Spread-Spectrum Modulation

By flattening the wideband spectral components using Maxim's patented spread-spectrum modulation* technology, EMI emissions that may be radiated by the speaker and cables are reduced. Note the lower peaks and wider spectral components in Figure 1 as compared to the peaks and spectral components of the conventional PWM Class D architecture shown in Figure 2.
The dramatic decrease in energy at the fundamental frequency and its harmonics is achieved by dithering the Class D switching frequency to spread its energy across a wider spectrum. Application Note 3881 (Spread-Spectrum-Modulation Mode Minimizes Electronmagnetic Interference in Class D Amps) provides a detailed discussion of this technique.
*U.S. Patent #6,847,257