Filter device and multiplexer

1. A filter device that has a first pass band and a first stop band on a lower frequency side than the first pass band, comprising:

a filter having a pass band including the first pass band;

a series arm resonator connected in series to the filter;

a first inductor directly connected in series to the series arm resonator; and

a first parallel arm resonator connected between a first node on a path connecting the filter and the series arm resonator, and the ground,

wherein the first parallel arm resonator constitutes a first resonance circuit having a resonant frequency at which an attenuation pole corresponding to a high frequency end of the first stop band is formed, and

the series arm resonator and the first inductor constitute a second resonance circuit having an anti-resonant frequency on a lower frequency side than the first pass band and a sub-resonant frequency higher than a resonant frequency of the first resonance circuit.

2. The filter device according to claim 1 ,

wherein the sub-resonant frequency of the second resonance circuit is included in a range of 100% to 110% of the resonant frequency of the first resonance circuit.

3. The filter device according to claim 2 ,

wherein the sub-resonant frequency of the second resonance circuit is included in a range of 100% to 105% of the resonant frequency of the first resonance circuit.

4. The filter device according to claim 2 , further comprising a second parallel arm resonator connected between a second node on a path connecting a first input/output terminal and a second input/output terminal,

wherein:

the filter, the series arm resonator, and the first inductor are disposed on the path connecting the first input/output terminal and the second input/output terminal,

the second parallel arm resonator constitutes a third resonance circuit having a resonant frequency on a lower frequency side than the first pass band, and

a sub-resonant frequency of the second resonance circuit is higher than the resonant frequency of the third resonance circuit.

5. The filter device according to claim 2 ,

wherein the filter is an acoustic wave resonator.

6. The filter device according to claim 2 ,

wherein the filter is an LC filter.

7. The filter device according to claim 2 ,

wherein the filter device has a second pass band on a lower frequency side than the first stop band,

the second pass band corresponds to a communication band of equal to or higher than 1710 MHz and equal to or lower than 2370 MHz,

the first stop band corresponds to a communication band of equal to or higher than 2402 MHz and equal to or lower than 2481.5 MHz, and

the first pass band corresponds to a communication band of equal to or higher than 2510 MHz and equal to or lower than 2690 MHz.

8. A multiplexer comprising:

the filter device according to claim 2 ; and

at least one other filter device, wherein the filter device and the at least one other filter device are connected to a common terminal.

9. The filter device according to claim 1 ,

wherein the filter, the series arm resonator and the first inductor are disposed on a path connecting a first input/output terminal and a second input/output terminal, and

the first inductor is directly connected to the first input/output terminal or the second input/output terminal.

10. The filter device according to claim 1 , further comprising a second parallel arm resonator connected between a second node on a path connecting a first input/output terminal and a second input/output terminal,

wherein:

the filter, the series arm resonator, and the first inductor are disposed on the path connecting the first input/output terminal and the second input/output terminal,

the second parallel arm resonator constitutes a third resonance circuit having a resonant frequency on a lower frequency side than the first pass band, and

a sub-resonant frequency of the second resonance circuit is higher than the resonant frequency of the third resonance circuit.

11. The filter device according to claim 10 ,

wherein the filter is disposed on a path connecting the first node and the second node.

12. The filter device according to claim 11 ,

further comprising a second inductor connected in parallel to the second parallel arm resonator, wherein:

the third resonance circuit comprises the second inductor and the second parallel arm resonator, and

an anti-resonant frequency of the third resonance circuit is higher than a resonant frequency of the first resonance circuit.

13. The filter device according to claim 10 ,

further comprising a second inductor connected in parallel to the second parallel arm resonator, wherein:

the third resonance circuit comprises the second inductor and the second parallel arm resonator, and

an anti-resonant frequency of the third resonance circuit is higher than a resonant frequency of the first resonance circuit.

14. The filter device according to claim 1 ,

wherein the filter is an acoustic wave resonator.

15. The filter device according to claim 1 ,

wherein the filter is an LC filter.

16. The filter device according to claim 1 ,

wherein the filter device has a second pass band on a lower frequency side than the first stop band,

the second pass band corresponds to a communication band of equal to or higher than 1710 MHz and equal to or lower than 2370 MHz,

the first stop band corresponds to a communication band of equal to or higher than 2402 MHz and equal to or lower than 2481.5 MHz, and

the first pass band corresponds to a communication band of equal to or higher than 2510 MHz and equal to or lower than 2690 MHz.

17. A multiplexer comprising:

the filter device according to claim 1 ; and

at least one other filter device, wherein the filter device and the at least one other filter device are connected to a common terminal.

18. The multiplexer according to claim 17 ,

wherein the filter device further has a second pass band, a second stop band, and a third stop band,

the second stop band corresponds to a communication band of equal to or higher than 1428 MHz and equal to or less than 1511 MHz,

the third stop band corresponds to a communication band of equal to or higher than 1559 MHz and equal to or lower than 1608 MHz,

the second pass band corresponds to a communication band of equal to or higher than 1710 MHz and equal to or lower than 2370 MHz,

the first stop band corresponds to a communication band of equal to or higher than 2402 MHz and equal to or lower than 2481.5 MHz,

the first pass band corresponds to a communication band of equal to or higher than 2510 MHz and equal to or lower than 2690 MHz, and

the at least one other filter devices includes:

a first filter device having a pass band corresponding to a communication band of equal to or higher than 690 MHz and equal to or lower than 960 MHz,

a second filter device having a pass band corresponding to the communication band of equal to or higher than 1428 MHz and equal to or lower than 1511 MHz,

a third filter device having a pass band corresponding to the communication band of equal to or higher than 1559 MHz and equal to or lower than 1608 MHz, and

a fourth filter device having a pass band corresponding to the communication band of equal to or higher than 2402 MHz and equal to or lower than 2481.5 MHz.

19. A filter device that has a first pass band and a first stop band on a lower frequency side than the first pass band, comprising:

a filter having a pass band including the first pass band;

a series arm resonator connected in series to the filter;

a first inductor directly connected in series to the series arm resonator; and

a first parallel arm resonator connected between a first node on a path connecting the filter and the series arm resonator, and the ground,

wherein the filter, the series arm resonator and the first inductor are disposed on a path connecting a first input/output terminal and a second input/output terminal, and

the first inductor is directly connected to the first input/output terminal or the second input/output terminal.