TWI704367B - Distance measuring device and method - Google Patents

Abstract

A distance measuring device includes a pulsed laser source, a light receiving unit and a computing module. The pulsed laser source is configured to emit a laser pulse to a target in accordance with a predetermined period. The light receiving unit has a photon receiving type of light receiving element that receives incident light and outputs a binary pulse, and the binary pulse is used to indicate whether a photon receiving event occurs. The computing module is configured to receive the binary pulse and determine whether an inter-period coincidence event occurs, and the inter-period coincidence event is ta relative position of the plurality of predetermined periods of a predetermined number of cycles Detecting multiple photon reception events exceeding a predetermined count. If the calculation module determines that the inter-period coincidence event occurs, the distance of the target is calculated according to time information related to the cross-cycle coincidence event.

Description

Ranging device and method

The invention relates to a distance measuring device and method, in particular to a distance measuring device and method applying cross-cycle coincidence technology.

Autonomous car (Autonomous car) has been a very popular topic in recent years, so the research on advanced driver assistance systems (ADAS) and Lidar (Light Detection And Ranging, LIDAR) related to it has also increased. more. Traditional LiDAR mainly uses charge-coupled device (CCD) or Avalanche photodiode (APD), while single photon cumulative collapse diode (SPAD) is due to its extremely high gain. Its output digital signal makes it come from behind and gradually stand out from other sensors.

Since LiDAR (Light Detection And Ranging, LIDAR) was studied, whether it is Direct Time of Flight (D-TOF) or Indirect Time of Flight (I-TOF) , The suppression of ambient light (Ambient Light) is always a major issue in LIDAR research. Since the amount of background light directly determines the accuracy of the measurement, if the detected background light is too strong, in order to avoid false detection, it is necessary to extend the integration time to obtain more events to increase the confidence level of the measurement, otherwise The power of the light source needs to be increased. However, the cost of extending the integration time is that each measurement time will be several times or even dozens of times longer, which directly affects the reduction of the detection rate.

On the other hand, increasing the laser power will cause eye safety issues, which is only suitable for experimental research or special circumstances related to space. It just so happens that automotive optical radars need to urgently pursue high frame rates and low laser power.

In the application of automotive optical radar and automatic driving, the suppression of background light is very important, and even directly determines the reliability of the product. However, in the traditional suppression technology, although the suppression effect can be achieved, the measurement rate is sacrificed.

Therefore, how to overcome the above-mentioned shortcomings by greatly increasing the signal-to-noise ratio (SNR) without affecting the detection rate through the improvement of the measurement mechanism has become one of the important issues to be solved by this business.

The technical problem to be solved by the present invention is to provide a distance measuring device and method using cross-cycle coincidence technology in view of the shortcomings of the prior art.

In order to solve the above technical problems, one of the technical solutions adopted by the present invention is to provide a distance measuring device, which includes a pulsed laser source, a light receiving unit and a calculation module. The pulsed laser source is configured to emit laser pulses to the target according to a predetermined period. The light receiving unit has a photon counting type light receiving element, which receives incident light and outputs a binary pulse, where the binary pulse is used to indicate whether a photon receiving event occurs. The calculation module is configured to receive binary pulses and determine whether an inter-period coincidence event has occurred, wherein the relative position of the inter-period coincidence event in a predetermined number of cycles in the predetermined period is detected to exceed a predetermined count. Multiple photon reception events. Wherein, if the calculation module determines that a cross-cycle coincident event occurs, it calculates the distance to the target based on time information related to the cross-cycle coincident event.

In order to solve the above-mentioned technical problem, another technical solution adopted by the present invention is to provide a ranging method, which includes: configuring a pulsed laser source to direct the target at a predetermined period Send out laser pulses; configure the light receiving element of the light receiving unit, which is a photon counting type and receives incident light and outputs binary pulses, where the binary pulses are used to indicate whether a photon receiving event occurs; configure the computing module to receive binary pulses and Determine whether an inter-period coincidence event occurs, where the inter-period coincidence event detects multiple photon receiving events exceeding a predetermined count at a relative position in a predetermined number of multiple predetermined periods; where, if The calculation module determines that the cross-cycle coincident event occurs, and then further configures the calculation module to calculate the distance to the target based on the time information related to the cross-cycle coincident event.

One of the beneficial effects of the present invention is that the distance measuring device and method provided by the present invention can greatly increase the signal-to-noise ratio (SNR) by detecting cross-cycle coincidence events without affecting the detection rate, so that LiDAR can be more competitive in the future market.

In addition, compared with the traditional background light suppression technology, the present invention improves the large loss of signal caused by the operation of the previous architecture, so that the measurement time is prolonged, and the amount of signal is reduced while maintaining the ability to suppress noise light. It has been increased several times to an order of magnitude, meeting and maintaining the biggest advantage of the single photon detector, that is, the application in low light. In addition, in terms of hardware consumption, due to the significant suppression of noise, the number of time to digital converters (TDC) required can be reduced, thereby reducing the area required for the system.

In order to further understand the features and technical content of the present invention, please refer to the following detailed description and drawings about the present invention. However, the provided drawings are only for reference and description, and are not used to limit the present invention.

1: Ranging device

10: Pulse laser source

11: Optical receiving unit

110: Light receiving element

12: Calculation module

P: Laser pulse

PW: pulse width

13: The first clock generating circuit

clk1: the first clock signal

TG: target

120: Delay circuit

120a, 120b,..., 120i, 122f: delay element

121: adder circuit

121a, 121b, 121c, 122d: adder

122: comparator circuit

122a: Comparator

122b, 122c: multiplier

122e: counter

123: processor

14: Second clock generation circuit

clk2: second clock signal

clk2b: Inverted signal

DFF: D-type flip-flop

CEL: Delay line unit

sig1: the first half delayed signal

sig2: second half delayed signal

Q2N, Q(2N+1): signal

THR: Threshold setting signal

DES: Delayed signal

Fig. 1 is a block diagram of a distance measuring device according to an embodiment of the present invention.

Fig. 2 is a corresponding diagram of the trigger probability and light intensity of the non-cross-period coincidence technology according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of 2P2C overlap according to an embodiment of the present invention.

Figure 4 is a schematic diagram of NPNC overlap according to an embodiment of the present invention.

Fig. 5 is a trigger path of 3P2C overlap according to an embodiment of the present invention.

Fig. 6 is a trigger probability diagram of multiple configurations overlapping across cycles according to an embodiment of the present invention.

FIG. 7 is a block diagram of a computing module according to an embodiment of the invention.

FIG. 8 is a combined block diagram of a delay circuit and an adder circuit according to an embodiment of the invention.

FIG. 9 is a block diagram of a comparator circuit according to an embodiment of the invention.

Fig. 10 is another schematic diagram of 2P2C overlap according to an embodiment of the present invention.

FIG. 11 is a delay line architecture according to an embodiment of the invention.

Fig. 12 is a signal timing diagram of a delay circuit according to an embodiment of the present invention.

FIG. 13 is a flowchart of a ranging method according to another embodiment of the present invention.

The following is a specific specific embodiment to illustrate the implementation of the "ranging device and method" disclosed in the present invention. Those skilled in the art can understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are merely schematic illustrations, and are not drawn according to actual dimensions, and are stated in advance. The following embodiments will further describe the related technical content of the present invention in detail, but the disclosed content is not intended to limit the protection scope of the present invention.

It should be understood that although terms such as “first”, “second”, and “third” may be used herein to describe various elements or signals, these elements or signals should not be limited by these terms. These terms are mainly used to distinguish one element from another, or a letter Number and another signal. In addition, the term "or" used in this document may include any one or a combination of more of the associated listed items depending on the actual situation.

Because LIDAR is very susceptible to background light (especially sunlight) when outdoors, it is impossible to avoid this problem with LiDAR for cars. Therefore, the present invention provides a circuit architecture that can effectively suppress the background light, which is called an inter-period coincidence technique.

Refer to FIG. 1, which is a block diagram of a distance measuring device according to an embodiment of the present invention. The embodiment of the present invention provides a distance measuring device 1, which includes a pulse laser source 10, a light receiving unit 11 and a calculation module 12. The pulsed laser source 10 emits a laser pulse P to the target according to a predetermined period, and it has a pulse width PW. The distance measuring device 1 further includes a first clock generating circuit 13, respectively connected to the pulsed laser source 10 and the calculation module 12, configured to generate a first clock signal clk1, wherein the pulsed laser source 10 passes the first clock The signal clk1 obtains a predetermined period.

The light receiving unit 11 has a photon counting type light receiving element 110, which receives incident light and outputs binary pulses.

In detail, the light receiving element 110 can be a single photon cumulative breakdown diode (SPADs) chip. The advantages of the SPAD element are high internal gain, low noise, and high time resolution, and since the output of the SPAD chip is a digital signal , Can apply the current technology's quite mature integrated design process to signal processing. SPADs mainly operate above the breakdown voltage of the diode. At this time, the ionization rate reaches its peak and the gain reaches millions, which is called Geiger mode. At this time, when photons enter the material, they are absorbed and generate carriers. A large amount of current is generated, and due to the extremely high gain, a single photon level can be detected, so it is called a single photon detector.

Among them, the binary pulse output by the light receiving element 110 is used to indicate whether a photon receiving event occurs. The light receiving element 110 as a SPAD in the Geiger mode theoretically has an infinite gain, the amplified current value does not contain information, and the presence or absence of an avalanche phenomenon by photon incidence is output as a binary information (voltage pulse).

As described above, in the light receiving unit 11 in this embodiment, binary information (voltage pulse) is output to indicate whether a photon incident event has occurred. Therefore, the total time of the pulse width of the voltage pulse is not affected by changes in the internal amplification gain, etc., and stable photon detection can be achieved independent of temperature.

The calculation module 12 is configured to receive binary pulses and determine whether an inter-period coincidence event occurs. Wherein, a predetermined number of cycles and a predetermined count can be preset, and the occurrence of a cross-cycle coincidence event indicates that multiple photon receiving events exceeding the predetermined count are detected at relative positions in multiple predetermined cycles of the predetermined number of cycles. In other words, assuming that the predetermined number of cycles is N and the predetermined count is M, the basis for judging whether a cross-cycle coincidence event occurs is to consider N consecutive consecutive cycles. If within a period of coincidence time (assuming θ), there are M cycles in relative When there is event detection at the time position, the signal can be output to the output stage circuit. Defined here as MPNC.

Wherein, if the calculation module 12 determines that a cross-cycle coincident event occurs, it calculates the distance to the target based on the time information related to the cross-cycle coincident event.

Before explaining the advantages of the cross-cycle coincidence technology, first consider the situation where the coincidence event occurs in a single cycle when there is no cross-cycle, which is defined as 1PMC here. For example, after the SPAD sensor detects the first photon, it needs to detect the (M-1) photon signal again within the next coincidence time θ before the signal can be output.

Here, we quote "Coincidence in SPAD-based time-of-flight sensors," 2017 13th Conference on Ph.D.Research in Microelectronics and Electronics() published by M. Beer, OMSchrey, BJHosticka and R. Kokozinski in 2017. PRIME), Giardini Naxos, 2017, pp.381-384.

為重合時間，意義為在重合時間

內有m次事件發生，即會觸發重合。 Since the distribution of laser light and ambient light can be regarded as a Poisson process, the probability distribution of the time difference between a photon event and an event can be approximated as a Poisson distribution. Then further consider the case of k-order coincidence. First, define the condition for coincidence to be that if more than m photon detection events occur within a period of time to trigger the coincidence, it is called the k-order coincidence. Because the coincidence is the detection of the first photon Measured as the starting time, so k=m-1, and the probability of coincidence can be obtained by correlation calculations. After obtaining the probability density function Pk , N ( t ), the probability of coincidence event Λ can be obtained by integrating the function, where

Is coincidence time, meaning in coincidence time

If there are m events inside, the coincidence will be triggered.

其中，Nλ代表光強度，m則是先前1PMC的M相對應，代表通過重合篩選的門檻，

則為重合時間。另外，返回機率可定義為下式(2)：

如此，便可得出重合機率與返回機率的關係並進行做圖。 Then, according to the derivation of papers and documents, the probability of coincidence Λ can be approximated as the following formula (1):

Among them, Nλ represents the light intensity, and m corresponds to the M of the previous 1PMC, which represents the threshold to pass the overlap screening.

It is the coincidence time. In addition, the return probability can be defined as the following formula (2):

In this way, the relationship between the coincidence probability and the return probability can be obtained and graphed.

內同時偵測到m個以上之事件才會觸發重合，分別對應到1P2C、1P3C、1P4C。由圖2可知，相較於無重合(1P1C)，1P2C等結果在圖中之斜率相較於重合前顯著上升，由於雷射產生的計數會集中在數個箱(bin)之內，而背景光產生的計數則會以亂數平均分布於每個箱(bin)中，因此雷射計數會落在圖中的右側而背景光則落在圖中的左側，因此重合過後，雖然雷射計數也會下降，但背景光下降的量更多，因此整體的SNR會大幅上升，增加精準度，而隨著m的上升，背景光的抑制以及SNR的上升會更加明顯。 Fig. 2 is a corresponding diagram of the trigger probability and light intensity of the non-cross-period coincidence technology according to an embodiment of the present invention. The horizontal axis is the probability of SPAD detecting the returning photons, and the vertical axis is the theoretical prediction that the returning photons will still enter the time-digital converter after being overlapped. In the figure, m=1 represents the original SPAD signal, that is, the result without overlap, and m=2, m=3, and m=4 represent the overlap time

Only when more than m events are detected at the same time will trigger the coincidence, corresponding to 1P2C, 1P3C, and 1P4C respectively. It can be seen from Figure 2 that compared to no coincidence (1P1C), the slope of results such as 1P2C in the figure is significantly higher than before coincidence. Because the counts generated by the laser will be concentrated in several bins, the background The counts generated by light will be evenly distributed in each bin as random numbers. Therefore, the laser count will fall on the right side of the figure and the background light will fall on the left side of the figure. Therefore, after the overlap, although the laser count is also It will decrease, but the amount of background light decreases more, so the overall SNR will increase significantly, increasing the accuracy, and as m increases, the suppression of background light and the increase of SNR will be more obvious.

The relevant derivation of non-cross-cycle coincidence has been explained above. Although the results can indeed suppress the background light and effectively increase the SNR, it is undeniable that the loss on the signal is also very significant, and if it is in a low light situation, the signal drop is even more It cannot be ignored, and the loss of the signal directly affects the shortest integration time required for each measurement and also affects the scanning speed.

內(在此取2ns)。如圖3所示，其為根據本發明實施例的2P2C重合示意圖。由於背景光在時間上為亂數分佈進入元件，因此圖中絕大多數事件無法通過重合的篩選，因此結果都並未觸發，反之，由於雷射光子返回時間具週期性，通過重合的機率相對提高。此處，所有的事件時間全部均為相對於週期起始點而言，且所示的週期彼此之間可為固定週期、固定變化週期、亂數週期，因此週期的結束時間可能不同。 For this reason, the present invention adopts the cross-cycle coincidence technology. Before extending the model to NPMC, the most basic configuration 2P2C is first explained. The trigger condition of 2P2C is that SPAD has detected a photon collapse event in two consecutive cycles, and the time difference between the detected events in the two cycles is a very short time.

Within (take 2ns here). As shown in FIG. 3, it is a schematic diagram of 2P2C overlap according to an embodiment of the present invention. Since the background light enters the component in a random number distribution in time, most of the events in the figure cannot pass the coincidence screening, so the results are not triggered. On the contrary, because the laser photon return time is periodic, the probability of passing the coincidence is relatively relative. improve. Here, all event times are relative to the starting point of the period, and the periods shown may be fixed periods, fixed changing periods, or random number periods, so the end times of the periods may be different.

有關，為背景光平均每秒返回的數量乘上重合時間

與脈沖雷射的頻率的比值，如式(10)所示：Preturn=在重合時間

內的平均背景光計數/雷射頻率......式(10)；得到返回機率(P)之後，則可得出兩個週期在相對時間的前後一段範圍內同時有事件偵測的機率，如式(11)所示：

同理，考慮NPNC的情形，亦即在連續的N個週期中對應的時間，皆有偵測到事件才會觸發coincidence，又因每個週期偵測到光子事件的機率(return-probability)皆為P，如圖4所示，其為根據本發明實施例NPNC重合示 意圖。因此同理可證，在NPNC情況下，可以得到相似的結果，如式(12)所示：

類似的，在圖4中，所有的事件時間全部均為相對於週期起始點而言，且所示的週期彼此之間可為固定週期、固定變化週期、亂數週期，因此週期的結束時間可能不同。 When discussing the coincidence trigger probability, it is necessary to consider the return probability Preturn mentioned earlier , and the return probability of the background light and the coincidence time

Relevant, it is the average number of background light returns per second multiplied by the coincidence time

The ratio of the frequency to the pulse laser frequency, as shown in equation (10): Preturn = at the coincidence time

The average background light count/laser frequency within...Equation (10); after the return probability (P) is obtained, it can be concluded that the two cycles are detected at the same time within a range of relative time before and after Probability, as shown in formula (11):

Similarly, consider the case of NPNC, that is, at the corresponding time in consecutive N cycles, the coincidence will be triggered only when the event is detected, and the return-probability of detecting a photon event in each cycle is all Is P , as shown in FIG. 4, which is a schematic diagram of NPNC overlap according to an embodiment of the present invention. Therefore, the same reason can be proved, in the case of NPNC, similar results can be obtained, as shown in formula (12):

Similarly, in Figure 4, all event times are relative to the start of the period, and the periods shown can be a fixed period, a fixed change period, or a random number period. Therefore, the end time of the period It may be different.

The following will further explain the case where the number of cycles is different from the coincidence order. For the 3P2C configuration, that is, within 3 cycles, 2 cycles are required to detect the photon event within the coincidence time. FIG. 5 is the trigger path of the 3P2C coincidence according to the embodiment of the present invention. As shown in FIG. 5, In the first cycle, SPAD has a probability of P to detect a photon, if it detects a photon, it will enter the back path; in the second cycle, SPAD also has a probability of P to detect a photon, so there is a probability of P Take the upper path. Relatively, there will be a (1- P ) probability that the lower path will be taken. At this time, when photons are detected in both the first and second periods, the coincidence condition has been met. The coincidence will be triggered regardless of whether there is an event in the following period, so the path ends here; and in the case of no event in the second period, then Enter the third cycle. The condition of the third cycle is the same as that of the second cycle. Therefore, the path where the event is detected will trigger the coincidence. However, since 3P2C only considers 3 cycles, the path of the photon not detected ends here and is judged as not triggered. The coincidence probability of passing 3P2C is shown in equation (13): Λ _{3 P 2 C} = P ( P +(1- P ) P )= P ² +( P ² - P ³ )=2 P ² - P ³ .. .... Formula (12); Compared with 2P2C, 3P2C has more ( P 2- P 3), that is, under the same input signal, the count value after 3P2C overlaps will be more than that of 2P2C. Therefore, when the return probability of the system is not high enough, that is, under low light conditions, the loss of signal counting in coincidence will be quite large. By increasing the number of predetermined cycles, the number of signal meters can be increased and the integration time can be avoided.

請參考圖6，其為根據本發明實施例的跨週期重合的多個組態觸發機率圖。如圖所示，圖中的1P2C與圖2之n=2相同，用來與跨週期重合的組態2P2C、3P2C、5P2C及1OP2C進行對照。相較於1P2C，跨週期重合的計數值顯然大幅上升，如2P2C大約上升了2倍，3P2C約上升了4倍，計數值數的提升代表的是積分時間的下降，而另外一個觀察重點為SNR，圖中曲線的斜率代表該組態抑制背景光的能力，可以發現不管是2P2C、3P2C、5P2C、1OP2C，在其提升計數值的同時，其曲線與1P2C是接近互相平行的，代表跨週期重合可以在不影響SNR的情形下提升計數值，以縮短每次測量所需的最短積分時間，此特性即為跨週期重合最大的特點之一。除此之外，跨週期重合亦可透過調整預定週期數量及預定計數來提升SNR，增加對背景光的抑制。 Therefore, the situation where NPMC overlaps across cycles can be further considered, and the trigger probability is shown in equation (13):

Please refer to FIG. 6, which is a diagram of the trigger probability of multiple configurations overlapping across cycles according to an embodiment of the present invention. As shown in the figure, 1P2C in the figure is the same as n=2 in figure 2, and is used to compare with the overlapping configurations 2P2C, 3P2C, 5P2C and 1OP2C across cycles. Compared with 1P2C, the cross-cycle coincident count value has obviously increased significantly. For example, 2P2C has increased by about 2 times, and 3P2C has increased by about 4 times. The increase in the number of counts represents a decrease in integration time, and another observation point is SNR , The slope of the curve in the figure represents the ability of the configuration to suppress background light. It can be found that whether it is 2P2C, 3P2C, 5P2C, 1OP2C, while increasing the count value, its curve and 1P2C are close to each other, which means that the cross-cycle overlap The count value can be increased without affecting the SNR to shorten the shortest integration time required for each measurement. This feature is one of the largest cross-cycle overlap characteristics. In addition, cross-cycle coincidence can also increase the SNR by adjusting the predetermined number of cycles and the predetermined count, and increase the suppression of background light.

In order to realize the above mechanism, at the hardware level, further reference can be made to FIGS. 7 and 8, which are block diagrams of the calculation module according to an embodiment of the invention, and the delay circuit and the adder circuit according to the embodiment of the invention. Combination block diagram. As shown in FIG. 7, the calculation module 12 includes a delay circuit 120, an adder circuit 121, a comparator circuit 122 and a processor 123.

The delay circuit 120 includes a plurality of delay elements 120a, 120b, ..., 120i, which are configured to receive a binary pulse therefrom, and the delay elements 120a, 120b, ..., 120i respectively delay the binary pulse by the predetermined period , To respectively generate multiple delay signals with the number of delay cycles. Here, the delay circuit 120 respectively delays the binary pulse by a predetermined period through the first clock signal clk1. The adder circuit 121 includes a plurality of adders 121a, 121b, and 121c, and selects at least one of the delay signals to accumulate according to a cycle counting configuration, such as 2P2C, 3P2C, 5P2C, and 10P2C, to generate an accumulation trigger signal.

It should be noted that the cycle count configuration defines a plurality of predetermined cycles with a predetermined number of cycles, and the cumulative trigger signal records binary pulse data within the predetermined number of cycles in different time intervals.

In detail, as shown in Figure 8, the cross-cycle overlap configuration to be performed includes 2P2C, 3P2C, 5P2C, and 10P2C, which is convenient for comparison with Figure 6, so the required delay line is 9 groups, each of which is 120a, 120b. ,...,120i is delayed by one period, that is, the predetermined period of the laser pulse P in FIG. 1, and all the required delay signals are accumulated by the adders 121a, 121b, and 121c, respectively, and the resulting signal is It is the sum of all events of N-1 cycles except the first cycle, and is sent to the next end for other work.

Further, the comparator circuit 122 respectively receives one of the delay signals and a threshold setting signal to determine whether there is a binary pulse exceeding a predetermined count in the predetermined periods of the predetermined number of periods to determine the Whether a cross-cycle coincident event occurs, and a judgment result signal is generated. Wherein, the threshold setting signal is related to the predetermined count.

As previously described, the output of the adder circuit 121 includes the accumulation of N-1 cycles outside the first cycle. The reason is that in the coincidence trigger condition, the photon event must be detected in the first cycle. Further reference may be made to FIG. 9, which is a block diagram of a comparator circuit according to an embodiment of the present invention. As shown in the figure, the comparator circuit 122 includes a comparator 122a, a multiplier 122b, a multiplier 122c, an adder 122d, a counter 122e, and a delay element 122f. Since the configuration trigger conditions selected this time are all two photons, after subtracting the first cycle, the count sum of other cycles needs to be more than 1, therefore, the input of the first input terminal of the comparator 122a is delayed by N cycles To delay the signal DES, the second input terminal of the comparator 122a inputs the threshold setting signal THR, which sets the threshold to 0.5. The output after the comparator 122a is a signal composed of 0 and 1. Perform an AND operation on this signal and the original SPAD signal from the photodetection unit 11 to obtain the NP2C cross-cycle overlap signal, and then multiply The counter 122b, the multiplier 122c, the adder 122d, the counter 122e, and the delay element 122f accumulate the total number and histogram.

In addition, the aforementioned predetermined period may include multiple variable periods in addition to the fixed period, and the delay elements 120a, 120b, ..., 120i respectively divide the binary pulses with these Variable cycles are used for delay to respectively generate the delay signals with the number of delay cycles. In other words, based on the above structure, further promotion can be carried out. If the delay time of the delay line (delay line) formed by the delay elements 120a, 120b, ..., 120i is set to be fixed, it is a fixed cycle cross-cycle coincidence mechanism. However, if it is changed every once in a while, a variable-cycle cross-cycle coincidence mechanism can be realized. By analogy, if the variable period changes with a specific or random rule, a cross-period coincidence mechanism with a specific or random rule can be realized.

Therefore, further reference may be made to FIG. 10, which is another schematic diagram of 2P2C overlap according to an embodiment of the present invention. In this embodiment, when the pulsed laser source 10 emits laser pulses P to the target in a variable or random number period, the incident photons within a predetermined time after the start of the period in the random number period can be reduced Record it, as shown in Figure 10.

For example, in the foregoing embodiment with a fixed period, if a 1 MHz laser is used as the pulse laser source 10, the predetermined period is always 1000 ns. However, when a random number period is used in this embodiment, if the shortest interval between the period and the period is 1000 ns, it is set that most of the periods randomly jump between 1000 and 1500 ns. At this time, the photon incident event is recorded within a predetermined recording time after the start of the period, for example 1000 ns, and at the same time, after the start of the period of the next cycle, the photon is incident within 1000 ns of the same predetermined recording time The event is recorded to determine whether a cross-cycle coincident event occurs.

Then, replace the information of the previous cycle with the data of the current cycle, and wait for the signal of the next cycle to enter, so that the cross-cycle coincidence technology under the random number cycle can be realized. In addition, the relationship between the return probability and the coincidence probability of a fixed period is also fully applicable when a variable period is used.

On the other hand, the adder circuit 122 may further design a cycle counting configuration according to the above-mentioned specific or random rule, and accordingly select one of the above-mentioned delay signals for accumulation, so as to generate an accumulation trigger signal. Among them, the cycle count configuration defines a variable predetermined cycle with a predetermined number of cycles.

Please refer to Figure 9 again. When the counter 122e is used for calculation, since the operation of the counter 122e needs to be triggered by the rising edge of the input signal, the counter 122e may not be detected when more than two consecutive signals enter. Therefore, the pulse width of the signal needs to be changed to half. For example, the method implemented here is to perform an AND operation between a pulse whose pulse width is half the original and the NP2C signal. In addition, the accumulation of the histogram is to delay the signal through the delay element 122f for one cycle, and then the output signal is fed back and added to the original signal, so that the output observed result will be from the first to the first in each cycle The accumulation of the current cycle. According to the accumulation result, the laser signal can be clearly identified on the time axis.

Then, the above result is input to the processor 123 as a judgment result signal, and the processor 123 executes a ranging algorithm to calculate the distance of the target based on the judgment result signal. For example, the direct time-of-flight (D-TOF) method can be used for calculation. When the laser pulse source 10 emits a pulse, a signal is sent to the processor 123, which may include a time-to-digital converter (TDC), for example, The start signal, when the photon hits the target TG and is reflected by the light sensing unit 11, the signal is regarded as a stop signal by the above judgment result. The processor 123 calculates the time difference △τ between the two signals and multiplies it by the speed of light c divided by 2 is the distance of the target TG.

The delay-line architecture of this embodiment will be described below based on FIG. 11. FIG. 11 is a delay line architecture according to an embodiment of the invention. Firstly, two frequencies of the system will be defined. One is the frequency emitted by the laser pulse source 10, that is, the first clock signal clk1 generated by the aforementioned first clock generating circuit 13. The frequency used here can be, for example, 5MHz. In addition, the distance measuring device 1 further includes a second clock generating circuit 14 for generating a second clock signal clk2 having a sampling period. The sampling period is related to the pulse width PW of the laser pulse P, and the second clock The period of the signal clk2 is smaller than the period of the first clock signal clk1. In detail, in order to ensure that the data signal can be detected, the pulse width of this signal must be smaller than the pulse width PW of the SPAD signal. These two frequencies will determine the number of delay elements 120a, 120b, ..., 120i required by the system. The delay elements 120a, 120b, ..., 120i can be, for example, D-type flip-flop DFF. The D-type flip-flops DFF receive the second clock signal clk2, and sample and delay the binary pulse P according to the sampling period to generate the delay signals.

In addition, to complete the delay function of the complete D-type flip-flop delay line, the architecture needs to be set up in two paths, so as to ensure that each incoming signal can be delayed. As shown in FIG. 10, the delay circuit 120 includes a plurality of delay line units CEL. Among the plurality of D-type flip-flops DFF, four adjacent D-type flip-flops DFF are used as one delay line unit CEL.

As shown in the figure, the clock terminals of two D-type flip-flops DFF receive the second clock signal clk2 and generate the first half-delay signal sig1, and the clock terminals of the other two D-type flip-flops DFF receive the second clock signal. The clock signal clk2 is an inverted signal clk2b, and a second half delay signal sig2 is generated. Each path is responsible for detecting half of the signal. In the figure, the second clock signal clk2 and the inverted signal clk2b can delay the signal by one cycle of the second clock signal clk2, so the two paths can be Every 4 D-type flip-flops DFF is regarded as a set of delay line units CEL, and the number of delay line units CEL contained in each delay line is the frequency of the second clock signal clk2 received by the D-type flip-flops DFF and the lightning The ratio of radio frequency. The adder circuit can be configured according to the cycle count, for example, NPMC selects the corresponding first half-delay signal sig1 and the second half-delay signal sig2 and adds them to generate the cumulative trigger signal.

In addition, when outputting the signal of the delay circuit, the size of the signal output window must also be taken into consideration together with the pulse width PW of the pulse signal. Because the pulse width PW will cause the width of the signal output window to change, and a wider pulse width PW will cause both paths to have signals at the same time. After the pulse width PW is greater than the half cycle of the second clock signal clk2, both the upper and lower paths will detect signals, one path is the earlier signal and the other is the later signal. Moreover, both paths will generate a signal output window, and the two signal output windows will be adjacent, as shown in FIG. 12, which is a signal timing diagram of the delay circuit according to an embodiment of the present invention. In order to solve this problem, it is necessary to select the first detected path as the output signal. The algorithm used in this embodiment is shown in equation (14). The feature is that it eliminates the need to determine which path to detect the signal first, but directly performs OR operation on the signal Q2N of the two paths, and the signal Q(2N+1) is the same.

Refer to FIG. 13, which is a flowchart of a ranging method according to another embodiment of the present invention. In detail, in the cross-cycle coincidence operation, in addition to using the hardware architecture mentioned in the above embodiment, it can also be implemented by software. Specifically, the time information of the SPAD signal can be recorded and calculated by software to realize cross-cycle coincidence event detection.

As shown in the figure, the distance measurement method provided by the embodiment of the present invention includes the following steps: Step S100: Configure a pulsed laser source to emit laser pulses to the target according to a predetermined period; Step S102: Configure the light receiving element of the light receiving unit , Which is a photon counting type and receives incident light and outputs binary pulses, where the binary pulses are used to indicate whether a photon receiving event occurs; step S103: configure a calculation module to receive binary pulses and determine whether inter-period coincidence occurs. coincidence) event. Wherein, the cross-cycle coincidence event is that a plurality of photon receiving events exceeding a predetermined count are detected at a relative position in a plurality of predetermined cycles of a predetermined number of cycles.

Wherein, if the calculation module determines that the cross-cycle coincidence event occurs, it further proceeds to step S103: the configuration calculation module calculates the distance of the target according to the time information related to the cross-cycle coincidence event.

[Beneficial effects of the embodiment]

One of the beneficial effects of the present invention is that the distance measuring device and method provided by the present invention can detect cross-period coincidence events, so as to greatly improve the detection rate without affecting the detection rate. The signal-to-signal ratio (SNR) enables LiDAR to be more competitive in the future market.

In addition, compared with the traditional background light suppression technology, the present invention improves the large loss of signal caused by the operation of the previous architecture, so that the measurement time is prolonged, and the amount of signal is reduced while maintaining the ability to suppress noise light. It has been increased several times to an order of magnitude, meeting and maintaining the biggest advantage of the single photon detector, that is, the application in low light. In addition, in terms of hardware consumption, due to the significant suppression of noise, the number of time to digital converters (TDC) required can be reduced, thereby reducing the area required for the system.

The content disclosed above is only a preferred and feasible embodiment of the present invention, and does not limit the scope of the patent application of the present invention. Therefore, all equivalent technical changes made using the description and schematic content of the present invention are included in the application of the present invention. Within the scope of the patent.

1: Ranging device

10: Pulse laser source

11: Optical receiving unit

110: Light receiving element

12: Calculation module

P: Laser pulse

PW: pulse width

13: The first clock generating circuit

clk1: the first clock signal

TG: target

Claims (18)

A distance measuring device includes: a pulse laser source configured to emit a laser pulse to a target according to a predetermined period, wherein the predetermined period includes a plurality of variable periods, and the pulse laser source is configured The laser pulse is emitted according to the variable periods; a light receiving unit has a photon counting type light receiving element, which receives incident light and outputs a binary pulse, wherein the binary pulse is used to indicate whether a photon receiving event occurs ; And a calculation module configured to receive the binary pulse and determine whether an inter-period coincidence event occurs, wherein the inter-period coincidence event is a predetermined number of cycles in a plurality of predetermined periods The relative position detects multiple photon receiving events exceeding a predetermined count; wherein, if the calculation module determines that the cross-cycle coincidence event occurs, it calculates the distance of the target based on a time information related to the cross-cycle coincidence event, Wherein, the calculation module is configured to further determine whether the photon receiving events exceeding the predetermined count are detected at relative positions in the variable periods included in the predetermined number of periods and the predetermined period. Whether this cross-cycle coincidence event occurs. For the distance measuring device described in claim 1, wherein the calculation module includes: a delay circuit, including a plurality of delay elements, configured to receive the binary pulse, and the delay elements respectively use the binary pulse Delay in a predetermined period to respectively generate a plurality of delay signals having a delay period number; an adder circuit selects at least one of the delay signals to accumulate according to a period counting configuration to generate an accumulative trigger signal, wherein , The cycle count configuration defines a plurality of the predetermined cycles with a predetermined number of cycles, and the cumulative trigger signal is recorded in different time intervals, the predetermined number of cycles The binary pulse data in the predetermined periods; a comparator circuit respectively receives one of the delay signals and a threshold setting signal to determine whether there is more than the predetermined period in the predetermined number of periods A predetermined count of the binary pulse is used to determine whether the cross-cycle coincidence event occurs, and a determination result signal is generated, wherein the threshold setting signal is related to the predetermined count; and a processor configured to perform a ranging calculation Method to calculate the distance of the target based on the judgment result signal. For example, the distance measuring device described in item 2 of the scope of patent application further includes: a first clock generating circuit respectively connected to the pulse laser source and the calculation module, and configured to generate a first clock signal, wherein The pulse laser source obtains the predetermined period through the first clock signal, and the delay circuit respectively delays the binary pulse by the predetermined period through the first clock signal. For the distance measuring device described in item 3 of the scope of patent application, the delay elements respectively delay the binary pulse with the variable periods to respectively generate the delay signals having the delay period number. For the distance measuring device described in item 4 of the patent application, the adder circuit selects one of the delay signals to accumulate according to the period count configuration to generate the accumulation trigger signal, wherein the period count configuration The variable predetermined periods with the predetermined number of periods are defined. As described in item 5 of the scope of patent application, the distance measuring device further includes: a second clock generating circuit for generating a second clock signal with a sampling period, wherein the sampling period and the laser pulse A pulse width is related, and the period of the second clock signal is smaller than the period of the first clock signal; wherein the delay elements include a plurality of D-type flip-flops, and the D-type flip-flops receive the second time Pulse signal, and sample the binary pulse according to the sampling period And delay to generate these delayed signals. The distance measuring device described in item 6 of the scope of the patent application, wherein the delay circuit includes a plurality of delay line units, and the D-type flip-flops use four adjacent D-type flip-flops as a delay line unit , The clock terminals of two D-type flip-flops receive the second clock signal and generate a first half-delay signal, and the clock terminals of the other two D-type flip-flops receive the second clock signal Invert the signal and generate a second half delayed signal. For example, in the distance measuring device described in item 7 of the scope of patent application, the adder selects the corresponding first half-delay signal and the second half-delay signal to generate the cumulative trigger signal according to the cycle count configuration. The distance measuring device described in claim 1, wherein the calculation module further includes a time-to-digital converter configured to calculate the time when the pulsed laser source emits the laser pulse and the occurrence of the photon receiving events The time difference between the time to generate a time information signal including the time information. A distance measuring method includes: configuring a pulsed laser source to send a laser pulse to a target according to a predetermined period; configuring a light receiving unit and a light receiving element, which are photon counting type and receive incident light and output A binary pulse, wherein the binary pulse is used to indicate whether a photon receiving event occurs; a calculation module is configured to receive the binary pulse and determine whether an inter-period coincidence event occurs, wherein the inter-period coincidence event A plurality of photon receiving events exceeding a predetermined count are detected at relative positions in a plurality of predetermined periods of a predetermined number of cycles, wherein the calculation module is configured to further determine whether there are multiple photon receiving events in the predetermined number of cycles. The relative positions in the variable periods included in the predetermined period detect the photon receiving events exceeding the predetermined count to determine whether the cross-period coincidence event occurs; Wherein, if the calculation module determines that the cross-cycle coincidence event occurs, the calculation module is further configured to calculate the distance to the target based on a piece of time information related to the cross-cycle coincidence event. The distance measurement method according to claim 10, wherein the calculation module includes a delay circuit, an adder circuit, a comparator circuit, and a processor, and the distance measurement method further includes: configuring multiple delays of the delay circuit The element receives the binary pulse to delay the binary pulse with the predetermined period to respectively generate a plurality of delay signals having a delay period number; the adder circuit is configured to select at least one of the delay signals according to a period count configuration An accumulation is performed to generate an accumulation trigger signal, wherein the cycle count configuration defines a plurality of the predetermined cycles with a predetermined number of cycles, and the accumulation trigger signal is recorded in different time intervals, the predetermined number of cycles The binary pulse data in a predetermined period; the comparator circuit is configured to receive one of the delay signals and a threshold setting signal to determine whether there is more than a predetermined period in the predetermined number of periods The binary pulses are counted to determine whether the cross-cycle coincidence event occurs, and a determination result signal is generated, wherein the threshold setting signal is related to the predetermined count; and a processor is configured to execute a ranging algorithm according to the The judgment result signal and the time information calculate the distance of the target. For example, the distance measurement method described in claim 11 further includes: configuring a first clock generating circuit respectively connected to the pulsed laser source and the calculation module to generate a first clock signal, wherein the pulse The laser source obtains the predetermined period through the first clock signal, and the delay circuit respectively delays the binary pulse by the predetermined period through the first clock signal. Such as the ranging method described in item 12 of the scope of patent application, wherein the delay elements are divided into Do not delay the binary pulse with the variable periods to generate the delay signals with the delay period number. For example, the ranging method described in item 13 of the scope of patent application, wherein the adder circuit selects one of the delay signals to accumulate according to the cycle count configuration to generate the accumulation trigger signal, wherein the cycle count configuration The variable predetermined periods with the predetermined number of periods are defined. The distance measurement method described in item 14 of the scope of the patent application further includes: a second clock generation circuit for generating a second clock signal having a sampling period, wherein the sampling period and the laser pulse A pulse width is related, and the period of the second clock signal is smaller than the period of the first clock signal; wherein the delay elements include a plurality of D-type flip-flops, and the D-type flip-flops receive the second time Pulse signal, and the binary pulse is sampled and delayed according to the sampling period to generate the delay signals. The distance measurement method described in item 15 of the scope of patent application, wherein the delay circuit includes a plurality of delay line units, and the D-type flip-flops use four adjacent D-type flip-flops as a delay line unit , The clock terminals of two D-type flip-flops receive the second clock signal and generate a first half-delay signal, and the clock terminals of the other two D-type flip-flops receive the second clock signal Invert the signal and generate a second half delayed signal. For example, in the ranging method described in the scope of patent application, the adder selects the corresponding first half-delay signal and the second half-delay signal according to the cycle count configuration to add to generate the accumulated trigger signal. For example, the ranging method described in item 10 of the scope of patent application further includes a time-to-digital converter configured with the calculation module to calculate the time when the pulsed laser source emits the laser pulse and the time when the photon receiving events occur Time difference between the two to generate a time information signal including the time information.

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