A −121.5 dB THD Class-D Audio Amplifier with 49 dB Suppression of LC Filter Nonlinearity and Robust to +/−30% LC Filter Spread

This paper reports a Class-D audio amplifier that uses multiloop feedback to suppress output LC filter nonlinearity by 49 dB, enabling the use of small, low-cost LC filters with ±30% spread while maintaining low distortion. Fabricated in a 180 nm BCD process, the prototype achieves a THD of −121.5 dB and a THD+N of −107.1 dB. It delivers 12W/21W into an 8-Ω/4-Ω load with 91%/87% efficiency.