Reduced bandwidth envelope tracking

1. Envelope power supply circuitry comprising:

envelope power converter circuitry configured to receive an envelope power converter control signal and a supply voltage and provide an envelope power supply signal for an amplifier based on the envelope power converter control signal; and

envelope tracking circuitry configured to provide the envelope power converter control signal to the envelope power supply circuitry, wherein:

in a first mode of operation in which a modulation bandwidth of an RF input signal provided to the amplifier is below a modulation bandwidth threshold, the envelope power converter control signal is provided such that the envelope power supply signal causes a gain of the amplifier to remain substantially constant over a range of input power provided to the amplifier; and

in a second mode of operation in which the modulation bandwidth of the RF input signal provided to the amplifier is above the modulation bandwidth threshold, the envelope power converter control signal is provided such that:

the envelope power supply signal remains substantially constant for values within the range of input power below a predetermined threshold; and

the envelope power supply signal causes the gain of the amplifier to remain substantially constant for values within the range of input power above the predetermined threshold.

2. The circuitry of claim 1 wherein the envelope tracking circuitry comprises a gain-shaping look-up table configured to receive an envelope tracking signal and provide the envelope power converter control signal.

3. The circuitry of claim 2 wherein the envelope tracking circuitry further comprises envelope detection circuitry configured to detect an envelope of an input signal provided to the amplifier to provide the envelope tracking signal.

4. The circuitry of claim 2 wherein the envelope power converter circuitry comprises:

switching power supply circuitry configured to provide an output current based on a switching control signal;

switching control circuitry configured to generate the switching control signal based on a control amplifier output signal;

a first control amplifier configured to receive the envelope power converter control signal and provide the control amplifier output signal in the first mode of operation; and

a second control amplifier configured to receive the envelope power converter control signal and provide the control amplifier output signal in the second mode of operation.

5. The circuitry of claim 4 wherein the second control amplifier is configured to operate at a lower supply voltage than the first control amplifier.

6. The circuitry of claim 5 wherein the envelope power converter circuitry further comprises:

a holding inductor coupled between an output of the switching power supply circuitry and an output of the envelope power converter circuitry; and

a smoothing capacitor coupled between an output of the envelope power converter circuitry and ground.

7. The circuitry of claim 1 wherein the envelope power converter circuitry comprises:

a first control amplifier configured to receive the envelope power converter control signal and provide a first control amplifier output signal that determines a magnitude of the envelope power supply signal in the first mode of operation; and

a second control amplifier configured to receive the envelope power converter control signal and provide a second control amplifier output signal that determines the magnitude of the envelope power supply signal in the second mode of operation.

8. The circuitry of claim 7 wherein the second control amplifier is configured to operate at a lower supply voltage than the first control amplifier.

9. The circuitry of claim 8 wherein the envelope power converter circuitry further comprises:

a holding inductor coupled between an output of the switching power supply circuitry and an output of the envelope power converter circuitry; and

a smoothing capacitor coupled between an output of the envelope power converter circuitry and ground.

10. A radio frequency (RF) transmitter comprising:

modulator circuitry configured to receive a baseband signal and provide an RF input signal;

an amplifier configured to receive and amplify the RF input signal using an envelope power supply signal to provide an RF output signal;

front end circuitry configured to receive the RF output signal and provide the RF output signal to an antenna for transmission;

envelope power converter circuitry configured to receive an envelope power converter control signal and a supply voltage and provide the envelope power supply signal; and

envelope tracking circuitry configured to provide the envelope power converter control signal to the envelope power supply circuitry, wherein:

in a first mode of operation in which a modulation bandwidth of the RF input signal is below a modulation bandwidth threshold, the envelope power converter control signal is provided such that the envelope power supply signal causes a gain of the amplifier to remain substantially constant over a range of input power provided to the amplifier; and

in a second mode of operation in which the modulation bandwidth of the RF input signal is above the modulation bandwidth threshold, the envelope power converter control signal is provided such that:

the envelope power supply signal remains substantially constant for values within the range of input power below a predetermined threshold; and

the envelope power supply signal causes the gain of the amplifier to remain substantially constant for values within the range of input power above the predetermined threshold.

11. The RF transmitter of claim 10 wherein the envelope power supply circuitry is configured to operate in the second mode of operation during non-contiguous carrier aggregation.

12. The RF transmitter of claim 10 wherein the envelope tracking circuitry comprises a gain-shaping look-up table configured to receive an envelope tracking signal and provide the envelope power converter control signal.

13. The RF transmitter of claim 12 wherein the envelope tracking circuitry further comprises envelope detection circuitry configured to detect an envelope of an input signal provided to the amplifier to provide the envelope tracking signal.

14. The RF transmitter of claim 12 wherein the envelope power converter circuitry comprises:

switching power supply circuitry configured to provide an output current based on a switching control signal;

switching control circuitry configured to generate the switching control signal based on a control amplifier output signal;

a first control amplifier configured to receive the envelope power converter control signal and provide the control amplifier output signal in the first mode of operation; and

a second control amplifier configured to receive the envelope power converter control signal and provide the control amplifier output signal in the second mode of operation.

15. The RF transmitter of claim 14 wherein the second control amplifier is configured to operate at a lower supply voltage than the first control amplifier.

16. The RF transmitter of claim 15 wherein the envelope power converter circuitry further comprises:

a holding inductor coupled between an output of the switching power supply circuitry and an output of the envelope power converter circuitry; and

a smoothing capacitor coupled between an output of the envelope power converter circuitry and ground.

17. The RF transmitter of claim 10 wherein the envelope power converter circuitry comprises:

a first control amplifier configured to receive the envelope power converter control signal and provide a first control output current that determines a magnitude of the envelope power supply signal in the first mode of operation; and

a second control amplifier configured to receive the envelope power converter control signal and provide a second control output current that determines the magnitude of the envelope power supply signal in the second mode of operation.

18. The RF transmitter of claim 17 wherein the second control amplifier is configured to operate at a lower supply voltage than the first control amplifier.

19. The RF transmitter of claim 18 wherein the envelope power converter circuitry further comprises:

a holding inductor coupled between an output of the switching power supply circuitry and an output of the envelope power converter circuitry; and

a smoothing capacitor coupled between an output of the envelope power converter circuitry and ground.

20. A method comprising:

in a first mode of operation of envelope power supply circuitry in which a modulation bandwidth of an RF input signal to an amplifier is below a modulation bandwidth threshold, providing an envelope power supply signal to the amplifier such that a gain of the amplifier remains substantially constant over a range of input power to the amplifier; and

in a second mode of operation of the envelope power supply circuitry in which the modulation bandwidth of the RF input signal provided to the amplifier is above the modulation bandwidth threshold, providing the envelope power supply signal to the amplifier such that:

for values within the range of input power below a predetermined threshold, the envelope power supply signal remains substantially constant; and

for values within the range of input power above the predetermined threshold, the gain of the amplifier remains substantially constant.