Resonator type filter
A resonator is connected in parallel to at least one serial-arm-connected resonator in a resonator type filter having a serial arm and a parallel arm. At this time, the resonance frequency of the resonator connected in parallel is set to be substantially the same as the resonance frequency of the parallel-arm-connected resonator. This makes it possible to prevent the deterioration of attenuation levels at the lower-frequency side of the filter, caused by an increase in the resistance of a connection element due to an increase in packaging density.
1. A resonator type filter comprising:
a serial arm resonator unit; and
a parallel arm resonator unit,
wherein the serial arm resonator unit has two different resonators connected in parallel thereto, and
wherein a resonance frequency of one of the two resonators forming the serial arm resonator unit is substantially equal to a resonance frequency of a resonator of the parallel arm resonator unit.
2. The resonator type filter according to claim 1 ,
wherein bonding wire or VIA hole is used to connect the parallel arm resonator unit and a grounding potential.
3. The resonator type filter according to claim 1 ,
wherein the resonator includes a surface acoustic wave element.
4. The resonator type filter according to claim 3 ,
wherein reflectors of both the two resonators connected in parallel to the serial arm resonator unit are integrally formed.
5. The resonator type filter according to claim 1 ,
wherein the resonator includes a BAW element.
6. The resonator type filter according to claim 4 ,
wherein an inductance element is connected in series to one of the two resonators connected in parallel to the serial arm resonator unit.
7. A branching filter using a resonator type filter, said filter comprising:
a serial arm resonator unit; and
a parallel arm resonator unit,
wherein the serial arm resonator unit has two different resonators connected in parallel thereto, and
wherein a resonance frequency of one of the two resonators forming the serial arm resonator unit is substantially equal to a resonance frequency of a resonator of the parallel arm resonator unit.
8. A front-end module using a resonator type filter, said filter comprising:
a serial arm resonator unit; and
a parallel arm resonator unit,
wherein the serial arm resonator unit has two different resonators connected in parallel thereto, and
wherein a resonance frequency of one of the two resonators forming the serial arm resonator unit is substantially equal to a resonance frequency of a resonator of the parallel arm resonator unit.