Tunable baluns for multimode power amplification

1. A variable-gain amplification system comprising:

a power amplifier configured to provide an amplified signal and to selectively operate in at least a first gain mode and a second gain mode; and

a tunable balun circuit including a first coil configured to receive the amplified signal from the power amplifier, a second coil configured to provide an output signal, a first switch coupled between a first portion of the second coil and a second portion of the second coil, and a second switch coupled to a node located between the first portion of the second coil and the second portion of the second coil, the tunable balun circuit being configured to implement a first turn ratio for the first gain mode and a second turn ratio for the second gain mode.

2. The variable-gain amplification system of claim 1 wherein the power amplifier includes a pair of amplifiers configured to generate a pair of amplified signal components and the first coil of the tunable balun circuit is configured to receive the pair of amplified signal components.

3. The variable-gain amplification system of claim 2 wherein the variable-gain amplification system includes a Doherty power amplifier.

4. The variable-gain amplification system of claim 1 wherein the second switch is coupled between the node and a ground.

5. The variable-gain amplification system of claim 1 wherein the second portion of the second coil includes a first end that is coupled to the first switch and a second end that is coupled to a ground.

6. The variable-gain amplification system of claim 1 wherein the first portion of the second coil includes a first end that is coupled to an output node and a second end that is coupled to the node.

7. The variable-gain amplification system of claim 1 further comprising a first substrate layer, a second substrate layer, and an insulation layer disposed between the first substrate layer and the second substrate layer, the first coil being disposed on the first substrate layer and the second coil being disposed on the second substrate layer.

8. A radio-frequency module comprising:

a packaging substrate;

a power amplifier implemented on the packaging substrate, the power amplifier being configured to selectively operate in at least a first gain mode and a second gain mode; and

a tunable balun circuit implemented on the packaging substrate, the tunable balun circuit being coupled to the power amplifier and being configured to implement a first turn ratio for the first gain mode and a second turn ratio for the second gain mode.

9. The radio-frequency module of claim 8 wherein the tunable balun circuit includes a primary coil, a secondary coil coupled to the primary coil, a first switch coupled between a first portion of the secondary coil and a second portion of the secondary coil, and a second switch coupled to a node located between the first portion of the secondary coil and the second portion of the secondary coil.

10. The radio-frequency module of claim 9 wherein the power amplifier includes a pair of amplifiers configured to generate a pair of amplified signal components and the primary coil of the tunable balun circuit is configured to receive the pair of amplified signal components.

11. The radio-frequency module of claim 9 wherein the power amplifier and the tunable balun circuit are configured as a Doherty power amplifier.

12. The radio-frequency module of claim 9 wherein the second switch is coupled between the node and a ground.

13. The radio-frequency module of claim 9 wherein the second portion of the secondary coil includes a first end that is coupled to the first switch and a second end that is coupled to a ground.

14. The radio-frequency module of claim 9 wherein the primary coil includes a first end that is coupled to an output node and a second end that is coupled to the node.

15. A radio-frequency device comprising:

a power amplifier configured to generate an amplified signal and to selectively operate in at least a first gain mode and a second gain mode;

a tunable balun circuit coupled to the power amplifier and configured to provide an output signal, the tunable balun circuit including a primary coil, a secondary coil coupled to the primary coil, a first switch coupled between a first portion of the secondary coil and a second portion of the secondary coil, and a second switch coupled to a node located between the first portion of the secondary coil and the second portion of the secondary coil, the tunable balun circuit being configured to implement a first turn ratio for the first gain mode and a second turn ratio for the second gain mode;

a controller coupled to the tunable balun circuit and configured to provide a control signal to the tunable balun circuit instructing the tunable balun circuit to implement the first turn ratio or the second turn ratio; and

an antenna coupled to the tunable balun circuit and configured to receive the output signal.

16. The radio-frequency device of claim 15 wherein the power amplifier includes a pair of amplifiers configured to generate a pair of amplified signal components and the primary coil of the tunable balun circuit is configured to receive the pair of amplified signal components.

17. The radio-frequency device of claim 15 wherein the second switch is coupled between the node and a ground.

18. The radio-frequency device of claim 15 wherein the primary coil includes a first end that is coupled to an output node and a second end that is coupled to the node.