Dual-band PWM audio coding for ultrasound artefact reduction

Abstract

Abstract-A novel approach to PWM coding is introduced based on generating two complementary PWM streams out of the in-band signal's spectrum. The 2 streams are then recombined in a suitable way, so that out-of-phase cancellation of the carrier frequency harmonics is achieved. The approach suppresses the strong out-of-band frequencies of the carrier signal without introducing distortion of the in-band coded signal. Such method can achieve superior reduction compared to the out-of-band artefact suppression induced by traditional analog low-pass filters employed in typical Class-D audio amplifiers or other switching power delivery systems, hence allowing designs with reduced filter requirements or even filterless implementations.

Projeto de circuito de bobina de Tesla com filtro de áudio FIR / Tesla coil circuit Project with FIR audio filter

“…A good way to filter an audio signal is through a finite response filter in time, FIR, because an audio signal is a discrete signal with a high sampling frequency, Fs. In addition, FIR filters do not use feedback and have a linear phase, because it truncates their response to the impulse in a window [24].…”

“…For this project, a low-pass FIR filter with windowing was chosen as it is one of the simplest to be applied to audio signals [21,24].…”