High-frequency module
A high-frequency module includes a longitudinally coupled surface acoustic wave filter and a low-noise amplifier that is connected to the surface acoustic wave filter. The input impedance of the surface acoustic wave filter connected to the low-noise amplifier differs from the output impedance thereof. On a Smith chart, the output impedance in the pass band of the surface acoustic wave filter is present in a region between a first output impedance and a second output impedance, the first output impedance being the output impedance of the surface acoustic wave filter where a gain of the low-noise amplifier is maximum, the second output impedance being the output impedance of the surface acoustic wave filter where a noise figure of the low-noise amplifier is minimum.
1. A high-frequency module comprising:
a longitudinally coupled surface acoustic wave filter including a plurality of resonators; and
a low-noise amplifier that is connected to the surface acoustic wave filter and that amplifies a high-frequency signal that has passed through the surface acoustic wave filter; wherein
an input impedance of the surface acoustic wave filter connected to the low-noise amplifier differs from an output impedance thereof; and
on a Smith chart, the output impedance in a pass band of the surface acoustic wave filter is present in a region between a first output impedance and a second output impedance, the first output impedance being the output impedance of the surface acoustic wave filter where a gain of the low-noise amplifier is maximum, the second output impedance being the output impedance of the surface acoustic wave filter where a noise figure of the low-noise amplifier is minimum.
2. The high-frequency module according to claim 1 , wherein the surface acoustic wave filter includes an electrode parameter to adjust the output impedance in the pass band of the surface acoustic wave filter to be in the region on the Smith chart.
3. The high-frequency module according to claim 2 , wherein
an interdigital transducer (IDT) electrode of at least one of the resonators that is connected to an output terminal of the surface acoustic wave filter includes a withdrawal electrode; and
the electrode parameter is a number of the withdrawal electrodes.
4. The high-frequency module according to claim 3 , wherein the withdrawal electrode is provided in an approximately central region of the resonator.
5. The high-frequency module according to claim 4 , wherein the withdrawal electrode is provided in an approximately 46% area portion in the approximately central region of the resonator.
6. The high-frequency module according to claim 2 , wherein
an interdigital transducer (IDT) electrode of one of the resonators that is connected to an output terminal of the surface acoustic wave filter is divided in an intersecting width direction; and
the electrode parameter is a number of divisions of the IDT electrode in the intersecting width direction.
7. The high-frequency module according to claim 2 , wherein
the electrode parameter includes a first main wave length and a second main wavelength, the first main wave length being an average main wave length of one or more of the resonators that are connected to an input terminal of the surface acoustic wave filter, the second main wave length being an average main wave length of one or more of the resonators that are connected to an output terminal of the surface acoustic wave filter; and
the first main wave length differs from the second main wave length.
8. The high-frequency module according to claim 7 , wherein
the electrode parameter is a main wave length ratio that is a ratio of a second main wave length to a first main wave length, the first main wave length being an average value of a main wave length of at least one of the resonators that is connected to an input terminal of the surface acoustic wave filter, the second main wave length being an average value of a main wave length of at least one of the resonators that is connected to an output terminal of the surface acoustic wave filter.
9. The high-frequency module according to claim 8 , wherein the main wave length ratio is higher than or equal to about 1.01.
10. The high-frequency module according to claim 2 , wherein the electrode parameter is a main duty of one of the resonators that is connected to an output terminal of the surface acoustic wave filter.
11. The high-frequency module according to claim 10 , wherein the main duty is higher than about 0.55 and lower than about 0.75.
12. The high-frequency module according to claim 1 , wherein, in the surface acoustic wave filter, a wiring between an interdigital transducer (IDT) electrode of one of the resonators that is connected to an output terminal of the surface acoustic wave filter and the output terminal of the surface acoustic wave filter is provided on an interlayer insulating film located on a substrate.
13. The high-frequency module according to claim 12 , wherein
the IDT electrode of one of the resonator that is connected to an output terminal of the surface acoustic wave filter includes a first electrode layer and a second electrode layer, the first electrode layer being provided on a substrate, the second electrode layer being provided on the first electrode layer; and
the wiring at a position where the interlayer insulating film is disposed includes the first electrode layer and the second electrode layer.
14. The high-frequency module according to claim 12 , wherein
the IDT electrode of one of the resonators that is connected to an output terminal of in the surface acoustic wave filter includes a first electrode layer and a second electrode layer, the first electrode layer being provided on a substrate, the second electrode layer being provided on the first electrode layer; and
the wiring at a position where the interlayer insulating film is disposed includes the second electrode layer being provided on the interlayer insulating film.
15. The high-frequency module according to claim 2 , wherein
an interdigital transducer (IDT) electrode of at least one of the resonators that is connected to an output terminal of the surface acoustic wave filter includes a withdrawal electrode; and
the electrode parameter is a pitch of electrode fingers of the IDT electrode.
16. The high-frequency module according to claim 2 , wherein
an interdigital transducer (IDT) electrode of at least one of the resonators that is connected to an output terminal of the surface acoustic wave filter includes a withdrawal electrode; and
the electrode parameter is a pitch of electrode fingers of the IDT electrode.
17. The high-frequency module according to claim 1 , wherein a number of the plurality of resonators is three.
18. The high-frequency module according to claim 1 , wherein a number of the plurality of resonators is five.
19. The high-frequency module according to claim 1 , wherein the surface acoustic wave filter is directly connected to the low-noise amplifier.
20. The high-frequency module according to claim 1 , further comprising a matching element provided between the surface acoustic wave filter and the low-noise amplifier.