A Distortion Suppression Technique for a Digital Class D Audio Power Amplifier with Pulse Density Modulation

A novel distortion suppression technique suitable for digital class D audio power amplifiers using pulse density modulation (DSM) is presented. Unlike traditional analog techniques, the proposed feedback scheme can also tolerate long latency. The distortion suppression circuit generates a digital measurement of the output stage error, and feeds it back to the DSM for noise shaping. A calibration technique of the error circuitry and mismatch between the complementary outputs at the H-bridge output stage is also presented. Experimental verification via a printed circuit board (PCB) prototype shows 10 dB reduction in THD at -8 dB (relative to full scale input), with a latency of 24 clock cycles for a DSM clock of 12.5 MHz.