Design and implementation of a fully-digital, high efficiency class-D amplifier system

Recent advances in semiconductor technology have renewed interest in class-D audio amplifiers, especially for portable devices and consumer electronics. The motivating factor driving research in class-D amplifiers is efficiency. In addition, one important benefit that class-D amplifiers bring is the ability to directly couple to a digital audio signal, removing the need to convert to analog first. In this paper, a FPGA based digital audio amplifier has been developed, implemented and tested. The proposed class-D amplifier system can keep the audio signal chain in the digital domain, which prevents transmission noise from distorting the audio signal. In order to achieve the goals of high fidelity and high efficiency, a zero voltage switching (ZVS) modulation strategy is also presented. The experimental system demonstrates that fully digital audio amplification is possible. According to the experimental results, the proposed test system is able to deliver more than 15 W into a 4 Ω load with an efficiency of 80% and total harmonic distortion less than 2%.