Extension of Pulsewidth Modulation From Carrier-Based to Dither-Based

The carrier-based pulsewidth modulation (PWM) is extended to a dither-based PWM by replacing a conventional triangular carrier with a binary dither signal. Such a simple extension is generally impractical due to serious performance degradation. However, this paper presents a novel binary dither generator that helps enhance the performance of the dither-based PWM and makes the idea possible. The binary dither is generated as determined by the sign of the filtered modulation noise. The dither generated in this way automatically eliminates low-frequency modulation noise and randomizes the switching frequency. As indicated by experiments, the resulting dither-based PWM has relatively lower THD+N and less pronounced high-frequency switching harmonics, as compared with the conventional fixed-frequency triangular carrier PWM.