Emission reduction in Class D audio amplifiers by optimizing spread spectrum modulation

Due to their high efficiency compared to conventional Class AB amplifiers, Class D audio amplifiers have increasingly become the amplifier of choice especially for low power applications such as portable electronics. However, Class D amplifiers are still a major source of electromagnetic emission of the electronic applications in which they are used. In this paper the benefits of using spread spectrum techniques in order to reduce the emission of Class D audio amplifiers is highlighted. Based on IC-level measurement results of a 10W Mono Class D speaker amplifier, that allows to be synchronized to an external clock, it is shown how spread spectrum parameters like deviation, modulation frequency and modulation signal can be optimized in order to maximize the reduction of the emission.