CN106645945A - Novel modulation domain analysis method based on FFT - Google Patents
Novel modulation domain analysis method based on FFT Download PDFInfo
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- CN106645945A CN106645945A CN201611132304.9A CN201611132304A CN106645945A CN 106645945 A CN106645945 A CN 106645945A CN 201611132304 A CN201611132304 A CN 201611132304A CN 106645945 A CN106645945 A CN 106645945A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
Abstract
The present invention discloses a novel modulation domain analysis method based on FFT (Fast Fourier Transformation). The method comprises the following steps: the step 1, the detected signals are subjected to the A/D sampling and then cache in a buffer, data is finally sent to a CPU, wherein the length of the data as follows: L=T/Ts, T is the time requiring display of a modulation domain analysis screen; the step 2, according to the measurement precision of the frequency, the number N of points of the FFT is calculated, and the calculation method of the N is as follows: N=Fs/(2XRBW), wherein RBW is a frequency resolution ratio, N is power of 2; the step 3, the number M of operation times of the FFT is calculated, and the calculation method of the M is as follows: M=L/N, wherein M is an integer; and the step 4, the FFT operation is performed for M times, and M frequency values are obtained. The novel modulation domain analysis method based on the FFT can improve the measurement precision, the method is novel, the cost is reduced, and the engineering is easy to realize.
Description
Technical field
The present invention relates to a kind of new type of modulation domain analysiss method, more particularly to a kind of new type of modulation domain based on FFT point
Analysis method.
Background technology
Modulation domain is the plane domain being made up of two axles of time and frequency of signal, and it has reacted signal frequency with the time
Relation, is to carry out three-dimensional (time domain, frequency domain, modulation domain) to measure an indispensable measurement field to signal.Modulating domain analyzing is used
In the frequency characteristic over time of measurement signal, in antijam communication, frequency-agile radar, electronic warfare system, Mechatronic Systems
In have important application, be the requisite instrumentation of developing, produce, safeguarding modern military and civil electronic system.
Traditionally, modulating domain analyzing based on to event and when target counting technology realize that measured signal Fx is whole through amplifying
Shape circuit, obtains pulse train Ex.Then to generate pulse train in signal strobe Tg inside countings, have two enumerators：
Time stamp counters and event counter.Time stamp counters calculate umber of pulse N in period Tg internal clock signal；Event counter meter
Calculate umber of pulse M of the pulse train in same period Tg.Tp is original signal strobe, and Ex is to be shaped rear measurement signal, To
It is timing signal, Tg is that Tc is a virtual signal, by markers by the actual signal strobe obtained after measured signal synchronization Tp
Signal synchronization Tg is obtained, and Err is exactly the error signal produced by measurement process.During continuous frequency measurement, time stamp counters, event meter
Number device continuous counter, under the control of Tg signals rising edge, sequential reads out time stamp counters value Nn, Nn+1 at n, n+1 moment, event
Counter Value Mn, Mn+1 and n, the Δ Tn at n+1 moment, Δ Tn+1, can calculate the frequency values at n moment according to above-mentioned measured value
Fx, shown in its computing formula such as following formula (1),
Fx=(Mn+1-Mn)/[(Nn+1-Nn) To+ (Δ Tn- Δ Tn+1)] ... (1)
In cycles of the wherein To for timing signal, repeat said process, you can measure the frequency _ time response of signal.
Ignore test error Δ Tn, Δ Tn+1, then measured signal frequency is, as shown in following formula (2), to be with respect to frequency measurement error
As shown in following formula (3),
Fx=(M/N) × fo...... (2)
E=Δs fx/fx=Δs M/M- Δs N/N+ Δ fo/fo...... (3)
Wherein fo is ticking frequency, and counting errors of the Δ M/M for event counter, Δ N/N are the counting of time stamp counters
Error, frequency accuracies of the Δ fo/fo for timing signal.
It is to carry out within the gate-control signal period Jing after event signal synchronization due to counting, therefore event counter counts
There is no error, i.e. Δ M=0 in value M.But due to the randomness of measured signal, result in gate-control signal Tg and timing signal f0
It is random, markers count value N yet suffers from ± 1 error.Ignore timing signal frequency stability error delta fo/fo, frequency measurement
Maximum error is as shown in following formula (4).
Above formula shows, if ignoring timing signal frequency stability error delta fo/fo, frequency-measurement accuracy and gate time
Tg, the frequency dependence of timing signal, gate time are longer, and timing signal frequency is higher, and frequency-measurement accuracy is higher.But in modulation
In domain analysiss, reflection frequency that be more careful situation over time, gate time are the smaller the better, and timing signal frequency is not yet
Infinitely may improve, because high frequency is proposed strict requirements to device and board design, in current technology
Under level and technique, realize that difficulty is very big.In the case where above-mentioned these objective factors are limited, certainty of measurement to be improved just accurately need to be surveyed
Going out Δ Tn, Δ Tn+1 carries out error compensation.Common error compensating method has analog interpolation, digital vernier method, delay interpolation
Method, markers phase-shifting method etc., though respectively there is advantage, but still have problems：Shortcoming using analog interpolation be circuit structure very
Complexity, can reduce the reliability of system, and extension multiple is limited, yet suffers from quantization error when surveying Δ Tn, Δ Tn+1；Using numeral
When the shortcoming of vernier method is that resolution is very high when surveying, two clock circuits strictly must be shielded, otherwise may be because of frequency pulling
And cannot normal work.Shortcoming using delay interpolation method is the delay unit engineering under the occasion that certainty of measurement requires high
Realize that difficulty is big, there are problems that nonsynchronous by the signal latch of delay unit；During using markers phase-shifting method, work as phase shifting times
When a lot, time stamp counters can increase, and generally, time stamp counters digit is a lot, if time stamp counters increase, addition
Device and FIFO hardware circuits resource can also be significantly increased, and hardware circuit volume increases, and system reliability is reduced, and also there is each counting
Device count value latches nonsynchronous problem.
In a word, the modulating domain analyzing that tradition is realized based on event and markers counting technology, in raising certainty of measurement and more
There is technology and Project Realization in terms of situation over time in careful reflection frequency.
The content of the invention
The technical problem to be solved is to provide a kind of new type of modulation domain analysiss method based on FFT, and which can
Certainty of measurement is improved, method is novel, and cost-effective, engineering is easily realized.
The present invention is solving above-mentioned technical problem by following technical proposals：A kind of new type of modulation domain based on FFT
Analysis method, which comprises the following steps：
Step one, in buffer after A/D samplings, data are finally sent to CPU, and data length is as follows for measured signal
Shown in formula：L=T/Ts, wherein T are the time that one screen of modulating domain analyzing needs to show, Ts is the cycle of A/D samplings；
Step 2, according to the certainty of measurement of frequency, calculates the points N of FFT, and the computational methods of N are shown below：N=Fs/
(2X RBW), wherein RBW are frequency resolution, and N is taken as 2 power side；
Step 3, calculates FFT operation times M, and the computational methods of M are shown below：M=L/N, wherein M round numbers；
Step 4, carries out M FFT computing, obtains M frequency values, and f1, f2 to fM, difference corresponding time are N X
Ts1, N X Ts2 to N X TsM；
Step 5, the transverse axis with N X Ts1, N X Ts2 to N X TsM as time shafts, f1, f2 to fM are the vertical of frequency axiss
Axle completes modulating domain analyzing drawing waveform.
Preferably, in the step one, Ts is sampling period, length of the L for buffer, and L >=M X N.
Preferably, sample rates of the Fs for A/D sampled signals in the step 2.
Preferably, the step 4, carries out M FFT computing within the time of L X Ts, and the computing points of each FFT are
N, and the corresponding time be N X Ts, each FFT computings can obtain the relation of amplitude and frequency, further calculate N X
Ts times corresponding frequency values, M FFT computing are obtained M frequency values, the i.e. corresponding frequency values of N X Ts1 for side f1, N X
The corresponding frequency values of Ts2 are side f2, and the corresponding frequency values of N X TsM are side fM, can so reflect frequency in the L X Ts times
Variation relation, so as to complete modulating domain analyzing.
The present invention positive effect be：The present invention can realize modulating domain analyzing, hardware engineering using FFT technique
Upper easily realization, algorithm are ripe, solve tradition and are improving survey based on the modulating domain analyzing that event and markers counting technology are realized
There is technology and Project Realization in terms of situation over time in accuracy of measurement and more careful reflection frequency, in addition, this
Invention with realize spectrum analyses, vector analyses, demodulation etc. be based on software radio framework reception hardware platform it is identical, in instrument reality
During existing integration test function, hardware can be saved.
Description of the drawings
Fig. 1 is the schematic diagram of the present invention.
Oscillograms of the Fig. 2 for frequency-domain analysiss.
Oscillograms of the Fig. 3 for the N X Ts1 moment.
Oscillograms of the Fig. 4 for the N X Ts2 moment.
Oscillograms of the Fig. 5 for the N X TsM moment.
Fig. 6 is the oscillogram that modulating domain analyzing is realized based on FFT.
Specific embodiment
Present pre-ferred embodiments are given below in conjunction with the accompanying drawings, to describe technical scheme in detail.
FFT is generally used for the analysis of frequency domain, and simplified hardware block diagram is as shown in Figure 2.Measured signal by A/D sampling after
Buffer, being finally sent to CPU carries out FFT computings, obtains the relation of frequency and amplitude, i.e. frequency-domain analysiss, as shown in Figure 2.
The present invention is new based on FFT's (Fast Fourier Transformation, the fast algorithm of discrete fourier transform)
Type modulating domain analyzing method is comprised the following steps：
Step one, measured signal are adopted by A/D (Digital Analog Converter, digital-to-analog signal converter)
In buffer after sample, data are finally sent to CPU (Central Processing Unit, central processing unit), data length
As shown in following formula (10), wherein T is the time that one screen of modulating domain analyzing needs to show；
L=T/Ts...... (10)
Step 2, according to the certainty of measurement of frequency, calculates the points N of FFT, shown in the computational methods such as following formula (11) of N, its
Middle RBW is frequency resolution, and N is taken as 2 power side；
N=Fs/ (2X RBW) ... (11)
Step 3, calculates FFT operation times M, shown in the computational methods such as following formula (12) of M, wherein M round numbers；
M=L/N...... (12)
Step 4, carries out M FFT computing, obtains M frequency values, i.e. f1, f2 to fM, and the difference corresponding time is N X
Ts1, N X Ts2 to N X TsM；
Step 5, the transverse axis with N X Ts1, N X Ts2 to N X TsM as time shafts, f1, f2 to fM are the vertical of frequency axiss
Axle completes modulating domain analyzing, as shown in Figures 3 to 6 drawing waveform.
In the step one, Ts is sampling period, length of the L for buffer, and L >=M X N.
Sample rates of the Fs for A/D sampled signals in the step 2.
The step 4, carries out M FFT computing within the time of L X Ts, and the computing points of each FFT are N, and right
The time answered is N X Ts, and each FFT computings can obtain the relation of amplitude and frequency, further calculate the NX Ts times pair
The frequency values answered, M FFT computing are obtained M frequency values, the i.e. corresponding frequency values of NX Ts1 for side f1, and N X Ts2 are corresponding
Frequency values are side f2, and the corresponding frequency values of N X TsM are side fM, can so reflect that the change of frequency in the L X Ts times is closed
System, so as to complete modulating domain analyzing.
Based on the modulating domain analyzing that FFT is realized, the points N of FFT is bigger, and frequency measurement accuracy is higher, A/D sampled signals
Sample rate Fs is bigger, and N X Ts are less, the time dependent situation of reflection frequency that more can be careful.Hold in hardware engineering of the present invention
Easily realize, algorithm is ripe, solve tradition and measurement essence is being improved based on the modulating domain analyzing that event and markers counting technology are realized
There is technology and Project Realization in terms of spending with more careful reflection frequency over time situation.
Particular embodiments described above, the technical problem, technical scheme and beneficial effect to the solution of the present invention are carried out
Further describe, it is be should be understood that to the foregoing is only specific embodiment of the invention, it is not limited to
The present invention, all any modification, equivalent substitution and improvements within the spirit and principles in the present invention, done etc., should be included in this
Within the protection domain of invention.
Claims (4)
1. a kind of new type of modulation domain analysiss method based on FFT, it is characterised in which comprises the following steps：
Step one, in buffer after A/D samplings, data are finally sent to CPU, data length such as following formula institute for measured signal
Show：L=T/Ts, wherein T are the time that one screen of modulating domain analyzing needs to show, Ts is the cycle of A/D samplings；
Step 2, according to the certainty of measurement of frequency, calculates the points N of FFT, and the computational methods of N are shown below：N=Fs/
(2XRBW), wherein RBW is frequency resolution, and N is taken as 2 power side；
Step 3, calculates FFT operation times M, and the computational methods of M are shown below：M=L/N, wherein M round numbers；
Step 4, carries out M FFT computing, obtains M frequency values, and f1, f2 to fM, difference corresponding time are NXTs1, NXTs2
To NXTsM；
Step 5, the transverse axis with NXTs1, NXTs2 to NXTsM as time shafts, f1, f2 to fM for frequency axiss the longitudinal axis drawing ripple
Shape, completes modulating domain analyzing.
2. the new type of modulation domain analysiss method based on FFT as claimed in claim 1, it is characterised in that Ts in the step one
For the sampling period, length of the L for buffer, and L >=MXN.
3. the new type of modulation domain analysiss method based on FFT as claimed in claim 1, it is characterised in that Fs in the step 2
For the sample rate of A/D sampled signals.
4. the new type of modulation domain analysiss method based on FFT as claimed in claim 1, it is characterised in that the step 4,
Carry out M FFT computing in the time of LXTs, the computing points of each FFT are N, and the corresponding time is NXTs, each FFT
Computing obtains the relation of amplitude and frequency, further calculates NXTs times corresponding frequency values, and M FFT computing obtains M frequency
Rate value, the corresponding frequency values of NXTs1 are side f1, and the corresponding frequency values of NXTs2 are side f2, and the corresponding frequency values of NXTsM are side fM,
So reflect the variation relation of frequency in the LXTs times, so as to complete modulating domain analyzing.
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| US20230003817A1 (en) * | 2021-07-02 | 2023-01-05 | Canon Medical Systems Corporation | Magnetic resonance imaging apparatus |
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Application publication date: 20170510 |