Laser ranging method and apparatus

Abstract

The application discloses a laser ranging method and device. The laser ranging method comprises the following steps: a first storage space is arranged; a trigger number of TDC output is stored and accumulated in the first storage space within a first exposure time, and a coarse histogram corresponding to coarse time precision is generated; M peak values in the coarse histogram are selected, and M coarse time boxes corresponding to the M peak values are obtained; complete time boxes corresponding to the M peak values are obtained according to the M coarse time boxes corresponding to the M peak values; and M object distance measurement values are determined according to the complete time boxes corresponding to the M peak values. The laser ranging method does not need to save all histogram data, and can significantly reduce the area of a ranging chip.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical ranging technology, and in particular to a laser ranging method and device. BACKGROUND

[0002] At present, in a laser radar measurement system based on dTOF (Direct time of flight) measurement, a transmitter and a receiver are generally included, wherein the receiver generally adopts a SPAD (Single Photon Avalanche Diode) array to receive a returned optical signal, and converts time information into a quantized multi-bit digital signal through a TDC (Time-to-Digital Converter), and then draws a statistical histogram based on distance through long-time exposure and TDC trigger cumulative value, so as to obtain distance information of an object according to the statistical histogram. However, this kind of laser ranging method generally needs a complete statistical histogram for one pixel, and with the resolution of a surface array laser radar becoming higher and higher, the scale of a TDC array and a memory (such as SRAM (Static Random-Access Memory)) in a later stage processing is larger and larger, which leads to a too large chip area of a ranging chip. SUMMARY

[0003] Therefore, the embodiments of the present application provide a laser ranging method and device to solve the problem of a too large chip area of a traditional statistical histogram based laser ranging method.

[0004] In a first aspect, the embodiments of the present application provide a laser ranging method, which comprises:

[0005] a first storage space is provided;

[0006] a trigger number of TDC output is stored and accumulated in the first storage space within a first exposure time, and a coarse histogram corresponding to a coarse time precision is generated;

[0007] M peaks in the coarse histogram are selected, and M coarse time bins corresponding to the M peaks are obtained;

[0008] Obtaining complete time bins corresponding to M peaks according to the coarse time bins corresponding to the M peaks, specifically comprising: storing first data in the first storage space during the second exposure time, comparing the time bin data output by the TDC in real time with the first data, where an initial value of the first data is the coarse time bin corresponding to the first peak; updating the first data by adding or subtracting a preset adjustment difference according to a comparison result, where the updated first data is the complete time bin corresponding to the first peak; storing Mth data in the first storage space during the M+1th exposure time, comparing the time bin data output by the TDC in real time with the Mth data, where an initial value of the Mth data is the coarse time bin corresponding to the Mth peak; updating the Mth data by adding or subtracting the adjustment difference according to a comparison result, where the updated Mth data is the complete time bin corresponding to the Mth peak;

[0009] M object distance measurement values ​​are determined based on the complete time bins corresponding to the M peaks.

[0010] In the above aspect and any possible implementation, further provided is an implementation, wherein the time bin data output in real time by the TDC is compared with the first data, an initial value of the first data is the coarse time bin corresponding to the first peak, and based on the comparison result, the first data is updated by adding or subtracting a preset adjustment difference, including:

[0011] comparing the time bin data outputted in real time by the TDC with the first data, and if the first data is smaller than the time bin data outputted in real time by the TDC, adding the adjustment difference to the first data to obtain updated first data, and storing the updated first data in the first storage space;

[0012] If the first data is greater than the time bin data outputted in real time by the TDC, the first data is subtracted from the adjustment difference to obtain the updated first data, and the updated first data is stored in the first storage space;

[0013] If the first data is equal to the time bin data output by the TDC in real time, the first data remains stored in the first storage space.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein the range of the adjustment difference is set according to the coarse time precision of the coarse histogram, and when the coarse time precision is lower, the value of the adjustment difference will be larger.

[0015] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the selecting M peaks in the coarse histogram comprises: sorting all peaks in the coarse histogram according to peak size from large to small, and selecting M peaks; or, setting a peak threshold, and selecting M peaks greater than the peak threshold.

[0016] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the method further comprises:

[0017] The second storage space has a larger storage capacity than the first storage space.

[0018] In the second exposure time, the first data is stored in the first storage space, the time bin data output by the TDC in real time is compared with the first data, the initial value of the first data is the coarse time bin corresponding to the first peak, according to the comparison result, the first data is updated by adding or subtracting the adjustment difference value, and is saved in the second storage space at the same time, the storage capacity of the second storage space can store N historical values of the first data, in the M+1th exposure time, the Mth data is stored in the first storage space, the time bin data output by the TDC in real time is compared with the Mth data, the initial value of the Mth data is the coarse time bin corresponding to the Mth peak, according to the comparison result, the Mth data is updated by adding or subtracting the adjustment difference value, and is saved in the second storage space at the same time, the storage capacity of the second storage space can store N historical values of the Mth data.

[0019] The average value of the N historical values of the first data is calculated, and the average value of the N historical values of the Mth data in the M+1th exposure time is calculated in the same manner.

[0020] The M object distance measurement values are determined according to the average value of the N historical values of the first data and the average value of the N historical values of the Mth data in the M+1th exposure time.

[0021] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the first storage space is a first-in-first-out memory.

[0022] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the method further comprises:

[0023] A peak preset interval range is obtained.

[0024] According to the peak preset interval range, M peaks are re-determined on the basis of the M peaks.

[0025] The corresponding complete time bins are obtained according to the re-determined M peaks.

[0026] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, the adjustment difference value includes a first adjustment difference value and a second adjustment difference value, a value of the first adjustment difference value is greater than a value of the second adjustment difference value, the adjustment difference value is changed according to a number of times of receiving of the TDC, and when the number of times of comparison reaches a preset threshold, the first adjustment difference value is changed to the second adjustment difference value.

[0027] In a second aspect, an embodiment of the present application provides a laser ranging device, the device comprising:

[0028] a laser emitter, configured to emit laser;

[0029] a SPAD array, configured to receive an optical signal;

[0030] a TDC array, configured to convert a time of flight of the optical signal into a digital signal;

[0031] a coarse histogram control circuit, configured to store and accumulate a number of triggers of TDC output in the first storage space within a first exposure time, to generate a coarse histogram corresponding to a coarse time precision, and to select M peaks in the coarse histogram, to obtain coarse time bins corresponding to the M peaks;

[0032] a memory, configured to store the coarse time bins corresponding to the M peaks in the coarse histogram;

[0033] a complete time bin adjustment control circuit, configured to obtain complete time bins corresponding to the M peaks according to the coarse time bins corresponding to the M peaks, and specifically comprising: storing first data in the first storage space within a second exposure time, comparing time bin data output by the TDC in real time with the first data, an initial value of the first data being the coarse time bin corresponding to a first peak, updating the first data by adding or subtracting a preset adjustment difference value according to a comparison result, the updated first data being the complete time bin corresponding to the first peak, storing Mth data in the first storage space within an M+1th exposure time, comparing time bin data output by the TDC in real time with the Mth data, an initial value of the Mth data being the coarse time bin corresponding to an Mth peak, updating the Mth data by adding or subtracting the adjustment difference value according to a comparison result, and the updated Mth data being the complete time bin corresponding to the Mth peak;

[0034] a readout circuit, configured to determine M object distance measurement values according to the complete time bins corresponding to the M peaks.

[0035] Furthermore, the apparatus further comprises a second storage space and a calculation unit, wherein the storage capacity of the second storage space is greater than that of the first storage space;

[0036] The complete time bin adjustment control circuit is further configured to store first data in the first storage space during the second exposure time, compare the time bin data output in real time by the TDC with the first data, wherein an initial value of the first data is the coarse time bin corresponding to the first peak; based on the comparison result, update the first data by adding or subtracting the adjustment difference, and simultaneously store the data in the second storage space; the storage capacity of the second storage space is sufficient to store N historical values ​​of the first data; and, during the M+1th exposure time, store the Mth data in the first storage space, compare the time bin data output in real time by the TDC with the Mth data, wherein an initial value of the Mth data is the coarse time bin corresponding to the Mth peak; based on the comparison result, update the Mth data by adding or subtracting the adjustment difference, and simultaneously store the data in the second storage space; the storage capacity of the second storage space is sufficient to store N historical values ​​of the Mth data;

[0037] The calculation unit is configured to calculate an average value of N historical values ​​of the first data, and so on, calculate according to the exposure time period to obtain an average value of the historical values ​​of the M-th data within the M+1-th exposure time;

[0038] The readout circuit is further configured to determine the M object distance measurement values ​​based on an average value of the N historical values ​​of the first data and an average value of the historical values ​​of the Mth data within an exposure time period to N M+1th exposure times.

[0039] In an embodiment of the present application, a first storage space is provided. During a first exposure time, the number of triggers output by the TDC is stored and accumulated in the first storage space to generate a coarse histogram corresponding to a coarse time precision. By generating the coarse histogram, storage requirements can be reduced and the data of the complete histogram can be roughly depicted. Then, M peaks are selected from the coarse histogram and coarse time bins corresponding to the M peaks are obtained, which can further reduce storage requirements. Coarse time bins with peak characteristics are selected from the coarse histogram to quickly determine the coarse time bins related to the object distance measurement value when performing distance detection on multiple target objects. Then, based on the coarse time bins corresponding to the M peaks, M complete time bins corresponding to the peaks are obtained. After the coarse time bins are located, the coarse time bins corresponding to the peaks are continuously updated and adjusted through each numerical comparison based on the coarse time bins, so that the coarse time bins quickly converge to the actual object distance measurement value at the initial value, and a complete time bin that can accurately reflect the object distance detection is obtained. Finally, M object distance measurement values ​​are determined based on the complete time bins corresponding to the M peaks. The laser ranging method does not need to save all histogram data, which can significantly reduce the area of ​​the ranging chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0041] Figure 1 This is a schematic diagram of the structure of optical ranging in the prior art;

[0042] Figure 2 This is a flow chart of the prior art using an optical distance measurement method to achieve histogram statistics;

[0043] Figure 3 This is a flow chart of a laser ranging method in an embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0045] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0046] The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the embodiments of the present application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0047] It should be understood that the term "and / or" used herein is merely used to describe associated objects, and / or can represent three relationships, for example, A and / or B can represent three cases of A alone, A and B together, and B alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0048] It should be understood that although the terms first, second, third, etc. may be used in the embodiments of the present application to describe the preset ranges, etc., these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from each other. For example, the first preset range can also be referred to as the second preset range, and similarly, the second preset range can also be referred to as the first preset range without departing from the scope of the embodiments of the present application.

[0049] Depending on the context, the word "if" as used herein can be interpreted to mean "when" or "while" or "in response to determining" or "in response to detecting". Similarly, the phrase "if it is determined" or "if (a stated condition or event) is detected" can be interpreted to mean "when it is determined" or "in response to determining" or "when (a stated condition or event) is detected" or "in response to detecting (a stated condition or event)".

[0050] Figure 1 is a schematic diagram of a structure for realizing optical ranging in the prior art. As shown in Figure 1 The laser radar device 100 includes a laser emitting device 110, a control module 120, a SPAD module 140, a TDC module 150 and a memory 160. In the implementation of optical ranging, the laser emitting device 110 emits laser, and the photons are irradiated on the target object 130 through the lens, and the target object 130 is continuously exposed. During the exposure of the target object 130, the photons are irradiated back to the laser radar device 100 through the lens by reflection. The laser radar device 100 receives the returned light signal through the SPAD module 140, and converts the time information into a quantized multi-bit digital signal through the TDC module 150, and then draws a dynamic histogram based on distance based on the long-time exposure and the TDC trigger cumulative value, so as to obtain the distance information of the target object 130. The control module 120 is used to control the SPAD module 140, the TDC module 150 and the memory 160 to complete the storage of the statistical histogram data.

[0051] It should be noted that in addition to the target object 130 shown in the figure, the laser radar device can also support distance detection of multiple target objects at the same time, and the number of detected target objects is not limited herein.

[0052] It can be understood that the SPAD module 140 includes a plurality of SPAD units, and each SPAD unit can realize the sensing detection of photons. The size of the SPAD array (the number of SPAD units included) in the SPAD module 140 represents the resolution of the ranging chip, for example, 320*240 or 640*480. When the resolution is higher, the required size and storage capacity of the TDC module 150 and the memory 160 for completing the histogram statistics in the later stage are also higher. Generally, one SPAD unit corresponds to a complete statistical histogram. In the statistical histogram, the abscissa represents time (which can also represent distance, and D=C*TOF / 2, where D represents distance, TOF is digital information representing time converted from time information, and C represents the speed of light). The minimum scale on the abscissa represents a time bin corresponding to the minimum accuracy of the TDC; and the ordinate represents the cumulative count value of each time bin in a period of time. It can be seen that for the storage requirement of the ranging chip, in order to realize long-distance laser ranging, the depth of the memory needs to be large enough (enough time bins can be stored); and in order to achieve high signal-to-noise ratio, the bit width of the memory needs to be wide enough (a larger cumulative count value can be stored). Assuming that a dTOF receiver has 80x60=4800 pixels (SPAD units), the TDC data bit width is 10 bits, the minimum accuracy is 0.1 ns (corresponding to a distance of 1.5 cm), and each time bin is represented by 8-bit count value (the maximum count value is 255). For a requirement of a maximum detection distance of 6 m (corresponding to 400 time bins, 400*1.5 cm=6 m), the minimum memory size required for one frame of image is: 400*8*4800=15.36 Mbit=1.92 Mbyte. If the resolution is changed to 320x240=76800, and the maximum detection distance is still 6 m, the memory size required for one frame of image is changed to: 400*8*76800=245.76 Mbit=30.72 Mbyte. It can be seen that as the resolution of the area array laser radar becomes higher, the size of the TDC array and the memory for later-stage processing becomes larger, and the chip area of the ranging chip also increases.

[0053] Figure 2 is a flowchart of a histogram statistics process using an optical ranging method in the prior art. As shown in Figure 2As shown, for SPAD (unit) 1, it uses TDC (unit) 1 to determine the cumulative counting position of SPAD1 in Memory1 (storage unit 1) by addressing. Specifically, Memory1 may include 1024 10-bit timebins. When the object is continuously exposed, Memory1 will count the light signals received on SPAD1, and finally output the statistical data as the actual result, using timebin as the minimum scale on the horizontal axis and the vertical axis as the cumulative count value of each timebin within a period of exposure time to generate a statistical histogram. Similarly, Memoryn (the nth storage unit) may include 1024 10-bit timebins. During the exposure of the object, Memory1 will count the light signals received on SPADn (the nth SPAD unit) and output the statistical histogram corresponding to SPADn.

[0054] It is understandable that since this ranging method uses histogram statistics, when long-distance laser ranging or high resolution is achieved, the scale of the memory 160 of the laser radar device 100 will become very large, and the storage requirements of the laser radar device 100 will be high, which will result in the chip area of ​​the ranging chip being too large.

[0055] In view of the problem of excessive chip area in the above-mentioned laser ranging method using statistical histogram, the present application proposes a laser ranging method and a laser ranging device.

[0056] Figure 3 This is a flow chart of a laser ranging method in an embodiment of the present application. Figure 3 As shown, the laser ranging method includes the following steps:

[0057] S10: A first storage space is provided.

[0058] In one embodiment, a first storage space is configured for the laser radar device. The first storage space is much smaller than the storage capacity for storing a complete statistical histogram. The first storage space is mainly used to store data related to the object distance detection value in the statistical histogram (coarse time bins corresponding to M peaks) so as to use these data related to the object distance detection value to more accurately calculate the object detection distance value.

[0059] S20: During the first exposure time, the number of triggers output by the TDC is stored and accumulated in the first storage space to generate a coarse histogram corresponding to the coarse time precision.

[0060] In an embodiment, the laser radar device exposes the target object by emitting photons, and during the exposure time, the number of triggers of the TDC output is stored and accumulated in the first storage space according to a preset coarse time precision, to generate a corresponding coarse histogram. Understandably, the minimum precision of a complete statistical histogram is one time bin unit, and the coarse histogram is generated according to the coarse time precision, and a plurality of minimum precision time bins can be combined to form a new time bin as a new minimum precision unit; or, the maximum range of the TDC is divided according to a preset time allocation, so that the laser radar device stores and accumulates the number of triggers of the TDC output according to the divided time unit during the first exposure time, to generate a corresponding coarse histogram. Understandably, since the time bin with the minimum precision is not used to draw the histogram, the storage capacity requirement of the first storage space is significantly reduced.

[0061] S30: selecting M peaks in the coarse histogram, and obtaining coarse time bins corresponding to the M peaks.

[0062] The complete statistical histogram has a curve formed by the values of the vertical coordinates (i.e., the number of triggers of the TDC output), and the curve can include a plurality of peaks, which can be used as distance measurement values of the multi-target objects in multi-target detection. In the embodiments of the present application, M peaks are selected in the coarse histogram, and coarse time bins corresponding to the M peaks are obtained. Understandably, since the coarse histogram is selected, the M peaks do not represent the peaks in the complete statistical histogram, and therefore the time bins corresponding to the M peaks can be referred to as coarse time bins.

[0063] S40: obtaining complete time bins corresponding to the M peaks according to the coarse time bins corresponding to the M peaks.

[0064] In step S40, the following steps are specifically included: during the second exposure time, storing first data in the first storage space, comparing the time bin data output by the TDC in real time with the first data, the initial value of the first data being the coarse time bin corresponding to the first peak, and the first data being updated by adding or subtracting a preset adjustment difference value according to the comparison result, the updated first data being the complete time bin corresponding to the first peak, during the M+1th exposure time, storing Mth data in the first storage space, comparing the time bin data output by the TDC in real time with the Mth data, the initial value of the Mth data being the coarse time bin corresponding to the Mth peak, and the Mth data being updated by adding or subtracting the adjustment difference value according to the comparison result, the updated Mth data being the complete time bin corresponding to the Mth peak.

[0065] It can be understood that the first exposure time obtains M peak values corresponding to the coarse time box. These coarse time boxes can roughly represent the object detection distance of multiple targets. In the embodiment of the present application, the coarse time box corresponding to the M peak values is updated in value, so that the updated coarse time box is closer to the time box corresponding to the peak value in the complete statistical histogram. The updating process makes the coarse time box close to the accurate time box. Finally, the time box obtained by value comparison and updating can be called a complete time box.

[0066] In an embodiment, for multi-target object detection, since different peaks correspond to different object distance measurement values, it is necessary to update and adjust the coarse time box corresponding to each peak value. Specifically, the value of the coarse time box is compensated according to the numerical difference between the data output by the TDC in real time and the coarse time box corresponding to the peak value. The compensation value is the adjustment difference value. The compensation can be positive compensation or negative compensation, that is, the coarse time box can increase or decrease the adjustment difference value during updating. Wherein, only the coarse time box corresponding to one peak value is adjusted in value each time, and when there are M peak values corresponding to the coarse time box, plus the first exposure time, a total of M+1 exposures are required. Specifically, in the second exposure time, the first storage space stores the first data, and the time box data output by the TDC in real time is compared with the first data. The initial value of the first data is the coarse time box corresponding to the first peak value. According to the comparison result, the first data is updated by adding or subtracting a preset adjustment difference value. The updated first data is the complete time box corresponding to the first peak value. In this way, in the M+1 exposure time, the first storage space stores the Mth data, and the time box data output by the TDC in real time is compared with the Mth data. The initial value of the Mth data is the coarse time box corresponding to the Mth peak value. According to the comparison result, the Mth data is updated by adding or subtracting the adjustment difference value. The updated Mth data is the complete time box corresponding to the Mth peak value.

[0067] In the embodiment of the present application, when the coarse time box corresponding to each peak value is adjusted in value, the coarse time box will converge to the vicinity of the actual object distance measurement value after comparing the data output by the TDC in real time for multiple times.

[0068] For dTOF laser radar, its corresponding statistical histogram satisfies the Poisson distribution. Most of the values ​​of these seemingly discrete statistical histograms will be concentrated near a fixed value, and this fixed value is the distance value corresponding to the object. From the statistical histogram, the position of the peak represents the distance corresponding to the object. In the embodiment of the present application, the data output in real time by TDC is continuously adjusted and updated in the coarse time bin, so that the complete time bin finally obtained is close to the value corresponding to the peak collected by the statistical histogram collection method. Specifically, the present application abandons the traditional statistical histogram statistical method, and there is no need to record the data representing the measured distance of the object converted by each SPAD through TDC. Instead, for the coarse time bins corresponding to M peaks, the data output in real time by TDC obtained in different exposure time periods is used, and the coarse time bins corresponding to the peaks are compensated by adjusting the difference, so that the coarse time bins converge to the vicinity of the actual object distance measurement value.

[0069] S50: Determine M object distance measurement values ​​according to the complete time bins corresponding to the M peaks.

[0070] In one embodiment, after M+1 exposures, the coarse time bins corresponding to the M peaks are updated by adjusting the difference, so that the coarse time bins corresponding to the M peaks converge to a complete time bin. The peak corresponding to the complete time bin can be considered equivalent to the peak in the complete statistical histogram, thus determining M object distance measurements. It should be understood that the laser ranging method of the present application can maintain the accuracy of object distance measurements for multi-target detection while using less storage capacity.

[0071] In steps S10-S50, a first storage space is provided. By numerically comparing the coarse time bins corresponding to the peak values ​​in the first storage space with the real-time output data of the TDC, the coarse time bins corresponding to the peak values ​​are adjusted and updated for convergence using the adjusted difference, so that the coarse time bins corresponding to the peak values ​​are closer to the actual object distance measurement values. After M+1 exposures, M object distance measurement values ​​are determined. The error between the adjusted and updated complete time bins and the actual object distance measurement values ​​is small and is essentially equivalent to the actual object distance measurement values. The laser ranging method of the present application does not require the storage of complete statistical histogram data within the ranging chip, which can effectively reduce storage requirements and significantly reduce the area of ​​the ranging chip. In particular, when detecting multiple targets, the accuracy of the object distance measurement values ​​for multi-target detection can still be maintained.

[0072] Furthermore, in step S40, the time bin data outputted in real time by the TDC is compared with the first data. The initial value of the first data is the coarse time bin corresponding to the first peak. Based on the comparison result, the first data is updated by adding or subtracting a preset adjustment difference. Specifically, the steps include:

[0073] S41: Compare the time bin data outputted in real time by the TDC with the first data. If the first data is smaller than the time bin data outputted in real time by the TDC, add the adjustment difference to the first data to obtain updated first data, and store the updated data in the first storage space.

[0074] In one embodiment, the first data in the first storage space may be referred to as PEAK_BIN, indicating that the first data corresponds to the coarse time bin corresponding to the first peak in the histogram. Understandably, during the initial comparison between the time bin data output by the real-time TDC and the first data in the first storage space, PEAK_BIN has not yet fully converged and may not accurately correspond to the peak in the histogram. However, as the number of comparisons increases until completion, PEAK_BIN will eventually approximate the object distance measurement corresponding to the first peak.

[0075] S42: If the first data is greater than the time bin data outputted in real time by the TDC, the first data is subtracted from the adjustment difference to obtain updated first data, which is stored in the first storage space.

[0076] S43: If the first data is equal to the time bin data outputted in real time by the TDC, the first data is retained and stored in the first storage space.

[0077] In steps S41-S43, it can be expressed as follows: when TDCdata (time bin data output by TDC in real time)>PEAK_BIN, PEAK_BIN(new)=PEAK_BIN(old)+delta; when TDCdata <PEAK_BIN时,PEAK_BIN(new)=PEAK_BIN(old)-delta;当TDCdata=PEAK_BIN时,PEAK_BIN保持不变,其中,PEAK_BIN(new)是指比较后更新的第一数据,PEAK_BIN(old)是指比较时的第一数据,delta表示调整差值。可以理解地,第一数据是对于第二段曝光时间中对第一个峰值对应的粗时间箱的概念表述,以此类推,第M数据是对于第M+1段曝光时间中对第M个峰值对应的粗时间箱的概念表述。可以理解地,步骤S41-S43是对第一个峰值对应的粗时间箱进行调整更新的具体实施例,其他粗直方图中选取的峰值对应的粗时间箱调整更新的实施例与此类似,在此不再赘述。

[0078] In steps S41-S43, the user can update PEAK_BIN according to the comparison result of TDCdata and PEAK_BIN by adjusting the difference delta, so that PEAK_BIN is closer to the timebin corresponding to the peak in the statistical histogram after multiple updates, that is, closer to the actual object detection distance.

[0079] Furthermore, the range of the adjustment difference is set based on the coarse time precision of the coarse histogram. The lower the coarse time precision, the larger the adjustment difference. The adjustment difference can be set within a range of 0.5-3. Users can adjust and update the coarse time bins using a smaller adjustment difference, so that the resulting complete time bins are closer to the object detection distance corresponding to the peak. In one embodiment, if the coarse time precision of the coarse histogram is set to a low value, the error between the coarse time bin corresponding to the peak and the actual object detection distance may be large. In this case, to achieve rapid convergence and rapid updates, the adjustment difference can be appropriately increased.

[0080] Furthermore, M peaks are selected in the coarse histogram, including: sorting all the peaks in the coarse histogram according to the peak size, from large to small, and selecting M peaks; or, by setting a peak threshold, selecting M peaks that are greater than the peak threshold. It can be understood that the coarse histogram may include more than M peaks, and some peaks can be considered as noise data. If the user's actual requirement is to measure the distance of M objects, then M peaks can be selected, and specifically, M peaks can be selected by sorting the peaks from large to small. Alternatively, the user can select M peaks of interest that are greater than the peak threshold based on the set peak threshold, and analyze the object distances corresponding to these peaks of interest.

[0081] Furthermore, the laser ranging method further includes:

[0082] S60: A second storage space is provided, and the storage capacity of the second storage space is greater than that of the first storage space.

[0083] In one embodiment, a second storage space may be provided to further improve the accuracy of the complete time bin by utilizing the historical data stored in the second storage space.

[0084] S70: During the second exposure time, the first data is stored in the first storage space, and the time bin data output by the TDC in real time is compared with the first data. The initial value of the first data is the coarse time bin corresponding to the first peak. According to the comparison result, the first data is updated by adding and subtracting the adjustment difference, and is simultaneously saved in the second storage space. The storage capacity of the second storage space can store N historical values ​​of the first data. During the M+1th exposure time, the Mth data is stored in the first storage space, and the time bin data output by the TDC in real time is compared with the Mth data. The initial value of the Mth data is the coarse time bin corresponding to the Mth peak. According to the comparison result, the Mth data is updated by adding and subtracting the adjustment difference, and is simultaneously saved in the second storage space. The storage capacity of the second storage space can store N historical values ​​of the Mth data.

[0085] In one embodiment, the second storage space may store some relatively new PEAK_BINs that have just been updated and replaced. That is, it can be understood that the second storage space may store N historical records of PEAK_BINs.

[0086] Furthermore, the second storage space is a shift register that supports storing N coarse time bins. In one embodiment, the characteristics of the shift register can be utilized. After each PEAK_BIN update (using the second exposure time as an example), the recently updated PEAK_BIN (new) is stored as the first data in the first storage space, and the recently updated PEAK_BIN (old) is moved to the next storage space after the first storage space. The remaining storage space in the second storage space is also shifted and replaced accordingly. When the second storage space is full, the oldest stored PEAK_BIN (N+1) is removed. The first storage space stores the most recent historical PEAK_BIN value.

[0087] S80: Calculate and obtain an average value of the historical values ​​of the N first data, and so on, calculate according to the exposure time period to obtain the average value of the historical values ​​of the Mth data in the M+1th exposure time.

[0088] S90: Determine M object distance measurement values ​​according to an average value of the N first data history values ​​and an average value of the Mth data history values ​​within the exposure time period to the Nth (M+1)th exposure time period.

[0089] In steps S60-S90, the second storage space may store the historical values ​​of the coarse time bins corresponding to the most recent N peak values. That is, the values ​​stored in the second storage space are the coarse time bins updated after the last N comparisons. In this embodiment of the present application, the object distance measurement value may be determined by rounding the average of the historical values ​​of the N coarse time bins. This method is more fault-tolerant than the method of using the complete coarse time bin obtained from the last update in steps S10-S50, and the determined M object distance measurements are closer to the actual object distance measurement value.

[0090] Furthermore, the first storage space is a first-in-first-out memory. Specifically, the first storage space may be an SRAM. Using SRAM as the first storage space can support the storage of the above data.

[0091] Furthermore, the laser ranging method further includes:

[0092] A peak preset interval range is obtained, and then M peaks are re-determined based on the M peaks according to the peak preset interval range, and finally corresponding complete time bins are obtained according to the re-determined M peaks.

[0093] It can be understood that the peak on the coarse histogram does not represent the peak situation on the complete statistical histogram. In the selection of M peaks, points can be taken near the M peaks (limited to the preset interval of each peak). These points may be closer to the peak situation on the complete statistical histogram. In this way, the complete time box obtained based on the re-determined M peaks will be more accurate.

[0094] Furthermore, the adjustment difference includes a first adjustment difference and a second adjustment difference, the value of the first adjustment difference is greater than the value of the second adjustment difference, and the adjustment difference changes according to the number of times TDC is received, wherein when the number of comparisons reaches a preset threshold, the first adjustment difference is changed to the second adjustment difference.

[0095] In one embodiment, delta1 and delta2 are provided, where delta1 is greater than delta2. In the initial stages of the numerical comparison, to ensure rapid convergence of the coarse time bin corresponding to the peak, the larger delta1 may be used. In the middle or later stages of the comparison, to ensure more stable convergence of the first data to the actual object detection distance, the smaller delta2 may be used. This further improves the efficiency of updating the first data and minimizes the difference between the coarse time bin corresponding to the peak and the actual object detection distance. The preset threshold can be determined based on the number of comparisons, such as 1 / 5 or 1 / 4 of the total number of comparisons. This means that in the first 1 / 5 or 1 / 4 of the comparisons, the larger delta1 is used, while in the later stages, the smaller delta2 is used. Furthermore, the difference value is adjusted to a range of 0.5-3, for example, delta1 is specifically set to 2 and delta2 is specifically set to 1.

[0096] The laser ranging method of the present application has the following advantages over the prior art ranging methods:

[0097] There is no need to store complete statistical histogram data inside the chip, so the chip area can be significantly reduced. As the chip area is reduced, the chip power consumption and cost are significantly reduced. Compared with SRAM memory, which requires at least two beats to complete data accumulation (one beat for reading and one beat for writing), the method of adjusting the difference to update the coarse time bin can realize data addition or subtraction calculation in one beat, thereby improving the data processing speed of the entire TDC module. Since the statistical histogram is no longer used to calculate the depth value, but the depth data (timebin value) is directly output on the chip side, the data output volume of the chip and the post-stage calculation volume of the statistical histogram (such as matched filtering + peak finding algorithm, etc.) will be significantly reduced, which can improve the processing efficiency of the chip.

[0098] In an embodiment of the present application, a first storage space is provided. During a first exposure time, the number of triggers output by the TDC is stored and accumulated in the first storage space to generate a coarse histogram corresponding to a coarse time precision. By generating the coarse histogram, storage requirements can be reduced and the data of the complete histogram can be roughly depicted. Then, M peaks are selected from the coarse histogram and coarse time bins corresponding to the M peaks are obtained, which can further reduce storage requirements. Coarse time bins with peak characteristics are selected from the coarse histogram to quickly determine the coarse time bins related to the object distance measurement value when performing distance detection on multiple target objects. Then, based on the coarse time bins corresponding to the M peaks, M complete time bins corresponding to the peaks are obtained. After the coarse time bins are located, the coarse time bins corresponding to the peaks are continuously updated and adjusted through each numerical comparison based on the coarse time bins, so that the coarse time bins quickly converge to the actual object distance measurement value at the initial value, and a complete time bin that can accurately reflect the object distance detection is obtained. Finally, M object distance measurement values ​​are determined based on the complete time bins corresponding to the M peaks. The laser ranging method does not need to save all histogram data, which can significantly reduce the area of ​​the ranging chip.

[0099] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0100] The present invention provides a laser distance measuring device. The laser distance measuring device includes:

[0101] A laser transmitter, used for emitting laser;

[0102] A SPAD array for receiving optical signals;

[0103] A TDC array for converting the time of flight of an optical signal into a digital signal;

[0104] a coarse histogram control circuit, configured to store and accumulate the number of triggers output by the TDC in a first storage space during a first exposure time to generate a coarse histogram corresponding to a coarse time precision; and to select M peaks in the coarse histogram to obtain coarse time bins corresponding to the M peaks;

[0105] A memory, used to store coarse time bins corresponding to M peaks in the coarse histogram;

[0106] A complete time bin adjustment control circuit is configured to obtain complete time bins corresponding to M peaks based on coarse time bins corresponding to M peaks, specifically comprising: storing first data in a first storage space during a second exposure time, comparing the time bin data output in real time by a TDC with the first data, where an initial value of the first data is the coarse time bin corresponding to the first peak; updating the first data by adding or subtracting a preset adjustment difference based on a comparison result, where the updated first data is the complete time bin corresponding to the first peak; storing an Mth data in the first storage space during an M+1th exposure time, comparing the time bin data output in real time by a TDC with the Mth data, where an initial value of the Mth data is the coarse time bin corresponding to the Mth peak; updating the Mth data by adding or subtracting an adjustment difference based on a comparison result, where the updated Mth data is the complete time bin corresponding to the Mth peak;

[0107] A readout circuit is configured to determine M object distance measurements based on the complete time bins corresponding to the M peaks.

[0108] The laser distance measuring device further includes a second storage space and a calculation unit, wherein the storage capacity of the second storage space is greater than that of the first storage space;

[0109] The complete time bin adjustment control circuit is further configured to store first data in the first storage space during the second exposure time, compare the time bin data output in real time by the TDC with the first data, wherein an initial value of the first data is the coarse time bin corresponding to the first peak; based on the comparison result, update the first data by adding or subtracting the adjustment difference, and simultaneously store the data in the second storage space; the storage capacity of the second storage space is sufficient to store N historical values ​​of the first data; and, during the M+1th exposure time, store the Mth data in the first storage space, compare the time bin data output in real time by the TDC with the Mth data, wherein an initial value of the Mth data is the coarse time bin corresponding to the Mth peak; based on the comparison result, update the Mth data by adding or subtracting the adjustment difference, and simultaneously store the data in the second storage space; the storage capacity of the second storage space is sufficient to store N historical values ​​of the Mth data;

[0110] The calculation unit is configured to calculate an average value of N historical values ​​of the first data, and so on, calculate according to the exposure time period to obtain an average value of the historical values ​​of the M-th data within the M+1-th exposure time;

[0111] The readout circuit is further configured to determine the M object distance measurement values ​​based on an average value of the N historical values ​​of the first data and an average value of the historical values ​​of the Mth data within an exposure time period to N M+1th exposure times.

[0112] In an embodiment of the present application, a first storage space is provided. During a first exposure time, the number of triggers output by the TDC is stored and accumulated in the first storage space to generate a coarse histogram corresponding to a coarse time precision. By generating the coarse histogram, storage requirements can be reduced and the data of the complete histogram can be roughly depicted. Then, M peaks are selected from the coarse histogram and coarse time bins corresponding to the M peaks are obtained, which can further reduce storage requirements. Coarse time bins with peak characteristics are selected from the coarse histogram to quickly determine the coarse time bins related to the object distance measurement value when performing distance detection on multiple target objects. Then, based on the coarse time bins corresponding to the M peaks, M complete time bins corresponding to the peaks are obtained. After the coarse time bins are located, the coarse time bins corresponding to the peaks are continuously updated and adjusted through each numerical comparison based on the coarse time bins, so that the coarse time bins quickly converge to the actual object distance measurement value at the initial value, and a complete time bin that can accurately reflect the object distance detection is obtained. Finally, M object distance measurement values ​​are determined based on the complete time bins corresponding to the M peaks. The laser ranging method does not need to save all histogram data, which can significantly reduce the area of ​​the ranging chip.

[0113] Those skilled in the art will clearly understand that for the sake of convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0114] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A laser ranging method, characterized in that: include: A first storage space is provided; During the first exposure time, the number of triggers output by the TDC is stored and accumulated in the first storage space to generate a coarse histogram corresponding to the coarse time accuracy; Selecting M peaks in the coarse histogram and obtaining coarse time bins corresponding to the M peaks; Obtaining complete time bins corresponding to M peaks according to the coarse time bins corresponding to the M peaks specifically includes: storing first data in the first storage space during the second exposure period, comparing the time bin data output in real time by the TDC with the first data, wherein the initial value of the first data is the coarse time bin corresponding to the first peak; updating the first data by adding or subtracting a preset adjustment difference according to the comparison result, and the updated first data is the complete time bin corresponding to the first peak; storing the Mth data in the first storage space during the M+1th exposure period, and comparing the time bin data output in real time by the TDC with the first data. The time bin data is compared with the M-th data, the initial value of the M-th data being the coarse time bin corresponding to the M-th peak; based on the comparison result, the M-th data is updated by adding or subtracting the adjustment difference; the updated M-th data is the complete time bin corresponding to the M-th peak, wherein the adjustment difference includes a first adjustment difference and a second adjustment difference, wherein the value of the first adjustment difference is greater than the value of the second adjustment difference; when comparing with the time bin data output in real time by the TDC, the first adjustment difference is first used for updating; when the number of comparisons reaches a preset threshold, the first adjustment difference is changed to the second adjustment difference; M object distance measurement values ​​are determined based on the complete time bins corresponding to the M peaks.

2. The method according to claim 1, characterized in that The step of comparing the time bin data outputted in real time by the TDC with the first data, wherein an initial value of the first data is the coarse time bin corresponding to the first peak, and updating the first data by adding or subtracting a preset adjustment difference according to the comparison result, comprises: comparing the time bin data outputted in real time by the TDC with the first data, and if the first data is smaller than the time bin data outputted in real time by the TDC, adding the adjustment difference to the first data to obtain updated first data, and storing the updated first data in the first storage space; If the first data is greater than the time bin data outputted in real time by the TDC, the first data is subtracted from the adjustment difference to obtain the updated first data, and the updated first data is stored in the first storage space; If the first data is equal to the time bin data output by the TDC in real time, the first data remains stored in the first storage space.

3. The method according to claim 1, characterized in that The range of the adjustment difference is set according to the coarse time precision of the coarse histogram. When the coarse time precision is lower, the value of the adjustment difference will be larger.

4. The method according to claim 1, wherein The selecting M peaks in the coarse histogram includes: sorting all peaks in the coarse histogram according to peak size, from large to small, and selecting the M peaks; or setting a peak threshold and selecting the M peaks that are greater than the peak threshold.

5. The method according to claim 1, wherein The method further comprises: A second storage space is provided, wherein the storage capacity of the second storage space is greater than that of the first storage space; During the second exposure time, first data is stored in the first storage space, time bin data output in real time by the TDC is compared with the first data, an initial value of the first data is the coarse time bin corresponding to the first peak, and based on the comparison result, the first data is updated by adding or subtracting the adjustment difference and is simultaneously stored in the second storage space, and the storage capacity of the second storage space is sufficient to store N historical values ​​of the first data; during the M+1th exposure time, the Mth data is stored in the first storage space, time bin data output in real time by the TDC is compared with the Mth data, an initial value of the Mth data is the coarse time bin corresponding to the Mth peak, and based on the comparison result, the Mth data is updated by adding or subtracting the adjustment difference and is simultaneously stored in the second storage space, and the storage capacity of the second storage space is sufficient to store N historical values ​​of the Mth data; Calculate and obtain an average value of N historical values ​​of the first data, and so on, calculate according to the exposure time period to obtain an average value of the historical values ​​of the M-th data within the M+1-th exposure time; M object distance measurement values ​​are determined according to an average value of the N historical values ​​of the first data and an average value of the historical values ​​of the Mth data within an exposure time period to N M+1th exposure time periods.

6. The method according to claim 1, characterized in that The first storage space is a first-in-first-out memory.

7. The method according to claim 1, characterized in that The method further comprises: Get the peak preset range; Re-determining M peak values ​​based on the M peak values ​​according to the preset peak interval range; The corresponding complete time bin is obtained according to the re-determined M peaks.

8. The method according to any one of claims 1 to 7, characterized in that The adjustment difference includes a first adjustment difference and a second adjustment difference, the value of the first adjustment difference is greater than the value of the second adjustment difference, and the adjustment difference is changed according to the number of times the TDC is received, wherein when the number of comparisons reaches a preset threshold, the first adjustment difference is changed to the second adjustment difference.

9. A laser ranging device, characterized in that: include: A laser transmitter, used for emitting laser; A SPAD array for receiving optical signals; A TDC array for converting the time of flight of an optical signal into a digital signal; A coarse histogram control circuit is used to store and accumulate the number of triggers output by the TDC in a first storage space during a first exposure time to generate a coarse histogram corresponding to a coarse time accuracy; and for selecting M peaks in the coarse histogram and obtaining coarse time bins corresponding to the M peaks; A memory, configured to store the coarse time bins corresponding to the M peaks in the coarse histogram; The complete time bin adjustment control circuit is configured to obtain complete time bins corresponding to M peaks based on the coarse time bins corresponding to the M peaks, specifically comprising: storing first data in the first storage space during the second exposure period, comparing the time bin data output in real time by the TDC with the first data, wherein the initial value of the first data is the coarse time bin corresponding to the first peak; updating the first data by adding or subtracting a preset adjustment difference based on the comparison result; the updated first data is the complete time bin corresponding to the first peak; storing the Mth data in the first storage space during the M+1th exposure period; and The time bin data output in real time by C is compared with the M-th data, the initial value of the M-th data being the coarse time bin corresponding to the M-th peak; and according to the comparison result, the M-th data is updated by adding or subtracting the adjustment difference, and the updated M-th data is the complete time bin corresponding to the M-th peak, wherein the adjustment difference includes a first adjustment difference and a second adjustment difference, wherein the value of the first adjustment difference is greater than the value of the second adjustment difference; when comparing with the time bin data output in real time by TDC, the first adjustment difference is first used for updating, and when the number of comparisons reaches a preset threshold, the first adjustment difference is changed to the second adjustment difference; A readout circuit is configured to determine M object distance measurements based on the complete time bins corresponding to the M peaks.

10. The device according to claim 9, characterized in that Also comprising a second storage space and a computing unit, wherein the second storage space has a greater storage capacity than the first storage space; The complete time bin adjustment control circuit is further configured to store first data in the first storage space during the second exposure time, compare the time bin data output in real time by the TDC with the first data, wherein an initial value of the first data is the coarse time bin corresponding to the first peak; based on the comparison result, update the first data by adding or subtracting the adjustment difference, and simultaneously store the data in the second storage space; the storage capacity of the second storage space is sufficient to store N historical values ​​of the first data; and, during the M+1th exposure time, store the Mth data in the first storage space, compare the time bin data output in real time by the TDC with the Mth data, wherein an initial value of the Mth data is the coarse time bin corresponding to the Mth peak; based on the comparison result, update the Mth data by adding or subtracting the adjustment difference, and simultaneously store the data in the second storage space; the storage capacity of the second storage space is sufficient to store N historical values ​​of the Mth data; The calculation unit is configured to calculate an average value of N historical values ​​of the first data, and so on, calculate according to the exposure time period to obtain an average value of the historical values ​​of the M-th data within the M+1-th exposure time; The readout circuit is further configured to determine the M object distance measurement values ​​based on an average value of the N historical values ​​of the first data and an average value of the historical values ​​of the Mth data within an exposure time period to N M+1th exposure times.

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