Digital multilevel audio power amplifier with a MASH sigma-delta modulator to reduce harmonic distortion

This paper presents a digital multi-level audio power amplifier with a MASH sigma-delta modulator, to eliminate narrow pulses, generated by conventional PWM modulators, but distorted by the non-ideal switching times of the power switches and by the non-linearity of the PCM-PWM conversion. To overcome these problems, usually a pre-distortion compensator along with over-sampling and high-order sigma-delta modulator with two-level PWM output is often proposed. However, high-order sigma-delta modulators present stability problems and narrow pulses are not completely eliminated. This work proposes the use of MASH structures with power multi-level inverters to solve the problem of stability and narrow pulse elimination. The proposed technique points a solution to overcome those stability problems without compromising the achieved reduction in the harmonic distortion. The effectiveness of the proposed system is established by simulation results.