# Patent

## Title
Distance measuring device with increased signal-to-noise ratio and method thereof

## Abstract

A method of increasing signal-to-noise ratio of a distance-measuring device includes a light-emitting component emitting a detecting light to a measured object during an emitting period for generating a reflected light, a delay period after the light-emitting component emitting the detecting light, a light-sensing component sensing the energy of the reflected light to generate a light-sensing signal, and obtaining a measured distance between the distance-measuring device and the measured object according to the energy of the detecting light and the light-sensing signal. Since the measured distance is longer than a predetermined shortest measured distance, the method can accordingly calculate a proper delay period for ensuring that the reflected light reaches the light-sensing component after the delay period. In this way, the light-sensing component does not sense the background light during the delay period, so that the signal-to-noise ratio of the light-sensing signal is improved.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 13/046,766 filed on Mar. 13, 2011, which is a continuation-in-part of U.S. application Ser. No. 12/817,172, filed on Jun. 16, 2010.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a distance-measuring device, and more particularly, to distance-measuring device with increased signal-to-noise ratio and method thereof.
2. Description of the Prior Art
In the prior art, the distance-measuring device emits a detecting light to a measured object, and receives the reflected light generated by the measured object reflecting the detecting light. The distance-measuring device calculates the distance between the distance-measuring device and the measured object by means of measuring the period of the detecting light going back and forth between the distance-measuring device and the measured object. However, when the reflectivity of the surface of the measured object is lower, the energy of the reflected light generated by the measured object is lower as well. Thus, the distance-measuring device is easily affected by the background light (noise) so that the distance-measuring device may obtain an incorrect measured distance.
SUMMARY OF THE INVENTION
The present invention provides a method of increasing signal-to-noise ratio of a distance-measuring device. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device has a light-emitting component for emitting a detecting light, and a first light-sensing component for sensing and accumulating energy of light to generate a first light-sensing signal according to a first shutter periodic signal. The method comprises the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period, a delay period after the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the first light-sensing component sensing and accumulating energy of the reflected light to generate the first light-sensing signal, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the first light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period, and obtaining the measured distance according to the time of flight. The delay period is calculated according to the predetermined shorted measured distance for the reflected light reaching the first light-sensing component after the delay period.
The present invention further provides a method of increasing signal-to-noise ratio of a distance-measuring device. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device has a light-emitting component for emitting a detecting light, a first light-sensing component for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and a second light-sensing component for sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The method comprises the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period, a delay period after the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal, switching the second shutter periodic signal to represent turning-on during a second sensing period for the second light-sensing component to sense and accumulate energy of the reflected light to generate the second light-sensing signal when the first light-sensing component stops sensing the reflected light, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal, and obtaining the measured distance according to the time of flight. The delay period is calculated according to the predetermined shorted measured distance for the reflected light reaching the first light-sensing component after the delay period.
The present invention further provides a method of increasing signal-to-noise ratio of a distance-measuring device. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device has a light-emitting component for emitting a detecting light, a light-sensing group for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The method comprises switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component emitting the detecting light to the measured object to generating a reflected light during an emitting period, and not emitting the detecting light during a non-emitting period, a delay period after every time the light-emitting component starts to emit the detecting light, switching the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal, switching the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal after the first sensing period, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio of the first light-sensing signal and the second light-sensing signal, and obtaining the measured distance according to the time of flight. The delay period is calculated according to the predetermined shorted measured distance for the reflected light reaching the light-sensing group after the delay period. The light-emitting periodic signal and the first shutter periodic signal are substantially in phase, and a phase of the light-emitting periodic signal is substantially opposite to a phase of the second shutter periodic signal.
The present invention further provides a distance-measuring device with increased signal-to-noise ratio. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device comprises an emitting component, a first light-sensing component, a light-emitting/sensing controlling circuit, and a distance-calculating circuit. The emitting component is utilized for emitting a detecting light. The first light-sensing component is utilized for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal. The light-emitting/sensing controlling circuit is utilized for controlling the emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period. A delay period after the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal representing turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal. The light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance for the reflected light reaching the first light-sensing component after the delay period. The distance-calculating circuit is utilized for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the first light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period, and generating an output signal representing the measured distance according to the time of flight.
The present invention further provides a distance-measuring device with increased signal-to-noise ratio. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device comprises an emitting component, a first light-sensing component, a second light-sensing component, a light-emitting/sensing controlling circuit, and a distance-calculating circuit. The emitting component is utilized for emitting a detecting light. The first light-sensing component is utilized for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal. The second light-sensing component is utilized for sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The light-emitting/sensing controlling circuit is utilized for controlling the emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period. A delay period after the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal representing turning-on during a first sensing period for the first light-sensing component to sense and accumulate energy of the reflected light to generate the first light-sensing signal. When the first light-sensing component stops sensing the reflected light, the light-emitting/sensing controlling circuit switches the second shutter periodic signal representing turning-on during a second sensing period for the second light-sensing component to sense and accumulate energy of the reflected light to generate the second light-sensing signal. The light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance for the reflected light reaching the first light-sensing component after the delay period. The distance-calculating circuit is utilized for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing the measured distance according to the time of flight.
The present invention further provides a distance-measuring device with increased signal-to-noise ratio. The distance-measuring device is utilized for measuring a measured distance between the distance-measuring device and a measured object. The measured distance is longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance. The distance-measuring device comprises an emitting component, a light-sensing group, a light-emitting/sensing controlling circuit, and a distance-calculating circuit. The emitting component is utilized for emitting a detecting light. The light-sensing group is utilized for sensing and accumulating energy of light according to a first shutter periodic signal to generate a first light-sensing signal, and sensing and accumulating energy of light according to a second shutter periodic signal to generate a second light-sensing signal. The light-emitting/sensing controlling circuit is utilized for switching the light-emitting periodic signal between representing turning-on and turning off with a detecting frequency, for the light-emitting component emitting the detecting light to the measured object to generating a reflected light during an emitting period, and not emitting the detecting light during a non-emitting period. A delay period after every time the light-emitting component starts to emit the detecting light, the light-emitting/sensing controlling circuit switches the first shutter periodic signal to represent turning-on during a first sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the first light-sensing signal. After the first sensing period, the light-emitting/sensing controlling circuit switches the second shutter periodic signal to represent turning-on during a second sensing period for the light-sensing group to sense and accumulate energy of the reflected light to generate the second light-sensing signal. The light-emitting periodic signal and the first shutter periodic signal are substantially in phase, and a phase of the light-emitting periodic signal is substantially opposite to a phase of the second shutter periodic signal. The light-emitting/sensing controlling circuit calculates the delay period according to the predetermined shortest measured distance for the reflected light reaching the first light-sensing component after the delay period. The distance-calculating circuit is utilized for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to a ratio between the first light-sensing signal and the second light-sensing signal, and generating an output signal representing the measured distance according to the time of flight.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating a distance-measuring device according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram of the control signals of the distance-measuring device in the “background-measuring phase”.
FIG. 3 is a waveform diagram of the control signals of the distance-measuring device in the “distance-calculating phase”.
FIG. 4 is a waveform diagram of the control signals of the distance-measuring device in the “frequency-adjusting phase”.
FIG. 5 is a diagram illustrating a distance-measuring device according to a second embodiment of the present invention.
FIG. 6 is a diagram illustrating the driving circuit generating the control signals, according to the shutter periodic signals and the reading signal.
FIG. 7 is a diagram illustrating the structure of the light-sensing group according to an embodiment of the present invention.
FIG. 8 is a diagram illustrating a distance-measuring device according to a third embodiment of the present invention.
FIG. 9 is a diagram illustrating the structure of the light-sensing group according to an embodiment of the present invention.
FIG. 10 and FIG. 11 are diagrams illustrating a 3D image-sensing device of the present invention.
FIG. 12, FIG. 13, FIG. 14, and FIG. 15 are diagrams illustrating a method of increasing signal-to-noise ratio of a distance-measuring device according to an embodiment of the present invention.
FIG. 16, FIG. 17, FIG. 18, and FIG. 19 are diagrams illustrating a method of increasing signal-to-noise ratio of a distance-measuring device according to another embodiment of the present invention.
FIG. 20 and FIG. 21 are diagrams illustrating a method of increasing signal-to-noise ratio of the distance-measuring device of FIG. 1 according to another embodiment of the present invention.



DETAILED DESCRIPTION
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a distance-measuring device 100 according to a first embodiment of the present invention. The distance-measuring device 100 is utilized for measuring the measured distance D, wherein the measured distance D is the distance between the measured object O1 and the distance-measuring device 100, as shown in FIG. 1. The distance-measuring device 100 comprises a light-emitting/sensing controlling circuit 110, a light-emitting component 120, a light-sensing group 130, a distance-calculating circuit 140, a background-calculating circuit 150, a frequency-adjusting circuit 160, and a focusing module 170.
The light-emitting/sensing controlling circuit 110 is utilized for generating a light-emitting periodic signal SLD, shutter periodic signals SST1 and SST2, a phase signal SP, a frequency-detecting signal SFQ, and a reading signal SRE. The light-emitting periodic signal SLD, and the shutter periodic signals SST1 and SST2 have the same frequency. The frequency-detecting signal SFQ indicates the magnitude of the frequency of the light-emitting periodic signal SLD, and the shutter periodic signals SST1 and SST2, which means when a device receives the frequency-detecting signal SFQ, the device obtains the magnitude of the frequency of the light-emitting periodic signal SLD. In addition, the phases of the light-emitting periodic signal SLD and the shutter periodic signal SST1 are approximately the same (in phase), and the phase of the light-emitting periodic signal SLD is approximately opposite to that of the shutter periodic signal SST2.
The light-emitting component 120 may be a Light-Emitting Diode (LED). The light-emitting component 120 emits a detecting light LID to the measured object O1 according to the light-emitting periodic signal SLD. For example, when the light-emitting periodic signal SLD represents “emitting”, the light-emitting component 120 emits the detecting light LID; otherwise, when the light-emitting periodic signal SLD represents “not-emitting”, the light-emitting component 120 does not emit the detecting light LID.
The focusing module 170 is utilized for focusing the reflected light LRD, which is generated by the measured object O1 reflecting the detecting light LID, to the light-sensing group 130.
The light-sensing group 130 is a Charge Coupled Device (CCD) or a Complementary Metal-Oxide-Semiconductor (CMOS) light sensor. The light-sensing group 130 senses and accumulates the energy of the reflected light LRD according to the shutter periodic signal SST1. In addition, the light-sensing group 130 outputs the light-sensing signal SLS1 according to the reading signal SRE. For instance, when the shutter periodic signal SST1 represents “turning-on”, the light-sensing group 130 senses the energy of the reflected light LRD so as to accordingly accumulate the energy ER1; when the shutter periodic signal SST1 represents “turning-off”, the light-sensing group 130 does not sense the energy of the reflected light LRD, and does not accumulate the energy ER1. When the reading signal SRE represents “reading”, the light-sensing group 130 outputs the light-sensing signal SLS1 according to the accumulated energy ER1. Besides, the light-sensing group 130 also senses and accumulates the energy of the reflected light LRD according to the shutter periodic signal SST2, and the light-sensing group 130 outputs the light-sensing signal SLS2 according to the reading signal SRE as well. For instance, when the shutter periodic signal SST2 represents “turning-on”, the light-sensing group 130 senses the energy of the reflected light LRD so as to accordingly accumulate the energy ER2; when the shutter periodic signal SST2 represents “turning-off”, the light-sensing group 130 does not sense the energy of the reflected light LRD, and does not accumulate the energy ER2. When the reading signal SRE represents “reading”, the light-sensing group 130 outputs the light-sensing signal SLS2 according to the accumulated energy ER2. In addition, it is noticeable that after the light-sensing group 130 outputs the light-sensing signals SLS1 and SLS2 according to the reading signal SRE representing “reading”, the light-sensing group 130 resets the accumulated energy ER1 and ER2 (which means the light-sensing group 130 releases the accumulated energy ER1 and ER2)
The background-calculating circuit 150 outputs the background signal SB according to the phase signal SP and the light-sensing signal SLS1.
The frequency-adjusting circuit 160 outputs the frequency-controlling signal SFC according to the phase signal SP and the light-sensing signal SLS1. The distance-calculating circuit 140 calculates the measured distance D between the measured object O1 and the distance-measuring device 100 according to the phase signal SP, the background signal SB, the light-sensing signals SLS1 and SLS2, and the frequency-detecting signal SFQ.
When the distance-measuring device 100 measures the measured distance D, the measuring process includes a “background-measuring phase”, a “frequency-adjusting phase”, and a “distance-calculating phase”. The operation principle of each phase is illustrated in detail as below.
Please refer to FIG. 2. FIG. 2 is a waveform diagram of the control signals of the distance-measuring device 100 in the “background-measuring phase”. When the distance-measuring device 100 enters the “background-measuring phase”, the distance-measuring device 100 measures the energy of the background light LB sensed by the light-sensing group 130 per unit time, so that the distance-measuring device 100 can reduce the effect of the background light LB in the “distance-calculating phase”. At the beginning of the “background-measuring phase”, the light-emitting/sensing controlling circuit 110 generates the reading signal SPE representing “reading” so as to reset the accumulated energy of the light-sensing group 130. Then, the light-emitting/sensing controlling circuit 110 generates the shutter periodic signal SST1 having a pulse width TB, wherein TB represents a background-measuring period. Meanwhile, since the light-emitting periodic signal SLD represents “not-emitting”, the light-emitting component 120 does not emit the detecting light LID. Hence, instead of the light-sensing group 130 sensing the energy of the reflected light LRD, the light-sensing group 130 only senses the energy of the background light LB so as to accumulate the energy EB corresponding to the background light LB. After the background-measuring period TB, the shutter periodic signal SST1 change to be “turning-off”. Meanwhile, the light-emitting/sensing controlling circuit 110 simultaneously generates the reading signal SRE representing “reading” and the phase signal SP representing “background-measuring”, so that the light-sensing group 130 outputs the light-sensing signal SLS1 according to the accumulated energy EB, and the background-calculating circuit 150 outputs the background signal SB to the distance-calculating circuit 140 according to the frequency-detecting signal SFQ, and the light-sensing signal SLS1. The value of the background signal SB represents the energy of the background light LB sensed by the light-sensing group 130 per unit time and can be represented as the following formula:

SB=EB/TB  (1);

wherein EB is the total energy accumulated by the light-sensing group 130 sensing the background light LB in the background-measuring period TB.

Please refer to FIG. 3. FIG. 3 is a waveform diagram of the control signals of the distance-measuring device 100 in the “distance-calculating phase”. When the distance-measuring device 100 enters the “distance-calculating phase”, the distance-measuring device 100 controls the light-emitting component 120 emitting the detecting light LID by means of the light-emitting periodic signal SLD of the detecting frequency FC, and the distance-measuring device 100 calculates the period length of the light going back and forth between the measured object O1 and the distance-measuring device 100, by means of the light-sensing group 130 sensing the energy of the reflected light LRD, so as to obtain the measured distance D. At the beginning of the “distance-calculating phase”, the light-emitting/sensing controlling circuit 110 generates the reading signal SRE representing “reading” to reset the accumulated energy of the light-sensing group 130. Then, the light-emitting/sensing controlling circuit 110 generates the shutter periodic signals SST1 and SST2, and the light-emitting periodic signals SLD with the detecting frequency FC in the detecting cycles TC1 ̃TCN. Therefore, in the detecting cycles TC1 ̃TCN, the shutter periodic signals SST1 and SST2 repeat being switched between “turning-on” and “turning-off”, and the light-emitting periodic signals SLD repeats being switched between “emitting” and “not-emitting”. The period length of each detecting cycle TC1 ̃TCN is equal to a detecting cycle TC, wherein the value of the detecting cycle TC is the inverse of the detecting frequency FC. In the detecting cycles TC1 ̃TCN, the phases of the light-emitting periodic signal SLD and the shutter periodic signal SST1 are approximately the same (in phase), and the phase of the shutter periodic signal SST1 is opposite to that of the shutter periodic signal SST2. More particularly, in the detecting cycles TC1 ̃TCN, when the light-emitting periodic signal SLD represents “emitting”, the shutter periodic signal SST1 represents “turning-on” and the shutter periodic signal SST2 represents “turning-off”; when the light-emitting periodic signal SLD represents “not-emitting”, the shutter periodic signal SST1 represents “turning-off” and the shutter periodic signal SST2 represents “turning-on”. In this way, in the first-half cycles of the detecting cycles TC1 ̃TCN, the light-emitting component 120 emits the detecting light LID and the light-sensing group 130 senses the energy of the reflected light LRD so as to accumulate the energy ER1; and in the second-half cycles of the detecting cycles TC1 ̃TCN, the light-sensing group 130 senses the energy of the reflected light LRD so as to accumulate the energy ER2.
After the detecting cycles TC1 ̃TCN, the light-emitting/sensing controlling circuit 110 simultaneously generates the reading signal SRE representing “reading” and the phase signal SP representing “distance-calculating”, so that the light-sensing group 130 outputs the light-sensing signal SLS1 to the distance-calculating circuit 140 according to the accumulated energy ER1 and EB1 and outputs the light-sensing signal SLS2 to the distance-calculating circuit 140 according to the accumulated energy ER2 and EB2, wherein the accumulated energy ER1 is generated by the light-sensing group 130 sensing the reflected light LRD in the first-half cycles of the detecting cycles TC1 ̃TCN; the accumulated energy EB1 is generated by the light-sensing group 130 sensing the background light LB in the first-half cycles of the detecting cycles TC1 ̃TCN; the accumulated energy ER2 is generated by the light-sensing group 130 sensing the reflected light LRD in the second-half cycles of the detecting cycles TC1 ̃TCN; and the accumulated energy EB2 is generated by the light-sensing group 130 sensing the background light LB in the second-half cycles of the detecting cycles TC1 ̃TCN. The distance-calculating circuit 140 calculates the measured distance D between the measured object O1 and the distance-measuring device 100 according the frequency-detecting signal SFQ, the light-sensing signals SLS1 and SLS2, and the background signal SB, wherein the values of the light-sensing signals SLS1 and SLS2 are respectively equal to (ER1+EB1) and (ER2+EB2), and the value of the frequency-detecting signal SFQ is equal to the detecting frequency FC. The operation principle of calculating measured distance D is illustrated as below.
It can be seen in FIG. 3 that a round-trip period TD after the light-emitting component 120 emitting the detecting light LID, the light-sensing group 130 starts to sense the reflected light LRD (that is, the reflected light LRD reaches the light-sensing group 130). In other words, the round-trip period TD is the sum of the period of the detecting light LID flying from the light-emitting component 120 to the measured object O1 and the period of the reflected light LRD flying from the measured object O1 to the light-sensing group (that is, the time the light going back and forth between the measured object O1 and the distance-measuring device 100). Since the period length of the light-sensing group 130 sensing the reflected light LRD to accumulate energy ER1 in the first-half cycle of the detecting cycle TC1 is [(TC/2)−TD] and the pulse width of the detecting light LID is equal to (TC/2), the period length of the light-sensing group 130 sensing the reflected light LRD to accumulate energy ER2 in the second-half cycle of the detecting cycle TC1 is equal to the period length of the pulse width of the detecting light LID deducting the period of the light-sensing group 130 sensing the reflected light LRD to accumulate energy ER1 in the first-half cycle of the detecting cycle TC1. That is, the period length of the light-sensing group 130 sensing the reflected light LRD to accumulate energy ER2 in the second-half cycle of the detecting cycle TC1 is equal to that of the round-trip period TD. In the detecting cycles TC1 ̃TCN, since the light-emitting/sensing controlling circuit 110 generates the light-emitting periodic signal SLD, and the shutter periodic signals SST1 and SST2 with the “fixed” detecting frequency FC, the period length of the light-sensing group 130 sensing the reflected light LRD to accumulate the energy ER1 in each first-half cycle is equal to [(TC/2)−TD], and the period length of the light-sensing group 130 sensing the reflected light LRD to accumulate the energy ER2 in each second-half cycle is equal to TD. In this way, the ratio between the accumulated energy ER1 and ER2 is equal to [(TC/2)−TD]/TD. As a result, the relation between the round-trip period TD, the light-sensing signals SLS1 and SLS2, the detecting frequency FC, and the background signal SB can be represented as the following formula:




  
    
      
        
          
            
              
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        2
        )
      
    
  




since the round-trip period TD is the time of the light going back and forth between the measured object O1 and the distance-measuring device 100, the measured distance D can be represented as the following formula:





  
    
      
        
          
            
              D
              =
              
              ⁢
              
                
                  T
                  D
                
                ×
                
                  C
                  /
                  2
                
              
            
          
        
        
          
            
              =
              
              ⁢
              
                
                  [
                  
                    C
                    /
                    
                      (
                      
                        4
                        ×
                        
                          F
                          C
                        
                      
                      )
                    
                  
                  ]
                
                ×
                
                  [
                  
                    
                      (
                      
                        
                          S
                          
                            LS
                            ⁢
                            
                              
                            
                            ⁢
                            2
                          
                        
                        -
                        
                          
                            S
                            B
                          
                          /
                          
                            (
                            
                              2
                              ×
                              
                                F
                                C
                              
                            
                            )
                          
                        
                      
                      )
                    
                    /
                  
                
              
            
          
        
        
          
            
              
                
                ⁢
                
                  (
                  
                    
                      S
                      
                        LS
                        ⁢
                        
                          
                        
                        ⁢
                        1
                      
                    
                    +
                    
                      S
                      
                        LS
                        ⁢
                        
                          
                        
                        ⁢
                        2
                      
                    
                    -
                    
                      
                        S
                        B
                      
                      /
                      
                        F
                        C
                      
                    
                  
                  )
                
                ]
              
              ;
            
          
        
      
    
    
      
        (
        3
        )
      
    
  




wherein C represents the light speed, N represents the number of the detecting cycles in the “distance-calculating phase”.

In addition, it is noticeable, in the “distance-calculating phase”, when N is equal to 1, it means the light-sensing group 130 senses the reflected light LRD in only one detecting cycle to accumulate the energy ER1 and ER2. However, if the reflectivity of the measured object O1 is lower or the measured distance D is longer, the energy of the reflected light LRD becomes lower. In this way, the accumulated energy ER1 and ER2 of the light-sensing group 130 is so small that the measuring error may become too large to cause the distance-measuring device 100 obtains an incorrect measured distance. When N becomes larger, the light-sensing group 130 senses the reflected light LRD in more detecting cycles to accumulate the energy ER1 and ER2, so that the energy ER1 and ER2 becomes larger. In this case, even if the reflectivity of the measured object O1 is lower or the measured distance D is longer, the accumulated energy still can be raised up to be large enough by increasing the number of the detecting cycles, so that the measuring error can be reduced.
In addition, in the “distance-calculating phase”, the measured distance D is calculated according to the round-trip period TD of the formula (2). However, if the measured distance D between the distance-measuring device 100 and the measured object O1 is too long, it may causes the round-trip period TD is longer than a half of the detecting cycle TC. That is, in the first-half cycle of the detecting cycle TC1, the light-sensing group does not sense the reflected light LRD to accumulate the energy ER1. In this way, the ratio between the accumulated energy ER1 and ER2 is not equal to [(TC/2)−TD]/TD, so that the distance-calculating circuit 140 can not correctly calculate the measured distance D according to the formula (3). Consequently, the present invention provide a method (“frequency-adjusting phase”) for the distance-measuring device 100 adjusting the detecting cycle TC (or the detecting frequency FC) before the “distance-calculating phase”, so as to assure that the round-trip period TD is shorter than a half of the detecting cycle TC and the distance-calculating circuit 140 can correctly calculate the measured distance D according to the formula (3).
Please refer to FIG. 4. FIG. 4 is a waveform diagram of the control signals of the distance-measuring device 100 in the “frequency-adjusting phase”. As shown in the left part of FIG. 4, when the distance-measuring device 100 enters the “frequency-adjusting phase”, the light-emitting/sensing controlling circuit 110 generates the reading signal SRE representing “reading” so as to reset the accumulated energy of the light-sensing group 130. After that, the light-sensing/emitting controlling circuit 110 simultaneously generates the light-emitting periodic signal SLD, which is representing “emitting” and having a pulse width (TC/2), and the shutter periodic signal SST1, which is representing “turning-on” and having a pulse width (TC/2). Finally, the light-emitting/sensing controlling circuit 110 generates the reading signal SRE representing “reading” and the phase signal SP representing “frequency-adjusting”, so that the light-sensing group 130 outputs the light-sensing signal SLS1 according to the energy ER accumulated by the light-sensing group 130 sensing the reflected light LRD and the energy EB accumulated by light-sensing group 130 sensing the background light LB (more particularly, SLS1=EB+ER). The frequency-adjusting circuit 160 outputs the frequency-controlling signal SFC according to the light-sensing signal SLS1 and the background signal SB. It can be seen in FIG. 4 that when the round-trip period TD of the light going back and forth between the distance-measuring device 100 and the measured object O1 is shorter than (TC/2), it means that the reflected light LRD can reach the light-sensing group 130 before the end of the period of the shutter periodic signal SST1 representing “turning-on”. Therefore, the light-sensing group 130 can sense the reflected light LRD so as to accumulate the energy ER. When the round-trip period TD is longer than (TC/2), it means that the reflected light LRD can not reach the light-sensing group 130 in time. Thus, the light-sensing group 130 can not sense the reflected light LRD and can not accumulate the energy ER. In addition, the energy ER can be represented as the following formula:

ER=SLS1−SR/(2×FC)  (4);

hence, when the frequency-adjusting circuit 160 determines that the accumulated energy ER is smaller or equal to a predetermined threshold energy ETH (for example, ETH is zero) according to formula (4), it means the round-trip period TD is longer than (TC/2) and the reflected light LRD can not reach the light-sensing group 130 in time. Meanwhile, the frequency-adjusting circuit 160 outputs the frequency-controlling signal SFC representing “reducing” so as to control the light-emitting/sensing controlling circuit 110 reducing the detecting frequency FC (that is, increasing the detecting cycle TC). After the light-emitting/sensing controlling circuit 110 reduces the detecting frequency FC, The light-emitting/sensing controlling circuit 110 repeats the above-mentioned process again to determine if the round-trip period TD is shorter than (TC/2) (that is, the reflected light LRD can reach the light-sensing group 130 in time). When the frequency-adjusting circuit 160 determines the accumulated energy ER is larger than the predetermined threshold energy ETH, it represents that the round-trip period TD is shorter than (TC/2). Meanwhile, the frequency 160 outputs the frequency-controlling signal FC representing “maintaining” so as to control the light-emitting/sensing controlling circuit 110 keeping the detecting frequency FC unchanged and finish the “frequency-adjusting phase”. In this way, the device-measuring device 100 assures the round-trip period TD is shorter than (TC/2) (that is, the reflected light LRD can reach the light-sensing group 130 in time) by means of the frequency-adjusting circuit 160 adjusting the detecting frequency FC in the “frequency-adjusting phase”.

In conclusion, In the “background-measuring phase”, the light-sensing group 130 senses the background light LB, so that the distance-measuring device 100 can calculates the energy accumulated by the light-sensing group 130 sensing the background light LB per unit time; In the “frequency-adjusting phase”, the distance-measuring device 100 reduces the detecting frequency FC until the round-trip period TD is shorter than (TC/2) (that is, the reflected light LRD can reach the light-sensing group 130 in time); in the “distance-calculating phase” the distance-measuring device 100 calculates the measured distance D, by means of the formula (3), according to the background signal SB, the frequency-detecting signal SFQ, and the light-sensing signals SLS1 and SLS2, which are outputted by the light-sensing group 130 sensing the reflected light in detecting cycles TC1 ̃TCN. The distance-measuring device 100 calibrates the ratio between the light-sensing signals SLS1 and SLS2 according to the background signal SB. In this way, the distance-measuring device 100 reduces the effect of the background light LB and the measuring error when the measured distance D is too long or when the reflectivity of the measured object O1 is too low, so that the distance-measuring device 100 can more correctly calculate the measured distance D.
Please refer to FIG. 5. FIG. 5 is a diagram illustrating a distance-measuring device 500 according to a second embodiment of the present invention. The structure and the operation principle of the light-emitting/sensing controlling circuit 511, the light-emitting component 520, the distance-calculating circuit 540, the background-calculating circuit 550, the frequency-adjusting circuit 560, and the focusing module 570 are respectively similar to those of the light-emitting/sensing controlling circuit 110, the light-emitting component 120, the distance-calculating circuit 140, the background-calculating circuit 150, the frequency-adjusting circuit 160, and the focusing module 170, and will not be repeated again for brevity. Compared with the distance-measuring device 100, the distance-measuring device 500 comprises a light-emitting/sensing module 510. The light-emitting/sensing module 510 includes the light-emitting/sensing controlling circuit 511, and a driving circuit 512. The driving circuit 512 generates shutter-on pulse signals SSOP1 and SSOP2, shutter-off pulse signals SSCP1 and SSCP2, reset pulse signals SRP1 and SRP2, and output pulse signals SOP1 and SOP2 according to the shutter periodic signals SST1 and SST2, and the reading signal SRE. The light-sensing group 530 comprises light-sensing components 531 and 532. The light-sensing component 531 senses the background light LB or the reflected light LRD to accumulate the energy according to the shutter-on pulse signal SSOP1, and the shutter-off pulse signal SSCP1; the light-sensing component 531 outputs the light-sensing signal SLS1 according to the output pulse signal SOP1 and the accumulated energy; and the light-sensing component 531 resets the accumulated energy according to the reset pulse signal SRP1. Similarly, the light-sensing component 532 senses the background light LB or the reflected light LRD to accumulate the energy according to the shutter-on pulse signal SSOP2, and the shutter-off pulse signal SSCP2; the light-sensing component 532 outputs the light-sensing signal SLS2 according to the output pulse signal SOP2 and the accumulated energy; and the light-sensing component 532 resets the accumulated energy according to the reset pulse signal SRP2.
Please refer to FIG. 6. FIG. 6 is a diagram illustrating the driving circuit 512 generating the shutter-on pulse signals SSOP1 and SSOP2, the shutter-off pulse signals SSCP1 and SSCP2, the reset pulse signals SRP1 and SRP2 and the output pulse signals SSCP1 and SSP2 according the shutter periodic signals SST1 and SST2, and the reading signal SRE. As shown in FIG. 6, when the shutter periodic signal SST1 changes from “turning-off” to “turning-on”, the driving circuit 512 generates the shutter-on pulse signal SSOP1; when the shutter periodic signal SST1 changes from “turning-on” to “turning-off”, the driving circuit 512 generates the shutter-off pulse signal SSCP1. When the shutter periodic signal SST2 changes from “turning-off” to “turning-on”, the driving circuit 512 generates the shutter-on pulse signal SSOP2; when the shutter periodic signal SST2 changes from “turning-on” to “turning-off”, the driving circuit 512 generates the shutter-off pulse signal SSCP2. When the reading signal SRE represents “reading”, the driving circuit 512 generates the output pulse signals SOP1 and SOP2, and then generates the reset pulse signals SRP1 and SRP2.
Please refer to FIG. 7. FIG. 7 is a diagram illustrating the structure of the light-sensing group 530 according to an embodiment of the present invention. The structure of the light-sensing group 530 is similar to that of the CMOS light sensor of the digital camera. The light-sensing component 531 comprises switches SW11, SW12, SW13 and SW14, a photo diode PD1, a capacitor C1, and a transistor Q1. When the control end C of the switch SW13 receives the reset pulse signal SRP1, the first end 1 of the switch SW13 is couple to the second end 2 of the switch SW13 (which means the switch SW13 is turned on), so that the capacitor C1 is couple to the voltage source VDD through the turned-on switch SW13 to reset the voltage VC1 to be at a predetermined voltage level (for instance, VDD). The photo diode PD1 is utilized for generating and accumulating electrons of a quantity NE1 according to the energy of the reflected light LRD. When the control end C of the switch SW12 receives the shutter-off pulse signal SSCP1, the first end 1 of the switch SW12 is couple to the second end 2 of the switch SW12 (which means the switch SW12 is turned on), so that the accumulated electrons of the photo diode PD1 flows to the capacitor C1, reducing the voltage VC1. The switch SW11 is utilized for eliminating the residual electrons of the photo diode PD1 according to the shutter-on pulse signal SSOP1 so as to reset the electron quantity NE1. More particularly, when the control end C of the switch SW11 receives the shutter-on pulse signal SSOP1 the first end 1 of the switch SW11 is coupled to the second end 2 of the switch SW11, so that the photo diode PD1 is coupled to the voltage source VDD through the turned-on switch SW11 and the accumulated electrons of the photo diode PD1 flow to the voltage source VDD through the turned-on switch SW11. The transistor Q1 is utilized as a voltage follower. As a result, the voltage on the second end 2 of the transistor Q1 varies with the voltage (VC1) on the control end (gate) C of the transistor Q1. When the control end C of the switch SW14 receives the output pulse signal SOP1 the first end 1 and the second 2 of the switch SW14 are coupled together. Therefore, the switch SW14 outputs the light-sensing signal SLS1 according to the voltage VC1 by means of the transistor Q1 (voltage follower). In this way, the voltage VC1 can be obtained according to the light-sensing signal SLS1, and the accumulated energy of the light-sensing component 531 can be calculated according to the voltage difference between voltage level of the voltage VC1 and the predetermined voltage level (for example, VDD).
The light-sensing component 532 comprises switches SW21, SW22, SW23 and SW24, a photo diode PD2, a capacitor C2, and a transistor Q2. The structure and the operation principle of the light-sensing component 532 are similar to those of the light-sensing component 531, and are omitted for brevity.
When the light-emitting/sensing controlling circuit 511 generates the shutter periodic signals SST1 or SST2, or the reading signal SRE, the driving circuit 512 accordingly generates the corresponding control signals (the shutter-on pulse signals SSOP1 and SSOP2, shutter-off pulse signals SSCP1 and SSCP2, reset pulse signals SRP1 and SRP2, and output pulse signals SOP1 and SOP2) to control the light-sensing components 531 and 532 of the light-sensing group 530. More particularly, when the shutter periodic signal SST1 represents “turning-on”, the light-sensing component 531 senses the energy of the reflected light LRD; when the shutter periodic signal SST2 represents “turning-on”, the light-sensing component 532 senses the energy of the reflected light LRD. When the reading signal SRE represents “reading”, the light-sensing component 531 outputs the light-sensing signal SLS1 and resets the accumulated energy of the light-sensing component 531 at the same time, and the light-sensing component 532 outputs the light-sensing signal SLS2 and resets the accumulated energy of the light-sensing component 532 at the same time. In other words, by means of the driving circuit 512, the light-sensing group 530 can operate as the light-sensing group 130 and the distance-measuring device 500 can operate as the distance-measuring device 100 as well. Consequently, the distance-measuring 500 can correctly measure the measured distance D by means of the methods of the “background-measuring phase”, the “frequency-adjusting phase”, and the “distance-calculating phase” mentioned in FIG. 2 ̃FIG. 4.
Please refer to FIG. 8. FIG. 8 is a diagram illustrating a distance-measuring device 800 according to a third embodiment of the present invention. The structure and the operation principle of the light-emitting/sensing controlling circuit 811, the light-emitting component 820, the distance-calculating circuit 840, the background-calculating circuit 850, the frequency-adjusting circuit 860, and the focusing module 870 are respectively similar to those of the light-emitting/sensing controlling circuit 110, the light-emitting component 120, the distance-calculating circuit 140, the background-calculating circuit 150, the frequency-adjusting circuit 160, and the focusing module 170, and will not be repeated again for brevity. The light-emitting/sensing module 810 comprises the light-emitting/sensing controlling circuit 811, and a driving circuit 812. The driving circuit 812 generates the shutter-on pulse signal SSOP, the shutter-off pulse signals SSCP1 and SSCP2, the reset pulse signals SRP1 and SRP2, and the output pulse signals SOP1 and SOP2 according to the shutter periodic signals SST1 and SST2, and the reading signal SRE. The operation principle of the driving circuit 812 is similar to that of the driving circuit 512. The difference between the driving circuits 512 and 812 is that no matter when the shutter periodic signal SST1 or the shutter periodic signal SST2 changes from “turning-off” to “turning-on”, the driving circuit 812 triggers the shutter-on pulse signal SSOP.
Please refer to FIG. 9. FIG. 9 is a diagram illustrating the structure of the light-sensing group 830 according to an embodiment of the present invention. The structure and the operation principle of the light-sensing group 830 are similar to those of the light-sensing group 530. Compared with the light-sensing group 530, the light-sensing group 830 does not have the switch SW21 and the photo diode PD2. Since in the “background-measuring phase” or in the “frequency-adjusting phase”, the distance-measuring device 500 uses only the light-sensing component 531 of the light-sensing group 530, it means that in the “background-measuring phase” or in the “frequency-adjusting phase”, the distance-measuring device 500 does not need the switch SW21 and the photo diode PD2. Therefore, n the “background-measuring phase” or in the “frequency-adjusting phase”, the distance-measuring device 800 can operate as the distance-measuring device 500 by means of the light-sensing group 830. In addition, since in the detecting cycles TC1 ̃TCN of the “distance-calculating phase”, when the shutter periodic signal SST1 represents “turning-on”, the shutter periodic signal SST2 represents “turning-off”; when the shutter periodic signal SST1 represents “turning-off”, the shutter periodic signal SST2 represents “turning-on”. That is, the shutter periodic signals SST1 and SST2 do not represent “turning-on” at the same time. Thus, in the first-half cycles of the detecting cycles TC1 ̃TCN (the shutter periodic signal SST1 represents “turning-on”), the distance-measuring device 800 can use the photo diode PD1 of the light-sensing group 830 to accumulate electrons. When the shutter periodic signal SST1 changes from “turning-on” to “turning-off”, the accumulated electrons of the photo diode PD1 flows to the capacitor C1 so as to change the voltage level of the voltage VC1. In the second-half cycles of the detecting cycles TC1 ̃TCN (the shutter periodic signal SST2 represents “turning-on”), the distance-measuring device 800 can use the photo diode PD1 of the light-sensing group 830 to accumulate electrons as well. When the shutter periodic signal SST2 changes from “turning-on” to “turning-off”, the accumulated electrons of the photo diode PD1 flows to the capacitor C2 so as to change the voltage level of the voltage VC2. That is, although the light-sensing group 830 has only one photo diode PD1, the light-sensing group 830 still can operate as the light-sensing group 530 in the “distance-calculating phase”. In other words, the distance-measuring device 800 can operate as the distance-measuring device 500 in the “distance-calculating phase”. In this way, since the distance-measuring device 800 can operate as the distance-measuring device 500 in the “background-measuring phase”, the “frequency-adjusting phase”, and the “distance-calculating phase”, the distance-measuring device 800 also can correctly measure the measured distance D by means of the methods of the “background-measuring phase”, the “frequency-adjusting phase”, and the “distance-calculating phase” mentioned in FIG. 2 ̃FIG. 4.
In addition, in the light-sensing group 530, the area occupied by the photo diode PD2 is large. Hence, compared with the light-sensing group 530, the area occupied by the light-sensing group 830 is smaller, so that the cost of the light-sensing group 830 is lower.
Please refer to FIG. 10 and FIG. 11. FIG. 10 and FIG. 11 are diagrams illustrating a 3D image-sensing device 1000 of the present invention. The 3D image-sensing device 1000 comprises a distance-measuring device 1090 and a 2D image-sensing device 1100. The distance-measuring device 1090 comprises a light-emitting/sensing controlling circuit 1010, a light-emitting component 1020, a light-sensing module 1030, a distance-calculating circuit 1040, a background-calculating circuit 1050, a frequency-adjusting circuit 1060, and a focusing module 1070. The 2D image-sensing device 1100 comprises an image-sensing controlling circuit 1080, and the light-sensing module 1030, wherein the light-sensing module 1030 is shared by the 2D image-sensing device 1100 and the distance-measuring device 1090. The operation principle and the structure of the light-emitting/sensing controlling circuit 1010, the light-emitting component 1020, the distance-calculating circuit 1040, the background-calculating circuit 1050, the frequency-adjusting circuit 1060 are respectively similar to those of the light-emitting/sensing controlling circuit 110 (or the light-emitting/sensing controlling circuit 511), the light-emitting component 120 (or the light-emitting component 520 or 820), the distance-calculating circuit 140 (or the distance-calculating circuit 540 or 840), the background-calculating circuit 150 (or the background-calculating circuit 550 or 850), the frequency-adjusting circuit 160 (or the frequency-adjusting circuit 560 or 860). Compared with the distance-measuring devices 130, 500, and 800, the light-sensing module 1030 of the 3D image-sensing device 1000 comprises light-sensing groups CS1 ̃CSM, wherein M represents a positive integer. The operation principle and the structure of the light-sensing groups CS1 ̃CSM are similar to those of the light-sensing group 130 or 530. In addition, the light-sensing groups CS1 ̃CSM are controlled by the image-sensing controlling circuit 1080 for sensing a scene P (as shown in FIG. 11) so as to obtain a 2D image SIM. The scene P comprises reflecting points PN1 ̃PNM. The 2D image SIM comprises M pixels, and each pixel comprises two sub-pixels. The reflecting points PN1 ̃PNM of the scene P are respectively correspond to the M pixels of the 2D image SIM.
The 3D image-sensing device 1000 can use the image-sensing controlling circuit 1080 to control the light-sensing module 1030 sensing each reflecting point of the scene P so as to obtain the sub-pixel image data of the M pixels corresponding to reflecting points PN1 ̃PNM. In addition, the 3D image-sensing device 1000 also can use the distance-measuring module 1090 to measure the distance between each reflecting point of the scene P and the 3D image-sensing device 1000. In other words, the 3D image-sensing device 1000 can obtain the 2D image SIM corresponding to the reflecting points PN1 ̃PNM and the distance data corresponding to the measured distances D1 ̃DM between the reflecting points PN1 ̃PNM and the 3D image-sensing device 1000.
For example, the structures of the light-sensing groups CS1 ̃CSM are similar to that of the light-sensing group 530. That is, each of the light-sensing groups CS1 ̃CSM comprises two light-sensing components. The light-sensing group CS1 comprises light-sensing components CSA1 and CSB1; the light-sensing group CS2 comprises light-sensing components CSA2 and CSB2; and the light-sensing group CSM comprises light-sensing components CSAM and CSBM and so on. As a result, the 3D image-sensing device 1000 generates the shutter periodic signals SST1 and SST2, and the reading signal SRE by means of the light-emitting/sensing controlling circuit 1010 of the distance-measuring device 1090 to control the light-sensing groups CS1 ̃CSM. For example, the light-sensing group CSK comprises light-sensing components CSAK and CSBK. When the shutter periodic signal SST1 represents “turning-on”, the light-sensing component CSAK senses the energy of the reflected light LRD, which is generated by the reflecting point PNK of the scene P reflecting the detecting light LID, so as to accordingly accumulate the energy ER1K; when the shutter periodic signal SST1 represents “turning-off”, the light-sensing component CSAK does not sense the energy of the reflected light LRD generated by the reflecting point PNK of the scene P reflecting the detecting light LID, and does not accumulate the energy ER1K. When the reading signal SRE represents “reading”, the light-sensing component CSAK outputs the light-sensing signal SLS1K according to the accumulated energy ER1K. When the shutter periodic signal SST2 represents “turning-on”, the light-sensing component CSBK senses the energy of the reflected light LRD generated by the reflecting point PNK of the scene P reflecting the detecting light LID, so as to accordingly accumulate the energy ER2K; when the shutter periodic signal SST2 represents “turning-off”, the light-sensing component CSBK does not sense the energy of the reflected light LRD generated by the reflecting point PNK of the scene P reflecting the detecting light LID, and does not accumulate the energy ER2K. When the reading signal SRE represents “reading”, the light-sensing component CSBK outputs the light-sensing signal SLS2K according to the accumulated energy ER2K. In addition, when the reading signal SRE represents “reading”, the light-sensing components CSAK and CSBK reset the accumulated energy ER1K and ER2K after the light-sensing components CSAK and CSBK output the light-sensing signals SLS1K and SLS2K.
In this way, the light-emitting/sensing controlling circuit 1010 respectively controls the light-sensing groups CS1 ̃CSM measuring the measured distances D1 ̃DM between the reflecting points PN1 ̃PNM of the scene P and the 3D image-sensing device 1000, by means of the methods of the “background-measuring phase” mentioned in FIG. 2, the “frequency-adjusting phase” mentioned in FIG. 4, and the “distance-calculating phase” mentioned in FIG. 3.
On the other hand, the 3D-image sensing device 1000 uses the image-sensing controlling circuit 1080 to control the light-sensing module 1030 sensing the reflecting points PN1 ̃PNM of the scene P to obtain the 2D image SIM, wherein the 2D image SIM comprises the sub-pixel image data GA1 ̃GAM and GB1 ̃GBM. More particularly, the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSA1 and CSB1 sensing the reflecting point PN1 of the scene P so as to obtain the two sub-pixel image data GA1 and GB1; the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSAX and CSBX sensing the reflecting point PNX of the scene P so as to obtain the two sub-pixel image data GAX and GBX, wherein the distance between the reflecting point PNX and the 3D image-sensing device 1000 is DX; the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSA and CSB sensing the reflecting point PNY of the scene P so as to obtain the two sub-pixel image data GAY and GBY, wherein the distance between the reflecting point PNY and the 3D image-sensing device 1000 is Dy; the image-sensing controlling circuit 1080 respectively controls the light-sensing components CSAM and CSBM sensing the reflecting point PNM of the scene P so as to obtain the two sub-pixel image data GAM and GBM and so on. In this way, the 3D image-sensing device 100 can construct a 3D image by means of the sub-pixel image data GA1 ̃GAM and GB1 ̃GBM, and the distance data D1 ̃DM.
In addition, the light-sensing groups CS1 ̃CSM of the light-sensing module 1030 are CMOS or CCD light sensors. That is, the structure and the principle of the light-sensing module 1030 are similar to those of the image-sensing module of the digital camera. In other words, when the 3D image-sensing device is applied in the digital camera, the digital camera can control the light-sensing module 1030 sensing the scene so as to obtain the 2D image by means of the image-sensing controlling circuit 1080 of the 3D image-sensing device 1000, and also can measure each distance between each reflecting point of the scene and the digital camera so as to obtain each distance data corresponding to each pixel by means of the distance-measuring device 1090 of the 3D image-sensing device 1000. In this way, the digital camera can construct a 3D image according to the distance data and the 2D image. Since the 2D image-sensing device 1100 and the distance-measuring device 1090 of the 3D image-sensing device 1000 share the light-sensing module 1030, the cost of constructing the 3D image is reduced.
For the distance-measuring device to more correctly calculate the measured distance, the present invention further provides a method of increasing signal-to-noise ratio of the distance-measuring device.
Please refer to FIG. 12. FIG. 12 is a diagram illustrating a method 1200 of increasing signal-to-noise ratio of the distance-measuring device according to an embodiment of the present invention. Please refer to FIG. 13. The method 1200 is applied for a distance-measuring device 1300. The distance-measuring device 1300 is utilized for measuring a measured distance DM between a measured object MO and the distance-measuring device 1300. The distance-measuring device 1300 includes a light-emitting/sensing controlling circuit 1310, a distance-calculating circuit 1320, a light-emitting component LD, a focusing module LEN, and a light-sensing component CSU1. The structures and the operational principles of the light-emitting component LD and the focusing module LEN are similar to those of the light-emitting components 120, 520, 820, and 1020, and the focusing modules 170, 570, and 870, respectively. The light-sensing component CSU1 can be realized by the light-sensing component 531 (or 532). The light-sensing component CSU1 senses and accumulates energy of light according to a shutter periodic signal SST1, so as to generate a light-sensing signal SLS1. The steps of the method 1200 are illustrated as below:

    step 1210: by means of the light-emitting periodic signal SLD, the light-emitting/sensing controlling circuit 1310 controls the light-emitting component LD to continuously emit a detecting light LID to the measured object MO during an emitting period TLD for generating a reflected light LRD;
    step 1220: a delay period TDELAY after the light-emitting component LD starts to emit the detecting light LID, the light-emitting sensing controlling circuit 1310 switches the shutter periodic signal SST1 to represent “turning-on” during a sensing period TSEN1 for the light-sensing component CSU1 to sense and accumulate energy of the reflected light LRD, and accordingly generate the light-sensing signal SLS1;
    step 1230: the distance-calculating circuit 1320 obtains a time of flight TTOF of light going back and forth between the distance-measuring device 1300 and the measured object MO according to the light-sensing signal SLS1 and energy of the detecting light LID emitted by the light-emitting component LD during the emitting period TLD;
    step 1240: the distance-calculating circuit 1320 obtains the measured distance DM according to the time of flight TTOF, and accordingly generates an output signal SOUT, for representing length of the measured distance DM.


Please refer to FIG. 14. In the step 1210, by means of the light-emitting periodic signal SLD, the light-emitting/sensing controlling circuit 1310 controls the light-emitting component LD to continuously emit a detecting light LID to the measured object MO during an emitting period TLD for generating a reflected light LRD. A time of flight TTOF after the light-emitting component LD starts to emit the detecting light LID, the reflected light LRD reaches the light-sensing component CSU1. The period length of the time of flight TTOF is the sum of period lengths of the period of the detecting light LID emitted from the light-emitting component LD to the measured object MO and the period of the reflected light LRD emitted from the measured object MO to the light-sensing component CSU1. In other words, the period length of the time of flight TTOF is equal to that of the period of light going back and forth between the distance-measuring device 1300 and the measured object MO.
In the step 1220, a delay period TDELAY after the light-emitting component LD starts to emit the detecting light LID, the light-emitting sensing controlling circuit 1310 switches the shutter periodic signal SST1 to represent “turning-on” for a sensing period TSEN1. Thus, the light-sensing component CSU1 senses and accumulates energy of light and accordingly generates the light-sensing signal SLS1. In addition, generally speaking, the range of length of the measured distance DM is limited according to the application of the distance-measuring device 1300. In the present invention, the length of the measured distance DM that the distance-measuring device 1300 can measure is limited to between a predetermined shortest measured distance DMIN and a predetermined longest measured distance DMAX. For example, the distance-measuring device 1300 may be applied in a video game console. The distance-measuring device 1300 is disposed near a display device. The video game console detects the measured distance DM between the user and the display device by means of the distance-measuring device 1300, and interacts with the user according to the measured distance DM. For example, the user plays a tennis game. When the measured distance DM decreases, the player in the game controlled by the user moves forward; when the measured distance DM increases, the player in the game controlled by the user moves backward. However, when the measured distance DM between the display device and the user is too short (that is, the measured distance DM is shorter than the predetermined shortest measured distance DMIN), the user cannot see the whole image displayed by the display device and cannot easily play the tennis game. In other words, only when the measured distance DM is longer than the predetermined shortest measured distance DMIN is the measured distance DM valid for the video game console to interact with the user. Since the measured distance DM is longer than the predetermined shortest measured distance DM, in the step 1220, the light-emitting/sensing controlling circuit 1310 calculates the delay period TDELAY according to the predetermined shortest measured distance DMIN for ensuring that the reflected light LRD reaches the light-sensing component CSU1 after the delay period TDELAY. The light-emitting/sensing controlling circuit 1310 calculates the delay period TDELAY according to the following formula:

TDELAY=2×DMIN/C  (6).

Since the measured distance DM is longer than the predetermined shortest measured distance DM, the time of flight TTOF when the distance-measuring device 1300 measures the measured distance DM is longer than the delay period TDELAY calculated according to the formula (6). In other words, although the light-sensing component CSU1 starts to sense the energy of the light a delay period TDELAY after the light-emitting component LD starts to emit the detecting light LID, the light-sensing component CSU1 can still sense the reflected light LRD in time.
In the step 1230, the light-sensing signal SLS1 can represent the energy of the reflected light LRD sensed by the light-sensing component CSU1. In this way, the distance-calculating circuit 1320 can obtain the time of flight TTOF of the light going back and forth between the distance-measuring device 1300 and the measured object MO, according to the ratio between the energy of the reflected light LRD sensed by the light-sensing component CSU1 and the energy of the detecting light LID emitted by the light-emitting component LD during the emitting period TLD.
In the step 1240, since the time of flight TTOF is the period of the light going back and forth between the distance-measuring device 1300 and the measured object MO, the distance-calculating circuit 1320 can calculate the measured distance DM according to the following formula:

DM=TTOF×C/2  (7);

wherein C represents speed of light. In this way, the distance-calculating circuit 1320 can generate the output signal SOUT representing the length of the measured distance DM.

In the conventional method, the light-sensing component CSU1 of the distance-measuring device 1300 starts to sense energy of light immediately after the light-emitting component LD starts to emit the detecting light LID. In the step 1220 of the method 1200, the light-emitting sensing controlling circuit 1310 controls the light-sensing component CSU1 to start to sense energy of light a delay period TDELAY after the light-emitting component LD starts to emit the detecting light LID. In this way, the light-emitting component CSU1 does not sense the energy of the background light LB (noise) during the delay period TDELAY. Therefore, the signal-to-noise ratio of the light-sensing signal SLS1 generated by the light-sensing component CSU1 is improved. More particularly, provided that the light-sensing component CSU1 stops sensing energy of light when the light-emitting component LD stops emitting detecting light LID (as shown in FIG. 14), in the conventional method, the energy EB—OLD of the background light LB sensed by the light-sensing component CSU1 is proportional to the emitting period TLD, and the energy of the reflected light LRD sensed by the light-sensing component CSU1 is ER—OLD. In the method 1200, the energy EB—NEW of the background light LB sensed by the light-sensing component CSU1 is proportional to the sensing period TSEN1. Since the reflected light LRD reaches the light-sensing component CSU1 after the delay period TDELAY, the energy of the reflected light LRD sensed by the light-sensing component CSU1 is still ER—OLD. Hence, the energy EB—NEW is less than the energy EB—OLD. Compared with the signal-to-noise ratio (ER—OLD/EB—OLD) of the conventional method, the light-sensing signal SLS1 obtained by the method 1200 has a higher signal-to-noise ratio (ER—OLD/EB—NEW). In other words, the light-sensing signal SLS1 obtained by the method 1200 can more correctly represent the energy of the reflected light LRD sensed by the light-sensing component CSU1. As a result, the time of flight TTOF obtained in the step 1230 is more correct. In this way, a more correct measured distance DM can be calculated in the step 1240.
In addition, in FIG. 14, the reflected light LRD has to reach the light-sensing component CSU1 before the end of the sensing period TSEN1 for the distance-measuring device 1300 to be capable of measuring the measured distance DM. That is, the period length of the time of flight TTOF has to be shorter than the sum of period lengths of the sensing period TSEN1 and the delay period TDELAY. In other words, the predetermined longest measured distance DMAX that the distance-measuring device can measure is represented by the following formula:

DMAX=2×(TSEN1+TDELAY)/C  (8).

In addition, in FIG. 14, the sum of the period lengths of the sensing period TSEN1 and the delay period TDELAY is equal to the period length of the emitting period TLD. That is, the light-emitting/sensing controlling circuit 1310 controls the light-sensing components CSU1 to immediately stop sensing the energy of the reflected light LRD when the light-emitting component LD stops emitting the detecting light LID. However, the light-sensing components CSU1 are not limited to immediately stop sensing the energy of the reflected light LRD when the light-emitting component LD stops emitting the detecting light LID. For example, please refer to FIG. 15. The light-emitting/sensing controlling circuit 1310 can set the period length of the sensing period TSEN1 equal to that of the emitting period TLD. It can be seen from formula (8) that since the sensing period TSEN1 increases, the predetermined longest measured distance DMAX increases.
Please refer to FIG. 16. FIG. 16 is a diagram illustrating a method 1600 of increasing signal-to-noise ratio of the distance-measuring device according to another embodiment of the present invention. Please refer to FIG. 17. The method 1600 is applied for a distance-measuring device 1700. The distance-measuring device 1700 is utilized for measuring a measured distance DM between a measured object MO and the distance-measuring device 1700. The distance-measuring device 1700 includes a light-emitting/sensing controlling circuit 1710, a distance-calculating circuit 1720, a light-emitting component LD, a focusing module LEN, and light-sensing components CSU1 and CSU2. The structures and the operational principles of the light-emitting component LD and the focusing module LEN are similar to those of the light-emitting components 120, 520, 820, and 1020, and the focusing modules 170, 570, and 870, respectively. The light-sensing components CSU1 and CSU2 can be realized by the light-sensing components 531 and 532. The light-sensing component CSU1 senses and accumulates energy of light according to a shutter periodic signal SST1, so as to generate a light-sensing signal SLS1. The light-sensing component CSU2 senses and accumulates energy of light according to a shutter periodic signal SST2, so as to generate a light-sensing signal SLS2. The steps of the method 1600 are illustrated as below:

    step 1610: by means of the light-emitting periodic signal SLD, the light-emitting/sensing controlling circuit 1710 controls the light-emitting component LD to continuously emit a detecting light LID to the measured object MO during an emitting period TLD for generating a reflected light LRD;
    step 1620: a delay period TDELAY after the light-emitting component LD starts to emit the detecting light LID, the light-emitting sensing controlling circuit 1610 switches the shutter periodic signal SST1 to represent “turning-on” during a sensing period TSEN1 for the light-sensing component CSU1 to sense and accumulate energy of the reflected light LRD, and accordingly generate the light-sensing signal SLS1;
    step 1630: when the light-sensing component CSU1 stops sensing the reflected light LRD, the light-emitting/sensing controlling circuit 1710 switches the shutter periodic signal SST2 to represent “turning-on” during a sensing period TSEN2 for the light-sensing component CSU2 to sense and accumulate energy of the reflected light LRD, and accordingly generate the light-sensing signal SLS2;
    step 1640: the distance-calculating circuit 1720 obtains a time of flight TTOF of light going back and forth between the distance-measuring device 1700 and the measured object MO according to the ratio between the light-sensing signals SLS1 and SLS2;
    step 1650: the distance-calculating circuit 1720 obtains the measured distance DM according to the time of flight TTOF, and accordingly generates an output signal SOUT, for representing length of the measured distance DM.


Please refer to FIG. 18. In the step 1610, by means of the light-emitting periodic signal SLD, the light-emitting/sensing controlling circuit 1710 controls the light-emitting component LD to continuously emit a detecting light LID to the measured object MO during an emitting period TLD for generating a reflected light LRD. A time of flight TTOF after the light-emitting component LD starts to emit the detecting light LID, the reflected light LRD reaches the light-sensing component CSU1. The time of flight TTOF is equal to the period of light going back and forth between the distance-measuring device 1700 and the measured object MO.
In the step 1620, a delay period TDELAY after the light-emitting component LD starts to emit the detecting light LID, the light-emitting sensing controlling circuit 1710 switches the shutter periodic signal SST1 to represent “turning-on” for a sensing period TSEN1. Thus, the light-sensing component CSU1 senses and accumulates energy of light and accordingly generates the light-sensing signal SLS1. In the present embodiment, the length of the measured distance DM that the distance-measuring device 1700 can measure is limited between the predetermined shortest measured distance DMIN and the predetermined longest measured distance DMAX. Therefore, in the step 1620, the light-emitting/sensing controlling circuit 1710 calculates the delay period TDELAY according to the formula (6) for the reflected light LRD to reach the light-sensing component CSU1 after the delay period TDELAY, so that the light-sensing component CSU1 can sense the reflected light LRD in time to generate a correct light-sensing signal SLS1. In addition, in FIG. 18, the reflected light LRD still has to reach the light-sensing component CSU1 before the end of the sensing period TSEN1 for the distance-measuring device 1700 to be capable of measuring the measured distance DM. That is, the period length of the time of flight TTOF has to be shorter than the sum of period lengths of the sensing period TSEN1 and the delay period TDELAY. In other words, the predetermined longest measured distance DMAX that the distance-measuring device can measure can still be represented by the formula (8).
In the step 1630, when the light-sensing component CSU1 stops sensing the reflected light LRD, the light-emitting/sensing controlling circuit 1710 switches the shutter periodic signal SST2 to represent “turning-on” for a sensing period TSEN2. Hence, in the sensing period TSEN2, the light-sensing component CSU2 senses and accumulates the energy of the reflected light LRD, and accordingly generates the light-sensing signal SLS2.
In the step 1640, the light-sensing signal SLS1 represents the energy of the reflected light LRD sensed by the light-sensing component CSU1. The light-sensing signal SLS2 represents the energy of the reflected light LRD sensed by the light-sensing component CSU2. According to the operational principle illustrated in FIG. 3, the distance-calculating circuit 1720 obtains the time of flight TTOF of the light going back and forth between the distance-measuring device 1700 and the measured object MO according to the ratio between the light-sensing signals SLS1 and SLS2. More particularly, it can be seen from FIG. 18 that the time of flight TTOF can be represented by the following formula:




  
    
      
        
          
            
              
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When the distance-measuring device 1700 further includes a background-calculating circuit, the energy of the background light EB1 and EB2 can be calculated by means of the method illustrated in FIG. 2, so that the time of flight TTOF can be calculated according to the formula (9). In addition, when the energy of the background light EB1 and EB2 is much less than the energy of reflected light ER1 and ER2, the formula (9) can be simplified to be the following formula:

TTOF=TDELAY+TSEN1−[(SLS1/(SLS1+SLS2)]×TLD  (10).

In the step 1650, since the period length of the time of flight TTOF is equal to that of the period of light going back and forth between the distance-measuring device 1700 and the measured object MO, the distance-calculating circuit 1720 can calculate the measured distance DM according to the formula (7), and accordingly generates the output signal SOUT representing the length of the measured distance DM.
Compared with the method 1200 illustrated in FIG. 12, in the method 1600, the time of flight TTOF is calculated according to the ratio between the light-sensing signals SLS1 and SLS2. As a result, in the method 1600, the energy of the reflected light LR1 and LR2 can be repeatedly measured as shown in FIG. 18. When the energy of the reflected light LR1 and LR2 is measured N times, the light-sensing signals SLS11 ̃SLS1N and SLS21 ̃SLS2N are obtained. The distance-calculating circuit 1720 substitutes the light-sensing signal SLS1 obtained by accumulating the light-sensing signals SLD11 ̃SLD1N and the light-sensing signal SLS2 obtained by accumulating the light-sensing signals SLS21 ̃SLS2N into the formula (9) or (10) to calculate the time of flight TTOF. In this way, the measuring error due to the low energy of reflected light LRD is reduced, so that the measured distance DM is more correctly calculated in the step 1650.
In addition, in the method 1600, the duty cycle of the light-emitting component LD emitting the detecting light LID when the measured distance DM is measured, namely the ratio between the emitting period TLD and the detecting cycle TC, can be controlled by setting the period lengths of the sensing periods TSEN1 and TSEN2, and the emitting period TLD. For example, please refer to FIG. 19. The period length of detecting cycle TC is set to be 2TLD. The period length of the sensing period TSEN1 and the sensing period TSEN2 are both equal to (TLD−TDELAY/2). In this way, the duty cycle of the light-emitting component LD emitting the detecting light LID is equal to 50%.
Based on the spirit of the methods 1200 and 1600, the present invention further provides a method 2000 for the distance-measuring device 100 of FIG. 1. Please refer to FIG. 20 and FIG. 21, which are diagrams illustrating the method 2000 of increasing the signal-to-noise ratio of the distance-measuring device 100. The steps of the method 2000 are illustrated as below:

    step 2010: the light-emitting/sensing controlling circuit 110 switches the light-emitting periodic signal SLD between representing “turning-on” and “turning-off” with a detecting frequency FC, for the light-emitting component 120 to emit the detecting light LID to the measured object MO to generate a reflected light LRD during an emitting period TLD, and not emit the detecting light LID during a non-emitting period TNLD;
    step 2020: a delay period TDELAY after every time the light-emitting component 120 starts to emit the detecting light LID, the light-emitting/sensing controlling circuit 110 switches the shutter periodic signal SST1 to represent “turning-on” during a sensing period TSEN1 for the light-sensing group 130 to sense and accumulate energy of the reflected light LRD to generate the light-sensing signal SLS1;
    step 2030: the light-emitting/sensing controlling circuit 110 switches the shutter periodic signal SST2 to represent “turning-on” during a sensing period TSEN2 for the light-sensing group 130 to sense and accumulate energy of the reflected light LRD to generate the light-sensing signal SLS2 after the sensing period TSEN1;
    step 2040: the distance-calculating circuit 140 obtains a time of flight TTOF of light going back and forth between the distance-measuring device 100 and the measured object MO according to a ratio of the light-sensing signals SLS1 and SLS2;
    step 2050: the distance-calculating circuit 140 obtains the measured distance MO according to the time of flight TTOF, and accordingly generates an output signal SOUT (not shown in FIG. 1) representing the length of the measured distance DM.


Please refer to FIG. 21. The period of the distance-measuring device 100 measuring the measured distance DM includes detecting cycles TC1 ̃TCN. The period length of each detecting cycle TC1 ̃TCN is equal to (1/FC). In the step 2010, the light-emitting/sensing controlling circuit 110 switches the light-emitting periodic signal SLD between representing “turning-on” and “turning-off” with a detecting frequency FC, for the light-emitting component 120 to emit the detecting light LID to the measured object MO to generating a reflected light LRD during the emitting period TLD of each detecting cycle TC1 ̃TON, and not emit the detecting light LID during the non-emitting period TNLD of each detecting cycle TC1 ̃TON. Thus, in each detecting cycle TC1 ̃TON, the measured object MO reflects the detecting light LID to generate reflected light LRD. More particularly, a time of flight TTOF after the light-emitting component 120 starts to emit the detecting light LID, the reflected light LRD reaches the light-sensing group 130, wherein the time of flight TTOF is equal to the period of light going back and forth between the distance-measuring device 100 and measured object MO.
In the step 2020, in each detecting cycle TC1 ̃TCN, a delay period TDELAY after every time the light-emitting component 120 starts to emit the detecting light LID, the light-emitting/sensing controlling circuit 110 switches the shutter periodic signal SST1 to represent “turning-on” during a sensing period TSEN1 for the light-sensing group 130 to sense and accumulate energy of the reflected light LRD to generate the light-sensing signal SLS1. Provided that the measured distance DM is limited to between the predetermined shortest measured distance DMIN and the predetermined longest measured distance DMAX, in the step 2020, the light-emitting/sensing controlling circuit 110 calculates the delay period TDELAY according to the formula (6) for the reflected light LRD to reach the light-sensing component CSU1 after the delay period TDELAY, so that the light-sensing component CSU1 can sense the reflected light LRD in time to generate a correct light-sensing signal SLS1. In addition, the reflected light LRD still has to reach the light-sensing component CSU1 before the end of the sensing period TSEN1 for the light-sensing group 130 to be capable of sensing the reflected light LRD. Hence, the predetermined longest measured distance DMAX that the distance-measuring device can measure can still be represented by the formula (8).
In the step 2030, after the sensing period TSEN1 of each detecting cycle TC1 ̃TCN, the light-emitting/sensing controlling circuit 110 switches the shutter periodic signal SST2 to represent “turning-on” during a sensing period TSEN2. Hence, in the sensing period TSEN2, the light-sensing group 130 senses and accumulates the energy of the reflected light LRD, and accordingly generates the light-sensing signal SLS2. In addition, it can be seen in FIG. 21 that the light-emitting periodic signal SLD and the shutter periodic signal SST1 are approximately in phase (the only difference is the delay period TDELAY), and the phase of the shutter periodic signal SST1 (or the light-emitting periodic signal SLD) is approximately opposite the phase of the second shutter periodic signal SST2.
In the step 2040, the light-sensing signal SLS1 represents the energy of the reflected light LRD sensed by the light-sensing group 130 in the sensing periods TSEN1. The light-sensing signal SLS2 represents the energy of the reflected light LRD sensed by the light-sensing group 130 in the sensing periods TSEN2. Similar to the step 1640, the distance-calculating circuit 140 obtains the time of flight TTOF of the light going back and forth between the distance-measuring device 100 and the measured object MO according to the ratio between the light-sensing signals SLS1 and SLS2. That is, in the step 2040, the distance-calculating circuit 140 can still calculate the time of flight TTOF according to the formula (9).
In addition, since the distance-measuring device 100 can obtain the background signal SB, which represents the energy of background light LB sensed by the light-sensing group 130 per unit time, by means of the method illustrated in FIG. 2, the energy of background light EB1 and EB2 in FIG. 21 can be calculated according to the following formulas:

EB1=SB×TSEN1  (11); and

EB2=SB×TSEN2  (12).

In this way, according to the formulas (9), (11), and (12), the time of flight TTOF can be calculated by the following formula:

TTOF=TDELAY+TSEN1−[(SLS1−SB×TSEN1)/(SLS1−SB×TSEN1+SLS2−SB×TSEN2)]×TLD  (13).

Therefore, from the formula (13), the distance-calculating circuit 140 can calibrate the ratio between the light-sensing signals SLS1 and SLS2 according to the background signal SB, and can obtain a more correct time of flight TTOF according to the calibrated ratio between the light-sensing signals SLS1 and SLS2.
In the step 2050, since the time of flight TTOF is equal to the period of the light going back and forth between the distance-measuring device 100 and the measured object MO, the distance-calculating circuit 140 can calculate the measured distance DM according to the formulas (7) and (13), and accordingly generate the output signal SOUT (not shown in FIG. 1) representing the length of the measured distance DM.
In conclusion, the method provided by the present invention is capable of increasing the signal-to-noise ratio of the distance-measuring device. The method provided by the present invention includes a light-emitting component emitting a detecting light to a measured object during an emitting period for generating a reflected light, a delay period after the light-emitting component emitting the detecting light, a light-sensing component sensing the energy of the reflected light so as to generate a light-sensing signal, obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the energy of the detecting light and the light-sensing signal, and obtaining a measured distance between the distance-measuring device and the measured object according to the time of flight. Since the measured distance is larger than a predetermined shortest measured distance, the method can accordingly calculate a proper delay period for ensuring that the reflected light reaches the light-sensing component after the delay period. In this way, since the light-sensing component does not sense the background light during the delay period, the signal-to-noise ratio of the light-sensing signal is improved.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

## Claims

1. A method of increasing signal-to-noise ratio of a distance-measuring device, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device having a light-emitting component for emitting a detecting light, and a first light-sensing component for sensing and accumulating energy of light according to a first shutter periodic signal to generate a light-sensing signal, the method comprising:
the light-emitting component continuously emitting the detecting light to the measured object to generate a reflected light during an emitting period;
a delay period after the light-emitting component starts to emit the detecting light, the first light-sensing component sensing and accumulating energy of the reflected light during a sensing period to generate the light-sensing signal;
obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period; and
obtaining the measured distance according to the time of flight;
wherein:
the delay period is calculated according to the predetermined shortest measured distance;
a relationship between the predetermined longest measured distance and the sensing period is represented by DMAX=2×(TSEN1+TDELAY)/C;
DMAX represents the predetermined longest measured distance;
TSEN1 represents the sensing period;
TDELAY represents the delay period; and
C represents speed of light.

2. The method of claim 1, wherein obtaining the measured distance according to the time of flight comprises:
calculating the measured distance according to the following formula:


DM=TTOF×C/2;

wherein DM represents the measured distance; TTOF represents the time of flight; and C represents speed of light.

3. The method of claim 1, wherein a sum of period lengths of the sensing period and the delay period is equal to period length of the emitting period.

4. The method of claim 1, wherein period length of the sensing period is equal to period length of the emitting period.

5. The method of claim 1, further comprising calculating the delay period according to TDELAY=2×DMIN/C, wherein DMIN represents the predetermined shortest measured distance.

6. A distance-measuring device with increased signal-to-noise ratio, the distance-measuring device being utilized for measuring a measured distance between the distance-measuring device and a measured object, the measured distance being longer than a predetermined shortest measured distance and shorter than a predetermined longest measured distance, the distance-measuring device comprising:
an emitting component, for emitting a detecting light;
a light-sensing component, for sensing and accumulating energy of light to generate a light-sensing signal;
a controlling circuit, for controlling the emitting component to continuously emit the detecting light to the measured object to generate a reflected light during an emitting period, and a delay period after the light-emitting component starts to emit the detecting light, for controlling the light-sensing component to sense and accumulate energy of the reflected light during a sensing period to generate the light-sensing signal; and
a calculating circuit, for obtaining a time of flight of light going back and forth between the distance-measuring device and the measured object according to the light-sensing signal and energy of the detecting light emitted by the light-emitting component during the emitting period, and generating an output signal representing length of the measured distance according to the time of flight; wherein:
the delay period is calculated according to the predetermined shortest measured distance;
a relationship between the predetermined longest measured distance and the sensing period is represented by DMAX=2×(TSEN1+TDELAY)/C;
DMAX represents the predetermined longest measured distance;
TSEN1 represents the sensing period;
TDELAY represents the delay period; and
C represents speed of light.

7. The distance-measuring device of claim 6, wherein the distance-calculating circuit calculates the measured distance according to the following formula:


DM=TTOF×C/2;

wherein DM represents the measured distance; TTOF represents the time of flight; and C represents speed of light.

8. The distance-measuring device of claim 6, wherein a sum of period lengths of the sensing period and the delay period is equal to period length of the emitting period.

9. The distance-measuring device of claim 6, wherein period length of the sensing period is equal to period length of the emitting period.

10. The distance-measuring device of claim 6, further comprising:
a focusing module, for focusing the reflected light onto the-light-sensing component.

11. The distance-measuring device of claim 6, wherein the calculating circuit is configured to calculate the delay period according to TDELAY=2×DMIN/C, wherein DMIN represents the predetermined shortest measured distance.