CN115267743A

CN115267743A - Method and apparatus for determining time of flight

Info

Publication number: CN115267743A
Application number: CN202210541902.0A
Authority: CN
Inventors: 张耿立
Original assignee: Shenzhen Fushi Technology Co Ltd
Current assignee: Shenzhen Fushi Technology Co Ltd
Priority date: 2021-05-18
Filing date: 2022-05-17
Publication date: 2022-11-01

Abstract

The present application provides a method and apparatus for determining time of flight that can simplify control of the measurement process. The method comprises the following steps: according to the receiving time of the photosensitive device for receiving the photon signals in the preset time range, constructing a first histogram in the preset time range according to the width of a first time box; determining a first time range in which a photon signal reflected by an object is located according to a first histogram; controlling the photosensitive device to receive photon signals within a preset time range; selecting a photon signal in a first time range from photon signals received by the photosensitive device in a preset time range; according to the receiving time of the photon signals in the first time range, constructing a second histogram in the first time range by using a second time box width, wherein the second time box width is smaller than the first time box width; from the second histogram, a time of flight of the photon signal reflected by the object is determined.

Description

Method and apparatus for determining time of flight

Technical Field

The present application relates to the field of computer technologies, and in particular, to a method and an apparatus for determining a time of flight.

Background

The direct time-of-flight technique is based on the receiving time of the photosensitive device for receiving photon signals, counts the number of photons in different time boxes, constructs a histogram, and then determines the time-of-flight of the photons according to the histogram. The narrower the bin width of the histogram, the higher the accuracy of the determined time of flight, but at the same time the number of bins is increased, increasing the memory requirements.

The method comprises the steps of firstly constructing a first histogram by rough measurement to determine a first time range in which a photon signal is positioned, and only constructing a second histogram in the first time range by fine measurement, so that the time range of the second histogram is reduced, the number of time boxes required by the second histogram is reduced, and the requirement on a memory is reduced. In the way of using the rough measurement and the fine measurement, how to realize the control of the measurement process in a simple way becomes an urgent problem to be solved.

Disclosure of Invention

In view of the above, embodiments of the present application provide a method and an apparatus for determining a time of flight, which can simplify control of a measurement process.

In a first aspect, there is provided a method for determining time of flight, comprising: according to the receiving time of the photosensitive device for receiving the photon signals in the preset time range, constructing a first histogram in the preset time range according to the width of a first time box; determining a first time range in which a photon signal reflected by an object is located according to the first histogram; controlling the photosensitive device to receive photon signals within the preset time range; constructing a second histogram in the first time range with a second time bin width according to the receiving time of the photon signal received in the first time range, the second time bin width being smaller than the first time bin width; determining a time of flight of a photon signal reflected by the object from the second histogram.

In one embodiment, the first time range is a time range corresponding to one or more time bins in the first histogram.

In one embodiment, the method further comprises: determining the one or more time bins according to a maximum method, a centroid method, or a machine learning method.

In one embodiment, the one or more time bins are time bins in which peaks in the first histogram are located; alternatively, the one or more time bins include a time bin at which a peak in the first histogram is located and a time bin adjacent to the time bin at which the peak is located.

In one embodiment, the first time range is greater than or equal to a pulse width of a photon signal reflected by the object.

In one embodiment, the method further comprises: determining a reception time of a photon signal for constructing the first histogram using a first time-to-digital converter (TDC) having a measurement time interval equal to the first time bin width; determining a time of reception of the photon signal for constructing the second histogram using a second TDC having a measurement time interval equal to the second time bin width.

In one embodiment, the memory space for counting photon signals in the first histogram is at least partially the same as the memory space for counting photon signals in the second histogram.

In one embodiment, the photosensitive device is an avalanche photodiode.

In one embodiment, the method further comprises: and determining the distance of the object according to the flight time.

In a second aspect, there is provided an apparatus for determining time of flight, comprising: the first histogram construction unit is used for constructing a first histogram in a preset time range according to the receiving time of the photosensitive device for receiving the photon signals in the preset time range and the width of a first time box; the first determining unit is used for determining a first time range in which the photon signals reflected by the object are located according to the first histogram; the control unit is used for controlling the photosensitive device to receive photon signals within the preset time range; a second histogram construction unit, configured to construct a second histogram in the first time range with a second time bin width according to a receiving time of the photon signal received in the first time range, where the second time bin width is smaller than the first time bin width; a second determining unit for determining the time of flight of the photon signal reflected by the object according to the second histogram.

In one embodiment, the apparatus further comprises: a third determining unit for determining the one or more time bins according to a maximum method, a centroid method or a machine learning method.

In one embodiment, the apparatus further comprises: a first time-to-digital converter, TDC, for determining the reception time of the photon signals used to construct the first histogram, the first TDC having a measurement time interval equal to the first time bin width; a second TDC for determining a time of reception of the photon signals for constructing the second histogram, the second TDC having a measurement time interval equal to the second time bin width.

In one embodiment, the photosensitive device is an avalanche photodiode.

In one embodiment, the apparatus further comprises: a fourth determining unit, configured to determine the distance to the object according to the flight time.

In a third aspect, an apparatus is provided, comprising: an emitter for emitting a photonic signal towards an object; a light sensing device for receiving the photon signal reflected by the object; and an apparatus for determining time of flight as set forth in the second aspect or any embodiment of the second aspect.

In a fourth aspect, an apparatus for determining time of flight is provided, comprising a memory having executable code stored therein and a processor configured to execute the executable code to implement a method as set forth in the first aspect or any one of the embodiments of the first aspect.

In a fifth aspect, there is provided a computer readable storage medium having stored thereon executable code that, when executed, is capable of implementing a method as set forth in the first aspect or any one of the embodiments of the first aspect.

Based on the scheme of the application, whether in the process of constructing the first histogram (rough measurement process) or the process of constructing the second histogram (fine measurement process), the photosensitive device is controlled to receive photon signals within a preset time range, and the two measurement processes keep consistent control over the photosensitive device, so that the control over the photosensitive device can be simplified. When the second histogram is generated, the second histogram in the first time range can be constructed by selecting the photon signals according to the receiving time, and the control process of the process is simple and easy to realize.

Drawings

Fig. 1 is a schematic diagram of a measurement system applicable to the embodiments of the present application.

Fig. 2 is a schematic diagram of a possible histogram provided in an embodiment of the present application.

Fig. 3 is a flowchart illustrating a method for determining time of flight according to an embodiment of the present application.

Fig. 4 is a schematic diagram of another possible histogram provided in the embodiment of the present application.

Fig. 5 is a schematic diagram of a second histogram provided in an embodiment of the present application.

Fig. 6 is a schematic diagram of a manner of determining a time of flight using a TDC according to an embodiment of the present application.

Fig. 7 is a schematic diagram of a delay chain according to an embodiment of the present application.

Fig. 8 is a schematic diagram of enable time of a photosensitive device according to an embodiment of the present application.

Fig. 9 is a schematic diagram of an enable time of another photosensitive device provided in an embodiment of the present application.

FIG. 10 is a schematic flow chart diagram of another method for determining time of flight provided by an embodiment of the present application.

Fig. 11 is a schematic diagram illustrating enable times of another photosensitive device according to an embodiment of the present application.

Fig. 12 is a schematic block diagram of an apparatus for determining time of flight according to an embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, and not all embodiments.

The Time of Flight (ToF) technique is a technique of calculating a distance of an object by measuring a Time of Flight of light in a space, and is widely applied to the fields of consumer electronics, unmanned driving, laser focusing, presence recognition, AR/VR, three-dimensional modeling, live-action navigation, and the like because of its advantages of high precision, large measurement range, and the like.

ToF may include direct-time-of-flight (dToF). The principle of dtod measurement is that an emitter periodically emits a pulsed photon signal that is reflected off of an object and received by a light sensing device, and then the distance to the object can be determined by calculating the time of flight of the photons from emission to reflection.

The distance of the object can be calculated by the following formula:

D＝c*t/2

where c is the speed of light and t is the time of flight.

The dtofs measurement system of the embodiment of the present application is described below with reference to fig. 1. The measurement system shown in fig. 1 may comprise an emitter 1, a photosensitive device 3, a time determination unit 4, a histogram construction unit 5 and a processing unit (not shown in the figure). The time determination unit 4 may be connected to the light sensing device 3 and the histogram construction unit 5 may be connected to the time determination unit 4. Emitter 1 may emit pulsed photon signals outwardly at a frequency that, after reflection by object 2, form reflected photon signals that may be received by light sensing device 3. The time determination unit 4 may determine the time interval between the emission of a photon signal from the emitter 1 to the reception by the photosensitive device 3. The measurement system can emit and receive photon signals for a plurality of times in the measurement process, the time determining unit 4 can send time intervals of the plurality of times of measurement to the histogram constructing unit 5, and the histogram constructing unit 5 can construct a histogram according to the recorded time intervals of the plurality of times of measurement. The processing unit may determine the time of flight of the photons from the histogram.

The emitter 1 may include a light source 12, where the light source 12 may be a light source such as a light emitting diode, an edge emitting laser, a Vertical Cavity Surface Emitting Laser (VCSEL), or an array light source composed of a plurality of light sources. Preferably, the array light source may be a VCSEL array light source chip formed by generating a plurality of VCSEL light sources on a single semiconductor substrate. The light signal emitted by the light source 12 may be visible light, infrared light, ultraviolet light, or the like. The transmitter 1 may further include a driver 11, and the light source 12 may transmit a light signal under the driving of the driver 11. For example, for a dtod, the light source may emit a pulsed light beam at a certain frequency (or pulse period) driven by the driver. The frequency can be set according to the measuring distance, for example, the frequency can be set between 1MHz and 100MHz, and the measuring distance can be between several meters and several hundred meters.

The emitter 1 may further comprise an optical element 13. The optical element 13 may receive the light signal emitted by the light source 12 and modulate the light signal, such as diffraction, refraction, reflection, and the like, and the modulated light signal may be a focused light signal, a flood light signal, a structured light signal, and the like. The optical element 13 may be one or more of a lens, a diffractive optical element, a mask, a mirror, a micro-electro-mechanical system (MEMS) galvanometer, and the like. The optical element 13 may direct the modulated optical signal to the object 2 to be detected, and the object 2 to be detected may reflect the optical signal to the light-sensing device 3.

The processing unit may be a stand-alone dedicated circuit, such as a system-on-a-chip (SOC) chip, a Field Programmable Gate Array (FPGA) chip, an Application Specific Integrated Circuit (ASIC) chip, or the like. Alternatively, the processing unit may be a general-purpose processor, for example, when the depth camera is integrated into a smart terminal such as a mobile phone, a television, a computer, etc., the processor in the terminal may be at least a part of the processing unit.

The light sensing device 3 may comprise a plurality of light sensing units distributed in an array, and different light sensing units may be used for receiving photon signals reflected by different parts of the object. The photosensitive device in the embodiment of the present application may be a photomultiplier tube, an avalanche photodiode, or the like. The avalanche photodiode may be, for example, a Single Photon Avalanche Diode (SPAD) that is responsive to an incident single photon. When a photon is incident on the SPAD, an electron is formed, and the electron is accelerated to impact in the depletion region to generate more electrons, so that the SPAD avalanche breakdown is caused, and the SPAD can output an avalanche signal to the time determination unit 4.

The time determination unit 4 may comprise a plurality of time determination subunits distributed in an array. The plurality of time determination subunits have a corresponding relationship with the plurality of photosensitive units, for example, one time determination subunit corresponds to one photosensitive unit, or one time determination subunit corresponds to the plurality of photosensitive units. The time determination unit may be, for example, a time interval Table (TIM), a time digitizer (time divider), a Time Counter (TC), a time To Digital Converter (TDC), and the like.

Taking TDC and SPAD as an example, TDC may be coupled to SPAD. To more accurately determine the time of receipt of the photon signal, the TDC may begin timing when the SPAD is activated to determine the time of receipt of the photon signal by the SPAD. In a measurement system using SPAD, the incidence of a single photon on the SPAD will cause an avalanche, the SPAD will output an avalanche signal to the TDC, which can detect the time of receipt of the photon signal by the SPAD. In the case where the TDC and SPAD are synchronized with the transmitter, the reception time of the SPAD receiving photon signal determined by the TDC can represent the time interval between the emission of the photon from the transmitter and the reception by the SPAD.

After a plurality of measurements, the histogram construction unit 5 may construct a histogram according to the receiving time of the photon signal received by the light sensing device 3. The histogram is collected in a memory that includes a plurality of memory cells, where each memory cell holds a photon count for a time bin (time bin), which may represent a time period or interval. The time determination unit 4 may convert the reception time into a time code (e.g., a binary code, a temperature code, etc.) and transmit the time code to the histogram construction unit 5. The histogram construction unit 5 may count, such as add 1, on the corresponding memory location based on the time code. After multiple measurements, the histogram construction unit 5 may count the photon counts in all the memory cells and construct a histogram. The photon counting can be realized by time-correlated single-photon counting (TCSPC) in the histogram construction unit 5.

Fig. 2 is a schematic illustration of one possible histogram. In the histogram, the abscissa represents a time bin and the ordinate represents the number of photons. The histogram shown in fig. 2 comprises 23 time bins, each time bin having an equal width, which may also be referred to as a time interval. One time bin corresponds to one memory unit for storing the photon counts in the time bin corresponding to the memory unit. The width of the time box can be adjusted according to the measurement accuracy. The processing unit may determine the time of flight of the photons from the number of photons stored in each time bin.

The measurement range of the measurement system is related to the number of time bins and the time bin width, e.g. measurement range = time bin width x number of time bins. Taking the example of a time bin width of 1.6ns, if the measurement system includes 23 time bins, the measurement range of the measurement system is 36.8ns.

It will be appreciated that the light sensing device 3 receives not only photon signals reflected by an object (which may be referred to simply as reflected photon signals), but also ambient light signals. Thus, not only the count of photon signals reflected by an object but also the count of ambient light signals is included in the histogram. The measurement system can determine the time of flight of the photon signal that is actually reflected by the object based on the number of photons in different time bins. Referring to fig. 2, taking the case where the time bin width is 1.6ns as an example, assuming that it is finally determined that the photon signal reflected by the object is stored in the 11 th time bin, it can be determined that the flight time of the photon is 17.6ns.

As can be seen from fig. 2, the narrower the width of the time bin, the higher the accuracy of the measured time of flight. Under the condition of ensuring that the measuring range is unchanged, the narrower the width of the time box is, the more the number of the time boxes is required, and thus the larger the required memory space is. In addition, in order to increase the measurement distance, the number of time bins required is also increased, and the memory space required is also increased. In addition, as the pixel resolution of the dTOF array is increased, the memory requirement is further increased. In summary, the above situations all put greater demands on the memory, resulting in increased cost.

Based on this, the embodiment of the application provides a method for determining flight time based on rough measurement and fine measurement, which can reduce occupation of memory space under the condition of improving measurement accuracy and measurement range. The concrete mode is as follows: firstly, roughly measuring with a larger first time box width to obtain a first histogram; determining a first time range in which the reflected photon signal is approximately located according to a first histogram; then, within the first time range, performing detail measurement with a smaller second time box width to obtain a second histogram; the time of flight of the photons is further determined from the second histogram. Since the fine measurement generates the histogram only within the first time range determined by the coarse measurement, the time range required for the second histogram can be reduced, thereby enabling the required memory space to be reduced.

The scheme of the embodiment of the present application is described in detail below with reference to fig. 3. The method shown in fig. 3 includes steps S310 to S340, and the method is applicable to a dTOF measurement system.

Step S310, constructing a first histogram in a preset time range according to the receiving time of the photosensitive device for receiving the photon signal in the preset time range and the width of a first time box.

The preset time range may be determined according to the measured distance. For example, to meet a measurement distance of 5m and reserve time for the photosensitive device to quench and data process, a total pulse period of approximately 50ns, the preset time range may be 50ns. Alternatively, the preset time may be less than 50ns, for example, the preset time may be set to 40ns, so as to reserve a certain time to the time determination unit as the delay time.

Since the actual distance of the object is not known before the measurement, the object can be measured within the maximum measurement range of the measurement system. That is, the preset time range may be determined according to a maximum measurement distance of the measurement system.

The first histogram in the preset time range indicates that the time range in which the time box in the first histogram is located is the preset time range. Taking fig. 2 as an example, the time range represented by the 23 time bins is the preset time range.

Optionally, before step S310, the method may further include: controlling the photosensitive device to receive photon signals within a preset time range; the time determination unit is used for determining the receiving time of the photon signal received by the photosensitive device in the preset time range.

Step S320, determining a first time range in which the photon signal reflected by the object is located according to the first histogram.

The first time range may represent a time range in which the photon signal reflected by the object is approximately present, and the first time range is smaller than the preset time range. Typically the first time range only needs to correspond to a smaller time range that can contain the real time of flight. For example, the first time range may be a time range corresponding to one time bin or a plurality of time bins, such as 2 time bins or 3 time bins. Taking fig. 2 as an example, the first time range is a time range corresponding to the 10 th and 11 th time bins (shaded areas). Alternatively, the first time range may be a time range of any length, for example, the first time range may be a time range corresponding to 1.5 time bins.

The first time range may be determined in various manners, such as a maximum method, a centroid method, a machine learning method, and the like, which is not specifically limited in this embodiment of the application. The following exemplifies the maximum method and the machine learning method.

For the maximum method, the peak position of the first histogram may be determined according to the first histogram, and then the first time range may be determined according to the peak position. For example, the time bin in which the peak is located may be selected as the first time range. For another example, the time bin in which the peak is located and the time bin adjacent to the time bin in which the peak is located may be selected as the first time range. The time bin adjacent to the peak time bin may be the time bin to the left of the peak, or the time bin to the right of the peak, or the time bin with a larger number of photons in the time bins on both sides, or the time bins including the left and right of the peak. The number of time bins adjacent to a peak may be 1, 2 or more.

For machine learning methods, a deep learning algorithm may be used to determine the first time range. The deep learning algorithm may include a Convolutional Neural Network (CNN), a Recurrent Neural Network (RNN), a residual network (ResNet), an extreme gradient boosting (XGBoost) model, or other neural network models. The method can directly extract the index (index) of the left time box of the two time boxes from the first histogram, so as to obtain the first time range. For example, assuming that the indices are counted from 0, the first resulting time range is [ index, index +1 ]. Times bin width. In addition to two time bins, the method can also extract 3 and more time bins. Compared with a maximum value method, the machine learning method can correctly find the time range of the photon signal reflected by the object under the conditions of poor signal-to-noise ratio and the ambient light stacking effect (pile-up), so that the determined first time range is more accurate.

Taking fig. 4 as an example, in the case of stronger ambient light, the possible distribution of the first histogram is shown in fig. 4. The time box of the photon signal reflected by the object is the position of the 10 th and 11 th time boxes. If the first time range is determined according to a maximum method, because the number of photons of the 1 st time box is the largest, the determined first time range is the time range corresponding to the 1 st time box, but the 1 st time box is not the time box where the photon signal really reflected by the object is located. Therefore, if the first time range is determined according to the maximum method, the determined first time range may be inaccurate. And if a machine learning method is adopted, the 10 th time box and the 11 th time box can be correctly found, and the measurement accuracy can be improved.

In order to ensure the accuracy of the subsequent detailed measurement process, the pulse width of the photon signal can be considered when determining the first time range, so that the first time range is not less than the pulse width of the photon signal, namely the first time range is greater than or equal to the pulse width of the photon signal emitted by the emitter, and the influence on the detection accuracy due to the fact that the complete light signal cannot be detected in the first time range is avoided. For example, if the pulse width of the photon signal is between 1 time bin width and 2 time bin widths, the first time range needs to include at least the width of 2 time bins.

And step S330, constructing a second histogram in the first time range by the second time box width according to the receiving time of the photosensitive device for receiving the photon signal in the first time range. Wherein the second time bin width is less than the first time bin width.

Since the second time bin width is smaller than the first time bin width, the second histogram is finer than the first histogram. The first histogram may also be referred to as a coarse histogram and the second histogram may also be referred to as a fine histogram.

Taking fig. 2 and 5 as an example, the histogram shown in fig. 2 may be referred to as a coarse histogram, and the histogram shown in fig. 5 may be referred to as a fine histogram. The first time range is the time range corresponding to 2 time bins (shaded areas) in fig. 2, and based on the first time range, a second histogram is constructed as shown in fig. 5. That is, fig. 5 narrows down the two time bin widths in fig. 2 into 22 time bins, and the time bin width of the first histogram shown in fig. 2 is 11 times the time bin width of the second histogram shown in fig. 5.

And step S340, determining the flight time of the photon signal reflected by the object according to the second histogram.

There are various ways to determine the flight time, such as the maximum method, the centroid method, and the machine learning method described above, and for brevity, the description is omitted here.

It is understood that the rough measurement process in the embodiment of the present application may include step S310 and step S320 in fig. 3, and the fine measurement process may include step S330 and step S340 in fig. 3.

According to the method, firstly, the rough histogram is used for determining the approximate time range of the reflected photon signal, then the fine histogram is generated in the time range, and the accurate flight time is determined according to the fine histogram. The time range for generating the histogram by the detail measurement is greatly reduced, so that the number of time boxes required by the histogram by the detail measurement can be greatly reduced, and the occupation of the memory space can be reduced.

For example, to ensure the accuracy of the time-of-flight measurement, it is assumed that a 100ps bin width is required to generate a histogram to determine the time-of-flight. For a measurement period of 40ns, 400 time bins are required in a conventional manner. If the scheme of the embodiment of the present application is adopted, assuming that the first time bin width is 1.6ns, the number of time bins required by the first histogram is approximately 25. Then 2 time bins are selected from the first histogram as the first time range, the width of the 2 time bins being 3.2ns, then the refinement only needs to generate 3.2ns histogram. If 100ps is used as the second bin width, the second histogram requires 32 bins. Compared with the scheme that 400 time boxes are needed in the traditional mode, the method and the device can greatly reduce the number of the needed time boxes, and therefore occupation of memory space and transmission bandwidth can be reduced.

In addition, because the rough measurement process and the fine measurement process are separately performed, the rough measurement process and the fine measurement process in the embodiment of the application can reuse the memory space, so that the occupation of the memory can be further reduced. In other words, the memory space used for counting photon signals in the first histogram may be at least partially the same as the memory space used for counting photon signals in the second histogram. Still by way of example, the 32 time bins in the fine measurement process can be reused for the 25 time bins in the rough measurement process, i.e. only 32 time bins are needed for the whole measurement process.

The time of reception of the photon signal by the light sensing device may be determined by the time determination unit. The time determination unit may be one or more of the TIM, time digitizer, TC, TDC described above. Taking TDC as an example, the resolution of TDC typically determines the width of the time bin in the histogram. The resolution of the TDC represents the measurement time interval of the TDC, i.e., the TDC is clocked once every time interval elapses. The measurement time interval of the TDC may be equal to the width of the time bin in the histogram.

In order to obtain the first histogram and the second histogram, the embodiment of the present application may be implemented by using two TDCs with different resolutions. Specifically, the first TDC may be used to determine the receiving time of the photon signal for constructing the first histogram, and the second TDC may be used to determine the receiving time of the photon signal for constructing the second histogram, where the resolution of the second TDC is greater than that of the first TDC, i.e., the measurement time interval of the first TDC is equal to the first time bin width, and the measurement time interval of the second TDC is equal to the second time bin width.

The first TDC and the second TDC may be two different TDCs. For example, a plurality of TDCs may be provided in the measurement system, with a TDC with low resolution being used for coarse measurement and a TDC with high resolution being used for fine measurement. For another example, the first TDC and the second TDC may be two operating states of the same TDC, the first TDC may be an operating state in which the same TDC is clocked by a reference clock, and the second TDC may be an operating state in which the same TDC is connected to the interpolator. Specifically, when the interpolator is not connected, the coarse measurement may be performed by using a reference clock of the TDC, that is, the first time bin width is equal to the clock period of the TDC; and when the fine measurement is carried out, the TDC can be connected with an interpolator to carry out the fine measurement. Wherein the interpolator may vary the resolution of the TDC, which may be, for example, a Nutt interpolator.

The operation of the TDC will be described with reference to fig. 6 and 7.

To acquire ToF data with high accuracy, a TDC with very high accuracy is required, for example, to achieve a range accuracy of the order of centimeters, a resolution of the TDC of the order of 100ps is required. In general, a TDC counts a time range to be measured by sampling with a clock signal, and calculates a time value according to a count value, where a minimum resolution of time measurement is a clock period of the TDC. The clock frequency of the TDC does not reach such a high precision, as the clock frequency generally reaches a precision of ns class at most. To achieve higher accuracy timing, the present application can be implemented using a Nutt interpolator. The Nutt interpolator may comprise, for example, a delay chain based Flash TDC, a ring oscillator, or a vernier type TDC.

Taking the delay chain as an example, after using the delay chain, the time measurement process of the TDC can be divided into two steps, i.e., a first measurement process and a second measurement process. The first measurement process only records the time NT corresponding to the total number of cycles of the reference clock_CLKThe time difference between the clock rising edge and the emission time, end time of the photon signal is derived by a second measurement process, as shown in fig. 6. The time interval between photon emission and reception was finally determined as:

Δt＝NT_CLK+Δt₁-Δt₂

wherein, Δ t₁Representing the time difference, Δ t, between the emission time of the photon signal and the rising edge of the clock₂Representing the time difference between the time of receipt of the photon signal and the rising edge of the clock.

The embodiment of the application can adopt a simple delay chain as shown in fig. 7 to realize the pair of delta t₁And Δ t₂The measurement of (2). When implemented in a circuit, a delay chain is generally formed by delay cells, and the delay chain may include N delay cells (buffers) and a flip-flop that samples an output of each delay cell. The principle of measurement based on a delay chain is to have a start signal measuredThe transmission is made by the delay unit, and the position to which it has been transmitted during the measured time period is detected by the delay unit, thereby judging the result of the time measurement. The signal delay time between adjacent delay cells is the resolution of the measurement.

The output of the TDC shown in FIG. 7 is Q_N-1…Q₂Q₁Q₀. Taking binary as an example, Q_i(i is more than or equal to 0 and less than or equal to N-1) is 0 or 1.

According to the embodiment of the application, one clock period of the TDC can be divided into a plurality of phases through the delay chain, and the number of delay units in the delay chain determines the resolution of the TDC. The larger the number of delay cells, the greater the resolution of the resulting TDC. Assuming that the clock period of the TDC is 1.6ns and the delay chain includes 16 delay units, the clock period of 1.6ns is divided into 16 phases by the delay chain, so as to obtain a resolution of the TDC of 100ps.

The time difference delta t between the emission time of the photon signal and the rising edge of the clock can be respectively measured through the delay chain₁And the time difference Deltat between the time of reception of the photon signal and the rising edge of the clock₂Thereby determining the time interval at.

The above is to determine Δ t with reference to the rising edge of the clock signal₁And Δ t₂Of course, Δ t may be determined with reference to the falling edge of the clock signal₁And Δ t₂Namely, the time difference between the emission time of the photon signal and the clock falling edge and the time difference between the reception time of the photon signal and the clock falling edge are calculated.

In order to improve the tolerance of the measurement system to ambient light when performing the refinement, one way is to control the photosensitive device to be enabled at the beginning of the first time range, so that photons before the first range are not received, and when generating the refinement histogram, counts with timestamps greater than the first time range are thrown away, as shown in fig. 8. Alternatively, the photosensitive device may be enabled (i.e., activated) only during the first time range, while outside the first time range, the photosensitive device is in an off state, i.e., does not receive a photon signal, as shown in fig. 9. However, in the process of multiple measurements, the above methods all need to monitor the first time range, and the photosensitive device is individually controlled to be turned on within the first time range and turned off outside the first time range. In addition, for the rough measurement process and the fine measurement process, different control modes are required to control the photosensitive devices. This puts high demands on the control process of the measurement system, which results in a complex control process, high cost, and is not easy to implement.

Based on this, the embodiment of the application provides another method for determining the flight time, which can simplify the control process of the measurement system and is beneficial to reducing the cost. As shown in fig. 10, it can be understood that, in fig. 10, step S322 and step S324 are added on the basis of fig. 3, and the remaining steps are the same as those in fig. 3, and for brevity, the same steps are not repeated.

Referring to fig. 10, in step S322, the photosensitive device is controlled to receive the photon signal within a preset time range.

In step S324, a photon signal in a first time range is selected from the photon signals received by the light sensing device in a preset time range.

Because the photosensitive device can receive photon signals in a preset range, when the second histogram is generated, the photon signals need to be screened, only the photon signals with the receiving time within the first time range are selected, and the photon signals with the receiving time outside the first time range are abandoned. In generating the second histogram, only photon signals within the first time range are used for generation.

In the scheme shown in fig. 8, whether the rough measurement process or the fine measurement process is performed, the measurement system can control the photosensitive device to enable only when the emitter emits the photon signal, and the on and off processes of the photosensitive device do not need to be controlled separately, so that the control process of the measurement system can be simplified. And when the second histogram is generated, the second histogram can be obtained by directly screening the photons according to the receiving time of the photons.

The rough measurement process and the fine measurement process are described in detail below, taking SPAD and TDC as examples.

During the course of the coarse measurement, the transmitter may be controlled to periodically transmit a photon signal to the object, and the SPAD start enable and the first TDC start timing may be controlled simultaneously with the transmission of the photon signal by the transmitter. The SPAD triggers avalanche after receiving the photon signal and sends the avalanche signal to the first TDC. After the first TDC receives the avalanche signal, a reception time for receiving the avalanche signal is determined, which represents a reception time for the SPAD to receive the photon signal and also represents a time interval between the transmission of the photon signal from the transmitter to the SPAD to be received. The first TDC may transmit the reception time to a histogram construction unit, and the histogram construction unit may construct a first histogram with a first time bin width according to the reception time. The first time bin width is a measurement time interval of the first TDC. After obtaining the first histogram, the processing unit may determine a first time range in which the photon signal reflected by the object is located according to the first histogram.

During the fine measurement, the control unit continues to control the emitter to periodically emit a photon signal to the object, and controls the SPAD start enable and the TDC start timing while the emitter emits the photon signal. The SPAD triggers avalanche after receiving the photon signal and sends the avalanche signal to the second TDC. After the second TDC receives the avalanche signal, a reception time for receiving the avalanche signal is determined, which represents a reception time for the SPAD to receive the photon signal and also represents a time interval between the transmission of the photon signal from the transmitter to the SPAD to be received. The second TDC may transmit the reception time to a histogram construction unit, and the histogram construction unit may select only photon signals within the first time range to be generated when generating the second histogram, and photon signals outside the first time range may be discarded, that is, when generating the second histogram, counts of photon signals whose time information is not within the first time range may be discarded without participating in the counting. The histogram construction unit may construct a second histogram in the first time range with a second time bin width according to the reception time of the photon signal in the first time range. The second time bin width is a measurement time interval of the second TDC. After obtaining the second histogram, the processing unit may determine a time of flight of the photon signal reflected by the object according to the second histogram, thereby further determining the distance of the object.

Method embodiments of the present application are described in detail above in conjunction with fig. 1-11, and apparatus embodiments of the present application are described in detail below in conjunction with fig. 12. It is to be understood that the description of the method embodiments corresponds to the description of the apparatus embodiments, and therefore reference may be made to the preceding method embodiments for parts not described in detail.

Fig. 12 is a schematic block diagram of an apparatus for determining time of flight provided by an embodiment of the present application. The apparatus 400 may include a first histogram construction unit 410, a first determination unit 420, a control unit 430, a selection unit 440, a second histogram construction unit 450, and a second determination unit 460. These units are described in detail below.

The first histogram construction unit 410 may be configured to construct a first histogram within a preset time range according to a receiving time of the photosensitive device for receiving the photon signal within the preset time range, and with a first time bin width.

The first determining unit 420 may be configured to determine a first time range in which the photon signal reflected by the object is located according to the first histogram.

And a control unit 430, configured to control the light sensing device to receive the photon signal within the preset time range.

The selecting unit 440 may be configured to select a photon signal within the first time range from photon signals received by the light sensing device within the preset time range.

A second histogram constructing unit 450, configured to construct a second histogram in the first time range with a second time bin width according to the receiving time of the photon signal in the first time range, where the second time bin width is smaller than the first time bin width.

A second determination unit 460 operable to determine a time of flight of the photon signal reflected by the object from the second histogram.

Alternatively, in some embodiments, the selection unit 440 may be omitted.

Optionally, in some embodiments, the first time range is a time range corresponding to one or more time bins in the first histogram.

Optionally, in some embodiments, the apparatus 400 further comprises: a third determining unit for determining the one or more time bins according to a maximum method, a centroid method or a machine learning method.

Optionally, in some embodiments, the one or more time bins are time bins in which peaks in the first histogram are located; alternatively, the one or more time bins include a time bin in which the peak in the first histogram is located and a time bin adjacent to the time bin in which the peak is located.

Optionally, in some embodiments, the first time range is greater than or equal to a pulse width of the photon signal.

Optionally, in some embodiments, the apparatus 400 further comprises: a first TDC for determining a reception time of a photon signal for constructing the first histogram, a measurement time interval of the first TDC being equal to the first time bin width; a second TDC for determining a time of reception of the photon signals for constructing the second histogram, the second TDC having a measurement time interval equal to the second time bin width.

Optionally, in some embodiments, the memory space for counting photon signals in the first histogram is the same as at least part of the memory space for counting photon signals in the second histogram.

Optionally, in some embodiments, the photosensitive device is an avalanche photodiode.

Optionally, in some embodiments, the apparatus 400 further comprises: a fourth determining unit, configured to determine the distance to the object according to the flight time.

Embodiments of the present application also provide an apparatus, which may include the above-described means for determining time of flight. The device may be, for example, the measurement system described above. The apparatus may comprise an emitter, a light sensing device and any of the means for determining time of flight described above. The emitter may be configured to emit a photon signal toward the object and the light sensing device may be configured to receive the photon signal reflected by the object.

The device may perform the corresponding function according to the time of flight determined by the apparatus shown in fig. 12. The corresponding functions include but are not limited to unlocking after identifying the identity of the user, payment, starting a preset application program, avoiding barriers, and judging any one or more of the emotion and the health condition of the user by utilizing a deep learning technology after identifying the facial expression of the user.

The device in the embodiment of the present application may further include a color camera, an infrared camera, an Inertial Measurement Unit (IMU), and other devices. The apparatus combined with these devices can realize more abundant functions, such as 3D texture modeling, infrared face recognition, simultaneous localization and mapping (SLAM) functions, and the like.

The device may be a ranging device, a 3D imaging device. The ranging device may be, for example, a radar ranging device.

Such as, but not limited to, consumer electronics, home electronics, vehicle-mounted electronics, financial terminal products, and the like. The consumer electronic products include, but are not limited to, mobile phones, tablet computers, notebook computers, desktop displays, all-in-one computers, and the like. Examples of household electronic products include, but are not limited to, smart door locks, televisions, refrigerators, wearable devices, and the like. Examples of the vehicle-mounted electronic product include, but are not limited to, a vehicle-mounted navigator, a Digital Video Disc (DVD), and the like. Examples of financial end products include, but are not limited to, automatic Teller Machine (ATM) machines, self-service terminals, and the like.

In the above embodiments, all or part of the implementation may be realized by software, hardware, firmware, or any other combination. When implemented in software, it may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When loaded and executed on a computer, cause the processes or functions described in accordance with the embodiments of the application to occur, in whole or in part. The computer may be a general purpose computer, a special purpose computer, a network of computers, or other programmable device. The computer instructions may be stored on a computer readable storage medium or transmitted from one computer readable storage medium to another, for example, from one website, computer, server, or data center to another website, computer, server, or data center via wire (e.g., coaxial cable, fiber optic, digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device, such as a server, a data center, etc., that incorporates one or more of the available media. The usable medium may be a magnetic medium (e.g., floppy Disk, hard Disk, magnetic tape), an optical medium (e.g., digital Video Disk (DVD)), or a semiconductor medium (e.g., solid State Disk (SSD)), among others.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the technical solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A method for determining time of flight, comprising:

according to the receiving time of the photosensitive device for receiving the photon signals in the preset time range, constructing a first histogram in the preset time range according to the width of a first time box;

determining a first time range in which a photon signal reflected by an object is located according to the first histogram;

controlling the photosensitive device to receive photon signals within the preset time range;

constructing a second histogram in the first time range with a second time bin width according to the receiving time of the photon signal received in the first time range, the second time bin width being smaller than the first time bin width;

determining a time of flight of a photon signal reflected by the object from the second histogram.

2. The method of claim 1, wherein the first time range is a time range corresponding to one or more time bins in the first histogram.

3. The method of claim 2, further comprising:

determining the one or more time bins according to a maximum method, a centroid method, or a machine learning method.

4. The method of claim 2, wherein the one or more time bins are time bins in which peaks in the first histogram are located; or,

the one or more time bins include a time bin at which a peak in the first histogram is located and a time bin adjacent to the time bin at which the peak is located.

5. The method of claim 1, wherein the first time range is greater than or equal to a pulse width of a photon signal reflected by the object.

6. The method of claim 1, wherein at least a portion of the memory space used to count photon signals in the first histogram is the same as the memory space used to count photon signals in the second histogram.

7. An apparatus for determining time of flight, comprising:

the first histogram construction unit is used for constructing a first histogram in a preset time range according to the receiving time of the photosensitive device for receiving the photon signals in the preset time range and the width of a first time box;

the first determining unit is used for determining a first time range in which the photon signals reflected by the object are located according to the first histogram;

the control unit is used for controlling the photosensitive device to receive photon signals within the preset time range;

a second histogram construction unit, configured to construct a second histogram in the first time range with a second time bin width according to a receiving time of the photon signal received in the first time range, where the second time bin width is smaller than the first time bin width;

a second determining unit for determining the time of flight of the photon signal reflected by the object according to the second histogram.

8. The apparatus of claim 7, wherein the first time range is a time range corresponding to one or more time bins in the first histogram.

9. The apparatus of claim 8, further comprising:

a third determining unit for determining the one or more time bins according to a maximum method, a centroid method or a machine learning method.

10. The apparatus of claim 8, wherein the one or more time bins are time bins in which peaks in the first histogram are located; or,

11. The apparatus of claim 7, wherein the first time range is greater than or equal to a pulse width of a photon signal reflected by the object.

12. The apparatus of claim 7, further comprising:

a first time-to-digital converter, TDC, for determining the reception time of the photon signals used to construct the first histogram, the first TDC having a measurement time interval equal to the first time bin width;

a second TDC for determining a time of reception of the photon signals for constructing the second histogram, the second TDC having a measurement time interval equal to the second time bin width.

13. The apparatus of claim 7, wherein at least a portion of a memory space used for counting photon signals in the first histogram is the same as a memory space used for counting photon signals in the second histogram.

14. An apparatus, comprising:

an emitter for emitting a photonic signal towards an object;

a light sensing device for receiving the photon signal reflected by the object;

and an apparatus for determining time of flight according to any one of claims 7 to 13.