Randomized Carrier PWM With Exponential Frequency Mapping

Abstract

Pulsewidth modulation (PWM) and sigma-delta modulation (SDM) have been used in several high linearity, high accuracy power delivery applications such as dc-dc power converters, audio, and radio frequency power amplifiers and data converters. While PWM can generate high linearity signals with high efficiency, it suffers from discrete tonal output spectrums. SDM, on the other hand, can generate high linearity output spectrums with shaped quantization noise spectrums and lower efficiencies due to oversampling requirements. In this paper we present a particular class of carrier frequency modulated PWM (CFMPWM), which spreads the tonal content of regular PWM uniformly in frequency and reduces the baseband noise with respect to SDM by up to 15 dB. The new modulation scheme preserves the high efficiency properties of PWM. An approximate method to estimate the spectrum of CFMPWM signals with both deterministic and random modulation is also presented. Simulation results and experimental data are reported to analyze the spectral spreading properties of the proposed CFMPWM scheme