负反馈和状态空间重构的UPWM失真问题校正方法

针对数字D类音频功率放大器中的均匀采样脉冲宽度调制(Uniform-Sampling Pulse Width Modulation,UPWM)失真,提出了一种负反馈和状态空间重构的全数字UPWM失真问题校正方法。该方法利用数字Σ-Δ(Sigma-Delta)调制器的高开环增益特性,通过构造包含数字Σ-Δ调制器和UPWM发生器的闭环负反馈环路,使得环路的输入与输出近似呈线性关系,从而校正UPWM产生的失真。在构造闭环时,通过对数字Σ-Δ调制器的状态空间表达式进行重构,并添加插零值模块和抽取模块使该环路在保持稳定性的同时,拥有与原数字Σ-Δ调制器相同的噪声整形效果。实验结果表明,该方法相比其他的UPWM失真校正方法,不仅能降低谐波失真,还能大幅降低数字UPWM调制器输出信号的本底噪声,从而可使数字UPWM调制器在频率6 kHz和幅度为满量程的-5 dB的正弦数字信号输入情况下,输出信噪失真比达到95.26 dB,同时所提方法可全数字电路实现、硬件实现简单且易于移植。

UPWM distortion correction method based on negative feedback and state-space reconstruction

Aiming at the distortion problem of uniform-sampling pulse width modulation(UPWM) in digital class-D audio power amplifiers, an all-digital uniform-sampling pulse width modulation(UPWM) distortion correction method based on negative feedback and state-space reconstruction is proposed. This method utilizes the high open-loop gain characteristic of the digital Σ-Δ(Sigma-Delta) modulator and constructs a closed-loop negative feedback loop including the digital Σ-Δ modulator and the UPWM generator to make the relationship between the input and the output of the loop approximately linear, thereby the distortion caused by UPWM is corrected. When constructing the closed-loop,the state-space expression of the digital Σ-Δ modulator is reconstructed, and the interpolation block and the decimation block are added to make the loop have the same noise shaping effect as the original digital Σ-Δ modulator while maintaining stability. Experimental results show that compared with other UPWM distortion correction methods, the proposed method can not only reduce harmonic distortion, but also greatly reduce the background noise in the output signal of the digital UPWM modulator. Therefore, the digital UPWM modulator with the proposed method achieves an output signal to noise and distortion ratio(SNDR) of 95.26 dB in the case of sinusoidal digital signal input at the frequency of 6 kHz and the amplitude of-5 dB of the full scale(FS). The proposed method can be implemented by all digital circuits with features of simple hardware implementation and portability.