JP2007189335A - Driving method of solid-state imaging element and solid-state imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method of a solid-state imaging element capable of reducing the flicker noise of an imaging signal caused by the flickering of light emission from a fluorescent light. <P>SOLUTION: The driving method of the solid-state imaging element 2 for outputting imaging signals in response to electric charges stored in photoelectric conversion elements in a desired electric charge storage time for a prescribed imaging period includes: an imaging period determining step of determining an imaging period on the basis of a flickering period of illumination light for lighting an object and a desired electric charge storage time; and a drive signal supplying step of supplying a drive signal which is used for the solid-state imaging element 2 for its imaging for the determined imaging period and in the desired electric charge storage time to the solid-state imaging element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for driving a solid-state imaging element that outputs an imaging signal corresponding to the charge accumulated in a photoelectric conversion element in a desired charge accumulation time at a predetermined imaging period.

  In an imaging apparatus including a solid-state imaging device, when shooting is performed under illumination such as a fluorescent lamp, flicker noise in which the level of an imaging signal output from the solid-state imaging device varies due to blinking of the illumination light. Hereinafter, flicker noise will be described with reference to FIG.

FIG. 6 is a timing chart showing drive timings at the time of moving image shooting of an imaging apparatus including a conventional CCD (Charge Coupled Device) type solid-state imaging device.
In FIG. 6, a waveform Tk is a waveform indicating the blinking cycle of illumination such as a fluorescent lamp at the shooting location. The signal V is a vertical synchronization signal that determines a frame rate (imaging cycle) for moving image shooting. The signal SUB is a charge sweep signal for sweeping out the charge accumulated in the photoelectric conversion element of the solid-state imaging device to the substrate. The signal TG is a charge readout signal for reading out the charges accumulated in the photoelectric conversion element of the solid-state imaging device to the CCD. The signal OUT is an imaging signal output from the solid-state imaging device.

  In the example of FIG. 6, the imaging cycle is 1/60 seconds, and the period from the signal SUB to the high level last until the signal TG becomes the high level in 1/60 seconds corresponds to one frame. The charge accumulation time, which is the time for accumulating the charge necessary for obtaining the image data, in the photoelectric conversion element. In the example of FIG. 6, this charge accumulation time is, for example, 1/150 seconds. When the signal TG becomes high level and the charge accumulation time ends, the charge accumulated in the photoelectric conversion element during this charge accumulation time is read out and transferred to the CCD, and the imaging signal OUT is output. In the example of FIG. 6, the illumination device is operated with an AC power supply of 50 Hz, and the blinking cycle of illumination light that illuminates the subject is 1/100 second.

  In the driving timing shown in FIG. 6, since the blinking period of illumination light (1/100 seconds) and the charge accumulation time (1/150 seconds) are not in a natural number multiple relationship, they are accumulated at each charge accumulation time. As a result, the level of the imaging signal fluctuates as shown by the imaging signal OUT in FIG. 6, resulting in flicker noise.

  Patent Document 1 discloses a method of reducing flicker noise by adjusting the signal SUB so that the charge accumulation time is a natural number times the blinking period of illumination light. FIG. 7 is a timing chart showing the drive timing when the charge accumulation time shown in FIG. 6 is 1/100 second, which is one time the blinking period of illumination light. As shown in FIG. 7, if the charge accumulation time and the blinking period of the illumination light are the same, the amount of illumination light incident on the photoelectric conversion element during each charge accumulation time is constant, so that the level of the imaging signal OUT is also constant. Thus, flicker noise is reduced.

JP 2003-244555 A

  However, in the method described in Patent Document 1, there is a restriction that the charge accumulation time must be a natural number multiple of the blinking period of the illumination light. Therefore, the exposure amount cannot be finely controlled. The control must be performed by controlling the gain of an amplifier that outputs an imaging signal. Increasing the gain amplifies noise, which is not preferable because S / N deteriorates. In addition, the imaging device described in Patent Document 1 requires a storage unit in addition to a normal light receiving unit, which increases the chip size and is disadvantageous in terms of cost.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for driving a solid-state imaging device capable of reducing flicker noise while preventing image quality deterioration and cost increase.

  A driving method of a solid-state imaging device according to the present invention is a driving method of a solid-state imaging device that outputs an imaging signal corresponding to a charge accumulated in a photoelectric conversion device in a desired charge accumulation time at a predetermined imaging cycle, and illuminates a subject. An imaging cycle determining step for determining the imaging cycle based on a blinking cycle of illumination light to be performed and the desired charge accumulation time; and the solid-state imaging device captures an image with the determined imaging cycle and the desired charge accumulation time. A drive signal supplying step of supplying a drive signal for performing the operation to the solid-state imaging device.

  In the solid-state imaging device driving method according to the present invention, in the imaging cycle determination step, the imaging cycle is set to a value that satisfies a condition that is not less than the desired charge accumulation time and is a natural number multiple of the blinking cycle.

  The solid-state imaging device driving method according to the present invention includes: a luminance level detection step for detecting a luminance level of an imaging signal output from the solid-state imaging device for each imaging cycle; and the desired level based on a variation amount of the luminance level. A charge storage time correction step for correcting the charge storage time of the solid-state image pickup device, and in the drive signal supply step, the solid-state image pickup device performs imaging in the desired charge storage time after the correction. The drive signal to be supplied is controlled.

  The solid-state imaging device according to the present invention includes a solid-state imaging device that outputs an imaging signal corresponding to the charge accumulated in the photoelectric conversion element in a desired charge accumulation time at a predetermined imaging period, An imaging period determining unit that determines the imaging period based on a desired charge accumulation time, and a driving signal for the solid-state imaging device to perform imaging with the determined imaging period and the desired charge accumulation time. Drive signal supply means for supplying to the image sensor.

  In the solid-state imaging device according to the present invention, the imaging cycle determining means sets the imaging cycle to a value that satisfies a condition that is not less than the desired charge accumulation time and is a natural number multiple of the blinking cycle.

  The solid-state imaging device according to the present invention includes a luminance level detection unit that detects a luminance level of an imaging signal output from the solid-state imaging device for each imaging cycle, and the desired charge accumulation based on the variation amount of the luminance level Charge accumulation time correction means for correcting time, and the drive signal supply means supplies the drive to the solid-state image sensor so that the solid-state image sensor performs imaging in the desired charge accumulation time after the correction. Control the signal.

  According to the present invention, it is possible to provide a driving method of a solid-state imaging device capable of reducing flicker noise while preventing image quality deterioration and cost increase.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of a solid-state imaging device for explaining a first embodiment of the present invention.
A solid-state imaging device 1 shown in FIG. 1 includes a CCD-type or MOS-type solid-state imaging device 2, an analog front end (AFE) 3, a signal processing unit 4, a timing generation unit (Timing Generator) 5, and a control unit 6. With.

  The solid-state imaging device 2 operates in accordance with an imaging drive signal supplied from the timing generator 5 and outputs an analog imaging signal. The imaging drive signal includes a vertical synchronization signal V, a horizontal synchronization signal H, a charge sweep signal SUB, a charge readout signal TG, a vertical transfer pulse, a horizontal transfer pulse, and the like.

  The AFE 3 performs a correlated double sampling process, an A / D conversion process, and the like on the imaging signal output from the solid-state imaging device 2 and outputs a digital imaging signal. The AFE 3 is operated by an AFE drive signal supplied from the timing generator 5.

  The signal processing unit 4 performs predetermined digital signal processing such as white balance adjustment processing and gamma correction processing on the imaging signal output from the AFE 3.

  The control unit 6 controls the timing generation unit 5 and the signal processing unit 4. The controller 6 determines the charge accumulation time according to the brightness of the subject in the moving image shooting mode, and notifies the timing generator 5 of the determined charge accumulation time. Note that the charge accumulation time can also be manually set by the user of the solid-state imaging device 1, and in this case, the control unit 6 notifies the timing generation unit 5 of the manually set charge accumulation time.

  The timing generator 5 generates the drive signal and supplies it to the solid-state imaging device 2, the AFE 3, and the signal processor 4. The blinking cycle of the illumination light that illuminates the subject is stored in advance in the memory in the solid-state imaging device 1, and the timing generation unit 5 is based on the blinking cycle and a desired charge accumulation time notified from the control unit 6. Thus, the imaging cycle of moving image shooting is determined. The imaging cycle to be determined is a value that satisfies the condition that it is longer than the desired charge accumulation time and is a natural number times the blinking cycle. The reason why the imaging cycle is longer than the desired charge accumulation time is that the charge accumulation time cannot be longer than the imaging cycle. The reason why the imaging period is a natural number times the blinking period is to make the amount of illumination light incident on the photoelectric conversion element constant in each imaging period. The timing generator 5 generates a drive signal for imaging including a drive signal H, V, SUB, and TG for the solid-state imaging device 2 to perform imaging with a desired charge accumulation time and the imaging cycle determined as described above. This is supplied to the solid-state imaging device 2.

The operation at the time of moving image shooting of the solid-state imaging device 1 will be described.
When the moving image shooting mode is set, the control unit 6 determines the charge accumulation time and notifies the timing generation unit 5 of it. The timing generation unit 5 determines an imaging cycle that satisfies a condition that is not less than the notified charge accumulation time and that is a natural number multiple of the blinking cycle of known illumination light. For example, when the blinking cycle is 1/100 seconds and the charge accumulation time is 1/80 seconds or 1/50 seconds, the imaging cycle is set to 2/100 seconds. When the blinking cycle is 1/100 seconds and the charge accumulation time is 1/400 seconds, the imaging cycle is set to 1/100 seconds. If the blinking cycle is 1/100 seconds and the charge accumulation time is 1/10 seconds, the imaging cycle is set to 10/100 seconds. The timing generation unit 5 generates drive signals H, V, SUB, and TG for the solid-state imaging device 2 to perform imaging with the determined imaging cycle and the charge accumulation time notified from the control unit 6, and the solid-state imaging device 2. To supply. The solid-state imaging device 2 operates according to this drive signal, accumulates charges during the charge accumulation time, and outputs an imaging signal at the determined imaging cycle.

  2 and 3 are timing charts showing an example of drive timing of the imaging apparatus shown in FIG. FIG. 2 is a diagram illustrating the drive timing when the charge accumulation time is 1/50 seconds, and FIG. 3 is a diagram illustrating the drive timing when the charge accumulation time is 1/80 seconds. The description of each signal shown in FIGS. 2 and 3 is the same as each signal shown in FIGS. According to the driving based on the timing charts shown in FIGS. 2 and 3, since the imaging cycle is twice the blinking cycle of the illumination light, the amount of illumination light incident on the photoelectric conversion element is constant in each imaging cycle. Become. Furthermore, since the charge accumulation time is constant, such as 1/50 second or 1/80 second, the amount of illumination light incident on the photoelectric conversion element during each charge accumulation time is also constant, and the level of the imaging signal OUT is also high. It becomes constant. As a result, flicker noise caused by flickering of illumination light can be reduced.

  As described above, according to the solid-state imaging device 1, when the charge accumulation time is determined, it is possible to automatically determine an imaging cycle in which flicker noise does not occur during the charge accumulation time. There are imaging devices that can manually set the imaging cycle. In such an imaging device, flicker noise can be reduced by setting the imaging cycle to a natural number times the blinking cycle of illumination light. However, since the maximum value of the charge accumulation time is determined by the manually set imaging cycle, there is a possibility that good imaging cannot be performed depending on the imaging environment such as the brightness of the subject. On the other hand, since the imaging cycle is determined in accordance with the shooting environment, the solid-state imaging device 1 can perform favorable imaging while reducing flicker noise.

  Further, according to the solid-state imaging device 1, since the charge accumulation time can be arbitrarily set, the exposure amount can be controlled without increasing the gain of the output amplifier of the solid-state imaging device 2 that outputs the imaging signal. Image quality can be improved.

  Further, according to the solid-state imaging device 1, unlike the device described in Patent Document 1, it is not necessary to make the solid-state imaging device 2 a frame interline type or a frame transfer type, and while preventing an increase in chip size and manufacturing cost, Flicker noise can be reduced.

(Second embodiment)
Even in the solid-state imaging device 1 having the configuration described in the first embodiment, flicker noise with a different period as shown in FIG. May be. As shown in FIG. 4A, the imaging signal OUT does not reach a constant level as indicated by a broken line as time passes, and slowly deviates from the broken line, and flicker noise with another fluctuation period is observed. This is because even if the imaging cycle is controlled to be a natural number multiple of the blinking cycle of the illumination light, the imaging cycle does not completely match the natural number multiple of the blinking cycle of the illumination light. This is because flicker noise corresponding to the difference (hereinafter referred to as long-term noise) is generated. Therefore, in this embodiment, by configuring the imaging apparatus as shown in FIG. 5 below, it is possible to obtain an imaging signal OUT at a constant level even after a long time has elapsed, as shown in FIG. 4B. I have to.

FIG. 5 is a block diagram showing a schematic configuration of an imaging apparatus for explaining the second embodiment of the present invention. In FIG. 5, the same components as those in FIG.
A solid-state imaging device 1 ′ shown in FIG. 5 adds a luminance level detection unit 7 and a correction charge accumulation time calculation unit 8 to the configuration of the solid-state imaging device 1 shown in FIG. It is changed to part 5 ′.

  The control unit 6 controls the timing generation unit 5 ′ and the signal processing unit 4. In the moving image shooting mode, the control unit 6 determines the charge accumulation time based on the brightness of the subject and notifies the timing generation unit 5 ′ of the determined charge accumulation time. The charge accumulation time can also be manually set by the user of the solid-state imaging device 1 ′. In this case, the control unit 6 notifies the timing generation unit 5 ′ of the manually set charge accumulation time. .

  The luminance level detection unit 7 detects the luminance level of the imaging signal for one frame output from the AFE 3 during the moving image shooting period, calculates the integrated value, and outputs the calculation result to the correction charge accumulation time calculation unit 8. Supply.

  The correction charge accumulation time calculation unit 8 calculates a correction charge accumulation time for correcting a desired charge accumulation time based on the fluctuation amount of the luminance level integrated value, and notifies the timing generation unit 5 ′ of this. To do. The correction charge accumulation time is, for example, data such as minus how many seconds and plus how many seconds.

  The timing generator 5 ′ has substantially the same function as the timing generator 5, but has a slightly different function for generating a drive signal for imaging. The timing generation unit 5 ′ corrects the desired charge accumulation time notified from the control unit 6 by the correction charge accumulation time, and the solid-state imaging element 2 performs imaging in the corrected charge accumulation time. The drive signal SUB supplied to 2 is controlled.

Hereinafter, an operation at the time of moving image shooting of the solid-state imaging device 1 ′ will be described.
When the moving image shooting mode is set, the control unit 6 determines the charge accumulation time and notifies the timing generation unit 5 ′. The timing generation unit 5 ′ determines an imaging period that satisfies a condition that is not less than the notified charge accumulation time and that is a natural number multiple of the blinking period of known illumination light. For example, when the blinking cycle is 1/100 seconds and the charge accumulation time is 1/80 seconds or 1/50 seconds, the imaging cycle is set to 2/100 seconds. When the blinking cycle is 1/100 seconds and the charge accumulation time is 1/400 seconds, the imaging cycle is set to 1/100 seconds. If the blinking cycle is 1/100 seconds and the charge accumulation time is 1/10 seconds, the imaging cycle is set to 10/100 seconds. The timing generation unit 5 ′ generates drive signals H, V, SUB, and TG for the solid-state imaging device 2 to perform imaging with the determined imaging cycle and the charge accumulation time notified from the control unit 6, and the solid-state imaging device 2 is supplied. The solid-state imaging device 2 operates according to this drive signal, accumulates charges during the charge accumulation time, and outputs an imaging signal at the determined imaging cycle.

  When an imaging signal for one frame is output from the AFE 3, the luminance level detection unit 7 obtains an integrated value of the imaging signal and supplies the integrated value to the correction charge accumulation time calculation unit 8. The correction charge accumulation time calculation unit 8 obtains an average value of the two integrated values at the time when the two integrated values are supplied from the luminance level detection unit 7. And the average value calculated | required here is compared with the integrated value supplied from the brightness | luminance level detection part 7 next.

  When the newly supplied integrated value is larger than the average value, the correction charge accumulation time calculating unit 8 is notified from the control unit 6 to the timing generating unit 5 ′ according to the difference between the integrated value and the average value. The correction charge storage time for shortening the charge storage time is calculated. On the other hand, when the newly supplied integrated value is smaller than the average value, the correction charge accumulation time calculating unit 8 changes the control unit 6 to the timing generating unit 5 ′ according to the difference between the integrated value and the average value. A correction charge accumulation time for increasing the notified charge accumulation time is calculated.

  After calculating the correction charge accumulation time, the correction charge accumulation time calculation unit 8 notifies the timing generation unit 5 ′ of the calculated correction charge accumulation time. Then, the correction charge accumulation time calculation unit 8 obtains the average value of the two integrated values already supplied and the newly supplied integrated value, updates the average value, and the next integrated value is supplied. Sometimes, the correction charge accumulation time is calculated using the updated average value.

  When the correction charge accumulation time is notified to the timing generation unit 5 ′, the timing generation unit 5 ′ adds the correction charge accumulation time to the desired charge accumulation time notified from the control unit 6 to obtain the desired charge. Correct the accumulation time. Then, the timing generation unit 5 ′ controls the drive signal SUB in order to cause the solid-state imaging device 2 to perform imaging with the corrected charge accumulation time.

  As the timing generator 5 ′ repeats the process of correcting the charge accumulation time and controlling the drive signal SUB, the correction charge accumulation time converges to zero, that is, the luminance level of the imaging signal in each frame is constant. Therefore, long-term noise as shown in FIG. 4A can be reduced.

  As described above, according to the solid-state imaging device 1 ′, since the charge accumulation time is corrected so that the luminance level of the imaging signal during the imaging period is constant, long-term noise can be reduced.

  In the above embodiment, the timing generation unit 5 corresponds to an imaging cycle determination unit and a drive signal supply unit in the claims. The timing generator 5 'corresponds to an imaging cycle determination unit, a drive signal supply unit, and a charge accumulation time correction unit.

  In the first embodiment and the second embodiment, the timing generation unit 5 or 5 ′ determines the imaging period. However, this may be performed by another part, for example, the control unit 6. In this case, the control unit 6 may notify the timing generation unit 5 or 5 ′ of the determined imaging cycle and desired charge accumulation time. Further, although the charge generation time is corrected by the timing generation unit 5 ′, this may be performed by another part, for example, the control unit 6.

The block diagram which shows schematic structure of the imaging device for describing 1st embodiment of this invention FIG. 1 is a timing chart showing drive timing of the imaging apparatus shown in FIG. FIG. 1 is a timing chart showing drive timing of the imaging apparatus shown in FIG. (A) is a figure which shows an example of the level of the imaging signal at the time of image | photographing for a long time, (b) is a figure which shows an example of the level of the imaging signal after charge accumulation time correction | amendment The block diagram which shows schematic structure of the imaging device for describing 2nd embodiment of this invention. Timing chart showing operation timing of conventional imaging device Timing chart showing the operation timing of the conventional imaging device with general flicker countermeasures

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1 'Solid-state imaging device 2 Solid-state image sensor 3 Analog front end 4 Signal processing part 5, 5' Timing generation part 6 Control part 7 Luminance level detection part 8 Compensation charge accumulation time calculation part

Claims (6)

A solid-state image sensor driving method for outputting an imaging signal corresponding to the charge accumulated in the photoelectric conversion element in a desired charge accumulation time at a predetermined imaging cycle,
An imaging period determining step for determining the imaging period based on a blinking period of illumination light that illuminates a subject and the desired charge accumulation time;
A driving signal supply step of supplying a driving signal for the solid-state imaging device to perform imaging in the determined imaging cycle and the desired charge accumulation time to the solid-state imaging device; A method for driving a solid-state imaging device according to claim 1,
In the imaging cycle determination step, the solid-state imaging device driving method, wherein the imaging cycle is set to a value that satisfies a condition of not less than the desired charge accumulation time and a natural number times the blinking cycle. A method for driving a solid-state imaging device according to claim 1 or 2,
A luminance level detection step of detecting a luminance level of an imaging signal output from the solid-state imaging device for each imaging cycle;
A charge accumulation time correction step of correcting the desired charge accumulation time based on the amount of change in the luminance level,
In the driving signal supply step, the solid-state imaging device driving method for controlling the driving signal supplied to the solid-state imaging device so that the solid-state imaging device performs imaging in the desired charge accumulation time after the correction. A solid-state imaging device that outputs an imaging signal corresponding to the charge accumulated in the photoelectric conversion element in a desired charge accumulation time at a predetermined imaging cycle;
An imaging period determining means for determining the imaging period based on a blinking period of illumination light for illuminating a subject and the desired charge accumulation time;
A solid-state imaging device comprising: a driving signal supply unit that supplies the solid-state imaging device with a driving signal for the solid-state imaging device to perform imaging at the determined imaging cycle and the desired charge accumulation time. The solid-state imaging device according to claim 4,
The imaging cycle determination unit is a solid-state imaging device that sets the imaging cycle to a value that satisfies a condition that is not less than the desired charge accumulation time and is a natural number multiple of the blinking cycle. The solid-state imaging device according to claim 4 or 5,
A luminance level detecting means for detecting a luminance level of an imaging signal output from the solid-state imaging device for each imaging cycle;
Charge accumulation time correcting means for correcting the desired charge accumulation time based on the amount of change in the luminance level;
The drive signal supply means controls the drive signal supplied to the solid-state image sensor so that the solid-state image sensor performs imaging in the desired charge accumulation time after the correction.

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