An RF communications system, which includes an RF power amplifier, an envelope tracking power supply, and supply control circuitry, is disclosed. The RF communications system operates in one of a normal operation mode and a calibration mode. During the calibration mode, the RF power amplifier receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which is provided by the envelope tracking power supply. Further, the supply control circuitry controls the envelope tracking power supply to cause a sharp transition of the envelope power supply signal when a setpoint of the envelope power supply signal transitions through a setpoint threshold of the envelope power supply signal.