Filterless Class-D Amplifier With Pseudorandomized Carrier Frequency Modulation for EMI Reduction

This paper presents a filterless Class-D amplifier with pseudorandomized carrier frequency modulation (PRCFM) to mitigate electromagnetic interference (EMI) issue associated with the removal of an off-chip LC filter. The designed filterless Class-D amplifier occupies a total area of 1 mm² and is fabricated in 0.18-μm CMOS process technology. The proposed PRCFM circuit occupies only less than 1% of the IC area. Measurement results have demonstrated the effectiveness of the PRCFM scheme for EMI reduction. The PRCFM scheme consumes very little additional power and therefore does not affect the power efficiency of the amplifier. In addition, the proposed scheme also maintains very good total harmonic distortion over the audio band of interest (100 Hz to 6 kHz) and modulation index range.