Implementation of THD-reduction stereo audio amplifier using compensators and sigma-delta modulators

This paper presents an integrated stereo audio amplifier that employs sigma-delta (ΣΔ) modulation techniques with compensators. Traditional closed-loop audio amplifiers adopt pulse-width modulation or ΣΔ modulation techniques. The design method proposed in this study uses a negative feedback closed-loop system with compensator and ΣΔ modulator. This combination of compensator and ΣΔ modulator significantly reduces the noise and total harmonic distortion (THD) compared with a traditional closed-loop system. The proposed negative feedback loop can automatically compensate for external perturbations, improving the precision of the eventual output. The compensator increases the audio-frequency loop gain, and leads to better rejection of audio-frequency disturbances. At a sample rate of 10 MHz, the proposed audio amplifier achieves 0.04% THD and a signal to noise ratio of 87 dB with efficiency above 92%. The proposed audio amplifier was implemented in a TSMC 3.3 V 0.35 μm 2P4M CMOS process.