This paper presents a novel spread spectrum (SS) method with a pseudo-natural sampling technique for filterless digital class-D audio amplifiers. This method is proposed to reduce the electromagnetic interference (EMI) emissions of amplifiers by lowering the output out-of-band spectral amplitudes around the pulse width modulator carrier frequency and its multiples. The main idea of this method is that the sampling frequency of the modulating signal and the carrier frequency are varied synchronously and randomly among three different values. Since the carrier frequency is variable, the polynomial interpolation Newton–Raphson (PI-NR) algorithm is modified to correct the harmonic distortion caused by uniform-sampling pulse width modulation (UPWM). Based on a field programmable gate array (FPGA), an experimental system is established to analyze the performances of the proposed method and other six reported SS methods. Experimental results show that the proposed method features the lowest total harmonic distortion (THD) of 0.009% with a 6.6 kHz, 0 dBFS (full scale) input, a relatively high signal-to-noise ratio (SNR) of 52.68 dB and a relatively high output out-of-band peak spectral amplitude reduction of 17.75 dB.

中文翻译：

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无滤波器数字D类音频放大器的三频伪随机变扩频方法

本文提出了一种新的扩频 (SS) 方法，它采用伪自然采样技术，用于无滤波器数字 D 类音频放大器。该方法旨在通过降低脉宽调制器载波频率及其倍数附近的输出带外频谱幅度来减少放大器的电磁干扰 (EMI) 发射。这种方法的主要思想是调制信号的采样频率和载波频率在三个不同的值之间同步随机变化。由于载波频率是可变的，因此修改了多项式插值牛顿-拉夫森 (PI-NR) 算法以校正均匀采样脉宽调制 (UPWM) 引起的谐波失真。基于现场可编程门阵列（FPGA），建立了一个实验系统来分析所提出的方法和其他六种报告的 SS 方法的性能。实验结果表明，所提出的方法具有 0.009% 的最低总谐波失真 (THD)，6.6 kHz、0 dBFS（满量程）输入、52.68 dB 的相对较高的信噪比 (SNR) 和相对高输出带外峰值频谱幅度降低 17.75 dB。