The present disclosure relates to using windowing to reduce the bandwidth of an amplitude modulation (AM) power supply input signal (PSIS), which is fed to an AM power supply to provide envelope power to an RF power amplifier stage via an AM power supply output signal. By reducing the bandwidth, noise levels from the AM power supply may be reduced. However, although the bandwidth of the AM PSIS is reduced, the AM power supply output signal may track the AM of the RF power amplifier stage closely enough to meet linearity requirements and to provide high efficiency. The windowing may be based on dividing a stream of AM input samples into a stream of input windows, from which a stream of output windows is created to provide a stream of windowed AM input samples that are used to provide a windowed AM PSIS to the AM power supply.