JP2013085191A - Imaging device and imaging element driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely detect a dark current with a simple structure during an imaging operation.SOLUTION: In reading of a first screen in CCD 15, a charge of a photodiode 30 is transferred to a vertical CCD 31 (Fig 3(a)), a charge signal of an upper vertical optical black region shown by a black circle is left and vertical transfer is stopped (Fig 3(c)). A second screen is imaged and the charge of the photodiode 30 is transferred to the vertical CCD 31. Thus, a charge signal of a lower vertical optical black region shown by the black circle is added to the charge signal of the upper vertical optical black region which is left in the reading of the first screen and shown by a shaded circle (Fig 3(d)). The dark current of the CCD 15 is detected from the added charge signal.

Description

  The present invention relates to an apparatus and a method for measuring a dark current generated in an image sensor.

  In an electronic endoscope apparatus, a configuration is known in which the pixel signal level of a CCD optical black region and the pixel signal level of a dummy region provided at the distal end of the insertion portion are detected, and the temperature at the distal end of the insertion portion is estimated from the difference therebetween. (Patent Document 1).

JP-A-3-151929

  However, since the signal level in the optical black region is extremely low, it is difficult to detect the dark current level with high accuracy.

  An object of the present invention is to detect a dark current with high accuracy with a simple configuration during a photographing operation.

  The image pickup apparatus of the present invention is characterized in that, in reading out one screen of the CCD, the vertical transfer is stopped while leaving one or more horizontal lines corresponding to the vertical optical black area, and the next screen is read out sequentially. .

  Further, the image pickup apparatus detects the value of the dark current of the CCD based on the charge signal of the horizontal line read in the reading of the next screen, without performing the reading in the reading of the previous screen. The imaging apparatus may estimate the temperature of the CCD based on the charge signal of the horizontal line read in the reading of the next screen without reading in the reading of the previous screen.

  An electronic endoscope apparatus according to the present invention is an electronic endoscope apparatus in which the imaging apparatus is mounted, and is characterized in that the amount of light supplied to the light guide is reduced when the temperature is higher than a predetermined value.

  Further, another electronic endoscope apparatus according to the present invention is an electronic endoscope apparatus equipped with the above-described imaging device, characterized by comprising warning means for giving a warning when the temperature is higher than a predetermined value. .

  The image sensor driving method of the present invention is characterized in that, in reading out one screen of a CCD, the vertical transfer is stopped while leaving one or more horizontal lines corresponding to the vertical optical black area, and the next screen is read out sequentially. It is said.

  According to the present invention, dark current can be detected with high accuracy with a simple configuration during a photographing operation.

It is a block diagram which shows roughly the electrical structure of the imaging device of this embodiment. It is a top view which shows the structure of CCD used with the imaging device of FIG. It is a schematic diagram for demonstrating the principle of the electric charge read-out operation | movement of CCD of this embodiment. 6 is a timing chart showing a relationship between a vertical drive signal and a CCD output in a conventional CCD charge reading operation and a CCD charge reading operation of the present embodiment. It is a graph which shows the relationship between the dark current obtained by the CCD output in the past and this embodiment, and temperature. It is a flowchart of the process which applied the CCD charge read-out operation | movement of this embodiment to the temperature estimation of the electronic endoscope insertion part front-end | tip.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to an embodiment of the present invention.

  The imaging device 10 is, for example, an electronic endoscope device, and includes a scope 12 having an insertion portion 11 made of a flexible tube, a processor device 13 to which the scope 12 is detachably connected, and a processor device 13 that is detachably connected. The monitor 14 is mainly configured.

  A CCD 15 is provided at the distal end of the insertion portion 11, and its driving is controlled by a drive circuit 16 provided in the processor device 13, for example. The analog image signal generated by the CCD 15 is sent to an analog signal processing circuit 17 provided in the processor device 13 through an amplifier, and subjected to predetermined analog image processing. Thereafter, the image signal is A / D converted by the pre-stage signal processing circuit 18, subjected to predetermined digital image processing, and temporarily stored in the image memory 19 for each frame.

  The image data stored in the image memory 19 is output to the subsequent signal processing circuit 20 at a predetermined timing for each frame, and converted into a video signal of a predetermined standard, for example, an external device such as a monitor 14 or a printer (not shown). Or output to a recording device. Note that the drive timing of the drive circuit 16, analog signal processing circuit 17, pre-stage signal processing circuit 18, image memory 19, and post-stage signal processing circuit 20 is controlled by a timing controller 21.

  The pre-stage signal processing circuit 18 outputs an image signal in the optical black (OB) area of the CCD 15 to the temperature processing circuit 35. In the temperature processing circuit 35, the temperature of the imaging element 15, that is, the tip of the insertion portion 11 is estimated based on the input image signal, and the result is sent to the system controller 22.

  The system controller 22 controls the light source power source 23 and the motor driver 24, and the motor driver 24 controls the driving of the motor 26 that moves the dimming diaphragm 25. The system controller 22 is also connected with a front panel 36 having various operation keys and a display unit.

  The light source power supply 23 supplies power to the light source 27, and the light from the light source 27 is collected and incident on the incident end of the light guide 29 provided in the scope 12 by the condenser lens 28. On the optical path from the light source 27 to the incident end of the light guide 29, a dimming diaphragm 25 is disposed, and the amount of light incident on the light guide 29 is controlled by driving thereof. The light incident on the light guide 29 is transmitted through the light guide 29 and is emitted as illumination light from the emission end disposed at the tip of the insertion portion 11.

  FIG. 2 is a plan view schematically showing a general configuration of the CCD 15. A rectangular area 15A shown as a grid-like area in FIG. 2 is an effective pixel area used for imaging, and an optical black (OB) area that is shielded by a metal film or the like is provided around it. An upper vertical optical black region 15B is provided above the effective pixel region 15A in the vertical line direction, and a lower vertical optical black region 15C is provided below the effective pixel region 15A. Further, a subsequent horizontal optical black area 15D used for determining the pedestal level is provided on the right side of the effective pixel area 15A in the horizontal line direction.

  Next, the principle of the CCD readout process of this embodiment will be described with reference to FIG. 3A to 3D, the photodiodes 30, the vertical CCDs 31 arranged adjacent to the columns of the photodiodes 30 aligned in the vertical direction, and the lower ends of the vertical CCDs 31 are horizontal. An arrangement of the horizontal CCDs 32 arranged in the line direction is schematically shown.

  FIG. 3A shows how charges accumulated in each photodiode 30 are transferred to the vertical CCD 31. The uppermost (n-th row) photodiode 30 is a pixel in the upper vertical optical black region 15B. The photodiode 30 in the lowermost stage (first row) represents a pixel in the lower vertical optical black region 15C. In the figure, black circles indicate charges accumulated in the optical black areas 15B and 15C, that is, charges corresponding to dark current, and white circles indicate charges accumulated in the effective pixel area 15A, that is, charges corresponding to image data.

  FIG. 3B shows a state in which the charges transferred to the vertical CCD 31 are sequentially transferred to the horizontal CCD 32 by the vertical transfer of the vertical CCD 31 and are sequentially output to the outside of the CCD 15 by the horizontal transfer of the horizontal CCD 32. FIG. 3C shows a state in which the charge in the upper vertical optical black region 15B, which was at the uppermost level, has been transferred to the lowermost level (first row) of the vertical CCD 31 corresponding to the lower vertical optical black region 15C.

  In the conventional readout of each frame, the charges of all the horizontal lines are output from the CCD 15, so that the lowermost stage charge (first row) shown in FIG. 3C is also output together with other charges. However, in the present embodiment, reading of the frame is performed in a state where the charge (uppermost charge) detected in the upper vertical optical black area 31 is transferred to the vertical CCD 31 (lowermost stage) in the lower vertical optical black area 32. Exit.

  FIG. 3D shows a state in which the imaging of the next frame is finished and the electric charge accumulated in each photodiode 30 is transferred to the vertical CCD 31. At this time, the uppermost charge of the previous frame (charge of the upper vertical optical black region 15B) remains in the lowermost vertical CCD 31. That is, the white circle hatched with diagonal lines in FIG. 3D is the uppermost charge of the previous frame. When the charge of each photodiode 30 is transferred to the vertical CCD 31, the charge accumulated in the lowermost photodiode 30 corresponding to the lower vertical optical black region 15C is detected in the upper vertical optical black region 15B of the previous frame. The amount of charge is added to the charge, and the amount of charge of the lowermost vertical CCD 31 is approximately doubled.

  FIGS. 4A and 4B are timing charts showing the relationship between the vertical drive signal and the CCD output in the conventional CCD readout process and the CCD readout process of the present embodiment described with reference to FIG. is there.

When the number of horizontal lines including the upper and lower vertical optical black regions 15B and 15C is, for example, n rows as shown in FIG. 3, the conventional CCD readout process of FIG. 4A outputs an image of one frame (one screen). 1, n vertical drive signals are output from the drive circuit 16 (FIG. 1) to the CCD 15 (FIG. 1), and the charge OB ₁₁ at the lowest level (first row) to the charge OB at the highest level (nth row). All up to _1n are output.

  On the other hand, in the CCD readout process of the present embodiment, for example, the vertical drive signal of the nth row is not output. That is, only one (n−1) vertical drive signals are output from the drive circuit 16 to the CCD 15 in outputting one frame of image. Thereby, the CCD output signal of one frame (one screen) does not include the pixel signal (charge) in the uppermost stage (n-th row), and as shown in FIG. 3C, the lowermost stage of the vertical CCD 31. The next frame is imaged while being held in (first row).

When the charge of each photodiode 30 is transferred to the vertical CCD 31 after the charge accumulation in the next frame, the charge OB ₂₁ of the lowermost (first row) photodiode 30 is changed to the lowermost (first row) vertical CCD 31. _Is added to the electric charge OB _1n held in. When a vertical drive signal is output from the drive circuit 16 to the CCD 15 for image output of the next frame (next screen), the charge obtained by adding the charge OB _1n and the charge OB ₂₁ is the lowermost stage (one row) of the next frame. Eye) as a pixel signal. Similarly, the pixel signals in the lowermost stage (first row) are added and output in the subsequent frames. The added charge signals (charges OB _1n , OB ₂₁ ) are output, and the difference from the pixel signal in the dummy area is taken to determine the level.

  In FIG. 4, charges accumulated in the photodiodes of the optical black regions 15B and 15C are shown as black rectangular regions, and charges accumulated in the photodiodes of the effective pixel region 15A are shown as white rectangular regions. It is. Further, the electric charge accumulated by the photodiode in the optical black area of the previous frame (previous screen) is shown as a rectangular area hatched with diagonal lines.

  As described above, the charge accumulated in the light-shielded optical black regions 15B and 15C corresponds to the dark current of the CCD 15, but the amount of charge accumulated in each photodiode during the exposure period is extremely small. Therefore, sufficient accuracy cannot be obtained by detecting the dark current using the conventional CCD readout process.

  However, according to the CCD readout process of the present embodiment, the dark current is monitored using approximately twice the signal charge of the prior art, for example, by monitoring the charge added by the vertical CCD 31 in the lowermost stage (first row). It becomes possible to do. Thereby, the dark current can be detected with high accuracy even during the photographing operation.

  FIG. 5 is a graph showing the relationship between temperature and dark current (voltage level). FIG. 5 compares the relationship between the temperature and dark current (voltage) when the CCD readout process of the present embodiment is used and when the conventional CCD readout process is used. As shown in the figure, the dark current (voltage) level increases as the temperature of the CCD 15 rises. In this embodiment, the level of the pixel signal caused by the dark current is approximately twice that of the conventional one, so that the accuracy is high. The temperature can be estimated.

  The flowchart of FIG. 6 is an example when the CCD reading process of the present embodiment is applied to the temperature estimation of the tip of the electronic endoscope insertion portion. This process is executed, for example, while the electronic endoscope apparatus 10 is performing photographing for endoscope observation. Hereinafter, this processing will be described with reference to FIGS.

  In step S <b> 100, the CCD readout process of the present embodiment is executed by the drive circuit 16, and the output from the CCD 15 is input to the previous stage signal processing circuit 18. At this time, the pixel signal in the lowermost stage (first row) is output to the temperature processing circuit 35. Note that the signal output to the temperature processing circuit 35 is, for example, an average value of pixel signals in the lowest stage (first row).

  In step S102, the temperature processing circuit 35 performs a temperature estimation process using the relationship shown in FIG. 5, for example, and obtains a temperature corresponding to the current dark current level. This temperature information is sent to the system controller 22.

  In step S104, it is determined whether or not the estimated temperature is higher than a predetermined value. If it is determined that the value is not high, the process returns to step S100 and the same process is repeated. On the other hand, if it is determined that the estimated temperature is higher than the predetermined value, illumination light dimming processing is executed in step S106. That is, the system controller 22 controls the driving of the light control diaphragm 25 through the motor driver 24 to reduce the amount of light incident on the light guide 29 to a predetermined value, for example.

  In step S108, a warning process for notifying the user that the temperature at the tip of the insertion portion 11 is high is executed. In the warning process, for example, a warning message may be displayed on the display unit of the monitor 14 or the front panel 36, a warning lamp may be turned on, or a warning sound may be generated. When the warning process is executed, the process returns to step S100, and the same process, that is, the process of reading the next frame is started.

  As described above, according to the present embodiment, the dark current can be detected with high accuracy during the photographing operation without adding a new configuration. In addition, this makes it possible to estimate the temperature of the CCD during the photographing operation, that is, the temperature of the distal end of the insertion portion such as an endoscope with high accuracy.

  Furthermore, according to the electronic endoscope apparatus of the present embodiment, when the estimated temperature is higher than a predetermined value, the amount of light supplied to the light guide can be limited, and the temperature rise at the distal end of the insertion portion can be suppressed, and It is possible to warn of a temperature rise at the distal end of the insertion portion.

  In the present embodiment, the case where the charges of one horizontal line in the vertical optical black region are added has been described as an example. However, for example, reading is performed while leaving a plurality of horizontal lines (for example, 1 to 5 lines) in the vertical optical black region. May be added to two frames for a plurality of horizontal lines, and dark current detection and temperature estimation may be performed based on this.

  For example, when n horizontal lines are included in each of the vertical vertical optical black areas, the charges for n rows are doubled by not reading the horizontal lines for n rows in the reading of the first frame, and the average value thereof Can be used for dark current detection and temperature estimation. That is, the charge addition of the present embodiment can be applied to the number of lines with the smaller number of horizontal lines in the upper and lower vertical optical black regions.

  In the present embodiment, the reading for each frame has been described as an example, but this can also be applied to the reading for each field. In the present embodiment, the temperature processing circuit is described as an independent circuit, but the temperature may be calculated in the system controller.

DESCRIPTION OF SYMBOLS 10 Imaging device 11 Insertion part 12 Scope 15 CCD
15A Effective pixel area 15B Upper vertical optical black area 15C Lower vertical optical black area 16 Drive circuit 18 Pre-stage signal processing circuit 22 System controller 24 Motor driver 24
25 Light control diaphragm 26 Motor 27 Light source 29 Light guide 35 Temperature processing circuit

Claims (6)

  An image pickup apparatus for reading one screen of a CCD by stopping vertical transfer while leaving one or more horizontal lines corresponding to a vertical optical black area in reading one screen of a CCD.   2. The imaging device according to claim 1, wherein no reading is performed in the reading of the previous screen, and the dark current value of the CCD is detected based on the charge signal of the horizontal line read in the reading of the next screen. .   2. The image pickup apparatus according to claim 1, wherein no reading is performed in the reading of the previous screen, and the temperature of the CCD is estimated based on the charge signal of the horizontal line read in the reading of the next screen.   4. An electronic endoscope apparatus equipped with the imaging apparatus according to claim 3, wherein the amount of light supplied to the light guide is reduced when the temperature is higher than a predetermined value. .   4. An electronic endoscope apparatus comprising the imaging apparatus according to claim 3, further comprising a warning unit that issues a warning when the temperature is higher than a predetermined value.   A method for driving an image sensor, comprising: reading out a next screen in a sequential manner by stopping vertical transfer while leaving one or more horizontal lines corresponding to a vertical optical black area in reading out one screen of a CCD.

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