Peak value searching method used in phase measurement Fourier transform

Abstract

The invention discloses a method for identifying spectrum peaks in phase measurement based on an FPGA (Field Programmable Gate Array), and belongs to the field of FPGA signal processing. For digital signal processing, the method mainly aims at obtaining useful information, highlighting the characteristics of signals and extracting corresponding characteristics. In nuclear fusion research, the plasma electron density is an important physical parameter, and accurate and stable monitoring of the plasma electron density can help experimenters to improve fusion reaction conditions. The parameter can be realized by measuring the phase difference of the light beam after passing through the plasma and propagating in vacuum (namely not passing through the plasma), so that the key point is to acquire the phase information. A signal subjected to Fourier transform is located in a frequency domain, the peak value of a spectrogram of the signal needs to be positioned, the most important peak value frequency of the signal is extracted, and then important data is extracted according to the peak value position and the filtering window width of the signal. In FPGA implementation, in order to improve the accuracy and simplicity of phase measurement peak value recognition, the invention provides a peak value searching method capable of reducing comparison times, and the phase measurement process of the FPGA can be accurately and simply completed.

Description

Technical Field

[0001] The present invention relates to a real-time data processing technology in the field of FPGA signal processing, and in particular to a peak value search method for phase measurement based on FPGA. Background Art

[0002] In the field of FPGA signal processing, important features of signals can be extracted by analyzing and transforming them. The processing function is very extensive and is applied to sound, images, etc. In the field of fusion, signal processing is also involved. During the operation of the fusion device, the key link is to accurately measure the electron density of the plasma and use it as a feedback signal to control the fusion reaction. By obtaining two signals from the fusion device, one is the reference signal, which is the light beam that has not been refracted by the plasma (or in a vacuum), and the optical path will not be affected. The other is the refraction effect produced by the plasma, which changes the path of the light path and produces a phase difference. Therefore, the phase difference between the two light signals becomes a physical quantity that needs to be measured, which can directly reflect the electron density of the plasma. Phase detection is crucial to achieve accurate electron density measurement. Generally, the Fourier transform is used to transform the signal. The transformed signal belongs to the frequency domain signal, which describes the overall frequency distribution of the signal. The extracted features focus on the peak frequency, which is the most important frequency component in the signal. An important step is spectral peak recognition. Accurately and concisely finding the peak position can ensure the accuracy of phase measurement in Fourier transform. Summary of the invention

[0003] The present invention proposes an accurate and concise peak search method for phase measurement based on FPGA for plasma diagnosis in the field of FPGA signal processing. Compared with the method of obtaining the peak value by direct comparison, this method can reduce the number of comparisons between data and improve the accuracy and simplicity of phase measurement in FPGA.

[0004] The technical solution adopted by the present invention to solve the above problem is: a peak search method for phase measurement Fourier transform, comprising the following steps:

[0005] (1): After determining the number of conversion points N, the signal R at point N is simulated in the FPGA. The signal is processed twice by a D flip-flop to obtain signals R1 and R2, each delayed by one clock cycle. There are three groups of signals in total, R, R1 and R2.

[0006] (2): R and R1 are group 1, R1 and R2 are group 2, and the signals in these two groups are compared. The results of group 1 are recorded as large1 and small1, and the results of group 2 are recorded as large2 and small2. Taking group 1 as an example, the comparison steps are as follows:

[0007] 1): The first data in the R and R1 signals are compared in terms of sign, integer part, and fractional part simultaneously, and the results of the comparison are recorded using six variables, denoted as Var1, Var2, Var3, Var4, Var5, and Var6.

[0008] 2): Compare the signs of the signals R and R1. If the sign of R is 0 and the sign of R1 is 1, then Var1 is 1. If the sign of R is 1 and the sign of R1 is 0, then Var2 is 1. The same applies to the other four variables.

[0009] 3): By comparing the six variables, the comparison result of the magnitudes of the signals R and R1 is obtained, denoted as large1 and small1.

[0010] (3): When both small1 and large2 are high, record the corresponding data and the current position of the data. At this time, the recorded data and position are the maximum value data, denoted as R3.

[0011] (4): Compare the R3 data, that is, compare the first data and the second data of R3 and record the larger data, and then compare the larger data with the third data and record the larger data, and so on. Compare all the maximum value data to obtain the peak value.

[0012] Compared with the traditional method, the advantage of the method of the present invention is that:

[0013] This method adopts an accurate and concise peak search method, which can realize the process of spectral peak identification in the phase measurement based on FPGA, thereby simplifying the logical implementation of FPGA and improving the calculation accuracy of the phase. Description of the Drawings

[0014] Figure 1 It is a flow chart of an accurate and concise peak search method for phase measurement based on FPGA. Detailed Embodiment

[0015] The method of the present invention will be compared in detail below in combination with the drawings and specific implementation cases.

[0016] In the embodiment, FPGA, Vivado, and Modelsim software are used as the experimental platform, and the corresponding program is written using Vivado software to complete the preprocessing process of the two-channel signal data.

[0017] In the experiment, the input is two-channel signals, and the input simulation data is stored in the Block MemoryGenerator IP core of Vivado software as the input for the subsequent steps.

[0018] The splicing length of data preprocessing is 26 points, and the input data is preprocessed into frames through ping-pong caching and data head and tail splicing.

[0019] The number of points for Fourier transform is 256 points, and the processed data is subjected to Fourier transform using the Fast Fourier Transform IP core of Vivado software.

[0020] Then calculate the sum of squares: A = Re 2 + Im 2 , and obtain the sum of squares data.

[0021] Figure 1 is a flowchart of an accurate and concise peak search method in phase measurement based on FPGA. As shown in the figure, the process of the present invention includes the following steps:

[0022] (1): Simulate in the FPGA to obtain the sum of squares signal R with 256 points in each group, and perform a two-beat process on this signal to obtain a total of three groups of signals, denoted as R, R1, and R2.

[0023] (2): Take R and R1 as group 1, and R1 and R2 as group 2. Compare the signals within these two groups respectively to obtain the results of group 1 denoted as large1 and small1, and the results of group 2 denoted as large2 and small2. The specific comparison process is as follows:

[0024] 1): Compare the first data in the R and R1 signals simultaneously in terms of sign, integer part, and decimal part, and use six variables to record the comparison results, denoted as Var1, Var2, Var3, Var4, Var5, and Var6.

[0025] 2): Compare the signs of the signals R and R1. If the sign of R is 0 and the sign of R1 is 1, then Var1 is 1. If the sign of R is 1 and the sign of R1 is 0, then Var2 is 1. The same applies to the other four variables.

[0026] 3): By comparing the six variables, obtain the comparison result of the sizes of the signals R and R1, denoted as large1 and small1.

[0027] (3): When small1 and large2 are both high, record the corresponding data and the current position of the data. At this time, the data and position are the maximum value data, denoted as R3.

[0028] (4): Compare the maximum value data R3, that is, compare the first data and the second data of R3 and record the larger data, and then compare the larger data with the third data and record the larger data, and so on. Compare all the maximum value data to obtain the peak value and the position corresponding to the peak value.

[0029] The above are all steps of peak search. After finding the peak position, according to the digital window filtering width (52 points) sent from the PC side, the corresponding frequency band can be intercepted, and subsequent processing can be performed on the intercepted data, including: inverse Fourier transform, phase calculation and other related processing.

[0030] Through the digital window width data sent from the PC side, the start position and end position of the data to be intercepted can be obtained, and relevant data can be extracted within this range.

[0031] In the embodiment of the present invention, a peak search method for phase measurement Fourier transform is adopted. This method can adapt to different numbers of conversion points to perform peak search on the preprocessed original signal, and then complete the subsequent phase calculation to obtain the final phase. It can reduce the number of data comparisons and streamline the operation process while completing the phase calculation.

[0032] The above-mentioned embodiments are only used to explain the specific implementation of the present invention, rather than limiting the present invention. Therefore, all changes made according to the shape and principle of the present invention should be covered within the scope of the present invention.

Claims

1. A peak search method for phase measurement Fourier transform, characterized in that: The method includes the following steps: After determining the number of conversion points N, in the FPGA, the signal R is also obtained as N points through simulation. The signal is processed by two D flip-flops to obtain signals R1 and R2 each delayed by one clock cycle, resulting in a total of three groups of signals: R, R1, and R2. In step (2), taking R and R1 as group 1, and R1 and R2 as group 2, the signals within each of these two groups are compared in size respectively. The results of group 1 are denoted as large1 and small1, and the results of group 2 are denoted as large2 and small2. Taking group 1 as an example, the specific comparison steps are as follows: 1) The first data in the R and R1 signals are compared simultaneously in terms of sign, integer part, and fractional part, and six variables are used to record the comparison results respectively, denoted as Var1, Var2, Var3, Var4, Var5, and Var6. 2) Compare the signs of signals R and R1. If the sign of R is 0 and the sign of R1 is 1, then Var1 is 1. If the sign of R is 1 and the sign of R1 is 0, then Var2 is 1. The same applies to the other four variables. 3) By comparing the six variables, the comparison result of the sizes of signals R and R1 is obtained, denoted as large1 and small1. In step (3), when both small1 and large2 are high, the corresponding data and the current position of the data are recorded. The data and position recorded at this time are the maximum value data, denoted as R3. In step (4), the R3 data is compared, that is, the first data of R3 is compared with the second data and the larger data is recorded, and then the larger data is compared with the third data and the larger data is recorded, and so on. All the maximum value data are compared to obtain the peak value.

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