A method of detecting

Abstract

The application discloses a detection method, which comprises the following steps: obtaining a first flight time in an Nth frame; drawing a second histogram in an N+1th frame with a second time precision unit based on the first flight time in the Nth frame; and judging whether a second flight time can be obtained according to the second histogram, wherein N is a positive integer greater than or equal to 1. Through the design, the detection can be directly started from the second histogram or the third histogram, and the detection is started from the first flight time only when the flight time cannot be obtained. Thus, the data storage amount of the TDC can be further reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection, in particular to a detection method. BACKGROUND

[0002] Time of flight (TOF) is a principle that continuously sends light pulses to a target object, and then uses a sensor to receive light returned from the object, and obtains the distance of the target object by detecting the flight (round trip) time of the light pulse.

[0003] Direct time of flight (DTOF) is a kind of TOF. DTOF technology directly obtains the distance of the target by calculating the emission and reception time of the light pulse, has the advantages of simple principle, good signal-to-noise ratio, high sensitivity, high accuracy, etc., and has received more and more attention. The scheme using ITOF can also obtain a high-precision and high-sensitivity distance detection scheme.

[0004] Direct time of flight detection includes directly measuring the length of time between emitted radiation and detected radiation after reflection from an object or other target. From this, the distance to the target can be determined.

[0005] In some applications, sensing of reflected radiation can be performed using an array of photodetectors including single-photon detectors (e.g., single-photon avalanche diodes, SPADs).

[0006] A SPAD array can be used as a solid-state photodetector in imaging applications that can require high sensitivity and timing resolution. A SPAD is based on a semiconductor junction (e.g., a p-n junction) that can detect incident photons when biased outside its breakdown region, for example, by or in response to a strobe signal having a desired pulse width. A high reverse bias voltage creates an electric field large enough that a single charge carrier introduced into the device’s depletion layer can cause a self-sustaining avalanche through impact ionization. The avalanche can be quenched actively (e.g., by reducing the bias voltage) or passively (e.g., by using a voltage drop across a series resistance) by a quenching circuit to “reset” the device for further detection of photons. The initiating charge carrier can be photoelectrically generated by a single incident photon striking a high-field region. It is this functionality that has led to the name “single-photon avalanche diode.” This single-photon detection mode of operation is often referred to as “Geiger mode.”

[0007] To count photons incident on a SPAD array, certain ToF pixel methods can use digital counters or analog counters to indicate detection and time of arrival, also known as time stamping, of photons. Digital counters can be easier to implement and scale, but can be more expensive in terms of area (e.g., relative to the physical size of the array). Analog counters can be more compact, but can be limited by photon counting depth (bit depth), noise, and / or uniformity issues.

[0008] To time stamp incident photons, some SPAD array-based ToF pixel methods use time-to-digital converters (TDCs). TDCs can be used in time-of-flight imaging applications to improve timing resolution of a single clock cycle. Some advantages of this digital approach can include that the size of a TDC tends to scale with technology nodes, and that the stored value can be more robust to leakage.

[0009] However, TDC circuits can only handle one event measurement period per single event, so a row of SPADs can require multiple TDCs. TDCs can also be relatively power hungry, which makes larger arrays more difficult to implement. TDCs can also generate a relatively large amount of data, e.g., a 16-bit time stamp per photon. A single SPAD connected to a TDC can produce millions of such time stamps per second. Therefore, an imaging array of greater than 100,000 pixels can produce an unfeasibly large data rate relative to the available input / output bandwidth or functionality. But not using TDCs at all can not achieve the measurement precision. Therefore, there is an urgent need for a detection device and a detection method to solve the above problems. SUMMARY

[0010] The present application aims at the deficiencies in the prior art, and provides a detection device and a detection method to solve the technical problem of excessive TDC data in the prior detection method.

[0011] To achieve the above object, the technical solutions adopted by the embodiments of the present application are as follows:

[0012] In a first aspect, the embodiments of the present application provide a detection method, characterized in that comprising:

[0013] obtaining a first time of flight in the Nth frame, drawing a second histogram in the N+1th frame with a second time precision unit based on the first time of flight in the Nth frame, and determining whether a second time of flight can be obtained according to the second histogram, wherein N is a positive integer greater than or equal to 1.

[0014] Optionally, a first histogram is drawn in the Nth frame with a first time precision unit, and a first time of flight is obtained according to the first histogram;

[0015] In the Nth frame, a second histogram is drawn in a second time precision unit, and a second time of flight is obtained according to the second histogram, where N is a positive integer greater than or equal to 1.

[0016] Optionally, in the N+1th frame, a second histogram is drawn in the second time precision unit, where N is a positive integer greater than or equal to 1.

[0017] Optionally, a second time of flight is obtained according to the second histogram drawn in the second time precision unit, and the second time of flight is output.

[0018] Optionally, a second time of flight cannot be obtained according to the second histogram drawn in the second time precision unit, and a first histogram is drawn in a first time precision unit in the N+1th frame.

[0019] Optionally, the first time precision unit is greater than the second time precision unit.

[0020] Optionally, the first or second time of flight is obtained by using a maximum peak value method based on the first or second histogram.

[0021] Optionally, a second histogram is drawn in the second time precision unit within a range of one first time precision unit based on the first time of flight.

[0022] Optionally, a second histogram is drawn in the second time precision unit within a range of one first time precision unit expanded around the first time of flight.

[0023] Optionally, a third histogram is drawn in a third time precision unit. The second time precision unit is greater than the third time precision unit.

[0024] The application has the following beneficial effects:

[0025] The application provides a detection method, which comprises: drawing a second histogram in a second time precision unit; and determining whether a second time of flight can be obtained according to the second histogram. Through the design, the detection can be directly started from the second histogram or the third histogram, and the detection is started from the first time of flight only when the time of flight cannot be obtained. In this way, the data storage amount of the TDC can be further reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as limiting the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor.

[0027] Figure 1 A functional module diagram of a detection device provided by the embodiments of the present application;

[0028] Figure 2 A histogram diagram provided by the embodiments of the present application;

[0029] Figure 3 A detection method diagram provided by the embodiments of the present application;

[0030] Figure 4 A diagram of the relationship between a first histogram and a second histogram provided by the embodiments of the present application;

[0031] Figure 5 Another detection method diagram provided by the embodiments of the present application;

[0032] Figure 6 Another diagram of the relationship between a first histogram and a second histogram provided by the embodiments of the present application;

[0033] Figure 7 Another detection method diagram provided by the embodiments of the present application;

[0034] Figure 8 Still another detection method diagram provided by the embodiments of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] It should be noted that like reference numerals and characters refer to like items throughout the attached drawings and alternative embodiments thereof, noting that, once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0038] Figure 1 A functional module schematic diagram of a detection device provided by an embodiment of the present application is shown in FIG. 1. As shown in the figure, the detection device comprises a pulsed light source 101, a to-be-detected object 102, a detector array 103, and a processing module 104. Figure 1

[0039] The pulsed light source 101 is configured to emit a detection pulse to the to-be-detected object 102, and the to-be-detected object 102 reflects part of the pulsed light source to the detector array 103. The detector array 103 can be a SPAD array. When the reflected photons hit a high electric field region, the photoelectric generation causes the SAPD to avalanche. The TDC module generates a time code according to the arrival time of the reflected photons, and the processing module 104 can generate a histogram according to the time code, and finally obtain the accurate time of arrival of the reflected photons according to the histogram. The TDC module can be in the detector array or can be a separate module electrically connected to the detector array, and the present application does not make specific limitations.

[0040] After obtaining the arrival time of the reflected photons, the distance of the to-be-detected object can be detected according to the arrival time of the photons. The distance D can be calculated by the following formula:

[0041] D = c · t / 2 (1)

[0042] Wherein, c is the speed of light.

[0043] Figure 2 A histogram schematic diagram provided by an embodiment of the present application is shown in FIG. 2. As shown in the figure, Figure 2

[0044] Wherein, ΔT refers to the width of the detection window, T1 and T2 respectively refer to the start and end time of the histogram drawing, [T1, T2] is the time interval of the histogram, T = T2-T1 refers to the total time width, and the ordinate of the time unit ΔT is the photon count value received in the corresponding detection window. Based on the histogram, the position of the pulse waveform can be determined by using the maximum peak value method, and the corresponding flight time t can be obtained.

[0045] In some existing solutions, in order to reduce the data amount of the TDC, a first histogram is first drawn with a first time precision unit, and the first histogram is used to determine the position of the pulse waveform by using the maximum peak value method, and the corresponding flight time t is obtained. Figure 2 ​​The method shown calculates a first flight time. According to the first flight time, a second histogram is drawn in a second time precision unit; the second flight time is calculated using the second histogram. Wherein the time interval of the first histogram is greater than the time interval of the second histogram, or the time resolution of the first histogram is less than the time resolution of the second histogram. In this way, the amount of TDC data of a part can be reduced, but the first flight time and the second flight time detection are still needed in each detection, and the amount of TDC data is still quite large.

[0046] Figure 3 A detection method provided by the embodiment of the application is shown in the schematic diagram. Figure 3 The detection method shown in the schematic diagram, S301 starts the first frame of detection, first draws a first histogram in a first time precision unit, S302 calculates a first flight time according to the first histogram, S303 draws a second histogram in a second precision, S304 calculates a second flight time according to the second histogram and outputs the second flight time, wherein the time interval of the first histogram is greater than the time interval of the second histogram, or the time precision of the first histogram is less than the time precision of the second histogram. In this way, the position of the target to be detected that meets the accuracy requirement can be obtained. In the detection process, the ΔT in the process of obtaining the first flight time is large, the resolution is poor, and cannot meet the detection requirement, but because the resolution is relatively small, the TDC data to be stored is relatively small, the rough position of the object to be detected can be obtained through the first flight time, for example, in the schematic diagram shown in Figure 2 In the schematic diagram shown, it is difficult to determine the accurate position of t according to the histogram, and the resolution ratio of ΔT is relatively small, that is, the time interval of ΔT is relatively large, which cannot meet the detection requirement, and only the rough position of the object to be detected can be obtained. Therefore, in the process of obtaining the second flight time, the time interval of ΔT2 of the second flight time is smaller than the time interval of ΔT of the first flight time, and the resolution is improved, as shown in the schematic diagram shown in Figure 4

[0047] Figure 4 A schematic diagram of the relationship between the first histogram and the second histogram provided by the embodiment of the application is shown in the schematic diagram. Figure 4 According to the first histogram, the first flight time can be obtained between t1-t2, and there are many schemes for determining the first flight time in the prior art, which will not be described here. For example, the ΔT of the first histogram can be 500ps, that is, the time resolution of the first histogram is 500ps. The ΔT2 of the second histogram can be 62.5ps on the basis of the first histogram, and the time resolution here is only for illustrative purposes and is not limited specifically. As shown in Figure 4 ​As shown in the first histogram, the time accuracy is improved to 62.5 ps within the range of t1-t2. The second flight time t3 is obtained from the second histogram. If the second flight time t3 still does not meet the detection accuracy requirements, a third flight time can be obtained based on the second flight time to further improve the detection accuracy until the obtained flight time meets the detection accuracy requirements.

[0048] Although the above-mentioned probing process is divided into a first histogram and a second histogram in order to reduce the amount of data stored in the TDC, the first histogram and the second histogram still need to be probing each time, so the reduction in the amount of data generated by the TDC is very limited. Figure 3 A novel detection method is proposed, which can further reduce the amount of data generated by TDC. For example... Figure 3 As shown, during the initial detection process, the first flight time and second flight time are detected according to the above-described procedure. In the Nth frame (e.g., the first frame), the first and second flight times are detected according to procedures S301-S304, and the second flight time that meets the detection requirements is obtained. In S305, in the N+1th frame (e.g., the second frame), a second histogram is directly plotted using the second time precision unit. In S306, the second flight time of the N+1th frame is calculated based on the histogram. If the second flight time can be calculated correctly, the result is output in S307. If the second flight time cannot be obtained, it indicates that the object under test has moved out of the detection range of the second histogram. Therefore, the detection process of the first histogram must be repeated, and the detection of the first and second flight times must be repeated. Thus, the detection process returns to S301. Figure 3 In the detection method shown, if the second flight time can be obtained directly from the second histogram in the N+1th frame, the data storage and computation of the TDC can be further reduced, thereby further improving the detection efficiency.

[0049] Figure 3 The detection process of obtaining the second flight time by directly plotting the second histogram with the second time precision in the N+1th frame shown can also be achieved in some embodiments through methods such as... Figure 5 The method shown is used to achieve this. Figure 3 During the detection process shown, when directly drawing the second histogram in the N+1th frame using the second time precision unit, it is constrained by the starting point of the first time precision unit because the drawing of the second histogram is based on the first flight time. Figure 5 The process of obtaining the second flight time in the Nth frame in the detection method shown is similar to... Figure 3The method shown is the same, that is, S501-S504 and S301-S304 shown in the detection process is the same here will not repeat. Then get the second time of flight of the N frame, S505 to the second time of flight center expansion a time range, the expansion of the time range is the first time accuracy time unit. Then in this extended time range S506 to the second time accuracy unit drawing second histogram, according to the histogram of the N+1 frame, the second time of flight of the N+1 frame is calculated, S507 if the second time of flight can be calculated normally, S508 output the result of the second time of flight, if the second time of flight can not be obtained, indicating that the measured object has moved out of the detection range of the second histogram. So you have to re do the first histogram of the detection process, re do the first time of flight and the second time of flight detection, that is, the N+1 frame to start from S501 detection. Figure 5 The detection process shown is relative to Figure 3 The advantage of the detection process shown is not limited by the starting point of the first time accuracy unit. The relationship between the first histogram and the second histogram is shown as Figure 6

[0050] Figure 6 Another schematic diagram of the relationship between the first histogram and the second histogram provided by the embodiment of the application is shown as Figure 6 According to the first histogram, the first time of flight can be obtained, and based on the first time of flight, 1 / 2 ΔT is expanded before and after, as Figure 6 The first time of flight obtained from the first histogram is t1, then t1 is taken as the center, and 1 / 2 ΔT is expanded before and after, and then the second histogram is drawn in the range of t1-ΔT / 2~t1+ΔT / 2 with the second time accuracy unit. For example, the second time of flight obtained in the detection process of the N frame is 1000ps, and the time unit of the first accuracy is 500ps, then 1000ps is taken as the center, and 500 / 2ps is expanded before and after, and then the second histogram is drawn in the range of 1250ps~750ps with the second time accuracy unit in the N+1 frame.

[0051] Figure 7 Another detection method schematic diagram provided by the embodiment of the application is shown as Figure 7 ​The detection process of S701-S704 is similar to the detection process of S301-S304, which will not be described here. S705 draws a third histogram based on S704 with a third time unit, wherein the above embodiments are illustrated based on the second time unit to meet the detection requirement, but in the actual detection process, the second time unit may not meet the detection requirement, which requires drawing a third histogram based on the second histogram with a third time unit, and obtaining a third flight time according to the third histogram. The time interval of the second histogram is greater than that of the third histogram, or the time resolution of the second histogram is less than that of the third histogram. S705 draws a third histogram with a third time unit, S706 obtains a third flight time according to the third histogram and outputs the third flight time of the Nth frame. In S707, a time range is expanded based on the third flight time, and the expanded time range is a second time unit. Of course, in S707, the time range can not be expanded, but a second time unit detection is performed based on the second flight time. For example, Figure 3 The method is shown. Then in the expanded time range, S708 draws a third histogram with a third time unit, S709 calculates a third flight time of the N+1th frame according to the histogram of the N+1th frame, and S710 outputs the second flight time if the second flight time can be normally calculated. If the third flight time cannot be obtained, it indicates that the object to be detected has moved out of the detection range of the third histogram. Therefore, the first histogram detection process needs to be performed again, and the first flight time and the second flight time need to be detected again, that is, the N+1th frame needs to be detected from S701 again.

[0052] Figure 8 Another detection method provided by the embodiment of the application is shown in the schematic diagram. Figure 8The detection process of S801-S803 is similar to the detection process of S701-S703, which will not be described here. Then, in S804, it is determined whether the second flight time can be obtained according to the second histogram. If yes, the detection process of S805-S809 is performed, which is similar to the process of S705-S709, which will not be described here. If the second flight time can be normally calculated, the result of the third flight time is output in S810. If the third flight time cannot be obtained, it indicates that the object to be detected has moved out of the detection range of the third histogram. Therefore, the detection process of the second histogram is performed again, and the detection is returned to S803. Then, in S804, it is determined whether the second flight time can be obtained according to the second histogram. If yes, the detection process of S805-S809 is performed. If the second flight time cannot be obtained, S804 needs to return to S801 to perform the detection of the first flight time.

[0053] Figure 7 and Figure 8 The embodiment shown illustrates the process of detecting the flight time in three time precisions, but is not limited to only three flight times, but is only for illustration.

[0054] It should be noted that, in this document, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element preceded by "comprises... a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0055] The above descriptions are only the preferred embodiment of the present application, but not intended to limit the present application. Various modifications and changes can be carried out by those skilled in the art, which should be included in the scope of the present application so far as these modifications and changes do not deviate from the spirit and principle of the present application. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and once an item is defined in one drawing, it need not be further defined and explained in the subsequent drawings. The above descriptions are only the preferred embodiment of the present application, but not intended to limit the present application. Various modifications and changes can be carried out by those skilled in the art, which should be included in the scope of the present application so far as these modifications and changes do not deviate from the spirit and principle of the present application.

Claims

1. A detection method, characterized in that, include: Obtain the first flight time in the Nth frame, and plot the first histogram with a first time precision; obtain the first flight time based on the first histogram; A second histogram is plotted in the Nth frame with a second time precision unit, and the second flight time is obtained based on the second histogram; In the N+1th frame, a second histogram is plotted using the second time precision unit. Based on the second histogram, it is determined whether the second flight time can be obtained. If so, the second flight time is obtained by drawing a second histogram based on the second time precision unit, and the second flight time is output. If not, draw the first histogram in the N+1th frame using the first time precision unit; The process of drawing a second histogram in the N+1th frame with a second time precision unit includes: after obtaining the second flight time of the Nth frame, expanding a time range centered on the second flight time, wherein the expanded time range is a time unit with a first time precision, and drawing a second histogram in the second time precision unit within the expanded range. Calculate the second flight time of the (N+1)th frame based on the histogram of the (N+1)th frame, where N is a positive integer greater than or equal to 1.

2. The detection method according to claim 1, characterized in that, The first time precision unit is greater than the second time precision unit.

3. The detection method according to claim 1, characterized in that: The first flight time or the second flight time is obtained using the peak-to-maximum method based on the first or second histogram.

4. The detection method according to claim 1, characterized in that, The N+1 frame also includes drawing a third histogram with a third time precision unit, where the second time precision unit is larger than the third time precision unit.

Images