Apple Inc.
Supply modulator for polar power amplifier

Abstract:

A supply modulator for a polar power amplifier and method for operating the same are disclosed. An apparatus includes an amplifier having an input for receiving a phase modulated (PM) signal. A modulator is arranged to receive an amplitude modulated (AM) signal and provide a supply voltage to the amplifier, the supply voltage varying based on the AM signal. A detector circuit may detect the supply voltage exceeding a first threshold or falling below a second threshold. The detector circuit includes a current source arranged to provide a bias current to the modulator. When the supply voltage exceeds the first threshold, the detector causes an increase in the bias current provided to the modulator. Similarly, when the supply voltage falls below a second threshold, the detector causes an increase of the bias current supplied to the modulator.