Multi-band impedance tuners using weakly-coupled LC resonators
Radio frequency (RF) filter structures and related methods and RF front-end circuitry are disclosed. In one embodiment, an RF filter structure includes a first terminal and a first tunable RF filter path defined between the first terminal and a second terminal. The first tunable RF filter path is tunable to provide impedance matching between the first terminal and the second terminal at a first frequency. The first frequency may be provided within a first frequency band. Additionally, the RF filter structure includes a second tunable RF filter path defined between the first terminal and the second terminal. The second tunable RF filter path is tunable to provide impedance matching between the first terminal and the second terminal at a second frequency. The second frequency may be within a second frequency band. In this manner, the RF filter structure is configured to provide impedance tuning for multiple impedance bands simultaneously.
1. A radio frequency (RF) filter structure, comprising:
a first terminal;
a second terminal;
a first tunable RF filter path defined between the first terminal and the second terminal, wherein the first tunable RF filter path is configured to be tunable to provide impedance matching between the first terminal and the second terminal at a first frequency and wherein the first tunable RF filter path comprises a first subset of the plurality of resonators wherein at least a pair of the first subset of the plurality of resonators are weakly coupled to one another;
a second tunable RF filter path defined between the first terminal and the second terminal, wherein the second tunable RF filter path is configured to be tunable to provide impedance matching between the first terminal and the second terminal at a second frequency and wherein the second tunable RF filter path comprises a second subset of the plurality of resonators; and
wherein the first subset of the plurality of resonators and the second subset of the plurality of resonators are not mutually exclusive.
2. The RF filter structure of claim 1 wherein the RF filter structure has a tunable transfer response and is further tunable to:
define a first passband between the first terminal and the second terminal such that the first frequency is in the first passband;
define a second passband between the first terminal and the second terminal such that the second frequency is in the second passband.
3. The RF frequency filter structure of claim 1 wherein the first subset of the plurality of resonators and the second subset of the plurality of resonators both include a first resonator coupled to the first terminal, the first resonator being coupled in the first tunable RF filter path and the second tunable RF filter path so as to operate as a splitter between the first tunable RF filter path and the second tunable RF filter path.
4. The RF frequency filter structure of claim 3 wherein the first subset of the plurality of resonators and the second subset of the plurality of resonators both include a second resonator coupled to the second terminal, the second resonator being coupled in the first tunable RF filter path and the second tunable RF filter path so as to operate as a combiner between the first tunable RF filter path and the second tunable RF filter path.
5. The RF frequency filter structure of claim 1 wherein at least a pair of the second subset of the plurality of resonators are weakly coupled to one another.
6. The RF frequency filter structure of claim 1 further comprising a second cross-coupling capacitive structure wherein:
the second cross-coupling capacitive structure is coupled between the pair of weakly coupled resonators, wherein the second cross-coupling capacitive structure is operable to provide a second variable capacitance.
7. The RF frequency filter structure of claim 6 further comprising a third cross-coupling capacitive structure wherein:
the second subset of the plurality of resonators includes a second pair of weakly coupled resonators;
the third cross-coupling capacitive structure is coupled between the second pair of weakly coupled resonators, wherein the third cross-coupling capacitive structure is operable to provide a third variable capacitance.
8. Radio frequency (RF) front-end circuitry, comprising:
a first terminal;
a second terminal;
a first tunable RF filter path defined between the first terminal and the second terminal, wherein the first tunable RF filter path comprises a pair of weakly coupled resonators and the first tunable RF filter path is configured to be tunable to provide impedance matching between the first terminal and the second terminal at a first frequency; and
a third resonator coupled to one of the pair of weakly coupled resonators so as to provide a first subpath connected to the first tunable RF filter path;
a first cross-coupling capacitive structure operable to provide a first variable capacitance and coupled in the first subpath between the one of the pair of weakly coupled resonators and the third resonator; and
a control circuit configured to tune the first tunable RF filter path to provide impedance matching between the first terminal and the second terminal at the first frequency by adjusting the first variable capacitance so as to adjust a phase of the first tunable RF filter path and provide the impedance matching between the first terminal and the second terminal at the first frequency.
9. The RF front-end circuitry of claim 8 further comprising a second cross-coupling capacitive structure and a third cross-coupling capacitive structure, wherein the second cross-coupling capacitive structure and the third cross-coupling capacitive structure are arranged to form a first capacitive voltage divider.
10. The RF front-end circuitry of claim 9 further comprising a fourth cross-coupling capacitive structure and a fifth cross-coupling capacitive structure, wherein:
the fourth cross-coupling capacitive structure and the fifth cross-coupling capacitive structure are arranged so as to form a second capacitive voltage divider;
the first capacitive voltage divider is electrically connected to the one of the pair of weakly coupled resonators; and
the second capacitive voltage divider is electrically connected to an other of the pair of weakly coupled resonators.
11. The RF front-end circuitry of claim 10 wherein each of the second cross-coupling capacitive structure, the third cross-coupling capacitive structure, the fourth cross-coupling capacitive structure, and the fifth cross-coupling capacitive structure is a variable capacitive structure.
12. The RF front-end circuitry of claim 8 wherein the first tunable RF filter path further comprises a second cross-coupling capacitive structure coupled between the pair of weakly coupled resonators, wherein:
the second cross-coupling capacitive structure is operable to provide a second variable capacitance;
the control circuit is further configured to tune the first tunable RF filter path by adjusting the second variable capacitance so as to provide the impedance matching between the first terminal and the second terminal at the first frequency.
13. The RF front-end circuitry of claim 12 wherein the first tunable RF filter path further comprises a first matching capacitive structure coupled between the first terminal and the one of the pair of weakly coupled resonators, wherein:
the first matching capacitive structure is operable to provide a third variable capacitance;
the control circuit is configured to tune the first tunable RF filter path by adjusting the third variable capacitance so as to provide the impedance matching between the first terminal and the second terminal at the first frequency.
14. The RF front-end circuitry of claim 13 wherein the first tunable RF filter path further comprises a second matching capacitive structure coupled between the second terminal and the other of the pair of weakly coupled resonators, wherein:
the second matching capacitive structure is operable to provide a fourth variable capacitance;
the control circuit is further configured to tune the first tunable RF filter path by adjusting the fourth variable capacitance so as to provide the impedance matching between the first terminal and the second terminal at the first frequency.
15. The RF front-end circuitry of claim 8 further comprising a fourth resonator wherein the third resonator and the fourth resonator are coupled between the pair of weakly coupled resonators so as to provide the first subpath connected to the first tunable RF filter path.
16. The RF front-end circuitry of claim 15 further comprising a second cross-coupling capacitive structure, and a third cross-coupling capacitive structure wherein the second cross-coupling capacitive structure is coupled in the first subpath between the third resonator and the fourth resonator and the third cross-coupling capacitive structure is coupled in the first subpath between an other of the pair of weakly coupled resonators and the fourth resonator wherein:
the second cross-coupling capacitive structure is operable to provide a second variable capacitance;
the third cross-coupling capacitive structure is operable to provide a third variable capacitance; and
the control circuit is further configured to tune the first tunable RF filter path by adjusting the second variable capacitance and the third variable capacitance so as to adjust the phase of the first tunable RF filter path and provide the impedance matching between the first terminal and the second terminal at the first frequency.
17. The RF front-end circuitry of claim 8 wherein the third resonator is coupled between the pair of weakly coupled resonators so as to provide the first subpath connected to the first tunable RF filter path.
18. The RF front-end circuitry of claim 17 further comprising a second cross-coupling capacitive structure coupled in the first subpath between an other of the pair of weakly coupled resonators and the third resonator wherein:
the second cross-coupling capacitive structure is operable to provide a second variable capacitance;
the control circuit is further configured to tune the first tunable RF filter path by adjusting the second variable capacitance so as to adjust the phase of the first tunable RF filter path and provide the impedance matching between the first terminal and the second terminal at the first frequency.
19. The RF front-end circuitry of claim 8 wherein the pair of weakly coupled resonators comprises a first resonator having a first inductor and a second resonator having a second inductor, wherein the first inductor is weakly coupled to the second inductor.
20. The RF front-end circuitry of claim 19 wherein the first resonator further comprises a first plurality of switchable inductive elements, wherein each of the first plurality of switchable inductive elements is configured to be switched so as to be strongly coupled to the first inductor and adjust a first inductance of the first resonator.
21. The RF front-end circuitry of claim 20 wherein the second resonator further comprises a second plurality of switchable inductive elements, wherein each of the second plurality of switchable inductive elements is configured to be switched so as to be strongly coupled to the second inductor and adjust a second inductance of the second resonator.
22. The RF front-end circuitry of claim 19 wherein the first tunable RF filter path further comprises a second cross-coupling capacitive structure electrically connected between the pair of weakly coupled resonators so as to provide a first electric coupling coefficient between the pair of weakly coupled resonators.
23. The RF front-end circuitry of claim 22 wherein the first tunable RF filter path further comprises a third cross-coupling capacitive structure wherein the third cross-coupling capacitive structure is electrically connected between the pair of weakly coupled resonators so as to provide a second electric coupling coefficient between the pair of weakly coupled resonators.
24. The RF front-end circuitry of claim 23 wherein the control circuit is configured to adjust the first electric coupling coefficient and the second electric coupling coefficient.
25. The RF front-end circuitry of claim 24 wherein the third cross-coupling capacitive structure is coupled between the first inductor and the second inductor such that the first electric coupling coefficient is adjusted positively and the third cross-coupling capacitive structure is coupled between the first inductor and the second inductor so that the second electric coupling coefficient is adjusted negatively.