CN101051085B - Coherent laser height measuring frequency demodulation circuit - Google Patents
Coherent laser height measuring frequency demodulation circuit Download PDFInfo
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- CN101051085B CN101051085B CN2007100400907A CN200710040090A CN101051085B CN 101051085 B CN101051085 B CN 101051085B CN 2007100400907 A CN2007100400907 A CN 2007100400907A CN 200710040090 A CN200710040090 A CN 200710040090A CN 101051085 B CN101051085 B CN 101051085B
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Abstract
A demodulation circuit of using coherent laser to detect high frequency consists of photoelectric detector, high-pass filter, local oscillator, chirp signal generator, frequency mixture, 90 degree phase shift, low-pass filter and data collection card for carrying out detection and pick-up on coherent distance information accurately in real time.
Description
Technical field
The present invention relates to photosignal, particularly a kind of coherent laser height measuring frequency demodulation circuit, it is a kind of circuit that adopts various electronics devices to realize coherent laser height measuring frequency demodulation.
Background technology
Develop rapidly along with the coherent laser height-finding technique, it has had usual method be beyond one's reach precision and sensitivity, characteristics such as its high s/n ratio, high-resolution sensitivity more and more receive publicity it, thereby have obtained using widely in earth observation and survey of deep space.
The long-run development of laser technology itself is not only depended in the development of coherent laser height-finding technique, also depends on the generation of various new methods and the fast development of device simultaneously.Accurate, the stable and simple coherence detection of Doppler frequency is to realizing that effectively crucial effects is played in range finding.Simultaneously, can according to the corresponding data that obtains over the ground surface condition be described, and then reappear terrain feature.
Coherent laser is surveyed high principle of work, be system emission single longitudinal mode continuous laser as carrier signal after, be pulse signal with its copped wave again, and chirp signal is modulated on this laser beam, launch this laser pulse to ground, receive echo by system at last, carry out time-frequency inverted, thereby obtain required range information.
The metering system of distance height is divided into three kinds of recurrent interval mensuration, direct probe method and coherent detection methods.The recurrent interval measuring method is to utilize the flight time of measuring pulse to obtain range information at interval.The direct detection method is by regulating the transmission frequency of transmitter, the direct detection echoed signal, utilize transmit and received signal between difference on the frequency extrapolate time delay, thereby obtain range information.The coherent detection method then is to introduce the relevant and method measured of a branch of reference beam on the basis of direct detection.
The shortcoming that the laser life-span that the relative pulse interval measurement can cause because of high-peak power, short pulse, the high power of laser shortens says that coherent detection adopts low peak power, long pulse to survey, and has reduced the influence to the laser works life-span; The relative low signal-to-noise ratio problem that is caused during direct detection, coherent detection has significantly improved the signal to noise ratio (S/N ratio) of received signal, thereby has improved the measuring accuracy of distance.Reason in view of the above, coherent detection has more advantage than other two kinds of detection modes, thereby adopts coherent detection to carry out apart from high-acruracy survey.
The U.S. carries out the country that coherent laser is surveyed high research the earliest, surveys the development aspect high and use at coherent laser to be in rank first.In the Apollo lunar exploration engineering in 1971-1972, use laser altimeter the earliest.Launched spaceborne lunar exploration laser altimeter Ke Laimangdina in 1994.Launched spaceborne Mars observation laser altimeter in 1996 again.Launched spaceborne geoscience laser altimeter in 2003.
China is in Tenth Five-Year Plan Period, the Shanghai ray machine and Anhui ray machine institute also carried out the high research of coherent laser survey.Having carried laser altimeter in " goddess in the moon " lunar exploration engineering that started in 2002, be used for the three-dimensional measurement of moonscape, is the first active laser detection instrument of China's independent research.
Summary of the invention
Purpose of the present invention will provide a kind of coherent laser height measuring frequency demodulation circuit exactly, to reduce the volume of system.Function that this circuit should have the real-time frequency demodulation, produces chirp signal, acoustooptic modulation drives and continuous coverage, simple in structure, easy and simple to handle, advantage that cost is low.
Technical solution of the present invention is as follows:
A kind of coherent laser height measuring frequency demodulation circuit is characterised in that its formation comprises:
One photodetector, the output termination Hi-pass filter of this photodetector, an input end of output termination first frequency mixer of this Hi-pass filter;
The input end of the output termination chirp signal generator of one signal generator, another input end of output termination first frequency mixer of this chirp signal generator;
Output termination first low-pass filter of described first frequency mixer, the output of this first low-pass filter is divided into two-way: the one tunnel connects an input end of second frequency mixer, and another road connects an input end of three-mixer;
The output terminal of local oscillator connects another input end of second frequency mixer through 90 ° of phase shifters, and the output terminal of this second frequency mixer connects data collecting card through second low-pass filter;
Another input end of the output termination three-mixer of local oscillator, the output terminal of this three-mixer connects described data collecting card through the 3rd low-pass filter;
The output that obtains behind the low-pass filter of crystal oscillator output signal in local oscillator of local oscillator is as the drive source of acousto-optic modulator.
The course of work of coherent laser height measuring frequency demodulation circuit of the present invention:
Photodetector receives the light signal that contains range information, and the electric signal of its output passes through first mixer action jointly with chirp signal generator output signal after the Hi-pass filter effect, obtain output signal through the first low-pass filter effect again.This output signal is divided into two-way again, one the tunnel outputs to data collecting card by second low-pass filter with the local oscillator output signal after by first mixer action again, another road with output to data collecting card by the 3rd low-pass filter through the local oscillator output signal of 90 ° of phase shifts again after by second mixer action.Wherein, the input signal of chirp signal generator is provided by signal generator.Simultaneously, with the output signal that obtains behind the low-pass filter of crystal oscillator output signal in local oscillator in the local oscillator drive source as AOM.
Described photodetector is PIN photodiode (P-type intrinsic N-type PhotoDiode is designated hereinafter simply as PIN photodiode).
Described local oscillator is made up of the bandpass filter that crystal oscillator and the band connection frequency of 55MHz is 55MHz.
Described 90 ° of phase shifts are made of chip and concentric cable.
The external power supply of described circuit is ± 15V that all the other voltages are obtained by the internal circuit variation.
Described acousto-optic modulator (AOM) is made up of crystal oscillator and one-level low-pass filter.
Described chirp signal generator is made of analog multichannel switch.
The course of work is as follows:
Photodetector receives the chirp signal that contains range information, and the electric signal of its output passes through first mixer action jointly with chirp signal generator output signal after the first Hi-pass filter effect, obtain output signal through the first low-pass filter effect again.This output signal is divided into two-way again, one the tunnel outputs to data collecting card by second low-pass filter with the local oscillator output signal after by first mixer action again, another road with output to data collecting card by the 3rd low-pass filter through the local oscillator output signal of 90 ° of phase shifts again after by second mixer action.Wherein, the input signal of chirp signal generator is provided by signal generator.
Simultaneously, with the output signal that obtains behind the low-pass filter of crystal oscillator output signal in local oscillator in the local oscillator drive source as AOM.
Coherent laser height measuring frequency demodulation circuit of the present invention is promptly realized the circuit that range information extracts, and its principle of work is described as follows:
The principle of work of coherent laser height-finding system is mainly chirp signal and handles.
Chirp signal can be expressed as:
Wherein, f
0,
Be respectively original frequency and initial phase, T is the signal pulse duration, and k=B/T is the chirp signal frequency change rate, and B is the chirp signal bandwidth.
System launches chirp signal earthward, and this signal is got back to system receiving terminal after the ground return effect, and be τ time delay, and the chirp signal that then returns can be expressed as:
Wherein,
Random phase for return signal.To launch chirp signal and return chirp signal and carry out mixing, and after the low-pass filter effect filters high fdrequency component, obtain:
As can be seen, relevant with time t have only second 2 π kt τ, just can obtain signal frequency f thus
τAnd the pass between measuring distance L is
Wherein, c is the light velocity.Therefore, as long as measure signal frequency f
τ, just can directly obtain measuring distance L.
Owing to the existence of the reasons such as frequency drift of system works environment, polarization and laser instrument self, the phase place of the light signal that system detects is changed, in coherent detection, will influence the precision of measurement.Therefore, in coherent laser height measuring frequency demodulation circuit by 90 ° of phase shifts to address the above problem.Its principle is as follows, promptly successively is respectively through output signal after mixing and the low-pass filtering without 90 ° of phase shifts with through two channel signals of 90 ° of phase shifts
With
P (t wherein
n) be the envelope value of detectable signal, φ (t
n) be the arbitrary phase value of detectable signal.Therefore,
Removed the component composition that contains the arbitrary phase value, reached the removal arbitrary phase and changed the detectable signal influence on signal-to-noise ratio (SNR).
For 90 ° of phase shifters of this circuit is that to choose gain be that the method for concentric cable by electronics of 1 operational amplifier and certain-length realizes 90 ° of phase shifts, signal is that the transmission delay on the coaxial wire of 50 Ω is 5ns/m in characteristic impedance, can calculate corresponding to time delay of 90 ° of phase shifts according to the transmission signals cycle thus, eliminate the influence of extraneous factor the detectable signal phase place thereby reach.
In this circuit design process, thereby local oscillator makes it and electric signal of gained carries out mixing after the photodetector conversion, low-pass filtering reduces the intractability to output data greatly by designing, and bandwidth is controlled in the 2MHz scope.
Technique effect of the present invention is as follows:
1, the present invention is 1 the operational amplifier and the coaxial wire of certain-length by electronics method by adopting gain, is easy to realize 90 ° of phase shifts, has that debugging is convenient, stable performance and a low advantage of cost.
2, local oscillator and low-pass filtering reduce the output signal bandwidth simultaneously, and bandwidth is in the 2MHz, has reduced the sample frequency to the back data collecting card, the requirement of bandwidth and the difficulty of data processing.
3, AOM driving, chirp signal generator and frequency demodulation circuit are integrated on the circuit board, plank is of a size of 85 * 63mm
2Thereby, reduced system bulk, reduced system cost.
Description of drawings
Fig. 1 is the structural representation of coherent laser height measuring frequency demodulation circuit of the present invention.
Among the figure: 1-photodetector, 2-the first Hi-pass filter, 3-signal generator, 4-chirp signal generator, 5-the first frequency mixer, 6-the first low-pass filter, 7-local oscillator, 8-90 ° of phase shift, 9-the second frequency mixer, 10-the three-mixer, 11-the second low-pass filter, 12-the three low-pass filter, 13-data collecting card.
Embodiment
The invention will be further described below in conjunction with drawings and Examples.
See also Fig. 1 earlier, Fig. 1 is the structural representation of coherent laser height measuring frequency demodulation circuit embodiment of the present invention.As seen from the figure, the formation of coherent laser height measuring frequency demodulation circuit of the present invention comprises photodetector 1, Hi-pass filter 2, signal generator 3, chirp signal generator 4, first frequency mixer 5, first low-pass filter 6, second frequency mixer 9, three-mixer 10, local oscillator 7,90 ° of phase shifters 8, second low-pass filter 11, the 3rd low-pass filter 12, data collecting card 13, its position relation is: photodetector 1 receives the light signal that contains range information, the electric signal of its output is after Hi-pass filter 2 effects, act on by first frequency mixer 5 jointly with the output signal of chirp signal generator 4, obtain output signal through 6 effects of first low-pass filter again.This output signal is divided into two-way again, one the tunnel outputs to data collecting card 13 by the 3rd low-pass filter 12 with local oscillator 7 output signals after by three-mixer 10 effect again, another road with output to data collecting card 13 by second low-pass filter 11 through local oscillator 7 output signals of 90 ° of phase shifts 8 again after by 9 effects of second frequency mixer.Wherein, the input signal of chirp signal generator 4 is provided by signal generator 3.
Present embodiment is with the output signal that obtains behind the low-pass filter of crystal oscillator output signal in local oscillator in the local oscillator 7 drive source as acousto-optic modulator (Acousto-opticalModulators is designated hereinafter simply as AOM).Concrete selection is as follows in the present embodiment:
Described photodetector 1 is a PIN photodiode, and described PIN photodiode is the InGaAs G9806 series with preposition enlarging function.Simultaneously, placing the one-level cutoff frequency after PIN photodiode is that the Hi-pass filter 2 of 55MHz is to eliminate The noise.
Described first low-pass filter 5, its cutoff frequency is 120MHz.
Described local oscillator 7 is made up of the bandpass filter that crystal oscillator and the band connection frequency of 55MHz is 55MHz, described crystal oscillator is the KDS-6D model, described bandpass filter is combined by low-pass filter and Hi-pass filter, and the definite of its cutoff frequency obtained by following formula:
Described 90 ° of phase shifters 8 are made of the concentric cable of integrated operational amplifier chip AD811 and certain-length, and according to the actual conditions of circuit design, the concentric cable line length is chosen as 120cm.
The external power supply of described circuit is ± 15V, and all the other voltages are changed by internal circuit and obtain, circuit is inner need uses+3.3V ,+5V, employing MC7805 and LM317 obtain required voltage.
Described AOM drives and is made up of crystal oscillator and one-level low-pass filter, drives requirement according to AOM, and obtaining frequency by low-pass filter filtering is that 55MHz, voltage are the sinusoidal signal driving AOM of 4.8V.
Described chirp signal generator 4 is made of analog multichannel switch MAX4644.
The centre frequency of considering the processing of circuit signal is 55MHz, belongs to the high-frequency circuit scope of design.Therefore, the making situation of its printed circuit board (PCB) is directly determining the degree of functioning of circuit output signal.When drawing the printed circuit board (PCB) of system circuit, feedback resistance and the wire length between gain resistor of operational amplifier A D811 must be crosstalked with minimizing less than 6.35mm, and the line line length is taken as 2.286mm in this circuit design.Distance between each components and parts is the shortest as far as possible, simultaneously, and in order to reduce the area that electromagnetic radiation also will reduce printed circuit board (PCB) self.
The present invention adopts the electronics components and parts to realize coherent laser height measuring frequency demodulation circuit, thereby eliminated the high and big influence of late time data intractability to the light path alignment requirements when realizing the range information extraction, realized simultaneously the function that chirp signal output and AOM drive again, make easy operating simple in structure, and owing to adopt electronics method not need to calibrate repeatedly the requirement that has directly realized 90 ° of phase shifts, can once finish the debugging of system, therefore have simple in structurely be easy to regulate, cost is low, volume is little advantage.
Claims (5)
1. coherent laser height measuring frequency demodulation circuit is characterised in that its formation comprises:
The output termination Hi-pass filter (2) of photodetector (1), an input end of output termination first frequency mixer (5) of this Hi-pass filter (2);
The input end of the output termination chirp signal generator (4) of signal generator (3), another input end of output termination first frequency mixer (5) of this chirp signal generator (4);
Output termination first low-pass filter (6) of described first frequency mixer (5), the output of this first low-pass filter (6) is divided into two-way: the one tunnel connects an input end of second frequency mixer (9), and another road connects an input end of three-mixer (10);
90 ° of phase shifters of the output terminal of local oscillator (7) (8) connect another input end of second frequency mixer (9), and the output terminal of this second frequency mixer (9) connects data collecting card (13) through second low-pass filter (11);
Another input end of the output termination three-mixer (10) of local oscillator (7), the output terminal of this three-mixer (10) connects described data collecting card (13) through the 3rd low-pass filter (12);
The output that the output signal of crystal oscillator obtains after the bandpass filter of local oscillator in the local oscillator (7) is as the drive source of acousto-optic modulator.
2. coherent laser height measuring frequency demodulation circuit according to claim 1 is characterized in that described photodetector (1) is PIN photodiode.
3. coherent laser height measuring frequency demodulation circuit according to claim 1 is characterized in that described local oscillator (7) is made up of the bandpass filter that crystal oscillator and the band connection frequency of 55MHz is 55MHz.
4. coherent laser height measuring frequency demodulation circuit according to claim 1 is characterized in that described 90 ° of phase shifters (8) are made of integrated operational amplifier chip and concentric cable.
5. according to each described coherent laser height measuring frequency demodulation circuit of claim 1 to 4, it is characterized in that described chirp signal generator (4) is made of analog multichannel switch.
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| CN101261323B (en) * | 2008-04-29 | 2010-10-27 | 中国科学院上海光学精密机械研究所 | Synthetic aperture laser image-forming radar non-linear chirp phase error overcoming method and device |
| CN102608615B (en) * | 2012-03-08 | 2013-10-09 | 东华大学 | Laser radar speed/range measurement method based on chirp amplitude modulation and coherent detection |
| TWI708070B (en) * | 2015-10-22 | 2020-10-21 | 新加坡商海特根微光學公司 | Optical crosstalk calibration for ranging systems |
| CN111580068A (en) * | 2020-05-28 | 2020-08-25 | 云南电网有限责任公司电力科学研究院 | Remote sensing data processing method based on satellite laser radar technology |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1063891C (en) * | 1993-08-10 | 2001-03-28 | 索尼公司 | Frequency demodulation circuit |
| CN1436396A (en) * | 2000-06-14 | 2003-08-13 | 因芬尼昂技术股份公司 | Demodulation circuit and demodulation method |
| CN201044432Y (en) * | 2007-04-27 | 2008-04-02 | 中国科学院上海光学精密机械研究所 | Coherent laser altimetry frequency demodulation device |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1063891C (en) * | 1993-08-10 | 2001-03-28 | 索尼公司 | Frequency demodulation circuit |
| CN1436396A (en) * | 2000-06-14 | 2003-08-13 | 因芬尼昂技术股份公司 | Demodulation circuit and demodulation method |
| CN201044432Y (en) * | 2007-04-27 | 2008-04-02 | 中国科学院上海光学精密机械研究所 | Coherent laser altimetry frequency demodulation device |
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