Acoustic wave filter with series resonator for filter steepness
Aspects of this disclosure relate to an acoustic wave filter with series bulk acoustic wave resonators. In some embodiments, the acoustic wave filter is a band pass filter having a pass band. One of the series bulk acoustic wave resonators can contribute to forming a lower edge of the pass band. That series bulk acoustic wave resonator can be smaller than another series bulk acoustic wave resonator of the acoustic wave filter.
1. An acoustic wave filter comprising:
a plurality of shunt acoustic wave resonators; and
a plurality of series acoustic wave resonators including a first bulk acoustic wave resonator and
a second bulk acoustic wave resonator,
the plurality of series acoustic wave resonators and the plurality of shunt acoustic wave resonators together arranged as a band pass filter with a pass band,
the second bulk acoustic wave resonator is configured to contribute to forming a lower edge of the pass band,
the first bulk acoustic wave resonator and the second bulk acoustic wave resonator are in parallel with each other, and
the second bulk acoustic wave resonator is smaller than the first bulk acoustic wave resonator.
2. The acoustic wave filter of claim 1 wherein the first bulk acoustic wave resonator and the second bulk acoustic wave resonator each include a raised frame, the raised frame of the second bulk acoustic wave resonator is wider as a percentage of total resonator width than the raised frame of the first bulk acoustic wave resonator.
3. The acoustic wave filter of claim 1 wherein the first bulk acoustic wave resonator and the second bulk acoustic wave resonator each include a recessed frame, the recessed frame of the second bulk acoustic wave resonator is narrower as a percentage of total resonator width than the recessed frame of the first bulk acoustic wave resonator.
4. The acoustic wave filter of claim 1 wherein the second bulk acoustic wave resonator does not include a recessed frame.
5. The acoustic wave filter of claim 4 wherein the first bulk acoustic wave resonator includes a recessed frame.
6. The acoustic wave filter of claim 1 wherein a resonant frequency of the second bulk acoustic wave resonator is lower than the lower edge of the pass band.
7. The acoustic wave filter of claim 1 wherein the second bulk acoustic wave resonator is configured to increase power ruggedness of the acoustic wave filter in the pass band.
8. The acoustic wave filter of claim 1 wherein the first bulk acoustic wave resonator has an area that is at least 1.5 times an area of the second bulk acoustic wave resonator.
9. The acoustic wave filter of claim 1 wherein the first bulk acoustic wave resonator has an area in a range from 1.5 to 15 times an area of the second bulk acoustic wave resonator.
10. The acoustic wave filter of claim 1 wherein the second bulk acoustic wave resonator is a film bulk acoustic wave resonator.
11. An acoustic wave filter comprising:
a plurality of shunt acoustic wave resonators; and
a plurality of series acoustic wave resonators including a first bulk acoustic wave resonator and
a second bulk acoustic wave resonator,
the second bulk acoustic wave resonator together with at least one of the plurality of shuntacoustic wave resonators configured to contribute to forming a skirt of the acoustic wave filter,
the first bulk acoustic wave resonator and the second bulk acoustic wave resonator being in parallel with each other, and
the second bulk acoustic wave resonator being smaller than the first bulk acoustic wave resonator.
12. The acoustic wave filter of claim 11 wherein the first bulk acoustic wave resonator and the second bulk acoustic wave resonator each include a raised frame, and the raised frame of the second bulk acoustic wave resonator is wider as a percentage of total resonator width than the raised frame of the first bulk acoustic wave resonator.
13. The acoustic wave filter of claim 12 wherein the first bulk acoustic wave resonator and the second bulk acoustic wave resonator each include a recessed frame, and the recessed frame of the second bulk acoustic wave resonator is narrower as a percentage of total resonator width than the recessed frame of the first bulk acoustic wave resonator.
14. The acoustic wave filter of claim 12 wherein the second bulk acoustic wave resonator does not include a recessed frame.
15. The acoustic wave filter of claim 14 wherein the first bulk acoustic wave resonator includes a recessed frame.
16. The acoustic wave filter of claim 11 wherein the acoustic wave filter is a band pass filter having a pass band, and the skirt corresponds to a lower edge of the pass band.
17. The acoustic wave filter of claim 16 wherein the second bulk acoustic wave resonator is configured to increase power ruggedness of the acoustic wave filter in the pass band.
18. The acoustic wave filter of claim 11 wherein the acoustic wave filter is a band stop filter with a stop band, and the skirt corresponds to an upper edge of the stop band.
19. The acoustic wave filter of claim 11 wherein the first bulk acoustic wave resonator has an area in a range from 1.5 to 15 times an area of the second bulk acoustic wave resonator.
20. A wireless communication device comprising:
an acoustic wave filter including plurality of shunt acoustic wave resonators and
a plurality of series acoustic wave resonators together arranged as a band pass filter with a pass band,
the plurality of series acoustic wave resonators including a first bulk acoustic wave resonator and
a second bulk acoustic wave resonator,
the second bulk acoustic wave resonator is configured to contribute to forming a lower edge of the pass band,
the first bulk acoustic wave resonator and the second bulk acoustic wave resonator are in parallel with each other, and
the second bulk acoustic wave resonator is smaller than the first bulk acoustic wave resonator; and
an antenna operatively coupled to the acoustic wave filter.