Filter and multiplexer
A filter includes a transmission filter circuit and an additional circuit that is electrically connected in parallel with at least a portion of the transmission filter circuit. The additional circuit includes a resonator group including a plurality of interdigital transducer electrodes provided adjacent to or in a vicinity of each other in an acoustic wave propagation direction, a first capacitive element electrically connected between the resonator group and one end of the additional circuit, and a second capacitive element connected between a ground and a signal path electrically connecting the resonator group and the first capacitive element. A capacitance of the second capacitive element is greater than about 0 pF and less than or substantially equal to about 2.0 pF.
1. A filter comprising:
a filter circuit including an input and an output; and
an additional circuit electrically connected in parallel with the filter circuit; wherein
the additional circuit includes:
a resonator group including a plurality of interdigital transducers, each including an input electrode and an output electrode, provided adjacent to or in a vicinity of each other in an acoustic wave propagation direction;
a first capacitive element electrically connected between the input of the filter circuit and the input electrode of a first interdigital transducer of the plurality of interdigital transducers, and the output electrode of the first interdigital transducer connected to a ground; and
a second capacitive element electrically connected between the input electrode of a second interdigital transducer of the plurality of interdigital transducers and the ground; and
a capacitance of the second capacitive element is greater than about 0 pF and less than or equal to about 2.0 pF.
2. The filter according to claim 1 , wherein the first capacitive element is connected to the input of the filter circuit at an input end of the additional circuit.
3. The filter according to claim 1 , wherein
the resonator group and the second capacitive element are provided on a piezoelectric substrate; and
the resonator group and the second capacitive element are electrically connected to different ground electrodes on the piezoelectric substrate.
4. The filter according to claim 1 , wherein the resonator group defines a longitudinally coupled resonator.
5. A multiplexer comprising:
a first filter; and
a second filter; wherein
one end of the first filter is electrically connected to one end of the second filter; and
at least one of the first filter and the second filter is the filter according to claim 1 .
6. The multiplexer according to claim 5 , wherein the first capacitive element is connected to the input of the filter circuit at an input end of the additional circuit.
7. The multiplexer according to claim 5 , wherein
the resonator group and the second capacitive element are provided on a piezoelectric substrate; and
the resonator group and the second capacitive element are electrically connected to different ground electrodes on the piezoelectric substrate.
8. The multiplexer according to claim 5 , wherein the resonator group defines a longitudinally coupled resonator.
9. The multiplexer according to claim 5 , wherein at least one of the first filter and the second filter is included in a reception filter circuit that is electrically connected to an antenna.
10. The multiplexer according to claim 5 , further comprising:
a first terminal;
a second terminal; and
a third terminal; wherein
the first filter is provided between the first terminal and the second terminal; and
the second filter is provided between the first terminal and the third terminal.
11. The filter according to claim 1 , wherein the filter circuit is an acoustic wave filter circuit including an acoustic wave resonator or an LC resonator filter.
12. The filter according to claim 1 , wherein
the first interdigital transducer includes a first interdigital transducer electrode, and the second interdigital transducer includes a second interdigital transducer electrode;
a first end of the first interdigital transducer electrode is electrically connected to the first capacitive element, and a second end of the first interdigital transducer electrode is electrically connected to the ground; and
a first end of the second interdigital transducer electrode is electrically connected to the second capacitive element, and a second end of the second interdigital transducer electrode is electrically connected to the ground.
13. The filter according to claim 1 , wherein the additional circuit further includes a first reflector and a second reflector that are provided on opposing sides of the resonator group in the acoustic wave propagation direction.
14. The filter according to claim 1 , wherein a signal generated by the additional circuit has a phase that is opposite or substantially opposite to a phase of a signal generated by the filter circuit.
15. The filter according to claim 1 , wherein a signal generated by the additional circuit has an amplitude that is opposite or substantially opposite to an amplitude of a signal generated by the filter circuit.