Patent Publication Number: US-2020300975-A1

Title: Electronic apparatus and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2019-50178, filed on Mar. 18, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments of the present invention relate to an electronic apparatus and a method for measuring distance. 
     BACKGROUND 
     There has been developed an electronic apparatus that measures, using a time from emission of light to reception of reflected light reflected by an object, a distance to the object. An electronic apparatus capable of suppressing an error of time until receiving the reflected light reflected by the object and improving accuracy in measuring a distance to the object is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a distance measurement system including an electronic apparatus according to a first embodiment; 
         FIG. 2  is a diagram for illustrating emission of pulsed light by a light source and signals output from a light receiving unit; 
         FIG. 3  is a flowchart of operation of the electronic apparatus; 
         FIG. 4  is a diagram for illustrating a histogram of light receiving time and light receiving time distribution; 
         FIG. 5  is a diagram for illustrating calculation of time of flight (ToF) from light receiving times included in a frequency calculation zone; 
         FIG. 6  is a diagram for illustrating standard deviation of the light receiving times included in the frequency calculation zone; 
         FIG. 7  is a diagram for illustrating accuracy of ToF calculated from the light receiving times included in the frequency calculation zone; 
         FIG. 8  is an example of the frequency calculation zone that can be applied to the first embodiment; 
         FIG. 9  is another example of the frequency calculation zone that can be applied to the first embodiment; 
         FIG. 10  is a diagram for illustrating a threshold value for a histogram of the light receiving time distribution that can be applied to the first embodiment; 
         FIG. 11  is a diagram of the distance measurement system including the electronic apparatus; 
         FIG. 12  is a diagram for illustrating arrangement of objects in two dimensions; 
         FIG. 13  is a diagram for illustrating a layout of objects in two dimensions; 
         FIG. 14  is a diagram for illustrating arrangement of objects in three dimensions; 
         FIG. 15  is a diagram for illustrating a layout of objects in three dimensions; 
         FIG. 16  is a configuration diagram of a mobile object including the electronic apparatus; and 
         FIG. 17  is a block diagram showing a schematic configuration of a LiDAR apparatus provided with the electronic apparatus according to the present embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According an embodiment of the present disclosure, an electronic apparatus capable of determining a distance to an object based on reflected light provided by a reflection of pulsed light on the object has detectors configured to detect reception light to measure times from an emission of the pulsed light to detections of the reception light; and processing circuitry configured to determine a duration in which the reflected light is received based on the times, determine, based on one of the times in the duration, a reception timing of the reflected light included in the reception light, and determine the distance from the electronic apparatus to the object according to the reception timing of the reflected light. 
     Hereinafter, embodiments for carrying out the invention will be described. 
     First Embodiment 
       FIG. 1  illustrates a distance measurement system according to the present embodiment. In the distance measurement system, an electronic apparatus (electronic device)  100  is an electronic apparatus that measures a distance to an object  200 . 
     The electronic apparatus  100  includes a light source  101 , a light receiving unit  102 , a measurement unit  103 , and a processing unit (processing circuitry)  110 . The light source  101  emits an electromagnetic wave having a duration of time to the object  200 . The duration of time will be hereinafter referred to as a pulse width, and the electromagnetic wave will be hereinafter referred to as pulsed light. The pulsed light is reflected by the object  200 , and a part of (hereinafter also referred to as reflected light) of the reflected pulsed light is received by the light receiving unit  102 . 
     In addition, as illustrated in  FIG. 1 , the light receiving unit  102  also receives light other than the reflected light. That is, for example, light (lighting or lighting of a lamp) emitted by a device other than the electronic apparatus  100 , light derived from sunlight, and the like. Hereinafter, the light other than the reflected light will be referred to as ambient light. The measurement unit  103  measures a time from the time at which the light source  101  emits the pulsed light to the time at which the light receiving unit  102  receives the light (hereinafter also referred to as light receiving time). Since the light receiving unit  102  also receives ambient light in addition to the reflected light, there is a plurality of the light receiving times measured by the measurement unit  103 . The light receiving unit  102  has detectors that detect reception light to measure times from an emission of the pulsed light to detections of the reception light. 
     The processing unit  110  determines a duration in which the reflected light is received based on the times, determines, based on one of the times in the duration, a reception timing of the reflected light included in the reception light, and determines the distance from the electronic apparatus to the object according to the reception timing of the reflected light. The processing unit  110  determines a duration to maximize a number of the times included in the duration. The processing unit  110  determines, from the plurality of light receiving times, a time (time of flight: hereinafter also referred to as ToF) from the emission of the pulsed light to the reception of the reflected light. 
     On the basis of the ToF, the processing unit  110  calculates a distance d between the electronic apparatus  100  and the object  200  according to the following formula (1). 
     
       
         
           
             
               
                 
                   d 
                   = 
                   
                     
                       
                         
                           T 
                           o 
                         
                          
                         F 
                       
                       2 
                     
                     · 
                     c 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Here, c represents the speed of light (approximately 3×10 8  m/s). 
     Accuracy of the ToF needs to be improved to improve accuracy of the distance d. The influence of the ambient light needs to be reduced to improve the accuracy of ToF. In the electronic apparatus  100  according to the present embodiment, the light receiving unit  102  includes a plurality of optical receivers, and the measurement unit  103  includes a plurality of measuring instruments. Each of the optical receivers receives photons of pulsed light and ambient light, and a measuring instrument corresponding to the optical receiver measures a time from the time at which the light source  101  emits the pulsed light to the time at which the optical receiver receives the photons (hereinafter also referred to as light receiving time in a similar manner to the case of light). 
     Once the optical receiver receives a photon, it cannot receive the next photon for a predetermined time dependent on the optical receiver. The light receiving unit  102  includes a plurality of optical receivers so that photons can be received even during the predetermined time. The measurement unit  103  includes measuring instruments corresponding to the optical receivers to measure the light receiving time in each of the plurality of optical receivers. 
     The processing unit  110  generates light receiving time data including the time until the optical receiver receives a photon. The light receiving times included in a predetermined time zone (hereinafter referred to as light receiving time distribution) are calculated from the light receiving time data. The time zone may be also called as a duration in the present specification. In the present embodiment, the light receiving time distribution is calculated by counting the light receiving times included in the predetermined time zone. In more detail, the processing unit  110  determines a time zone in which reflected light is received on a basis of light receiving times output from a plurality of measuring units in the measurement unit  103 , and determines a light receiving time at which the reflected light has been received on a basis of the number of light receiving times per section included in the time zone, thereby determining the distance from the electronic apparatus  100  to the object  200  on a basis of the determined receiving time. In more specific example, the processing unit  110  calculates the distribution of light receiving times of light received by a plurality of optical receivers in the light receiving unit  102 , and determines the time zone on a basis of the calculated distribution of light receiving times. In the following, an example of determining the time zone on a basis of the calculated distribution of light receiving times will be explained. However, it is also possible to determine the time zone without calculating the distribution of light receiving times. For example, by detecting the density of the number of light receiving times, the location of higher density may be determined as the time zone. 
     The pulsed light used in the embodiment has density of the number of photons higher than that of ambient light. Accordingly, the number of photons of the pulsed light included in the predetermined time zone is larger than that of the ambient light. The number of the light receiving times of the pulsed light to be measured is therefore larger than the number of the light receiving times of the ambient light to be measured in the same time zone. In other words, the number of the light receiving times of the reflected light to be measured is larger than the number of the light receiving times of the ambient light to be measured in the same time zone. 
     The electronic apparatus  100  selects a time zone in which the optical receiver receives the reflected light on the basis of the light receiving time distribution. Furthermore, the electronic apparatus  100  determines ToF on the basis of the time zone in which the reflected light is received. Hereinafter, reception of the reflected light indicates that the reflected light is received by the optical receiver. The electronic apparatus  100  calculates the distance d on the basis of the determined ToF and the formula (1). 
     By selecting the time zone in which the reflected light is received from the light receiving time data and determining ToF, the electronic apparatus  100  can determine the reflected light while the influence of ambient light is reduced, whereby the accuracy of the ToF can be improved. In addition, the electronic apparatus  100  is capable of reducing occurrence of an error of ToF, whereby the accuracy of the ToF can be improved. In other words, the electronic apparatus  100  is capable of calculating the distance d highly accurately. 
     The electronic apparatus  100  includes a storage  104  and an output unit  105  in addition to the light source  101 , the light receiving unit  102 , the measurement unit  103 , and the processing unit  110 . The processing unit  110  includes a control unit  111 , a generation unit  112 , a data processing unit  113 , a selection unit  114 , and a calculation unit  115 . 
     The light source  101  is a device that receives a command from the control unit  111  and emits pulsed light to the object  200 . For example, the light source  101  may be a combination of a laser light source, such as a laser diode, and a circuit that generates a pulse. The light source  101  may also be a combination of a light emitting diode (LED) or various lamps and the circuit that generates a pulse. 
     Furthermore, there is no limitation on a frequency band of the pulsed light emitted by the light source  101 . The pulsed light may be, for example, visible light, infrared light, near-infrared light, ultraviolet light, or a combination thereof. As an example, the pulsed light in the present embodiment is assumed to include a visible light component. 
     Furthermore, there is no limitation on a shape of the pulsed light emitted by the light source  101 . It may be rectangular, triangular, a shape of a sinc function, or a shape of a Gaussian curve. 
     Examples of the command that the light source  101  receives from the control unit  111  include a pulse width (e.g., 24 ns) and a shape of the pulsed light to be emitted, and a timing and a direction for emitting the pulsed light. 
     The pulsed light emitted by the light source  101  is reflected by the object  200 , and is made incident on the light receiving unit  102  as reflected light. The reflected light may be either diffused reflected light or specular reflected light of the pulsed light on the object  200 , or may be a combination thereof. 
     The light receiving unit  102  includes a plurality of optical receivers. Each of the optical receivers receives a photon, and outputs signals indicating that that photon is received. The signals are transmitted to the corresponding measuring instrument of the measurement unit  103 , and are used to measure the light receiving time. In the present embodiment, as an example, the light receiving unit  102  includes three optical receivers  102   a ,  102   b , and  102   c.    
     Any type of devices can be used as the optical receivers  102   a ,  102   b , and  102   c  as long as photons can be detected. For example, it may be photodiodes, photomultiplier tubes, and the like. An avalanche photo diode (APD) having high detection sensitivity of light may be used as the photodiode. The APD may be used in the Geiger mode. A multi-pixel photon counter (MPPC) may be used as an array of the APD. Furthermore, a silicon photomultiplier (SiPM) may be used as the photomultiplier tube. In the present embodiment, it is assumed that the APD is used in the Geiger mode as an example. 
     The optical receivers  102   a ,  102   b , and  102   c  receive photons and output signals indicating that the photons are received, and do not distinguish the received photons. That is, the optical receivers  102   a ,  102   b , and  102   c  do not distinguish between the reflected light and the ambient light. 
     Note that the reflected light is light obtained by the pulsed light being reflected by the object  200 , which does not include light obtained by the ambient light being reflected by the object  200 , and is classified as the ambient light. 
     The measurement unit  103  includes a plurality of measuring instruments  103   a ,  103   b , and  103   c . Each of the measuring instruments measures light receiving time on the basis of the signals transmitted from the corresponding optical receiver. For example, the measuring instrument  103   a  measures the light receiving time on the basis of the signals transmitted from the optical receiver  102   a . The measuring instruments  103   b  and  103   c  are also similar to the case of the measuring instrument  103   a . The measurement unit  103  receives, from the control unit  111 , a command of a time range (hereinafter also referred to as a measurement range) from the time at which measurement of the light receiving time starts to the time at which the measurement is terminated, and the like. 
     The measurement unit  103  measures the light receiving time on the basis of the commands and the signals transmitted from the light receiving unit  102 . Since the light receiving unit  102  receives photons without distinguishing between the reflected light and the ambient light, the light receiving time measured by the measurement unit  103  is measured without distinguishing between the reflected light and the ambient light. The light receiving time is used by the generation unit  112  to generate light receiving time data including the light receiving time within the measurement range. That is, the light receiving time data includes the light receiving times of both the reflected light and the ambient light. The time at which the reflected light is received is determined from the light receiving time data. 
     Note that the measurement unit  103  may measure a time required for transmission between components of the electronic apparatus  100  in advance, and may correct the measured ToF. The corrected ToF is also included in the time from the time at which the light source  101  emits the pulsed light to the time at which the light receiving unit  102  receives the reflected light. Any type of devices can be used as the measuring instruments  103   a ,  103   b , and  103   c  as long as the light receiving time can be measured on the basis of the command from the control unit  111  and the signals transmitted from the light receiving unit  102 . In the present embodiment, a time to digital converter (TDC) is used as an example. 
     The storage  104  is an electronic apparatus that retains information. In the present embodiment, for example, the light receiving time data generated by the generation unit  112  is retained. 
     The storage  104  is a memory or the like, which is, for example, a random access memory (RAM), a read-only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically EPROM (EEPROM), a flash memory, a register, or the like. 
     The control unit  111  transmits commands to the light source  101 , the measurement unit  103 , and the generation unit  112 . The command to the light source  101  is a pulse width (e.g., 24 ns) and a shape of the pulsed light to be emitted, time and a direction to start the emission of the pulsed light, and the like. 
     The command to the measurement unit  103  is a measurement range from the time at which the measurement of the light receiving time starts to the time at which the measurement is terminated, and the like. In the command transmitted from the control unit  111  to the light source  101  and the measurement unit  103 , the time at which the emission of the pulsed light starts coincides with the time at which the measurement of the light receiving time starts. This coincidence includes a time lag that does not affect the determination of ToF. In addition, this coincidence includes, in a case where there is a delay or the like in the route for transmitting each command, a time lag in consideration of the delay. 
     The command to the generation unit  112  is a time range to be a target of light receiving time data to be generated. As an example, the time range is similar to the measurement range in the present embodiment. That is, the control unit  111  commands the generation unit  112  to include the light receiving time transmitted from the measurement unit  103  in the light receiving time data if it is within the measurement range, and not to include the light receiving time in the light receiving time data if it is outside the measurement range. 
     The generation unit  112  generates light receiving time data in which the light receiving times transmitted from the measurement unit  103  are arranged on the basis of the command transmitted from the control unit  111 . The light receiving time data includes both the light receiving time of the reflected light and the light receiving time of the ambient light within the measurement range. The time zone in which the reflected light is received is selected from the light receiving time data. 
     The generation unit  112  causes the storage  104  to retain the generated light receiving time data. In addition, after the generation of the light receiving time data is complete, the generation unit  112  notifies the data processing unit  113  of the fact that the light receiving time data is available. 
     The data processing unit  113  calculates light receiving time distribution representing the light receiving times included in a predetermined time zone on the basis of the light receiving time data retained in the storage  104 . The light receiving time data includes the light receiving times of both the reflected light and the ambient light. With the data processing unit  113  calculating the light receiving time distribution on the basis of the light receiving time data, the selection unit  114  can determine the light receiving time of the reflected light. 
     Note that the data processing unit  113  can calculate the light receiving time distribution by any method. In the present embodiment, the data processing unit  113  calculates a histogram of the light receiving time distribution as an example. 
     The selection unit  114  determines ToF. In order to determine the ToF, the selection unit  114  selects a time zone at which the reflected light is received on the basis of the light receiving time distribution transmitted from the data processing unit  113 . Since the number of the light receiving times of the reflected light included in the predetermined time zone is larger than the number of the light receiving times of the ambient light, the selection unit  114  selects the time zone with the larger number of the light receiving times as the time zone in which the reflected light is received. 
     The selection unit  114  extracts the light receiving time in the time zone in which the reflected light is received from the selected time zone in which the reflected light is received and the light receiving time data read from the storage  104 . The selection unit  114  determines the ToF on the basis of the extracted light receiving time. The ToF is transmitted to the calculation unit  115 , and is used to calculate the distance d. The calculation unit  115  calculates the distance d between the electronic apparatus  100  and the object  200  on the basis of the ToF transmitted from the selection unit  114  and the formula (1). The distance d is transmitted to the output unit  105 . The transmission of the distance d to the output unit  105  may be performed on the basis of the command from the control unit  111 . 
     The output unit  105  outputs information including the distance d transmitted from the calculation unit  115 . An output destination is not limited, and may be a device and a system that operate at least on the basis of the distance d, an electronic apparatus including a display, a storage device (not illustrated) that retains the distance d, and the like. Note that those devices and systems may be inside or outside the electronic apparatus  100 . In addition, a format of information indicating the distance d is not limited, and may be a format that can be used as data, text, a two-dimensional drawing, a three-dimensional drawing, and the like. Moreover, an output format may be wired or wireless. 
     The processing unit  110  including the control unit  111 , the generation unit  112 , the data processing unit  113 , the selection unit  114 , and the calculation unit  115  is electronic circuitry (processor) including an arithmetic device and a controller of hardware. Examples of the processor include a general-purpose processor, a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), and a combination thereof. 
     The components of the electronic apparatus  100  have been described above. The connection between the components may be wired or wireless. Furthermore, the electronic apparatus  100  is mounted as integrated circuitry, such as an integrated circuit (IC) and large scale integration (LSI). It may be collectively mounted on one chip, or a part of the components may be mounted on another chip. 
     In calculating the distance d, the electronic apparatus  100  according to the present embodiment calculates light receiving time distribution representing the frequency of the received light, and selects the time zone in which the reflected light is received. The electronic apparatus  100  determines ToF on the basis of the time zone in which the reflected light is received, and calculates the distance d. The operation of calculating the distance d performed by the electronic apparatus  100  according to the present embodiment will be described with reference to  FIGS. 2 to 5 . 
       FIG. 2  illustrates the emission of the pulsed light by the light source  101  and the signals output from the light receiving unit  102  at each time. The signals output from the light receiving unit  102  indicates that the light receiving unit  102  has received light. 
       FIG. 3  is a flowchart of the operation of the electronic apparatus  100  in calculating the distance d. Hereinafter, the operation of the electronic apparatus  100  will be described with reference to  FIG. 2  and the flowchart of the operation. 
     First, operation of the electronic apparatus  100  until generating light receiving time data will be described using steps S 101  to S 103 . The electronic apparatus  100  measures, using a predetermined measurement range and pulsed light, the time when photons are received within the measurement range, and generates light receiving time data. The light receiving time data includes both the light receiving time of the reflected light and the light receiving time of the ambient light within the measurement range. 
     The control unit  111  transmits commands necessary for generating the light receiving time data, such as the content of the pulsed light and the measurement range, to the light source  101 , the measurement unit  103 , and the generation unit  112  (step S 101 ). 
     Specifically, the control unit  111  issues commands regarding the pulse width and the shape of the pulsed light to be emitted by the light source  101 , and the start time and the direction of the emission of the pulsed light. In the present embodiment, as an example, the control unit  111  commands the light source  101  to emit rectangular pulsed light with a pulse width PW at the start time 0 toward the direction in which the object  200  exists. 
     The control unit  111  issues, to the measurement unit  103 , a command regarding the measurement range that is a range in which the time at which the light receiving unit  102  receives light is measured. In  FIG. 2 , the measurement range according to the present embodiment is represented as a time length T M  from the time 0 at which the light source  101  emits light to time t 1 . The control unit  111  sets a predetermined value for the time length T M . Note that the command is transmitted to the measuring instruments  103   a ,  103   b , and  103   c  included in the measurement unit  103 . 
     The control unit  111  issues, to the generation unit  112 , a command regarding a time range to be a target of light receiving time data to be generated. In the present embodiment, the time range represents a measurement range. 
     Next, the light source  101  emits pulsed light (step S 102 ).  FIG. 2  illustrates that the light source  101  emits pulsed light with the pulse width PW at the time 0. At the time same as the emission of the light source  101 , the measuring instruments  103   a ,  103   b , and  103   c  start measuring the light receiving time. 
     The pulsed light emitted from the light source  101  is at least partially reflected by the object  200  that is a distance measurement target, and is received by the optical receivers  102   a ,  102   b , and  102   c  as reflected light. 
     Upon reception of photons, the optical receivers  102   a ,  102   b , and  102   c  transmit signals indicating that the photons have been received to the corresponding measuring instruments  103   a ,  103   b , and  103   c . The measuring instruments  103   a ,  103   b , and  103   c  measure the light receiving time on the basis of the signals, and transmits it to the generation unit  112 . 
       FIG. 2  illustrates that, in the measurement range, the measuring instruments  103   a ,  103   b , and  103   c  have received photons from time t R1  to time t R12 . Since the time at which the pulsed light is emitted is the time 0, the light receiving times measured by the measuring instruments  103   a ,  103   b , and  103   c  is the light receiving time t R1  to the light receiving time t R12 . The measuring instruments  103   a ,  103   b , and  103   c  transmit those light receiving times t R1  to t R12  to the generation unit  112 . 
     The generation unit  112  generates light receiving time data in which the light receiving times transmitted from the measuring instruments  103   a ,  103   b , and  103   c  are arranged (step S 103 ). In the present embodiment, the light receiving time data includes the light receiving times t R1  to t R12 . The generation unit  112  causes the storage  104  to retain the light receiving time data. 
     After the measurement range ends, the generation unit  112  notifies the data processing unit  113  of the fact that the light receiving time data is available. Since the end of the measurement range is the time t 1  in  FIG. 2 , the generation unit  112  notifies the data processing unit  113  of the fact that the light receiving time data is available after the time t 1 . 
     The foregoing has described the operation of the electronic apparatus  100  until the light receiving time data is generated. Next, operation of the electronic apparatus  100  until calculating the distance d will be described using steps S 104  to S 107 . The electronic apparatus  100  calculates light receiving time distribution on the basis of the generated light receiving time data. The electronic apparatus  100  selects a time zone in which the reflected light is received on the basis of the calculated light receiving time distribution. The electronic apparatus  100  determines ToF on the basis of the time zone in which the reflected light is received, and calculates the distance d. 
     In response to the notification from the generation unit  112 , the data processing unit  113  calculates light receiving time distribution on the basis of the light receiving time data retained in the storage  104  (step S 104 ). That is, the data processing unit  113  calculates the light receiving time distribution after the measurement range ends. The light receiving time distribution is calculated in the form of a histogram in which the light receiving times included in the predetermined time zone are counted. The calculation of the light receiving time distribution will be specifically described with reference to  FIG. 4 . 
       FIG. 4  illustrates the light receiving times included in the light receiving time data and the light receiving time distribution calculated by the data processing unit  113 . Hereinafter, a predetermined time zone for counting the light receiving times will be referred to as a frequency calculation zone. In  FIG. 4 , the time length of the frequency calculation zone is represented as TA. The data processing unit  113  sets a predetermined value for the time length TA. In the present embodiment, as an example, the time length TA is assumed to be the same as the pulse width PW of the pulsed light emitted by the light source  101 . 
     The data processing unit  113  counts the light receiving times included in the frequency calculation zone of the time length TA centered on a predetermined light receiving time. The predetermined light receiving time is optionally selected from a light receiving time 0 to a light receiving time T M . The data processing unit  113  sets the number of counts as the light receiving time distribution at the predetermined light receiving time. The data processing unit  113  calculates the light receiving time distribution at each predetermined light receiving time while changing the predetermined light receiving time, thereby calculating a histogram of the light receiving time distribution. In the present embodiment, as an example, the light receiving time distribution is calculated from the light receiving time 0 at 1 ns intervals, thereby calculating the histogram of the light receiving time distribution. 
     The calculation of the light receiving time distribution at a light receiving time t AC  illustrated in  FIG. 4  will be described as an example. The data processing unit  113  counts the light receiving times included in the frequency calculation zone of the time length TA centered on the light receiving time t AC . The frequency calculation zone illustrated in  FIG. 4  is a zone from a light receiving time t A1  to a light receiving time t A2 . The light receiving times included in the frequency calculation zone from the light receiving time t A1  to the light receiving time t A2  are from a light receiving time t R4  to a light receiving time t R11 . The data processing unit  113  sets the number of counts as a light receiving time distribution F max  at the time t AC . The data processing unit  113  transmits the calculated histogram of the light receiving time distribution to the selection unit  114 . 
     The selection unit  114  selects the time zone in which the reflected light is received on the basis of the calculated histogram of the light receiving time distribution (step S 105 ). Specifically, the selection unit  114  selects the frequency calculation zone with the largest number of light receiving times in the histogram of the light receiving time distribution as the time zone in which the reflected light is received. 
     This is because, as described above, the number of the light receiving times of the reflected light to be measured is larger than the number of the light receiving times of the ambient light to be measured in the same time zone. In the present embodiment, as an example, the selection unit  114  selects the frequency calculation zone from the light receiving time t A1  to the light receiving time t A2  as the time zone in which the reflected light is received. 
     The selection unit  114  determines ToF on the basis of the time zone in which the reflected light is received (step S 106 ). The determination will be described with reference to  FIG. 5 . The selection unit  114  extracts the light receiving times included in the time zone in which the reflected light is received from the light receiving time data retained in the storage  104 . In  FIG. 5 , the light receiving time t R4  to the light receiving time t R11  are shown as the light receiving times included in the frequency calculation zone from the time t A1  to the time t A2 . 
     The selection unit  114  determines ToF on the basis of the extracted light receiving time. In the present embodiment, as an example, the selection unit  114  determines, as ToF, an average value of the first light receiving time t R4  and the last light receiving time t R11  included in the frequency calculation zone. The reason for the determination method will be described after description of the operation of the electronic apparatus  100  is complete. The selection unit  114  transmits the determined ToF to the calculation unit  115 . 
     The calculation unit  115  calculates the distance d on the basis of the ToF transmitted from the selection unit  114  and the formula (1) (step S 107 ). The calculated distance d is transmitted to the output unit  105 . 
     Next, the output unit  105  outputs information including the distance d transmitted from the calculation unit  115  (step S 108 ). The output destination and the output format are not limited as described above. 
     Next, the control unit  111  checks whether or not an end command for terminating the operation of the electronic apparatus  100  has arrived (step S 108 ). The end command is a command for terminating the operation of the electronic apparatus  100  in the present flow. The end command is transmitted to the control unit  111  by a user making input to the electronic apparatus  100 , the electronic apparatus  100  obtaining signals including the end command, or the like. The end command may be a command for immediately terminating the operation of the electronic apparatus  100 . 
     In the case where the end command has not arrived at the control unit  111  (No in step S 108 ), the process returns to step S 101 . On the other hand, in the case where the end command has arrived at the control unit  111  (Yes in step S 108 ), the flow is terminated, and the electronic apparatus  100  terminates the operation. 
     The foregoing has described the operation of the electronic apparatus  100  according to the present embodiment. Hereinafter, the method of determining ToF will be described with reference to  FIGS. 6 and 7 . Note that the time from the light receiving time t R4  to the light receiving time t R11  described in the present embodiment is also the time from the time at which the pulsed light is actually emitted to the time at which the reflected light is received. 
     The pulsed light used in the present embodiment is generally in a coherent state. The number of emitted photons of the pulsed light in the coherent state follows Poisson distribution. Since the number of photons emitted as the pulsed light is not always constant, a time lag may occur between the time at which the pulsed light is emitted and the time at which the reflected light is received. 
     In addition, errors included in the previous (or later) light receiving times are accumulated except for the first light receiving time t R4  and the last light receiving time t R11  in the time from the emission of the pulsed light to the reception of the reflected light. Therefore, possibility of occurrence of a time lag in the light receiving time becomes higher than that in the light receiving time t R4  and the light receiving time t R11 . 
       FIG. 6  illustrates standard deviation in the case where each of the light receiving times from the light receiving time t R4  to the light receiving time t R11  is measured a plurality of times. The standard deviation of the light receiving time t R4  and the light receiving time t R11  is small. On the other hand, the standard deviation becomes larger as the time is closer to the center of the time zone in which the reflected light is received, such as a light receiving time t R7  and a light receiving time t R3 . 
     It is indicated that the standard deviation is smaller in the average value of the light receiving time t R4  and the light receiving time t R11  and the possibility of including an error as ToF is low. 
       FIG. 7  is a diagram for illustrating an error of the determined ToF.  FIG. 7  illustrates an occurrence rate of the ToF in the case where each of the light receiving time t R4 , the light receiving time t R11  the average value between the light receiving time t R4  and the light receiving time t R11 , and the average value among the light receiving time t R4  to the light receiving time t R11  is set to be the ToF. ToF ave  represents an average value in the case where the determination of the ToF corresponding to each of the four light receiving times mentioned above is performed a plurality of times. 
     For example, in the case where the light receiving time t R4  is ToF (hereinafter also referred to as ToF tR4 ), the average value in the case where the ToF tR4  is determined a plurality of times is illustrated as ToF ave . In the case where the light receiving time t R11  is ToF (hereinafter also referred to as ToF tR11 ), the average value in the case where the ToF tR11  is determined a plurality of times is illustrated as ToF ave . 
     Assuming that the average value among the light receiving time t R4  to the light receiving time t R11  is ToF, the ToF is highly likely to include an error. This is because the light receiving time with large standard deviation is used to determine ToF as described with reference to  FIG. 6 . 
     Meanwhile, ToFs determined on the basis of the light receiving time with small standard deviation described with reference to  FIG. 6 , that is, the light receiving time t R4 , the light receiving time t R11 , and the average value between the light receiving time t R4  and the light receiving time t R11  are highly likely to take specific values, and are less likely to include errors. 
     In order to enhance the accuracy of the distance d, it is preferable to employ a method that is less likely to include an error in the ToF. Therefore, in the present embodiment, ToF is determined on the basis of the average value between the first light receiving time t R4  and the last light receiving time t R11  among the light receiving times included in the time zone in which the reflected light is received. Alternatively, either the first light receiving time t R4  or the last light receiving time t R11  may be set as ToF among the light receiving times included in the time zone in which the reflected light is received. 
     While the present embodiment has been described as above, various modifications can be implemented and executed. Hereinafter, variations of the operation of the electronic apparatus  100  will be described. For example, in the present embodiment, the control unit  111  issues commands to the light source  101 , the measurement unit  103 , and the generation unit  112  in step S 101 . As a variation, a command and notification to another component of the electronic apparatus  100  may be further added, a command may be issued with content different from that of the command described, or at least a part of the commands described may not be issued. 
     As a variation, an exemplary command and notification added by the control unit  111  will be described below. The control unit  111  may notify the light receiving unit  102  of information regarding pulsed light to be emitted by the light source  101 . The information regarding the pulsed light is, for example, a pulse width, emission time, a shape, an emission direction, and the like of the pulsed light. 
     The control unit  111  may transmit a command to cause the light receiving unit  102  to output signals indicating that photons have been received in a predetermined time zone. For example, in the present embodiment illustrated in  FIG. 2 , the control unit  111  may command the light receiving unit  102  to transmit, to the measurement unit  103 , signals indicating that photons have been received in the measurement range from the time 0 to the time t 1 . The commands are transmitted to the optical receivers  102   a ,  102   b , and  102   c  included in the light receiving unit  102 . 
     The control unit  111  may transmit, to the measurement unit  103 , a command to start measurement of the light receiving time and a command to terminate the measurement of the light receiving time without issuing a command of the measurement range. That is, in the present embodiment illustrated in  FIG. 2 , the control unit  111  may transmit, to the measurement unit  103 , a command to start measurement of the light receiving time at the time 0, and may transmit a command to terminate the measurement of the light receiving time at the time t 1 . Furthermore, the control unit  111  may transmit, to the measurement unit  103 , a command to immediately start the measurement of the light receiving time at the time 0, and may transmit, to the measurement unit  103 , a command to immediately terminate the measurement of the light receiving time at the time t 1 . Note that those commands are transmitted to the measuring instruments  103   a ,  103   b , and  103   c  included in the measurement unit  103 . 
     Moreover, as a variation, the light source  101 , the measurement unit  103 , and the generation unit  112  may set a part of the content of the command described in the present embodiment in advance. Along with this, the commands from the control unit  111  may not be issued partially. For example, the light source  101  may be set to emit rectangular pulsed light with the pulse width PW, and the control unit  111  may issue commands regarding the time at which the pulsed light is emitted and the direction in which the pulse width is emitted. 
     Further, the measurement unit  103  and the generation unit  112  may set the time length T M  of the measurement range in advance, and may set the measurement range in response to a command to start measurement of the light receiving time from the control unit  111 . 
     Furthermore, as a variation of the command of the control unit  111 , although the starting end of the measurement range is the time 0 in the present embodiment, the starting end of the measurement range is not limited to the time 0. For example, the time at which the light receiving time is measured may not be included in the measurement range. The control unit  111  can set a predetermined time zone as the measurement range, such as, in the case where the time at which the reflected light is received can be predicted to a certain extent, setting the periphery (e.g., 10 ns before and after) of the time as the measurement range. Even in this case, the start time of the measurement of the light receiving time performed by the measurement unit  103  coincides with the emission time of the pulsed light performed by the light source  101 . 
     In the present embodiment, in step S 103 , the measurement unit  103  and the generation unit  112  measure the light receiving time with the time at which the pulsed light is emitted as the time 0, thereby generating light receiving time data. The setting of the time is not limited to the case of the present embodiment. As a variation, time other than zero may be assigned as the time at which the pulsed light is emitted. Taking the present embodiment illustrated in  FIG. 2  as an example, the measurement unit  103  and the generation unit  112  may measure the light receiving time and generate the light receiving time data using actual time. 
     As a variation of step S 103 , the measurement unit  103  and the generation unit  112  may perform the measurement and generate the light receiving time data on the basis of time. For example, the measuring instruments  103   a ,  103   b , and  103   c  included in the measurement unit  103  may transmit, to the generation unit  112 , the time at which the corresponding optical receiver has received a photon. The generation unit may generate light receiving time data in which the time at which the pulsed light is emitted and the time at which the optical receiver receives a photon are arranged. 
     Note that, in this case as well, operation is similar to the operation of the electronic apparatus  100  described in the present embodiment. Since the difference is the time in the variation, the selection unit  114  only determines the time at which the reflected light is received. The calculation unit  115  calculates ToF by subtracting the time at which the pulsed light is emitted from the time at which the reflected light is received. The operation of the electronic apparatus  100  other than the difference is similar to the case of the present embodiment. 
     As a variation of step S 103 , the generation unit  112  may not receive a command regarding the measurement range from the control unit  111 , and may generate the light receiving time data while the electronic apparatus  100  is in operation. Note that, in the case of performing the variation, the control unit  111  may issue, to the data processing unit  113 , a command regarding a time range for which the light receiving time distribution is to be calculated from the light receiving time data. 
     In the present embodiment, in step S 104 , the data processing unit  113  calculates the light receiving time distribution upon reception of the notification from the generation unit  112 . As a variation, the data processing unit  113  may receive a command from the control unit  111  to calculate the light receiving time distribution. In that case, the generation unit  112  transmits, to the control unit  111 , notification indicating that the generation of the light receiving time data in the measurement range has been complete. 
     As a variation of step S 104 , the data processing unit  113  may calculate the light receiving time distribution without the end of the measurement range. For example, the data processing unit  113  may calculate the light receiving time distribution in the light receiving time interlocked with the current time, or may calculate the light receiving time distribution in the light receiving time interlocked with the time before the current time by a predetermined time. 
     As a variation of step S 104 , the frequency calculation zone described in the present embodiment is not limited to the case of being centered on the predetermined light receiving time. For example,  FIG. 8  illustrates, as one of variations, an exemplary case where a zone following the light receiving time t A1  by the time length TA is set as a frequency calculation zone.  FIG. 9  illustrates, as one of variations, an exemplary case where a zone preceding the light receiving time t A2  by the time length TA is set as a frequency calculation zone. 
     As a variation of step S 104 , the time length TA of the frequency calculation zone described in the present embodiment is not limited to the pulse width PW. The data processing unit  113  can set the time length TA optionally. Note that, since the reflected light is highly likely to fall within the pulse width PW, there is a high possibility that the time zone in which the reflected light is received can be selected from the light receiving time distribution in the case where the time length TA is equal to or more than the pulse width. 
     As a variation of step S 104 , the data processing unit  113  may cause the storage  104  to retain the calculated light receiving time distribution. At the stage of transition to step S 105 , the control unit  111  may transmit a command to the selection unit  114 , and the selection unit  114  may read the light receiving time distribution from the storage  104 . 
     In the present embodiment, the selection unit  114  selects the time zone in which the reflected light is received on the basis of the histogram of the light receiving time distribution in step S 105 . As a variation, the selection unit  114  may set a threshold value in the histogram of the light receiving time distribution. 
     The variation will be described with reference to  FIG. 10 . In  FIG. 10 , in addition to  FIG. 4  described in the present embodiment, a threshold value FT is set in the light receiving time distribution. The selection unit  114  may select, as the time zone in which the reflected light is received, a time zone in which the number of the light receiving times included is equal to or higher than the threshold value FT and the number of the light receiving times included is the largest from among a plurality of frequency calculation zones. 
     By setting the threshold value, it becomes possible to suppress erroneous measurement of the ToF in the case where no reflected light is received within the measurement range. Further, as a variation, in the case where no reflected light is received within the measurement range, the selection unit  114  may make notification to the control unit  111 , or may cause the output unit  105  to output information notifying the user of an error. Upon reception of the notification, the control unit  111  may start over from the previous step. For example, it may start over from step S 101  described in the present embodiment. 
     As a variation of steps S 104  and S 105 , the data processing unit  113  may not calculate the histogram of the light receiving time distribution, and the selection unit  114  may select the time zone in which the reflected light is received. For example, the selection unit  114  may set a frequency calculation zone centered on the light receiving time, and may select the time zone in which the reflected light is received on the basis of the number of the light receiving times included in the frequency calculation zone. 
     By reducing the frequency calculation zones to be set, the load on the processing unit  110  is reduced. 
     In the present embodiment, in step S 106 , the selection unit  114  determines the ToF to be the average value between the first light receiving time t R4  and the last light receiving time t R11  among the light receiving times included in the time zone in which the reflected light is received. The ToF is not limited to the average value. As described with reference to  FIGS. 6  and  7 , it is sufficient if the selection unit  114  make determination such that the ToF has a low possibility of including an error. As a variation, for example, ToF may be the light receiving time t R4  and the light receiving time t R11  with small standard deviation in  FIG. 6 . The ToF may be the average value between a first light receiving time t R5  and a second light receiving time t R10  from the last among the light receiving times included in the time zone in which the reflected light is received. 
     In addition to the above, the selection unit  114  can select the time at which the reflected light is received in a similar manner to the present embodiment even if the light receiving time measured by a method different from that of the light receiving time described in the present embodiment and the variations is used. 
     As a variation of step S 106 , the selection unit  114  may cause the storage  104  to retain the determined ToF. At the stage of transition to step S 106 , the control unit  111  may transmit a command to the calculation unit  115 , and the calculation unit  115  may read the ToF from the storage  104 . 
     In the present embodiment, in step S 107 , the calculation unit  115  calculates the distance d between the electronic apparatus  100  and the object  200  on the basis of the ToF and the formula (1). The distance d is transmitted to the output unit  105 . As a variation, the calculation unit  115  may cause the storage  104  to retain at least one of the ToF and the distance d. At the stage of transition to step S 108 , the control unit  111  may transmit a command to the output unit  105 , and the output unit  105  may read at least one of the ToF and the distance d from the storage  104 . 
     In the present embodiment, the output unit  105  outputs information including the distance d in step S 108 . As a variation, the output unit  105  may receive the ToF from the calculation unit  115 , and may output it as information including the ToF. Further, the output unit  105  may combine and output information including the distance d and information including the ToF. 
     The transmission of commands, data, and information in each step described in the present embodiment may be performed on the basis of a command from the control unit  111 . 
     The foregoing has described the variations of the operation of the electronic apparatus  100 . Next, variations of the configuration of the electronic apparatus  100  will be described. 
     In the present embodiment, in step S 101 , the control unit  111  issues a command such that the time at which the light source  101  emits the pulsed light and the time at which the generation unit  112  starts the data generation are the same time. As a variation, the pulsed light emitted from the light source  101  may be partially reflected, and a command to start the data generation may be transmitted to the generation unit  113  upon reception of the light. In the variation, the command to start data generation is immediately after the light source  101  emits the pulsed light. 
     Such an electronic apparatus (electronic device)  150  will be described as an example with reference to  FIG. 11 . In addition to the electronic apparatus  100 , the electronic apparatus  150  includes a reflection unit  106 , and a detection unit  107 . Among components included in an electronic apparatus (electronic device)  160 , the components included in the electronic apparatus  100  are denoted by the same reference signs, and descriptions thereof will be omitted. 
     The reflection unit  106  partially reflects the pulsed light emitted from the light source  101 , and transmits the remaining pulsed light. 
     The detection unit  107  detects the pulsed light reflected by the reflection unit  106 , and transmits, to the measurement unit  103  and the generation unit  112 , signals indicating that the light source  101  has emitted the pulsed light. The measurement unit  103  sets the time at which the signals are received as the time at which the pulsed light is emitted. The measurement range is determined on the basis of the set time. The generation unit  112  sets the time at which the signals are received as the time at which the pulsed light is emitted, and generates light receiving time data. 
     Note that, in the variation, the control unit  111  does not command the measurement unit  103  and the generation unit  112  to start measurement of the light receiving time and to start generation of the light receiving time data. The control unit  111  may issue commands regarding the time length T M  of the measurement range, termination of the measurement of the light receiving time, and termination of the generation of the light receiving time data to the measurement unit  103  and the generation unit  112 . 
     The operation of the electronic apparatus  150  is similar to the operation of the electronic apparatus  100  described in the present embodiment except for the handling of the time at which the pulsed light is emitted described in the variation, and thus descriptions of the subsequent operation will be omitted. 
     Further, the detection unit  107  may detect the pulsed light reflected by the reflection unit  106 , and may transmit a command to start measurement of the light receiving time and a command to start generation of the light receiving time data to the measurement unit  103  and the generation unit  112 , respectively. Furthermore, the detection unit  107  may transmit signals indicating that the light source  101  has emitted the pulsed light to the control unit  111 . 
     The control unit  111  that has received the signals may transmit a command to start measurement of the light receiving time and a command to start generation of the light receiving time data to the measurement unit  103  and the generation unit  112 , respectively. In the case where the signals are not received from the detection unit  107  even when a predetermined period of time has elapsed from the time of the pulsed light emission, the control unit  111  may restart from step S 101 , or may cause the output unit  105  to output information notifying the user of an error. 
     With this arrangement, it becomes possible to cope with the case where the light source  101  does not emit pulsed light due to failure or the like. 
     The operation in the processing unit  110  described in the present embodiment and the variation may be implemented by a program being processed. For example, a general-purpose computer incorporating the program may be caused to perform the operation in the processing unit  110 . 
     The program may be stored and provided in a computer readable storage medium, such as a compact disc read-only memory (CD-ROM), a memory card, a CD recordable (CD-R), and a digital versatile disk (DVD), as a file in an installable or executable format. Furthermore, the program may be stored in a computer connected to a network, such as the Internet, to be provided via the network, or may be incorporated and provided in a storage medium, such as a ROM, a hard disk drive (HDD), and a solid state drive (SSD). 
     The present embodiment and the variations have been described above. Next, examples of application of the electronic apparatus  100  described in the present embodiment will be described below. 
     In the present embodiment, the electronic apparatus  100  calculates the distance d to the object  200 . As an example of application, the electronic apparatus  100  emits pulsed light in various directions and receives reflected light to determine ToF, thereby making it possible to create a layout showing the arrangement of objects around the electronic apparatus  100 . 
     A case where the electronic apparatus  100  creates the layout will be described with reference to  FIG. 12 . In  FIG. 12 , objects  200   a  to  200   e  are arranged around the electronic apparatus  100 . 
     The electronic apparatus  100  emits pulsed light in various directions, and calculates the distances between the electronic apparatus  100  and the objects  200   a  to  200   e  in a similar manner to the present embodiment. The calculation unit  115  creates a layout showing the arrangement of the surrounding objects on the basis of the distance. 
     An example of the created layout is illustrated in  FIG. 13 . The calculation unit  115  can plot points at the coordinates of the objects  200   a  to  200   e  to create a layout of the objects  200   a  to  200   e.    
     Information regarding the coordinates included in the points may be orthogonal coordinates, polar coordinates, absolute coordinates (world coordinates), or relative coordinates. As the relative coordinates, for example, the center of gravity of the electronic apparatus  100  may be used as a reference, or the position of the light source  101  may be used as a reference. In addition, a means for displaying the information regarding the coordinates is not limited to points, but may be vectors. 
     In the layout, for example, a mobile object that performs autonomous operation, on which the electronic apparatus  100  is mounted, is used to control a power unit. In addition, by adding location information to the layout and using it as obstacle data, the mobile object that performs autonomous operation can easily obtain the data to use it. The acquisition of the location information can use an existing method. 
     Although the layout illustrated in  FIG. 13  is a plane surface, a three-dimensional space (real space) at three-dimensional points may be shown. An example of the layout in the three-dimensional space will be described with reference to  FIGS. 14 and 15 . 
       FIG. 14  illustrates that objects  200   f  and  200   g  are arranged around the electronic apparatus  100 . The electronic apparatus  100  emits pulsed light in various directions, and calculates the distances between the electronic apparatus  100  and the objects  200   f  and  200   g  in a similar manner to the present embodiment. The calculation unit  115  creates a layout showing the arrangement of the surrounding objects on the basis of the distance. 
     An example of the created layout is illustrated in  FIG. 15 . The calculation unit  115  can plot points at the coordinates of the objects  200   f  and  200   g  to create a layout of the objects  200   f  and  200   g.    
     In a similar manner to the case of the two-dimensional layout, information regarding the coordinates included in the three-dimensional points may be orthogonal coordinates, polar coordinates, absolute positions (world positions), or relative positions. As the relative positions, for example, the center of gravity of the electronic apparatus  100  may be used as a reference, or the position of the light source  101  may be used as a reference. In addition, a means for displaying the information regarding the coordinates is not limited to three-dimensional points, but may be three-dimensional vectors. 
     In a similar manner to the two-dimensional layout, in the three-dimensional layout as well, location information may be added to be used as obstacle data. 
     The calculation unit  115  may transmit the created layout to the output unit  105 , or may cause the storage  104  to retain it. In a similar manner to the distance d described in the present embodiment, the output unit  105  outputs it to an output destination. 
     Furthermore, an example of application of the layout is not limited to the position of an object. For example, a state in vivo can be expressed in a three-dimensional view when it is applied to an endoscope, and a state of a construction can be expressed in a two-dimensional view or a three-dimensional view when it is applied to a construction. The state in vivo is, for example, the arrangement of organs, the presence or absence of swellings, depressions, holes, and tumors, and the like. The state of a construction is, for example, no abnormality, cracks, unevenness, holes, deflection, and the like. Note that those examples are also included in the layout. 
     As a further example of application, a mobile object that moves using the layout will be described. An example of the mobile object is illustrated in  FIG. 16 . A mobile object  500  is a movable object, which is, for example, a vehicle, a wagon, a flyable object (manned plane and unmanned plane (e.g., unmanned aerial vehicle (UAV) and drone)), a robot (including an endoscope with a movable distal end), or the like. In addition, the mobile object  500  is, for example, a mobile object that travels through driving operation by a person, or a mobile object capable of automatically (autonomously) traveling without driving operation by a person. An exemplary case where the mobile object  500  is a four-wheeled vehicle capable of autonomously traveling will be described below. 
     In addition to the electronic apparatus  100 , the mobile object  500  includes a power control unit  501 , a power unit  502 , and an acquisition unit  503 . Further, the output unit  105  transmits the layout created by the calculation unit  115  to the power control unit  501 . 
     The power control unit  501  commands the power unit  502  to drive. More specifically, the power control unit  501  determines a direction, speed, and acceleration in which the mobile object  500  moves on the basis of the layout transmitted from the output unit  105  and the information transmitted from the acquisition unit  503 , and commands the power unit  502  to drive such that the direction, the speed, and the acceleration are implemented. 
     By the command of the power control unit  501 , an accelerating amount, a braking amount, a steering angle, and the like of the mobile object  500  are controlled. For example, the power control unit  501  controls the drive of the mobile object  500  such that, while objects such as obstacles are avoided, the ongoing lane is maintained and an inter-vehicular distance of a predetermined distance or more is maintained with a preceding vehicle. 
     The power unit  502  is a driving device mounted on the mobile object  500 . The power unit  502  is, for example, an engine, a motor, a wheel, or the like. The power unit  502  is driven by a command of the power control unit  501  to drive the mobile object  500 . 
     The acquisition unit  503  obtains various kinds of information necessary for autonomous traveling. That is, for example, location information of the mobile object  500 , an image around the mobile object  500 , relative location information transmitted from mobile objects around the mobile object  500 , and the like. In order to obtain those various kinds of information, the acquisition unit  503  includes any device such as a millimeter-wave radar sensor, a sonar sensor for detecting an object using sound waves, an ultrasonic sensor, a stereo camera, a monocular camera, and a wired or wireless communication device. 
     Note that the power control unit  501  is mounted as a processor or the like described in the present embodiment. The power control unit  501  and the acquisition unit  503  may be mounted on one chip, or may be mounted separately. Furthermore, the power control unit  501  and the acquisition unit  503  may be incorporated in the electronic apparatus  100 . In that case, the power control unit  501  may be incorporated in the processing unit  110 . 
     As described above, the mobile object  500  is capable of autonomously traveling while avoiding objects, such as obstacles, at least on the basis of the layout showing the arrangement of objects created by emitting pulsed light and receiving reflected light. 
     While the case of a four-wheeled vehicle capable of autonomously traveling has been described in the example of application, it is also possible to autonomously travel in a similar manner even in the case of other mobile objects mentioned as examples of the mobile object  500 , although the power unit  502  is different. 
     For example, in the case where the mobile object  500  is a drone, the power unit  502  is a motor that rotates blades, and a motor that adjusts the angles of the blades. The power control unit  501  determines a rotating speed of the motor that rotates the blades, an angle of the motor that adjusts the angles of the blades, acceleration of each motor, and the like on the basis of the layout and the acquisition unit  503 , and provides the power unit  502  with a command. The power unit  502  drives on the basis of the command of the power control unit  501 , whereby the mobile object  500  can travel autonomously. 
     For example, in the case where the mobile object  500  is a robot, the power unit  502  is a motor that circles, rotates, and adjusts the angle of at least one of an arm and a leg. The arm is, for example, a robot arm or the like. Furthermore, in the case where the robot is an endoscope with a movable distal end, the movable portion is included in the arm. The leg may be, for example, a leg with a wheel and a joint. The power control unit  501  determines rotating speeds of the motors in the arm and the leg, angles of the motors, acceleration of each motor, and the like on the basis of the layout and the acquisition unit  503 , and provides the power unit  502  with a command. The power unit  502  drives on the basis of the command of the power control unit  501 , whereby the mobile object  500  can travel autonomously. 
     The electronic apparatus  100  according to the present embodiment can be implemented in a LiDAR (Light Detecting And Ranging) apparatus  150  used for autonomous operation or the like.  FIG. 17  is a block diagram of showing a schematic configuration of the LiDAR apparatus  150  provided with the electronic apparatus according to the present embodiment. 
     The electronic apparatus  100  of  FIG. 17  includes a floodlight unit  120 , a light controller  130 , a light receiving unit  102 , and a signal processing unit  140 . At least part of the electronic apparatus  100  of  FIG. 17  can be configured with one or plurality of semiconductor ICs (Integrated Circuits). For example, at least partial components in the signal processing unit  140  may be integrated into one semiconductor chip or the light receiving unit  102  may also be integrated into the semiconductor chip. Moreover, the light floodlight unit  120  may also be integrated into the semiconductor chip. 
     The floodlight unit  120  emits the above-described pulsed lights cyclically as flood lights. The time from when the floodlight unit  120  emits the first pulsed light until the floodlight unit  120  emits the second pulsed light is a period of time equal to or longer than the time required for the light receiving unit  102  to receive reflected light in accordance with the first pulsed light. 
     The floodlight unit  120  has an oscillator  121 , a floodlight controller  122 , a light source  101 , a first driver  123 , and a second driver  124 . The oscillator  121  generates an oscillation signal in accordance with the period of emitting the pulsed light as flood lights. The first driver  123  intermittently supplies power to the light source  101  in synchronism with the oscillation signal. The light source  101  intermittently emits the pulsed light on a basis of the power from the first driver  123 . The floodlight controller  122  controls the second driver  124  in synchronism with the oscillation signal. The second driver  124  supplies a drive signal to the light controller  130  in synchronism with the oscillation signal in response to a command from the floodlight controller  122 . 
     The light controller  130  controls the travel direction of the pulsed light emitted from the light source  101 . Moreover, the light controller  130  controls the travel direction of received pulsed light. 
     The light controller  130  has a first lens  131 , a beam splitter  132 , a second lens  133 , a half mirror  134 , and a scanning mirror  135 . 
     The first lens  131  collects the pulsed light emitted from the floodlight unit  120  and guides them to the beam splitter  132 . The beam splitter  132  divides the pulsed light from the first lens  131  in two directions and guides them to the second lens  133  and the half mirror  134  separately. The second lens  133  guides the divided light from the beam splitter  132  to the light receiving unit  102 . The reason for guiding the pulsed light to the light receiving unit  102  is that the light receiving unit  102  detects floodlighting timing. 
     The half mirror  134  passes the divided light from the beam splitter  132  to guide it to the scanning mirror  135 . Moreover, the half mirror  134  reflects light including reflected light incident on the electronic apparatus  100  to the direction of the light receiving unit  102 . 
     The scanning mirror  135  rotates the mirror surface in synchronism with a drive signal from the second driver  124  in the floodlight unit  120 . In this way, the scanning mirror  135  controls the reflection direction of the divided light incident on the mirror surface of the scanning mirror  135 . By controlling the rotation of the mirror surface of the scanning mirror  135  at a constant cycle, it is possible to scan the pulsed light emitted from the light controller  130  at least in a one-dimensional direction. By providing two shafts in two directions for rotating the mirror surface, it is also possible to scan the pulsed light emitted from the light controller  130  in a two-dimensional direction.  FIG. 17  shows an example of scanning the pulsed light emitted from the electronic apparatus  100  as floodlights in an X-direction and a Y-direction by the scanning mirror  135 . 
     In the case where an object  10 , such as a human or an object, is present in a scanning range of the pulsed light emitted from the electronic apparatus  100  as floodlights, the pulsed light are reflected by the object  10 . At least part of the reflected light reflected by the object  10  propagates in the reverse direction through the passage almost the same as that of the pulsed light and is incident on the scanning mirror  135  in the light controller  130 . Although the mirror surface of the scanning mirror  135  is being rotated at a predetermined cycle, since the pulsed light propagate at the speed of light, the reflected light from the object  10  is incident on the mirror surface while there is almost no change in the angle of the mirror surface of the scanning mirror  135 . The reflected light from the object  10  incident on the mirror surface is reflected by the half mirror  134  and received by the light receiving unit  102 . 
     The light receiving unit  102  has a light detector  136 , an amplifier  137 , a third lens  138 , a photo-sensor  139 , and an A/D converter  141 . The light detector  136  receives light divided by the beam splitter  132  and converts it to an electric signal. The light detector  136  can detect the floodlighting timing of the pulsed light. The amplifier  137  amplifies the electric signal output from the light detector  136 . 
     The third lens  138  forms an image of the light reflected by the half mirror  134  on the photo-sensor  139 . The photo-sensor  139  receives light and converts it to an electric signal. The photo-sensor  139  has the above-described SiPM (Silicon Photomultiplier). 
     The A/D converter  141  samples the electric signal output from the photo-sensor  139  at a predetermined sampling rate for A/D conversion to generate a digital signal. 
     The signal processing unit  140  measures the distance to the object  10  that reflected the pulsed light and stores a digital signal in accordance with the intensity of received light in a storage  104 . The signal processing unit  140  has the storage  104 , a measuring unit  103 , a processing unit  110 , and an output unit  105 . The storage  104  stores the digital signal A/D-converted by the A/D-converter  141 . The measuring unit  103  reads out a digital signal corresponding to the light received by the light receiving unit  102  from the storage  104  to determine the light receiving timing and determine the distance to the object by means of the time difference from the floodlighting timing to the light receiving timing. The measuring unit  103  detects the floodlighting timing of the floodlight unit  120  via the light detector  136  and the amplifier  137 . The floodlight unit  120  may notify the measuring unit  103  of information relating to the pulse widths of the pulse lights. 
     While the present embodiment, the variations, and the examples of application have been described above, those may be performed in combination. 
     As described above, the electronic apparatus according to the present embodiment and the electronic apparatus according to the variations emit pulsed light to generate light receiving time data for determining ToF. The electronic apparatus calculates light receiving time distribution on the basis of the light receiving time data. The electronic apparatus selects a time zone in which reflected light is received on the basis of the light receiving time distribution. The electronic apparatus determines ToF on the basis of at least one of the first light receiving time and the last light receiving time among the light receiving times included in the time zone in which the reflected light is received. The electronic apparatus calculates a distance to the object by which the pulsed light is reflected on the basis of the determined ToF. With this arrangement, the influence of ambient light can be suppressed, the influence of an error in the number of photons emitted as pulsed light can be suppressed, and the accuracy of distance measurement can be improved. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.