A True Digital Feedforward Active Noise Control System with no Analog-to-Digital and Digital-to-Analog Converters

An active noise control (ANC) system emits sound waves to attenuate noise. With constraints on cost and size, the ANC system often outperforms passive noise control (PNC) measures when the noise frequency is low. Electro-acoustic devices, such as microphones and loudspeakers, are conventionally used in ANC systems. They convert sound pressure with different voltages. The analog-to-digital and digital-to-analog converters have to be connected to the digital controller in the ANC system with electro-acoustic devices. With the development of digital acoustic devices, sound pressure can be converted straightforwardly into and from the digital signal in the format of pulse density modulation (PDM), which is also known as the 1-bit quantized signal. Incorporating with the digital acoustic devices, this paper proposes a true digital ANC system design that has no analog-to-digital (AD) and digital-to-analog (DA) converters. Specifically, the feedforward filtered reference least mean square (LMS) algorithm with online secondary path modeling is implemented in a newly proposed systolic structure on the FPGA, where the digital acoustic devices are connected directly to the FPGA I/O pins.