Ladder-type filter, duplexer, and module
A ladder-type filter includes: one or more series resonators connected in series between an input terminal and an output terminal; one or more parallel resonators connected in parallel between the input terminal and the output terminal; divided parallel resonators formed by serially dividing at least one parallel resonator of the one or more parallel resonators; and an inductor of which a first end is coupled to a first node located in a path from the input terminal to the output terminal through the one or more series resonators, and of which a second end is coupled to a second node located between the divided parallel resonators.
1. A ladder-type filter comprising:
one or more series resonators connected in series between an input terminal and an output terminal;
one or more parallel resonators connected in parallel between the input terminal and the output terminal;
divided parallel resonators formed by serially dividing at least one parallel resonator of the one or more parallel resonators; and
an inductor of which a first end is coupled to a first node located in a path from the input terminal to the output terminal through the one or more series resonators, and of which a second end is coupled to a second node located between the divided parallel resonators.
2. The ladder-type filter according to claim 1 , wherein
the at least one parallel resonator is at least one of a parallel resonator closest to the input terminal and a parallel resonator closest to the output terminal.
3. The ladder-type filter according to claim 2 , wherein
the first node is at least one of a node between the input terminal and the at least one parallel resonator and a node between the output terminal and the at least one parallel resonator.
4. The ladder-type filter according to claim 1 , wherein
no series resonator is connected between the first node and the at least one parallel resonator.
5. The ladder-type filter according to claim 1 , wherein
none of a remaining parallel resonator, which is not divided, of the one or more parallel resonators is connected between the first node and the at least one parallel resonator.
6. The ladder-type filter according to claim 1 , wherein
the divide parallel resonators have approximately equal capacitance values.
7. The ladder-type filter according to claim 1 , further comprising:
a filter chip including the one or more series resonators and the one or more parallel resonators formed therein; and
a substrate on which the filter chip is mounted,
wherein the inductor is a chip component mounted on the substrate.
8. The ladder-type filter according to claim 1 , further comprising:
a filter chip including the one or more series resonators and the one or more parallel resonators formed therein; and
a substrate on which the filter chip is mounted,
wherein the inductor is formed in the substrate.
9. A duplexer comprising:
a transmit filter connected between a transmit terminal and a common terminal; and
a receive filter connected between a receive terminal and the common terminal,
wherein at least one of the transmit filter and the receive filter is the ladder-type filter according to claim 1 .
10. A module comprising:
the ladder-type filter according to claim 1 .
11. The ladder-type filter according to claim 1 , wherein
the at least one parallel resonator is at least one of a parallel resonator closest to the input terminal in terms of electrical connection and a parallel resonator electrically closest to the output terminal in terms of electrical connection.