小信号放大电路任意波形THD全自动测量系统研究

总谐波失真THD是衡量信道非线性程度的重要指标，应用于音频小信号放大电路的任意输出波形识别和总谐波失真的全自动测量系统成为检测信号放大性能的有效手段。为准确计算放大后的波形总谐波失真度，采用了快速傅里叶变换FFT技术。从提高系统效率角度，使用高频率采样并半数提取的技术方案。通过动态控制继电器、阻容元件及多级放大等手段，合理调整放大系统静态工作点的位置和输入波形大小，实现不同类型的失真波形输出。基于stm32f103c6单片机，联动开关一键式完成任意波形采集、识别、计算和显示，极大提升了小信号放大电路失真度测量的工作效率。Matlab运算仿真、Multisim电路仿真及实物测试表明，多级晶体管放大一致性调节电路和单片机FFT运算组成的小信号放大电路任意波形THD全自动测量系统，可准确、实时识别波形并计算出总谐波失真，一键式切换设计操作方便、节约成本，颇具实用价值。

An automatic calculation system of arbitrary waveformTHD for small signal amplification circuit

Total Harmonic Distortion (THD) is an important index to measure the nonlinear degree of channel. The automatic measurement device applied in arbitrary output waveform identification and total harmonic distortion of the audio small signal amplification system has become an effective means to detect the signal amplification performance. In order to accurately calculate the total harmonic distortion of the amplified waveform, FFT technique is adopted. In order to improve the system efficiency, high frequency sampling and half extraction techniques are adopted. Dynamic control relays, resistance-capacitance components and multi-stage amplification are used to reasonably adjust the position of the static operating point of the amplification system and the size of the input waveform to realize the output of different types of distorted waveforms. Based on microcontroller stm32f103c6, the combination switch completes the collection, identification, calculation and display of arbitrary waveform in one-button, greatly improving the working efficiency of small signal amplification systems. Matlab algorithm simulation, Multisim circuit simulation and practical test show that, the automatic calculation device of arbitrary waveform THD for small signal amplification systems consisting of multi-stage transistor amplification consistency adjustment circuit and microcontroller FFT operations can accurately and real-time identify waveforms and calculate THD. The one-button switching design is convenient to operate, saves cost, and has practical value.