to claim 3 , wherein
the first capacitor is defined by the substrate and a first interdigital capacitor electrode including a plurality of electrode fingers provided on the substrate; and
a pitch of the plurality of electrode fingers in the first interdigital capacitor electrode is narrower than a pitch of the plurality of electrode fingers in the first series arm resonator.
5. The filter apparatus according to claim 4 , wherein a film thickness of the plurality of electrode fingers in the first interdigital capacitor electrode is smaller than or equal to a film thickness of the plurality of electrode fingers in the first series arm resonator.
6. The filter apparatus according to claim 1 , wherein
the first series arm resonator is connected on the path; and
the first capacitor is connected in parallel to the first series arm resonator.
7. The filter apparatus according to claim 1 , wherein
the first series arm resonator is connected on the path;
the series arm resonant circuit includes a first impedance element connected in series to the first series arm resonator;
a circuit in which the first series arm resonator is connected in series to the first impedance element is connected in parallel to the first capacitor; and
the first impedance element is one of a second capacitor or an inductor.
8. The filter apparatus according to claim 1 , wherein
the first series arm resonator is connected on the path;
the series arm resonant circuit further includes:
a first impedance element connected in series to the first series arm resonator; and
a first switch connected in series to the first capacitor;
a circuit in which the first series arm resonator is connected in series to the first impedance element is connected in parallel to a circuit in which the first capacitor is connected in series to the first switch; and
the first impedance element is one of a second capacitor or an inductor.
9. The filter apparatus according to claim 7 , wherein the series arm resonant circuit further includes a second switch connected in parallel to the first impedance element.
10. The filter apparatus according to claim 1 , wherein
the first series arm resonator is connected on the path;
the series arm resonant circuit further includes a first switch connected in series to the first capacitor; and
the first series arm resonator is connected in parallel to a circuit in which the first capacitor is connected in series to the first switch.
11. The filter apparatus according to claim 1 , wherein
the parallel arm resonant circuit includes a first parallel arm resonator connected between the node and the ground;
the band width ratio of the first parallel arm resonator is narrower than the band width ratio of the first series arm resonator; and
the resonant frequency of the first parallel arm resonator is lower than the resonant frequency of the first series arm resonator, and the anti-resonant frequency of the first parallel arm resonator is lower than the anti-resonant frequency of the first series arm resonator.
12. The filter apparatus according to claim 1 , wherein the parallel arm resonant circuit includes:
a first parallel arm resonator connected between the node and the ground; and
a third capacitor connected in series to the first parallel arm resonator;
the band width ratio of the first parallel arm resonator is equal to or narrower than the band width ratio of the first series arm resonator; and
the resonant frequency of the first parallel arm resonator is lower than the resonant frequency of the first series arm resonator, and the anti-resonant frequency of the first parallel arm resonator is lower than the anti-resonant frequency of the first series arm resonator.
13. The filter apparatus according to claim 1 , wherein the parallel arm resonant circuit includes:
a first parallel arm resonator connected between the node and the ground; and
a first variable frequency circuit connected to the first parallel arm resonator and that varies at least one of the resonant frequency and the anti-resonant frequency of the parallel arm resonant circuit;
the first variable frequency circuit includes:
a third capacitor connected in series to the first parallel arm resonator; and
a third switch connected in parallel to the third capacitor;
the band width ratio of the first parallel arm resonator is equal to or narrower than the band width ratio of the first series arm resonator; and
the resonant frequency of the first parallel arm resonator is lower than the resonant frequency of the first series arm resonator, and the anti-resonant frequency of the first parallel arm resonator is lower than the anti-resonant frequency of the first series arm resonator.
14. The filter apparatus according to claim 13 , wherein
the parallel arm resonant circuit further includes a second parallel arm resonator connected between the node and the ground;
the second parallel arm resonator is connected in parallel to a circuit in which the first parallel arm resonator is connected in series to the first variable frequency circuit;
the band width ratio of the second parallel arm resonator is equal to or narrower than the band width ratio of the first series arm resonator; and
the resonant frequency of the second parallel arm resonator is higher than the resonant frequency of the first parallel arm resonator, and the anti-resonant frequency of the second parallel arm resonator is higher than the anti-resonant frequency of the first parallel arm resonator.
15. The filter apparatus according to claim 1 , wherein the parallel arm resonant circuit includes:
a first parallel arm resonator connected between the node and the ground;
a second parallel arm resonator connected between the node and the ground; and
a second variable frequency circuit connected to the second parallel arm resonator and that varies at least one of the resonant frequency and the anti-resonant frequency of the parallel arm resonant circuit;
the second variable frequency circuit includes:
a fourth capacitor connected in series to the second parallel arm resonator; and
a fourth switch connected in parallel to the fourth capacitor;
the first parallel arm resonator is connected in parallel to a circuit in which the second parallel arm resonator is connected in series to the fourth capacitor;
the band width ratio of the first parallel arm resonator is equal to or narrower than the band width ratio of the first series arm resonator;
the resonant frequency of the first parallel arm resonator is lower than the resonant frequency of the first series arm resonator, and the anti-resonant frequency of the first parallel arm resonator is lower than the anti-resonant frequency of the first series arm resonator;
the band width ratio of the second parallel arm resonator is equal to or narrower than the band width ratio of the first series arm resonator; and
the resonant frequency of the second parallel arm resonator is higher than the resonant frequency of the first parallel arm resonator, and the anti-resonant frequency of the second parallel arm resonator is higher than the anti-resonant frequency of the first parallel arm resonator.
16. The filter apparatus according to claim 11 , wherein
each of the first series arm resonator and the first parallel arm resonator is an acoustic wave resonator including an IDT electrode including a plurality of electrode fingers provided on a substrate at least partially having piezoelectricity; and
a first adjustment film that adjusts the band width ratio is provided between the IDT electrode of at least the first parallel arm resonator, in the first series arm resonator and the first parallel arm resonator, and the substrate.
17. The filter apparatus according to claim 11 , wherein
each of the first series arm resonator and the first parallel arm resonator is an acoustic wave resonator including an IDT electrode including a plurality of electrode fingers provided on a substrate at least partially having piezoelectricity; and
a second adjustment film that adjusts the band width ratio covers the IDT electrode of at least the first parallel arm resonator, in the first series arm resonator and the first parallel arm resonator.
18. A multiplexer comprising:
a common terminal;
the filter apparatus according to claim 1 ; and
a first filter having a pass band at a high frequency side of a pass band of the filter apparatus; wherein
the first input/output terminal and the first filter are connected to the common terminal.
19. The multiplexer according to claim 18 , wherein
the filter apparatus further includes one or more acoustic wave resonators; and
the series arm resonant circuit is connected to the common terminal without the one or more acoustic wave resonators and the parallel arm resonant circuit interposed therebetween.
20. A multiplexer comprising:
a common terminal;
the filter apparatus according to claim 8 , in which the first input/output terminal is connected to the common terminal;
a first filter including a first terminal and a second terminal and in which the first terminal is connected to the common terminal; and
a switch circuit including a third terminal, a first selection terminal, and a second selection terminal and in which the first selection terminal is connected to the second input/output terminal and the second selection terminal is connected to the second terminal to switch between a connection of the third terminal to the first selection terminal and a connection of the third terminal to the second selection terminal; wherein
the frequency of a pass band of the first filter is higher than the frequency of a pass band of the filter apparatus;
the filter apparatus further includes one or more acoustic wave resonators;
the series arm resonant circuit is connected to the common terminal without the one or more acoustic wave resonators and the parallel arm resonant circuit interposed therebetween; and
when the third terminal is not connected to the first selection terminal, the first switch is in a conducting state.
21. A radio-frequency front end circuit comprising:
the filter apparatus according to claim 1 ; and
an amplifier circuit connected to the filter apparatus.
22. A communication apparatus comprising:
an RF signal processing circuit that processes a radio-frequency signal transmitted and received through an antenna element; and
the radio-frequency front end circuit according to claim 21 , which transmits the radio-frequency signal between the antenna element and the RF signal processing circuit.