Full waveform and single photon counting mixed distance measurement system and method

Abstract

The invention discloses a full waveform and single photon counting mixed distance measurement system and method, and the method employs a high-speed ADC to directly collect analog pulse signals generated by a single photon detector, obtains the full waveform, achieves the waveform recognition and cutting through the analysis of a first-order local extreme point, and employs a single photon waveform high-speed fitting algorithm to achieve the measurement of the full waveform and single photon counting mixed distance. The peak moment of the analog pulse signal is obtained with high precision, distance walking errors and time interval measurement errors are effectively suppressed, and the improvement of the single-photon distance measurement precision is realized by further combining with a time-dependent single-photon coincidence counting method.

Description

Technical Field

[0001] The invention relates to a full waveform and single photon counting hybrid distance measurement system and method, belonging to the technical field of deep space detection and inter-satellite distance measurement. Background Art

[0002] Single photon ranging is a time-of-flight laser ranging technology based on single photon detection. It uses single photon detectors and time-correlated single photon coincidence counting (TCSPC) to achieve quantum limit sensitivity at the single photon level. In a typical single photon ranging system, the analog pulse signal generated by the single photon detector needs to enter the signal conditioning circuit to obtain a digital pulse signal before single photon counting time measurement. The signal conditioning module includes devices such as the front-end amplifier, LVPECL level high-speed comparator, and high-speed LVTTL level converter. Combined with fixed threshold identification technology, it realizes analog pulse to digital pulse conversion; then the processor (FPGA, etc.) accumulates the digital pulses collected from multiple laser pulse cycles, forms a counting peak in the time domain to achieve flight time measurement, and eliminates randomly distributed dark counts. However, the time measurement of this method is easily affected by the intensity of the analog pulse. The time when the voltage of different intensities reaches the threshold will vary, resulting in distance travel errors; and due to the limited clock frequency of the multi-phase clock sampling method, the pulse and clock are difficult to synchronize, introducing time interval measurement errors. The above factors lead to a decrease in the accuracy of single photon ranging. Summary of the invention

[0003] The technical problem solved by the present invention is: in view of the problem that the single-photon distance measurement accuracy is insufficient and easily affected in the current prior art, a full-waveform and single-photon counting hybrid distance measurement system and method are proposed.

[0004] The present invention solves the above technical problems by the following technical solutions:

[0005] A full-waveform and single-photon counting hybrid distance measurement system includes an optical receiving module, a single-photon detector, a full-waveform acquisition module, an FPGA processor, a DSP processor, a laser control module, a pulsed laser, and an optical transmitting module. Figure 1 As shown, where:

[0006] The optical receiving module receives an externally transmitted optical signal and transmits it to a single-photon detector;

[0007] The single-photon detector collects the optical signal transmitted by the optical receiving module, performs photoelectric conversion, and then outputs the single-photon analog signal to the full waveform acquisition module;

[0008] The full waveform acquisition module receives the single photon analog signal output by the single photon detector, performs sampling processing, and then sends the electrical analog signal to the FPGA processor;

[0009] The FPGA processor receives the electrical analog signal for signal recognition and waveform fitting, and transmits the peak moment obtained after processing to the DSP processor; it sends pulse control instructions to the laser control module according to the requirements of the light detection task;

[0010] The DSP processor performs single photon counting and histogram statistics according to the peak moment sent by the FPGA processor to obtain the distance measurement value;

[0011] The laser control module generates a laser pulse signal according to the received pulse control instruction and transmits it to the optical transmitting module;

[0012] The optical transmitting module receives the laser pulse signal and sends it to the target surface according to the beam direction determined by the light detection task requirements.

[0013] The full waveform acquisition module is provided with a high-speed ADC to acquire the single-photon analog signal generated by the single-photon detector, convert the single-photon analog signal into an electrical analog signal, obtain the full waveform according to the electrical analog signal, perform waveform recognition and clipping on the full waveform, and obtain the peak moment of the electrical analog signal through single-photon waveform fitting processing to suppress distance travel error and time interval measurement error.

[0014] The optical emission module emits the laser pulse signal according to the light beam direction determined by the light detection task requirements; the single-photon detection module converts the single-photon analog signal into an electrical analog signal through photoelectric conversion; the FPGA processor is used to perform a first-order local extreme point analysis on the electrical analog signal output by the full waveform acquisition module to determine the peak moment.

[0015] The single photon waveform criterion is:

[0016]

[0017] Where P l is the number of cropping points on the left side of the local maximum point, P r is the number of cropping points on the right side of the local maximum point, and the waveform that meets the single-photon waveform criterion is regarded as a single-photon waveform.

[0018] The method by which the FPGA processor receives an electrical analog signal for signal recognition is:

[0019] The electrical analog signal is received to perform single photon waveform judgment to eliminate noise errors, and the P centered at the local maximum point of the electrical analog signal is l +P r +1 point and the sampling point number t corresponding to the local maximum point n The signal is cached in the FPGA processor and the next single-photon analog signal is converted into photoelectric format and recognized.

[0020] The method for fitting the signal waveform and obtaining the peak moment is:

[0021] The single-photon analog signal is converted into a quadratic curve representation, and the single-photon waveform is identified and processed with the local maximum point of the electrical analog signal as the center. l +P r The +1 point waveform is rewritten into a rectangular form, and the complete waveform is determined using the least squares method, and the peak moment is marked according to the coordinates of the waveform center point.

[0022] The single photon simulation signal expression is:

[0023] z=a·t 2 +b·t+c

[0024] Intercepted P l +P r The matrix form expression of the +1 point waveform is:

[0025]

[0026] In the formula, D=(X T X)X T Z, coordinate of the center point of the waveform t n '=-b / 2a, recorded as the peak moment.

[0027] A measurement method implemented by a hybrid distance measurement system, comprising:

[0028] Start the hybrid distance measurement system, generate pulse control instructions according to the light detection task requirements and send them to the laser control module;

[0029] The laser control module controls the pulse laser to emit laser pulses, and emits them toward the target surface according to the beam direction preset by the optical emission;

[0030] The optical receiving module receives the externally transmitted optical signal, and the single-photon detector collects the signal and outputs the single-photon analog signal to the full-waveform acquisition module;

[0031] After receiving the full waveform acquisition module, the sample processing is performed and the electrical analog signal is sent to the FPGA processor;

[0032] The electrical analog signal is processed by the FPGA processor for signal recognition and waveform fitting, and the peak moment obtained after processing is transmitted to the DSP processor;

[0033] Single photon counting and histogram statistics are performed at the peak moment to obtain distance measurement values.

[0034] The waveform fitting processing method is:

[0035] A standard Gaussian model is used to describe the single-photon simulation signal, and the single-photon simulation signal is converted into a quadratic curve representation;

[0036] Perform waveform fitting on the quadratic curve to obtain the peak value, select a preset number of points with the peak value as the center, confirm the count value and parabola value at the corresponding time, and use the matrix solution method to calculate the count value at the time corresponding to the center coordinate of the parabola;

[0037] Perform histogram statistics on all the count values ​​corresponding to a single laser emission, select the count value at the moment with the largest amount of corresponding data, and subtract it from the count value at the moment of a single laser emission to the final count value at the moment of this laser exposure. Convert the final count value into a distance value as the distance measurement value for this measurement.

[0038] The single-photon simulation signal is converted into a quadratic curve representation, and the single-photon signal is described using the standard Gaussian model:

[0039]

[0040] Where t is the sampling time, A, τ and w are the pulse amplitude, pulse time scale and pulse width respectively. The parabola parameters are set after taking the logarithm of both sides to simplify the single-photon simulation signal into a parabola:

[0041]

[0042] Then the single photon simulation signal can be simplified to a parabola:

[0043] z=a·t 2 +b·t+c

[0044] The peak moment is obtained by waveform fitting, and the P centered at the local maximum point l +P r +1 point waveform, a total of n points, its time count values ​​are t0-1, t0-1+1, ...t0, t0+1, t0+2..., t0+r, and the parabola values ​​are z1, z2, ...z l+r+1 ;

[0045] Calculate the time count value t' corresponding to the center coordinate of the parabola by matrix solution;

[0046] t' is transmitted to the DSP processor. After the DSP processor obtains all t' values ​​after a single laser emission, a histogram statistics is performed on the moment count values ​​obtained for the laser emission.

[0047] The advantages of the present invention compared with the prior art are:

[0048] The present invention provides a full-waveform and single-photon counting hybrid distance measurement system and method. To address the problem that distance measurement is easily affected by analog pulse intensity and causes distance walking errors, a high-speed ADC is used to directly collect the output signal of the single-photon detector, and waveform recognition and clipping of the single-photon signal are realized through first-order local extreme point analysis, which supports the identification of the single-photon peak moment and reduces the amount of calculation. At the same time, to address the problem that the distance measurement accuracy is easily affected by the time interval measurement error, the method uses a waveform fitting algorithm to identify the waveform peak moment, thereby improving the time measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A block diagram of a full waveform and single photon counting hybrid distance measurement system provided by the present invention;

[0050] Figure 2 A schematic diagram of single photon signal recognition and clipping based on first-order local extreme point analysis provided by the present invention;

[0051] Figure 3 A schematic diagram of the waveform fitting algorithm provided by the present invention for identifying the peak moment of a waveform. DETAILED DESCRIPTION

[0052] A full-waveform and single-photon counting hybrid distance measurement system and method, which uses a high-speed ADC to directly collect the analog pulse signal generated by a single-photon detector to obtain its full waveform, realizes waveform recognition and clipping through first-order local extreme point analysis, and uses a single-photon waveform high-speed fitting algorithm to obtain the peak moment of the analog pulse signal with high precision, effectively suppressing the distance travel error and time interval measurement error, and further combines the time-correlated single-photon coincidence counting method to achieve the improvement of single-photon ranging accuracy.

[0053] The following is further described in conjunction with the accompanying drawings and preferred embodiments of the specification:

[0054] In the current embodiment, the full-waveform and single-photon counting hybrid distance measurement system mainly includes an optical receiving module, a single-photon detector, a full-waveform acquisition module, an FPGA processor, a DSP processor, a laser control module, a pulsed laser, and an optical transmitting module;

[0055] The measurement system of the full-waveform and single-photon counting hybrid distance measurement method is shown in Figure 1, and its components include a full-waveform sampling circuit for collecting single-photon analog signals; a laser control circuit for generating a driving signal for a pulsed laser; an FPGA for implementing first-order local extreme point analysis and waveform fitting algorithms; a DSP for time measurement histogram statistics; a pulsed laser for emitting laser pulses; an optical transmitting system for beam pointing; an optical receiving system for stray light suppression and return light reception; and a single-photon detection circuit for generating single-photon analog signal electrical pulses through photoelectric conversion.

[0056] The full waveform and single photon counting hybrid distance measurement method has the following specific steps:

[0057] The system starts, and the FPGA controls the laser control circuit to generate a pulse signal to drive the pulse laser to emit laser pulses;

[0058] The single-photon detection circuit receives the single-photon signal and converts it into an electrical analog signal;

[0059] The full waveform sampling circuit uses a high-speed ADC to collect the electrical analog signal output by the single-photon detector, and the collection result is transmitted to the FPGA;

[0060] The FPGA continues to use the first-order local extreme point analysis algorithm to realize the recognition and clipping of multiple single-photon signals, and then obtains the precise peak moment through the waveform fitting algorithm, and transmits the peak moment to the DSP;

[0061] DSP receives multiple peak moments, and performs single photon counting and histogram statistics on the peak moments, further obtaining more accurate moments, and converting them into distance measurement values ​​based on the time-distance conversion relationship;

[0062] After completing a distance measurement, switch to single photon signal and electrical analog signal conversion and start the next measurement again.

[0063] In the specific steps of the full waveform and single photon counting hybrid distance measurement method, the schematic diagram of the first-order local extreme point analysis algorithm is as follows: Figure 2 When the FPGA receives the sampling data transmitted in real time by the high-speed ADC, it determines whether the current waveform is a single-photon waveform through the following criteria. The synchronous use of the digital recognition threshold Vth and the local comparison can effectively eliminate the misidentification of noise.

[0064]

[0065] Where P l is the number of cropping points on the left side of the local maximum point, P r is the number of cropping points on the right side of the local maximum point. The waveform that meets the following conditions is confirmed as a valid waveform. l +P r +1 point and the sampling point number t corresponding to the local maximum point n It is cached inside the FPGA and then sent to the waveform fitting algorithm module, while continuing to identify and cut out the next valid single-photon signal.

[0066] In the specific steps of the full waveform and single photon counting hybrid distance measurement method, the waveform fitting algorithm schematic diagram is as follows Figure 3 According to the properties of the single-photon simulation signal, it is approximated as a quadratic curve and can be expressed by the following formula:

[0067] z=a·t 2 +b·t+c

[0068] The intercepted P l +P r +1 point waveform rewritten in matrix form:

[0069]

[0070] Then use the least squares principle to get the value of D, D = (X T X)X T Z, and then obtain the coordinates of the waveform center point t n '=-b / 2a, recorded as the peak moment, and sent to DSP.

[0071] The waveform fitting processing method is:

[0072] First, the single-photon simulation signal is converted into a quadratic curve representation. The process is as follows: First, the single-photon signal is described using a standard Gaussian model:

[0073]

[0074] In the formula, t is the sampling time, A, τ and w are the pulse amplitude, pulse time scale and pulse width respectively. Taking the logarithm of both sides, we can get:

[0075]

[0076] make:

[0077]

[0078] Then the single photon simulation signal can be simplified to a parabola:

[0079] z=a·t 2 +b·t+c

[0080] Secondly, the peak moment is obtained by waveform fitting, and the P centered at the local maximum point is l +P r +1 point waveform, a total of n points, its time count values ​​are t0-1, t0-1+1, ...t0, t0+1, t0+2..., t0+r, and the parabola values ​​are z1, z2, ...z l+r+1 .

[0081] Then, the time count value t' corresponding to the center coordinate of the parabola can be calculated by matrix solution. Taking l=2 and r=2 as an example, t' can be expressed as:

[0082]

[0083] Then, t' is transmitted to the DSP processor. After the DSP processor obtains multiple t' values ​​after a single laser emission, it performs histogram statistics on the moment count values ​​obtained for this laser emission. The moment value with the largest amount of data in the histogram is subtracted from the laser emission moment count value to obtain the final moment count value of this laser detection. According to the principle of flight time, the final moment count value is converted into the corresponding distance value to obtain the distance value of this measurement.

[0084] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0085] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A full waveform and single photon counting hybrid distance measurement system, characterized in that: It includes an optical receiving module, a single photon detector, a full waveform acquisition module, an FPGA processor, a DSP processor, a laser control module, a pulse laser, and an optical transmitting module, wherein: The optical receiving module receives an externally transmitted optical signal and transmits it to a single-photon detector; The single-photon detector collects the optical signal transmitted by the optical receiving module, performs photoelectric conversion, and then outputs the single-photon analog signal to the full waveform acquisition module; The full waveform acquisition module receives the single photon analog signal output by the single photon detector, performs sampling processing, and then sends the electrical analog signal to the FPGA processor; The FPGA processor receives the electrical analog signal for signal recognition and waveform fitting, and transmits the peak moment obtained after processing to the DSP processor; it sends pulse control instructions to the laser control module according to the requirements of the light detection task; The DSP processor performs single photon counting and histogram statistics according to the peak moment sent by the FPGA processor to obtain the distance measurement value; The laser control module generates a laser pulse signal according to the received pulse control instruction and transmits it to the optical transmitting module; The optical transmitting module receives the laser pulse signal and sends it to the target surface according to the beam direction determined by the light detection task requirements.

2. A full waveform and single photon counting hybrid distance measurement system according to claim 1, characterized in that: The full waveform acquisition module is provided with a high-speed ADC to acquire the single-photon analog signal generated by the single-photon detector, convert the single-photon analog signal into an electrical analog signal, obtain the full waveform according to the electrical analog signal, perform waveform recognition and clipping on the full waveform, and obtain the peak moment of the electrical analog signal through single-photon waveform fitting processing to suppress distance travel error and time interval measurement error.

3. A full waveform and single photon counting hybrid distance measurement system according to claim 1, characterized in that: The method for the FPGA processor to receive the electrical analog signal and perform signal recognition is: The electrical analog signal is received to perform single photon waveform judgment to eliminate noise errors, and the P centered at the local maximum point of the electrical analog signal is l +P r +1 point and the sampling point number t corresponding to the local maximum point n The signal is cached in the FPGA processor and the next single-photon analog signal is converted into photoelectric format and recognized.

4. A full waveform and single photon counting hybrid distance measurement system according to claim 3, characterized in that: The method for fitting the signal waveform and obtaining the peak moment is: The single-photon analog signal is converted into a quadratic curve representation, and the single-photon waveform is identified and processed with the local maximum point of the electrical analog signal as the center. l +P r The +1 point waveform is rewritten into a rectangular form, and the complete waveform is determined using the least squares method, and the peak moment is marked according to the coordinates of the waveform center point.

5. The full waveform and single photon counting hybrid distance measurement system according to claim 3, characterized in that: The single photon waveform criterion is: Where P l is the number of cropping points on the left side of the local maximum point, P r is the number of cropping points on the right side of the local maximum point, and the waveform that meets the single-photon waveform criterion is regarded as a single-photon waveform.

6. A full waveform and single photon counting hybrid distance measurement system according to claim 3, characterized in that: The single photon simulation signal expression is: z=a·t 2 +b·t+c Intercepted P l +P r The matrix form expression of the +1 point waveform is: In the formula, D = (X T X)X T Z, coordinate of the center point of the waveform t n '=-b / 2a, recorded as the peak moment.

7. A measurement method implemented by the hybrid distance measurement system according to claim 1, characterized in that include: Start the hybrid distance measurement system, generate pulse control instructions according to the light detection task requirements and send them to the laser control module; The laser control module controls the pulse laser to emit laser pulses, and emits them toward the target surface according to the beam direction preset by the optical emission; The optical receiving module receives the externally transmitted optical signal, and the single-photon detector collects the signal and outputs the single-photon analog signal to the full-waveform acquisition module; After receiving the full waveform acquisition module, the sample processing is performed and the electrical analog signal is sent to the FPGA processor; The electrical analog signal is processed by the FPGA processor for signal recognition and waveform fitting, and the peak moment obtained after processing is transmitted to the DSP processor; Single photon counting and histogram statistics are performed at the peak moment to obtain distance measurement values.

8. A full waveform and single photon counting hybrid distance measurement system according to claim 7, characterized in that: The waveform fitting processing method is: A standard Gaussian model is used to describe the single-photon simulation signal, and the single-photon simulation signal is converted into a quadratic curve representation; Perform waveform fitting on the quadratic curve to obtain the peak value, select a preset number of points with the peak value as the center, confirm the count value and parabola value at the corresponding time, and use the matrix solution method to calculate the count value at the time corresponding to the center coordinate of the parabola; Perform histogram statistics on all the count values ​​corresponding to a single laser emission, select the count value at the moment with the largest amount of corresponding data, and subtract it from the count value at the moment of a single laser emission to the final count value at the moment of this laser exposure. Convert the final count value into a distance value as the distance measurement value for this measurement.

9. A full waveform and single photon counting hybrid distance measurement system according to claim 8, characterized in that: The method to convert the single photon simulation signal into a quadratic curve representation is: The single photon simulation signal is described using the standard Gaussian model: Where t is the sampling time, A, τ and w are the pulse amplitude, pulse time scale and pulse width respectively. After taking the logarithm of both sides, the parabola parameters are set to simplify the single-photon simulation signal into a parabola for subsequent signal processing.

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