Laser ranging device based on FPGA and single photon avalanche diode

Abstract

The invention provides a laser ranging device based on an FPGA (Field Programmable Gate Array) and a single photon avalanche diode. The device is characterized in that the distance measuring device is composed of a field programmable logic gate array calculation core (1), a quenching circuit (2), a single photon avalanche diode (3), a pulse laser driving circuit (4), a pulse laser (5) and an optical lens system (6), and the field programmable logic gate array calculation core (1) comprises time digital conversion logic (11) and calculation logic (12). Wherein the time-to-digital conversion logic comprises correction algorithm logic (111) and carry chain logic (112). According to the invention, a single photon avalanche diode and a dark counting correction algorithm are combined to solve the problems of low precision, low linearity and short measurement distance of the existing distance measurement device. The method can be used for detecting the distance by laser, and can be widely applied to the fields of automotive electronics, medical treatment, industrial robots, national defense, aerospace and the like.

Description

(I) Technical field

[0001] The present invention relates to a laser distance measuring device based on FPGA and single photon avalanche diode, which can be used in laser radar, industrial distance measurement, aerospace distance measurement field, and belongs to the field of photoelectric detection technology. (II) Background technology

[0002] The single photon detection technology used in this device is a photoelectric detection technology. The principle is to use the photoelectric effect to count the incident single photons to detect extremely weak signals. It is the core of extremely weak light measurement such as laser ranging, DNA sequencing, quantum key distribution, lidar and medical imaging. With the advancement of semiconductor process technology and the improvement of integrated circuit design level, it is possible to design single photon avalanche diodes using standard integrated circuit technology and integrate single photon avalanche diodes with related integrated circuits such as avalanche event sensing circuits, quenching circuits, and back-end signal processing circuits on the same chip. Compared with traditional single photon detection devices such as photomultiplier tubes (PMT) or microchannel plates (MCP), such products operate at lower bias voltages, have smaller size, lower power consumption, are insensitive to electromagnetic noise, have high integration, low cost, good repeatability, and have broad application prospects.

[0003] In the photon detection / imaging system based on the single-photon avalanche diode, the system detects and counts the avalanche events stimulated by the hole-electron pairs generated inside the single-photon avalanche diode. The avalanche breakdown events in the single-photon avalanche diode are not only stimulated by photon absorption, but also by other factors. The avalanche events stimulated under lightless conditions are independent of photon absorption, and the counting of these avalanche events is called dark count. The dark count rate is an important parameter of the single-photon avalanche diode. A high dark count rate will reduce the signal-to-noise ratio of the single-photon system, increase the system bit error rate, increase the integration (exposure) time required by the imaging system, and reduce the detection sensitivity. The dark count has a random characteristic and is approximately uniformly distributed over the entire time range. The device using SPAD for ranging uses the direct time-of-fly (DTOF) technology. This technology requires measuring the time difference between the laser sending the signal and the receiving signal, and using the time-to-digital convert (TDC) to convert it into a digital signal for subsequent algorithm processing. The current mainstream solutions include 1) using an external integrated TDC chip and 2) using the internal delay chain resources of the FPGA. The internal delay chain resources of the FPGA require correction of the delay chain, usually using average correction count or code density correction technology.

[0004] Among them, the solution using an external integrated TDC chip is usually limited to about 100 frames in measurement frame rate due to communication limitations with external chips, and requires additional dedicated chips, resulting in high system complexity and cost. The solution using the internal delay chain resources of the FPGA can achieve a higher measurement frame rate. Among them, the average correction solution in the correction solution has poor linearity and cannot achieve linear measurement. In the traditional code density correction solution, if the internally generated random signal is used as the correction source to start the correction solution when it is first powered on, linearity errors will still occur after the chip temperature changes. If correction is performed after temperature changes, additional temperature sensors and temperature monitoring logic need to be added. The solution of correcting once at a fixed time cannot perform measurements during the correction process.

[0005] The present invention proposes a laser ranging device based on FPGA and single photon avalanche diode, which uses the internal delay chain resources of FPGA to realize TDC, improves the code density correction scheme, and uses the dark count of SPAD in the ranging interval as the random signal source for code density correction, which is different from the traditional internal random signal generation scheme. The probability histogram statistics are performed during ranging, and the correction parameters are updated after the statistics reach 10,000 times. The improved code density correction scheme for this device is called the dark count correction scheme. The device can continuously perform linearity correction without affecting real-time measurement, and greatly enhances the linearity and stability of the system without increasing the complexity of the system. (III) Summary of the invention

[0006] The object of the present invention is to provide a low-noise single-photon detection system, which comprises a distance measuring device, a field programmable logic gate array computing core (1), a quenching circuit (2), a single-photon avalanche diode (3), a pulse laser driving circuit (4), a pulse laser (5), and an optical lens system (6), wherein the field programmable logic gate array computing core (1) comprises a time-to-digital conversion logic (11) and a computing logic (12), wherein the time-to-digital conversion logic comprises a correction algorithm logic (111) and a carry chain logic (112).

[0007] The object of the present invention is achieved as follows: the distance measuring device is composed of a field programmable logic gate array computing core (1), a quenching circuit (2), a single photon avalanche diode (3), a pulse laser driving circuit (4), a pulse laser (5), and an optical lens system (6), wherein the field programmable logic gate array computing core (1) contains time digital conversion logic (11) and computing logic (12), wherein the time digital conversion logic contains correction algorithm logic (111) and carry chain logic (112); in the system, the field programmable logic gate array (1) generates a signal to enable the pulse laser driving circuit (4) to drive the pulse laser (5) to generate a pulse laser, and the pulse laser is emitted through the optical lens system (6) to emit a high-power collimated pulse laser, and the laser is reflected by the target object and passes through the optical lens system (6) to cause avalanche breakdown of the single photon avalanche diode (3), and the single photon avalanche diode is quenched through the quenching circuit (2), and the avalanche breakdown signal is converted into a pulse square wave and transmitted to the field programmable logic gate array computing core (1). The time-to-digital conversion logic (11) of the field programmable logic gate array computing core (1) directly converts the signal transmitted to the laser pulse driving circuit (4) to the quenching circuit (2) to a digital quantity, and the digital quantity converted to time is counted and converted into distance by the computing logic (12). The time-to-digital conversion logic mainly records the time difference by the carry chain logic (112), and the linearity correction of the output digital quantity time difference is performed by the correction algorithm logic (111), wherein the correction algorithm logic needs to be driven by a random signal, and the random signal sources include two, the first is the random signal generated inside the field programmable logic gate array computing core (1), and the second is the signal recorded after the dark count of the single photon avalanche diode (3) is processed by the quenching circuit (2); both random signals are random; after the above process and algorithm, the device finally outputs the distance information with high accuracy and good linearity.

[0008] In the device, a single photon avalanche diode and a quenching circuit are used as the laser pulse receiving part. When a reverse bias voltage higher than the avalanche voltage is applied to both ends of the SPAD, a high-multiple internal current gain can be obtained by utilizing the avalanche breakdown effect, thereby triggering a chain reaction. At this time, a large current is generated, which is quenched by the back-end quenching circuit, and an avalanche breakdown signal is output. However, since electron-hole pairs can be generated by heat in semiconductors, even if there are no photons, that is, in dark conditions, avalanches can be triggered. This avalanche is called dark noise. This avalanche has strong randomness and can be approximately understood as being uniformly distributed over the entire time range. After the quenching circuit, a digital signal is output. The behavior of counting this signal is called dark counting. Dark counting will have a certain impact on the ranging performance, but dark counting cannot be completely eliminated. A 905nm band infrared laser is used as a generating device, and a pulsed laser driving circuit is used to drive the laser to generate a high-power laser pulse signal with a width of less than 5ns.

[0009] The FPGA internal carry chain resources are used to implement the time-to-digital converter (TDC) function. The FPGA uses the Xilinx A7 series. The carry chain is implemented by the internal CARRY4 cascade. One CARRY4 leads to four taps (CO0, CO1, CO2, CO3) corresponding to different delays. 50 delay units are used in the design, corresponding to 200 taps, a total of 200 time units, of which the average delay of the time unit is about 33ps. The entire TDC conversion logic includes coarse counting and fine counting. The coarse counting clock cycle roughly records the number of clock cycles t1 included in the time difference. The fine counting is used to reflect the fixed time difference between the clock edge and the real edge. This time is reflected by the number of carry chain time units. The final calculation method is: T=kt1+iτ-jτ In the formula, T represents the time difference, k is the number of coarse counting times, i is the number of carry chain time units of the start signal, j is the number of carry chain time units of the end signal, and τ is the average delay of the carry chain time unit.

[0010] However, due to the internal structural characteristics of the delay chain, there are time deviations in different time units, and certain changes will occur as the chip temperature changes. Usually, for scenarios with low linearity requirements, the average correction method is used, and for scenarios with high linearity requirements, the code density method is generally used for linearity correction. This ranging device has high linearity requirements and adopts an improved linearity correction scheme based on the code density method. The code density method requires the input of a set of random signals for correction. After the signal is input into the delay chain, it randomly falls at a certain position in the delay chain, and a large number of random results are counted as a histogram. A large number of random jump pulses are input into the delay chain, and the rising edge of the random pulse is sampled. The sampled data is the code density data. Since the jump signal is a random signal, it is assumed that the probability of it falling at any phase point in the reference clock (0, T) is the same, that is, the time interval t between any pulse signal and the rising edge of the reference clock is also completely random, where t ranges from (0, T). Random time interval t <t i The probability is: Then the probability that the pulse signal falls in the i-th time unit is When the number of tests is large enough, the delay time τ of the i-th time unit can be obtained i for: In the formula, T represents the middle of the reference clock, h(i) represents the height of the i-th time unit in the statistical histogram, and N represents the total number. This algorithm can obtain the delay of each time unit, and use this delay as a correction coefficient to correct the carry chain result to obtain an accurate and linear time difference digital quantity.

[0011] Delay chain correction requires the use of a random signal, and if the chip temperature changes after correction, the linearity will still change. At this time, correction can only be performed again to maintain accuracy. The present invention proposes that the first delay chain correction uses the random signal generator inside the FPGA for correction. After the first correction is completed, in the ranging gap, the position of the SPAD dark count in the delay chain is continuously counted in the histogram, and the number of dark counts is counted. When the dark count reaches a certain amount N, the histogram is calculated to obtain a new linearity correction relationship to ensure that the calibrated TDC linearity meets expectations.

[0012] After the real-time correction, the TDC has good linearity. The statistical results are filtered using the average algorithm, and the light flight time is converted into distance information Dis In the formula, Δt i represents the laser flight time obtained for each ranging, K represents the cumulative number of times, and λ represents the speed of light. Taking the average of multiple results can ensure data stability. After calculation by this algorithm, the absolute distance between the measured target and the ranging device is finally obtained. (IV) Description of the drawings

[0013] Figure 1 The distance measuring device is composed of a field programmable logic gate array computing core (1), a quenching circuit (2), a single photon avalanche diode (3), a pulse laser driving circuit (4), a pulse laser (5), and an optical lens system (6). The field programmable logic gate array computing core (1) includes a time digital conversion logic (11) and a computing logic (12). The time digital conversion logic includes a correction algorithm logic (111) and a carry chain logic (112).

[0014] Figure 2 It is a histogram of the distribution of dark counts in the time domain when SPAD is working normally. From the histogram, we can see that the SPAD dark counts are random in the time domain, which meets the requirements for random signals in the linearity correction algorithm. This signal can be recorded and used for correction algorithm statistics to perform linearity correction on the TDC implemented in the FPGA.

[0015] Figure 3This is a flowchart of linearity correction in the device. After the device is started, the first linearity correction is performed. The random signal in this linearity correction is generated by the FPGA. When the first correction parameters are completed, the ranging can be performed. This process is part of the power-on initialization. After the first linearity correction is completed, normal ranging is performed. Each ranging process is to perform laser emission, record the SPAD receiving signal, and perform algorithm calculation after accumulating 100 signals. Laser emission is not performed during the algorithm calculation. At this time, the SPAD produces a probabilistic avalanche breakdown with strong randomness. The quenching signal in this time period is recorded for statistics; the quenching signal between the ranging gaps is counted and counted. When it reaches 10,000 times, new linearity correction data is calculated. This data is updated after the calculation is completed, and subsequent ranging results are corrected according to the updated data.

[0016] Figure 4 It is the distribution statistical histogram of the avalanche breakdown signal generated by SPAD during the ranging interval and then input into the FPGA signal on the carry chain after being processed by the quenching circuit. The linearity correction parameters of the carry chain are further calculated based on this histogram. Using a 200-level carry chain, the random signal will randomly fall in a certain carry chain. If the delay of this level of carry chain is large, the probability of the random signal falling in this carry chain is higher. When the amount of data is large enough, it is reflected in the histogram that the position with a larger carry chain delay has a higher intensity, and the position with a smaller carry chain delay has a lower intensity.

[0017] Figure 5 It is a line graph comparing the impact of three different correction schemes on the ranging results: first correction only, temperature reference correction, and dark count automatic correction; the first correction only scheme can only guarantee the ranging accuracy for a short time after the device is turned on, but when the ambient temperature changes, the ranging accuracy accumulates errors. The more the ambient temperature changes, the greater the error, and the faster the ambient temperature changes, the greater the error slope; the temperature reference correction scheme combines the temperature sensor in the system, and triggers a correction when the temperature deviation reaches a certain value, but the measurement needs to be suspended during the correction process and then restarted after the correction is completed; in the dark count automatic correction scheme, the SPAD dark counts in the ranging gap are counted, and a correction is performed when a certain number is accumulated; it can be seen from the line graph that the dark count automatic correction scheme has the best repeatability accuracy.

[0018] Figure 6 After 10 hours of continuous operation, the devices using different schemes were retested at different distances to measure the effects of time and temperature on different linearity calibration schemes. The horizontal axis represents different distances, and the vertical axis represents the output distance of the device. The ideal curve is standard linear. It can be seen that only the first correction curve is greatly affected after 10 hours of continuous operation. The temperature reference correction scheme is also affected to a certain extent, and the dark count automatic correction scheme is almost not affected. (V) Specific implementation methods Embodiment 1:

[0019] Combination Figure 4 , Figure 5 To illustrate this embodiment, Figure 4 The histogram of dark counts generated in the process of the dark count automatic correction scheme in the embodiment of the laser ranging device based on FPGA and single photon avalanche diode is as follows: Figure 5 The present invention is a performance comparison diagram of the distance measuring device and other devices with the same functions but different principles. The distance measuring device is composed of a field programmable logic gate array computing core (1), a quenching circuit (2), a single photon avalanche diode (3), a pulse laser driving circuit (4), a pulse laser (5), and an optical lens system (6). The field programmable logic gate array computing core (1) includes a time digital conversion logic (11) and a computing logic (12). The time digital conversion logic includes a correction algorithm logic (111) and a carry chain logic (112). In the system, the field programmable logic gate array (1) generates a signal to enable the pulse laser driving circuit (4) to drive the pulse laser (5) to generate a pulse laser. The pulse laser is emitted through the optical lens system (6) to generate a high-power collimated pulse laser. After being reflected by the target object, the laser passes through the optical lens system (6) to cause avalanche breakdown of the single photon avalanche diode (3). The single photon avalanche diode is quenched through the quenching circuit (2), and the avalanche breakdown signal is converted into a pulse square wave and transmitted to the field programmable logic gate array computing core (1). The time-to-digital conversion logic (11) of the field programmable logic gate array computing core (1) directly converts the signal transmitted to the laser pulse driving circuit (4) to the quenching circuit (2) to a digital quantity, and the digital quantity converted to time is counted and converted into distance by the computing logic (12). The time-to-digital conversion logic mainly records the time difference by the carry chain logic (112), and the linearity correction of the output digital quantity time difference is performed by the correction algorithm logic (111). The correction algorithm logic needs to be driven by a random signal. There are two random signal sources, the first of which is a random signal generated inside the field programmable logic gate array computing core (1), and the second is a signal recorded after the dark count of the single photon avalanche diode (3) is processed by the quenching circuit (2). Both random signals have randomness.

[0020] After placing the device at a distance of 50.35 cm from the target object, the dark count correction method proposed by the present invention is compared with other correction methods. Figure 3 Flowchart, first perform the first linear correction, start distance measurement after the first linear correction, the measured distance D is 50.35 meters, keep measuring, the dark count correction histogram during the operation of the device is derived Figure 4 , the height of the first bin of the histogram is 47, and the height of the second bin is 52. The delay of the first time unit of the carry chain can be calculated The second unit delay τ2 = 26ps; the corrected delay of each delay unit can be calculated according to the formula. In one measurement, the coarse count K = 5, the fine count i = 150, and the fine count j = 49; the calculated time interval T = 60470ps, which includes the calibration system delay of 57110ps, the final TOF = 3359ps, and the conversion distance is 50.35cm, which is consistent with the actual distance.

[0021] The whole distance measurement process lasted for 180 minutes, and the distance value output by the device was continuously recorded. In order to reflect the excellence of the dark count correction algorithm adopted by the device, the measurement method was kept unchanged, and different algorithm devices were used. Two additional experiments were conducted: the first correction device and the temperature reference correction device. The final experimental data are shown in Figure 5 , sort out the experimental data and use the calculation formula The root mean square error under different conditions is calculated, among which the output root mean square error of the dark count automatic correction algorithm is RMSE1=0.0052, which is less than the expected 0.006; the root mean square error of the first correction algorithm output is RMSE2=0.0372, which is poor and fluctuates greatly due to the ambient temperature; the root mean square error of the temperature reference correction algorithm output is RMSE3=0.0071, which is greater than RMSE1, and an additional temperature sensor needs to be added to the device, which is more costly and complex. By comparing the RMSE of the ranging output under the three algorithms, it can be seen that the ranging device composed of the single photon avalanche diode and the dark count correction algorithm has high measurement accuracy and low root mean square error. At the same time, due to the high sensitivity of the single photon avalanche diode, it can be seen that the device has great innovation and improvement in ranging accuracy, linearity, maximum measurement distance and cost compared with traditional ranging devices. Embodiment 2:

[0022] Combination Figure 6 To illustrate this embodiment, Figure 6 This is a comparison chart of the output data of this device and devices with the same function but different principles under the same conditions. In order to consider the impact of different temperatures and working time on the invented device, the distance measurement module was retested at different distances after working continuously for 10 hours, and the final output results of devices using different algorithms were compared; the results are as follows Figure 6 As shown. The horizontal axis represents different distances, and the vertical axis represents the output distance of the device. The ideal curve is standard linear. It can be seen that only the first correction curve is greatly affected after 10 hours of continuous operation. The temperature reference correction curve is also affected to a certain extent. The dark count automatic correction scheme is almost unaffected. By calculating the Pearson correlation coefficient r with the ideal curve, the degree of closeness to the ideal curve can be obtained. The calculation formula is: in the formula and It represents the average of two sets of data.

[0023] The calculation shows that the Pearson correlation coefficient of the device for the first correction scheme only is r1=0.987, the Pearson correlation coefficient of the temperature reference correction scheme in the yellow paper is r2=0.991, and the Pearson correlation coefficient of this device is r3=0.997; from the data, it can be seen that the dark count automatic correction scheme has great advantages in maintaining linearity under long-term working conditions.

Claims

1. A laser distance measuring device based on FPGA and single photon avalanche diode. Its characteristics are: The distance measuring device is composed of a field programmable logic gate array computing core (1), a quenching circuit (2), a single photon avalanche diode (3), a pulse laser driving circuit (4), a pulse laser (5), and an optical lens system (6), wherein the field programmable logic gate array computing core (1) includes time digital conversion logic (11) and calculation logic (12), wherein the time digital conversion logic includes correction algorithm logic (111) and carry chain logic (112); in the system, the field programmable logic gate array (1) generates a signal to enable the pulse laser driving circuit (4) to drive the pulse laser (5) to generate a pulse laser, and the pulse laser is The optical lens system (6) emits a high-power collimated pulse laser, which is reflected by a target object and then passes through the optical lens system (6) to cause a single-photon avalanche diode (3) to avalanche breakdown. The single-photon avalanche diode is quenched by a quenching circuit (2), and the avalanche breakdown signal is converted into a pulse square wave and transmitted to a field programmable logic gate array computing core (1); the field programmable logic gate array computing core (1) converts the signal transmitted to the laser pulse driving circuit (4) to a digital quantity directly received by the quenching circuit (2), and the digital quantity converted into time is counted and converted into distance by a computing logic (12). The time-to-digital conversion logic mainly records the time difference by the carry chain logic (112), and the correction algorithm logic (111) performs linear correction on the output digital time difference, wherein the correction algorithm logic needs to be driven by a random signal, and the random signal sources include two, the first is a random signal generated inside the programmable logic gate array computing core (1), and the second is a signal recorded after the dark count of the single photon avalanche diode (3) is processed by the quenching circuit (2), and both random signals are random; after the above process and algorithm, the device finally outputs distance information with high accuracy and good linearity.

2. The laser distance measuring device based on field programmable gate array FPGA and single photon avalanche diode according to claim 1 is characterized in that: The device uses a combination of a single photon avalanche diode (SPAD) and a quenching circuit (QC) as a laser pulse receiving part. When a reverse bias voltage higher than the avalanche voltage is applied to both ends of the SPAD, a high-multiple internal current gain can be obtained by utilizing the avalanche breakdown effect of the device, thereby triggering a chain reaction; at this time, a relatively large current is generated, which is quenched by the back-end quenching circuit, and an avalanche breakdown signal is output; however, since electron-hole pairs can be generated through heat in semiconductors, avalanches can be triggered even without any photons, that is, under dark conditions. This avalanche is called dark noise, which has strong randomness and can be approximately understood as being uniformly distributed over the entire time range. After the quenching circuit, a digital signal is output, and the behavior of counting this signal is called dark counting. Dark counting will have a certain impact on the ranging performance, but dark counting cannot be completely eliminated; a 905nm band infrared laser is used as a generating device, and a pulse laser driving circuit is used to drive the laser to generate a high-power laser pulse signal with a width of less than 5ns; based on the direct time of flight (DTF) Compared with the traditional distance measurement scheme using photodiodes or avalanche photodiodes as the return light receiving device, SPAD has higher sensitivity and can achieve a longer detection distance. In addition, the flight time of light in the air is stable, so it can achieve higher measurement accuracy.

3. The laser ranging device based on FPGA and single photon avalanche diode according to claim 1, characterized in that: The time-to-digital converter (TDC) function is implemented using the FPGA internal carry chain resources. The FPGA uses the Xilinx A7 series. The carry chain is implemented by the internal CARRY4 cascade. One CARRY4 leads to four taps (CO0, CO1, CO2, CO3) corresponding to different delays. 50 delay units are used in the design, corresponding to 200 taps, with a total of 200 time units, of which the average delay of the time unit is about 25ps; however, due to the internal structural characteristics of the delay chain, there is a time deviation between different time units, and it will change to a certain extent with the change of chip temperature. Usually, for scenarios with low linearity requirements, the average correction method is used, and for scenarios with high linearity requirements, the code density method is generally used for linearity correction. This ranging device has high requirements for linearity and adopts an improved linearity correction scheme based on the code density method. The code density method needs to input a set of random signals for correction. After the signal is input into the delay chain, it randomly falls at a certain position in the delay chain, and a large number of random results are counted as a histogram. A large number of random jump pulses are input into the delay chain, and the rising edge of the random pulses is sampled. The sampled data is the code density data. Since the jump signal is a random signal, it is assumed that the probability of it falling on any phase point within the reference clock (0, T) is the same, that is, the time interval t between any pulse signal and the rising edge of the reference clock is also completely random, where t ranges from (0, T). Random time interval t <t i The probability is: Then the probability that the pulse signal falls in the i-th time unit is When the number of tests is large enough, the delay time τ of the i-th time unit can be obtained i for: In the formula, T represents the middle of the reference clock, h(i) represents the height of the i-th time unit in the histogram after statistics, and N represents the total number. This algorithm obtains the delay of each time unit, and uses this delay as a correction coefficient to correct the carry chain result to obtain an accurate and linear time difference digital quantity.

4. The laser ranging device based on FPGA and single photon avalanche diode according to claim 1 is characterized in that: a dark count linear correction scheme is adopted for the delay chain correction part of the device, and a random signal is required for the delay chain correction. If the chip temperature changes after the correction, the linearity will still change. At this time, correction can only be performed again to maintain accuracy; the present invention proposes that the first delay chain correction is performed using the random signal generator inside the FPGA. After the first correction is completed, in the ranging interval, the position of the SPAD dark count in the delay chain is continuously counted in the histogram, and the number of dark counts is counted. When the dark count reaches a certain amount N, the histogram is calculated to obtain a new linearity correction relationship. Through good linearity correction, it can be used to ensure that the root mean square error (RMSE) of the calibration TDC linearity and the ideal value is less than 0.006; the RMSE calculation formula is: In the formula, n represents the number of data, x i Indicates the current data. It represents the average value of all data, which can reflect the repeatability of the distance measuring device.

5. The laser distance measuring device based on FPGA and single photon avalanche diode according to claim 1, characterized in that: After the real-time correction, the TDC has good linearity. The statistical results are filtered using the average value algorithm, and the light flight time is converted into distance information Dis: In the formula, Δt i It represents the laser flight time obtained for each ranging, K represents the cumulative number of times, and λ represents the speed of light. Taking the average of multiple results can ensure data stability. The absolute distance between the measured target and the ranging device is finally obtained through calculation by this algorithm.

Images