Apparatus and methods for power amplifiers with phase compensation

1. A method of phase compensation in a power amplifier, the method comprising:

amplifying a radio frequency signal using a power amplifier that includes an input stage including a first bipolar transistor and an output stage including a second bipolar transistor;

powering a collector of the first bipolar transistor using a first supply voltage and a collector of the second bipolar transistor using a second supply voltage;

changing a voltage level of the second supply voltage, the second bipolar transistor having an input reactance that changes in response to the change in the voltage level of the second supply voltage; and

compensating for a variation in a phase delay of the power amplifier arising from the change in the input reactance of the second bipolar transistor using a compensation circuit that includes a compensation inductor electrically connected between the collector of the first bipolar transistor and the first supply voltage.

2. The method of claim 1 wherein compensating for the variation in the phase delay of the power amplifier includes compensating for a variation in a parasitic capacitance between a base of the second bipolar transistor and the collector of the second bipolar transistor associated with the change in the voltage level of the second supply voltage.

3. The method of claim 1 further comprising controlling the voltage level of the second supply voltage based on an envelope of the radio frequency signal using an envelope tracker.

4. The method of claim 3 further comprising generating an envelope signal based on shaping envelope data in a transceiver to control a gain compression of the power amplifier, and providing the envelope signal to the envelope tracker.

5. The method of claim 1 further comprising providing a bias current from a bias current generation circuit to a base of the bipolar transistor via a bias inductor of the compensation circuit.

6. A power amplifier system comprising:

a power amplifier input stage including a first bipolar transistor including a collector configured to receive power from a first supply voltage, the first bipolar transistor configured to amplify a radio frequency signal to generate a first amplified radio frequency signal;

a power amplifier output stage including a second bipolar transistor including a collector configured to receive power from a second supply voltage, the second bipolar transistor configured to generate a second amplified radio frequency signal by further amplifying the first amplified radio frequency signal and having an input reactance that changes in response to a change in the voltage level of the second supply voltage; and

a compensation circuit configured to compensate for a variation in a power amplifier phase delay associated with the change in the input reactance of the second bipolar transistor, the compensation circuit including a first compensation inductor electrically connected between the collector of the first bipolar transistor and the first supply voltage.

7. The power amplifier system of claim 6 wherein the compensation circuit further includes a bias inductor, the power amplifier system further comprising a bias current generation circuit that provides a bias current to a base of the second bipolar transistor via the bias inductor.

8. The power amplifier system of claim 7 wherein the power amplifier input stage is configured to provide a portion of the first amplified radio frequency signal to the bias current generation circuit to provide phase compensation.

9. The power amplifier system of claim 6 wherein the compensation circuit further includes a second compensation inductor electrically connected in series with the first compensation inductor between the collector of the first bipolar transistor and the second power supply.

10. The power amplifier system of claim 9 wherein the compensation circuit further includes a third compensation inductor and a compensation capacitor connected in series between a ground supply and a node that is between the first and second compensation inductors.

11. The power amplifier system of claim 6 further comprising an envelope tracker configured to control the voltage level of the second supply voltage based on an envelope of the radio frequency signal.

12. The power amplifier system of claim 11 further comprising a transceiver configured to provide the radio frequency signal to the power amplifier input stage and to provide an envelope signal to the envelope tracker.

13. The power amplifier system of claim 12 wherein the transceiver is configured to generate the envelope signal based on shaping envelope data to control a power amplifier gain compression.

14. A mobile device comprising:

a transceiver configured to generate a radio frequency signal; and

a power amplifier including an input stage including a first bipolar transistor having a collector configured to receive power from a first supply voltage and an output stage including a second bipolar transistor having a collector configured to receive power from a second supply voltage, the first bipolar transistor configured to amplify the radio frequency signal to generate a first amplified radio frequency signal, and the second bipolar transistor configured to generate a second amplified radio frequency signal by further amplifying the first amplified radio frequency signal and having an input reactance that changes in response to a change in the voltage level of the second supply voltage, the power amplifier further including a compensation circuit configured to compensate for a variation in a phase delay of the power amplifier associated with the change in the input reactance of the second bipolar transistor, the compensation circuit including a first compensation inductor electrically connected between the collector of the first bipolar transistor and the first supply voltage.

15. The mobile device of claim 14 wherein the compensation circuit includes a bias inductor, the power amplifier further including a bias current generation circuit that provides a bias current to a base of the second bipolar transistor via the bias inductor.

16. The mobile device of claim 15 wherein the input stage is configured to provide a portion of the first amplified radio frequency signal to the bias current generation circuit to provide phase compensation.

17. The mobile device of claim 14 wherein the compensation circuit includes a second compensation inductor electrically connected in series with the first compensation inductor between the collector of the first bipolar transistor and the first supply voltage.

18. The mobile device of claim 17 wherein the compensation circuit further includes a third compensation inductor and a compensation capacitor connected in series between a ground supply and a node that is between the first and second compensation inductors.

19. The mobile device of claim 14 further comprising an envelope tracker configured to control the voltage level of the second supply voltage based on an envelope of the radio frequency signal.

20. The mobile device of claim 19 wherein the transceiver is configured to generate an envelope signal based on shaping envelope data to control a gain compression of the power amplifier, and to provide the envelope signal to the envelope tracker.