Experiment And Research On Method For Coherent Detection Of Weak Signal

Weak signal detection is a test technique that obtain signal in the noise. It hasbeen attracting widespread attention. Its widely used in various fields of science. Inthe detection technology of weak signals, this method can effectively remove noisethat mixed in the signal frequency band. In the measurement method of weak signal,coherent detection has high precision, good stability, convenient operation etc.so ithas been widely used.Through consulted the literature and analyzed the noise,this thesis is carried outin three parts experiments on coherent detection of weak signal. In the weak signalmeasurement and study of coherent detection,this paper did a lot of work whichhave uniqueness, specific summarized as follows:First, in this paper, the random noise was analyzed, and summarizes the methodsto eliminate noise. This article analysis and compares the weak signal detectionmethod。Second, The signal is diversified, so the research on coherent detectionof sinusoidal signal has essential meaning. the first part of the experimental is theexperiment research on coherent detection of sinusoidal signal, Analyzed theperformance of the circuit and the design standards, And test the performance of eachpart.Third, For the sake of practicality, the second part of the experimental is theexperiment research on coherent detection of pulse signal. On the basis of method forcoherent detection of sinusoidal signal, method of Coherent detection is applied tomeasure the pulse signal carried out the measurement of the pulse signal, stabilityof the system are tested under different condition of the human body, compared thepulse signal that collected in different people.Study the influence of the circuit for pulse signal measurement, Experiments show the feasibility of system, Theexperiment system has the characteristics of convenient operation, low cost and goodstability etc. this system is suitable for the development of the measuring instrument.Fourth, in order to realize automation, the third part of the experiment is theresearch of the coherent detection based on phase-locked loop. Based on the coherentdetection of sinusoidal signal, the third part of the experimental is using phase-lockedloop to complete the phase shift of the signal, Compared with the RC phase-shiftcircuit, PLL has the functions of automatic frequency tracking, In addition to theerror caused by human factors, by using the PLL,the veracity of the system wasimproved the experimental result shows that the system stability was obviouslyimproved.