Apparatus and methods for envelope tracking
Envelope tracking systems for power amplifiers are provided herein. In certain embodiments, an envelope tracker supplies power to a power amplifier that amplifies an RF signal. The envelope tracker includes a multi-level switching circuit that generates an output current based on an envelope signal indicating an envelope of the RF signal. The envelope tracker further includes a combiner that combines a DC voltage with the output current of the multi-level switching circuit to generate a power amplifier supply voltage for the power amplifier. Accordingly, the output current of the multi-level switching circuit and a DC voltage are combined to generate the power amplifier supply voltage. Implementing the envelope tracking system in this manner can provide enhanced efficiency and/or higher bandwidth relative to an envelope tracking system in which a multi-level switching circuit directly outputs a power amplifier supply voltage.
1. A mobile device comprising:
a transceiver configured to generate a radio frequency transmit signal;
a front end circuit including a power amplifier configured to amplify the radio frequency transmit signal; and
a power management circuit including an envelope tracker configured to generate a power amplifier supply voltage of the power amplifier, the envelope tracker including a multi-level switching circuit configured to generate an output current based on an envelope signal indicating an envelope of the radio frequency transmit signal, and a combiner configured to combine a DC voltage with the output current to generate a power amplifier supply voltage of the power amplifier, the multi-level switching circuit including a multi-level supply DC-to-DC converter configured to generate a plurality of regulated voltages of different voltage levels, a modulator configured to receive the plurality of regulated voltages and to generate the output current, a control circuit configured to control the modulator based on the envelope signal, and an amplifier interposed between the modulator and the combiner.
2. The mobile device of claim 1 wherein the multi-level supply DC-to-DC converter is further configured to generate the DC voltage.
3. The mobile device of claim 1 wherein the multi-level switching circuit has an output providing the output current, the modulator further including a plurality of switches each electrically connected between a corresponding one of the plurality of regulated voltages and the output.
4. A mobile device comprising:
a transceiver configured to generate a radio frequency transmit signal;
a front end circuit including a power amplifier configured to amplify the radio frequency transmit signal; and
a power management circuit including an envelope tracker configured to generate a power amplifier supply voltage of the power amplifier, the envelope tracker including a multi-level switching circuit configured to generate an output current based on an envelope signal indicating an envelope of the radio frequency transmit signal, and a combiner configured to combine a DC voltage with the output current to generate a power amplifier supply voltage of the power amplifier, the multi-level switching circuit including a multi-level supply DC-to-DC converter configured to generate a plurality of regulated voltages of different voltage levels, a modulator configured to receive the plurality of regulated voltages and to generate the output current, and a control circuit configured to control the modulator based on the envelope signal, the control circuit including a sigma-delta encoder.
5. A mobile device comprising:
a transceiver configured to generate a radio frequency transmit signal;
a front end circuit including a power amplifier configured to amplify the radio frequency transmit signal; and
a power management circuit including an envelope tracker configured to generate a power amplifier supply voltage of the power amplifier, the envelope tracker including a multi-level switching circuit configured to generate an output current based on an envelope signal indicating an envelope of the radio frequency transmit signal, and a combiner configured to combine a DC voltage with the output current to generate a power amplifier supply voltage of the power amplifier, the multi-level switching circuit having an output providing the output current, the combiner including a first inductor electrically connected between the DC voltage and the power amplifier supply voltage, and a series capacitor connected between the output and the power amplifier supply voltage.
6. The mobile device of claim 5 wherein the multi-level switching circuit includes a switched capacitor multi-level supply circuit configured to generate a plurality of regulated voltages of different voltage levels, a modulator configured to receive the plurality of regulated voltages and to generate the output current, and a control circuit configured to control the modulator based on the envelope signal.
7. The mobile device of claim 5 wherein the combiner further includes a second inductor electrically connected in series with the series capacitor between the output and the power amplifier supply voltage.
8. The mobile device of claim 5 wherein the combiner further includes a controllable bandwidth adjustment capacitor electrically connected between the power amplifier supply voltage and ground.
9. The mobile device of claim 1 further comprising a battery operable to provide a battery voltage to the multi-level switching circuit.
10. A method of envelope tracking, the method comprising:
amplifying a radio frequency transmit signal using a power amplifier;
generating an output current based on an envelope signal using a multi-level switching circuit, the envelope signal indicating an envelope of the radio frequency transmit signal;
generating a power amplifier supply voltage of the power amplifier by combining a DC voltage and the output current using a combiner; and
adjusting a modulation bandwidth of envelope tracking using a controllable bandwidth adjustment capacitor of the combiner.
11. The method of claim 10 wherein generating the output current includes generating a plurality of regulated voltages of different voltage levels using a multi-level supply DC-to-DC converter, and modulating the plurality of regulated voltages based on the envelope signal to generate the output current using a modulator.
12. The method of claim 11 further comprising generating the DC voltage using the multi-level supply DC-to-DC converter.
13. The method of claim 11 further comprising controlling the modulator based on the envelope signal using a sigma-delta encoder.
14. The method of claim 10 further comprising generating the DC voltage using a DC-to-DC converter.
15. The mobile device of claim 4 wherein the multi-level supply DC-to-DC converter is further configured to generate the DC voltage.
16. The mobile device of claim 4 wherein the multi-level switching circuit has an output providing the output current, the modulator further including a plurality of switches each electrically connected between a corresponding one of the plurality of regulated voltages and the output.
17. The mobile device of claim 4 further comprising a battery operable to provide a battery voltage to the multi-level switching circuit.
18. The mobile device of claim 5 wherein the multi-level supply DC-to-DC converter is further configured to generate the DC voltage.
19. The mobile device of claim 5 wherein the modulator further includes a plurality of switches each electrically connected between a corresponding one of the plurality of regulated voltages and the output.
20. The mobile device of claim 5 further comprising a battery operable to provide a battery voltage to the multi-level switching circuit.