CN109870677A - A kind of CW with frequency modulation interference signal amplitude normalization method - Google Patents
A kind of CW with frequency modulation interference signal amplitude normalization method Download PDFInfo
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- CN109870677A CN109870677A CN201910191248.3A CN201910191248A CN109870677A CN 109870677 A CN109870677 A CN 109870677A CN 201910191248 A CN201910191248 A CN 201910191248A CN 109870677 A CN109870677 A CN 109870677A
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Abstract
A kind of amplitude normalization method of CW with frequency modulation interference signal is the self-sustained oscillation signal of constant amplitude interference signal correction, while not changing the frequency and phase attributes of interference signal for correcting to interference signal.Its process is to be sampled to interference signal and be converted to digital signal, amplitude demodulation is carried out to interference signal according to the PI characteristic of semiconductor laser, adaptive gain is carried out to signal according to the virtual value of interference signal simultaneously, obtains the interference signal of the self-sustained oscillation of amplitude constant.This method influences the amplitude of interference signal by factors such as the current-modulation of semiconductor laser and detection ranges, and the stability of CW with frequency modulation interference system can be improved and carry out the precision of phase demodulation to interference signal.
Description
Technical field
The present invention relates to signal disposal and analysis technical field more particularly to a kind of amplitude normalization methods, further relate to
A kind of and CW with frequency modulation interference signal amplitude normalization method.
Background technique
CW with frequency modulation (FMCW) laser interferometry can using light path as measurement object originating from frequency modulated continuous wave radar
Directly or indirectly to realize the measurement of a variety of physical quantitys such as displacement, strain, stress, temperature, angular speed, electric current, magnetic field.Frequency modulation
Continuous wave optical fibre displacement sensor is based on CW with frequency modulation principle of interference, using the semiconductor laser of frequency chirp
The light wave of optical frequency linear modulation out, by optical fibre Fabry-perot interferometer structure, by reference light and the transmitted light of signal light
Cheng Butong, so that generation time postpones, therefore there are frequency differences between two-beam, so that difference interference, which occurs, forms interference signal.
The frequency of the interference signal is related with absolute optical path difference, meanwhile, the variation (i.e. phase shift) of interference signal initial phase and optical path difference
Variable quantity it is related.By carrying out frequency discrimination to interference signal, its optical path difference can be obtained in phase demodulation, to realize its a variety of physical quantity
Measurement.
Since semiconductor laser realizes frequency modulation(PFM), but semiconductor laser using the method for driving current internal modulation
Output optical power also change with its driving current, therefore within a modulation period, CW with frequency modulation interference interference
Signal amplitude is unequal, changes with modulation electric current.Meanwhile the amplitude of interference signal can also change with the variation of detection range
Become.
In signal frequency discrimination, phase demodulation, the amplitude modulation and the fluctuation of amplitude of interference signal will lead to frequency discrimination, phase demodulation occurs
Large error.Therefore, before carrying out signal frequency discrimination, phase demodulation, amplitude normalization is carried out to interference signal, makes interference signal width
It is worth the precision that signal frequency discrimination, phase demodulation can be improved in constant self-sustained oscillation signal.
When modulating electric current linear change, the amplitude of interference signal is also linear change.In such a case, it is possible to logical
Cross the peak-seeking of interference signal, the straight line fitting of peak point calculates the modulation slope of interference signal amplitude, to realize amplitude solution
It adjusts.But the calculation amount of peak-seeking and straight line fitting is larger in this method, influences the real-time of interference signal phase demodulation.Frequency modulation is connected
Continuous wave displacement sensor, it is adjacent measure twice during if change in displacement is more than 1/4 wavelength, can not judge the direction being displaced with
And displacement increment.Therefore, when measuring to fast-moving target, existing method has real-time difference.And
When modulating electric current is not linear change, above-mentioned method will fail.And peak value location sensitivity is poor, by signal noise shadow
It rings, peak computational error is larger, requires interference signal signal-to-noise ratio high, universal difference.
Summary of the invention
The present invention provides a kind of CW with frequency modulation interference signal amplitude normalization method, to overcome reality of the existing technology
When property is poor and to the demanding problem of interference signal signal-to-noise ratio.
To achieve the goals above, present invention provide the technical scheme that a kind of amplitude of CW with frequency modulation interference signal
Method for normalizing comprising the steps of:
Step 1, interference signal sample and obtain digital signal by analog-to-digital conversion；
Step 2, amplitude demodulation: signal width is carried out to CW with frequency modulation interference signal according to the PI characteristic of semiconductor laser
It is worth the formula of demodulation are as follows:
Wherein St' for demodulation after interference signal, StFor the interference signal before demodulation, ImeanFor the average value of driving current,
ItFor driving current instantaneous value, IthFor the threshold current of laser；
Step 3: calculating the virtual value of interference signal after amplitude demodulation；
Step 4: calculating the signal amplitude of interference signal after amplitude demodulation；
Step 5: gain coefficient, and adaptive gain is carried out to signal.
In the step 3 calculate amplitude demodulation after interference signal virtual value, the calculation formula of the virtual value of signal are as follows:
Wherein U is signal virtual value,For the mean value of signal, n is sample point number, and i is sample point serial number.
Signal amplitude, the amplitude A of CW with frequency modulation interference signal are calculated in the step 4pWith the relationship between virtual value U
Are as follows:
Compared with prior art, beneficial effects of the present invention are as follows:
1, amplitude demodulation of the present invention eliminates the amplitude modulation of interference signal, and interference signal is corrected as self-sustained oscillation just
String wave, this is conducive to the raising of interference signal precision of phase discrimination.
2, the present invention carries out amplitude demodulation, amplitude rectification mistake to digital interference signal according to the PI characteristic of semiconductor laser
Without calculating the amplitude modulation slope of interference signal in journey, reduce calculation amount, improve the real-time of displacement measurement algorithm with
And the detectable target velocity upper limit.
3, the present invention has increased digital resources obtainment newly after amplitude reconciles step, is obtained according to interference signal virtual value
Signal amplitude, and then signal gain is accurately calculated, interference signal is amplified to fixed amplitude, makes the amplitude of interference signal not
It will receive the changes of factors such as measurement distance, target reflectivity and alignment and change, improve the stability and adaptation of system
Property, while improving the precision of subsequent frequency discrimination and phase demodulation algorithm.
4, the present invention has versatility: not requiring the waveform of modulation electric current, amplitude demodulation effect is not by interference signal
Noise influence, it is versatile.
Detailed description of the invention
Fig. 1 is the PI characteristic curve and CW with frequency modulation interference signal figure of laser；
Fig. 2 is that amplitude normalization is carried out to CW with frequency modulation interference signal, and normalization amplitude is set as 3V.
Specific embodiment:
The present invention will be describe below in further detail with reference to the accompanying drawings.
A kind of CW with frequency modulation interference signal amplitude normalization method provided by the invention adjusts one using sampling unit
Interference signal in period processed is sampled and is converted to digital signal, is connected according to the PI characteristic of semiconductor laser to frequency modulation
Continuous wave interference signal carries out amplitude demodulation.
It is characterized in that amplitude demodulation is carried out according to amplitude modulation of the modulation electric current of semiconductor laser to interference signal,
Adaptive gain is carried out according to the virtual value of interference signal simultaneously, interference signal is made to be changed into the self-sustained oscillation letter of amplitude constant
Number.
Referring to Fig. 1 and Fig. 2, a kind of CW with frequency modulation interference signal amplitude normalization method, comprising the following steps:
Step 1: to one modulation period internal interference signal sample and obtain digital signal by analog-to-digital conversion；
Step 2, amplitude demodulation is carried out to CW with frequency modulation interference signal according to the PI characteristic of semiconductor laser, it is specific to walk
It is rapid as follows:
According to the PI characteristic of semiconductor laser, the output power of laser can be indicated are as follows:
P=k (It-Ith),
Wherein k is the characteristic slope of laser PI, ItFor driving current instantaneous value, IthFor the threshold value electricity of laser
Stream.
According to the principle of optical heterodyne detection, the photoelectric current of photodetector output are as follows:
Wherein R is detector sensitivity, psFor signal light power, prFor with reference to optical power, ps、prWith the output of laser
Power is directly proportional, and f is the difference on the frequency of signal light and reference light.
The power and modulation electric current of laser are linear relationships；Photodetector output photoelectric current (i.e. interference signal) with
The power of laser is directly proportional.So interference signal amplitude AsIt is the driving current modulation of stimulated light device, AsWith driving current
Relationship are as follows:
As=ks(It-Ith),
Wherein ksFor proportionality coefficient, the formula of signal amplitude demodulation can be obtained are as follows:
Wherein StFor the interference signal after demodulation, StFor the interference signal before demodulation, ImeanFor the average value of driving current.
Step 3, calculate amplitude demodulation after interference signal virtual value:
The calculation formula of the virtual value of signal is
Wherein U is signal virtual value,For the mean value of signal, n is sample point number, and i is sample point serial number.
Step 4: calculating the amplitude of interference signal after amplitude demodulation, CW with frequency modulation interference signal is cosine signal, letter
Number amplitude ApWith the relationship between virtual value U are as follows:
Step 5: calculating signal gain, the amplitude set is Ar, such as amplitude ArIt may be set to 3V, gain is
Signal amplification is carried out with gain L to signal after amplitude demodulation, realizes the automatic gain of CW with frequency modulation interference signal
Control.
Based on the embodiments of the present invention, those of ordinary skill in the art are obtained without making creative work
The all other embodiment obtained, shall fall within the protection scope of the present invention.
Claims (3)
1. a kind of amplitude normalization method of CW with frequency modulation interference signal comprising the steps of:
Step 1, interference signal sample and obtain digital signal by analog-to-digital conversion；
Step 2, amplitude demodulation: signal amplitude solution is carried out to CW with frequency modulation interference signal according to the PI characteristic of semiconductor laser
The formula of tune are as follows:
Wherein St' for demodulation after interference signal, StFor the interference signal before demodulation, ImeanFor the average value of driving current, ItFor
Driving current instantaneous value, IthFor the threshold current of laser；
Step 3: calculating the virtual value of interference signal after amplitude demodulation；
Step 4: calculating the signal amplitude of interference signal after amplitude demodulation；
Step 5: gain coefficient, and adaptive gain is carried out to signal.
2. a kind of amplitude normalization method of CW with frequency modulation interference signal as described in claim 1, it is characterised in that: the step
In rapid 3 calculate amplitude demodulation after interference signal virtual value, the calculation formula of the virtual value of signal are as follows:
Wherein U is signal virtual value,For the mean value of signal, n is sample point number, and i is sample point serial number.
3. a kind of amplitude normalization method of CW with frequency modulation interference signal as claimed in claim 1 or 2, it is characterised in that: institute
It states and calculates signal amplitude in step 4, the amplitude A of CW with frequency modulation interference signalpWith the relationship between virtual value U are as follows:
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| CN110646789A (en) * | 2019-09-24 | 2020-01-03 | 西安工业大学 | Rapid phase discrimination method for frequency modulation continuous wave interference signal |
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| JP2006105669A (en) * | 2004-10-01 | 2006-04-20 | Niigata Univ | Method and apparatus for measuring laser interference displacement |
| US20160124075A1 (en) * | 2013-06-03 | 2016-05-05 | Robert Bosch Gmbh | Interference cancellation in an fmcw radar |
| US20180210068A1 (en) * | 2017-01-24 | 2018-07-26 | Hrl Laboratories, Llc | Dual frequency fmcw lidar and method |
| CN108444381A (en) * | 2018-05-15 | 2018-08-24 | 西安工业大学 | One kind is for eliminating the nonlinear bearing calibration of semiconductor laser frequency modulation interference signal |
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2019
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Patent Citations (4)
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|---|---|---|---|---|
| JP2006105669A (en) * | 2004-10-01 | 2006-04-20 | Niigata Univ | Method and apparatus for measuring laser interference displacement |
| US20160124075A1 (en) * | 2013-06-03 | 2016-05-05 | Robert Bosch Gmbh | Interference cancellation in an fmcw radar |
| US20180210068A1 (en) * | 2017-01-24 | 2018-07-26 | Hrl Laboratories, Llc | Dual frequency fmcw lidar and method |
| CN108444381A (en) * | 2018-05-15 | 2018-08-24 | 西安工业大学 | One kind is for eliminating the nonlinear bearing calibration of semiconductor laser frequency modulation interference signal |
Non-Patent Citations (2)
| Title |
|---|
| YOUNGWOOK KIM: "Identification of FMCW radar in mutual interference environments using frequency ramp modulation", 《2016 10TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP)》 * |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110646789A (en) * | 2019-09-24 | 2020-01-03 | 西安工业大学 | Rapid phase discrimination method for frequency modulation continuous wave interference signal |
| CN110646789B (en) * | 2019-09-24 | 2023-02-24 | 西安工业大学 | Rapid phase discrimination method for frequency modulation continuous wave interference signal |
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