Duplexer
A duplexer includes: a first filter of which first and second ends connect to a common terminal and a first terminal respectively; and a second filter having a passband higher than that of the first filter, a first end and second end thereof connecting to the common terminal and a second terminal respectively, wherein a phase shifter is located neither between the first filter and the common terminal nor between the second filter and the common terminal, the second filter is a ladder-type filter including piezoelectric thin film resonators connected in a ladder shape, a propagation constant in a direction perpendicular to a thickness direction of a piezoelectric thin film in the piezoelectric thin film resonator is a real number at frequencies lower than a resonance frequency of the piezoelectric thin film resonator, and a resonator at a first stage is a parallel resonator in the second filter.
1. A duplexer comprising:
a first filter of which a first end is coupled to a common terminal, and a second end is coupled to a first terminal; and
a second filter having a passband higher than a passband of the first filter, a first end of the second filter being coupled to the common terminal, and a second end of the second filter being coupled to a second terminal, wherein
a phase shifter is located neither between the first filter and the common terminal nor between the second filter and the common terminal,
the second filter is a ladder-type filter including piezoelectric thin film resonators connected in a ladder shape,
a propagation constant in a direction perpendicular to a thickness direction of a piezoelectric thin film included in each of the piezoelectric thin film resonators is a real number at frequencies lower than a resonance frequency of corresponding one of the piezoelectric thin film resonators,
a resonator at a first stage as viewed from a side of the common terminal is a parallel resonator in the second filter, and
the duplexer comprises no inductor of which a first end is connected to a node between the common terminal and at least one of the first filter and the second filter, and a second end is connected to a ground.
2. The duplexer according to claim 1 , wherein
the first filter is a transmission filter, and
the second filter is a reception filter.
3. The duplexer according to claim 1 , wherein
a gap between the passband of the first filter and the passband of the second filter is less than or equal to 40 MHz.
4. The duplexer according to claim 1 , wherein
the duplexer is a duplexer supporting W-CDMA (Wideband Code Division Multiple Access) Band 2.
5. A duplexer comprising:
a first filter of which a first end is coupled to a common terminal, and a second end is coupled to a first terminal; and
a second filter having a passband higher than a passband of the first filter, a first end of the second filter being coupled to the common terminal, and a second end being coupled to a second terminal, wherein
a phase shifter is located neither between the first filter and the common terminal nor between the second filter and the common terminal,
the second filter is a ladder-type filter including piezoelectric thin film resonators connected in a ladder shape,
a propagation constant in a direction perpendicular to a thickness direction of a piezoelectric thin film included in each of the piezoelectric thin film resonators is a real number at frequencies lower than a resonance frequency of corresponding one of the piezoelectric thin film resonators,
a resonator at a first stage as viewed from a side of the common terminal is a parallel resonator in the second filter, and
a first series resonator that is included in the second filter and is located closest to the common terminal is serially divided.
6. The duplexer according to claim 5 , wherein
at least one second series resonator of second series resonators formed by serially dividing the first series resonator has a capacitance different from a capacitance of at least one of the second series resonators other than the at least one second series resonator.
7. The duplexer according to claim 5 , wherein
a gap between the passband of the first filter and the passband of the second filter is less than or equal to 40 MHz.
8. The duplexer according to claim 5 , wherein
the duplexer is a duplexer supporting W-CDMA Band 2.
9. The duplexer according to claim 5 , wherein
the first filter is a transmission filter, and
the second filter is a reception filter.
10. A duplexer comprising:
a first filter of which a first end is coupled to a common terminal, and a second end is coupled to a first terminal; and
a second filter having a passband higher than a passband of the first filter, a first end of the second filter being coupled to the common terminal, and a second end being coupled to a second terminal, wherein
at least a part of a phase shifter is connected neither between the common terminal and a ground, between the first filter and the common terminal nor between the second filter and the common terminal,
the second filter is a ladder-type filter including piezoelectric thin film resonators connected in a ladder shape,
a propagation constant in a direction perpendicular to a thickness direction of a piezoelectric thin film of each of the piezoelectric thin film resonators is a real number at frequencies lower than a resonance frequency of corresponding one of the piezoelectric thin film resonators,
a resonator at a first stage as viewed from a side of the common terminal is a first series resonator in the second filter, and
the first series resonator is serially divided.
11. The duplexer according to claim 10 , wherein
at least one second series resonator of second series resonators formed by serially dividing the first series resonator has a capacitance different from a capacitance of at least one of the second series resonators other than the at least one second series resonator.
12. The duplexer according to claim 10 , wherein
a region, in which an upper electrode and a lower electrode overlap each other across the piezoelectric thin film, of at least one second series resonator of second series resonators formed by serially dividing the first series resonator has a shape different from that of at least one of the second series resonators other than the at least one second series resonator.
13. The duplexer according to claim 10 , wherein
the first filter is a transmission filter, and
the second filter is a reception filter.
14. The duplexer according to claim 10 , wherein
a gap between the passband of the first filter and the passband of the second filter is less than or equal to 40 MHz.
15. The duplexer according to claim 10 , wherein
the duplexer is a duplexer supporting W-CDMA Band 2.
16. A duplexer comprising:
a first filter of which a first end is coupled to a common terminal, and a second end is coupled to a first terminal; and
a second filter having a passband higher than a passband of the first filter, a first end of the second filter being coupled to the common terminal, and a second end being coupled to a second terminal, wherein
at least a part of a phase shifter is connected neither between the common terminal and a ground, between the first filter and the common terminal nor between the second filter and the common terminal;
the second filter is a ladder-type filter including piezoelectric thin film resonators connected in a ladder shape,
a propagation constant in a direction perpendicular to a thickness direction of a piezoelectric thin film included in each of the piezoelectric thin film resonators is a real number at frequencies higher than a resonance frequency of corresponding one of the piezoelectric thin film resonators, and
a resonator at a first stage as viewed from a side of the common terminal is a series resonator in the second filter.
17. The duplexer according to claim 16 , wherein
the first filter is a transmission filter, and
the second filter is a reception filter.