Acoustic filter apparatus having configurable parallel resonance frequencies
An acoustic filter apparatus is provided. In examples discussed herein, the acoustic filter apparatus includes an acoustic ladder network configured to pass a signal in a series resonance frequency and block the signal in a number of parallel resonance frequencies. The acoustic ladder network is coupled to a microelectromechanical systems (MEMS) switch circuit that includes a number of MEMS switches. The MEMS switches may be selectively controlled (e.g., closed and/or opened) to cause a modification to a selected parallel resonance frequency(s) among the parallel resonance frequencies. As such, it may be possible to flexibly configure the parallel resonance frequencies of the acoustic ladder network based on application scenarios. Further, by employing the MEMS switches having improved figure-of-merit (FOM) over conventional silicon-on-insulator (SOI) switches, it may be possible to reconfigure the parallel resonance frequencies with reduced insertion loss, thus helping to improve performance of the acoustic filter apparatus.
1. An acoustic filter apparatus comprising:
an acoustic ladder network configured to:
resonate in a series resonance frequency to pass a signal from an input node to an output node; and
block the signal from the output node in a plurality of parallel resonance frequencies different from the series resonance frequency; and
a microelectromechanical systems (MEMS) switch circuit coupled to the acoustic ladder network via an inductance circuit and configured to cause a modification to at least one selected parallel resonance frequency among the plurality of parallel resonance frequencies.
2. The acoustic filter apparatus of claim 1 further comprising a control circuit configured to control the MEMS switch circuit to cause the at least one selected parallel resonance frequency to be modified.
3. The acoustic filter apparatus of claim 1 wherein the acoustic ladder network comprises:
an output-stage series acoustic resonator coupled to the output node and configured to:
resonate in the series resonance frequency to pass the signal to the output node; and
block the signal from the output node in a respective parallel resonance frequency among the plurality of parallel resonance frequencies; and
an output-stage shunt branch comprising an output-stage shunt acoustic resonator and the inductance circuit comprising an output-stage inductance circuit coupled between the output-stage series acoustic resonator and a ground, the output-stage shunt branch is configured to shunt the signal to the ground in a respective parallel resonance frequency among the plurality of parallel resonance frequencies.
4. The acoustic filter apparatus of claim 3 wherein:
the output-stage shunt acoustic resonator is coupled directly to the output-stage series acoustic resonator; and
the output-stage inductance circuit is coupled between the output-stage shunt acoustic resonator and the ground.
5. The acoustic filter apparatus of claim 3 wherein:
the output-stage inductance circuit is coupled directly to the output-stage series acoustic resonator; and
the output-stage shunt acoustic resonator is coupled between the output-stage inductance circuit and the ground.
6. The acoustic filter apparatus of claim 3 wherein the output-stage inductance circuit comprises:
a first output-stage inductor coupled to the output-stage shunt acoustic resonator; and
a second output-stage inductor negatively coupled to the first output-stage inductor.
7. The acoustic filter apparatus of claim 6 wherein the MEMS switch circuit comprises:
a first output-stage MEMS switch coupled between the output node and a signal output;
an output-stage series MEMS switch coupled between the second output-stage inductor and the signal output; and
an output-stage shunt MEMS switch coupled between the second output-stage inductor and the ground.
8. The acoustic filter apparatus of claim 7 wherein the MEMS switch circuit is further configured to close the first output-stage MEMS switch concurrent to opening the output-stage series MEMS switch and the output-stage shunt MEMS switch to cause the respective parallel resonance frequency of the output-stage shunt branch to be modified.
9. The acoustic filter apparatus of claim 7 wherein the MEMS switch circuit is further configured to close the first output-stage MEMS switch and the output-stage shunt MEMS switch concurrent to opening the output-stage series MEMS switch to cause the respective parallel resonance frequency of the output-stage shunt branch to be modified.
10. The acoustic filter apparatus of claim 7 wherein the MEMS switch circuit is further configured to close the first output-stage MEMS switch and the output-stage series MEMS switch concurrent to opening the output-stage shunt MEMS switch to cause the respective parallel resonance frequency of the output-stage series acoustic resonator to be modified.
11. The acoustic filter apparatus of claim 7 wherein:
the acoustic ladder network further comprises at least one second output-stage series acoustic resonator coupled in parallel to the output-stage series acoustic resonator; and
the MEMS switch circuit further comprises at least one second output-stage MEMS switch coupled between the at least one second output-stage series acoustic resonator and the signal output.
12. The acoustic filter apparatus of claim 3 wherein the acoustic ladder network further comprises:
an input-stage series acoustic resonator coupled to the input node and configured to:
resonate in the series resonance frequency to pass the signal from the input node to the output node; and
block the signal from the output node in a respective parallel resonance frequency among the plurality of parallel resonance frequencies; and
an input-stage shunt branch comprising an input-stage shunt acoustic resonator and the inductance circuit comprising an input-stage inductance circuit coupled between the input-stage series acoustic resonator and the ground, the input-stage shunt branch is configured to shunt the signal to the ground in a respective parallel resonance frequency among the plurality of parallel resonance frequencies.
13. The acoustic filter apparatus of claim 12 wherein:
the input-stage shunt acoustic resonator is coupled directly to the input-stage series acoustic resonator; and
the input-stage inductance circuit is coupled between the input-stage shunt acoustic resonator and the ground.
14. The acoustic filter apparatus of claim 12 wherein:
the input-stage inductance circuit is coupled directly to the input-stage series acoustic resonator; and
the input-stage shunt acoustic resonator is coupled between the input-stage inductance circuit and the ground.
15. The acoustic filter apparatus of claim 12 wherein the input-stage inductance circuit comprises an input-stage inductor coupled between the input-stage series acoustic resonator and the ground.
16. The acoustic filter apparatus of claim 12 wherein the input-stage inductance circuit comprises:
a first input-stage inductor coupled to the input-stage shunt acoustic resonator; and
a second input-stage inductor negatively coupled to the first input-stage inductor.
17. The acoustic filter apparatus of claim 16 further comprising a second MEMS switch circuit comprising:
an input-stage MEMS switch coupled between a signal input and the input node;
an input-stage series MEMS switch coupled between the signal input and the second input-stage inductor; and
an input-stage shunt MEMS switch coupled between the second input-stage inductor and the ground.
18. The acoustic filter apparatus of claim 17 wherein the second MEMS switch circuit is configured to close the input-stage MEMS switch concurrent to opening the input-stage series MEMS switch and the input-stage shunt MEMS switch to cause the respective parallel resonance frequency of the input-stage shunt branch to be modified.
19. The acoustic filter apparatus of claim 17 wherein the second MEMS switch circuit is configured to close the input-stage MEMS switch and the input-stage shunt MEMS switch concurrent to opening the input-stage series MEMS switch to cause the respective parallel resonance frequency of the input-stage shunt branch to be modified.
20. The acoustic filter apparatus of claim 17 wherein the MEMS switch circuit is further configured to close the input-stage MEMS switch and the input-stage series MEMS switch concurrent to opening the input-stage shunt MEMS switch to cause the respective parallel resonance frequency of the input-stage series acoustic resonator to be modified.