Patent Publication Number: US-2023156362-A1

Title: Imaging system, endoscope, and control device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of International Application No. PCT/JP2020/027410, filed on Jul. 14, 2020, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an imaging system, an endoscope, and a control device that generate image data by imaging the inside of a subject. 
     2. Related Art 
     Hitherto, there is known a technology of driving an imaging element in an optimum state regardless of an individual difference between imaging elements or an individual difference between cables by adjusting a power supply voltage for driving the imaging element provided at a distal end portion of an insertion portion to be inserted into a subject to an appropriate value according to the imaging element in an endoscope (for example, see JP 6397603 B2). With this technology, an A/D conversion circuit provided inside the imaging element measures the power supply voltage supplied from a control device to the imaging element via a signal line, and outputs the power supply voltage measurement result to the control device. The control device compares the power supply voltage measurement result input from the imaging element via the signal line with an optimum value, and adjusts a value of the power supply voltage to be output to the imaging element in such a way that the value of the power supply voltage approaches the optimum value. 
     SUMMARY 
     In some embodiments, an imaging system includes: an imaging unit configured to generate a video signal by imaging a subject; a control device configured to control the imaging unit; a first signal line configured to transmit a predetermined power supply voltage to the imaging unit; and a second signal line configured to transmit the video signal to the  284  control device. The imaging unit includes an imaging element including a pixel portion configured to generate the video signal according to a light reception amount and output the generated video signal to the second signal line, and a first detector configured to detect a voltage value of a power supply voltage that has reached the imaging unit via the first signal line as a voltage value of a first power supply voltage and output the voltage value to the second signal line, and the control device includes: a power source configured to supply a voltage value of a second power supply voltage to the imaging element via the first signal line; a second detector configured to detect a current value in the first signal line; a third detector configured to detect the voltage value of the second power supply voltage supplied by the power source; a calculator configured to calculate a resistance value of the first signal line based on the voltage value of the first power supply voltage, the current value, and a voltage detection value of the second power supply voltage detected by the third detector; and a power source controller configured to adjust the voltage value of the second power supply voltage to be supplied to the imaging element by the power source based on the current value, the resistance value, and a voltage value of a target power supply voltage in the imaging element, and supply the adjusted second power supply voltage to the first signal line. 
     In some embodiments, an endoscope includes: an imaging unit configured to generate a video signal by imaging a subject; a connector that is connectable to a control device; a first signal line configured to transmit a predetermined power supply voltage to the imaging unit; and a second signal line configured to transmit the video signal to the control device. The imaging unit includes an imaging element including a pixel portion configured to generate the video signal according to a light reception amount and output the generated video signal to the second signal line, and a first detector configured to detect a voltage value of a power supply voltage that has reached the imaging unit via the first signal line as a voltage value of a first power supply voltage and output the voltage value to the second signal line, and the connector includes: a power source configured to supply a second power supply voltage to the imaging element via the first signal line; a second detector configured to detect a current value in the first signal line; a calculator configured to calculate a resistance value of the first signal line based on the voltage value of the first power supply voltage, the current value, and a voltage detection value of the second power supply voltage; and a power source controller configured to adjust the voltage value of the second power supply voltage to be supplied to the imaging element by the power source based on the current value, the resistance value, and a voltage value of a target power supply voltage which is an optimum value of the power supply voltage in the imaging element, and supply the adjusted second power supply voltage to the first signal line. 
     In some embodiments, provided is a control device electrically connectable to an imaging unit configured to generate a video signal by imaging a subject by using a first signal line configured to transmit a predetermined power supply voltage to the imaging unit and a second signal line configured to transmit the video signal. The control device includes: a power source configured to supply a second power supply voltage to the imaging unit via the first signal line; a second detector configured to detect a current value in the first signal line; a third detector configured to detect a voltage value of the second power supply voltage; a calculator configured to calculate a resistance value of the first signal line based on a voltage value of a first power supply voltage that has reached the imaging unit via the first signal line and that is detected in the imaging unit, the current value, and a voltage detection value of the second power supply voltage detected by the third detector; and a power source controller configured to adjust the voltage value of the second power supply voltage to be supplied to the imaging unit by the power source based on the current value, the resistance value, and a voltage value of a target power supply voltage which is an optimum value of the power supply voltage in the imaging unit, and supply the adjusted second power supply voltage to the first signal line. 
     The above and other features, advantages and technical and industrial significance of this disclosure will be better understood by reading the following detailed description of presently preferred embodiments of the disclosure, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram schematically illustrating an overall configuration of an endoscope system according to a first embodiment; 
         FIG.  2    is a block diagram illustrating a functional configuration of main parts of an endoscope and a control device in the endoscope system according to the first embodiment; 
         FIG.  3    is a flowchart illustrating an outline of processing executed by the endoscope system according to the first embodiment; 
         FIG.  4    is a timing chart illustrating a relationship between a reaching voltage value, a vertical synchronization signal, a current value, and a resistance value of a transmission cable during processing executed by the endoscope system according to the first embodiment; 
         FIG.  5    is a block diagram illustrating a functional configuration of a main part of an endoscope and a control device in an endoscope system according to a second embodiment; 
         FIG.  6    is a flowchart illustrating an outline of processing executed by the endoscope system according to the second embodiment; and 
         FIG.  7    is a block diagram illustrating a functional configuration of a main part of an endoscope and a control device in an endoscope system according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an endoscope system including an imaging device will be described as a mode for carrying out the present disclosure (hereinafter, referred to as “embodiment”), but the present disclosure is not limited thereto, and for example, an in-vehicle camera, a surgical microscope, a machine vision camera, and a monitoring camera including an imaging device can also be applied. Further, the disclosure is not limited by these embodiments. Further, in the description of the drawings, the same reference signs denote the same parts. Furthermore, it should be noted that the drawings are schematic, and a relationship between a thickness and a width of each member, a ratio of each member, and the like are different from actual ones. Further, the drawings include portions having different dimensions and ratios. 
     First Embodiment 
     Configuration of Endoscope System 
       FIG.  1    is a diagram schematically illustrating an overall configuration of an endoscope system according to a first embodiment. An endoscope system  1  illustrated in  FIG.  1    images the inside of a subject such as a patient by inserting an insertion portion of an endoscope into the subject, and displays a display image based on a video signal obtained by the imaging on a display device. A user such as a doctor observes the display image displayed on the display device. The endoscope system  1  includes an endoscope  2 , a light source device  3 , a display device  4 , and a control device  5 . 
     Configuration of Endoscope 
     First, a configuration of the endoscope  2  will be described. 
     The endoscope  2  generates a video signal (raw data) obtained by imaging the inside of a body of a subject, and outputs the generated video signal to the control device  5 . The endoscope  2  includes an insertion portion  21 , an operating unit  22 , and a universal cord  23 . 
     The insertion portion  21  is inserted into the subject. The insertion portion  21  has an elongated shape having flexibility. The insertion portion  21  includes a distal end portion  24  incorporating an imaging device  100  to be described later, a bendable bending portion  25  including a plurality of bending pieces, and an elongated flexible tube portion  26  connected to a proximal end side of the bending portion  25  and having flexibility. 
     The distal end portion  24  is implemented using glass fiber or the like. The distal end portion  24  includes a light guide (not illustrated) forming a light guide path for illumination light supplied from the light source device  3 , an illumination optical system provided at a distal end of the light guide, and the imaging device  100  to be described later. 
     The operating unit  22  includes a bending knob  221  that bends the bending portion  25  in a vertical direction and a horizontal direction, a treatment tool insertion portion  222  that inserts a treatment tool such as a biopsy forceps, a laser scalpel, or an inspection probe into a body cavity, and a plurality of switches  223  that are operation input units that input an operation instruction signal for a peripheral device such as an air supply unit, a water supply unit, or a gas supply unit in addition to the light source device  3  and the control device  5  or a pre-freeze signal that instructs the imaging device  100  to capture a still image. The treatment tool inserted from the treatment tool insertion portion  222  comes out from an aperture (not illustrated) via a treatment tool channel (not illustrated) of the distal end portion  24 . 
     The universal cord  23  incorporates at least a light guide and a cable assembly including one or more cables. The cable assembly is a signal line for transmitting and receiving signals between the endoscope  2  and the light source device  3 , and the control device  5 , and includes a signal line for transmitting and receiving a captured image (image data), a signal line for transmitting and receiving a timing signal for driving the imaging device  100  (a synchronization signal and a clock signal), a signal line for supplying power to the imaging device  100 , and the like. The universal cord  23  includes a connector  27  detachable from the light source device  3 . A coil-shaped coil cable  27   a  extends in the connector  27 , and a connector  28  detachably attached to the control device  5  at an extending end of the coil cable  27   a  is provided. 
     Configuration of Light Source Device 
     Next, a configuration of the light source device  3  will be described. 
     The light source device  3  supplies the illumination light for the endoscope  2  to irradiate the subject under the control of the control device  5 . The light source device  3  is implemented by using, for example, a halogen lamp, a laser diode (LD), a white light emitting diode (LED), and the like. The light source device  3  supplies the illumination light to the distal end portion  24  of the insertion portion  21  via the connector  27 , the universal cord  23 , and the insertion portion  21 . Here, the illumination light is either white light or special light (for example, narrow band imaging (NBI) or infrared light). 
     Configuration of Display Device 
     Next, a configuration of the display device  4  will be described. 
     The display device  4  displays the display image based on an imaging signal input from the control device  5  under the control of the control device  5 . The display device  4  is implemented by using a display panel such as organic electro luminescence (EL) or liquid crystal. 
     Configuration of Control Device 
     Next, a configuration of the control device  5  will be described. 
     The control device  5  controls each unit of the endoscope system  1 . The control device  5  performs various types of image processing on the video signal input from the endoscope  2  and outputs the video signal to the display device  4 . In addition, the control device  5  controls the light source device  3  to supply the illumination light to the endoscope  2 . 
     Main Part of Endoscope System 
     Next, a configuration of main parts of the endoscope  2   and the control device  5  described above will be described.  FIG.  2    is a block diagram illustrating a functional configuration of main parts of the endoscope  2  and the control device  5  in the endoscope system  1 . 
     Main Part of Endoscope 
     First, a functional configuration of the main part of the endoscope  2  will be described. 
     The endoscope  2  includes the imaging device  100 , a transmission cable  200  incorporated in the universal cord  23 , and the connector  28 . 
     First, the imaging device  100  will be described. 
     The imaging device  100  is arranged at the distal end portion  24  of the endoscope  2 , generates the video signal (raw data) by imaging the inside of the subject, and outputs the video signal to the control device  5  via the transmission cable  200  of the universal cord  23  and the connector  28 . The imaging device  100  includes an optical system  110  and an imaging element  120 . 
     The optical system  110  condenses reflected light of the illumination light reflected by the subject to form a subject image on a light receiving surface of the imaging element  120 . The optical system  110  is implemented by using one or more lenses and the like. 
     The imaging element  120  receives the subject image formed by the optical system  110 , generates a pixel signal by performing photoelectric conversion, and generates a digital video signal (raw data) by performing A/D conversion processing, signal processing, and the like on the pixel signal. Then, the imaging element  120  outputs the video signal to the connector  28  via the transmission cable  200 . The imaging element  120  is implemented by using an image sensor such as a complementary metal oxide semiconductor (CMOS) image sensor or a charge coupled device (CCD) image sensor. The imaging element  120  includes a pixel portion  121 , an A/D converter  122 , a signal processor  123 , a memory  124 , and an imaging controller  125 . 
     The pixel portion  121  includes a plurality of pixels arranged in a two-dimensional matrix. The pixel portion  121  is implemented by using a photoelectric conversion element (photodiode) or the like. The pixel portion  121  outputs a pixel signal of each pixel to the A/D converter  122  under the control of the imaging controller  125 . Furthermore, the pixel portion  121  is driven according to a power supply voltage input from the control device  5  via the transmission cable  200 . 
     Under the control of the imaging controller  125 , the A/D converter  122  performs A/D conversion processing on the pixel signal input from the pixel portion  121  based on a reference voltage V ref  transmitted from a control unit  57  of the control device  5  via the transmission cable  200  to be described later, and outputs the pixel signal to the signal processor  123 . The reference voltage V ref  can also be generated inside the imaging element  120  based on any of power supply voltages VDD1 to VDD3. Furthermore, under the control of the imaging controller  125 , the A/D converter  122  performs A/D conversion on a voltage value of a first power supply voltage that has reached the imaging element  120  via the transmission cable  200  and is to be transmitted to the control unit  57  of the control device  5  to be described later as being detected in the imaging element  120  (hereinafter, simply referred to as “reaching voltage value V cis ”), and outputs a result of the A/D conversion to the signal processor  123 . Specifically, under the control of the imaging controller  125 , the A/D converter  122  outputs a result of performing A/D conversion on the reaching voltage value V cis to the signal processor  123  in a current consumption fluctuation period between a blanking period of the imaging element  120  and a pixel reading period. The A/D converter  122  is electrically connected to each of a signal line  201 , a signal line  202 , and a signal line  203  of the transmission cable  200  described later. The A/D converter  122  is implemented by using an A/D conversion circuit or the like. 
     Under the control of the imaging controller  125 , the signal processor  123  performs various types of signal processing on the digital pixel signal input from the A/D converter  122  to generate the digital video signal, and outputs the video signal to the transmission cable  200 . Here, the various types of signal processing include noise reduction processing, amplification processing, and the like. In addition, the signal processor  123  outputs the reaching voltage value V cis input from the A/D converter  122  to the transmission cable  200  under the control of the imaging controller  125 . The signal processor  123  is implemented using a noise reduction circuit, an output amplifier circuit, and the like. 
     The memory  124  is implemented by using a read only memory (ROM), a random access memory (RAM), or the like, and records various types of information regarding the imaging element  120 . The memory  124  records various programs to be executed by the imaging element  120 , data being processed, identification information for identifying the imaging element  120 , performance information (a drive voltage and a drive current) of the imaging element  120 , defective pixel information such as a black defect and white defect in the pixel portion  121 , and the like. 
     The imaging controller  125  controls operation of each unit included in the imaging element  120  according to a control signal input from the control device  5  via the transmission cable  200 . Here, the control signal includes, for example, a synchronization signal (a vertical synchronization signal or a horizontal synchronization signal), a clock signal, a mode signal for instructing the operation of the imaging element  120 , and the like. The imaging controller  125  outputs a pixel signal from each pixel of a predetermined read line in the pixel portion  121  to the A/D converter  122  according to the control signal input from the control device  5  via the transmission cable  200 . The imaging controller  125  includes a timing generator (TG), a vertical scanning circuit, a horizontal scanning circuit, and the like. 
     Next, the transmission cable  200  will be described. 
     The transmission cable  200  is implemented by using a plurality of signal lines. Specifically, the transmission cable  200  includes at least the signal line  201 , the signal line  202 , the signal line  203 , a signal line  204 , a signal line  205 , and a signal line  206 . The signal line  201  transmits the power supply voltage VDD1 input from the control device  5  to the imaging element  120 . The signal line  202  transmits the power supply voltage VDD2 input from the control device  5  to the imaging element  120 . The signal line  203  transmits the power supply voltage VDD3 input from the control device  5  to the imaging element  120 . The signal line  204  transmits, to the imaging element  120 , the control signal input from the control device  5 , and transmits, to the control device  5 , the reaching voltage values of the power supply voltages VDD1 to VDD3 that are input from the imaging element  120  and have reached the imaging element  120 . The signal line  205  transmits a video signal V out  input from the imaging element  120  to the connector  28 . The signal line  206  transmits the reference voltage V ref  input from the control unit  57  of the control device  5  to the imaging element  120 . 
     Next, the connector  28  will be described. 
     The connector  28  is detachably connected to the control device  5 . The connector  28  includes at least an analog front end unit  281  (hereinafter, referred to as an “AFE unit  281 ”) and a signal processor  282 . 
     The AFE unit  281  performs processing such as noise removal on the video signal V out  transmitted from the signal line  205  or the reaching voltage value V cis , and outputs the video signal V out  or the reaching voltage value V cis  to the signal processor  282 . 
     The signal processor  282  performs predetermined signal processing, such as format conversion processing, gain-up processing, or D/A conversion processing, on the video signal V out  or the reaching voltage value V cis  input from the AFE unit  281 , and outputs the video signal V out  or the reaching voltage value V cis  to the control device  5 . 
     Main Part of Control Device 
     Next, the main part of the control device  5  will be described. 
     The control device  5  includes a power source  51 , a current detector  52 , a voltage detector  53 , a power source controller  54 , an image processor  55 , a memory  56 , and the control unit  57 . 
     Under the control of the power source controller  54 , the power source  51  adjusts a power supply voltage input from an external power supply to the plurality of power supply voltages VDD1 to VDD3, and outputs the power supply voltages VDD1 to VDD3 to the transmission cable  200  (the signal lines  201  to  203 ). The power source  51  is implemented by using, for example, a smoothing circuit, a rectifier circuit, a transformer, or the like. Hereinafter, the voltage value of the power supply voltage VDD1 supplied from the power source  51  to the signal line  201  will be described as a voltage value V out1  of a second power supply voltage. Hereinafter, the power supply voltage VDD1 output from the power source  51  to the signal line  201  will be described. Although the voltage value of the power supply voltage VDD2 and the voltage value of the power supply voltage VDD3 output to the signal line  202  and the signal line  203 , respectively, are described as a voltage value V out2  of the second power supply voltage and a voltage value V out3  of the second power supply voltage, respectively, in a case where any one of the voltage value V out1  the voltage value V out2 , and the voltage value V out3  of the second power supply voltage is referred to, it is simply described as the voltage value V out . 
     The current detector  52  is electrically connected to each of the signal lines  201  to  203 . The current detector  52  detects a current value of each of the signal lines  201  to  203  and outputs the detection result to the control unit  57 . The current detector  52  is implemented by using an ammeter or the like. 
     The voltage detector  53  is electrically connected to each of the signal lines  201  to  203 . The voltage detector  53  detects the voltage value V out  of each of the signal lines  201  to  203  and outputs the detection result to the control unit  57  as the voltage detection value V mon . The voltage detector  53  is implemented by using a voltmeter or the like. 
     Under the control of the control unit  57 , the power source controller  54  adjusts the voltage values of the plurality of power supply voltages output from the power source  51  to predetermined voltage values and outputs the voltage values to the power source  51 . The power source controller  54  is implemented by using a memory and hardware such as a central processing unit (CPU). 
     The image processor  55  performs various types of image processing on the video signal input from the signal processor  282  of the connector  28 , and outputs the video signal to the display device  4 . Here, the various types of image processing include demosaic processing, white balance adjustment processing, γcorrection processing, and the like. The image processor  55  is implemented by using a memory and hardware such as a field programmable gate array (FPGA) or a graphics processing unit (GPU). 
     The memory  56  records various types of information regarding the control device  5 , image data corresponding to the video signal, data being processed, and the like. The memory  56  further includes a program recording unit  581  that records various programs to be executed by the control device  5 . The memory  56  is implemented by using a volatile memory, a nonvolatile memory, or the like. The memory  56  may be implemented by using a memory card or the like that is detachable from the outside. 
     The control unit  57  controls each unit included in the endoscope system  1 . The control unit  57  is implemented by using a memory and hardware such as a central processing unit (CPU) or an FPGA. The control unit  57  includes a calculator  571 . 
     The calculator  571  calculates a resistance value R of the signal line  201  of the transmission cable  200  based on the reaching voltage value V cis  input from the imaging element  120 , a current value I input from the current detector  52 , and the voltage detection value V mon . In addition, the calculator  571  calculates the resistance value R of the signal line  201  of the transmission cable  200  a plurality of times in a predetermined period, and calculates an average value of the plurality of calculation results as the resistance value R of the signal line  201  of the transmission cable  200 . Specifically, the calculator  571  calculates the resistance value R of the signal line  201  of the transmission cable  200  based on the reaching voltage value V cis  input from the imaging element  120  and the current value I input from the current detector  52  for each blinking period of the imaging element  120  based on a vertical synchronization signal V D  input from the control unit  57 . Similarly to the signal line  201 , the calculator  571  calculates a resistance value of each of the signal line  202  and the signal line  203  of the transmission cable  200 , but a detailed description thereof is omitted in order to simplify the description. 
     Processing in Endoscope System 
     Next, processing executed by the endoscope system  1  will be described.  FIG.  3    is a flowchart illustrating an outline of processing executed by the control device  5 .  FIG.  4    is a timing chart illustrating a relationship between the reaching voltage value V cis , the vertical synchronization signal V D , the current value I, and the resistance value R of the transmission cable  200  at the time of processing executed by the endoscope system  1 . In  FIG.  4   , (a) from the top illustrates the reaching voltage value V cis , (b) illustrates the vertical synchronization signal V D , (c) illustrates the current value I, and (d) illustrates the voltage value V out  of the power supply voltage supplied to the imaging element by the power source  51 . In  FIG.  4   , the current value I and the resistance value R in the signal line  201  of the transmission cable  200  are described. However, since similar processing is executed in the other signal lines  202  and  203 , a detailed description is omitted. 
     As illustrated in  FIG.  3   , first, under the control of the imaging controller  125 , the A/D converter  122  detects the power supply voltage VDD1 supplied from the control device  5  via the signal line  201  of the transmission cable  200  as the reaching voltage value V cis  that has reached the imaging element  120  (Step S 101 ). In this case, as illustrated in  FIG.  4   , the A/D converter  122  adds an elapsed time (for example, times t1, t2, t3, and t4) elapsed from the vertical synchronization signal V D  as time information and outputs the time information and the reaching voltage value V cis  to the signal processor  123   every time the reaching voltage value V cis  (P 1 , P 2 , P 3 , and P 4 ) is detected at a predetermined interval under the control of the imaging controller  125 . At this time, under the control of the imaging controller  125 , the signal processor  123  outputs the time information and the reaching voltage value V cis  to the control device  5  via the signal line  201  of the transmission cable  200  every time the reaching voltage value V cis  and the time information are input from the A/D converter  122 . 
     Subsequently, the current detector  52  detects the current value I of the signal line  201  of the transmission cable  200  (Step S 102 ). Specifically, as illustrated in  FIG.  4   , the current detector  52  detects the current value I of the current flowing through the signal line  201  at predetermined intervals under the control of the control unit  57 , and outputs the detection result to the control unit  57 . In this case, every time the current value I (P 11 , P 12 , P 13 , and P 14 ) is detected, the current detector  52  adds an elapsed time (for example, times t1, t2, t3, and t4) elapsed from the vertical synchronization signal V D  as the time information and outputs the current value I and the time information to the control unit  57 . 
     Thereafter, the control unit  57  determines whether or not one imaging frame of the imaging element  120  has ended based on the vertical synchronization signal V D  supplied to the imaging element  120  (Step S 103 ). In a case where the control unit  57  determines that one imaging frame of the imaging element  120  has ended (Step S 103 : Yes), the endoscope system  1  proceeds to Step S 104  to be described later. On the other hand, in a case where the control unit  57  determines that one imaging frame of the imaging element  120  has not ended (Step S 103 : No), the endoscope system  1  returns to Step S 101  described above. 
     Next, the calculator  571  calculates the resistance value of the signal line  201  of the transmission cable  200  based on the reaching voltage value V cis  input from the imaging element  120 , the current value I input from the current detector  52 , and the voltage detection value V mon  (Step S 104 ). Specifically, assuming that the resistance value of the signal line  201  is R, the reaching voltage value is V cis , the current value flowing through the signal line  201  is I, and the voltage detection value of the power supply voltage supplied by the power source  51  and detected by the voltage detector  53  is V mon , the resistance value R of the signal line  201  is calculated based on the following Equation (1). 
     
       
         
           
             R =  
             
               
                 
                   
                     
                       V 
                       
                         mon 
                       
                     
                     − 
                     
                       V 
                       
                         cis 
                       
                     
                   
                 
               
               / 
               I 
             
           
         
       
     
     In addition, the calculator  571  calculates the resistance value R of the signal line  201  based on the reaching voltage value V cis  and the current value I at the same time recorded in the memory  56 . In this case, the calculator  571  calculates the resistance value R of the signal line  201  a plurality of times for each same time based on the reaching voltage value V cis  and the current value I at the same time recorded in the memory  56 , and calculates the average value of the plurality of calculation results as the resistance value of the signal line  201 . 
     Thereafter, under the control of the control unit  57 , the power source controller  54  adjusts the power supply voltage to be supplied from the power source  51  to the imaging element  120  and outputs the adjusted power supply voltage (Step S 105 ). Specifically, in a case where a voltage value of the power supply voltage VDD1, which is the second power supply voltage, is V out , and a voltage value of a target power supply voltage, which is an optimum value of the power supply voltage in the imaging element  120 , is V target , the power source controller  54  adjusts the power supply voltage to be supplied to the imaging element  120  by the power source  51  by using the following Equation (2) and outputs the adjusted power supply voltage. 
     
       
         
           
             
               V 
               
                 out 
               
             
             = 
             
               
                 RI + V 
               
               
                 target 
               
             
           
         
       
     
     In this case, as indicated by an arrow A1in  FIG.  4   , the power source controller  54  outputs the voltage value V out  of the power supply voltage VDD1, which is the second power supply voltage adjusted in the previous frame of the imaging element  120 , in the next frame of the imaging element  120  based on the vertical synchronization signal V D . 
     Subsequently, in a case where an instruction signal for ending inspection of the subject is input (Step S 106 : Yes), the endoscope system  1  ends the processing. On the other hand, in a case where the instruction signal for ending the inspection of the subject is not input (Step S 106 : No), the endoscope system  1  returns to Step S 101  described above. 
     According to the first embodiment described above, the power source controller  54  adjusts the voltage value V out  of the power supply voltage VDD1 to be supplied from the power source  51  to the imaging element  120  based on the current value detected by the current detector  52 , the reaching voltage value V cis  calculated by the control unit  57 , the voltage value V target  of the target power supply voltage, and the voltage detection value V mon  of the second power supply voltage, and supplies the adjusted voltage value of the power supply voltage VDD1 to the signal line  201  of the transmission cable  200 . Therefore, it is possible to operate the imaging element  120  at an appropriate power supply voltage while preventing a diameter of the signal line  201  from being increased while maintaining a transmission rate. As a result, a diameter of a power supply line connecting the control device  5  and the imaging element  120  can be decreased, and an optimum power supply voltage can be supplied, so that heat generated by the power supply voltage can be minimized to suppress an influence on a body tissue. 
     Furthermore, according to the first embodiment, since the A/D converter  122  provided in the imaging element  120  detects the reaching voltage value V cis , and it is not necessary to separately provide a detection circuit for detecting the voltage value in the imaging element  120 , it is possible to prevent an increase in size of the imaging element  120 . 
     In addition, according to the first embodiment, since the control unit  57  calculates the resistance value of the signal line  201  for each detection based on the time information at the time of detection of each of the reaching voltage value V cis  and the current value I, and the reaching voltage value V cis  and the current value I at the same time, it is possible to accurately calculate the resistance value R of the signal line  201 . 
     In addition, according to the first embodiment, since the time information at the time of the detection of the reaching voltage value V cis  by the A/D converter  122  based on the vertical synchronization signal V D  is output to the signal line  205  of the transmission cable  200 , the control unit  57  can accurately calculate the resistance value R of the signal line  201 . 
     In addition, according to the first embodiment, since the control unit  57  calculates the resistance value of the signal line  201  of the transmission cable  200  a plurality of times in a predetermined period, and calculates the average value of the plurality of calculation results as the resistance value of the signal line  201 , it is possible to accurately calculate the resistance value R of the signal line  201 . 
     Furthermore, according to the first embodiment, the A/D converter  122  detects the reaching voltage value V cis  for each blanking period of the imaging element  120 , and the control unit  57  calculates the resistance value R of the signal line  201  of the transmission cable  200  based on the reaching voltage value V cis  and the current value I detected by the current detector  52  for each blanking period. After the resistance value is once calculated, the optimum power supply voltage can be output following the current value detected based on Equation (2). 
     Second Embodiment 
     Next, a second embodiment will be described. An endoscope system according to the second embodiment is different from the endoscope  2  according to the first embodiment described above in terms of a configuration and a procedure to be executed. Hereinafter, the configuration of the endoscope system according to the second embodiment will be described, and then processing executed by the endoscope system will be described. Note that the same components as those of the endoscope system  1  according to the first embodiment described above are denoted by the same reference signs, and a detailed description thereof will be omitted. 
     Configuration of Endoscope System 
       FIG.  5    is a block diagram illustrating a functional configuration of main parts of an endoscope and a control device in the endoscope system according to the second embodiment. An endoscope system  1 A illustrated in  FIG.  5    includes an endoscope  2 A and a control device  5 A instead of the endoscope  2  according to the first embodiment described above. 
     Configuration of Endoscope 
     As illustrated in  FIG.  5   , the endoscope  2 A includes an imaging element  120 A instead of the imaging element  120  according to the above-described first embodiment in the endoscope  2  according to the above-described first embodiment. The imaging element  120 A includes an imaging controller  125 A, a constant current source  126 , and a switch  127  in addition to the configuration according to the first embodiment described above. 
     The constant current source  126  is electrically connected to each of signal lines  201  to  203  of a transmission cable  200 A. Under the control of the imaging controller  125 A, the constant current source  126  implements power supply voltages VDD1 to VDD3 supplied from the control device  5 A via the signal lines  201  to  203  of the transmission cable  200 A, and the constant current source  126  is implemented using a regulator or the like. Note that the constant current source  126  is grounded via a signal line  207  and the control device  5 A. The constant current source  126  can adjust a current value flowing through the signal lines  201  to  203 . Here, in a case where a current value at a timing when a resistance value is calculated is I mon  and a current value flowing at a timing when a voltage is adjusted is I, the following relationship holds. 
     
       
         
           
             
               V 
               
                 out 
               
             
             = 
             
               
                 
                   
                     
                       V 
                       
                         mon 
                       
                     
                     − 
                     
                       V 
                       
                         cis 
                       
                     
                   
                 
               
               / 
               
                 
                   I 
                   
                     mon 
                   
                 
                 × 
                   
                 I 
               
             
           
         
       
     
     Furthermore, an output voltage V out  has the following output due to an error α of the voltage detector or the AD converter of the imaging element. 
     
       
         
           
             
               V 
               
                 out 
               
             
             = 
             
               
                 
                   
                     
                       V 
                       
                         mon 
                       
                     
                     − 
                     
                       V 
                       
                         cis 
                       
                     
                   
                 
               
               / 
               
                 
                   I 
                   
                     mon 
                   
                 
                 × 
                 I + 
                 
                   α 
                   / 
                   
                     
                       I 
                       
                         mon 
                       
                     
                     × 
                     I 
                   
                 
               
             
           
         
       
     
     Therefore, in a case where the current value of I mon  is small, the influence of the error increases, so that the current value I mon  at the timing of resistance calculation can be increased using the constant current source  126  to increase the accuracy of DC resistance value calculation. 
     One end of the switch  127  is electrically connected to each of the signal lines  201  to  203  of the transmission cable  200 A, and the other end is electrically connected to the constant current source  126 . The switch  127  electrically connects each of the signal lines  201  to  203  of the transmission cable  200 A and the constant current source  126  under the control of the imaging controller  125 A. The switch  127  is implemented by using a switch, a semiconductor switch, or the like. 
     The imaging controller  125 A controls the switch  127  based on a control signal input from a control unit  57 A of the control device  5 A via a signal line  204  of the transmission cable  200 A. Specifically, in a calculation period in which the control unit  57 A calculates a resistance value R of the signal line  201  of the transmission cable  200 A, the imaging controller  125 A stops operation of units other than an A/D converter  122  and a signal processor  123  among units included in the imaging element  120 A. Furthermore, the imaging controller  125 A drives the switch  127  under the control of the control unit  57 A. Specifically, in a case where a determination signal of a determination result indicating that the current value detected by the current detector  52  is equal to or less than a predetermined threshold is input from a determination portion  572  of the control unit  57 A to be described later, the imaging controller  125 A electrically connects the constant current source  126  and the signal line  201  to the switch  127 . 
     Configuration of Control Device 
     Next, a configuration of the control device  5 A will be described. The control device  5 A includes the control unit  57 A instead of the control unit  57  according to the first embodiment described above. The control unit  57 A further includes the determination portion  572  in addition to the configuration of the control unit  57  according to the above-described first embodiment. 
     The determination portion  572  determines whether or not the current value calculated by the calculator  571  is equal to or less than a predetermined threshold. 
     Processing in Endoscope System 
     Next, processing executed by the endoscope system  1 A will be described.  FIG.  6    is a flowchart illustrating an outline of processing executed by the endoscope system  1 A. 
     As illustrated in  FIG.  6   , first, in a calculation period in which the control unit  57 A calculates the resistance value R of the signal line  201  of the transmission cable  200 A, the imaging controller  125 A stops operation of units other than the A/D converter  122  and the signal processor  123  among the units included in the imaging element  120 A (Step S 201 ). 
     Steps S 202  and S 203  correspond to Steps S 101  and S 102  described above, respectively. 
     In Step S 204 , the control unit  57 A determines whether or not the current value I of the current flowing through the signal line  201  of the transmission cable  200 A, detected by the current detector  52  is equal to or less than a predetermined threshold. In a case where the control unit  57 A determines that the current value I of the current flowing through the signal line  201  of the transmission cable  200 A, detected by the current detector  52  is equal to or less than the predetermined threshold (Step S 204 : Yes), the endoscope system  1 A proceeds to Step S 205  described later. On the other hand, in a case where the control unit  57 A determines that the current value I of the current flowing through the signal line  201  of the transmission cable  200 A, detected by the current detector  52  is not equal to or less than the predetermined threshold (Step S 204 : No), the endoscope system  1 A proceeds to Step S 206  described later. 
     In Step S 205 , the imaging controller  125 A electrically connects the constant current source  126  and the signal line  201  of the transmission cable  200 A to the switch  127 . After Step S 205 , the endoscope system  1 A proceeds to Step S 206  described later. 
     Steps S 206  to S 209  correspond to Steps S 103  to S 106  described above, respectively. After Step S 209 , the endoscope system  1 A ends the processing. 
     According to the second embodiment described above, in the calculation period in which the control unit  57 A calculates the resistance value R of the signal line  201  of the transmission cable  200 A, the imaging controller  125 A stops operation of units other than the A/D converter  122  and the signal processor  123  among the units included in the imaging element  120 A, so that the accurate resistance value R of the signal line  201  can be calculated. 
     In addition, according to the second embodiment, in a case where the control unit  57 A determines that the current value I of the current flowing through the signal line  201  of the transmission cable  200 A, detected by the current detector  52  is equal to or less than the predetermined threshold, the imaging controller  125 A electrically connects the constant current source  126  and the signal line  201  of the transmission cable  200 A to the switch  127 . Therefore, it is possible to increase the current value I mon  at the timing of resistance calculation by using the current source to increase the accuracy of DC resistance value calculation. Furthermore, noise generated in the A/D converter  122  can be reduced, and variation in current consumption can be suppressed. 
     Third Embodiment 
     Next, a third embodiment will be described. An endoscope system according to the third embodiment is different from the endoscope system  1  according to the first embodiment described above in terms of a configuration. Hereinafter, a configuration of the endoscope system according to the third embodiment will be described. Note that the same components as those of the endoscope system  1  according to the first embodiment described above are denoted by the same reference signs, and a detailed description thereof will be omitted. 
     Functional Configuration of Main Part of Endoscope System 
       FIG.  7    is a block diagram illustrating a functional configuration of a main part of an endoscope and a control device in the endoscope system according to the third embodiment. An endoscope system  1 B illustrated in  FIG.  7    includes an endoscope  2 B and a control device  5 B instead of the endoscope  2  and the control device  5  according to the first embodiment described above. 
     Configuration of Endoscope 
     First, a configuration of the endoscope  2 B will be described. The endoscope  2 B includes a connector  28 B  instead of the connector  28  according to the above-described first embodiment. The connector  28 B includes a power generation unit  283 , a current detector  284 , and a voltage detector  285  in addition to the configuration of the connector  28  according to the first embodiment described above. 
     Under the control of a connector controller  286 , the power generation unit  283  generates a plurality of power supply voltages (power supply voltages VDD1 to VDD3) from a power supply voltage input from a power source  51  of the control device  5 B, and outputs the generated power supply voltages to a transmission cable  200  (signal lines  201  to  203 ). The power generation unit  283  is implemented by using, for example, a smoothing circuit, a rectifier circuit, a transformer, or the like. 
     The current detector  284  is electrically connected to each of the signal lines  201  to  203 . The current detector  284  detects a current value of each of the signal lines  201  to  203  and outputs the detection result to the connector controller  286 . The current detector  284  is implemented using an ammeter or the like. 
     The voltage detector  285  is electrically connected to each of the signal lines  201  to  203 . The voltage detector  285  detects a voltage value of each of the signal lines  201  to  203  and outputs the detection result to the connector controller  286 . The voltage detector  285  is implemented using a voltmeter or the like. 
     The connector controller  286  adjusts voltage values of the plurality of power supply voltages output from the power generation unit  283  to predetermined voltage values and outputs the voltage values to the power generation unit  283 . The connector controller  286  is implemented by using a memory or hardware such as an FPGA. A calculator  286   a  is provided. The calculator  286   a  has the same function as the calculator  571  described above. 
     Main Part of Control Device 
     Next, a configuration of the control device  5 B will be described. 
     The control device  5 B does not include the current detector  52  and the voltage detector  53  in the configuration of the control device  5  according to the first embodiment described above. Furthermore, the control device  5 B includes a control unit  57 B instead of the control unit  57  according to the first embodiment described above. The control unit  57 B does not include the calculator  571  of the control unit  57  according to the first embodiment described above. 
     According to the third embodiment described above, the same effects as those of the first embodiment described above are obtained, and it is possible to perform an operation at an appropriate power supply voltage while preventing the diameter of the signal line  201  from being increased while maintaining the transmission rate. 
     In the third embodiment described above, the power generation unit  283 , the current detector  284 , the voltage detector  285 , and the connector controller  286  are provided in the connector  28 B. However, the present disclosure is not limited thereto, and for example, the power generation unit  283 , the current detector  284 , the voltage detector  285 , and the connector controller  286  may be provided in the operating unit  22 . 
     Other Embodiments 
     Various embodiments can be formed by appropriately combining a plurality of constituent elements disclosed in the endoscope systems according to the first to third embodiments of the present disclosure described above. For example, some constituent elements may be deleted from all the constituent elements described in the endoscope systems according to the embodiments of the present disclosure described above. Furthermore, the constituent elements described in the endoscope systems according to the embodiments of the present disclosure described above may be appropriately combined. 
     Furthermore, in the endoscope systems according to the first to third embodiments of the present disclosure, the “unit” or “portion” described above can be replaced with “means”, “circuit”, or the like. For example, the control unit can be replaced with control means or a control circuit. 
     Note that, in the description of the flowcharts in the present specification, the context of processing between steps is clearly indicated using expressions such as “first”, “thereafter”, and “subsequently”, but the order of processing necessary for implementing the disclosure is not uniquely determined by these expressions. That is, the order of processing in the flowcharts described in the present specification can be changed within a range without inconsistency. 
     Although some of the embodiments of the present application have been described in detail with reference to the drawings, these are merely examples, and the disclosure can be implemented in other forms in which various modifications and improvements have been made based on the knowledge of those skilled in the art, including the aspects described in the section of the present disclosure. 
     According to the disclosure, it is possible to perform an operation at an appropriate power supply voltage while preventing a diameter of a signal line from being increased while maintaining a transmission rate. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.