Filter device
A filter device includes a first path, a second path, and a capacitor. The first path includes at least one ladder filter circuit and connects a first terminal and a second terminal. The at least one ladder filter circuit includes a parallel arm resonator connected to a ground terminal. The second path includes a grounded resonator and is connected in parallel with any of the at least one ladder filter circuit. One end of the capacitor is connected to the second path, and the other end of the capacitor is connected to a third path which connects the parallel arm resonator and the ground terminal.
1. A filter device comprising:
a first path including at least one ladder filter circuit and connecting a first terminal and a second terminal, the at least one ladder filter circuit including a parallel arm resonator connected to a ground terminal;
a second path including a grounded resonator; and
a capacitor; wherein
the second path is connected in parallel with any of the at least one ladder filter circuit such that a first end of the second path is connected at a first portion of the at least one ladder filter circuit on the first path and a second end of the second path is connected at a second portion of the at least one ladder filter circuit on the first path; and
one end of the capacitor is connected to the second path, and another end of the capacitor is connected to a third path which connects the parallel arm resonator and the ground terminal.
2. The filter device according to claim 1 , wherein the grounded resonator is a longitudinally coupled resonator.
3. The filter device according to claim 1 , wherein the capacitor is defined by the second path and the third path opposing each other.
4. The filter device according to claim 3 , wherein a ceramic layer is disposed in at least a portion of a space sandwiched between the second path and the third path where the capacitor is provided.
5. The filter device according to claim 1 , wherein the first path includes a transmit filter circuit and a receive filter circuit, the transmit filter circuit being one of the at least one ladder filter circuit to transmit a signal, the receive filter circuit being another one of the at least one ladder filter circuit to receive a signal.
6. The filter device according to claim 5 , wherein the second path is connected in parallel with the transmit filter circuit and the receive filter circuit.
7. The filter device according to claim 5 , wherein the transmit filter circuit includes four series arm resonators disposed on a series arm and three parallel arm resonators disposed on a parallel arm.
8. The filter device according to claim 7 , wherein the series arm resonators and the parallel arm resonators define surface acoustic wave filters.
9. The filter device according to claim 5 , wherein the receive filter includes two series arm resonators, two parallel arm resonators, and a longitudinally coupled resonator unit.
10. The filter device according to claim 9 , wherein the longitudinally coupled resonator unit includes two 5-interdigital-transducer longitudinally coupled resonators and three reflectors.
11. The filter device according to claim 1 , further comprising a piezoelectric substrate on which the at least one ladder filter circuit and the second path are provided.
12. A filter device comprising:
a first path including at least one ladder filter circuit and connecting a first terminal and a second terminal, the at least one ladder filter circuit including a parallel arm resonator connected to a ground terminal;
a second path including a grounded resonator; and
a third path connecting the parallel arm resonator and the ground terminal; wherein
the second path is connected in parallel with any of the at least one ladder filter circuit such that a first end of the second path is connected at a first portion of the at least one ladder filter circuit on the first path and a second end of the second path is connected at a second portion of the at least one ladder filter circuit on the first path; and
a wiring defining the second path and a wiring defining the third path overlap each other as viewed from above.
13. The filter device according to claim 12 , wherein an insulator is disposed between the wiring defining the second path and the wiring defining the third path.
14. The filter device according to claim 12 , wherein the grounded resonator is a longitudinally coupled resonator.
15. The filter device according to claim 12 , wherein the first path includes a transmit filter circuit and a receive filter circuit, the transmit filter circuit being one of the at least one ladder filter circuit to transmit a signal, the receive filter circuit being another one of the at least one ladder filter circuit to receive a signal.
16. The filter device according to claim 15 , wherein the second path is connected in parallel with the transmit filter circuit and the receive filter circuit.
17. The filter device according to claim 15 , wherein the transmit filter circuit includes four series arm resonators disposed on a series arm and three parallel arm resonators disposed on a parallel arm.
18. The filter device according to claim 17 , wherein the series arm resonators and the parallel arm resonators define surface acoustic wave filters.
19. The filter device according to claim 15 , wherein the receive filter includes two series arm resonators, two parallel arm resonators, and a longitudinally coupled resonator unit.
20. The filter device according to claim 19 , wherein the longitudinally coupled resonator unit includes two 5-interdigital-transducer longitudinally coupled resonators and three reflectors.