A power amplifier system (100; 400; 600) comprising: a supply modulator circuit having a reference voltage input, a valley level input, and a supply output to output a supply voltage; a power amplifier circuit coupled with the supply output of the supply modulator circuit to receive the supply voltage, and having a signal input and a signal output (130a; 130b), and configured to apply a gain to the signal input according to the supply voltage, such that the signal output (130a; 130b) has a common mode offset corresponding to the supply voltage; and a valley detector circuit having a detection input (141a; 141b) coupled with the signal output (130a; 130b) of the power amplifier circuit, and having a detection output coupled with the valley level input of the supply modulator circuit, and configured to generate the detection output as a function of the detection input (141a; 141b), such that the detection output substantially tracks a valley level of an amplitude envelope of the signal output (130a; 130b) of the power amplifier circuit, wherein the supply modulator circuit is configured to regulate the supply voltage as a function of the valley level and a fixed reference voltage level, such that the supply voltage dynamically tracks the amplitude envelope of the signal output (130a; 130b); and a gating circuit coupled with the valley detector circuit and having a gated detection output generated, such that the gated detection output corresponds to the detection output when the supply voltage is above a predetermined minimum supply voltage level, and the gated detection output causes the supply modulator circuit to maintain the supply voltage at a level corresponding to the predetermined minimum supply voltage level otherwise. a supply modulator circuit having a reference voltage input, a valley level input, and a supply output to output a supply voltage; a power amplifier circuit coupled with the supply output of the supply modulator circuit to receive the supply voltage, and having a signal input and a signal output (130a; 130b), and configured to apply a gain to the signal input according to the supply voltage, such that the signal output (130a; 130b) has a common mode offset corresponding to the supply voltage; and a valley detector circuit having a detection input (141a; 141b) coupled with the signal output (130a; 130b) of the power amplifier circuit, and having a detection output coupled with the valley level input of the supply modulator circuit, and configured to generate the detection output as a function of the detection input (141a; 141b), such that the detection output substantially tracks a valley level of an amplitude envelope of the signal output (130a; 130b) of the power amplifier circuit, wherein the supply modulator circuit is configured to regulate the supply voltage as a function of the valley level and a fixed reference voltage level, such that the supply voltage dynamically tracks the amplitude envelope of the signal output (130a; 130b); and a gating circuit coupled with the valley detector circuit and having a gated detection output generated, such that the gated detection output corresponds to the detection output when the supply voltage is above a predetermined minimum supply voltage level, and the gated detection output causes the supply modulator circuit to maintain the supply voltage at a level corresponding to the predetermined minimum supply voltage level otherwise.