87C196KC-Based Digital Signal Distortion Meter

In the design and application of electronic engineering, both in open circuit and in closed circuit, signal is certainly affected by environment, the status of the transport network and the change of the parameters of the components applied. Then the characters of useful information will be changed more or less and the change is generally called as distortion, namely so-called signal distortion. Signal distortion includes three kinds of distortion: frequency, phase and waveform. The waveform distortion is caused by the nonlinearity of the amplifier circuit, so it is often called as nonlinear distortion.We can test the character of the transport network by detecting the nonlinear distortion and this is useful to improve the character of the network. In the generation, transport and reception of signal, we must carefully analyze and handle distortion. Kinds of nonlinear distortion meters have been widely used in many fields such as electronics, electricity and communication, and so on.Now, we can use two methods to detect the signal distortion: harmonic analysis method and the suppressed first harmonic method.The error of distortion which harmonic distortion meter detects can be least controlled 1‰. The lowest frequency which harmonic distortion meter can detect is 0.0001Hz. But, generally, this kind of meter is so costly and difficult to operate that the major portion of the distortion meters applies the method of suppressed fundamental harmonic.Most of analog distortion meters apply the method of suppressed first frequency. The lowest frequency that these meters can detect is 2Hz. It's obvious that its error is large when the distortion is large.As the development and application of microcomputer and single-chip microcomputer, the cost of harmonic distortion meter decreases rapidly. In practical project, we can have real-time processing by microcomputer to analyze the spectrum of the detected signal's harmonics.According to the theory of digital signal processing, discrete Fourier transform has selectivity to frequency just as spectrum analyzer. But the computing amount of DFT is so large that its practical use is restricted, especially real-time processing. In fact, we use Fast Fourier Transform (FFT) in practical engineering.Processing signal with single-chip microcomputer has great flexibility and highaccuracy. We can use software to take the place of hardware partly and this is useful to realize miniaturization and decrease the cost.The paper discusses digital signal distortion meter with the technology and method of digital signal processing. When the meter detects a signal, it digitizes the signal by analog-digital converter and completes the FFT of the signal. Then the single-chip microcomputer calculates the amplitudes of the signal's harmonics, calculates and displays the signal distortion degree.In this paper, the introduction part introduces detection principle and classification of kinds of distortion meters and introduces the design of digital distortion meter. The second chapter recommends spectrum analysis with FFT. The third chapter recommends the global scheme. The fourth chapter discusses the error of signal distortion detecting. The fifth chapter summarizes this paper...