Acoustic resonator structure
An acoustic resonator structure is provided. The acoustic resonator structure includes an acoustic resonator configured to resonate in a resonance frequency to pass a radio frequency (RF) signal from an input node to an output node. However, the acoustic resonator may create an electrical capacitance in parallel to the acoustic resonator. The electrical capacitance may cause the acoustic resonator to resonate outside the resonance frequency, thus compromising performance of the acoustic resonator. In this regard, an active circuit is provided in parallel to the acoustic resonator in the acoustic resonator structure. The active circuit can be configured to cause a negative capacitance between the input node and the output node. As such, it may be possible to cancel the electrical capacitance created by the acoustic resonator, thus helping to improve performance of the acoustic resonator.
1. An acoustic resonator structure comprising:
an input node and an output node;
an acoustic resonator coupled between the input node and the output node and configured to resonate in a resonance frequency to pass a radio frequency (RF) signal from the input node to the output node; and
an active circuit coupled in parallel to the acoustic resonator between the input node and the output node and configured to cause a negative capacitance being generated between the input node and the output node, wherein the active circuit comprises an impedance circuit comprising a passive impedance circuit and an active impedance circuit, wherein the active impedance circuit comprises at least one inductor coupled to a battery.
2. The acoustic resonator structure of claim 1 wherein:
the acoustic resonator causes an electrical capacitance between the input node and the output node in parallel to the acoustic resonator; and
the active circuit is further configured to cause the negative capacitance to be generated to cancel the electrical capacitance between the input node and the output node.
3. The acoustic resonator structure of claim 1 wherein the active circuit comprises:
a first inductor and a second inductor coupled in series between the input node and the output node;
wherein the impedance circuit is coupled to the first inductor and the second inductor and configured to cause the negative capacitance to be generated between the input node and the output node.
4. The acoustic resonator structure of claim 3 wherein the first inductor and the second inductor are configured to be negatively coupled.
5. The acoustic resonator structure of claim 3 wherein:
the acoustic resonator causes an electrical capacitance between the input node and the output node in parallel to the acoustic resonator; and
the impedance circuit is further configured to cause the negative capacitance to be generated to cancel the electrical capacitance.
6. The acoustic resonator structure of claim 5 wherein:
the first inductor is coupled between the input node and an intermediate node;
the second inductor is coupled between the intermediate node and the output node; and
the impedance circuit is coupled between the intermediate node and a ground.
7. The acoustic resonator structure of claim 6 wherein the passive impedance circuit and the active impedance circuit are coupled in series between the intermediate node and the ground, wherein the passive impedance circuit and the active impedance circuit are configured to collectively cause the negative capacitance to be generated between the input node and the output node.
8. The acoustic resonator structure of claim 7 wherein:
the passive impedance circuit is coupled to the intermediate node; and
the active impedance circuit is coupled between the passive impedance circuit and the ground.
9. The acoustic resonator structure of claim 7 wherein:
the active impedance circuit is coupled to the intermediate node; and
the passive impedance circuit is coupled between the active impedance circuit and the ground.
10. The acoustic resonator structure of claim 7 wherein the passive impedance circuit comprises at least one acoustic resonator.
11. The acoustic resonator structure of claim 7 wherein the passive impedance circuit comprises at least one capacitor.
12. The acoustic resonator structure of claim 7 wherein the impedance circuit is further configured to generate a shunt impedance having a positive capacitance term and a negative inductance term.
13. The acoustic resonator structure of claim 12 wherein the impedance circuit is further configured to generate the shunt impedance to equal approximately an equivalent impedance of the electrical capacitance.
14. The acoustic resonator structure of claim 13 wherein the shunt impedance is expressed approximately as [−j(1−k)L/2(2πf)+k/(j2(1+k)C 0 (2πf S ))], wherein:
L represents a respective inductance of the first inductor and the second inductor;
C 0 represents the electrical capacitance caused by the acoustic resonator;
k represents a coupling factor between the first inductor and the second inductor; and
f S represents the resonance frequency of the acoustic resonator.
15. The acoustic resonator structure of claim 12 wherein:
the passive impedance circuit is configured to generate the positive capacitance term; and
the active impedance circuit is configured to generate the negative inductance term.
16. The acoustic resonator structure of claim 12 wherein the positive capacitance term is mathematically expressed as 2C 0 (1+k)/k, wherein:
C 0 represents the electrical capacitance caused by the acoustic resonator; and
k represents a coupling factor between the first inductor and the second inductor.
17. The acoustic resonator structure of claim 12 wherein the negative inductance term is mathematically expressed as (1−k)L/2, wherein:
L represents a respective inductance of the first inductor and the second inductor; and
k represents a coupling factor between the first inductor and the second inductor.
18. The acoustic resonator structure of claim 3 wherein the active circuit further comprises:
a first auxiliary inductor coupled between the input node and the first inductor; and
a second auxiliary inductor coupled between the output node and the second inductor.
19. The acoustic resonator structure of claim 18 wherein the first auxiliary inductor and the second auxiliary inductor are configured to cancel at least a portion of a respective self-inductance of the first inductor and the second inductor without affecting a mutual-inductance between the first inductor and the second inductor.