Truly Aliasing-Free Digital RF-PWM Power Coding Scheme for Switched-Mode Power Amplifiers

This paper presents a novel method for multilevel power coding and upconversion to RF frequency, by the means of a digital radio-frequency pulse width modulation (RF-PWM). Delta-sigma modulation and memoryless predistortion are used to cancel spectral aliasing effects, inherent to digital RFPWM operation, and achieve high linearity of the transmitter. In this method, time-domain characterization of a multilevel digital RF-PWM was fully exploited in order to provide optimal parameter selection for the Delta-sigma modulation, which in turn enables aliasingfree digital RF-PWM that runs at reasonable clock speeds. Experiments with an arbitrary waveform generator are used to demonstrate effectiveness of the proposed novel power encoding scheme. The novel algorithm offers in-band SNR of -45dB, while maintaining coding efficiency of about 55%, for a 20MHzbandwidth 64QAM signal, while mere RF-PWM, running at the same clock speed, can achieve SNR of only -10dB.