CN108710026B - Frequency stability measuring method and system based on high-precision phase frequency analysis - Google Patents
Frequency stability measuring method and system based on high-precision phase frequency analysis Download PDFInfo
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Abstract
The invention discloses a frequency stability measuring method and a system based on high-precision phase frequency analysis, wherein the measuring method adopts a full digital implementation scheme, a multi-channel high-speed ADC is used for directly sampling and digitizing analog frequency signals of a frequency source to be measured and a reference signal source, then double-mixing measurement is realized by using a digital orthogonal down-conversion technology, a high-precision frequency differential measurement sequence is obtained through high-precision phase frequency analysis, phase differential calculation and frequency differential calculation, and overlapping Allan variance is calculated, so that the frequency stability measurement of the frequency source to be measured is obtained. The proposed measurement method avoids the disadvantages of difficult design, long development period and the like of analog and semi-digital implementation schemes; compared with the existing digital phase discriminator measuring method, the method has the advantages that the requirement on the quantization resolution of the ADC device of the measuring system is reduced by adopting a high-precision phase frequency analysis algorithm, the hardware cost is reduced, and the capability of improving the measurable frequency range of the system by adopting the ADC device with higher speed is provided.
Description
Technical Field
The invention relates to a frequency stability measuring method and system based on high-precision phase frequency analysis, and belongs to the technical field of electronic measurement.
Background
High-stability frequency signal sources, such as high-stability crystal oscillators, atomic clocks and the like, are widely applied to the fields of aerospace, navigation positioning, national defense and military, communication and the like. The frequency stability is an important index for evaluating the performance of the frequency signal source, reflects the capability of keeping the output frequency value of the frequency source at a value within a period of time, and usually uses AllenThe variance is quantitatively described. At present, the second-order stability of the crystal oscillator can reach 10-12The second-level stability of the atomic clock can reach 10-15Therefore, it is very important to study a frequency stability measurement method with high accuracy.
At present, the frequency stability measuring method with the highest measuring precision is a double-mixing measuring method. The implementation of the double mixing measurement method can adopt an analog implementation scheme, a semi-digital implementation scheme and a full digital implementation scheme. The analog and semi-digital implementation schemes realize double mixing through an analog circuit, wherein the analog circuit generally utilizes a time interval counter to directly measure the phase of an analog difference frequency signal; in the latter, a medium-low speed analog-to-digital converter (ADC) is used for sampling and digitizing an analog difference frequency signal to obtain a digital difference frequency signal, and then a digital signal processing method is used for realizing phase frequency measurement. The full digital implementation scheme uses a high-speed ADC to directly perform sampling and digital processing on analog frequency signals of a measured source and a reference source, generates a digital difference frequency signal through a digital down-conversion technology, and then completes phase frequency measurement through a digital signal processing method, wherein the most common method is a digital phase discriminator phase measurement method. Currently, most measurement methods use analog or semi-digital implementations, which are heavily dependent on the performance of analog devices and circuits. When the frequency source to be measured has high stability (such as an atomic clock), especially when the frequency stability of a plurality of sources to be measured needs to be measured simultaneously, a plurality of analog down-conversion modules with high performance and consistency as much as possible need to be manufactured, and the research and development difficulty is high and the period is long. The full digital implementation scheme synchronously converts the analog signal to be measured into a digital signal through the multi-channel ADC, and then realizes a double mixing measurement method through a digital down-conversion technology, so that the difficulty in designing a high-performance analog circuit is avoided, and a plurality of measurement channels with stable and completely consistent performance can be rapidly expanded. However, the measurement result of the most commonly used phase detection method of the digital phase detector is seriously affected by the quantization error of the ADC, and the quantization resolution of the ADC chip adopted by the measurement system hardware is required to be not lower than 12 bits, so that the system is difficult to use the ADC chip with a higher sampling frequency, the measurable frequency range of the system is limited, and the very high frequency band signal (such as a 100MHz signal output by an atomic clock) output by a frequency signal source cannot be measured. In addition, the phase measurement result sequence output by the digital phase discriminator must be processed by various data processing methods such as uncoiling, filtering, data fitting and the like, and then can provide high enough measurement precision.
Disclosure of Invention
Aiming at the problems and the defects in the prior art, the invention provides a frequency stability measuring method and a frequency stability measuring system based on high-precision phase frequency analysis. The measurement method adopts a full digital implementation scheme, directly performs sampling and digital processing on analog frequency signals of a frequency source to be measured and a reference signal source by using a multi-channel high-speed ADC (analog to digital converter), then realizes double-mixing measurement by using a digital orthogonal down-conversion technology, further obtains a high-precision frequency differential measurement sequence through high-precision phase frequency analysis, phase differential calculation and frequency differential calculation, and calculates overlapping Allan variance, thereby obtaining the frequency stability measurement of the frequency source to be measured. The proposed measurement method avoids the disadvantages of difficult design, long development period and the like of analog and semi-digital implementation schemes; compared with the current digital phase discriminator measuring method, the FFT + CZT combined frequency spectrum amplification algorithm reduces the requirement on the quantization resolution of the ADC device of the measuring system, reduces the hardware cost, and provides the capability of improving the measurable frequency range of the system by adopting the ADC device with higher speed.
The invention adopts the following technical scheme for solving the technical problems:
on one hand, the invention provides a frequency stability measuring method based on high-precision phase frequency analysis, which comprises the following specific steps:
s1, respectively carrying out analog-to-digital conversion on an analog frequency signal to be detected and a reference analog frequency signal to obtain two paths of digital sampling signals;
s2, after the two paths of digital sampling signals obtained by the S1 are respectively subjected to digital quadrature down-conversion processing, two paths of digital difference frequency signals are obtained;
s3, respectively carrying out high-precision phase frequency analysis processing on the two paths of digital difference frequency signals obtained in S2 to obtain two paths of frequency phase measurement results;
s4, respectively carrying out phase difference calculation on the two paths of frequency phase measurement results obtained by S3 to obtain two paths of frequency measurement result sequences;
s5, performing frequency difference component calculation on the two paths of frequency measurement result sequences obtained in the step S4 to obtain frequency difference measurement result sequences of the analog frequency signal to be measured and the reference analog frequency signal;
and S6, performing overlapping Allen variance calculation on the frequency difference measurement result sequence obtained in the step S5 to obtain a frequency stability measurement result of the analog frequency signal to be measured relative to the reference analog frequency signal.
As a further technical solution of the present invention, in S2, two paths of digital sampling signals are respectively subjected to digital quadrature down-conversion processing by two independent synchronous digital quadrature down-conversion units.
As a further technical solution of the present invention, the analog frequency signal to be measured and the reference analog frequency signal in S1 are subjected to analog-to-digital conversion in parallel and synchronously.
As a further technical scheme of the invention, the high-precision phase frequency analysis processing in S3 adopts a Fast Fourier Transform (FFT) and CZT combined spectrum amplification algorithm: firstly, calculating FFT of the digital difference frequency signal to obtain a low-resolution frequency spectrum of the digital difference frequency signal so as to obtain a coarse frequency estimation result; then, the coarse frequency estimation result is used as an amplification center, high-resolution local spectrum amplification is carried out through CZT, a high-precision signal spectrum result is obtained, and a high-precision frequency and phase measurement result is obtained.
In another aspect, the present invention further provides a frequency stability measuring system based on high-precision phase frequency analysis, the measuring system includes a frequency source to be measured, a reference frequency source, first and second analog-to-digital converters, first and second digital orthogonal down-conversion units, first and second high-precision phase frequency analysis units, first and second phase difference calculation units, a frequency difference calculation unit, and an overlapping arrhenal variance calculation unit, wherein the frequency source to be measured, the first analog-to-digital converter, the first digital orthogonal down-conversion unit, the first high-precision phase frequency analysis unit are sequentially connected to the first phase difference calculation unit, the reference frequency source, the second analog-to-digital converter, the second digital orthogonal down-conversion unit, the second high-precision phase frequency analysis unit are sequentially connected to the second phase difference calculation unit, the first and second phase difference calculation units are respectively connected to the frequency difference calculation unit, the frequency difference calculation unit is connected with the overlapping Allan variance calculation unit.
As a further technical scheme of the invention, the first and second digital orthogonal down-conversion units realize digital orthogonal down-conversion through a numerical control oscillator and a multiplier, the local oscillation frequency and the initial phase of which are accurately adjustable, and further reduce the sampling frequency of the output digital signal through a down-sampling technology, and synchronously output the digital difference frequency signal in parallel in real time.
As a further technical scheme of the invention, the first analog-to-digital converter and the second analog-to-digital converter perform sampling and digital processing on analog frequency signals output by the frequency source to be tested and the reference frequency source in parallel and synchronously.
As a further technical scheme of the invention, the first digital quadrature down-conversion unit and the second digital quadrature down-conversion unit are two digital quadrature down-conversion units which are independently synchronous.
As a further technical solution of the present invention, the first and second high-precision phase frequency analysis units both use a fast fourier transform FFT and CZT joint spectrum amplification algorithm to perform high-precision phase frequency analysis processing, specifically: firstly, calculating FFT of the digital difference frequency signal to obtain a low-resolution frequency spectrum of the digital difference frequency signal so as to obtain a coarse frequency estimation result; then, the coarse frequency estimation result is used as an amplification center, high-resolution local spectrum amplification is carried out through CZT, a high-precision signal spectrum result is obtained, and a high-precision frequency and phase measurement result is obtained.
Compared with the prior art, the invention adopting the technical scheme has the following technical effects:
1) compared with analog and semi-digital implementation schemes, the method has the advantages that the hardware system is low in research and development difficulty, easy to implement, stable in performance, capable of rapidly expanding the number of measurement channels and simple to maintain and upgrade;
2) the adopted high-precision phase frequency analysis algorithm replaces a common phase detection method of a digital phase discriminator by combining an FFT + CZT combined spectrum amplification algorithm with a phase difference calculation method, so that the requirement of a measurement system on the quantization resolution of an ADC chip is effectively reduced, and the hardware cost is reduced;
3) the high-precision phase frequency analysis algorithm allows the measuring system to adopt the single-core multi-channel ADC with low quantization resolution and high sampling frequency to expand the frequency measuring range of the system according to specific measurement requirements, but the multi-core multi-channel ADC with high quantization resolution and high sampling frequency is difficult to obtain;
4) the overlapping Allan variance is adopted to replace the Allan variance, so that the defects that when the average time tau is large, the number of data points used for calculating the Allan variance is reduced, and the reliability is reduced are avoided.
Drawings
FIG. 1 is a schematic diagram of a scheme of a frequency stability measuring method based on high-precision phase frequency analysis;
FIG. 2 is a schematic diagram of the FFT + CZT joint spectrum amplification algorithm adopted by the high-precision phase-frequency analysis unit.
Fig. 3 is a system background noise measurement result in the embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The measuring method of the present invention will be better understood with reference to the following drawings and detailed description.
The invention provides a frequency stability measuring method based on high-precision phase frequency analysis, which is characterized by comprising the following specific steps of:
s1, respectively carrying out analog-to-digital conversion on an analog frequency signal to be detected and a reference analog frequency signal to obtain two paths of digital sampling signals;
s2, after the two paths of digital sampling signals obtained by the S1 are respectively subjected to digital quadrature down-conversion processing, two paths of digital difference frequency signals are obtained;
s3, respectively carrying out high-precision phase frequency analysis processing on the two paths of digital difference frequency signals obtained in S2 to obtain two paths of frequency phase measurement results;
s4, respectively carrying out phase difference calculation on the two paths of frequency phase measurement results obtained by S3 to obtain two paths of frequency measurement result sequences;
s5, performing frequency difference component calculation on the two paths of frequency measurement result sequences obtained in the step S4 to obtain frequency difference measurement result sequences of the analog frequency signal to be measured and the reference analog frequency signal;
and S6, performing overlapping Allen variance calculation on the frequency difference measurement result sequence obtained in the step S5 to obtain a frequency stability measurement result of the analog frequency signal to be measured relative to the reference analog frequency signal.
The present invention also provides a frequency stability measuring system based on high-precision phase frequency analysis, as shown in fig. 1, the measuring system includes: the device comprises a frequency source to be tested 100, a reference frequency source 110, analog-to- digital converters 101 and 111, digital quadrature down- conversion units 102 and 112, high-precision phase- frequency analysis units 103 and 113, phase difference calculation units 104 and 114, a frequency difference calculation unit 120 and an overlapping Allan variance calculation unit 121. The analog-to- digital converters 101 and 111 perform sampling and digitization on two paths of analog frequency signals output by the source to be measured 100 and the reference source 110 in parallel and synchronously. The digital orthogonal down- conversion units 102 and 112 implement digital orthogonal down-conversion by using an orthogonal numerically controlled oscillator and a multiplier, of which the local oscillation frequency and the initial phase are precisely adjustable, so as to reduce the sampling frequency of the output signal by using a down-sampling technology, and output the digital difference frequency signal in parallel, in real time and synchronously. The high-precision phase frequency analysis units 103 and 113 measure the frequency and the phase in parallel, in real time and accurately by using an FFT + CZT combined spectrum amplification algorithm. The phase difference calculation units 104 and 114 calculate the phase difference using the frequency phase results of the high-precision phase frequency analysis units 103 and 113, and output a frequency measurement result sequence with higher precision and high significances. The frequency difference calculating unit 120 calculates and outputs a frequency difference result sequence at a corresponding time of the two-channel frequency measurement sequence. The overlapping allen variance unit 121 calculates and outputs an overlapping allen variance measurement result according to the frequency difference division result sequence output by the frequency difference calculation unit 120.
The technical scheme of the invention is further explained by the following specific embodiments:
(1) the nominal frequencies output by the frequency source to be measured 100 and the reference frequency source 110 are both f0The analog frequency signal of (2). Wherein, the analog frequency signal x to be tested output by the frequency source 100 to be testedmea(t) reference analog frequency signal x output by reference frequency sourceref(t) respectively entering the analog-to- digital converters 101 and 111 to respectively obtain output to-be-detected and reference digital sampling signals xmea(n) and xref(n)。
In this example, a 100MHz analog frequency signal output by the same frequency source is divided into two parts by a power divider, and the two parts are regarded as analog frequency signals from the frequency source to be measured 100 and the reference frequency source 110, and are respectively connected to the analog-to- digital converters 101 and 111.
In this example, the measurement system employs an analog-to-digital converter ADC having four channels, a sampling frequency of up to 1.2GHz, and a quantization resolution of 8 bits. The analog-to- digital converters 101 and 111 are two of the 4 cores of the chip respectively. Sampling frequency fs1152MHz, the measurable nominal frequency range is f0≤500MHz。
(2) According to the nominal frequency f of the input signal0Setting the local oscillator frequency f of the digitally controlled oscillators of the digital quadrature downconversion units 102 and 112LO＝f0-fbWherein f isbIs the frequency of the digital difference frequency signal.
Digital quadrature down- conversion units 102 and 112 are parallel in real time according to fLOAnd the same initial phase theta0X according to equations (1) and (2)mea(n) and xref(n) performing a digital quadrature downconversion process:
wherein
And
are each xmea(n) and xref(n) two corresponding digital quadrature down-conversion output complex signals.
Then, digital quadrature down- conversion units 102 and 112 are respectively paired
And
performing anti-aliasing low-pass filtering and D-time down-sampling to obtain complex digital signal with sampling frequency of fsDown to fbase＝fsD, where D is a positive integer, outputting the difference frequency signal of the reference number to be measured
And
wherein n isD＝nD。
The digital orthogonal down conversion can effectively avoid the problems of local oscillator imbalance and the like in the analog orthogonal down conversion, can ensure the synchronism and consistency among a plurality of modules, and is easy to expand a multi-channel measurement system. The down-sampling technology can realize data compression on the premise of not losing information, and greatly reduces the data volume and the operation amount of subsequent signal processing.
In this example, the digital orthogonal down-conversion unit is implemented on the FPGA chip of the programmable device through a hardware programming language, and a multi-stage digital down-conversion cascade structure is adopted. Frequency f of digital difference frequency signalb100Hz, local oscillator frequency set to fLO99.999900 MHz. After down-sampling, the sampling frequency of the digital difference frequency signal is fbase1000 Hz. The extraction multiple is D-1152000, anda total of 9 stages of anti-aliasing decimation filter implementations are provided.
(3) The high-precision phase- frequency analysis units 103 and 113, according to the minimum value τ of the average time τ designated by the user0As integration time, will
And
is divided into a data frame, where N ═ τ0×fbase. The sequence number of the data frame is set to I, where I is 1, 2. I total measurement duration T specified by the user, in terms of I ═ T/τ0And (4) calculating.
High-precision phase- frequency analysis units 103 and 113 respectively process digital difference frequency signals
And
each data frame executes an FFT + CZT combined spectrum amplification algorithm, the principle of which is shown in figure 2, and further the frequency phase measurement result of the frequency source to be measured of the ith data frame
And frequency phase measurement of a reference frequency source
The method comprises the following specific steps:
a. let x (n)D) A digital signal sequence of the i-th data frame of a digital difference frequency signal, for x (n)D) Performing L-point complex FFT to obtain x (n)D) L-point complex FFT result sequence XFFT(l)：
Where l represents the frequency domain number of the complex FFT result sequence.
And then calculate XFFT(l) Modulus | X at each lFFT(l)|：
Wherein Re {. cndot } and Im {. cndot } represent taking real and imaginary parts of the complex number, respectively.
b. According to | XFFT(l) Frequency domain serial number l corresponding to maximum value |maxCalculating the starting position l of CZTstart＝lmax-0.5. Then, x (n) is calculated by the following formulaD) Obtaining M point complex CZT result sequence XCZT(m)：
Wherein m represents the frequency domain serial number of the CZT result sequence. And then calculate XCZT(m) modulus | X of each complex resultCZT(m)|。
c. According to lmaxAnd | XCZTFrequency domain serial number m corresponding to maximum value of (m) |maxThe digital difference frequency signal x (n) is obtained by calculation according to the following formulaD) High precision frequency measurement of
Wherein the frequency resolution of the FFT is Δ fFFT＝fbaseFrequency resolution Δ f of/L, CZTCZT＝fbase/(L×M)。
d. Reference digital difference signal x (n) as followsD) High accuracy phase analysis result of
Wherein the arg {. operator represents the argument of the computational complex number.
The frequency and phase measurement is carried out by adopting high-precision phase frequency analysis (FFT + CZT combined spectrum amplification algorithm), so that the influence of noise introduced by quantization errors in ADC digitization and digital signal processing on the precision of a measurement result can be effectively reduced.
In this example, the minimum mean time τ0The number of sampling points N included in each data frame is 1000 points, the total measurement time T is 40000 seconds, and the total number of data frames I is 40000. The FFT point number L is 2048, the CZT magnification M is 1024, and the frequency resolution of FFT is delta fFFT＝fbaseFrequency resolution delta f of/L approximately equal to 0.488Hz and CZTCZT＝fbase/(L×M)≈0.477mHz
(4) The phase difference calculating units 104 and 114 measure the frequency phase of the frequency source to be measured according to the frequency phase measurement result sequence of the frequency source to be measured given by the high-precision phase frequency analyzing units 103 and 113
And a sequence of frequency phase measurements of a reference frequency source
Calculating a sequence of frequency measurements with higher accuracy and significance according to equations (8) and (9)
And
wherein, I ═ 1, 2.., I-1, operator
Indicating a rounding down.
(5) The frequency difference calculating unit 120 calculates the difference between the source signal to be measured and the reference signal
With reference to a source signal
Each result of (A) is subtracted correspondingly to obtain a differential frequency measurement sequence
Wherein I-1, 2.
Because the signal paths passed by the source to be measured 100 and the reference source 110 are basically consistent, especially the digital signal processing paths are completely consistent, after differential processing, the noise (especially the instability of the system working clock) and the influence of the measurement system can be effectively counteracted, and an accurate frequency stability measurement result is obtained.
In this example, a difference frequency result sequence F is obtainedb[i]The physical meaning is the system noise floor of the measurement system in the example.
(6) The overlapping Allan variance is calculated 121, according to Fb[i]And y [ i ]]＝Fb[i]/f0Calculating fractional frequency result sequence y [ i ]]Wherein is f0Is the nominal frequency of the signal. According to the formula
() Calculating the overlapping Allan variance:
wherein τ is τ s τ0An average time specified for the user.
Although the Allan variance is a classical metric in frequency stability measurementsHowever, when the mean time τ is increased, fractional frequency data F used to calculate the Allan variance is calculatedb[i]The number of points decreases, and the reliability of the result decreases. The Overlapping Allen Variance (Overlapping Allan Variance) is adopted to overcome the shortcoming of the Allen Variance and improve the reliability of the evaluation result.
In this example, the average time τ is 1,10,100,1000,3600,7200 seconds. Fig. 3 shows the system noise floor results of an actual measurement. As can be seen, the system noise floor is only 9.8 × 10 at 1 second average time-15(ii) a The system noise floor is only 3.6 multiplied by 10 under the average time of 1000 seconds-17It can meet the measurement requirement of high-stability frequency signal source (such as hydrogen atomic clock).
In the invention, a frequency signal source to be detected and a reference frequency signal source are sampled and digitalized by a multi-channel analog-to-digital converter, and then are processed in parallel by a multi-channel digital orthogonal down-conversion unit and output digital difference frequency signals; the digital difference frequency signal is sent to a high-precision phase-frequency analysis unit and a phase difference calculation unit, and a frequency measurement sequence with high precision and high effective digit is output; after the frequency difference calculating unit calculates the difference frequency sequence of the frequency source to be measured and the reference frequency source, the overlapping Allan variance calculating unit calculates the overlapping Allan variance. The method has the following advantages: compared with an analog implementation scheme and a semi-digital implementation scheme, the full-digital implementation scheme reduces the hardware research and development difficulty of the measurement system, improves the performance and the system stability, and is easy to implement, maintain and upgrade; high-precision phase frequency analysis and phase difference calculation method can realize 10-kilosecond level by using ADC with 8-bit quantization resolution-17The magnitude system measures the background noise, breaks through the limitation that the quantization resolution of the ADC is not lower than 12 bits in the existing full digital implementation scheme, and can be expanded to a wider frequency measurement range by using an ADC device with higher sampling frequency; the overlapping Allan variance is adopted to replace the Allan variance, so that the reliability of the measurement result in the long-average-time measurement is improved.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can understand that the modifications or substitutions within the technical scope of the present invention are included in the scope of the present invention, and therefore, the scope of the present invention should be subject to the protection scope of the claims.
Claims (9)
1. The frequency stability measuring method based on high-precision phase frequency analysis is characterized by comprising the following specific steps of:
s1, respectively carrying out analog-to-digital conversion on an analog frequency signal to be detected and a reference analog frequency signal to obtain two paths of digital sampling signals;
s2, after the two paths of digital sampling signals obtained by the S1 are respectively subjected to digital quadrature down-conversion processing, two paths of digital difference frequency signals are obtained;
s3, respectively carrying out high-precision phase frequency analysis processing on the two paths of digital difference frequency signals obtained in S2 to obtain two paths of frequency phase measurement results;
s4, respectively carrying out phase difference calculation on the two paths of frequency phase measurement results obtained by S3 to obtain two paths of frequency measurement result sequences;
s5, performing frequency difference component calculation on the two paths of frequency measurement result sequences obtained in the step S4 to obtain frequency difference measurement result sequences of the analog frequency signal to be measured and the reference analog frequency signal;
and S6, performing overlapping Allen variance calculation on the frequency difference measurement result sequence obtained in the step S5 to obtain a frequency stability measurement result of the analog frequency signal to be measured relative to the reference analog frequency signal.
2. The method for measuring frequency stability based on high-precision phase-frequency analysis according to claim 1, wherein in S2, two paths of digital sampling signals are respectively subjected to digital quadrature down-conversion processing through two independent synchronous digital quadrature down-conversion units.
3. The method for measuring frequency stability based on high-precision phase-frequency analysis according to claim 1, wherein the analog frequency signal to be measured and the reference analog frequency signal in S1 are subjected to analog-to-digital conversion in parallel and synchronously.
4. The method for measuring frequency stability based on high-precision phase-frequency analysis according to claim 1, wherein the high-precision phase-frequency analysis processing in S3 adopts a fast fourier transform FFT and CZT combined spectrum amplification algorithm: firstly, calculating FFT of the digital difference frequency signal to obtain a low-resolution frequency spectrum of the digital difference frequency signal so as to obtain a coarse frequency estimation result; then, the coarse frequency estimation result is used as an amplification center, high-resolution local spectrum amplification is carried out through CZT, a high-precision signal spectrum result is obtained, and a high-precision frequency and phase measurement result is obtained.
5. The frequency stability measuring system based on high-precision phase frequency analysis is characterized by comprising a frequency source to be measured, a reference frequency source, a first analog-to-digital converter, a second analog-to-digital converter, a first digital orthogonal down-conversion unit, a second digital orthogonal down-conversion unit, a first high-precision phase frequency analysis unit, a second phase difference calculation unit, a frequency difference calculation unit and an overlapping Allen variance calculation unit, wherein the frequency source to be measured, the first analog-to-digital converter, the first digital orthogonal down-conversion unit and the first high-precision phase frequency analysis unit are sequentially connected with the first phase difference calculation unit, the reference frequency source, the second analog-to-digital converter, the second digital orthogonal down-conversion unit and the second high-precision phase frequency analysis unit are sequentially connected with the second phase difference calculation unit, and the first phase difference calculation unit and the second phase difference calculation unit are respectively connected with the frequency difference calculation unit, the frequency difference calculation unit is connected with the overlapping Allan variance calculation unit.
6. The system according to claim 5, wherein the first and second digital quadrature down-conversion units implement digital quadrature down-conversion by a digital controlled oscillator and a multiplier, the local oscillator frequency and the initial phase of which are precisely adjustable, and further reduce the sampling frequency of the output digital signal by a down-sampling technique, and synchronously output the digital difference frequency signal in parallel in real time.
7. The system of claim 5, wherein the first and second analog-to-digital converters perform sampling and digitizing on the analog frequency signals output by the frequency source under test and the reference frequency source in parallel and synchronously.
8. The system of claim 5, wherein the first and second digital quadrature downconverter units are two digital quadrature downconverter units that are independently synchronized.
9. The system according to claim 5, wherein the first and second high-precision phase frequency analysis units each perform the high-precision phase frequency analysis processing by using a Fast Fourier Transform (FFT) and CZT joint spectrum amplification algorithm, and specifically comprises: firstly, calculating FFT of the digital difference frequency signal to obtain a low-resolution frequency spectrum of the digital difference frequency signal so as to obtain a coarse frequency estimation result; then, the coarse frequency estimation result is used as an amplification center, high-resolution local spectrum amplification is carried out through CZT, a high-precision signal spectrum result is obtained, and a high-precision frequency and phase measurement result is obtained.
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