Research On A Phase Sensitive Detector Based On Voltage-Frequency Conversion

The design and research of weak signal detection technology is the key to solve the problem of how to extract feature signals from complex signals with low SNR.With the development of modern electronic communication technology,the exploration of this content is deepening,mainly because it shows great vitality in all aspects of social development,ranging from biomedical related to our bodies to national military aviation and other fields.All these have been urging the society and the country to continue to develop weak signal detection technology,and explore various new ways and concepts,only to achieve more efficient detection.The weak signal detection method also develops with it.Up to now,both the initia l research and development methods of frequency spectral density analys is,sampling integration and other technologies,as well as new technologies such as stochastic resonance and wavelet analysis in recent years,have strong vitality in the industry.This project needs to design a weak signal detection instrument which is suitable for industrial use,with high reliability,simple principle and low price.Therefore,in combination with the needs of the project,correlation detection method is finally selected for weak signal recognition.In order to recognize and extract the weak signal,a phase sensitive detector based on voltage frequency conversion is proposed.Using the voltage frequency conversion circuit,the analog voltage in the measured signal is converted into frequency,and FPGA is used to count and filter the converted frequency signal according to the reference signal,so as to realize weak signal detection.The voltage frequency conversion circuit transforms the analog voltage signal into the frequency signal whose size is a function of one time,and realizes the conversion from voltage signal to frequency signal,so that the multiplica t io n operation between the measured signal and the reference signal in the correlation detection is changed into the addition and subtraction operation,and the integra l operation of the calculated piezoelectric signal is converted into the counting operation of the calculated frequency signal,so as to realize the original modular operation The conversion from the complex processing of pseudo signal to the relatively simple processing of quasi digital signal is realized by using FPGA for signal measurement,data processing and communication.The recursive average filtering algorithm is selected for data processing.By adjusting the queue length N,the integral time constant can be adjusted,and each measurement can get a filtered output,so as to speed up the signal processing ability and achieve the effect of effective constraint on periodic random interference.In this project,ad7741 chip is used to build the voltage frequency conversion circuit,ep4ce6f17c8 chip is used in FPGA,and the bias circuit and level conversion circuit are designed.Through the bias circuit,we can adjust the measured voltage(AC signal)to a positive signal,then convert it to a frequency signal through the voltage frequency conversion circuit,and finally send it to FPGA through the level conversion circuit processing;at the same time,send the reference signal with the same frequency and phase as the measured signal to FPGA,FPGA counts the above processed signals according to the reference,and according to the count value and signal size Finally,the final recognition value is obtained after the recursive average filtering of the calculated data.In this paper,through the voltage frequency conversion circuit,the measured signal is processed into a quasi digital signal for recognition.The whole system is implemented based on FPGA,with simple structure and recursive average filte r ing algorithm selected for data processing,so as to realize the controllability of the system and improve the speed and accuracy of the system.