Amplifier with switchable transformer

1. An apparatus, comprising:

a first amplifier having a first output and a second output;

a transformer comprising:

a first switchable inductor coupled between the first output and the second output;

a first capacitor coupled in parallel with the first switchable inductor;

a second switchable inductor magnetically coupled to the first switchable inductor;

a second capacitor coupled in parallel with the second switchable inductor;

a third switchable inductor magnetically coupled to the first switchable inductor; and

a third capacitor coupled in parallel with the third switchable inductor.

2. The apparatus of claim 1 , further comprising:

a second amplifier coupled to the second switchable inductor; and

a third amplifier coupled to the third switchable inductor.

3. The apparatus of claim 2 , wherein the second amplifier has a first input and a second input, and the second switchable inductor is coupled between the first input of the second amplifier and the second input of the second amplifier.

4. The apparatus of claim 2 , further comprising a mixer coupled to an output of the second amplifier.

5. The apparatus of claim 4 , further comprising a power amplifier coupled to the mixer.

6. The apparatus of claim 3 , wherein the third amplifier has a first input and a second input, and the third switchable inductor is coupled between the first input of the third amplifier and the second input of the third amplifier.

7. The apparatus of claim 1 , wherein the first switchable inductor is switchable between a first inductance and a second inductance.

8. The apparatus of claim 7 , wherein the second switchable inductor comprises:

at least one inductor; and

at least one switch coupled in series with the at least one inductor.

9. The apparatus of claim 8 , further comprising a controller configured to:

in a first mode, switch the first switchable inductor to the first inductance and close the at least one switch; and

in a second mode, switch the first switchable inductor to the second inductance and open the at least one switch.

10. The apparatus of claim 8 , further comprising a second amplifier having a first input and a second input, wherein the second switchable inductor is coupled between the first input of the second amplifier and the second input of the second amplifier.

11. The apparatus of claim 7 , wherein:

the second switchable inductor comprises:

at least one first inductor; and

at least one first switch coupled in series with the at least one first inductor; and

the third switchable inductor comprises:

at least one second inductor; and

at least one second switch coupled in series with the at least one second inductor.

12. The apparatus of claim 11 , further comprising a controller configured to:

in a first mode, switch the first switchable inductor to the first inductance, close the at least one first switch, and open the at least one second switch; and

in a second mode, switch the first switchable inductor to the second inductance, open the at least one first switch, and close the at least one second switch.

13. The apparatus of claim 11 , further comprising:

a second amplifier having a first input and a second input, wherein the second switchable inductor is coupled between the first input of the second amplifier and the second input of the second amplifier; and

a third amplifier having a first input and a second input, wherein the third switchable inductor is coupled between the first input of the third amplifier and the second input of the third amplifier.

14. The apparatus of claim 1 , wherein the first switchable inductor comprises:

a first inductor;

a second inductor;

a third inductor;

a fourth inductor; and

a switching circuit, wherein the switching circuit is configured to:

couple the first inductor, the second inductor, the third inductor, and the fourth inductor in series between the first output of the first amplifier and the second output of the first amplifier; and

couple the first inductor and the fourth inductor in series between the first output of the first amplifier and the second output of the first amplifier.

15. The apparatus of claim 14 , wherein the second switchable inductor comprises:

a fifth inductor;

a sixth inductor; and

a first switch coupled between the fifth inductor and the sixth inductor.

16. The apparatus of claim 15 , further comprising a second amplifier having a first input and a second input, wherein the second switchable inductor is coupled between the first input of the second amplifier and the second input of the second amplifier.

17. The apparatus of claim 15 , wherein the third switchable inductor comprises:

a seventh inductor;

an eighth inductor; and

a second switch coupled between the seventh inductor and the eighth inductor.

18. The apparatus of claim 17 , further comprising:

a second amplifier having a first input and a second input, wherein the second switchable inductor is coupled between the first input of the second amplifier and the second input of the second amplifier; and

a third amplifier having a first input and a second input, wherein the third switchable inductor is coupled between the first input of the third amplifier and the second input of the third amplifier.

19. A method for operating an apparatus, wherein the apparatus includes a first amplifier, and a transformer including a first switchable inductor coupled to the first amplifier, a second switchable inductor magnetically coupled to the first switchable inductor, and a third switchable inductor magnetically coupled to the first switchable inductor, the method comprising:

in a first mode,

switching the first switchable inductor to a first inductance;

enabling the second switchable inductor; and

disabling the third switchable inductor;

in a second mode,

switching the first switchable inductor to a second inductance;

disabling the second switchable inductor; and

enabling the third switchable inductor.

20. The method of claim 19 , where the apparatus further comprises:

a second amplifier coupled to the second switchable inductor; and

a third amplifier coupled to the third switchable inductor.

21. The method of claim 20 , further comprising:

amplifying a first signal in a first frequency band and a second signal in a second frequency band using the first amplifier;

amplifying the first signal in the first frequency band using the second amplifier; and

amplifying the second signal in the second frequency band using the third amplifier.

22. The method of claim 19 , wherein:

the second switchable inductor includes:

at least one first inductor; and

at least one first switch coupled in series with the at least one first inductor;

enabling the second switchable inductor comprises closing the at least one first switch; and

disabling the second switchable inductor comprises opening the at least one first switch.

23. The method of claim 22 , wherein:

the third switchable inductor includes:

at least one second inductor; and

at least one second switch coupled in series with the at least one second inductor;

enabling the third switchable inductor comprises closing the at least one second switch; and

disabling the third switchable inductor comprises opening the at least one second switch.

24. The method of claim 19 , wherein:

the first switchable inductor comprises:

at least one first inductor;

at least one second inductor; and

at least one switch coupled in parallel with the at least one second inductor;

switching the first switchable inductor to the first inductance comprises opening the at least one switch; and

switching the second switchable inductor to the second inductance comprises closing the at least one switch.

25. The method of claim 19 , wherein the apparatus further includes:

a first capacitor coupled in parallel with the first switchable inductor;

a second capacitor coupled in parallel with the second switchable inductor; and

a third capacitor coupled in parallel with the third switchable inductor.

26. An apparatus, comprising:

a first amplifier having a first output and a second output;

a transformer comprising:

at least one first inductor;

at least one second inductor, wherein the at least one first inductor and the at least one second inductor are coupled between the first output and the second output of the first amplifier;

at least one first switch coupled in parallel with the at least one second inductor;

at least one third inductor magnetically coupled to the at least one first inductor and the at least one second inductor;

at least one second switch coupled in series with the at least one third inductor;

a second capacitor coupled in parallel with the at least one third inductor and the at least one second switch;

at least one fourth inductor magnetically coupled to the at least one first inductor;

at least one third switch coupled in series with the at least one fourth inductor; and

a third capacitor coupled in parallel with the at least one fourth inductor and the at least one third switch.

27. The apparatus of claim 26 , further comprising a second amplifier having a first input and a second input, wherein the at least one third inductor and the at least one second switch are coupled in series between the first input of the second amplifier and the second input of the second amplifier.

28. The apparatus of claim 27 , further comprising a third amplifier having a first input and a second input, wherein the at least one fourth inductor and the at least one third switch are coupled in series between the first input of the third amplifier and the second input of the third amplifier.