Patent Publication Number: US-2013235364-A1

Title: Time of flight sensor, camera using time of flight sensor, and related method of operation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2012-0023600 filed on Mar. 7, 2012, the subject matter of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The inventive concept relates generally to time of flight (ToF) sensors. More particularly, certain embodiments of the inventive concept relate to a ToF sensor that can be adjusted in response to activity such as motion within its sensing field. 
     A ToF sensor is a device that determines the flight time of a signal of interest. For example, an optical ToF sensor may determine the time of flight of an optical signal (e.g., near infrared light at ˜850 nm) by detecting its time of emission from a light source (t_em), detecting its time of reception at a light sensor (t_re), and then subtracting the time of reception from the time of emission according to the following equation ToF=t_re−t_em, referred to as equation (1). 
     In some applications, a ToF sensor may be used to determine the location of nearby objects. For instance, an optical ToF sensor may determine an approximate distance “D” to an object by relating the time of flight as calculated in equation (1) to the speed of light “c”, as in the following equation D=(ToF*c)/2, referred to as equation (2). In equation (2), it is assumed that the distance D between the ToF sensor and the object is one half of the total distance traveled by the emitted optical signal. 
     In addition to determining the location of objects, a ToF sensor can also be used to detect motion. This can be accomplished, for instance, by detecting changes in the distance D over time. In particular, if the detected distance D changes for a particular sensing region of the ToF sensor, these changes can be interpreted to indicate relative motion between the ToF sensor and one or more objects. 
     Although many ToF sensors can obtain relatively accurate distance information, they are somewhat limited due to low resolution. For example, unlike digital cameras, ToF sensors are not generally designed with large arrays of pixel sensors. Consequently, it can be difficult for conventional ToF sensors to produce high resolution information regarding motion or other phenomena within its field of sensing. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the inventive concept, a ToF sensor comprises a light source configured to irradiate light on a subject, a sensing unit comprising a sensing pixel array configured to sense light reflected from the subject and to generate a distance data signal, and a control unit comprising a view angle control circuit. The view angle control circuit is configured to detect movement of the subject based on the distance data signal received from the sensing unit and to control a view angle of the sensing unit to increase a number of sensing pixels in the sensing pixel array that are used to sense a region in which the detected movement occurs. 
     In another embodiment of the inventive concept, a ToF camera comprises a light source configured to irradiate light on a subject, a sensing unit comprising a sensing pixel array configured to sense light reflected from the subject and to generate a distance data signal, a ToF sensor comprising a control unit comprising a view angle control circuit, and a two-dimensional (2D) image sensor configured to obtain 2D image information of the subject. The view angle control circuit is configured to detect movement of the subject based on the distance data signal received from the sensing unit and to control a view angle of the sensing unit to increase a number of sensing pixels in the sensing pixel array that are used to sense a region in which the detected movement occurs. 
     In another embodiment of the inventive concept, a method comprises irradiating light on a subject, sensing light reflected from the subject and generating a distance data signal based on the sensed light, detecting movement of the subject based on the distance data signal, and controlling a view angle of the sensing unit to increase a number of sensing pixels in the sensing pixel array that are used to sense a region in which the detected movement occurs. 
     These and other embodiments of the inventive concept can potentially improve the sensing performed by a ToF sensor or ToF camera by increasing the sensor&#39;s resolution according to observed motion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate selected embodiments of the inventive concept. In the drawings, like reference numbers indicate like features, and the relative sizes of various features may be exaggerated for clarity of illustration. 
         FIG. 1  is a block diagram of a ToF sensor according to an embodiment of the inventive concept. 
         FIGS. 2A through 3B  are pixel array diagrams illustrating operations of the ToF sensor of  FIG. 1  according to an embodiment of the inventive concept. 
         FIG. 4  is a more detailed block diagram of the ToF sensor of  FIG. 1  according to an embodiment of the inventive concept. 
         FIG. 5  is a block diagram of a ToF sensor according to another embodiment of the inventive concept. 
         FIG. 6  is a block diagram of a ToF sensor according to another embodiment of the inventive concept. 
         FIGS. 7A through 7D  are diagrams of segment shapes classified according to segment shape sample data stored in a segment shape sample buffer according to an embodiment of the inventive concept. 
         FIG. 8  is a block diagram of a ToF sensor according to another embodiment of the inventive concept. 
         FIGS. 9A through 9C  are diagrams illustrating operations of an action calculation circuit according to an embodiment of the inventive concept. 
         FIG. 10  is a block diagram of a ToF sensor according to another embodiment of the inventive concept. 
         FIG. 11  is a block diagram of a system comprising the ToF sensor of  FIG. 1 ,  5 ,  6 , or  8  according to an embodiment of the inventive concept. 
         FIG. 12  is a block diagram of a computing system comprising the system of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the inventive concept are described below with reference to the accompanying drawings. These embodiments are presented as teaching examples and should not be construed to limit the scope of the inventive concept. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments of the inventive concept. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, indicate the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Although the terms first, second, third etc. may be used herein to describe various features, the described features should not be limited by these terms. Rather, these terms are used merely to distinguish between different features. Thus, a first feature could be termed a second feature and vice versa without materially changing the meaning of the relevant description. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
       FIG. 1  is a block diagram illustrating a ToF sensor  100  according to an embodiment of the inventive concept. 
     Referring to  FIG. 1 , ToF sensor  100  comprises a light source  110 , a sensing unit  130 , and a control unit  150 . Control unit  150  comprises a view angle control circuit  151 . 
     Light source  110  emits light in response to a light source control signal LSCS. This light (“emitted light EL”) is irradiated onto subjects STH_ 1 , SHT_ 2 , STH_ 3 , . . . , STH_n  170 , which are defined as the contents of distinct regions of the sensing field of ToF sensor  100 . Emitted light EL is reflected off of the subjects to produce reflected light RL, and reflected light RL is sensed by sensing unit  130 . 
     Light source  110  typically comprises a device capable of high speed modulation such as a light-emitting diode (LED) or laser diode (LD). The light emitted by light source  110  may be light modulated into a waveform of a high frequency pulse P of about 200 MHz, for instance. The light may be continuously irradiated or it may be output in discrete pulses. 
     Sensing unit  130  senses light RL reflected from the subjects and generates a distance data signal DDS indicating respective distances between ToF sensor  100  and each of the subjects. Distance data signal DDS can be calculated based on equations (1) and (2) as described above. 
     Sensing unit  130  comprises a sensing pixel array comprising a plurality of sensing pixels. Sensing unit  130  determines the respective distances between ToF sensor  100  and each of the subjects based on different signals sensed by each of the sensing pixels. For example, as illustrated in  FIGS. 2 and 3 , the sensing pixel array may comprise a 4×4 array of pixels to determine distances for sixteen different subjects within the sensing field. 
     Sensing unit  130  transfers distance data signal DDS to control unit  150  and receives a view angle control signal VACS. Sensing unit  130  the controls a view angle according to view angle control signal VACS. The view angle can be controlled, for instance, using a lens distance control method, a digital zooming method, or a super resolution method. 
     In certain embodiments, sensing unit  130  controls the view angle to include a region in which a certain pattern of motion is detected. For instance, it may adjust the view angle to focus on a region where the distance D exhibits a relatively large change over time. Such a region can be referred to as a dynamic region. The adjustment of the view angle can also be performed on the basis of segmented portions of the sensing pixel array. For instance, the view angle may be adjusted to focus on a segment comprising multiple pixels that change in a similar manner, indicating that they may be part of the same object. 
     Control unit  150  receives distance data signal DDS from sensing unit  130  to generate view angle control signal VACS. Control unit  150  comprises a view angle control circuit  151 , which processes distance data signal DDS to generate view angle control signal VACS. A method of generating view angle control signal VACS is described below in further detail. 
     During typical operation of ToF sensor  100 , light source  110  transmits emitted light EL to subjects STH_ 1 , SHT_ 2 , STH_ 3 , . . . , STH_n  170 . Sensing unit  130  senses light RL reflected from subjects STH_ 1 , SHT_ 2 , STH_ 3 , . . . , STH_n  170 , generates distance data signal DDS and transmits it to control unit  150 . Control unit  150  may receive distance data signal DDS to generate view angle control signal VACS. The operation of receiving distance data signal DDS and generating view angle control signal VACS is typically performed by view angle control circuit  151 . 
     Sensing unit  130  controls the view angle according to view angle control signal VACS. For example, if subject STH_ 3  exhibits a greatest amount of motion among subjects STH_ 1 , SHT_ 2 , STH_ 3 , . . . , STH_n  170 , the view angle may be contracted from θ 1  to θ 2  so that sensing unit  130  receives only light reflected from the subject STH_ 3  may be received. Where the view angle is contracted from θ 1  to θ 2 , an area of a subject corresponding to a sensing pixel included in sensing unit  130  is reduced. Thus, the number of pixels corresponding to the subject STH_ 3  increases, and data regarding subject STH_ 3  may be collected with higher resolution. In other words, data regarding a more dynamic or active region may be collected with higher resolution. 
       FIGS. 2A through 3B  are pixel array diagrams illustrating operations of ToF sensor  100  according to an embodiment of the inventive concept. In each of  FIGS. 2A through 3B , a pixel array is illustrated as a 4×4 grid of sensing pixels. Each sensing pixel captures a portion of reflected light RL in order to generate a distance measurement for a corresponding subject within a sensing field defined by the viewing angle of sensing unit  130 . These distance measurements are shown in each of the sensing pixels of  FIGS. 2A through 3B . The distance measurements shown in  FIGS. 2A and 2B  were captured with a relatively wide viewing angle, and the distance measurements shown in  FIGS. 3A and 3B  were captured with narrower viewing angle. 
     Referring to  FIG. 2A , at a time “t”, distance measurements were captured by the sensing pixels for each of 16 different regions. Based on these distance measurements, the sensing pixels were segmented based on the similarity of values. For instance, a first segment is formed by sensing pixels X 12 , X 13 , and X 14  having the same value of distance measurements. A second segment is formed by sensing pixels X 11 , X 21 , and X 31 , X 41 , X 42 , X 43 , X 44  having the same value of distance measurements. Similarly, third through fifth segments were formed in a similar manner. 
     Referring to  FIG. 2B , at a time t+Δt, distance measurements were again captured by the sensing pixels for each of 16 different regions. Motion can then be detected based on differences between the distances measurements as shown in  FIGS. 2A and 2B . In particular, differences between the distance measurements in the fourth and fifth segments indicates that motion has occurred in these segments. Accordingly, the viewing angle of sensing unit  130  can be adjusted to focus on the fourth and fifth segments. 
     Referring to  FIG. 3A , at a time t+2Δt, the sensing pixels of sensing unit  130  are adjusted to capture higher resolution data of the fourth and fifth segments shown in  FIGS. 2A and 2B . These higher resolution versions of the fourth and fifth segments are referred to as  4   —   a  segment and  5   —   a  segment, respectively. 
     Referring to  FIG. 3B , at a time t+3Δt, the distance measurements of the sensing pixels again change, reflecting further motion in the fourth and fifth segments. However, due to the adjusted viewing angle, the further motion is reflected in higher resolution than in  FIGS. 2A and 2B . 
       FIG. 4  is a more detailed block diagram of ToF sensor  100  of  FIG. 1  according to an embodiment of the inventive concept. 
     Referring to  FIG. 4 , ToF  100  is formed with the features as in  FIG. 1 , but sensing unit  130  is shown with a lens  131 , row decoder  133 , and a sensing pixel array  135 . Lens  131  has a substantially uniform time interval and receives reflected light RL reflected from subject  170 . For example, where light source  110  continuously emits a pulse light, lens  131  may receive the reflected light RL reflected at the uniform time interval by opening and closing an aperture thereof. The reflected light RL is converted into an electrical signal in a sensing pixel. 
     Sensing pixel array  135  comprises a plurality of pixels Xij (iε1˜m, jε1˜n) in a 2D matrix of rows and columns and constitutes a rectangular imaging region. Pixels Xij can be identified by a combination of row and column addresses. Each of pixels Xij typically comprises at least one photoelectric conversion device implemented as a photo diode, a photo transistor, a photo gate, or a pinned photo diode. 
     Row decoder  133  generates driving signals and gate signals to drive each row of sensing pixel array  135 . Row decoder  133  selects pixels Xij (where i=1˜m, j=1˜n) of sensing pixel array  135  in a row unit using the driving signals and gate signals. Sensing unit  130  generates the distance data signal from pixel signals output from pixels Xij. 
       FIG. 5  is a block diagram of a ToF sensor  100   —   a , according to another embodiment of the inventive concept. 
     Referring to  FIG. 5 , ToF sensor  100   —   a  comprises a light source  110   —   a , a sensing unit  130   —   a , and a control unit  150   —   a . Control unit  150   —   a  comprises a view angle control circuit  151   —   a  and a focus control circuit  153   —   a . Light source  110   —   a  and sensing unit  130   —   a  operate similar to light source  110  and sensing unit  130 , respectively. Thus, redundant descriptions of these features will be omitted. 
     Sensing unit  130   —   a  transfers distance data signal DDS to control unit  150   —   a  and receives view angle control signal VACS and a focus control signal FCS. Sensing unit  130   —   a  controls a view angle according to view angle control signal VACS and a focus according to focus control signal FCS. 
     Control unit  150   —   a  receives distance data signal DDS from sensing unit  130   —   a  and generates view angle control signal VACS and focus control signal FCS. Control unit  150   —   a  comprises view angle control circuit  151   —   a  and focus control circuit  153   —   a . View angle control circuit  151   —   a  processes distance data signal DDS to generate view angle control signal VACS. Focus control circuit  153   —   a  processes distance data signal DDS and view angle control signal VACS to generate focus control signal FCS. 
     During typical operation of ToF sensor  100   —   a , sensing unit  130   —   a  senses light reflected from subjects and generates distance data signal DDS. Sensing unit  130   —   a  transfers distance data signal DDS to control unit  150   —   a . Control unit  150   —   a  receives distance data signal DDS and generates view angle control signal VACS and focus control signal FCS. The operation of receiving distance data signal DDS and generating view angle control signal VACS may be performed by view angle control circuit  151   —   a  of control unit  150   —   a . Sensing unit  130   —   a  controls the view angle and the focus according to view angle control signal VACS and focus control signal FCS. This may allow data to be collected with greater precision. 
       FIG. 6  is a block diagram of a ToF sensor  100   —   c  according to another embodiment of the inventive concept. 
     Referring to  FIG. 6 , ToF sensor  100   —   c  comprises a light source  110   —   c , a sensing unit  130   —   c , and a control unit  150   —   c . Control unit  150   —   c  comprises a view angle control circuit  151   —   c , a segment shape determination circuit  155   —   c , and a segment shape sample buffer  157   —   c . Light source  110   —   c  and sensing unit  130   —   c  of ToF sensor  100   —   c  operate similar to light source  110  and sensing unit  130 , respectively, so a redundant description of these features will be omitted. 
     Control unit  150   —   c  receives distance data signal DDS from sensing unit  130   —   c  and transfers distance data signal DDS to segment shape determination circuit  155   —   c . Segment shape determination circuit  155   —   c  processes distance data signal DDS and generates a segment shape data signal SSDS. Segment shape data signal SSDS is used to classify each part of a subject corresponding to a pixel array into one or more segments. More specifically, a segment shape may be determined by classifying pixels having the same distance data or within a previously determined range into the same segment. For example, referring to  FIG. 2A , a distance from ToF sensor  100  to a subject is 2.1 meters, and corresponding pixels X 12 , X 13 , and X 14  are designated as the first segment. Similarly, a distance from ToF sensor  100  to another subject is 4 meters, and the corresponding pixels X 11 , X 21 , X 31 , and X 41  are designated as the second segment. 
       FIGS. 7A through 7D  are diagrams of shapes of segments classified according to segment shape sample data DSSD stored in segment shape sample buffer  157   —   c  according to an embodiment of the inventive concept. 
     Referring to  FIGS. 7A through 7D , segment shape determination circuit  155   —   c  generates segment shape data signal SSDS based on segment shape sample data SSSD stored in segment shape sample buffer  157   —   c . Segment shape determination circuit  155   —   c  generates segment shape data signal SSDS according to properties of a subject. For example, where the subject has a uniform pattern, segment shape data signal SSDS may be generated by using database regarding a previously stored outline shape of a human face. Thus, a variety of segments may be determined more efficiently according to an outline shape of the subject. 
       FIG. 8  is a block diagram of a ToF sensor  100   —   d  according to another embodiment of the inventive concept. 
     Referring to  FIG. 8 , ToF sensor  100   —   d  comprises a light source  110   —   d , a sensing unit  130   —   d , and a control unit  150   —   d . Control unit  150   —   d  comprises a view angle control circuit  151   —   d , an action calculation circuit  159   —   d , and a sensing data buffer  152   —   d . Light source  110   —   d  and sensing unit  130   —   d  of ToF sensor  100   —   d  operate similar to light source  110  and sensing unit  130  of ToF sensor  100 , so a redundant description of these features will be omitted. 
     Control unit  150   —   d  receives distance data signal DDS from sensing unit  130   —   dc  and generates view angle control signal VACS. Sensing data buffer  152   —   d  receives distance data signal DDS, which is a signal generated by receiving light in a lens in sensing unit  130   —   d  at a substantially uniform time interval. For example, a distance data signal DDS[t 1 ] generated at a time t 1  may correspond to each subject as shown in  FIG. 2A . Further, a distance data signal DDS[t 2 ] generated at a time t 2  may correspond to each subject as shown in  FIG. 2B . In this case, distance data signal DDS[t 1 ] may be stored in a first buffer BF 1   154   —   d , and distance data signal DDS[t 2 ] may be stored in a second buffer BF 2   156   —   d . Sensing data buffer  152   —   d  may continuously receive distance data signal DDS and alternately store distance data signal DDS in the first buffer BF 1   154   —   d  and the second buffer BF 2   156   —   d.    
     Action calculation circuit  159   —   d  processes distance data signal DDS and generates an action determination signal ADS. Action calculation circuit  159   —   d  receives distance data stored in first buffer BF 1   154   —   d  and second buffer BF 2   156   —   d  and calculates a difference between the distance data corresponding to each cell. The difference between the distance data corresponding to each cell may be defined as an action value indicating an action of a par corresponding to each cell. Action calculation circuit  159   —   d  classifies a segment into a region in which an action of a subject takes place and a background region according to whether the action value is greater than a threshold. Action determination signal ADS may include information regarding the action value. Action calculation circuit  159   —   d  calculates the action value according to a variation in a distance from the subject to a reflected subject. 
     Control unit  150   —   d  classifies the segment as a dynamic region in which a relatively high amount of motion or action occurs or a background region in which a relatively low amount of motion or action occurs. The distinctions between high and low amounts of action can be determined, for instance, by assigning an action value to a segment and comparing the action values to a threshold. Where the action value is greater than the threshold, control unit  150   —   d  may classify the segment as a dynamic region. Otherwise, it may classify the segment as a background region. 
     Control unit  150   —   d  may controls the view angle of sensing unit  130   —   d  to exclude the background region. Control unit  150   —   d  may update the action values of different segments, and reclassify segments as dynamic regions of background regions. Where a segment includes two or more regions where action takes place, control unit  150   —   d  may select a region in which the action occurs more frequently to control the view angle. The region in which the action of the subject occurs more frequently may be a region having the highest action value among the plurality of segments shown in  FIGS. 7A through 7D . View angle control circuit  151   —   c  receives action determination signal ADS and generates view angle control signal VACS. 
       FIGS. 9A through 9C  are diagrams illustrating operations of action calculation circuit  159   —   d  according to an embodiment of the inventive concept. 
       FIG. 9A  is a diagram of action values calculated through continuous sensing with respect to the segments of  FIGS. 2A and 2B . Referring to  FIG. 9A , action calculation circuit  159   —   d  measures each action of a subject with respect to the segments of  FIGS. 2A and 2B . A difference in distance data corresponding to each cell, i.e. an action value, may be calculated as shown in  FIG. 9A . Where the action value exceeds a threshold thr, action of the subject may be determined to take place. 
       FIG. 9B  is a graph illustrating whether action values of the classified segments of  FIGS. 2A and 2B  exceed threshold thr. Referring to  FIG. 9B , the action of the subject may be determined to take place with respect to the fourth and fifth segments having action values that exceed threshold thr. Control unit  150   —   d  generates view angle control signal VACS in such a way that sensing unit  130   —   d  controls a view angle in accordance with the fourth and fifth segments. 
       FIG. 9C  is a graph illustrating whether action values of the classified segments of  FIGS. 2A and 2B  exceed threshold thr with respect to distances. Referring to  FIG. 9C , control unit  150   —   d  focuses a distance to a segment including an action determined by action calculation circuit  159   —   d . For example, where the fourth and fifth segments have high action values as shown in  FIG. 9B , control unit  150   —   d  focuses an average distance of the fourth and fifth segments. 
       FIG. 10  is a block diagram of a ToF sensor  100   —   e  according to another embodiment of the inventive concept. 
     Referring to  FIG. 10 , ToF sensor  100   —   e  comprises a light source  100   —   e , a sensing unit  130   —   e , a view angle control unit  151   —   e , a focus control unit  153   —   e , a segment shape determination unit  155   —   e , a segment shape sample buffer  157   —   e , a sensing data buffer  152   —   e , a comparison unit  158   —   e , and an action determination unit  159   —   e.    
     During typical operation of ToF sensor  100   —   e , light source  110   —   e  irradiates the light EL to a subject. A lens  131   —   e  of sensing unit  130   —   e  receives light EL reflected from the subject at a uniform time interval. For example, where light source  110   —   e  continuously emits pulse light, lens  131   —   e  may receive emitted light EL reflected at the uniform time interval by opening and closing an aperture thereof. Row decoder  133   —   e  selects pixels Xij of sensing pixel array  135   —   e  in a unit of row in response to driving signals and gate signals. Sensing unit  130   —   e  generates distance data signal DDS from pixel signals output from pixels Xij. 
     Sensing data buffer  152   —   e  receives distance data signal DDS. Distance data signal DDS[t 1 ] generated at time t 1  is stored in first buffer BF 1   154   —   e , and distance data signal DDS[t 2 ] is stored in second buffer BF 2   156   —   e . Sensing data buffer  152   —   e  continuously receives distance data signal DDS and alternately stores distance data signal DDS in first buffer BF 1   154   —   e  and second buffer BF 2   156   —   e . Distance data signal DDS[t 1 ] stored in first buffer BF 1   154   —   e  is transferred to segment shape determination unit  155   —   e . Segment shape determination unit  155   —   e  generates segment shape data signal SSDS based on segment shape sample data SSSD. 
     Distance data signal DDS[t 1 ] and distance data signal DDS[t 2 ] is transferred to comparison unit  158   —   e  to compare distance information corresponding to each pixel. Comparison unit  158   —   e  calculates a difference in the distance information corresponding to each pixel to generate a comparison signal CS. Comparison unit  158   —   e  transfers comparison signal CS to action determination unit  159   —   e . Action determination unit  159   —   e  determines whether the difference in the distance information corresponding to each pixel exceeds a threshold to generate action determination signal ADS. Action determination signal ADS may include information regarding whether there is an action in each corresponding cell. Action determination signal ADS comprises information used to classify a cell including the action and a cell including no action. 
     Action determination signal ADS is transferred to view angle control unit  151   —   e  and focus control unit  153   —   e . View angle control unit  151   —   e  generates view angle control signal VACS using action determination signal ADS in such a way that sensing unit  130   —   e  may control a view angle in accordance with a size and location of a part including the action. Focus control unit  153   —   e  generates focus control signal FCS in such a way that sensing unit  130   —   e  controls a focus in accordance with a distance of the part including the action. Thus, data regarding a part including many actions may be more concretely collected. 
       FIG. 11  is a block diagram of a ToF sensor system  160  using ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  of  FIG. 1 ,  5 ,  6 , or  8 , according to an embodiment of the inventive concept. ToF sensor system  160  may be, for instance, a ToF camera. 
     Referring to  FIG. 11 , ToF sensor system  160  comprises a processor  161  coupled to the ToF sensors  100 ,  100   —   a ,  100   —   c , and  100   —   d . ToF sensor system  160  may include an individual integrated circuit or, processor  161  and ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  may be disposed on the same integrated circuit. Processor  161  may be a microprocessor, an image processor, or any of other types of control circuits such as an application-specific integrated circuit (ASIC). Processor  161  comprises an image sensor control unit  162 , an image signal processing unit  163 , and an interface unit  164 . Image sensor control unit  162  outputs a control signal to ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d . Image signal processing unit  163  receives image data including distance information output from ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  and performs signal processing on the image data. Interface unit  164  transfers the image data on which signal processing is performed to a display  165  to reproduce the image data. 
     ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  comprises a plurality of pixels, and it obtains the distance information from at least one of the pixels. ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  removes a pixel signal obtained from background light from the pixel signal obtained from modulation light and the background light. ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  generates a distance image by calculating the distance information of a corresponding pixel based on the pixel signal from which the pixel signal obtained from the background light is removed. ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  may generate a distance image of a target by combining the distance information of the pixels. 
       FIG. 12  is a block diagram of a computing system  180  comprising ToF sensor system  160  of  FIG. 11 . 
     Referring to  FIG. 12 , computing system  180  comprises ToF sensor system  160 , a central processing unit  181 , a memory  182 , and an I/O device  183 . Computing system  180  further comprises a floppy disk drive  184  and a CD ROM drive  185 . Computing system  180  is connected to central processing unit  181 , memory  182 , I/O device  183 , floppy disk drive  184 , CD ROM drive  185 , and ToF sensor system  160  via a system bus  186 . Data provided through I/O device  183  or ToF sensor system  160  or processed by central processing unit  181  is stored in memory  182 . Memory  182  may be configured as a RAM. Memory  182  may be configured as a memory card including a non-volatile memory device like a NAND flash memory. 
     ToF sensor system  160  includes ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  and processor  161  for controlling ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d . ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  includes a plurality of pixels, and may obtain the distance information from at least one of the pixels. ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  removes a pixel signal obtained from background light from the pixel signal obtained from modulation light and the background light. ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  generates a distance image by calculating the distance information of a corresponding pixel based on the pixel signal from which the pixel signal obtained from the background light is removed. ToF sensor  100 ,  100   —   a ,  100   —   c , or  100   —   d  generates a distance image of a target by combining the distance information of the pixels. 
     The foregoing is illustrative of embodiments and is not to be construed as limiting thereof. Although a few embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the inventive concept. Accordingly, all such modifications are intended to be included within the scope of the inventive concept as defined in the claims.