Acoustic wave filter device
An acoustic wave filter device includes plural filter circuits between an input terminal and an output terminal. Plural inductors are connected in series in a series arm that connects the input terminal and the output terminal, and plural first acoustic wave resonators are connected between the series arm and a ground potential. Each of the filter circuits includes at least one of the inductors and one of the first acoustic wave resonators. A second acoustic wave resonator in the series arm connects adjacent filter circuits. The acoustic wave filter device has a pass band lower than a trap band, steep attenuation characteristics in a range from the pass band to the trap band, and is capable of providing a large amount of attenuation in the trap band.
1. An acoustic wave filter device having a trap band and a pass band lower than the trap band, the acoustic wave filter device comprising:
a plurality of inductors connected in series in a series arm having and connecting an input terminal and an output terminal; and
a plurality of first acoustic wave resonators connected between the series arm and a ground potential, the plurality of inductors and the plurality of first acoustic wave resonators being arranged as a plurality of π-type filter circuits
in a direction from the input terminal to the output terminal, each of the plurality of π-type filter circuits being composed of at least one of the plurality of inductors and the first acoustic wave resonators connected between the ground potential and respective ends of the at least one of the plurality of inductors,
the acoustic wave filter device further comprising a second acoustic wave resonator having an anti-resonance frequency provided in the series arm, wherein in at least one of portions where the plurality of filter circuits are adjacent to each other, the adjacent π-type filter circuits are electrically connected by the second acoustic wave resonator, and
wherein the anti-resonance frequency of the second acoustic wave resonator is located in the trap band defined by a resonance frequency of at least one of the plurality of first acoustic wave resonators.
2. The acoustic wave filter device according to claim 1 , wherein in every portion where π-type_filter circuits are adjacent to each other, the adjacent π-type filter circuits are electrically connected by the second acoustic wave resonator.
3. The acoustic wave filter device according to claim 1 , wherein the plurality of π-type filter circuits are first and second filter circuits, and the first and second filter circuits are electrically connected to each other by the second acoustic wave resonator.
4. The acoustic wave filter device according to claim 2 , wherein the plurality of π-type filter circuits are first and second filter circuits, and the first and second filter circuits are electrically connected to each other by the second acoustic wave resonator.
5. The acoustic wave filter device according to claim 1 , wherein a resonance frequency of at least one of the plurality of first acoustic wave resonators is outside the trap band.
6. The acoustic wave filter device according to claim 2 , wherein a resonance frequency of at least one of the plurality of first acoustic wave resonators is outside the trap band.
7. The acoustic wave filter device according to claim 3 , wherein a resonance frequency of at least one of the plurality of first acoustic wave resonators is outside the trap band.
8. The acoustic wave filter device according to claim 4 , wherein a resonance frequency of at least one of the plurality of first acoustic wave resonators is outside the trap band.
9. The acoustic wave filter device according to claim 5 , wherein the at least one of the plurality of first acoustic wave resonators having the resonance frequency outside the trap band is connected between the output terminal and the ground potential.
10. The acoustic wave filter device according to claim 6 , wherein the at least one of the plurality of first acoustic wave resonators having the resonance frequency outside the trap band is connected between the output terminal and the ground potential.
11. The acoustic wave filter device according to claim 7 , wherein the at least one of the plurality of first acoustic wave resonators having the resonance frequency outside the trap band is connected between the output terminal and the ground potential.
12. The acoustic wave filter device according to claim 8 , wherein the at least one of the plurality of first acoustic wave resonators having the resonance frequency outside the trap band is connected between the output terminal and the ground potential.
13. The acoustic wave filter device according to claim 1 , further comprising a piezoelectric substrate, wherein the plurality of the first acoustic wave resonators and the second acoustic wave resonator are provided on the piezoelectric substrate.
14. The acoustic wave filter device according to claim 1 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.
15. The acoustic wave filter device according to claim 2 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.
16. The acoustic wave filter device according to claim 3 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.
17. The acoustic wave filter device according to claim 4 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.
18. The acoustic wave filter device according to claim 5 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.
19. The acoustic wave filter device according to claim 9 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.
20. The acoustic wave filter device according to claim 13 , wherein an antiresonance frequency of the second acoustic wave resonator is set to be lower than resonance frequencies of the plurality of the first acoustic wave resonators, the resonance frequencies defining the trap band.