A method (200) and circuit (100) for substantially maintaining an amplified constant envelope modulation signal at a constant pre-defined amplitude. The circuit (100) comprises a constant envelope modulation providing circuitry (104), a power amplifier (102), a power amplifier driver (106), a coupler (108) and a feedback circuit (110). In operation the sensor (110) has an output (120) that provides a radio frequency output signal proportional to an amplitude of an amplified constant envelope modulated radio frequency signal provided to the amplifier input (118) from the power amplifier driver (106). The feedback circuit (110) provides a gain control voltage a driver gain control input to maintain the constant envelope modulation signal at a constant pre-defined amplitude supplied to the amplifier input (118).