The present disclosure relates to RF circuitry having delay locked loop (DLL) circuitry that may be used to measure amplitude modulation-to-phase modulation (AMPM) distortion of an RF power amplifier during factory calibration or during real time operation of the RF circuitry. During a calibration mode, the DLL circuitry may be calibrated using a reference clock signal. During a phase measurement mode, the DLL circuitry may use the reference clock signal, which is representative of an RF input signal to the RF power amplifier, and a feedback signal, which is representative of an RF output signal from the RF power amplifier, to measure a phase difference between the RF input signal and the RF output signal. By measuring the phase difference at different amplitudes of the RF output signal, the AMPM distortion of the RF power amplifier may be determined and used to correct for the AMPM distortion.