CN107340050B - Optical fiber distributed vibration sensing system and phase discrimination nonlinear error correction method - Google Patents
Optical fiber distributed vibration sensing system and phase discrimination nonlinear error correction method Download PDFInfo
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Abstract
The invention discloses an optical fiber distributed vibration sensing system and a phase discrimination non-limiting error correction method, which relate to the technical field of signal processing and comprise a continuous laser light source, a first coupler, an acousto-optic modulator, an optical fiber amplifier, a circulator, an optical fiber coupler, a balance detector, an analog phase discrimination circuit module, a control display terminal and an acousto-optic modulator driver which are sequentially connected, and further comprise a signal generator connected with the analog phase discrimination circuit module; the acousto-optic modulator driver is connected with the acousto-optic modulator; the output end of the first coupler is connected with the acousto-optic modulator and the optical fiber coupler respectively; the output end of the circulator is connected with the optical fiber coupler, and the other output end of the circulator is sequentially connected with the sensing optical fiber and the piezoelectric ceramic; the analog phase discrimination circuit module is a two-way reference phase discrimination circuit. The invention solves the problems that: (1) The digital signal detection and processing equipment with higher performance is needed, and the cost is high; (2) The traditional digital phase-discrimination processing processes such as DCM and arctangent are adopted, and the process is complicated.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing and signal processing, in particular to an optical fiber distributed vibration sensing system and a corresponding phase discrimination nonlinear error correction method.
Background
In recent years, the distributed optical fiber sensing technology is increasingly valued by the industry and the national security departments because of the unique congenital advantages, so that the national security departments and the security monitoring industry invest and develop the distributed optical fiber sensing technology in a dispute way, and are expected to be widely applied within a few years. The basic theory of all the distributed optical fiber sensing systems is based on the elasto-optic effect of the optical fiber, and external parameters such as disturbance, sound wave, temperature, pressure, electromagnetic force and the like of a sensing area are utilized to act on a certain area of the optical fiber, so that the conversion rate and the length of the optical fiber near the area are changed accordingly, and the monitored external vibration position, vibration frequency, temperature, gas concentration and the like can be indirectly known by detecting the parameters such as the light intensity, the polarization state, the phase and the wavelength of an optical signal in the optical fiber. As the cost of the various devices required for optical communication systems has tended to be a reasonable range of large-scale applications, this has made long-range distributed fiber optic sensing technology possible from previous military and laboratory studies to a wide range of civilian fields.
The optical fiber distributed sensor is a distributed stress sensing system based on Optical Time Domain Reflectometry (OTDR). The technology is characterized in that the density of each point on the optical fiber is uneven due to the limitation of the preparation technology of the optical fiber, and the refractive index is uneven, and Rayleigh scattering occurs when light is transmitted in the optical fiber due to the uneven refractive index. Meanwhile, when the optical fiber is subjected to various applied external forces (strong mechanical vibration or weak acoustic vibration), the local refractive index changes, and scattered light in the optical fiber also changes. Thus, when a pulse laser is injected into one end of the optical fiber for transmission, a portion of the backscattered light is transmitted back to the light-incident end, which is typically a reflection loss for optical fiber communications, however, because of this characteristic, the stress variations experienced on the optical fiber link can be monitored by detecting the received time-varying backscattered light signal, which is known as an optical time domain reflectometry technique. As the first choice of long-distance fence technology application, plays an important role in the fields of perimeter security protection, long-distance oil and gas pipeline safety, large-scale structure health monitoring and the like, and meets the important requirements of the national safety monitoring in the aspects of border lines, important infrastructure and the like.
In the related art of the design of the optical fiber distributed sensing system based on the optical time domain reflection technology, the distributed optical fiber sensing system based on digital heterodyne demodulation utilizes a coherent detection method, so that the detection sensitivity is improved, and vibration sensing and phase detection are realized.
Digital heterodyne methods require sample rates on the order of hundreds of megameters and more, while high-rate data acquisition and processing have high demands on both computational and storage performance of the data processing apparatus. The digital heterodyne scheme determines that the cost of the signal detection and processing module in the digital heterodyne phi-OTDR system cannot be reduced. And the digital heterodyne demodulation scheme adopts traditional digital phase demodulation processing processes such as DCM, arctangent and the like, the data processing process is complicated, the system response capability is greatly influenced, and the practical engineering application field range of the system is limited.
Disclosure of Invention
The invention aims at: the existing implementation of the distributed optical fiber sensing system based on digital heterodyne mediation has the following problems: (1) The digital signal detection and processing equipment with higher performance is required, and the cost is high; (2) The traditional digital phase-discrimination processing processes such as DCM and arctangent are adopted, so that the data processing process is complicated, the response capability of the system is greatly influenced, and the application field range of the actual engineering of the system is limited; to solve these two problems, the present invention provides an optical fiber distributed vibration sensing system. The common analog phase discrimination circuit module can only discriminate 0-180 DEG and can not be suitable for a large dynamic range optical fiber distributed sensing system.
The technical scheme of the invention is as follows:
an optical fiber distributed vibration sensing system comprises a continuous laser light source, a first coupler, an acousto-optic modulator, an optical fiber amplifier, a circulator, an optical fiber coupler, a balance detector, an analog phase discrimination circuit module, a control display terminal and an acousto-optic modulator driver which are sequentially connected, and further comprises a signal generator connected with the analog phase discrimination circuit module; the acousto-optic modulator driver is connected with the acousto-optic modulator; one path of output end of 99% light output in the first coupler is connected with the acousto-optic modulator, and the other path of output end is connected with the optical fiber coupler; one output end of the circulator is connected with the optical fiber coupler, and the other output end of the circulator is sequentially connected with the sensing optical fiber and the piezoelectric ceramic; the analog phase discrimination circuit module is a two-way reference phase discrimination circuit.
Specifically, the analog phase discrimination circuit module comprises a 90-degree bridge chip, a power division chip, a first phase discrimination chip, a second phase discrimination chip and a demodulation module, wherein the 90-degree bridge chip is respectively connected with the first phase discrimination chip and the second phase discrimination chip, the power division chip is respectively connected with the first phase discrimination chip and the second phase discrimination chip, the first phase discrimination chip and the second phase discrimination chip are both connected with the demodulation module, and the demodulation module is a computer or other terminals.
Further, the first phase-discrimination chip and the second phase-discrimination chip are both AD8302 phase-discrimination chips.
Further, a filter is connected between the optical fiber amplifier and the circulator.
Further, the first coupler is a 2*1 coupler, and the optical fiber coupler is a 2×2 optical fiber coupler; the optical fiber amplifier is an EDFA amplifier.
The analog phase discrimination circuit module 9 is designed based on an AD8302 phase discrimination chip, the chip has a wider working frequency band, can discriminate the phase of an analog sine signal in the frequency range of 10MHz to 2.7GHz, has high detection sensitivity, and can detect the power range of the signal to be-60 dBm to 0dBm when the input impedance is 50Ω; the phase difference of 0 to 180 degrees can be detected theoretically, and the typical value of the theoretical phase discrimination precision is 0.1 degrees.
In the structure of the two-way AD8302 reference phase demodulation circuit, the signal to be phase-demodulated will first go through 1: the power divider chip, namely the power divider chip 92, divides phase discrimination into two signals with the same phase and the same amplitude, the other reference signal passes through the 90-degree bridge chip firstly, the 90-degree bridge carries out 90-degree phase setting on one of the signals, namely 90-degree phase delay is added, the other output signal is directly output, and the phase delay is not added, so that the two signals output by the 90-degree bridge chip have the phase difference of 90 degrees, and the amplitudes are basically the same. The phase discrimination result in the range of 0 DEG to 360 DEG can be obtained through the characteristic difference of the two paths of phase discrimination results.
The analog phase discrimination circuit module is based on an AD8302 phase discrimination chip, and the phase discrimination range of the AD8302 chip is 0-180 DEG, but the slope of the phase discrimination characteristic curve is opposite to that of the phase discrimination characteristic curve when the phase discrimination circuit module works at-180-0 DEG; and near 0 DEG and +/-180 DEG, the response characteristic has certain nonlinear effect, the phase discrimination characteristic curve has about 7 DEG error at the curve turning points of 0 DEG and 180 DEG, the phase discrimination characteristic curve of the two-way AD8302 reference phase discrimination circuit has poor linearity near the curve turning points of 0 DEG and 180 DEG and 90 DEG and 270 DEG, and the phase difference detection has great error. Therefore, according to the optical fiber distributed vibration sensing system provided by the invention, the invention further provides a phase discrimination nonlinear error correction method, which comprises the following steps:
and S1, performing characteristic curve test on a two-way reference phase discrimination circuit in the optical fiber distributed vibration sensing system, and fitting out a functional relation between voltage values and phase differences output by the first phase discrimination chip and the second phase discrimination chip according to test results.
S2: inputting the output voltage data of the first phase discrimination chip and the second phase discrimination chip acquired by the data acquisition card into a demodulation program, and then demodulating corresponding phase discrimination results in each section on the two phase discrimination characteristic curves by using a fitting functionThe phase values output by the two AD8302 phase detection chips in the ranges of 0-180 degrees and 180-360 degrees are respectively.
S3: will beComparing with the characteristic curve in S1, judging whether each phase discrimination result is in the linear region of the characteristic curve, if so, directly adding +.>Or->Outputting; if the phase discrimination result of one phase discrimination chip is located in the nonlinear region of the characteristic curve and the phase discrimination result of the other phase discrimination chip is exactly located in the linear region of the characteristic curve, the phase discrimination result of the other linear region is assigned to the phase discriminator located in the nonlinear region as an output result.
S4: the corrected phase discrimination resultAnd->Respectively subtracting, the difference is the smallest +.>And->Namely, the phase discrimination result is obtained by using +.>And->The average value of (2) is used as a phase discrimination result to further counteract the phase discrimination error of the single characteristic curve caused by the function fitting error.
S5: and (3) adding a correction value to the phase discrimination result obtained in the step (S4) to compensate and offset certain fixed drift of the phase difference of the signal generator when the phase discrimination circuit test is carried out, and outputting a final phase discrimination result.
In the above steps, the first phase-detecting chip (93) and the second phase-detecting chip (94) are both AD8302 phase-detecting chips.
After the scheme is adopted, the beneficial effects of the invention are as follows:
(1) The analog down-conversion processing of the mixed signal is realized through analog phase discrimination, so that the data sampling rate is reduced to 10MSa/s from hundreds of MHz to more than GHz through digital heterodyne demodulation, and the cost of the optical fiber distributed vibration sensing system of a heterodyne scheme can be greatly reduced; the analog phase discrimination circuit module designed by the invention realizes the great reduction of the cost of the distributed optical fiber vibration sensing system, and compared with high-speed data acquisition cards and high-performance data processing equipment which are required by the distributed optical fiber sensing system based on digital heterodyne demodulation and have hundreds of megahertz and even more than 1GHz, the analog phase discrimination circuit module has better mass production potential and larger practical application value, and is favorable for pushing the optical fiber distributed sensing system to realize wider application in the fields of perimeter security, long-distance pipeline security monitoring, large-scale structure health monitoring and the like.
(2) The two-way AD8032 is adopted to realize phase expansion, so that the limitation that the common analog phase discrimination circuit module can only discriminate 0-180 DEG and cannot be suitable for a large dynamic range optical fiber distributed sensing system is broken, and the 0-360 DEG phase discrimination is realized.
(3) The phase discrimination nonlinear error is corrected by adopting a bidirectional nonlinear correction method, the nonlinear region of the phase discrimination characteristic curve is corrected by utilizing a phase discrimination demodulation program, the phase discrimination error of AD8302 is reduced, the phase discrimination maximum error of the phase discrimination characteristic curve is reduced from about 7 degrees to 1.1795 degrees, and the maximum error probability is reduced from 1.97 percent to 0.33 percent.
Drawings
FIG. 1 is a block diagram of a distributed fiber vibration sensing system of the present invention;
FIG. 2 is a block diagram of a two-way AD8302 phase discrimination circuit;
FIG. 3 is the nonlinear error of the AD8302 characteristic curve;
FIG. 4 is a graph showing the results of a two-way AD8302 phase detection circuit characteristic curve test;
FIG. 5 is a flow chart of a two-way AD8302 phase-discrimination nonlinear error correction method;
fig. 6 is a two-way AD8302 demodulation error for the phase demodulation circuit;
fig. 7 is a phase demodulation test result corresponding to the two-way AD8302 phase demodulation circuit;
FIG. 8 is a phase demodulation time domain waveform of a vibration point when a periodic modulated signal is applied;
the marks in the figure: the device comprises a 1-continuous laser light source, a 2-first coupler, a 3-acousto-optic modulator, a 4-optical fiber amplifier, a 5-filter, a 6-circulator, a 7-optical fiber coupler, an 8-balance detector, a 9-analog phase discrimination circuit module, a 10-signal generator, an 11-acquisition and control terminal, 12-piezoelectric ceramics, a 13-sensing optical fiber and a 14-acousto-optic modulator driver.
Detailed Description
The present invention will be described in more detail below with reference to the drawings and examples.
The optical fiber distributed vibration sensing system comprises a continuous laser light source 1, a first coupler 2, an acousto-optic modulator 3, an optical fiber amplifier 4, a filter 5, a circulator 6, an optical fiber coupler 7, a balance detector 8, an analog phase discrimination circuit module 9, a control display terminal 11 and an acousto-optic modulator driver 14 which are sequentially connected, and further comprises a signal generator 10 connected with the analog phase discrimination circuit module 9; the acousto-optic modulator driver 14 is connected with the acousto-optic modulator 3; one output end of the first coupler 2 for outputting 99% light is connected with the acousto-optic modulator 3, and the other output end is connected with the optical fiber coupler 7; one output end of the circulator 6 is connected with the optical fiber coupler 7, and the other output end is sequentially connected with the sensing optical fiber 13 and the piezoelectric ceramic 12; the analog phase detection circuit module 9 is a two-way reference phase detection circuit.
The analog phase discrimination circuit module 9 comprises a 90-degree bridge chip 91, a power division chip 92, a first phase discrimination chip 93, a second phase discrimination chip 94 and a demodulation module 95, wherein the 90-degree bridge chip 91 is respectively connected with the first phase discrimination chip 93 and the second phase discrimination chip 94, the power division chip 92 is respectively connected with the first phase discrimination chip 93 and the second phase discrimination chip 94, the first phase discrimination chip 92 and the second phase discrimination chip 93 are both connected with the demodulation module 95, and the demodulation module 95 is a computer or other terminal.
The first phase-discrimination chip 93 and the second phase-discrimination chip 94 are both AD8302 phase-discrimination chips.
In the present embodiment, the continuous laser light source 1 is a 1550nm continuous light source with a narrow linewidth of a maximum linewidth of 5000 Hz; after passing through the 99:1 coupler 2, 99% of the continuous light enters the acousto-optic modulator 3 and is modulated into a pulse light signal with fixed frequency. The working frequency of the acousto-optic modulator 3 is 80MHz, and the control display terminal 11 controls an acousto-optic modulator driver to drive the acousto-optic modulator driver to generate a modulation signal, and the acousto-optic modulator modulates continuous light into a pulse light signal with fixed frequency and fixed duty ratio; since the pulse optical power modulated by the acousto-optic modulator 3 is drastically reduced, the pulse optical pulse is amplified by the pulse optical fiber amplifier 4 after the acousto-optic modulation in order to obtain strong backward rayleigh scattered light. The operating wavelength range 1525-1565nm of the optical fiber amplifier 4; the amplified pulse light is filtered by the filters 5 and 5 to carry out optical filtering on the detection pulse; the backward Rayleigh scattered light in the detection optical fiber is sequentially coupled into one port of the 2x2 optical fiber coupler 7 of the other 50:50 through the 2 port and the 3 port of the circulator 7; the continuous light from 1% port of coupler 2 is directly coupled into another port of coupler 7, and finally coupler 7 and balance detector 8 form a coherent balance detection structure, the mixed signal of balance detection and standard sine signal produced by signal generator 10 are simultaneously input into analog phase-discrimination circuit module 9, the mixed signal is undergone the process of phase detection, then the output result of phase-discrimination module 9 is undergone the process of data acquisition by means of acquisition and control terminal 11 so as to implement phase-discrimination result resolution and detection and positioning of vibration signal on the optical fiber.
Fig. 2 is a block diagram of a two-way AD8302 reference phase detection circuit, in which the two-way AD8302 reference phase detection circuit is configured such that a signal to be phase detected first passes through 1:1 Power divider chip dividing phase-identifying signal into two same-phase and equal-amplitude signals S 1 (t) and S 2 (t) assuming that the inputted phase-to-be-identified signal is:
where A represents the amplitude of the phase-identified signal, ω represents the signal frequency,representing the phase of the phase-authenticated signal. Then S 1 (t) and S 2 (t) can be expressed as:
k in S Representing the amplitude decay factor.
The other path of reference signal R (t) firstly passes through a 90-degree bridge chip, the 90-degree bridge sets 90-degree phase of one path of signal, namely 90-degree phase delay is increased, the other path of output signal is directly output, and the phase delay is not increased, so that the two paths of signals output by the 90-degree bridge chip have 90-degree phase difference, and the amplitudes are basically the same. If the reference signal is assumed to be:
where B represents the reference signal amplitude, ω represents the signal frequency,representing the phase of the reference signal. Through 90 DEG bridge coreThe two signals after the chip can be respectively expressed as:
then, the S is as follows 1 (t) and R 2 (t)、S 2 (t) and R 1 (t) phase discrimination detection is carried out by using two AD8302 sheets respectively, and the phase discrimination characteristic curve is calculated, S 1 (t) and R 2 The phase discrimination result of (t) is:
and S is 2 (t) and R 1 The phase discrimination result of (t) is:
if the true phase difference between the reference signal and the signal to be authenticated60 °, then->Will be 150 °; conversely if the true phase difference of the reference signal and the signal to be phase-detected +.>300 DEG, then->Will be 390 ° (i.e. 30 °). Therefore, the phase discrimination result in the range of 0 DEG to 360 DEG can be obtained by referring to the phase discrimination result through the other path.
The analog phase discrimination circuit module is based on an AD8302 phase discrimination chip, and the phase discrimination range of the AD8302 phase discrimination chip is 0-180 DEG, but the slope of the phase discrimination characteristic curve is opposite to that of the phase discrimination characteristic curve when the phase discrimination chip works at-180-0 DEG; the response characteristics of the phase-discrimination characteristic curve have certain nonlinear effects near 0 degrees and +/-180 degrees, the nonlinear error of the AD8302 characteristic curve is shown as a figure 3, and the phase-discrimination characteristic curve has about 7 degrees of error at the curve turning points of 0 degrees and 180 degrees; the test result of the characteristic curve of the two-way AD8302 reference phase detection circuit is shown in fig. 4, the characteristic curve of the two-way AD8302 reference phase detection circuit has poor linearity near the turning points of the curves of 0 DEG and 180 DEG and 90 DEG and 270 DEG, and the two-way AD8302 reference phase detection circuit has great error for phase difference detection. Therefore, the invention corrects the phase discrimination nonlinear error by utilizing bidirectional nonlinear correction, corrects the nonlinear region of the phase discrimination characteristic curve by the phase discrimination demodulation program, and reduces the phase discrimination error of the AD 8302.
According to the invention, the functional relation between the voltage value and the phase difference output by the two AD8302 circuits is fitted according to the test result of FIG. 4. Two paths of output voltage values are respectively set to V A And V B In this case, the phase difference detection results of the two input signals are respectivelyAnd->The sum of the fitted functional relationships is expressed as:
fig. 5 is a flow chart of the demodulation procedure of the two-way AD8302 reference phase demodulation circuit. Since a preset phase delay of 90 ° is used as a reference for the phase discrimination result, the output voltage results of two ADs 8302 need to be simultaneously processedAnd demodulating the line phase. Firstly, voltage data of two paths of AD8302 phase discrimination output acquired by a data acquisition card are input into a demodulation program, and then fitting functions shown in a formula (8) and a formula (9) are utilized to demodulate corresponding phase discrimination results in each section on two phase discrimination characteristic curvesComparing the four obtained phase discrimination results with the characteristic curve shown in FIG. 4, judging whether each phase discrimination result is located in the linear region of the characteristic curve, and if so, directly judging +.>Or (b)Outputting; if the phase discrimination result at this time is in the nonlinear region of the characteristic curve, and the phase discrimination result output by the other path AD8302 is just in the linear region, the phase discrimination result of the other linear region is assigned to the phase discriminator in the nonlinear region as the output result.
Finally, the corrected phase discrimination resultAnd->Respectively subtracting, the difference is the smallest +.>And (3) withI.e. phase discrimination results, in order to further counteract the phase discrimination errors of the single characteristic curve due to the function fitting errors, use is made here of +.>And->As phase discrimination results. In addition, since there is a certain fixed drift in the phase difference of the signal generator when the phase detection circuit test is performed, it is necessary to add a correction value to the output result at the time of final output and finally output the phase detection result. And the phase detection module output result is subjected to data acquisition by using a high-speed data acquisition card so as to finish phase detection result calculation and vibration signal positioning analysis.
The demodulation error result of the two-way AD8302 reference phase demodulation circuit is shown in figure 7. When the circuit works at 80MHz, the maximum error of the phase discrimination result is 1.1795 DEG within the range of 0 DEG to 360 DEG, and the linearity is as follows:
the maximum error of the AD8302 characteristic curve shown in fig. 3 is about 7 °, and the linearity thereof is 1.97%. The result of the demodulation test of the corresponding phase of the two-way AD8302 reference phase demodulation circuit is shown in fig. 6, and the corresponding relation between the actual demodulation output phase difference and the ideal state output phase difference is good, and the demodulation precision is greatly improved through the error correction of the demodulation program of the two-way AD8302 reference phase demodulation circuit.
The invention applies standard periodic vibration signals to the piezoelectric ceramics at the designated position, and carries out phase demodulation at the position, the phase demodulation time domain result of the vibration point is shown in figure 8, the phase characteristics of the signals can be basically distinguished, and further the invention further discloses that the analog phase discrimination circuit module designed by the invention is used in an optical fiber distributed type sensing system, thereby effectively realizing the phase demodulation and analysis of the vibration signals, and fully proving the feasibility of the application of the analog phase discrimination circuit module in the optical fiber distributed type vibration sensing system.
Claims (4)
1. The optical fiber distributed vibration sensing system is characterized by comprising a continuous laser light source (1), a first coupler (2), an acousto-optic modulator (3), an optical fiber amplifier (4), a circulator (6), an optical fiber coupler (7), a balance detector (8), an analog phase discrimination circuit module (9), an acquisition and control terminal (11) and an acousto-optic modulator driver (14) which are connected in sequence, and further comprising a signal generator (10) connected with the analog phase discrimination circuit module (9); the acousto-optic modulator driver (14) is also connected with the acousto-optic modulator (3); one output end of the first coupler (2) is connected with the acousto-optic modulator (3), the two output ends of the first coupler are connected with the optical fiber coupler (7), and the output light ratio of the one output end to the two output ends is 97:3-99:1; one output end of the circulator (6) is connected with the optical fiber coupler (7), and the other output end is connected with the piezoelectric ceramic (12) wound with the sensing optical fiber (13); the analog phase discrimination circuit module (9) is a double-path reference phase discrimination circuit;
the analog phase discrimination circuit module (9) comprises a 90-degree bridge chip (91), a power division chip (92), a first phase discrimination chip (93), a second phase discrimination chip (94) and a demodulation module (95), wherein the 90-degree bridge chip (91) is respectively connected with the first phase discrimination chip (93) and the second phase discrimination chip (94), the power division chip (92) is respectively connected with the first phase discrimination chip (93) and the second phase discrimination chip (94), the first phase discrimination chip (93) and the second phase discrimination chip (94) are both connected with the demodulation module (95), and the demodulation module (95) is a computer or other terminals;
a filter (5) is connected between the optical fiber amplifier (4) and the circulator (6).
2. The optical fiber distributed vibration sensing system according to claim 1, wherein the first phase detection chip (93) and the second phase detection chip (94) are both AD8302 phase detection chips.
3. A distributed optical fiber vibration sensing system according to claim 1, wherein the first coupler (2) is a 2*1 coupler and the optical fiber coupler (7) is a 2x2 optical fiber coupler; the optical fiber amplifier (4) is an EDFA amplifier.
4. A phase-discrimination nonlinear error correction method, comprising the steps of:
s1, performing characteristic curve test on a two-way reference phase discrimination circuit in an optical fiber distributed vibration sensing system, and fitting out a functional relation between voltage values and phase differences output by a first phase discrimination chip (93) and a second phase discrimination chip (94) according to test results;
s2: the output voltage data of the first phase discrimination chip (93) and the second phase discrimination chip (94) which are acquired by the data acquisition card are input into a demodulation program, and then the corresponding phase discrimination results in each section on the two phase discrimination characteristic curves are demodulated by using the fitted functional relationThe phase values output by the two AD8302 phase discrimination chips in the ranges of 0-180 DEG and 180-360 DEG are respectively;
s3: will beComparing with the characteristic curve in S1, judging whether each phase discrimination result is located in the linear region of the characteristic curve, if so, directly adding +.>Or->Where i, j = 1,2 output; if the phase discrimination result of one phase discrimination chip is positioned in the nonlinear region of the characteristic curve and the phase discrimination result of the other phase discrimination chip is positioned in the linear region, the phase discrimination result of the other linear region is assigned to the phase discriminator positioned in the nonlinear region as an output result;
s4: the corrected phase discrimination resultAnd->Respectively subtracting, wherein i, j=1, 2, the difference is the smallest +.>And (3) withNamely, the phase discrimination result is obtained by using +.>And->The average value of (2) is used as a phase discrimination result to further counteract the phase discrimination error of the single characteristic curve caused by the function fitting error;
s5: adding correction value to the phase discrimination result obtained in the step S4 to compensate and offset certain fixed drift of the phase difference of the signal generator when the characteristic curve test of the double-path reference phase discrimination circuit is carried out, and outputting a final phase discrimination result;
in the above steps, the first phase-detecting chip (93) and the second phase-detecting chip (94) are both AD8302 phase-detecting chips.
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