Surface acoustic wave device and duplexer and communication device using the same

1. A surface acoustic wave device comprising:

a first surface acoustic wave filter forming a ladder filter circuit; and

a second surface acoustic wave filter having a passband at a frequency range higher than that of the first surface acoustic wave filter,

the first surface acoustic wave filter comprising:

at least one series-arm surface acoustic wave resonator on a series arm of the ladder filter circuit including an IDT electrode;

at least one parallel-arm surface acoustic wave resonator on a parallel arm of the ladder filter circuit including an IDT electrode; and

an additional surface acoustic wave resonator including an IDT electrode, connected in parallel with the series-arm surface acoustic wave resonator and having a resonance frequency higher than the frequency range of the passband of the second surface acoustic wave filter.

2. The surface acoustic wave device of claim 1 , wherein an electrode-finger pitch of the IDT electrode of the additional surface acoustic wave resonator is smaller than that of the series-arm surface acoustic wave resonator to which the additional surface acoustic wave resonator is connected in parallel.

3. The surface acoustic wave device of claim 2 , wherein the electrode-finger pitch of the IDT electrode of the additional surface acoustic wave resonator is set 0.5 to 0.95 times that of the series-arm surface acoustic wave resonator to which the additional surface acoustic wave resonator is connected in parallel.

4. The surface acoustic wave device of claim 1 , wherein the second surface acoustic wave filter forms a ladder filter circuit and comprises:

a series-arm surface acoustic wave resonator including an IDT electrode and being on a series arm of the ladder filter circuit; and

a parallel-arm surface acoustic wave resonator on a parallel arm of the ladder filter circuit including an IDT electrode,

wherein the electrode-finger pitch of the IDT electrode of the additional surface acoustic wave resonator is smaller than that of the series-arm surface acoustic wave resonator of the second surface acoustic wave filter.

5. The surface acoustic wave device of claim 4 , wherein the electrode-finger pitch of the IDT electrode of the additional surface acoustic wave resonator is set 0.5 to 0.98 times that of the series-arm surface acoustic wave resonator of the second surface acoustic wave filter.

6. The surface acoustic wave device of claim 1 , wherein the ratio of the electrode-finger width to the electrode-finger pitch in the IDT electrode of the additional surface acoustic wave resonator is higher than that of the series-arm surface acoustic wave resonator to which the additional surface acoustic wave resonator is connected in parallel.

7. The surface acoustic wave device of claim 1 , wherein the ratio of the electrode-finger width to the electrode-finger pitch in the IDT electrode of the additional surface acoustic wave resonator is lower than that of the series-arm surface acoustic wave resonator to which the surface acoustic wave resonator is connected in parallel.

8. The surface acoustic wave device of claim 1 , wherein the first surface acoustic wave filter includes a plurality of series-arm surface acoustic wave resonators, and

wherein the additional surface acoustic wave resonator is connected in parallel with at least one series-arm surface acoustic wave resonator other than the closest series-arm surface acoustic wave resonator to an input terminal of the first surface acoustic wave filter.

9. The surface acoustic wave device of claim 1 , wherein the first surface acoustic wave filter includes a plurality of series-arm surface acoustic wave resonators and further including a plurality of additional surface acoustic wave resonators each being connected in parallel with each of at least two of the series-arm surface acoustic wave resonators.

10. The surface acoustic wave device of claim 9 , wherein the additional surface acoustic wave resonator has a capacitance not more than 20% of that of the series-arm surface acoustic wave resonator to which the additional surface acoustic wave resonator is connected in parallel.

11. The surface acoustic wave device of claim 9 , wherein the first surface acoustic wave filter includes at least two of the additional surface acoustic wave resonators which have the same capacitance and different electrode-finger pitches each other.

12. The surface acoustic wave device of claim 1 , wherein the second surface acoustic wave filter forms a DMS filter circuit.

13. A duplexer comprising:

the surface acoustic wave device of claim 1 ;

an input terminal of the first surface acoustic wave filter as a transmission side filter;

an output terminal of the second surface acoustic wave filter as a reception side filter;

a connecting portion which connects an antenna and an end portion of the first surface acoustic wave filter and a first portion of the second surface acoustic wave filter.

14. A communication device comprising:

a duplexer of claim 13 ;

an antenna;

a mixer mixing a transmission signal with a carrier signal and outputting the antenna transmission signal; and

a power amplifier amplifying the antenna transmission signal and outputting the amplified antenna transmission signal to the antenna via the duplexer.

15. A communication device comprising:

a duplexer including the surface acoustic wave device of claim 1 ;

an antenna outputting an antenna reception signal to the duplexer;

an amplifier amplifying the antenna reception signal received from the duplexer; and

a mixer separating the reception signal from a carrier signal of the amplified antenna reception signal received from the amplifier.