JP2004336473A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of outputting an appropriate video signal even when excessive light impinges thereon. <P>SOLUTION: In the imaging device, a CCD operates in response to horizontal transfer pulses FH1, FH2 and a reset pulse FR to output an electrical signal depending on the object light. When excessive light impinges on the CCD to cause leakage of excessive charges from an effective pixel region to an OB region during an OB period, reset processing is performed. Reset processing is performed by bringing the reset pulse FR to an "H" level during a period from two pixels before an optical black clamp pulse CLPOB falls down to an "L" level until the optical black clamp pulse CLPOB rises to the "H" level. Consequently, appropriate clamp processing can be carried out under a state where excessive charges leaked from the effective pixel region to the OB region during the OB interval are discharged entirely. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image pickup apparatus, and more particularly, to an image pickup apparatus including a CCD (Charge Coupled Device).
[0002]
[Prior art]
2. Description of the Related Art Conventionally, various types of imaging devices incorporating a CCD have been proposed. FIG. 11 is a block diagram illustrating a configuration of a conventional imaging device. 11, this imaging apparatus includes a CCD 61, a correlated double sampling (CDS) circuit 62, a clamp circuit 63, a video signal processing unit 64, an exposure control unit 65, and a timing pulse generation unit 66.
[0003]
The CCD 61 outputs an electric signal corresponding to the subject light. The CDS circuit 62 removes a clock component of an output signal of the CCD 61 and reduces noise. The clamp circuit 63 clamps the OB (optical black) level of the output signal of the CDS circuit 62 and controls the output signal so that the black level is always constant. The video signal processing unit 64 performs various video signal processing on the output signal of the clamp circuit 63, outputs an appropriate video signal to the outside, and outputs a luminance signal to the exposure control unit 65. The exposure control section 65 outputs a control signal for controlling the exposure of the imaging device based on the luminance signal from the video signal processing section 64. The timing pulse generator 66 drives and controls the CCD 61 based on a control signal from the exposure controller 65, and outputs various timing pulses to the CDS circuit 62, the clamp circuit 63, and the video signal processor 64.
[0004]
In recent years, such imaging devices have been used for surveillance cameras, door phone cameras, in-vehicle cameras, and the like, and the applications of the imaging devices have been remarkably expanding. Since this type of camera is often used outdoors, very strong light such as sunlight, spot light, or HID (High Intensity Discharge) lamp may enter the CCD.
[0005]
Therefore, when excessive light enters the CCD, by inverting the phase of the horizontal transfer pulse in a part of the horizontal period of the CCD, excess signal charges leaking from the effective pixel area to the OB (optical black) area are removed. A method has been proposed in which all exposure is performed and appropriate exposure control is performed (for example, see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-10-210370
[0007]
[Problems to be solved by the invention]
In the conventional imaging device, when excessive light enters the CCD, the signal charges generated by subjecting the subject light to photoelectric conversion in the effective pixel area of the CCD 61 become excessive, and the signal charges are also generated in the OB area where the signal charges are hardly transferred. Will be transferred. For this reason, the OB level of the output signal of the CDS circuit 62 increases, and as a result of clamping the CDS output signal by the clamp circuit 63, a video signal having a small signal level width, that is, a dark video signal is output to the outside.
[0008]
The present invention is intended to solve the above problem by a method different from the method disclosed in Patent Document 1.
[0009]
Therefore, a main object of the present invention is to provide an imaging device capable of outputting a proper video signal even when excessive light enters.
[0010]
[Means for Solving the Problems]
An imaging apparatus according to the present invention includes an effective pixel unit that photoelectrically converts subject light to generate a signal charge, an optical black unit that generates a black-level reference signal, and a transfer that transfers a signal charge in synchronization with a clock signal. Unit, a conversion unit that converts a potential change due to the signal charge transferred from the transfer unit into an electric signal and outputs the electric signal, and performs a reset process when the reset signal is the first potential to change the output signal of the conversion unit to a black level. A reset unit that does not perform a reset process when the reset signal is at the second potential; a charge-coupled device that outputs an electric signal according to subject light; and a video signal based on the electric signal from the charge-coupled device. When the signal level of the subject light is equal to or less than a predetermined value, the reset signal is set to the first or second potential at the same cycle as the clock signal, and If the signal level is greater than a predetermined value is obtained and a control means for holding the period reset signal a predetermined over one period of the clock signal to the first potential.
[0011]
Preferably, the video signal generating means is a correlated double sampling means for performing correlated double sampling processing on the electric signal from the charge-coupled device, and the output signal of the correlated double sampling means is clamped so that the black level is always constant. And a video signal processing means for performing video signal processing on an output signal of the clamp means and outputting a video signal and a luminance signal. Here, the control unit includes an exposure control unit that outputs a control signal for controlling the exposure of the imaging device based on the luminance signal from the video signal processing unit, and a reset signal based on the control signal from the exposure control unit. The reset signal generating unit that generates the signal, compares the average value of the luminance signal from the video signal processing unit with a predetermined reference luminance, and if the average value of the luminance signal is greater than the predetermined reference luminance, Brightness comparing means for holding the reset signal at the first potential for a predetermined period of one or more cycles of the signal.
[0012]
Preferably, the luminance comparing means compares an average value of luminance signals of two blocks in the upper left and lower right corners of a screen obtained by dividing one screen into 16 and a predetermined reference luminance.
[0013]
Preferably, the luminance comparing means compares an average value of luminance signals of two blocks in the upper right and lower right corners of a screen obtained by dividing one screen into 16 and a predetermined reference luminance.
[0014]
Preferably, the luminance comparing means operates when the shutter speed of the charge-coupled device becomes maximum.
[0015]
Preferably, the video signal generating means includes a correlated double sampling means for performing correlated double sampling processing on the electric signal from the charge-coupled device, and a clamper for an output signal of the correlated double sampling means so that the black level is always constant. And a video signal processing unit that performs video signal processing on an output signal of the clamp unit and outputs a video signal and a luminance signal. Here, the control unit includes an exposure control unit that outputs a control signal for controlling the exposure of the imaging device based on the luminance signal from the video signal processing unit, and a reset signal based on the control signal from the exposure control unit. The reset signal generating means to be generated compares the black level of the output signal of the correlated double sampling means with a predetermined reference black level, and the black level of the output signal of the correlated double sampling means is larger than the reference black level. In the case, a black level comparing unit that holds the reset signal at the first potential for a predetermined period of one or more cycles of the clock signal is included.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
FIG. 1 is a block diagram illustrating a configuration of an imaging device according to Embodiment 1 of the present invention. 1, this imaging device includes a CCD 1, a CDS circuit 2, a clamp circuit 3, a video signal processing unit 4, an exposure control unit 5, a timing pulse generation unit 6, and a luminance comparison unit 7.
[0017]
The CCD 1 is driven by a vertical transfer pulse, horizontal transfer pulses FH1 and FH2, and a reset pulse FR from the timing pulse generator 6, and outputs an electric signal corresponding to subject light.
[0018]
FIG. 2 is a layout diagram showing a pixel area of one chip of the CCD 1. In FIG. 2, on a chip of the CCD 1, an effective pixel area 11 for generating signal charges by photoelectrically converting subject light and an OB area 12 for generating a black-level reference signal are arranged. The OB area 12 is arranged so as to surround the effective pixel area 11, and is provided with a light shielding member such as aluminum so as not to receive the subject light.
[0019]
FIG. 3 is a block diagram showing a basic configuration of one chip of the CCD 1. 3, in the effective pixel area 11 and the OB area 12, a photodiode 21 corresponding to each pixel is provided, and a vertical transfer register 22 is provided along a column of each photodiode 21. The output signal of the photodiode 21 in the effective pixel area 11 is an electric signal obtained by photoelectrically converting the subject light. The output signal of the photodiode 21 in the OB region 12 is used as a black level reference signal.
[0020]
The CCD 1 further includes a horizontal transfer register 23 and an output unit 24. The vertical transfer register 22 sequentially transfers the signal charges generated by the corresponding photodiodes 21 to the horizontal transfer register 23 in synchronization with the vertical transfer pulses φV1 to φV4. The horizontal transfer register 23 sequentially transfers the signal charges transferred from the vertical transfer register 22 to the output unit 24 in synchronization with the horizontal transfer pulses φH1 and φH2. The output unit 24 outputs the signal charge transferred from the horizontal transfer register 23 to the outside as a CCD output signal.
[0021]
Returning to FIG. 1, the CDS circuit 2 is driven by timing pulses SHP and SHD from the timing pulse generator 6, and removes a clock component of a CCD output signal to reduce noise. That is, the CDS circuit 2 samples the reference level of the CCD output signal in response to the timing pulse SHP, samples the data level of the CCD output signal in accordance with the timing pulse SHD, and performs correlated double sampling for calculating the difference therebetween. Do.
[0022]
The clamp circuit 3 clamps the OB level of the CDS output signal in accordance with the optical black clamp pulse CLPOB from the timing pulse generator 6, and controls the black level to be always constant.
[0023]
The video signal processing unit 4 performs various video signal processing (color signal processing, luminance signal processing, gamma correction processing, encoder processing, etc.) on the output signal of the clamp circuit 3 according to the timing pulse from the timing pulse generation unit 6. Thus, a video signal suitable for a display device such as a television monitor is output to the outside, and a luminance signal is output to the exposure control unit 5.
[0024]
The exposure control unit 5 calculates the average luminance of the screen based on the luminance signal from the video signal processing unit 4 and outputs a control signal for performing appropriate exposure control to the timing pulse generation unit 6. That is, the exposure control unit 5 divides the effective pixel portion of one screen into four horizontal divisions and four vertical divisions, that is, a total of 4 × 4 = 16 divisions, and integrates the luminance signals of the respective blocks. To memorize. In accordance with the rising edge of the vertical synchronization signal VD from the timing pulse generator 6, the integrated value of the luminance signal of each block is read from the storage unit, and the exposure control of the imaging device is performed by obtaining the average luminance of the screen. This exposure control is performed by, for example, utilizing the electronic shutter function of the CCD 1 and outputting a shutter pulse control signal for controlling the electronic shutter of the CCD 1 to the timing pulse generator 6 so that the CCD output becomes constant.
[0025]
FIG. 4 is a diagram in which the effective pixel portion of one screen is divided into 16 parts. In FIG. 4, the effective pixel portion of one screen is divided into blocks Y1 to Y16. At the time of capturing a normal image, if excessive light is received and, for example, the most significant bit of the shutter pulse control signal composed of 9 bits becomes “H” level, that is, if the shutter speed becomes maximum, the left and right vertical angles 2 The average luminance of the blocks Y1 and Y13 is given to the luminance comparing section 7. Y1 and Y13 are locations susceptible to excessive signal charge leakage when excessive light is received during normal image capturing. When excessive light is received at the time of mirror image capturing, the average luminance of the two blocks Y4 and Y16 at the upper right and lower right corners is given to the luminance comparing section 7. Y4 and Y16 are locations susceptible to excessive signal charge leakage when excessive light is received during mirror image capturing. Accordingly, it is possible to efficiently and appropriately determine whether or not excessive signal charge leakage occurs when excessive light is incident on the CCD 1.
[0026]
Returning to FIG. 1, when the shutter speed is maximized by receiving the excessive light by the CCD 1, the luminance comparing unit 7 outputs the average luminance of the two blocks of the left and right angles or the right and left angles from the exposure control unit 5, the register and the like. Is compared with the reference luminance set in the above step. If the average luminance from the exposure control section 5 is larger than the reference luminance, the reset processing is performed. If the average luminance from the exposure control section 5 is lower than the reference luminance, the reset processing is performed. A control signal for controlling not to perform is output to the exposure control unit 5.
[0027]
The timing pulse generator 6 drives and controls the CCD 1 based on a control signal from the exposure controller 5 and outputs various timing pulses to the CDS circuit 2, the clamp circuit 3, and the video signal processor 4.
[0028]
Next, the operation of the imaging apparatus will be described with reference to FIGS. FIG. 5 is a waveform diagram showing the waveforms of the horizontal transfer pulses FH1 and FH2, the reset pulse FR, the CCD output signals, the timing pulses SHP and SHD, the CDS output signal, and the optical black clamp pulse CLPOB during normal operation. In FIG. 5, the effective pixel period and the OB period are a part of one horizontal period.
[0029]
The CCD 1 operates in response to a vertical transfer pulse, two horizontal transfer pulses FH1 and FH2 whose phases differ by 1/2 pixel, and a reset pulse FR. The CCD1 accumulates signal charges during an effective pixel period and accumulates signal charges during an OB period. Does not accumulate. The CDS circuit 2 samples the reference level of the CCD output signal at the falling edge of the timing pulse SHP, samples the data level of the CCD output signal at the falling edge of the timing pulse SHD, calculates the difference between them, and outputs the result. . The CDS output signal falls to the OB level at the first falling edge of the timing pulse SHD during the OB period. The clamp circuit 3 clamps the CDS output signal at the OB level in response to the fall of the optical black clamp pulse CLPOB to the “L” level, and controls the black level to be always constant.
[0030]
FIG. 6 shows horizontal transfer pulses FH1 and FH2, a reset pulse FR, a CCD output signal, timing pulses SHP, SHD, a CDS output signal, and an optical black clamp when reset processing is not performed when excessive light is received as in a conventional imaging apparatus. FIG. 6 is a waveform diagram showing a waveform of a pulse CLPOB, which is compared with FIG. 5. Referring to the waveform diagram of FIG. 6, the difference from the waveform diagram of FIG. 5 is that the CCD output signal has a waveform in which signal charges leak from the effective pixel area to the OB area during the OB period, and the CDS output signal The point is that the OB level of the signal is high.
[0031]
The CCD 1 operates according to a vertical transfer pulse, two horizontal transfer pulses FH1 and FH2 whose phases differ by １ ／ pixel, and a reset pulse FR, and accumulates signal charges during an effective pixel period. Next, in the OB period, signal light leaks from the effective pixel area of the CCD 1 to the OB area due to excessive light incident on the CCD 1. That is, referring to FIG. 3, the signal charge generated by the photodiode 21 in the effective pixel area 11 exceeds the capacity of the corresponding vertical transfer register 22 and is transferred to the horizontal transfer register 23 during the scanning period of the horizontal transfer register 23. Leak. Further, the signal charges leaking into the horizontal transfer register 23 are transferred to the OB region 12 beyond the capacity of the horizontal transfer register 23. That is, in the OB period, the signal charges leak into the OB region 12 where the signal charges are not normally transferred.
[0032]
Returning to FIG. 6, the CDS output signal falls to the OB level at the first falling edge of the timing pulse SHD in the OB period. Since the OB level is higher than the OB level in the normal operation, the level width of the video signal is reduced. The clamp circuit 3 clamps the CDS output signal according to the fall of the optical black clamp pulse CLPOB to the “L” level, and controls the black level to be always constant. In this case, the OB level higher than the OB level in the normal operation is used as a reference for the black level, and a dark video signal is output because the level width of the video signal is small. For example, when the OB level of the CDS output signal further increases and becomes the same signal level as the CDS output in the effective pixel period, a black video signal is output as a result.
[0033]
FIG. 7 is a waveform diagram showing waveforms of horizontal transfer pulses FH1 and FH2, a reset pulse FR, a CCD output signal, timing pulses SHP and SHD, a CDS output signal, and an optical black clamp pulse CLPOB when a reset process is performed when receiving excessive light. FIG. 7 is a diagram to be compared with FIG. 6. Referring to the waveform diagram of FIG. 7, the difference from the waveform diagram of FIG. 6 is that the reset pulse FR is always at the “H” level during the OB period, and that the CCD output signal changes from the effective pixel area during the OB period. The point is that the signal charge does not leak into the OB area, and the OB level of the CDS output signal is not high.
[0034]
This reset processing is performed when the optical black clamp pulse CLPOB is set to the “L” level when the average luminance of the left and right upper two corner blocks Y1 and Y13 or the right and right upper two blocks Y4 and Y16 shown in FIG. This is performed by setting the reset pulse FR to the “H” level during a period from two pixels before the fall to when the optical black clamp pulse CLPOB is raised to the “H” level. Thus, in the OB period, it is possible to perform an appropriate clamp process in a state where all the surplus signal charges leaked from the effective pixel region to the OB region are discharged.
[0035]
FIG. 8 is a diagram showing a potential distribution at the time of horizontal transfer near the output section of the CCD 1 in this case. 8, times T1 to T6 indicate times T1 to T6 shown in FIG. At time T1, no signal charge is accumulated in the conversion unit 31 and RD (reset drain) 33, and the reset pulse FR is at "L" level, so that the potential of the reset gate 32 is at "H" level.
[0036]
At time T2, since the reset pulse FR is at the “L” level, the potential of the reset gate 32 remains at the “H” level. The signal charges are transferred by the horizontal transfer pulses FH1 and FH2, and the signal charges are accumulated in the conversion unit 31. You.
[0037]
At time T3, since the reset pulse FR is at the “H” level, the potential of the reset gate 32 is reduced, and the barrier between the conversion unit 31 and the RD 33 disappears. Therefore, the signal charges stored in the conversion unit 31 are discharged to the RD 33. The change in potential of the conversion unit 31 at this time is read out as a CCD output signal via an AMP (amplifier) 34. During the effective pixel period, the state at times T1 to T3 is sequentially repeated.
[0038]
At time T4, since the reset pulse FR has been set to the “H” level by the reset process, the potential of the reset gate 32 remains lowered. At time T5 and time T6, the signal charge leaks from the effective pixel area to the OB area due to excessive light reception, but the potential of the reset gate 32 remains lowered by the reset processing, and the potential between the conversion unit 31 and the RD 33 is reduced. Since there is no barrier, all excess signal charges transferred to the conversion unit 31 are discharged to the RD 33.
[0039]
In the OB period, the state of times T4 to T6 is sequentially repeated. By this reset processing, the CCD 1 is driven and controlled so that signal charges are not always accumulated in the conversion unit 31 during the OB period, so that an appropriate video signal is output while avoiding a black screen phenomenon or a screen breakdown phenomenon. can do.
[0040]
As described above, in the first embodiment, by providing the brightness comparison unit 7 for comparing the average brightness from the exposure control unit 5 with the reference brightness, even if excessive light enters the CCD 1, a proper video signal Can be realized.
[0041]
[Embodiment 2]
FIG. 9 is a block diagram illustrating a configuration of an imaging device according to Embodiment 2 of the present invention, and is a diagram that is compared with FIG. Referring to the imaging device of FIG. 9, the difference from the imaging device of FIG. 1 is that the brightness comparison unit 7 is deleted and the OB comparison unit 41 is added.
[0042]
In FIG. 9, the OB comparison unit 41 is connected between the CDS circuit 2 and the exposure control unit 5. The OB comparator 41 compares the OB level of the output signal of the CDS circuit 2 with a reference OB set by a register or the like, and does not operate when the OB level of the output signal of the CDS circuit 2 is lower than the reference OB. When the OB level of the output signal of the CDS circuit 2 is higher than the reference OB, that is, when the OB level of the CDS output becomes high because the CCD 1 receives excessive light, the reset processing is performed.
[0043]
The waveform diagram of each signal when the reset processing is performed by the OB comparison unit 41 is the same as the waveform diagram shown in FIG. 7, and the reset pulse FR is always set to “H” level during the OB period. Appropriate clamping can be performed in a state in which all excess signal charges leaked from the effective pixel area to the OB area are discharged.
[0044]
As described above, in the second embodiment, the provision of the OB comparison unit 41 for comparing the OB level of the output signal of the CDS circuit 2 with the reference OB enables proper video even when excessive light enters the CCD 1. An imaging device capable of outputting a signal can be realized.
[0045]
[Embodiment 3]
FIG. 10 is a block diagram illustrating a configuration of an imaging device according to Embodiment 3 of the present invention, and is a diagram that is compared with FIG. Referring to the imaging device of FIG. 10, the difference from the imaging device of FIG. 1 is that an OB comparison unit 41 and a selector 51 are added.
[0046]
10, the OB comparison unit 41 is the same as the OB comparison unit 41 shown in FIG. The selector 51 is set by an external switch, a register, or the like. Thus, when the CCD 1 receives excessive light, the user can arbitrarily determine which function of the luminance comparing unit 7 described in the first embodiment and the OB comparing unit 41 described in the second embodiment is used. You can choose.
[0047]
As described above, in the third embodiment, the brightness comparison unit 7 that compares the average brightness from the exposure control unit 5 with the reference brightness, and the OB comparison that compares the OB level of the output signal of the CDS circuit 2 with the reference OB. By providing the selector 41 and the selector 51 for selecting which function of the luminance comparing unit 7 and the OB comparing unit 41 is used, an appropriate video signal can be output even when excessive light enters the CCD 1. An imaging device capable of performing the above can be realized.
[0048]
The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0049]
【The invention's effect】
As described above, in the imaging apparatus according to the present invention, the effective pixel unit that generates the signal charge by photoelectrically converting the subject light, the optical black unit that generates the black-level reference signal, and the signal synchronized with the clock signal A transfer unit that transfers the charge, a conversion unit that converts a potential change caused by the signal charge transferred from the transfer unit into an electrical signal and outputs the electrical signal, and performs a reset process when the reset signal has the first potential to perform the reset process. A charge-coupled device that outputs an electrical signal according to subject light, and a reset unit that does not perform a reset process when the reset signal is at the second potential, A video signal generating means for generating a video signal based on the first signal or a second signal at the same cycle as the clock signal when the signal level of the subject light is equal to or less than a predetermined value; To, when the signal level of the subject light is greater than a predetermined value, and a control means for holding the period reset signal a predetermined over one period of the clock signal to a first potential is provided. Therefore, even when excessive light enters the charge coupled device, an appropriate video signal can be output.
[0050]
Preferably, the video signal generating means is a correlated double sampling means for performing correlated double sampling processing on the electric signal from the charge-coupled device, and the output signal of the correlated double sampling means is clamped so that the black level is always constant. And a video signal processing means for performing video signal processing on an output signal of the clamp means and outputting a video signal and a luminance signal. Here, the control unit includes an exposure control unit that outputs a control signal for controlling the exposure of the imaging device based on the luminance signal from the video signal processing unit, and a reset signal based on the control signal from the exposure control unit. The reset signal generating unit that generates the signal, compares the average value of the luminance signal from the video signal processing unit with a predetermined reference luminance, and if the average value of the luminance signal is greater than the predetermined reference luminance, Brightness comparing means for holding the reset signal at the first potential for a predetermined period of one or more cycles of the signal. In this case, by providing the brightness comparison means for comparing the average value of the brightness signal from the video signal processing means with a predetermined reference brightness, a proper video signal can be obtained even when excessive light enters the charge-coupled device. Can be output.
[0051]
Preferably, the luminance comparing means compares an average value of luminance signals of two blocks in the upper left and lower right corners of a screen obtained by dividing one screen into 16 and a predetermined reference luminance. In this case, at the time of capturing a normal image, it is possible to properly determine whether excessive signal charge leakage occurs when excessive light is incident on the charge-coupled device.
[0052]
Preferably, the luminance comparing means compares an average value of luminance signals of two blocks in the upper right and lower right corners of a screen obtained by dividing one screen into 16 and a predetermined reference luminance. In this case, it is possible to appropriately determine whether excessive signal charge leakage has occurred when excessive light is incident on the charge-coupled device during mirror image capturing.
[0053]
Preferably, the luminance comparing means operates when the shutter speed of the charge-coupled device becomes maximum. In this case, by operating the luminance comparing means when the shutter speed of the charge-coupled device is maximized, it is determined whether excessive signal charge leakage occurs when excessive light enters the charge-coupled device. Can be determined efficiently.
[0054]
Preferably, the video signal generating means includes a correlated double sampling means for performing correlated double sampling processing on the electric signal from the charge-coupled device, and a clamper for an output signal of the correlated double sampling means so that the black level is always constant. And a video signal processing unit that performs video signal processing on an output signal of the clamp unit and outputs a video signal and a luminance signal. Here, the control unit includes an exposure control unit that outputs a control signal for controlling the exposure of the imaging device based on the luminance signal from the video signal processing unit, and a reset signal based on the control signal from the exposure control unit. The reset signal generating means to be generated compares the black level of the output signal of the correlated double sampling means with a predetermined reference black level, and the black level of the output signal of the correlated double sampling means is larger than the reference black level. In the case, a black level comparing unit that holds the reset signal at the first potential for a predetermined period of one or more cycles of the clock signal is included. In this case, by providing the black level comparing means for comparing the black level of the output signal of the correlated double sampling means with a predetermined reference black level, even if excessive light enters the charge-coupled device, appropriate Video signals can be output.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an imaging device according to a first embodiment of the present invention.
FIG. 2 is a layout diagram showing a pixel area of one chip of the CCD shown in FIG. 1;
FIG. 3 is a block diagram showing a basic configuration of one chip of the CCD shown in FIG.
FIG. 4 is a diagram in which an effective pixel portion of one screen is divided into 16 parts.
FIG. 5 is a waveform chart showing waveforms of various signals during a normal operation.
FIG. 6 is a waveform diagram showing waveforms of various signals when reset processing is not performed when excessive light is received.
FIG. 7 is a waveform diagram showing waveforms of various signals when a reset process is performed when excessive light is received.
FIG. 8 is a diagram showing a potential distribution at the time of horizontal transfer in the vicinity of an output portion of a CCD when a reset process is performed when excessive light is received.
FIG. 9 is a block diagram illustrating a configuration of an imaging device according to a second embodiment of the present invention.
FIG. 10 is a block diagram showing a configuration of an imaging device according to a third embodiment of the present invention.
FIG. 11 is a block diagram illustrating a configuration of a conventional imaging device.
[Explanation of symbols]
1,61 CCD, 2,62 CDS circuit, 3,63 clamp circuit, 4,64 video signal processing unit, 5,65 exposure control unit, 6,66 timing pulse generation unit, 7 brightness comparison unit, 11 effective pixel area, 12 OB area, 21 diode, 22 vertical transfer register, 23 horizontal transfer register, 24 output circuit, 31 conversion unit, 32 reset gate, 33 RD, 34 amplifier, 41 OB comparison unit, 51 selector.

Claims (6)

An imaging device,
An effective pixel unit that photoelectrically converts the subject light to generate a signal charge, an optical black unit that generates a black-level reference signal, a transfer unit that transfers the signal charge in synchronization with a clock signal, and A conversion unit for converting a potential change caused by the transferred signal charges into an electric signal and outputting the electric signal; and performing a reset process when the reset signal is at the first potential to set an output signal of the conversion unit to a black level, wherein the reset signal is A charge-coupled device that includes a reset unit that does not perform a reset process in the case of the second potential and that outputs an electric signal corresponding to subject light;
Video signal generating means for generating a video signal based on the electric signal from the charge-coupled device, and when the signal level of the subject light is equal to or less than a predetermined value, the reset signal is generated at the same cycle as the clock signal. When the signal level of the subject light is higher than the predetermined value, the reset signal is set to the first potential for a predetermined period of one or more cycles of the clock signal. An imaging device comprising a control unit for holding. The video signal generating means,
Correlated double sampling means for performing correlated double sampling on the electric signal from the charge-coupled device;
A clamp means for clamping the output signal of the correlated double sampling means so as to control the black level to be always constant; and performing video signal processing on the output signal of the clamp means to produce a video signal and a luminance signal. Including video signal processing means to output,
The control means,
Exposure control means for outputting a control signal for controlling exposure of the imaging device based on a luminance signal from the video signal processing means, and a reset signal for generating a reset signal based on a control signal from the exposure control means Generating means, and comparing an average value of the luminance signal from the video signal processing means with a predetermined reference luminance, and when the average value of the luminance signal is larger than the predetermined reference luminance, The imaging device according to claim 1, further comprising: a brightness comparison unit that holds the reset signal at a first potential for a predetermined period of one or more signal cycles. The imaging apparatus according to claim 2, wherein the brightness comparison unit compares an average value of brightness signals of two blocks in the upper left and lower left corners of a screen obtained by dividing one screen into 16 and the predetermined reference brightness. The imaging apparatus according to claim 2, wherein the brightness comparison unit compares an average value of brightness signals of two blocks in the upper right and lower right corners of a screen obtained by dividing one screen into 16 and the predetermined reference brightness. The imaging device according to claim 2, wherein the brightness comparison unit operates when a shutter speed of the charge-coupled device is maximized. The video signal generating means,
Correlated double sampling means for performing correlated double sampling on the electric signal from the charge-coupled device;
A clamp means for clamping the output signal of the correlated double sampling means so as to control the black level to be always constant; and performing video signal processing on the output signal of the clamp means to produce a video signal and a luminance signal. Including video signal processing means to output,
The control means,
Exposure control means for outputting a control signal for controlling exposure of the imaging device based on a luminance signal from the video signal processing means, and a reset signal for generating a reset signal based on a control signal from the exposure control means Generating means, and comparing the black level of the output signal of the correlated double sampling means with a predetermined reference black level, and adjusting the black level of the output signal of the correlated double sampling means to the predetermined reference black level. The imaging apparatus according to claim 1, further comprising a black level comparison unit that holds the reset signal at the first potential for a predetermined period of one or more cycles of the clock signal when the clock signal is larger than one cycle.

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