Apparatus and method for calibrating an envelope tracking lookup table

An envelope tracking (ET) power amplifier apparatus comprising:

• a power amplifier configured to amplify a radio frequency (RF) signal from a time-variant input power to a time-variant output power linearly related to the time-variant input power based on a time-variant ET voltage tracking the time-variant input power;
• and
• a power management integrated circuit (PMIC) comprising:
• a target voltage circuit configured to generate a time-variant ET target voltage based on an ET lookup table (LUT) that correlates the time-variant input power with the time-variant ET target voltage;
• an ET voltage circuit configured to generate the time-variant ET voltage based on the time-variant ET target voltage;
• and
• a calibration circuit configured to:
• receive a time-variant output power feedback nonlinearly related to the time-variant input power;
• determine a linear relationship between the time-variant input power and the time-variant output power based on the time-variant output power feedback;
• and
• calibrate the ET LUT based on the determined linear relationship.