A Randomized Modulation scheme for filterless digital Class D audio amplifiers

We propose to employ the Randomized Wrapped-Around Pulse Position Modulation scheme (RWAPPM) to mitigate the switching-frequency harmonics at the output signal of filterless digital Class D audio amplifiers. The conventional Pulse Width Modulation schemes (PWMs) typically have a non-zero common-mode voltage that contributes to the radiated Electromagnetic Interference (EMI), and generate high switching-frequency harmonics that dissipate extra power at the speaker and also contribute to the radiated EMI. We simulate and compare the RWAPPM (2-level) against the PWMs and a reported randomized modulation scheme. The 2-level RWAPPM has zero common-mode voltage, and amongst the modulation schemes, it features the highest attenuation of the switching-frequency harmonics, highest out-of-band Spurious Free Dynamic Range (22 dBc), and a relatively high Signal to Noise and Distortion Ratio (57 dB) at the output voltage.