This article describes the designing process of a low-cost class-D audio amplifier with digitized global feedback after the output filter, using a signal microcontroller. Various approaches to the feedback-based distortions elimination of class-D amplifiers are discussed. Hardware architecture of the author’s designed class-D amplifier with digital audio input interface, output voltage feedback path relays on SAR-ADC, and output power stage in multiphase bridge tide load configuration is shown. The selection method of the output low-pass filter parameters and power stage phase count was explained. A model of class-D amplifier with PID digital compensator and control loop interfaces is presented. Efficient high-speed digital PID compensator implementation on fixed-point 16-bit DSP core is exhibited. Procedure for control loop gain and phase plots measurements and self-tuning of PID feeding under damped second-order plants is presented along with simulations of loop properties influences on tuning effects. The results of the prototype device measurements such as Bode plots or output voltage frequency spectrum are presented. A big effort has been put on a useful, complete and transparent description for the development process of the presented class-D amplifier arrangement. The described class-D amplifier is the first solution with single feedback control from the output of LC filter based on a microcontroller with embedded ADC and PWM hardware with ensuring full audio bandwidth reproduction width THD distortion level below 0.25% at 1 kHz. The amplifier has been designed with the solicitude of device cost by using low-volume inductors in the output filter and by utilization of the built-in microcontroller ADC and PWM interfaces.

中文翻译：

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具有在数字信号控制器上实现的后置滤波器数字反馈的自调谐 D 类音频放大器

本文介绍了使用信号微控制器在输出滤波器后具有数字化全局反馈的低成本 D 类音频放大器的设计过程。讨论了消除 D 类放大器基于反馈的失真的各种方法。图中显示了作者设计的带有数字音频输入接口的 D 类放大器、SAR-ADC 上的输出电压反馈路径继电器以及多相桥式潮汐负载配置中的输出功率级的硬件架构。阐述了输出低通滤波器参数和功率级相位数的选择方法。提出了一种带有 PID 数字补偿器和控制回路接口的 D 类放大器模型。展示了在定点 16 位 DSP 内核上实现的高效高速数字 PID 补偿器。介绍了控制环路增益和相位图测量以及阻尼二阶设备下 PID 馈电的自调整过程，以及环路特性对调整效果影响的模拟。提供了原型设备测量的结果，例如波特图或输出电压频谱。已投入大量精力对所提出的 D 类放大器装置的开发过程进行有用、完整和透明的描述。所描述的 D 类放大器是第一个从基于带有嵌入式 ADC 和 PWM 硬件的微控制器的 LC 滤波器输出进行单反馈控制的解决方案，可确保全音频带宽再现宽度 THD 失真水平在 1 kHz 时低于 0.25%。