Method for acquiring average phase of sine wave signals with same frequency

Abstract

A method for acquiring the average phase of sine wave signals with the same frequency comprises the following steps of: performing synchronous reverse phase shift on sine wave signals A and B with the same frequency, namely reducing a phase shift angle theta for A and increasing the phase shift angle theta for B; and when the amplitude of a direct-current signal output after the formed sine wave signal An and the sine wave signal Bn are subjected to frequency mixing and filtering by the accumulated phase shift value theta n, determining that the coincident phase of the two mixed signals is the average value of the phases of the two signals A and B. The problem of poor signal-to-noise ratio caused by small signal and large noise of a sum frequency signal can be avoided; therefore, the signal-to-noise ratio of the average phase signal can be improved, and the average phase signal with better performance can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing, and more specifically, to a method for obtaining the average phase of sinusoidal signals with the same frequency. Background Art

[0002] Sinusoidal signals are widely used in communication systems, especially in time-frequency transfer. For example, in a high-precision time-frequency transfer network, since high-precision time synchronization between the local end and the remote end is achieved by sending a sinusoidal wave in advance at the local end according to the line delay, when high-precision frequency synchronization (point-to-point) is achieved between the local end and the remote end, as long as some light carrying modulated time-frequency signals is extracted at any intermediate node on the optical fiber link between the two, the signals transmitted bidirectionally in the optical fiber can be detected respectively by a photodetector. The sinusoidal signal detected at the intermediate node when the sinusoidal signal sent from the local end to the remote end is demodulated by the circuit, and the sinusoidal signal detected at the intermediate node when the sinusoidal signal sent from the remote end back to the local end, after deducting the fixed detection time delay of the intermediate node, the accurate phase of the sinusoidal signal is the average of the phases of the sinusoidal signals received successively. Obtaining the average phase signal of the two signals is the accurate time-frequency signal. Measuring the average phase signal can conveniently obtain the accurate time-frequency signal at the intermediate node, which is an important part of realizing the network. Currently, to obtain the average phase signal of two sinusoidal signals with the same frequency, generally, the two sinusoidal signals with the same frequency are first mixed to obtain a sum-frequency signal, and then the sum-frequency signal is divided by two. This solution conforms to the general mathematical idea of finding the average value, but there are two major defects in actual operation. The sum-frequency signal obtained through mixing and filtering is small and has a large noise, resulting in a poor signal-to-noise ratio of the signal; secondly, the signal is prone to phase drift when passing through the filter. Summary of the Invention

[0003] Aiming at the defects or deficiencies of the prior art, the present invention provides a method for obtaining the average phase of sinusoidal signals with the same frequency. By using the synchronous reverse phase shift technology, it can avoid the problems of poor signal-to-noise ratio caused by the small signal and large noise of the sum-frequency signal, and the phase drift caused by the signal passing through the filter, which is beneficial to improving the signal-to-noise ratio of the average phase signal and obtaining a better performance average phase signal.

[0004] The technical solution of the present invention is as follows:

[0005] A method for obtaining the average phase of sinusoidal signals with the same frequency, characterized by comprising the following steps:

[0006] Step 1: Use the first DDS phase shifter to shift the detected sine wave signal A to generate a sine wave signal A1, and use the second DDS phase shifter to shift the detected sine wave signal B to generate a sine wave signal B1. The sine wave signal A and the sine wave signal B have the same frequency. The phase of A1 changes by a phase shift angle θ1 relative to the phase of A, and the phase of B1 changes by a phase shift angle θ1 relative to the phase of B.

[0007] Step 2: Input A1 and B1 into the mixing and filtering module respectively, and measure the DC signal output after mixing and filtering A1 and B1.

[0008] Step 3: Determine whether the amplitude of the DC signal reaches 0. If it is, enter Step 4. If not, replace θ1 with a phase shift angle θ2 and repeat Steps 1 to 2 to obtain sine wave signals A2 and B2, and so on, until the amplitude of the DC signal output after mixing and filtering the sine wave signals An and Bn formed with the phase shift angle θn reaches 0.

[0009] Step 4: Determine that the overlapping phase of the two signals being mixed is the average value of the phases of the two signals A and B based on the fact that the amplitude of the DC signal reaches 0.

[0010] In Step 1, A, B, A1, and B1 are respectively characterized as follows:

[0011] S1 ∝ sin(ωt + α),

[0012] S2 ∝ sin(ωt + β),

[0013] S3 ∝ sin(ωt + α - θ1),

[0014] S4 ∝ sin(ωt + β + θ1),

[0015] where S1 is the characterization of A, ω is the angular frequency, t is the time, α is the initial phase of A, S2 is the characterization of B, β is the initial phase of B, S3 is the characterization of A1, and S4 is the characterization of B1.

[0016] In Step 2, the following expressions are included:

[0017] S 5-1 ∝ sin(α - θ1 - β - θ1),

[0018] where S 5-1 is the characterization of the DC signal output after mixing and filtering A1 and B1.

[0019] In Step 3, the following expressions are included:

[0020] S 5-2 ∝ sin(α - θ2 - β - θ2),

[0021] S5-n ∝ sin(α - θn - β - θn),

[0022]

[0023] where S 5-2 is the direct current signal representation output after mixing and filtering A2 and B2, and S 5-n is the direct current signal representation output after mixing and filtering An and Bn.

[0024] Step 4 includes the following expressions:

[0025]

[0026] where S is the average phase signal representation of the two signals A and B.

[0027] The technical effects of the present invention are as follows: A method for obtaining the average phase of sine wave signals with the same frequency according to the present invention synchronously and reversely shifts the phases of sine wave signals A and B with the same frequency, that is, decreases the phase shift angle θ for A and increases the phase shift angle θ for B until the cumulative phase shift value θn makes the amplitude of the direct current signal output after mixing and filtering the sine wave signal An and the sine wave signal Bn reach 0. Then, it is determined that the overlapping phase of the two mixed signals is the average value of the phases of the two signals A and B. This can avoid the problems of poor signal-to-noise ratio caused by the small and noisy sum-frequency signal, as well as the phase drift problem caused by the signal passing through the filter, which is beneficial to improving the signal-to-noise ratio of the average phase signal and obtaining a better-performance average phase signal. Description of the Drawings

[0028] Figure 1 is a schematic diagram of the principle of the average phase signal involved in implementing the method for obtaining the average phase of sine wave signals with the same frequency according to the present invention. Figure 1 Among them, the first sine signal from the left is signal A, the second sine signal is the average phase signal, and the third sine signal is signal B. Signal A is equivalent to its phase decreasing by θ relative to the average phase signal, and signal B is equivalent to its phase increasing by θ relative to the average phase signal.

[0029] Figure 2 is a schematic diagram of the system structure involved in implementing the method for obtaining the average phase of sine wave signals with the same frequency according to the present invention. Figure 2 It includes a first DDS phase shifter (DDS, Direct Digital Synthesis) for receiving signal A and a second DDS phase shifter for receiving signal B. The first DDS phase shifter generates signal A n after shifting the phase of signal A, and the second DDS phase shifter generates signal B n after shifting the phase of signal B, and signal A n and signal Bn They are respectively input into a mixing and filtering module, and the mixing and filtering module outputs a DC signal C to an acquisition and control module. The acquisition and control module is respectively connected to a first DDS phase shifter and a second DDS phase shifter. Detailed implementation manners

[0030] The following describes the present invention in conjunction with the accompanying drawings ( Figure 1 - Figure 2 ).

[0031] Figure 1 is a schematic diagram of the average phase signal principle involved in implementing a method for obtaining the average phase of sinusoidal signals with the same frequency according to the present invention. Figure 2 is a schematic diagram of the system structure involved in implementing a method for obtaining the average phase of sinusoidal signals with the same frequency according to the present invention. Refer to Figures 1 to 2 As shown, a method for obtaining the average phase of sinusoidal signals with the same frequency includes the following steps: Step 1, use a first DDS phase shifter to phase-shift the detected sinusoidal signal A to generate a sinusoidal signal A1, and use a second DDS phase shifter to phase-shift the detected sinusoidal signal B to generate a sinusoidal signal B1. The sinusoidal signal A and the sinusoidal signal B have the same frequency. The phase of A1 changes by a phase-shift angle θ1 relative to the phase of A, and the phase of B1 changes by a phase-shift angle θ1 relative to the phase of B; Step 2, input A1 and B1 into the mixing and filtering module respectively, and measure the DC signals output after mixing and filtering A1 and B1; Step 3, determine whether the amplitude of the DC signal reaches 0. If so, go to Step 4. If not, replace θ1 with a phase-shift angle θ2 and repeat Steps 1 to 2 to obtain sinusoidal signals A2 and sinusoidal signals B2, and so on, until the amplitude of the DC signal output after mixing and filtering the sinusoidal signals An and sinusoidal signals Bn formed by the phase-shift angle θn reaches 0; Step 4, based on the fact that the amplitude of the DC signal reaches 0, it is determined that the coincident phase of the two signals being mixed is the average value of the phases of the two signals A and B.

[0032] In Step 1, A, B, A1, and B1 are respectively characterized as follows:

[0033] S1 ∝ sin(ωt + α),

[0034] S2 ∝ sin(ωt + β),

[0035] S3 ∝ sin(ωt + α - θ1),

[0036] S4 ∝ sin(ωt + β + θ1),

[0037] where S1 is the representation of A, ω is the angular frequency, t is the time, α is the initial phase of A, S2 is the representation of B, β is the initial phase of B, S3 is the representation of A1, and S4 is the representation of B1.

[0038] Step 2 includes the following expressions:

[0039] S 5-1 ∝sin(α - θ1 - β - θ1),

[0040] where S 5-1 is the DC signal representation output after mixing and filtering of A1 and B1.

[0041] Step 3 includes the following expressions:

[0042] S 5-2 ∝sin(α - θ2 - β - θ2),

[0043] S 5-n ∝sin(α - θn - β - θn),

[0044]

[0045] where S 5-2 is the DC signal representation output after mixing and filtering of A2 and B2, and S 5-n is the DC signal representation output after mixing and filtering of An and Bn.

[0046] Step 4 includes the following expressions:

[0047]

[0048] where S is the average phase signal representation of the two signals A and B.

[0049] The present invention relates to a sine wave signal processing technology. In particular, due to the wide use of sine wave signals in communication systems, especially in time - frequency transfer, and the need to obtain the average phase of sine wave signals with the same frequency in communication systems, the inventor has invented a practical technology of synchronous reverse phase - shifting method.

[0050] Based on improving the signal - to - noise ratio of the average phase signal and obtaining a better - performance average phase signal, the present invention proposes a new synchronous reverse phase - shifting method scheme for obtaining the average phase signal of sine wave signals with the same frequency. Specifically, the sine wave signal A is phase - shifted through DDS, the phase of A is reduced by θ, and at the same time, the phase of the sine wave signal B with the same frequency is phase - shifted, the phase of B is increased by θ. The phase - shifted signals are mixed and filtered, and the above operations are repeated and the DC signal output after mixing and filtering is measured until the amplitude of the obtained DC signal reaches 0, that is, it is considered that the two signals being mixed coincide. At this time, the phase - shifted signals A n and B n have the same phase, and since the cumulative values of the reverse phase - shifting of the two signals are equal, the phase of the coincident signal at this time is the average value of the phases of the original A and B signals.

[0051] A method for obtaining the average phase of sine wave signals with the same frequency, which is a technique for obtaining the average phase signal of two sine wave signals with the same frequency.

[0052] Each time the two sine wave signals with the same frequency are phase-shifted, they are always synchronized and the magnitudes of the phase-shifted values are equal, but the phase-shifting directions are opposite.

[0053] First, phase-shift to find the minimum amplitude of the mixed-frequency signal and then continue to phase-shift in the same direction, avoiding the situation where when the amplitude of the mixed-frequency signal is 0, it is impossible to determine whether the phase of the mixed-frequency signal is 0 or π.

[0054] It is necessary to use AD acquisition and digital control of phase shift to obtain the average phase signal.

[0055] The step size of a single movement can determine the accuracy of the average phase signal. It is considered that the smaller the step size, the more accurate the final obtained average phase value.

[0056] A method for obtaining the average phase of sine wave signals with the same frequency. Each time the mixing operation is performed, the same mixer is always used. Therefore, the influence of the mixer on the amplitude of the mixing result is always stable.

[0057] The two signals are always phase-shifted synchronously in opposite directions and the phase-shifting directions do not change. Therefore, for any two signals with the same frequency, the cumulative phase-shift value θ n Within the range of 0 - π, the phase difference between the two signals changes within 0 - 2π. Therefore, it is certain to find the phase of the mixed-frequency signal (i.e., the phase difference between the two signals) at the point where the amplitude is the smallest and the point where the phase is 0 (the point where the amplitude is 0 obtained by continuing to phase-shift without changing the direction after the amplitude is the smallest).

[0058] A method for obtaining the average phase of sine wave signals with the same frequency, including the following steps:

[0059] Step 1: The signals to be processed are two sine wave signals with the same frequency, which are respectively represented as signal A and signal B.

[0060] Among them, signal A can be characterized as:

[0061] S1 ∝ sin(ωt + α)

[0062] Among them, in the above formula, S1 represents the detected signal A.

[0063] Signal B can be characterized as:

[0064] S2 ∝ sin(ωt + β)

[0065] Among them, in the above formula, S2 represents the detected signal B.

[0066] Step 2: Phase-shift the sine wave signal A through DDS, reduce the phase of A by θ to obtain signal S3, and at the same time phase-shift the phase of the sine wave signal B, increase the phase of B by θ to obtain signal S4.

[0067] S3 ∝ sin(ωt + α - θ)

[0068] Among them, in the above formula, S3 represents the phase-shifted signal.

[0069] S4 ∝ sin(ωt + β + θ)

[0070] Among them, in the above formula, S4 represents the phase-shifted signal.

[0071] Since signals A and B are signals with the same frequency, when the two signals move in opposite directions by the same phase θ at the same time, the change amount of the relative phase difference between the two signals within the range of 0 - π of the cumulative phase shift amount of each signal is within 0 - 2π, that is, there must be a value of θ when phase-shifting such that the phase difference between the two signals is 0, that is, the phases are the same after phase-shifting.

[0072] Step 3: Mix signal S3 and signal S4, and the difference frequency signal S5 obtained after mixing and filtering. Since the frequencies of S3 and S4 signals are equal, S5 is a DC signal and can be characterized as:

[0073] S5 ∝ sin(α - θ - β - θ)

[0074] Among them, in the above formula, S5 represents the mixing result.

[0075] Step 4: Continuously phase-shift the two signals in opposite directions by θ at the same time until the amplitude of the DC signal S5 obtained from the mixed signal reaches the minimum value (it is considered that when the amplitude of the DC signal starts to increase for the first time, the amplitude of the mixed result is the minimum value when the two sine signals are shifted back by a unit step). At this time, continue to phase-shift and mix with the above step size and direction until the mixed signal is 0. At this time, the phase difference between the two signals is 0, that is, the signals coincide after phase-shifting. The coincident signal obtained by phase-shifting is the average phase signal of the two signals, and the total phase shift value of the mixed signal is θ n , where 0 ≤ θ n ≤ π. This signal can be expressed as:

[0076] Sn ∝ sin(α - θn - β - θn)

[0077] Due to the limitation of the value of θ n , the phase of the intermediate phase signal must satisfy α - θ n - β - θ n = 0, that is:

[0078] At this time, the phase-shifted results of signals A and B can be expressed as S a , S b as follows:

[0079]

[0080] The average phase signal S can be expressed as:

[0081]

[0082] At this time, the signal phases obtained after phase shifting the original two signals A and B coincide and are the average phase signal of signals A and B.

[0083] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is hereby specified that the above description helps those skilled in the art to understand the present invention, but does not limit the protection scope of the present invention. Any implementation that makes equivalent replacements, modifications and improvements, and / or simplifies the above description without departing from the substantial content of the present invention falls within the protection scope of the present invention.

Claims

1. A method for obtaining the average phase of sine wave signals with the same frequency, characterized in that, It includes the following steps: Step 1: Use the first DDS phase shifter to shift the detected sine wave signal A to generate a sine wave signal A1, and use the second DDS phase shifter to shift the detected sine wave signal B to generate a sine wave signal B1. The sine wave signal A and the sine wave signal B have the same frequency. The phase of A1 changes by a phase shift angle θ1 relative to the phase of A, and the phase of B1 changes by a phase shift angle θ1 relative to the phase of B; Step 2: Input A1 and B1 into the mixing and filtering module respectively, and measure the DC signal output after mixing and filtering A1 and B1; Step 3: Determine whether the amplitude of the DC signal reaches 0. If so, enter Step 4. If not, replace θ1 with the phase shift angle θ2 and repeat Steps 1 to 2 to obtain the sine wave signal A2 and the sine wave signal B2, and so on, until the amplitude of the DC signal output after mixing and filtering the sine wave signal An and the sine wave signal Bn formed by the phase shift angle θn reaches 0; Step 4: Determine that the coincident phase of the two signals being mixed is the average value of the phases of the two signals A and B based on the fact that the amplitude of the DC signal reaches 0.

2. The method for obtaining the average phase of a sine wave signal with the same frequency according to claim 1, wherein In Step 1, A, B, A1, and B1 are respectively characterized as follows: S1 ∝ sin(ωt + α), S2 ∝ sin(ωt + β), S3 ∝ sin(ωt + α - θ1), S4 ∝ sin(ωt + β + θ1), where S1 is the characterization of A, ω is the angular frequency, t is the time, α is the initial phase of A, S2 is the characterization of B, β is the initial phase of B, S3 is the characterization of A1, and S4 is the characterization of B1.

3. The method for obtaining the average phase of a sine wave signal with the same frequency according to claim 1, characterized in that, In Step 2, it includes the following expressions: S 5-1 ∝ sin(α - θ1 - β - θ1), Where S 5-1 is the DC signal characterization output after mixing and filtering of A1 and B1.

4. The method for obtaining the average phase of a sine wave signal with the same frequency according to claim 1, characterized in that, In Step 3, it includes the following expressions: S 5-2 ∝ sin(α - θ2 - β - θ2), S 5-n ∝ sin(α - θn - β - θn), where S 5-2 is the DC signal representation output after mixing and filtering of A2 and B2, and S 5-n is the DC signal representation output after mixing and filtering of An and Bn.

5. The method for obtaining the average phase of a sine wave signal with the same frequency according to claim 1, wherein In Step 4, it includes the following expressions: where S is the characterization of the average phase signal of the two signals A and B.

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