Doherty power amplifier for radio-frequency applications
A power amplifier can include a carrier amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a carrier transformer, and a peaking amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a peaking transformer. The power amplifier can further include a combiner having a quarter-wave circuit implemented between the secondary loop of the carrier transformer and a secondary loop of the peaking transformer. The quarter-wave circuit can be configured to provide a characteristic impedance, such that the carrier and peaking amplifiers are presented with an impedance that is approximately the same as the characteristic impedance when both of the carrier and peaking amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the characteristic impedance when the carrier amplifier is turned on and the peaking amplifier is turned off.
1. A power amplifier comprising:
a carrier amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a carrier transformer;
a peaking amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a peaking transformer;
a combiner including a quarter-wave circuit implemented between a first end of a secondary loop of the carrier transformer and a first end of a secondary loop of the peaking transformer, the quarter-wave circuit configured such that the carrier and peaking amplifiers are presented with a desired impedance when both of the carrier and peaking amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the desired impedance when the carrier amplifier is turned on and the peaking amplifier is turned off; and
an output node implemented at a second end of the secondary loop of the carrier transformer.
2. The power amplifier of claim 1 wherein the desired impedance includes a characteristic impedance of the quarter-wave circuit.
3. The power amplifier of claim 1 wherein the carrier amplifier is configured to operate with a light Class AB bias, and the peaking amplifier is configured to operate with a deep Class AB bias.
4. The power amplifier of claim 1 wherein a second end of the secondary loop of the peaking transformer is coupled to a ground.
5. The power amplifier of claim 1 wherein the quarter-wave circuit includes an inductance L implemented between the secondary loops of the carrier and peaking transformers, a first capacitance C1 implemented between a first end of the inductance and a ground, and a second capacitance C2 implemented between a second end of the inductance and the ground.
6. The power amplifier of claim 5 wherein the first capacitance and the second capacitance have values that are approximately the same.
7. The power amplifier of claim 1 wherein each of the first and second differential amplification cells of the carrier amplifier and the peaking amplifier includes a plurality of transistors arranged in a stack.
8. The power amplifier of claim 1 wherein each of the first and second differential amplification cells of the carrier amplifier and the peaking amplifier is implemented as a complementary metal-oxide-semiconductor power amplifier.
9. The power amplifier of claim 1 wherein the carrier amplifier and the peaking amplifier are implemented as silicon-on-insulator devices.
10. The power amplifier of claim 1 wherein the combiner is implemented as a voltage combiner.
11. The power amplifier of claim 1 wherein the carrier amplifier is configured to operate with a Class A bias, and the peaking amplifier is configured to operate with a Class B bias.
12. A radio-frequency module comprising:
a packaging substrate configured to receive a plurality of components; and
a power amplifier implemented on the packaging substrate and including a carrier amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a carrier transformer, and a peaking amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a peaking transformer, the power amplifier further including a combiner having a quarter-wave circuit implemented between a first end of a secondary loop of the carrier transformer and a first end of a secondary loop of the peaking transformer, the quarter-wave circuit configured such that the carrier and peaking amplifiers are presented with a desired impedance when both of the carrier and peaking amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the desired impedance when the carrier amplifier is turned on and the peaking amplifier is turned off, the power amplifier further including an output node implemented at a second end of the secondary loop of the carrier transformer.
13. The radio-frequency module of claim 12 further comprising a bias circuit configured to provide bias signals to the carrier and peaking amplifiers.
14. The radio-frequency module of claim 12 wherein the radio-frequency module is a power amplifier module.
15. The radio-frequency module of claim 12 wherein the radio-frequency module is a front-end module.
16. The radio-frequency module of claim 12 wherein at least some of the power amplifier is implemented on a complementary metal-oxide-semiconductor die.
17. The radio-frequency module of claim 12 wherein at least some of the power amplifier is implemented on a silicon-on-insulator die.
18. A wireless device comprising:
a transmitter circuit configured to generate a signal;
a power amplifier configured to amplify the signal, and including a carrier amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a carrier transformer, and a peaking amplifier having first and second differential amplification cells with outputs coupled by a primary loop of a peaking transformer, the power amplifier further including a combiner having a quarter-wave circuit implemented between a first end of a secondary loop of the carrier transformer and a first end of a secondary loop of the peaking transformer, the quarter-wave circuit configured such that the carrier and peaking amplifiers are presented with a desired impedance when both of the carrier and peaking amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the desired impedance when the carrier amplifier is turned on and the peaking amplifier is turned off, the power amplifier further including an output node implemented at a second end of the secondary loop of the carrier transformer; and
an antenna in communication with the output node of the power amplifier and configured to support transmission of the amplified signal.
19. The wireless device of claim 18 wherein the power amplifier is configured to amplify the signal having a cellular frequency.