Development Of 10MHz Frequency Scale Comparison Measurement System Based On FPGA

The frequency standard refers to a device that can gain a single frequency value of sinusoidal oscillation signals with high accuracy,which plays an important role in modern military,communications,power,and navigation fields.Frequency scale comparison measurement is to have a measure and access of the accuracy and stability of the frequency standard.It is of great practical significance for the reasonable use of frequency standard in engineering.At present,the high-precision frequency ratio comparison measurement system often adopts the double mixing time difference method.The traditional double-mixing time difference method is to compare the measured signal and the reference signal with the common oscillator respectively.And then sends the two difference signals to the counter for counting measurements.However,the counting method to measure the phase difference is not precise,and it will produce error within one count.This thesis developed a measurement system of 10MHz frequency scale comparison.The system uses the basic framework of classical dual-mix time difference method.However,we used digital correlation method based FPGA instead of the traditional counting method for the beat signal measurement.Improve the formula of digital correlation method,Plus half a peak to the beat signal in order to facilitate the FPGA operation.At the same time,replace solving the arccosine to solving the arctangent.Design the inverse triangular function converter to compare the accuracy between solving the arccosine and solving the arctangent in the FPGA.The main research work of this thesis is as follows:(1)In this thesis,we developed 9.9999MHz deviation frequency source and sinusoidal deflector which makes the 10MHz measured signal and the reference signal down to 100Hz sine wave signal,improving the system's measurement resolution.(2)We developed a dual-channel data acquisition card which can transform two 100Hz low frequency beat sine wave signal into a discrete digital signal,sent to the FPGA for phase difference solution.(3)We designed the inverse trigonometric converter,digital correlator,multiplier,divider and other computing unit to achieve the correlation method to measure the phase difference In FPGA.(4)Inverse trigonometric converter is used to study the algorithm based on CORDIC,the CORDIC algorithm based on CORDIC and the algorithm of anti-tangent based on Chebyshev,we carried out Matlab simulation and performance comparison.The results show that the algorithm of anti-tangent based on Chebyshev is more approximate to the theoretical value.(5)In FGPA,the serial port driver is designed to output the the real-time measurement data of the phase difference between the measured signal and the reference signal to the host computer for displaying and saving.Load The measurement data which is saved in the host computer to Stable32-1.6 for stability index analysising.(6)We developed a prototype of the system,and designed a system test scheme.We also measured the channel delay,background noise and measurement accuracy of the prototype.The experimental results show that the channel delay of the prototype 10MHz frequency comparison system is 199.6ps and the background noise is 7.46E-12/s,that is,the resolution of the phase difference measurement system reaches the order of picoseconds.The design of the system design makes full use of the parallel processing capability of the FPGA to improve the operation speed of the algorithm,and completes the acquisition control,processing and data transmission of the sinusoidal beat signal in a FPGA.The system has the characteristics of real-time and miniaturization under the premise of ensuring the accuracy of the measurement.