The Study And Implementation Of Spectrum Analysis Of Digital Storage Oscilloscope

Digital oscilloscope takes an extremely important place in testing and measuring of the field of engineering research as a widely used apparatus.The digital oscilloscope is mainly used for the time-domain measurement of signals,its essence is to digitize the analog signals to digital signals which will be analyzed and displayed.And with the increasing complexity of modern information systems,signal's components are becoming more and more diversified.Digital oscilloscopes have added spectrum analysis function based on the time domain measurement which realize the expansion of the range of measurement from time domain to frequency domain.Nevertheless,the spectrum analysis function existing in digital oscilloscope at present adopts the traditional way to implement.Both the processing speed and the refresh rate are slow,frequency resolution is poor,and dynamic range is limited,which can not meet people's demand for measuring various kinds of complex signals.As a result,in order to solve those problems mentioned above,the Sparse Fast Fourier Transform(SFFT)algorithm and Digital-Down Conversion(DDC)technology are introduced into the spectrum analysis function of the oscilloscope,and then the implementation method of spectrum analysis is optimized by software algorithm.This thesis is based on PXI high-resolution digital oscilloscope,which combined with hardware device and PC software program to realize spectrum analysis function of the oscilloscope.The main research contents are as follows:1.The spectrum analysis dynamic range is studied in the first part of this thesis.Firstly,the error of the FFT analysis in the oscilloscope is introduced.Secondly,the relationship between the ADC and the dynamic range of the spectrum is analyzed,and the dynamic range depends on the effective quantization bits of the ADC.Finally,the influencing factors and optimization methods of the spectrum dynamic range are described.2.The Sparse Fourier Transform(SFFT)Algorithm is researched in the second part of the thesis.Firstly,the basic principle of SFFT algorithm is introduced.Secondly,the concrete realization of the algorithm and its application in oscilloscope are studied.Finally,the influencing factors and changing trends of its time complexity are analyzed.Generally,many signals which analyzed by the oscilloscope have sparse characteristics.The SFFT algorithm provides a fast and efficient way for the oscilloscope to calculate the spectrum of sparse signals.3.The Digital-Down Conversion(DDC)Technique is implemented in the third part of this thesis.Firstly,the basic principle and implementation of DDC technique are described.Secondly,the influencing factors of frequency resolution and the method of DDC technique's optimization of resolution are analyzed.Finally,the application of this technique in oscilloscope spectrum analysis is studied.4.The spectrum scale adjustment function is achieved in the last part of this thesis.When the spectrum of the signal is very narrow and small compared with the display interface,which is not conducive to analysis and observation,so the oscilloscope can use this function to achieve amplification of the signal spectrum in order to better analyze the signal characteristics.Spectrum scale adjustment function is divided into two modes: proportional mode and interval mode.This thesis analyzes and implements these two modes respectively.