Composite filter device
A composite filter device includes bandpass filters whose respective one ends are electrically connected in common. A first bandpass filter of the bandpass filters includes a first filter, a switch, a second filter, and an impedance element that is electrically connected to the switch and having an impedance value larger than the input impedance value of the second filter. The switch is configured to be switched between a first state in which the first filter and the second filter are electrically connected and a second state in which the first filter and the impedance element are electrically connected.
1. A composite filter device, comprising:
bandpass filters having different pass bands; wherein
each of the bandpass filters includes one end and another end;
the one ends of the bandpass filters are electrically connected in common;
at least one of the bandpass filters includes a switch electrically connected between the one end and the another end, a first bandpass filter electrically connected between the one end and the switch, a second bandpass filter electrically connected between the switch and the another end, and an impedance element electrically connected to the switch and having an impedance value larger than an input impedance value of the second bandpass filter; and
the switch is configured to be switched between a first state in which the first bandpass filter and the second bandpass filter are electrically connected and a second state in which the first bandpass filter and the impedance element are electrically connected.
2. The composite filter device according to claim 1 , wherein at least one of the first bandpass filter and the second bandpass filter is an elastic wave filter.
3. The composite filter device according to claim 2 , wherein the first bandpass filter and the second bandpass filter are elastic wave filters.
4. The composite filter device according to claim 2 , wherein
the elastic wave filter includes an elastic wave resonator; and
a range of frequencies higher than or equal to a resonant frequency of the elastic wave resonator and lower than or equal to an anti-resonant frequency of the elastic wave resonator is located in a pass band of another of the bandpass filters other than the at least one of the bandpass filters.
5. The composite filter device according to claim 2 , wherein the second bandpass filter is a longitudinally coupled resonator filter.
6. A high-frequency front end circuit device, comprising:
the composite filter device according to claim 1 ; and
an amplification circuit electrically connected to the composite filter device.
7. A communication device comprising:
the high-frequency front end circuit device according to claim 6 ;
an RF signal processing circuit; and
a baseband signal processing circuit.
8. The composite filter device according to claim 1 , wherein
the switch includes a first switch terminal electrically connected to the first bandpass filter, a second switch terminal electrically connected to the second bandpass filter, and a third switch terminal to which the impedance element is electrically connected;
the first switch terminal and the second switch terminal are electrically connected in the first state; and
the first switch terminal and the third switch terminal are electrically connected in the second state.
9. The composite filter device according to claim 1 , wherein, in the second state, the switch is brought into an OFF state and a value of the impedance element is infinite.
10. The composite filter device according to claim 1 , wherein an out-of-band attenuation of the first bandpass filter is larger than an out-of-band attenuation of the second bandpass filter.
11. The composite filter device according to claim 1 , wherein
the first bandpass filter and the second bandpass filter are ladder filters; and
a total number of stages of a ladder in the first bandpass filter is smaller than a total number of stages of a ladder in the second bandpass filter.
12. The composite filter device according to claim 1 , wherein an impedance matching element is electrically connected between the first bandpass filter and the second bandpass filter.
13. The composite filter device according to claim 1 , wherein
the second bandpass filter is one of a plurality of second bandpass filters; and
the switch includes a plurality of second switch terminals respectively connected to the plurality of second bandpass filters.
14. The composite filter device according to claim 1 , wherein
a pass band of one of the bandpass filters partially overlaps a pass band of another one of the bandpass filters.
15. The composite filter device according to claim 1 , wherein all of the bandpass filters include a switch electrically connected between the one end and the another end, a first bandpass filter electrically connected between the one end and the switch, and a second bandpass filter electrically connected between the switch and the another end, and an impedance element electrically connected to the switch and having an impedance value larger than an input impedance value of the second bandpass filter.
16. The composite filter device according to claim 1 , wherein the first bandpass filter and the second bandpass filter are both ladder filters respectively including series arm resonators and parallel arm resonators.
17. The composite filter device according to claim 1 , wherein the at least one of the bandpass filters includes an additional switch electrically connected between the one end and the another end.
18. The composite filter device according to claim 1 , further comprising an amplifier electrically connected to the second bandpass filter.
19. A composite filter device, comprising:
bandpass filters each including respective one ends and another ends; wherein
the one ends of the bandpass filters are electrically connected in common;
at least one of the bandpass filters includes a first bandpass filter electrically connected to the one end, a second bandpass filter electrically connected between the first bandpass filter and the another end, and a switch electrically connected between the first bandpass filter and the second bandpass filter; and
complex impedances of the first bandpass filter and the second bandpass filter have a same polarity in a pass band of another one of the bandpass filters different from the at least one of the bandpass filters when viewed from a same point in a circuit between the first bandpass filter and the second bandpass filter.
20. The composite filter device according to claim 19 , wherein
each of the bandpass filters includes a first bandpass filter electrically connected to the one end of the respective bandpass filter and a second bandpass filter electrically connected between the first bandpass filter and the another end of the respective bandpass filter; and
in a state in which the first bandpass filter and the second bandpass filter of the respective bandpass filter are electrically connected, complex impedances of the first bandpass filter and the second bandpass filter have a same polarity when viewed from a same point in a circuit between the first bandpass filter and the second bandpass filter of the respective bandpass filter.