Acoustic wave filter with shunt resonator having multiple resonant frequencies
Aspects of this disclosure relate to an acoustic wave resonator having at least two resonant frequencies. An acoustic wave filter can include series acoustic wave resonators and shunt acoustic wave resonators together arranged to filter a radio frequency signal. A first shunt resonator of the shunt acoustic wave resonators can include an interdigital transducer electrode and have at least a first resonant frequency and a second resonant frequency. Related acoustic wave resonators, multiplexers, wireless devices, and methods are disclosed.
1. An acoustic wave filter configured to filter a radio frequency signal, the acoustic wave filter comprising:
shunt acoustic wave resonators including a first shunt acoustic wave resonator, the first shunt acoustic wave resonator including an interdigital transducer electrode positioned between a first acoustic reflector and a second acoustic reflector, the first shunt acoustic wave resonator having at least a first resonant frequency corresponding to a first region of the interdigital transducer electrode and a second resonant frequency corresponding to a second region of the interdigital transducer electrode, an outer interdigital transducer electrode finger of the first region being spaced apart from the first acoustic reflector by a first gap, and an outer interdigital transducer electrode finger of the second region being spaced apart from the second acoustic reflector by a second gap; and
series acoustic wave resonators, the series acoustic wave resonators and the shunt acoustic wave resonators together arranged to filter the radio frequency signal.
2. The acoustic wave filter of claim 1 wherein the acoustic wave filter is a band pass filter having a pass band.
3. The acoustic wave filter of claim 2 wherein the second resonant frequency is between the first resonant frequency and an edge of the pass band.
4. The acoustic wave filter of claim 3 wherein the second resonant frequency is at least 5 megahertz above the first resonant frequency.
5. The acoustic wave filter of claim 1 wherein the acoustic wave filter has a pass band corresponding to a fifth generation New Radio operating band.
6. The acoustic wave filter of claim 1 wherein the first shunt acoustic wave resonator is a surface acoustic wave resonator.
7. The acoustic wave filter of claim 1 wherein the first shunt acoustic wave resonator is a temperature compensated surface acoustic wave resonator, and a first series resonator of the series acoustic wave resonators is a second temperature compensated surface acoustic wave resonator having a thinner temperature compensation layer than the first shunt acoustic wave resonator.
8. The acoustic wave filter of claim 1 wherein the first shunt acoustic wave resonator is a multilayer piezoelectric substrate surface acoustic wave resonator that includes a piezoelectric layer under the interdigital transducer electrode and a support substrate under the piezoelectric layer.
9. The acoustic wave filter of claim 1 wherein the first shunt acoustic wave resonator is a Lamb wave resonator.
10. The acoustic wave filter of claim 1 wherein the first shunt acoustic wave resonator is a boundary acoustic wave resonator.
11. The acoustic wave filter of claim 1 wherein the first shunt acoustic wave resonator has a third resonant frequency.
12. The acoustic wave filter of claim 1 wherein the shunt acoustic wave resonators include a second shunt acoustic wave resonator having a plurality of resonant frequencies.
13. A multiplexer with filters for filtering radio frequency signals, the multiplexer comprising:
a first filter including series acoustic wave resonators and shunt acoustic wave resonators together arranged to filter a first radio frequency signal, the shunt acoustic wave resonators including a first shunt acoustic wave resonator, the first shunt acoustic wave resonator including an interdigital transducer electrode, the first shunt acoustic wave resonator having a plurality of resonant frequencies, the interdigital transducer electrode including first interdigital transducer electrode fingers having a first pitch corresponding to a first resonant frequency of the plurality of resonant frequencies, and the interdigital transducer electrode including second interdigital transducer electrode fingers having a second pitch corresponding to a second resonant frequency of the plurality of resonant frequencies; and
a second filter coupled to the first filter at a common node, the second filter including second series acoustic wave resonators and second shunt acoustic wave resonators, and the second shunt acoustic wave resonators include a second shunt acoustic wave resonator having at least two resonant frequencies, the second filter configured to filter a second radio frequency signal.
14. The multiplexer of claim 13 wherein the interdigital transducer electrode is positioned between a first acoustic reflector and a second acoustic reflector, an outer interdigital transducer electrode finger of the first interdigital transducer electrode fingers is spaced apart from the first acoustic reflector by a first gap, and an outer interdigital transducer electrode finger of the second interdigital transducer electrode fingers is spaced apart from the second acoustic reflector by a second gap.
15. The multiplexer of claim 13 wherein the first shunt acoustic wave resonator includes a piezoelectric layer under the interdigital transducer electrode and a support substrate under the piezoelectric layer.
16. The multiplexer of claim 13 further comprising:
a third filter coupled to the common node, the third filter configured to filter a third radio frequency signal; and
a fourth filter coupled to the common node, the fourth filter configured to filter a fourth radio frequency signal.
17. The multiplexer of claim 16 wherein the multiplexer is configured to provide filtering for at least two carriers of a carrier aggregation.
18. A method of filtering a radio frequency signal with an acoustic wave filter, the method comprising:
receiving, by an acoustic wave filter, the radio frequency signal; and
generating, by a shunt acoustic wave resonator including an interdigital transducer electrode positioned between a first acoustic reflector and a second acoustic reflector and being included in the acoustic wave filter, a plurality of notches in a frequency response of the shunt acoustic wave resonator to thereby improve rejection of the acoustic wave filter, the interdigital transducer electrode including first interdigital transducer electrode fingers having a first pitch corresponding to a first resonant frequency that creates a first notch of the plurality of notches, an outer finger of the first interdigital transducer electrode fingers being separated from the first acoustic reflector by a first gap, the interdigital transducer electrode including second interdigital transducer electrode fingers having a second pitch corresponding to a second resonant frequency that creates a second notch of the plurality of notches, and an outer finger of the second interdigital transducer electrode fingers being separated from the second acoustic reflector by a second gap.
19. The method of claim 18 wherein the radio frequency signal is a fifth generation New Radio signal.
20. The method of claim 19 wherein the acoustic wave filter is a band pass filter having a pass band, and the second resonant frequency is between the first resonant frequency and a lower edge of the pass band.