A 20W/channel Class-D amplifier with significantly reduced common-mode radiated emissions

Due to their rail-to-rail switching nature, Class-D audio amplifiers are prone to generating electromagnetic interference (EMI) that is in excess of what is acceptable in many systems. Such systems typically require devices to limit their EMI to an accepted standard, such as the FCC Class-B standard. In Class-D audio amplifiers that employ Class-BD modulation [1] using a single supply, the common-mode output signal, VCM, has a significant EMI component because this signal also swings rail-to-rail at the amplifier switching frequency, typically in the hundreds of kHz. This phenomenon is illustrated in the upper signals of Fig. 26.4.1.