Radio frequency system with tunable filters including tunable filter with mutually coupled inductors

1. A radio frequency system with tunable notch filtering, the radio frequency system comprising:

a power amplifier having an output;

a radio frequency switch;

a first tunable filter coupled between the output of the power amplifier and the radio frequency switch;

an antenna switch coupled to the radio frequency switch by way of at least one radio frequency signal path; and

a second tunable filter coupled between the antenna switch and an antenna node, the second tunable filter including a first inductor, a second inductor mutually coupled to the first inductor, and a tunable impedance circuit coupled to the first inductor and including a switch, the first inductor associated with a tunable first notch, the second inductor associated with a second tunable notch, and the tunable impedance circuit configured to adjust a state of the switch such that locations of the first tunable notch and the second tunable notch are adjusted.

2. The radio frequency system of claim 1 wherein the first tunable filter has at least a third tunable notch, and the first tunable notch has a lower frequency than the first tunable notch.

3. The radio frequency system of claim 2 wherein the second tunable notch corresponds to a higher order harmonic than the third tunable notch.

4. The radio frequency system of claim 1 wherein the first tunable filter has a plurality of tunable notches.

5. The radio frequency system of claim 1 wherein the tunable impedance circuit further includes a capacitor in series with the switch.

6. The radio frequency system of claim 1 wherein the second tunable filter includes a third inductor, a fourth inductor mutually coupled to the third inductor, and a tunable capacitance circuit coupled to the third inductor.

7. The radio frequency system of claim 1 wherein the second tunable filter is an L network.

8. The radio frequency system of claim 1 wherein the at least one radio frequency signal path includes a band pass filter of a multiplexer.

9. The radio frequency system of claim 1 wherein the tunable impedance circuit includes a tunable capacitance circuit in parallel with the first inductor.

10. The radio frequency system of claim 9 wherein the first inductor is in series with the second inductor.

11. The radio frequency system of claim 10 wherein the second tunable filter further includes a second tunable capacitance circuit in parallel with the second inductor.

12. The radio frequency system of claim 1 wherein the tunable impedance circuit includes a tunable capacitance circuit, and the tunable capacitance circuit is arranged to provide a shunt capacitance between the first inductor and the second inductor.

13. The radio frequency system of claim 1 wherein the first inductor is in series with the second inductor, a first capacitance is in parallel with the first inductor, and a second capacitance is in parallel with the second inductor.

14. The radio frequency system of claim 13 wherein the tunable impedance circuit is configured to provide the first capacitance.

15. The radio frequency system of claim 1 wherein the first inductor is a series inductor, and the second inductor is a shunt inductor, and the tunable impedance circuit includes a tunable capacitance circuit in parallel with the first inductor.

16. The radio frequency system of claim 1 further comprising a tunable shunt capacitance circuit coupled to a node between the first tunable filter and the radio frequency switch, the tunable shunt capacitance circuit being configured to tune a load line.

17. A method of filtering radio frequency signals with tunable notch filtering, the method comprising:

filtering an output signal from a power amplifier with a first tunable filter in a first state, the first tunable filter coupled between an output of the power amplifier and a multi-throw switch;

processing an output signal from the first tunable filter with a signal path coupled between the multi-throw switch and an antenna switch;

filtering an output signal from the antenna switch with a second tunable filter, the second tunable filter including a first inductor, a second inductor mutually coupled to the first inductor, and a tunable impedance circuit coupled to the first inductor;

adjusting a state of the first tunable filter from the first state to a second state to thereby change a location of a first tunable notch of the first tunable filter in the frequency domain; and

filtering the output of the power amplifier with the first tunable filter in the second state.

18. The method of claim 17 further comprising:

adjusting a location of a second tunable notch of the second tunable filter in the frequency domain; and

filtering the output signal from the antenna switch with the second tunable filter after said adjusting the location of the second tunable notch.

19. A wireless communication device with tunable notch filtering, the wireless communication device comprising:

a power amplifier having an output;

a radio frequency switch;

a first tunable filter coupled between the output of the power amplifier and the radio frequency switch;

an antenna switch coupled to the radio frequency switch by way of at least one radio frequency signal path;

an antenna; and

a second tunable filter coupled between the antenna switch and the antenna, the second tunable filter including a first inductor, a second inductor mutually coupled to the first inductor, and a tunable impedance circuit coupled to the first inductor and including a switch, the first inductor associated with a first tunable notch, the second inductor associated with a second tunable notch, and the tunable impedance circuit configured to adjust a state of the switch such that locations of the first tunable notch and the second tunable notch are adjusted.

20. The wireless communication of claim 19 wherein the wireless communication device is a mobile phone.