Nonlinear distortion signal generation and THD measuring device

Abstract

In order to generate nonlinear distortion when the amplifiers work in the nonlinear region, the system uses the transistor amplifiers to combine the analog switch and MCU to realize nonlinear distortion signal generation and THD(Total Harmonic Distortion) measurement device. The system is mainly composed of fixed gain amplifier circuit, multi-type signal selection circuit, class A and B complementary symmetric circuit, analog switch and microcontroller. The input signal is fixed as a 1KHz, 20mVp-p sinusoidal signal. Based on the influence of quiescent operation point on the common emitter amplifier circuit and the characteristics of Type B push-pull circuit, the analog switch is turned on or off by pressing the button of MCU to adjust the static working point and circuit structure to realize output of different types of signals. THD was calculated by sampling ADC inside MCU and FFT processing. The experimental results show that the system can successfully output sinusoidal signals and four kinds of nonlinear distortion signals (top distortion, bottom distortion, bidirectional distortion and cross-over distortion), and the peak-to-peak values are all greater than 2Vp-p. THD measurement error is less than 0.6%, which can achieve a more accurate measurement of total harmonic distortion.