CN111474553B - Time-of-flight ranging method and device - Google Patents
Time-of-flight ranging method and device Download PDFInfo
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- CN111474553B CN111474553B CN202010570710.3A CN202010570710A CN111474553B CN 111474553 B CN111474553 B CN 111474553B CN 202010570710 A CN202010570710 A CN 202010570710A CN 111474553 B CN111474553 B CN 111474553B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/46—Indirect determination of position data
- G01S17/48—Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
Abstract
The invention discloses a time-of-flight distance measuring device and a time-of-flight distance measuring method, wherein the time-of-flight distance measuring method is used for measuring the distance between the time-of-flight distance measuring device and an object, and comprises the following operations: irradiating a first laser to an object and generating a first reflected laser (S501); sensing the first reflected laser light and obtaining a first phase shift between the first laser light and the first reflected laser light, wherein the first phase shift is smaller than 2 pi (S502); adding 2 pi to the first phase shift to obtain a second phase shift (S503); irradiating a second laser to the object and generating a second reflected laser (S504); sensing the second reflected laser and obtaining a first light intensity of the second reflected laser at the time point (S505); determining a first phase shift or a second phase shift as a phase delay between the first laser and the first reflected laser according to the first light intensity (S506); and calculating a distance according to the phase delay (S507). Therefore, the time-of-flight ranging method reduces the power consumption and the operation time of the system on the premise of not influencing the accuracy.
Description
Technical Field
The present invention relates to a system and method for measuring a distance, and more particularly, to a method and apparatus for measuring a distance using laser beams with different frequencies.
Background
Conventional image sensors can generate two-dimensional (2D) images and videos, and recently, image sensors and systems that can generate three-dimensional (3D) images (or depth images) are receiving wide attention, and these three-dimensional image sensors can be used for face recognition, Augmented Reality (AR)/Virtual Reality (VR), and can be applied to devices such as mobile phones, unmanned aerial vehicles, security systems, and artificial intelligence systems.
The existing three-dimensional image sensor has three main implementation modes: stereoscopic binocular, structured light and time of flight ranging (ToF).
The time-of-flight ranging is implemented by measuring the time of photon flight by adopting a specially designed pixel, and the computing complexity is high, so that the power consumption and the computing time are long, how to solve the problem on the premise of not influencing the accuracy is an important work item in the field.
Disclosure of Invention
An object of the present application is to provide a time-of-flight ranging method and a time-of-flight ranging apparatus, so as to solve the technical problem of time and power consumption of the time-of-flight ranging method in the prior art.
An embodiment of the present application discloses a time-of-flight ranging method, including: irradiating first laser light to the object and generating first reflected laser light; sensing the first reflected laser and obtaining a first phase shift between the first laser and the first reflected laser, wherein the first phase shift is smaller than 2 pi; adding 2 pi to the first phase shift to obtain a second phase shift; irradiating a second laser to the object and generating a second reflected laser; sensing the second reflected laser and obtaining first light intensity of the second reflected laser at a preset time point; determining the first phase shift or the second phase shift as a phase delay between the first laser and the first reflected laser according to the first light intensity; and calculating the distance according to the phase delay.
An embodiment of the application discloses a flight time range unit. The time-of-flight ranging device comprises a time-of-flight ranging system for executing the time-of-flight ranging method.
The time-of-flight ranging method disclosed by the application solves the problem of phase ambiguity of the time-of-flight distance in a novel manner, and further reduces power consumption and processing time.
Drawings
Fig. 1 is a block diagram of an embodiment of a time-of-flight ranging system of the present application.
Fig. 2 is a waveform diagram of a low frequency laser in a sensing operation.
Fig. 3 is a waveform diagram of a high frequency laser in a sensing operation.
FIG. 4 is a timing diagram of an operation of the time-of-flight ranging system of FIG. 1.
FIG. 5 is a flow chart of a method of time-of-flight ranging.
Fig. 6 is a schematic diagram of an embodiment of the time-of-flight ranging system shown in fig. 1 applied to an electronic device.
Detailed Description
The following disclosure provides various embodiments or illustrations that can be used to implement various features of the disclosure. The embodiments of components and arrangements described below serve to simplify the present disclosure. It is to be understood that such descriptions are merely illustrative and are not intended to limit the present disclosure. For example, in the description that follows, forming a first feature on or over a second feature may include certain embodiments in which the first and second features are in direct contact with each other; and may also include embodiments in which additional elements are formed between the first and second features described above, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or characters in the various embodiments. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Furthermore, the use of spatially relative terms, such as "below," "over," "above," and the like, herein may be used for convenience in describing the relationship of one element/component or feature to another element/component or feature in the figures. These spatially relative terms are intended to encompass a variety of different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
Although numerical ranges and parameters setting forth the broad scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain standard deviations found in their respective testing measurements. As used herein, "the same" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a particular value or range. Alternatively, the term "the same" means that the actual value falls within the acceptable standard error of the mean, subject to consideration by those of ordinary skill in the art to which this application pertains. It is understood that all ranges, amounts, values and percentages used herein (e.g., to describe amounts of materials, length of time, temperature, operating conditions, quantitative ratios, and the like) are "the same" unless otherwise specifically indicated or indicated. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, these numerical parameters are to be understood as meaning the number of significant digits recited and the number resulting from applying ordinary carry notation. Herein, numerical ranges are expressed from one end to the other or between the two ends; unless otherwise indicated, all numerical ranges set forth herein are inclusive of the endpoints.
The existing three-dimensional image sensor has three main implementation modes: stereoscopic binocular, structured light and time of flight ranging (ToF). Generally, in the implementation of time-of-flight ranging, a sensor emits laser to measure the time of flight of photons, and then the time-of-flight distance, i.e. the distance between the sensor and the measured object, is calculated by combining the speed of light, wherein the time of flight of photons is obtained by the inverse derivation of the phase delay between the emitted laser and the returned laser.
However, the distance to the object (i.e., the object) may delay the phase by more than one wavelength (i.e., 2 π), i.e., phase aliasing due to phase ambiguity.
Therefore, it is necessary to measure the time of flight of the photon by using the sensor to re-emit laser light with a lower frequency to help determine whether the phase delay exceeds one wavelength, as described in detail below.
Fig. 1 is a block diagram of an embodiment of a time-of-flight ranging system 100 of the present application. Referring to fig. 1, the time-of-flight ranging system 100 is configured to sense a phase delay θ +2n pi (where θ is smaller than 2 pi, and n is an integer) of emitted and received laser light and calculate a distance D from an object 101 according to the frequency and the phase delay of the laser light. In general, the phase delay is less than 2 pi, i.e., n =0, but as mentioned above, n may be greater than 0 if the emitted laser frequency is high or the distance D is too large. The time-of-flight ranging method described in the embodiments of fig. 2 to 5 can distinguish whether the phase delay is θ or θ +2 pi, and calculate the actual distance D accordingly. Compared with the general method, the method can reduce the irradiation times of the laser, and because a large amount of energy is needed for each irradiation of the laser, the reduction of the irradiation times of the laser can reduce the power consumption of the flight ranging system 100. It should be noted that although the embodiment exemplifies the resolution of the phase delay θ or θ +2 π, the application is not limited thereto, and θ +4 π, θ +6 π, θ +2n π, etc. may be resolved.
Time-of-flight ranging system 100 includes light emitting device 120, optical sensor 140, processing circuitry 160, and storage device 165. The light emitting device 120 is configured to emit laser light LT1, LT2 to the object 101, wherein the frequency of the laser light LT1 and the frequency of LT2 are different. The optical sensor 140 is used for receiving the laser beams LR1 and LR2 reflected from the object 101 and generating signals according to the received laser beams LR1 and LR 2. The processing circuit 160 is coupled to the light emitting device 120 and the optical sensor 140, and is used to control operations of the light emitting device 120 and the optical sensor 140, for example, to control the light emitting device 120 and the optical sensor 140 to be turned on and off by a clock signal. The processing circuit 160 is also used to process the signal generated by the optical sensor 140. In some embodiments, the processing circuit 160 includes a Micro Controller Unit (MCU), a Central Processing Unit (CPU), or a Graphics Processing Unit (GPU).
Since the phase of the laser light LT1 emitted from the light emitting device 120 is known, the phase shift θ can be obtained when the optical sensor 140 receives the laser light LR11However, based on the laser LT1 alone, the time-of-flight ranging system 100 cannot determine whether the real phase delay of the laser LT1 exceeds 2 pi, that is, cannot determine that the real phase shift (phase difference) between the received laser LR1 and LT1 is θ1Or theta1+2 π, or θ1+4 π, the smallest possible phase delay is therefore chosen as the phase shift θ1I.e. theta1Less than 2 pi. Similarly, the phase shift θ is obtained according to the transmitted laser LT2 and the received laser LR22Wherein theta2Less than 2 pi. Since the laser LT1 and the laser LT2 have different frequencies, the phase shift θ1And phase shift theta2Not the same, assume fHAnd fLThe frequencies of laser LT1 and laser LT2, respectively, and fHGreater than fLThen the phase is shifted by theta1Greater than phase shift theta2. For clarity, the laser beams LT1, LT2, LR1 and LR2 are expressed by the following signal equations 1-4.
Wherein A isH、A'H、ALAnd A'LIs amplitude, fHAnd fLIs frequency, t is time, and BHAnd BLSpecifically, when the light emitting device 120 generates the laser beams LT1 and LT2, the system noise B is generated in the flight ranging system 100HAnd BL. When system noise BHAnd BLIs reflected by an object to become B'HAnd B'LThe laser light LT1, LT2 is reflected back to the optical sensor 140.
Referring to FIG. 2, the phase shift θ is measured1At the same time, the light emitting device 120 generates the laser LT1 to illuminate the object 101, and the optical sensor 140 respectively senses the light intensities Q1, Q2, Q3 and Q4 of the laser LR1 varying with the phase at four different time points t1, t2, t3 and t 4. In some embodiments, the light emitting device 120 generates the laser LT1 to irradiate the object 101 four times, and the optical sensor 140 senses only one of the light intensities Q1, Q2, Q3 and Q4 in each irradiation. Because of the frequency f of the laser LR1HIt is known that the amplitude A 'can be obtained by substituting the time points t1, t2, t3 and t4 and the light intensities Q1, Q2, Q3 and Q4 into the equation 2 of the laser LR 1'HPhase shift theta1And system noise B'H. Wherein the phase is shifted by theta1Is a value less than 2 pi.
For computational convenience, time t1 is chosen to be half a cycle away from t 3. The phase change is converted to a phase change of π from time t1 to t 3. Accordingly, the time points t2 and t4 are also selected to be separated by a half cycle. Under this condition, the laser LR1 equation 2 can be solved as follows.
Where k is the phase change between time t2 and t1, the parameters A1-A4 are expressed by the following equations.
In some embodiments, k may be set to 0.5 π to further simplify the laser LR1 equation as follows.
Referring back to FIG. 1, assume that the actual phase delay may be θ1Or theta1+2π，θ1Corresponding to the distance D1, theta1+2 π corresponds to a distance D2, i.e., in terms of phase shift θ1And frequency fHAnd the light speed c is calculated to obtain the corresponding distance D1 according to the phase shift theta1+2 π and frequency fHAnd the speed of light c, the corresponding distance D2, but the calculation of D1, D2 need not be performed in this step, and the true distance may be calculated after the actual phase delay is determined. To confirm that the actual phase delay is θ1Or theta1+2 π, the light emitting device 120 irradiates the object 101 with the laser LT2 once again, and recognizes that the actual phase delay θ is due to the information of the reflected laser TR21Or theta1+2π。
In addition, the relative relationship between the amplitudes of the incident laser lights LT1 and LT2 and the reflected laser lights LR1 and LR2 and the noise is expressed by a reference function due to the reflectivity of the response object 101. In some embodiments, the processing circuit 160 is configured to establish the reference function and store the related data in the storage device 165 in the form of a lookup table (lookup table). In some embodiments, the time-of-flight ranging system 100 utilizes multiple different amplitudes of laser light to emit into the object 101 and reflects multiple different amplitudes of laser light back to the optical sensor 140. The processing circuit 160 is used to write the correspondence between the laser incidence and reflection of the plurality of different amplitudes into the storage 165 to form a lookup table. In the look-up table, a set of amplitudes AHAnd system noise BHCorresponding to only one set of amplitudes A'LAnd system noise B'L. Therefore, the amplitude A of the incident laser LT1HAnd system noise BHWhen known, processing circuit 160 may derive a corresponding amplitude A 'from the look-up table'LAnd system noise B'L. In some embodiments, the ginsengThe reference function may be pre-established before the time-of-flight ranging system 100 leaves the factory. The reference function is represented by equation 15 as follows:
Referring to fig. 3, after the light emitting device 120 irradiates the laser LT2, the optical sensor 140 senses Q5 of the laser LR2 at a time t 5.
Laser LR2 amplitude A 'in equation 4'LAnd system noise B'LCan be derived from the reference function (equation 15). Specifically, processing circuit 160 inputs amplitude A according to a look-up tableHAnd system noise BHAnd outputs an amplitude A 'corresponding to the reflected laser light LT 2'LAnd system noise B'LWherein A isHAnd BHIs a system-known quantity. Further, at the frequency f of the laser LR2LIn the conventional case, the laser LR2 has only the residual light intensity Q5, the time t and the phase shift θ in equation 42Is unknown. Then, the processing circuit 160 calculates the phase shift θ of the laser LR2 corresponding to the possible distances D1 and D2 respectively3And theta4. Wherein the phase is shifted by theta3And theta4Can be expressed by the following equation.
The phase shift theta obtained by the above calculation3And theta4It is known that LR2 may have a θ relative to LT23Is shifted in phase (provided that the actual distance is D1) or has a value of theta4(if the actual distance is D2), i.e. θ2 May be theta3Or theta4. At time t5, the phase shifts θ are calculated respectively3And theta4The light intensities Q6 and Q7 of the laser LR 2.
When measuring the light intensity Q5, the phase delay of the laser LR2 is unknown. However, processing circuitry 160 has calculated the due phase shift of laser LR2 to be θ3Or theta4. For example, if laser LR2 has a phase delay equal to phase shift θ3Then, the light intensity of the laser LR2 at the time point t5 should be Q6, i.e., Q5 equals Q6. Conversely, if the laser LR2 has a phase delay equal to the phase shift θ4Then, the light intensity of the laser LR2 at the time point t5 should be Q7, i.e., Q5 equals Q7.
Therefore, comparing the difference between the light intensity Q5 and the light intensities Q6 and Q7, respectively, it can be seen that the laser LR2 should have a phase delay equal to θ3Or theta4. When the intensity of light Q5 is closer to the intensity of light Q6 (as shown in the top of FIG. 3), the laser light LR2 should have a phase delay equal to θ3The actual distance from the object 101 is D1. When the intensity of light Q5 is closer to the intensity of light Q7 (as shown in the lower portion of FIG. 3), the laser light LR2 should have a phase delay equal to θ4The actual distance from the object 101 is D2.
In summary, the time-of-flight ranging method provided in the present application enables the time-of-flight ranging system 100 to obtain the actual distance by only emitting the laser five times (i.e. four times for the high frequency laser LT1 and one time for the low frequency laser LT 2) when measuring the distance to the object 101. For time-of-flight ranging system 100, the transmitted laser is not only power consuming, but also time consuming at the receiver light and processing the signal generated by the receiver light. Therefore, the time-of-flight ranging method implemented by the present invention implemented by the time-of-flight ranging system 100 reduces the power consumption of the system without changing the accuracy of the measurement, and improves the long-standing problem in the field.
Referring back to FIG. 3, the frequency f of the laser LR2LLess than frequency f of laser LR1H. In some embodiments, the frequency f of laser LR2LLess than or equal to frequency f of laser LR1HHalf of that. Under this condition, because of the phase shift θ1And theta1The difference between +2 pi is equal to 2 pi, so the phase shift is theta3And theta4The difference between them is less than pi (as can be seen with reference to equations 16, 17). The light intensity Q6 is less than half a period of the laser LR2 from the light intensity Q7 on the equation of the laser LR 2. Equation according to laser LR24 (i.e., the characteristic of cos (t) = Q), the range of half cycles may be located in an area of absolute decrease or absolute increase. Therefore, when sensing the light intensity Q5, the time t5 is selected when the light intensity Q6 and the light intensity Q7 are located in the region where the light intensity Q7 in equation 4 of the laser LR2 decreases (as shown by the dashed square DF1 in fig. 3). This avoids the situation where the light intensity Q6 is equal to the light intensity Q7 (as indicated by the dashed square DF2 in fig. 3). In other words, the above problem can be avoided by selecting the time t5 in the region where the light intensity Q6 and the light intensity Q7 are located in the absolute increasing range of the laser LR2 equation.
As described above, another example will be described. The true phase delay between the laser LR1 and the laser LT1 may be θ when it is to be resolved1、θ1+2 π or θ1+4 π or θ1+6 π, the phase shift θ can be determined according to equations 16 and 171、θ1+2π、θ1+4 π and θ1The +6 π calculation corresponds to a phase shift θ ', θ' +2 π/(f) between the lasers LR2 and LT2H/fL)、θ'+4π/(fH/fL) And theta' +6 pi/(f)H/fL). In this case, the frequency f of the laser LT2LCan be set to fH1/4 times, so that the phase shift theta ', theta' +2 pi/(f) can be madeH/fL)、θ'+4π/(fH/fL) And theta' +6 pi/(f)H/fL) The corresponding four light intensities may fall within one of the absolute increasing or absolute decreasing regions of laser LR 2. Thus, by comparing the light intensity Q5 with the corresponding four light intensities, the real phase delay θ can be obtained1、θ1+2 π or θ1+4 π or θ1+6π。
In some embodiments, the optical sensor 140 also senses background information BG. Background information BG is noise generated by the environment in which the time-of-flight ranging system 100 and the object 101 are located. Therefore, the equations for the laser beams LR1 and LR2 can be expressed as follows.
According to the above equation, when the light intensity Q1-Q5 is measured, a variable BG is added. When the processing circuit 160 calculates the distance D, an error may be generated due to the influence of the background information BG. To eliminate this additional variable, the optical sensor 140 is further used to sense the background information BG alone. That is, in the case of no laser irradiation, the optical sensor 140 senses the received energy, and then obtains the background information BG according to the received energy. After obtaining the background information BG, the background information BG is subtracted from the sensed light intensities Q1-Q4, and then the distance D is calculated according to the method. Therefore, the time-of-flight ranging system 100 can obtain the distance D that is not affected by the background information BG.
Refer to fig. 4. FIG. 4 is a timing diagram illustrating the operation of the time-of-flight ranging method. The light emitting device 120 irradiates the laser LT1 to the object 101 four times, and the optical sensor 140 senses the reflected laser LR1 to obtain the light intensities Q1-Q4 in sequence during each irradiation. Then, the light emitting device 120 irradiates the laser LT2 to the object 101 once, and the optical sensor 140 senses the reflected laser LR2 to obtain the light intensity Q5. Finally, the optical sensor 140 senses the background information BG when there is no laser irradiation.
Generally, the quality of the signal generated by the optical sensor 140 is related to the laser energy. If the received laser energy is low, the signal-to-noise ratio of the signal is low. On the contrary, if the received laser energy is high, the signal-to-noise ratio of the signal is high. To achieve a higher signal-to-noise ratio, the optical sensor 140 receives laser light for a longer period of time to increase the received laser light energy. To achieve this, in some embodiments, the optical sensor 140 is configured to sense the laser LR1 in two sensing periods S1 and S2 per one illumination. As shown in fig. 4, the sensing period S1 is connected with the sensing period S2, and the sensing period S1 is as long as the sensing period S2. The integrated quantity received and sensed in the sensing period S1 is energy E1, and the integrated quantity received and sensed in the sensing period S2 is energy E2. The optical sensor 140 obtains the light intensity according to the summation of the energy E1 and the energy E2. Accordingly, when the laser LR2 is sensed, the integrated amount received and sensed in the sensing period S3 is the energy E3, and the integrated amount received and sensed in the sensing period S4 is the energy E4. The optical sensor 140 obtains the light intensity according to the summation of the energy E3 and the energy E4.
In some embodiments, the optical sensor 140 has two switches TX1 and TX 0. When the switch TX1 and the switch TX0 are turned on, the optical sensor 140 can sense the laser light. At the time of the sensing period S1, the switch TX1 is turned on and the switch TX0 is turned off, and at the time of the sensing period S2, the switch TX0 is turned on and the switch TX1 is turned off.
In some embodiments, the optical sensor 140 has different conversion efficiencies when the switch TX1 is turned on and the switch TX0 is turned on, where the efficiency ratio is g. That is, the optical sensor 140 may generate signals according to the energy E1+ gE2 and E3+ gE 4.
In some cases, optical sensor 140 generates an offset (offset) of orientation upon sensing the time of the laser due to time-of-flight ranging system 100 and/or the environment. To eliminate the offset, in some embodiments, the energy E1 received during the sensing period S1 and the energy E2 received during the sensing period S2 are opposite phases. For example, if energy E1 and offset are represented by processing circuit 160 as E1+ offset by positive values, energy E2 and offset are represented as- (E2-offset) by negative values. In this case, when the sensing period S1 is equal to the sensing period S2, and the absolute values of the energy E1 and the energy E2 are added, there is a deviation in each period that will cancel each other out. Thus, the time-of-flight ranging system 100 can obtain a distance that is not affected by the orientation offset when sensed by the optical sensor 140.
As can be seen from the above description, as shown in fig. 5, the time-of-flight ranging method of the present application first irradiates the laser LT1 to the object 100 to generate the reflected laser LR1 (S501), senses the reflected laser LR1, and obtains the phase shift θ between the laser LT1 and the reflected laser LR11Wherein the phase is shifted by theta1Less than 2 π (S502). Then the phase shift is theta1Plus 2 pi to obtain a possible phase shift theta1+2 π (S503). Then, the laser LT2 is irradiated to the object 101 and the reflected laser LR2 is generated (S504), the reflected laser LR2 is sensed, and the light intensity Q5 of the reflected laser at the time point t5 is obtained (S505). According to the light intensity Q5Fixed phase shift theta1Or the phase shift theta1+2 pi is the phase delay of the laser LR1 (S506). Finally, the distance D is calculated from the phase delay (S507). Thus, the range to the object 101 obtained by the time-of-flight ranging method of the present application eliminates the disadvantage of phase aliasing.
Fig. 6 is a schematic diagram of an embodiment of the time-of-flight ranging system 100 shown in fig. 1 applied to an electronic device 600. Referring to fig. 6, the electronic device 600 may be any electronic device such as a smart phone, a personal digital assistant, a handheld computer system, or a tablet computer.
The invention calculates the phase mixing problem for solving the flight time distance measurement through the high and low frequency laser actual measurement data, and can reduce the laser irradiation times and ensure that the distance measurement is more accurate.
The foregoing description has set forth briefly the features of certain embodiments of the present application so that those skilled in the art may more fully appreciate the various aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should understand that they can still make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
Claims (10)
1. A time-of-flight ranging method for measuring a distance to an object, comprising:
irradiating first laser light to the object and generating first reflected laser light;
sensing the first reflected laser and obtaining a first phase shift between the first laser and the first reflected laser, wherein the first phase shift is smaller than 2 pi;
adding 2 pi to the first phase shift to obtain a second phase shift;
irradiating a second laser to the object and generating a second reflected laser;
sensing the second reflected laser and obtaining first light intensity of the second reflected laser at a preset time point;
calculating a third phase shift and a fourth phase shift between the second laser and the second reflected laser respectively corresponding to the first phase shift and the second phase shift, wherein a flight distance corresponding to the first phase shift causing the first laser to generate the first laser is equal to a flight distance corresponding to the third phase shift causing the second laser to generate the second laser, and a flight distance corresponding to the second phase shift causing the second laser to generate the fourth phase shift causing the first laser to generate the second laser is equal to a flight distance corresponding to the fourth phase shift causing the second laser to generate the second laser;
according to the preset time point, calculating second light intensity and third light intensity of the second reflected laser corresponding to the third phase displacement and the fourth phase displacement respectively;
determining a phase delay equal to the first phase shift when the first light intensity is closer to the second light intensity;
determining the phase delay to be equal to the second phase shift when the first light intensity is closer to the third light intensity; and
calculating the distance according to the phase delay.
2. The time-of-flight ranging method of claim 1, wherein the frequency of the second laser is less than one-half of the frequency of the first laser.
3. The time-of-flight ranging method of claim 1, wherein the second reflected laser light has a strictly increasing or strictly decreasing light intensity versus phase relationship between the third phase displacement and the fourth phase displacement.
4. The time-of-flight ranging method of claim 1, wherein sensing the first reflected laser light and obtaining the first phase shift between the first laser light and the first reflected laser light comprises:
irradiating the object with the first laser light 4 times; and
in each irradiation, the first reflected laser light is sensed in a first phase, a second phase, a third phase and a fourth phase respectively, wherein the third phase is different from the first phase by pi, and the fourth phase is different from the second phase by pi.
5. The time-of-flight ranging method of claim 4, wherein the second phase differs from the first phase by 0.5 pi.
6. The time-of-flight ranging method of claim 1, wherein sensing the first light intensity of the second reflected laser at the preset time point comprises:
irradiating the object with the second laser light 1 time; and
and measuring the first light intensity of the second reflected laser at the preset time point.
7. The time-of-flight ranging method of claim 6, wherein sensing the first light intensity of the second reflected laser at the preset time point further comprises:
measuring background information while said second laser is not being generated, wherein said time-of-flight ranging method further comprises:
calculating a third phase displacement and a fourth phase displacement between the second laser and the second reflected laser respectively corresponding to the first phase displacement and the second phase displacement;
calculating a second light intensity and a third light intensity of the second reflected laser light having the third phase displacement and the fourth phase displacement, respectively; and
removing the background information to update the second light intensity and the third light intensity.
8. The time-of-flight ranging method of claim 1, wherein sensing the first reflected laser light and obtaining the first phase shift between the first laser light and the first reflected laser light comprises:
sensing a first integral quantity of the first reflected laser light within a first sensing period;
sensing a second integral quantity of the first reflected laser light within a second sensing period; and
obtaining the first phase shift according to the first integral quantity and the second integral quantity,
the first sensing time interval is connected with the second sensing time interval, the first sensing time interval and the second sensing time interval are equal in length, and the first integral quantity and the second integral quantity are opposite in phase.
9. The time-of-flight ranging method of claim 1, wherein sensing the second reflected laser light and obtaining the first light intensity of the second reflected laser light at the preset time point comprises:
sensing a third integral quantity of the second reflected laser light within a third sensing period;
sensing a fourth integral quantity of the second reflected laser light within a fourth sensing period; and
obtaining the first light intensity at the preset time according to the third integral quantity and the fourth integral quantity,
the third sensing time interval is connected with the fourth sensing time interval, the third sensing time interval and the fourth sensing time interval are equal in length, the preset time point is between the third sensing time interval and the fourth sensing time interval, and the third integral quantity and the fourth integral quantity are opposite in phase.
10. A time-of-flight ranging apparatus for measuring a distance to an object, comprising:
a time-of-flight ranging system for performing the method of any one of claims 1 to 9.
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