Method and apparatus for calibrating an envelope tracking system

1. A method of calibrating an envelope tracking system for a supply voltage for a power amplifier module within a radio frequency (RF) transmitter module of a wireless communication unit; the method comprising, within at least one signal processing module of the wireless communication unit:

determining combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

obtaining battery current indications for the determined combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

selecting a combination of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power based at least partly on the obtained battery current indications therefore; and

calibrating the envelope tracking system using the selected combination of the power amplifier supply voltage and power amplifier input power.

2. The method of claim 1 , wherein the method comprises:

selecting a combination of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power comprising a lowest battery current therefore; and

calibrating the envelope tracking system using the selected combination of the power amplifier supply voltage and power amplifier input power.

3. The method of claim 1 , wherein the method comprises determining combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power within a tolerance range of the target output power.

4. The method of claim 1 , wherein the determining combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power comprises:

applying a continuous wave RF signal to an input of the power amplifier module;

varying at least one of the power amplifier supply voltage and power amplifier input power; and

monitoring at least an indication of the output power of the power amplifier to determine combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power.

5. The method of claim 4 , wherein the method comprises:

applying a continuous wave RF signal to an input of the power amplifier module;

sweeping at least one of the power amplifier supply voltage and power amplifier input power; and

monitoring at least an indication of the output power of the power amplifier to determine combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power.

6. The method of claim 1 , wherein determining combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power comprises:

apply a varying envelope RF signal to an input of the power amplifier module;

iteratively modifying an RF signal envelope to amplifier supply voltage mapping such that instantaneous power amplifier output power equals the target output power.

7. The method of claim 1 , wherein the method comprises, for each target output power level of interest:

determining combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to the target output power;

obtaining battery current indications for the determined combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

selecting a combination of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power based at least partly on the obtained battery current indications therefore; and

calibrating the envelope tracking system using the selected combination of the power amplifier supply voltage and power amplifier input power.

8. The method of claim 1 , wherein method comprises measuring at least one battery current of the wireless communication unit to obtain the battery current indications for the determined combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power.

9. The method of claim 8 , wherein the method comprises measuring at least one battery current for at least one of:

the power amplifier module;

a power amplifier supply voltage modulator; and

RF transmitter/modulation circuitry.

10. The method of claim 1 , wherein the method comprises:

determining combinations of the power amplifier supply voltage and power amplifier input envelope that provide a power amplifier output envelope equal to a target output envelope;

obtaining battery current indications for the determined combinations of the power amplifier supply voltage and power amplifier input power envelope that provide a power amplifier output envelope equal to a target output envelope;

selecting a combination of the power amplifier supply voltage and power amplifier input envelope that provide a power amplifier output envelope equal to a target output envelope based at least partly on the obtained battery current indications therefore; and

calibrating the envelope tracking system using the selected combination of the power amplifier supply voltage and power amplifier input envelope.

11. A non-transitory computer program product comprising executable program code for calibrating an envelope tracking system for a supply voltage for a power amplifier module within a radio frequency (RF) transmitter module of a wireless communication unit, the executable program code operable for, when executed at a communication unit, performing the method of claim 1 .

12. A communication unit comprising:

a radio frequency (RF) transmitter module comprising an envelope tracking system for a supply voltage for a power amplifier module within the RF transmitter module; and

at least one signal processing module for calibrating the envelope tracking system and arranged to:

determine combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

obtain battery current indications for the determined combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

select a combination of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power based at least partly on the obtained battery current indications therefore; and

calibrate the envelope tracking system using the selected combination of the power amplifier supply voltage and power amplifier input power.

13. An integrated circuit for a communication unit comprising a radio frequency (RF) transmitter module comprising an envelope tracking system for a supply voltage for a power amplifier module within the RF transmitter module; wherein the integrated circuit comprises:

at least one signal processing module for calibrating the envelope tracking system and arranged to:

determine combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

obtain battery current indications for the determined combinations of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power;

select a combination of the power amplifier supply voltage and power amplifier input power that provide a power amplifier output power equal to a target output power based at least partly on the obtained battery current indications therefore; and

calibrate the envelope tracking system using the selected combination of the power amplifier supply voltage and power amplifier input power.

14. A method of modulating a supply voltage for a power amplifier module within a radio frequency (RF) transmitter module of a wireless communication unit; the method comprising, within at least one signal processing module of the wireless communication unit:

receiving user data to be transmitted by the transmitter module of the wireless communication unit;

determining an output power waveform;

generating a power amplifier supply voltage waveform signal and a power amplifier input power waveform signal from combinations of power amplifier supply voltage and power amplifier input power calibrated in accordance with the method of claim 1 for individual points within the output power waveform;

applying the power amplifier supply voltage waveform signal to a voltage supply modulator for the power amplifier module; and

generating an input signal for the RF transmitter module to achieve the power amplifier input power waveform signal.

15. The method of claim 14 , wherein the method further comprises applying pre-distortion in the phase domain to the input signal for the RF transmitter module.

16. A non-transitory computer program product comprising executable program code for modulating a supply voltage for a power amplifier module within a radio frequency (RF) transmitter module of a wireless communication unit, the executable program code operable for, when executed at a communication unit, performing the method of claim 14 .

17. A communication unit comprising:

a radio frequency (RF) transmitter module comprising an envelope tracking system; the envelope tracking system comprising at least one signal processing module arranged to:

receive user data to be transmitted by the transmitter module of the wireless communication unit;

determine an output power waveform;

generate a power amplifier supply voltage waveform signal and a power amplifier input power waveform signal from combinations of power amplifier supply voltage and power amplifier input power calibrated in accordance with the method of claim 1 for individual points within the output power waveform;

apply the power amplifier supply voltage waveform signal to a voltage supply modulator for the power amplifier module; and

generate an input signal for the RF transmitter module to achieve the power amplifier input power waveform signal.

18. An integrated circuit for a communication unit comprising a radio frequency (RF) transmitter module comprising an envelope tracking system; the envelope tracking system comprising at least one signal processing module arranged to:

receive user data to be transmitted by the transmitter module of the wireless communication unit;

determine an output power waveform;

generate a power amplifier supply voltage waveform signal and a power amplifier input power waveform signal from combinations of power amplifier supply voltage and power amplifier input power calibrated in accordance with the method of claim 1 for individual points within the output power waveform;

apply the power amplifier supply voltage waveform signal to a voltage supply modulator for the power amplifier module; and

generate an input signal for the RF transmitter module to achieve the power amplifier input power waveform signal.