Pulse-density modulation for RF applications: The radio-frequency power amplifier (RF PA) as a power converter

Switching processes such as pulse-width and pulse-density modulation have been used for many years in power electronics applications. Due to rapid scaling of semiconductor technology, similar approaches may be successfully applied to blocks in the radio architecture. This work outlines the implementation of a class-D power amplifier for RF applications in low-GHz frequency bands. We describe the motivation for using pulse-density modulation (PDM) to achieve linear amplitude modulation of a nominally nonlinear switching power amplifier. The amplifier achieves linearity suitable for wideband wireless standards, with peak efficiency of 43.5% at 1.95 GHz and up to 20 dBm output power. The system generates amplitude-modulated waveforms with up to 20 MHz envelope bandwidth, demonstrating the validity of this approach for modern communication standards.