Apparatus and methods for envelope tracking calibration

A non-transitory computer-readable storage medium comprising instructions that when executed by a processor perform a method of calibrating an envelope tracking system, the method comprising:

• generating a supply voltage for a power amplifier using an envelope tracker, the envelope tracker having an envelope shaping table including shaping data generated at a desired gain compression of the power amplifier relating a plurality of scaled envelope signal amplitudes to a plurality of supply voltage levels;
• operating the supply voltage of the power amplifier at a first voltage level, the first voltage level associated with substantially no gain compression of the power amplifier;
• measuring an output power of the power amplifier at the first voltage level;
• decreasing a voltage level of the supply voltage one or more times and measuring the output power at each voltage level;
• determining a gain compression at each of the decreased voltage levels;
• determining a second voltage level of the supply voltage of the power amplifier corresponding to one of the decreased voltage levels that is associated with the determined gain compression equal to about that of the desired gain compression;
• retrieving the scaled envelope signal amplitude associated with the second voltage level from the envelope shaping table;
• and
• calibrating the envelope tracker based on the retrieved scaled envelope signal amplitude to correct for an envelope amplitude misalignment of the envelope tracker.

A power amplifier system comprising:

• a power amplifier;
• an envelope tracker configured to generate a supply voltage for the power amplifier, the envelope tracker including a shaping module having an envelope shaping table including shaping data generated at a desired gain compression of the power amplifier relating a plurality of scaled envelope signal amplitudes to a plurality of supply voltage levels, the envelope tracker further including a scaling module configured to scale an amplitude of an envelope signal and to provide the scaled envelope signal amplitude to the shaping module;
• a directional coupler electrically connected to an output of the power amplifier;
• a power detector electrically connected to the directional coupler and configured to measure the output power of the power amplifier using the directional coupler;
• and
• a calibration module configured to provide calibration data to the scaling module so as to change the scaled envelope signal amplitude generated by the scaling module, the calibration module configured to set the calibration data to a first value corresponding to a voltage level of the supply voltage associated with substantially no gain compression, and to reduce the voltage level of the supply voltage by changing the calibration data until the power detector indicates that the gain compression of the power amplifier is equal to about the desired gain compression to provide a reduced voltage level, the scaled envelope signal amplitude associated with the reduced voltage level in the envelope shaping table is used to calibrate the envelope tracker to correct for an envelope amplitude misalignment of the envelope tracker.