Transformer-based doherty power amplifier
Transformer-based Doherty power amplifier (PA). In some embodiments, a Doherty PA can include a carrier amplification path having an output that includes a carrier transformer, and a peaking amplification path having an output that includes a peaking transformer. The Doherty PA can further include a combiner configured to combine the outputs of the carrier and peaking amplification paths into an output node. The combiner can include a quarter-wave circuit implemented between the carrier and peaking transformers.
1. A Doherty power amplifier comprising:
a carrier amplifier having first and second differential amplificaton cells with outputs coupled by a primary loop of a carrier transformer;
a peaking amplifier having first and second differential amplificaton cells with outputs coupled by a primary loop of a peaking transformer;
an output node implemented at a second end of a secondary loop of the carrier transformer; and
a voltage combiner including a quarter-wave circuit implemented between a first end of the secondary loop of the carrier transformer and a secondary loop of the peaking transformer, the quarter-wave circuit 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 at the output node when both amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the characteristic impedance when the peaking amplifier is turned off.
2. The Doherty power amplifier of claim 1 wherein the quarter-wave circuit couples the first end of the secondary loop of the carrier transformer and a first end of the secondary loop of the peaking transformer.
3. The Doherty power amplifier of claim 2 wherein a second end of the secondary loop of the peaking transformer is coupled to a ground.
4. The Doherty 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.
5. The Doherty 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.
6. The Doherty power amplifier of claim 1 wherein the quarter-wave circuit includes an inductance L having first and second ends coupled to the secondary loops of the carrier and peaking transformers, respectively, a first capacitance C 1 implemented between the first end of the inductance and a ground, and a second capacitance C 2 implemented between the second end of the inductance and the ground.
7. The Doherty power amplifier of claim 6 wherein the first capacitance and the second capacitance have values that are substantially the same.
8. A radio-frequency module comprising:
a packaging substrate configured to receive a plurality of components; and
a Doherty power amplifier implemented on the packaging substrate and including a carrier amplifier having first and second differential amplificaton cells with outputs coupled by a primary loop of a carrier transformer, and a peaking amplifier having first and second differential amplificaton cells with outputs coupled by a primary loop of a peaking transformer, the Doherty power amplifier further including an output node implemented at a second end of a secondary loop of the carrier transformer, the Doherty power amplifier further including a voltage combiner having a quarter-wave circuit implemented between a first end of the secondary loop of the carrier transformer and a secondary loop of the peaking transformer, such that the carrier and peaking amplifiers are presented with an impedance that is approximately the same as the characteristic impedance at the output node when both amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the characteristic impedance when the peaking amplifier is turned off.
9. The radio-frequency module of claim 8 wherein the radio-frequency module is a power amplifier module.
10. The radio-frequency module of claim 8 wherein the radio-frequency module is a front-end module.
11. The radio-frequency module of claim 8 wherein at least some of the Doherty power amplifier is implemented on a complementary metal-oxide-semiconductor die.
12. The radio-frequency module of claim 11 further comprising a bias circuit configured to provide bias signals to the carrier and peaking amplifiers.
13. A wireless device comprising:
a transceiver configured to generate a signal;
a power amplifier system configured to amplify the signal, the power amplifier system including a Doherty power amplifier that includes a carrier amplifier having first and second differential amplificaton cells with outputs coupled by a primary loop of a carrier transformer, and a peaking amplifier having first and second differential amplificaton cells with outputs coupled by a primary loop of a peaking transformer, the Doherty power amplifier further including an output node implemented at a second end of a secondary loop of the carrier transformer, the Doherty power amplifier further including a voltage combiner having a quarter-wave circuit implemented between a first end of the secondary loop of the carrier transformer and a secondary loop of the peaking transformer, such that the carrier and peaking amplifiers are presented with an impedance that is approximately the same as the characteristic impedance at the output node when both amplifiers are turned on, and the carrier amplifier is presented with an impedance that is approximately twice the characteristic impedance when the peaking amplifier is turned off; and
an antenna in communication with the output node of the Doherty power amplifier and configured to facilitate transmission of the amplified signal.
14. The wireless device of claim 13 wherein the wireless device includes a cellular phone.