Duplexer including a low-pass filter capacitor
A duplexer includes a first band-pass filter and a second band-pass filter with a pass-band lower than the first band-pass filter. The first band-pass filter includes an unbalanced surface acoustic wave filter. First, second and third signal wire electrodes and a ground wire electrode are provided on a piezoelectric substrate in the first band-pass filter, and a bridging area is provided where any one of the first, second and third signal wire electrodes bridges the ground wire electrode. A width of a portion of the signal wire electrode that opposes the ground wire electrode with an interlayer insulating film located therebetween is greater than a width of a portion of the signal wire electrode other than the bridging area so that a low-pass filter capacitor is provided.
1. A duplexer comprising:
a first band-pass filter; and
a second band-pass filter with a pass-band located on a lower-frequency side compared to that of the first band-pass filter; wherein
the first band-pass filter includes an unbalanced surface acoustic wave filter including an unbalanced input-unbalanced output;
the first band-pass filter includes a piezoelectric substrate and an electrode structure provided on the piezoelectric substrate;
the electrode structure includes an input electrode pad, an output electrode pad, a ground electrode pad that is shunted to ground, a functional electrode portion that defines and functions as a surface acoustic wave filter including at least one interdigital transducer electrode, a first signal wire electrode that connects the functional electrode portion and the input electrode pad, a second signal wire electrode through which a signal current flows within the functional electrode portion, a third signal wire electrode that connects the functional electrode portion and the output electrode pad, and a ground wire electrode that connects the functional electrode portion and the ground electrode pad; and
a bridging area where any one of the first, second and third signal wire electrodes bridges the ground wire electrode is provided, an interlayer insulating film is provided in the bridging area between the ground wire electrode and the one of the first, second and third signal wire electrodes, and a width of a portion of the signal wire electrode that opposes the ground wire electrode with the interlayer insulating film located therebetween is greater than a width of a portion of the signal wire electrode other than the bridging area so as to define a low-pass filter capacitor.
2. The duplexer according to claim 1 , wherein the ground wire electrode is disposed between the interlayer insulating film and the piezoelectric substrate in the area where the low-pass filter capacitor is provided.
3. The duplexer according to claim 1 , wherein the unbalanced surface acoustic wave filter is a longitudinally coupled resonator surface acoustic wave filter.
4. The duplexer according to claim 3 , wherein a plurality of single-port surface acoustic wave resonators are connected to each other in series between the longitudinally coupled resonator surface acoustic wave filter and an antenna terminal.
5. The duplexer according to claim 4 , wherein the plurality of single-port surface acoustic wave resonators include interdigital transducer electrodes.
6. The duplexer according to claim 1 , wherein the first band-pass filter is a reception filter and the second band-pass filter is a transmission filter.
7. The duplexer according to claim 6 , wherein the transmission filter is a surface acoustic wave filter with a ladder circuit configuration.
8. The duplexer according to claim 1 , wherein at least three of the low-pass filter capacitor are provided.
9. The duplexer according to claim 1 , wherein the low-pass filter capacitor is connected between a signal potential and a ground potential in the first band-pass filter.
10. The duplexer according to claim 1 , wherein in the bridging area, a planar shape of the ground wire electrode that opposes the first signal wire electrode with the interlayer insulating film therebetween is the same as or larger than that of the first signal wire electrode.
11. A duplexer comprising:
a first band-pass filter; and
a second band-pass filter with a pass-band located on a lower-frequency side compared to that of the first band-pass filter; wherein
the first band-pass filter includes an unbalanced surface acoustic wave filter including an unbalanced input-unbalanced output;
the first band-pass filter includes a piezoelectric substrate and an electrode structure provided on the piezoelectric substrate;
the electrode structure includes an input electrode pad, an output electrode pad, a ground electrode pad that is shunted to ground, a functional electrode portion that defines and functions as a surface acoustic wave filter including at least one interdigital transducer electrode, a first signal wire electrode that connects the functional electrode portion and the input electrode pad, a second signal wire electrode through which a signal current flows within the functional electrode portion, a third signal wire electrode that connects the functional electrode portion and the output electrode pad, and a ground wire electrode that connects the functional electrode portion and the ground electrode pad; and
a ground electrode pad extending portion that extends from the ground electrode pad and is not directly electrically connected to the functional electrode portion is further provided, and the ground electrode pad extending portion overlaps with any one of the first, second and third signal wire electrodes with an interlayer insulating film located therebetween so as to define a low-pass filter capacitor.
12. The duplexer according to claim 11 , wherein the ground electrode pad extending portion is disposed between the interlayer insulating film and the piezoelectric substrate in the area where the low-pass filter capacitor is provided.
13. The duplexer according to claim 11 , wherein the unbalanced surface acoustic wave filter is a longitudinally coupled resonator surface acoustic wave filter.
14. The duplexer according to claim 13 , wherein a plurality of single-port surface acoustic wave resonators are connected to each other in series between the longitudinally coupled resonator surface acoustic wave filter and an antenna terminal.
15. The duplexer according to claim 14 , wherein the plurality of single-port surface acoustic wave resonators include interdigital transducer electrodes.
16. The duplexer according to claim 11 , wherein the first band-pass filter is a reception filter and the second band-pass filter is a transmission filter.
17. The duplexer according to claim 16 , wherein the transmission filter is a surface acoustic wave filter with a ladder circuit configuration.
18. The duplexer according to claim 11 , wherein at least three of the low-pass filter capacitor are provided.
19. The duplexer according to claim 11 , wherein the low-pass filter capacitor is connected between a signal potential and a ground potential in the first band-pass filter.
20. The duplexer according to claim 11 , wherein in the bridging area, a planar shape of the ground wire electrode that opposes the first signal wire electrode with the interlayer insulating film therebetween is the same as or larger than that of the first signal wire electrode.