CN113075679A - TOF ranging system - Google Patents

Abstract

The invention discloses a TOF ranging system which is characterized by comprising a VCSEL (vertical cavity surface emitting laser) for emitting a light source, a sensor for receiving reflected light, a reference surface and an object to be measured; the sensor receiving the reflected light is used for receiving the reflected light signal of the reference surface by at least part of pixels. By the structure of the invention, the problem of reduced distance measurement precision caused by inaccurate knowledge of the emission time of the light pulse can be solved, thereby effectively improving the distance measurement precision.

Description

TOF ranging system

Technical Field

The application relates to the technical field of TOF ranging, in particular to acquisition of a histogram reference point in a DTOF type distance information acquisition system.

Background

In recent years, with the progress of semiconductor technology, miniaturization of a ranging module for measuring a distance to an object has progressed. Therefore, for example, it has been realized to install a ranging module in a mobile terminal such as a so-called smart phone which is a small information processing apparatus having a communication function with the advancement of technology, and in the process of distance or depth information detection, a method frequently used is Time of flight ranging (TOF) whose principle is to obtain a target distance by continuously transmitting a light pulse to a target and then receiving light returned from the object with a sensor and detecting the Time of flight (round trip) of the light pulse, and a technique of directly measuring the light Time of flight in the TOF technique is called DTOF (Direct-TOF), Direct Time of flight ranging (DTOF flight) as one of TOF, and DTOF technique directly obtains the target distance by calculating the transmission and reception times of the light pulse, and has a simple principle, a good signal-to-noise ratio, and a good signal-to-noise ratio, The advantages of high sensitivity, high accuracy and the like are receiving more and more extensive attention, and especially in extreme low light conditions, optical sensors can convert single photons into measurable electric signals, and the sensors are called single photon detectors and can be used for a vision system with 3D imaging and ranging functions.

The DTOF distance measurement principle is also relatively simple and clear, the light source emits pulsed laser with a certain pulse width, for example, in the order of a few nanoseconds, the pulsed laser is reflected by the detection target and returns to the array type receiving module in which the SPAD is in an avalanche state, and when the avalanche photodiode SPAD operates in a known Geiger (Geiger) mode in the case where the breakdown voltage of the avalanche photodiode SPAD is exceeded, the avalanche photodiode can be made so that a single incident photon therein can trigger a strong photocurrent pulse, and the gain thereof can be approximately regarded as infinite. SPAD imaging sensors are semiconductor photosensitive devices consisting of an array of SPAD regions fabricated on a silicon substrate. The SPAD region produces an output pulse when struck by a photon. The SPAD region has a pn junction that is reverse biased above the breakdown voltage so that a single photogenerated carrier can trigger an avalanche multiplication process, photon signals received by the image sensor can be processed using a matched circuit detection to count output pulses from the SPAD region within a time window, wherein tens of thousands of laser pulses can be emitted for a high confidence result, the detection unit obtains a statistical result, such that a more accurate distance can be obtained by processing the statistical result.

The basic idea of measuring photon time information is to consider a photon as a random event, and count the photon after repeating measurement for multiple periods. When the optical signal is very weak and the detection frequency is very high, photons may not be detected in some periods, a photon can be detected in some periods, the detection time of the photon is corresponding to a certain time period, thus after a large number of repeated measurements are carried out, the frequency distribution histogram of the photon changing along with the time can be obtained by counting the number of the photons in each time period, and the intensity change of the optical signal can be obtained by fitting the histogram

The core of the DTOF ranging technique is to generate a histogram of photon counts, and the thickness of the histogram directly determines the accuracy of ranging. When the laser pulse power is large, the generated histogram needs a small number of laser pulses, but the histogram is greatly different from the original light intensity envelope. When the laser pulse power is low, although the number of laser pulses required for generating a histogram is large, the envelope drawn by the histogram is well matched with the envelope curve of the light intensity.

The VCSEL of the DTOF system transmits a pulse wave into the scene and the SPAD receives the pulse wave reflected back from the target object. The Time Digital Converter (TDC) is capable of recording the Time of flight of each received optical signal, i.e., the Time interval between a transmitted pulse and a received pulse. The DTOF transmits and receives optical signals for N times within single-frame measurement time, histogram statistics is carried out on the recorded N times of flight time, the flight time t with the highest occurrence frequency is used for calculating the distance of an object to be measured, and the time corresponding to the column with the highest height is the final optical flight time of the pixel point. The principle of DTOF seems simple, but it is difficult to actually achieve high accuracy. In addition to the very high accuracy requirements for clock synchronization, there are also high requirements for the accuracy of the pulse signal. For DTOF, since it employs a Single Photon Avalanche Diode (SPAD), the number of absorbed photons can be measured in a very short time interval, and the response current can be generated in a time of the order of picoseconds at a minimum. The time resolution of the TDC can also reach picosecond level, so the theoretical precision of the TDC can reach millimeter level. However, due to quantum noise and amplifier noise existing in the avalanche process and inherent noise existing in the TDC module in the DTOF, the actual accuracy of the DTOF can only reach centimeter level at present. Therefore, it is desirable to provide a high-precision DTOF detection apparatus and detection method to meet the requirement of high-precision distance measurement.

Disclosure of Invention

An object of this application lies in, to the not enough among the above-mentioned prior art, provides a TOF ranging system to avoid because can not accurately know the problem that the range finding precision that the emission time of light pulse leads to reduces, thereby effectual improvement range finding precision.

In order to achieve the above purpose, the technical solutions adopted in the embodiments of the present application are as follows:

the embodiment of the application provides a TOF ranging system, which is characterized by comprising a VCSEL (vertical cavity surface emitting laser) for emitting a light source, a sensor for receiving reflected light, a reference surface and an object to be measured; the sensor receiving the reflected light is used for receiving the reflected light signal of the reference surface by at least part of pixels.

Optionally, the reference surface is an internal component of the transmitting end optical path.

Optionally, the reference surface is a plenoptic sheet.

Optionally, the reference surface is a DOE or an emitted light collimating optical element.

Optionally, the reference surface is a reference object disposed outside the inner package.

Optionally, the reference surface is an additional object located outside the ranging system.

Optionally, at least one of the sensors receiving the reflected light is configured to receive a reflected light signal from a reference surface.

Optionally, the distance from the pixel for receiving the reference surface reflected light signal to the center of the VCSEL is 0.2mm to 0.5 mm.

Optionally, the distance between the sensor for receiving the reference surface reflected light signal and the center of the VCSEL is 0.2mm to 0.5 mm.

Optionally, the reference surface is a reference object disposed 1.7mm-2mm from the inner package.

The beneficial effect of this application is:

the TOF ranging system is characterized by comprising a VCSEL (vertical cavity surface emitting laser) for emitting a light source, a sensor for receiving reflected light, a reference surface and an object to be measured; at least part of pixels of the sensor for receiving the reflected light are used for receiving the reflected light signals of the reference surface, so that the problem of reduced distance measurement precision caused by the fact that the emitting time of the light pulse cannot be accurately known can be solved, and the distance measurement precision is effectively improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.

Fig. 1 is a schematic diagram of a distance measurement principle provided in an embodiment of the present application;

fig. 2 is a schematic diagram of a DTOF histogram provided in an embodiment of the present application;

fig. 3 is a schematic view of a TOF ranging system according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of TOF ranging optical path internal reflection provided in an embodiment of the present application;

FIG. 5 is an internally reflective imaging area provided by an embodiment of the present application;

FIG. 6 is a schematic view of another TOF ranging system provided in an embodiment of the present application;

FIG. 7a is a DOE internal reflection schematic diagram of a TOF ranging system provided by an embodiment of the present application;

FIG. 7b is a schematic diagram of an internal reflection of a collimating lens of a TOF ranging system according to an embodiment of the present application;

FIG. 8 is an alternative internally reflective imaging area provided by embodiments of the present application;

FIG. 9 is a schematic view of a TOF ranging system according to an embodiment of the present application;

FIG. 10 is a schematic illustration of a reference plane reflection provided by an embodiment of the present application;

11a-11f are imaging diagrams of continuously adjusting the distance of the reference plane from the inner package surface in the ranging system;

fig. 12 is an example of another histogram provided in an embodiment of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, 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 some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

Fig. 1 is a schematic diagram of a distance measurement principle provided by an embodiment of the present application, in the distance measurement, since a pixel unit of an array sensor is an SPAD (single photon avalanche photodiode) device, which operates in a geiger mode, in the geiger mode, an electron-hole pair is generated by absorption of photons by the avalanche photodiode, and is accelerated under the action of a strong electric field generated by a high reverse bias voltage, so as to obtain sufficient energy, and then collides with a crystal lattice, so as to form a chain effect, and as a result, a large number of electron-hole pairs are formed, which causes an avalanche phenomenon, and a current exponentially increases. At this time, the gain of the SPAD is theoretically infinite, and the single photon can saturate the photocurrent of the SPAD, so the SPAD becomes the first choice of a high-performance single photon detection system.

The distance measurement principle is simple in practice, the light source 110 emits a pulse laser with a certain pulse width, for example, in the order of several nanoseconds, the pulse laser is reflected by the detection object 140 and returns to the array type receiving module in the SPAD state, wherein the detection unit in the avalanche state can receive the returned signal, the processing of the processing module 120 can output the distance between the detection system and the detection object, so as to complete the detection, wherein thousands of laser pulses can be emitted for obtaining a high-reliability result, the detection unit obtains a statistical result, so that a more accurate distance can be obtained by processing the statistical result, the present invention is not limited, the light source 110 can output the emitted light in the form of a sheet light source or a light spot, the light source 110 can adopt a VCSEL vertical cavity surface emitting laser or other similar light source modules 110, and is not limited thereto.

Fig. 2 is a schematic diagram of a DTOF histogram provided in an embodiment of the present application; the distance measuring system starts timing when the optical pulse is emitted to the object, and records the time when the photon in the optical pulse reflected by the object 140 is detected, that is, the flight time t of the journey that a single photon reaches the object 140 from the emitting light source 110 and is reflected to the receiving module 130 by the object 140 can be obtained. Since the speed of light C is known, the distance S from the ranging system to the object 140 can be calculated. The time of flight t may be obtained in particular from a histogram. A histogram is established with respect to time and the number of times a photon is received by the receiving module 130 (count value of the count of photon signals). The histogram is an integration of distribution functions of photons with time in a plurality of preset periods, and can reflect a distribution relationship of the number of times of receiving photons by the receiving module 130 with time after one or more times of transmitting light beams, as shown in fig. 2. Specifically, it is assumed that each time unit is 1ns as shown in fig. 2. After the light source 110 emits the light pulse, if the receiving module 130 does not detect the photon, the counting value is not incremented in time unit, or the counting value is considered to be +0 in all time units. After the light source 110 emits the first light pulse, the receiving module 130 detects a photon in a time unit, and counts the value of +1 in the corresponding time unit. Knowing the end of the transmit pulse, the acquired histogram can be post-processed after stopping the statistics to calculate the distance S from the ranging system to the probe target 140. There may be one or more time cells in the histogram for which the count value is greater than 0. The processing module 120 may perform smooth filtering on the count values of the time units in the histogram to obtain waveform information about the time variation of the count values. The time unit in which the highest peak value is located can be reflected in a plurality of preset periods, and the number of times of detecting photons in the time unit is the largest. Therefore, the peak time corresponding to the highest peak of the histogram can more accurately reflect the time when the receiving module 130 receives the photon. The processing module 120 can obtain the flight time t of the optical pulse according to the peak time and the start time of the detection period, and then calculate the distance S between the ranging system and the detection target 140 by the method of calculating the flight time t and the speed of light C. As shown in fig. 2, the highest peak of the histogram appears at 13ns, but this is determined in the case that the 0ns position of the histogram is very accurate, and in the actual ranging process, due to the delay of the electrical signal and the like, the statistical histogram thereof is difficult to obtain the accurate time reference position (i.e. 0ns in fig. 2), and the finally measured ranging distance is the difference between the pulse peak value obtained from the histogram and the circuit time zero point (13 ns in fig. 2). The distance calculated from the time counted by the histogram is inaccurate. Therefore, the accurate time reference position in the histogram statistics has a great influence on the ranging accuracy, and is a problem to be solved urgently.

In order to solve the above-mentioned problem, a special pixel is introduced in the embodiments of the present application to determine the temporal reference position. Fig. 3 is a schematic view of a TOF ranging system according to an embodiment of the present disclosure. Where TOF ranging system 100 includes VCSEL40 for the emitting light source, a diffuser on the emitting side, and packaging of the emitting side. The main function of the diffuiser is to provide a uniform surface light source, the material needs to be a material with high light transmittance, the chemical particles are used as scattering particles, light can continuously pass through the diffusion layer, and meanwhile, the light can generate a plurality of refraction, reflection and scattering phenomena, so that the optical diffusion effect is formed. The receiving end portion of the ranging system 100 includes the TOF lens group 50, the sensor 60 of the receiving end, and the package 10 of the receiving end. The TOF lens group has the advantages that richer depth of field information can be provided, and images are more layered; the method can realize safer 3D face recognition and support face payment; the size of the TOF lens group is smaller, the TOF lens group has small requirement on the environment, the position of the lens system can be placed more flexibly, and the cost of the TOF lens group is lower. The TOF sensor (sensor 60) receives light that bounces off any object and returns to the sensor. The sensor may measure the distance between the object and the sensor based on the time difference between the emission of the light and the return of the light to the sensor after reflection by the object. TOF sensors are able to compose 3D images of a scene very quickly compared to other distance sensors (e.g. ultrasound or laser). For example, the TOF camera only needs to do this once. Furthermore, the TOF sensor can accurately detect an object in a short time and is not affected by humidity, air pressure, and temperature, making it suitable for indoor and outdoor use. Since TOF sensors use laser light, they are also capable of measuring long distances and ranges with high accuracy. For example, the range of a portable TOF laser scanner kit is 40 m. Thus, TOF sensors have flexibility in that they can detect near and far objects of various shapes and sizes.

It is also flexible in the sense that the optics of the system can be customized to achieve the best performance in which you can choose the transmitter and receiver types and lenses to obtain the desired field of view. Many TOF sensors use a low power infrared laser as the light source and drive it by modulating pulses. The sensor reaches the safety standard of the I-type laser, and the safety of the sensor to human eyes can be ensured. Compared to other 3D depth range scanning techniques (e.g. structured light camera systems or laser rangefinders), TOF sensors are much cheaper than them.

FIG. 4 is a schematic diagram of TOF ranging optical path internal reflection provided in an embodiment of the present application; as shown in fig. 4, the VCSEL430 emits uniform light, wherein most of the light is emitted toward the object to be measured via the diffuiser 410, but a small portion of the light source is reflected inside the emission path via the reflection of the diffuiser 410. The portion of the received pixel sensor 450 is used to receive light reflected back from the diffuiser. And the time when the photon of the light pulse reflected back by the sensor 410 is detected is recorded, so that the time of flight t that a single photon reaches the sensor 410 from the emission light source and is reflected to the receiving sensor by the sensor 410 during the journey can be obtained. A histogram is built of the time and the number of times the photon was received by the receiving sensor (count of the count of photon signals).

Fig. 5 is an image area of internal reflection according to an embodiment of the present disclosure. It can be seen from fig. 4 that the position of the conventional receiving sensor of the light reflected back from the light homogenizer 410 is not detectable, which requires the placement of a specialized receiving sensor. According to fig. 5, the receiving sensors are arranged to be within the imaging area 501 to receive the light reflected from the integrator. According to simulation, the distance from the right edge position of the receiving sensor to the center of the VCSEL is 0.2 mm-0.5 mm.

FIG. 6 is a schematic view of another TOF ranging system provided in an embodiment of the present application; the difference between fig. 6 and fig. 3 is that the transmitting optical path is different and the receiving end is the same. The light source emitted by the VCSEL in fig. 6 needs to pass through the collimating lens 602 and the DOE 601 and then be emitted toward the object to be measured, and other parts are the same as those shown in fig. 3, and are not described herein again. The collimating lens 602 is used for collimating the divergent laser light source to achieve the effect of parallel and uniform light spots; the DOE 601 (diffraction grating) is used to uniformly emit multiple laser beams after one or more light sources emitted in parallel pass through the diffraction grating, so as to increase the measurement accuracy and information amount and complete the recording of a comprehensive scene. The DOE is mainly applied to a structured light algorithm, and light collimated by the VCSEL is copied according to requirements through a diffraction method according to the algorithm requirements.

FIG. 7a is a DOE internal reflection schematic diagram of a TOF ranging system provided by an embodiment of the present application; FIG. 7b is a schematic diagram of an internal reflection of a collimating lens of a TOF ranging system according to an embodiment of the present application; as shown in fig. 7a, the VCSEL emits a light source, wherein most of the light is emitted toward the object to be measured through the collimating lens and the DOE, but a small part of the light source is reflected inside the emission light path through the reflection of the DOE. The received portion of the pixel sensor is used to receive the light reflected back from the DOE. And the time when the reflected light pulse photons are detected is recorded, so that the flight time t of the single photon from the emission light source to the DOE and then reflected to the receiving sensor by the DOE during the journey can be obtained. A histogram is built of the time and the number of times the photon was received by the receiving sensor (count of the count of photon signals). Similarly, in fig. 7b, the VCSEL emits the light source, wherein most of the light is emitted toward the object to be measured through the collimating lens and the DOE, but a small part of the light source is reflected inside the emission light path through the reflection of the collimating lens. The received portion of the pixel sensor is used to receive the light reflected back from the collimating lens. And the time when the reflected light pulse photon is detected is recorded, so that the flight time t of the single photon from the emission light source to the collimating lens and reflected by the collimating lens to the receiving sensor in the section of travel is obtained. A histogram is built of the time and the number of times the photon was received by the receiving sensor (count of the count of photon signals).

Fig. 8 is another internally reflective imaging area provided by an embodiment of the present application. From fig. 8, it can be seen that the position of the conventional receiving sensor cannot be detected by the light reflected back from the collimating lens and DOE, which requires a special receiving sensor to be disposed. According to fig. 8, the receiving sensors are arranged to be within the imaging area 801 to receive light reflected from the integrator plate. According to simulation, the distance from the right edge position of the receiving sensor to the center of the VCSEL is 0.2 mm-0.5 mm.

FIG. 9 is a schematic view of a TOF ranging system according to an embodiment of the present application; the system as shown in fig. 9 comprises components which differ from those shown in fig. 3 only in that a reference surface 901 and an outer package 902 are also comprised. The reference surface 901 may be any reference that is calibrated, typically a glass cover plate. The VCSEL for the ToF may be driven by a driver. To transmit a light pulse, a trigger (signal) may be provided from the processor to the transmitter driver to trigger the pulse. In response to the trigger, the driver may turn on and then prepare to output the light pulse. Although the processor may know the time, for example, through the system clock, delays may be incurred due to driver response time and trigger propagation time. The delay may further vary, for example, with process, voltage, and temperature variations. Therefore, the time at which the light pulse is emitted may not always be accurately known. The reference surface is introduced in order to be able to accurately determine the time at which the light pulse is emitted.

Fig. 10 is a schematic reflection diagram of a reference surface according to an embodiment of the present application. The emitted light is emitted from the light source and reflected from the reference surface 1001 and the reflected light of the reference surface 1001 is received at the sensor. Another part of the emitted light is emitted from the light source to the object to be measured and the light reflected from the object to be measured is received at the sensor. It is understood that light emission to the reference surface and light emission to the object to be measured are emitted from the light source as part of the same pulse and may both be considered to be simultaneous emissions.

Some pixels of the sensor or a dedicated sensor is configured to detect reflected light from the reference surface and indicate the light detected at time (t 1). The other pixels of the sensor or another sensor is configured to detect reflected light from the non-pattern to be measured and indicate the light detected at time (t 2).

The time t1 and the time t2 may be determined by a clock of the device. The time t1 may be based on a timer that starts counting when the light pulse is triggered and stops when incidence of the reference surface reflected light is detected. Also, the time t2 may determine a timer based on a timer that starts counting when the light pulse is triggered and stops when incidence of reflected light of the object to be measured is detected. In some embodiments, the timers for t1 and t2 may be the same timer.

The time at which the light pulse is triggered may not be equal to the time at which the pulse is actually emitted, and thus each of times t1 and t2 may include the reaction time of the emitter. To compensate for the reaction time, time t2 and time t1 are used to calculate the distance of the object to be measured. By subtracting t1 from t2, the reaction time is cancelled. The distance of the reference surface is calibrated, and if the distance of the reference surface is negligible, the distance of the object to be measured is directly calculated by subtracting t1 from t 2. If the distance of the reference surface is considered to have an influence on the ranging accuracy, the calibrated distance information can be used for compensating the distance of the object to be measured obtained by subtracting t1 from t 2.

Although not shown, the sensor for receiving the reference surface emitted light and the sensor for receiving the object to be measured reflected light may be further coupled to analog or digital circuitry for determining time and calculating distance to the object to be measured.

The sensor or a part of the pixels for receiving the reference surface reflected light needs to be disposed at a specific imaging position to receive the reference surface reflected light. 11a-11f are imaging diagrams of continuously adjusting the distance of the reference plane from the inner package surface in the ranging system. FIG. 11a is an image of the reference plane at a distance of 0-1.6 mm from the inner package; FIG. 11b is an imaging view of the inner package at a distance of 1.7mm from the reference plane; FIG. 11c is an imaging view of the inner package at a distance of 2mm from the reference plane; FIG. 11d is an imaging view of the inner package at a reference plane distance of 3 mm;

FIG. 11e is an imaging view of the inner package at a distance of 4mm from the reference plane; figure 11f is an imaging plot of the reference plane at 5mm from the inner package. From the results of fig. 11a-11 b, it can be seen that in practical application, the reference plane is within 2mm from the inner package, there is an image on the sensor, and the effect is ideal when the reference plane is within 1.7mm to 2mm from the inner package. It can be seen from the above figures that the pixel or sensor receiving the reference surface reflected light can receive the reference surface reflected light when the pixel or sensor is arranged at the leftmost end with a distance of 0.2mm to 0.5mm from the center of the VCSEL. The simulation data of fig. 11a-11f were performed using a glass cover plate as a reference surface. However, in practical applications, any calibrated distance reference can be used as the reference surface, and the installation distance will not be limited by the data of fig. 11a-11 f. However, the function of the reference surface is consistent with that of the glass cover plate, and the description is omitted here.

Fig. 12 is an example of another histogram provided in an embodiment of the present application. The driver may trigger the start of the pulse. The time at which the pulse is triggered may be known, but the emission time of the pulse cannot be accurately known due to the reaction time of the driver and the variations in voltage and temperature. For each pulse, the arrival of a photon can be considered to be the time between the triggering of the pulse and the detection of the photon. Thus, an arriving photon event for each of the plurality of pulses may include an indication of a photon arrival event and a time corresponding to a time period between the triggering of the pulse of photon arrival.

Fig. 12 shows a first peak 301 and a second peak 302. The first peak 301 may represent the arrival of a photon detected in each pulse period due to reflection off the reference surface, that is, the arrival of a detected photon due to reflection off a diffuiser or DOE or collimating lens or reference surface. It can be seen that the time t1 of the first peak 301, which is the time required for light to travel between the light source VCSEL and the reference plane.

The second peak 302 may represent arriving photons detected during each pulse period due to reflections off the object under test. The time t2 of the second peak 302 can be seen, which is the time required for light to travel between the light source VCSEL and the object to be measured.

The arrival photon data is collected for each pulse period and then combined from all pulse periods. The emission light source VCSEL may emit a plurality of pulses within a detection period, and detect the arriving photon data for each pulse period within the detection period. For each pulse cycle, information including any time and photon count corresponding to the time period between the pulse being triggered and the photon being detected will be collected to understand the number of photons detected within the pulse cycle. The time and number of arriving photons per pulse period information will be combined to generate a histogram.

The pulse period may include the period during which a light pulse occurs and the time period between a pulse and the next pulse. In one example, the pulses may be 1ns long, and there may be a 10ns separation between the pulses. However, it should be understood that this is merely exemplary and that the pulse period may be selected based on the component capabilities and/or the distance desired to be detected and depending on the application of the device.

Once the time and photon count information is collected from the pulses in the detection period and a histogram is generated, the distance between the object to be measured and the sensor can be determined from the time difference between the first peak 301 and the second peak 302. the subtraction of t2 and t1 can cancel the pulse emission time uncertainty factor. The distance between the sensor and the reference surface is fixed. The distance between the objects to be measured obtained by t2 and t1 can be determined by increasing the fixed distance, if necessary.

It is to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (10)

1. A TOF ranging system is characterized by comprising a VCSEL (vertical cavity surface emitting laser) for emitting a light source, a sensor for receiving reflected light, a reference surface and an object to be measured; the sensor receiving the reflected light is used for receiving the reflected light signal of the reference surface by at least part of pixels.

2. The TOF ranging system of claim 1 wherein said reference surface is a transmit end optical path internal component.

3. The TOF ranging system of claim 2 wherein said reference surface is a shim.

4. The TOF ranging system of claim 2 wherein the reference surface is a DOE or a transmitting light collimating optical element.

5. The TOF ranging system of claim 1, wherein the reference surface is a reference object disposed outside of the inner enclosure.

6. The TOF ranging system of claim 5 wherein said reference surface is an additional object located outside of the ranging system.

7. The TOF ranging system of claim 1 wherein the at least one reflected light receiving sensor is configured to receive a reflected light signal from a reference surface.

8. The TOF ranging system of claim 1, wherein the pixels for receiving the reference surface reflected light signal are at a distance of 0.2mm to 0.5mm from the center of the VCSEL.

9. The TOF ranging system of claim 7 wherein the sensor for receiving the reference surface reflected light signal is located between 0.2mm and 0.5mm from the center of the VCSEL.

10. The TOF ranging system of claim 5 wherein said reference surface is a reference object positioned within a 1.7mm-2mm distance envelope.

Images