JP3255464B2 - Image sensor driving method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for driving an image pickup device provided in a still video camera, for example, for generating a video signal corresponding to a subject image.

[0002]

2. Description of the Related Art Conventionally, for example, a still video camera or the like is provided with a CCD (solid-state image sensor) for converting a subject image obtained by an optical system into an electric video signal. The CCD has a photodiode corresponding to each pixel, and charges accumulated in the photodiode by the exposure are shielded from light by the vertical transfer CCD and the horizontal transfer CCD after light shielding.
Output to outside via CD.

However, during the exposure period, if the amount of light received by the photodiode is too large, excess charge leaks from the photodiode into the vertical transfer CCD, and this excess charge mixes with the signal charge stored in the photodiode. Smear and the like are generated, and the image quality is reduced. Also, a dark current is generated due to the influence of heat generated in the CCD, and the vertical transfer CCD
In the case where unnecessary charges are generated, the image quality is similarly reduced. In order to prevent such a decrease in image quality, a configuration has been proposed in which excess charges remaining in the vertical transfer CCD are swept out at high speed to the horizontal transfer CCD.

[0004]

However, the vertical transfer CC
If the charge remaining in D is to be swept out at high speed, excess charge may overflow from the horizontal transfer CCD or an error may occur in the timing of the transfer operation of the excess charge. There is a problem in that excess charge leaks into the diode, and the image quality in this portion deteriorates. Further, in order to drive the vertical transfer CCD at a high speed, it is necessary to increase the capability of the driving circuit, so that there is a problem that power consumption increases.

It is an object of the present invention to provide a method of driving an image pickup device capable of reliably sweeping out unnecessary charges remaining in a vertical transfer CCD without providing a circuit for high-speed driving.

[0006]

[Means for Solving the Problems] In the image pickup device driving method according to the present invention, the charge remaining in the vertical transfer CCD is removed by one filter.
A first step of sweeping out to the outside via the horizontal transfer CCD over a period corresponding to the threshold, and a second step of transferring the charge accumulated in the photodiode by exposure to the vertical transfer CCD after the completion of the first step. After the completion of the second step, the third step of outputting the charge accumulated in the photodiode via the vertical transfer CCD and the horizontal transfer CCD to the outside, and after the aperture starts to close, The first step is started before the shutter is completely closed, and in the optical black area where no effective signal charge is formed in the first step, a horizontal transfer CCD is provided.
The exposure is completed before the sweeping out of the charge remaining in the vertical transfer CCD connected to the photodiode in the portion close to the photodiode, and the sweeping out of the charge in the first step is the same as the charge transfer operation in the third step. It is characterized by being performed at a high speed.

In the image pickup device driving apparatus according to the present invention, the electric charges remaining in the vertical transfer CCD correspond to one field.
Means for sweeping out to the outside via the horizontal transfer CCD over a period, means for transferring the charge accumulated in the photodiode by exposure to the vertical transfer CCD, and, after the transfer by the transfer means is completed, the vertical transfer CCD and the horizontal transfer CC
Means for outputting the charge accumulated in the photodiode to the outside via D, and a sweeping operation of the charge by the sweeping means after the diaphragm starts to close and before the diaphragm completely closes.
Starts, and in the sweeping operation, before the sweeping out of the charge remaining in the vertical transfer CCD connected to the photodiode in the optical black area where the effective signal charge is not formed and adjacent to the horizontal transfer CCD is completed. The exposure is completed, and the sweeping operation is performed at the same speed as the charge transfer operation by the output unit.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a block diagram of a still video camera provided with an image sensor driving device according to an embodiment of the present invention.

A system control circuit 10 is a microcomputer and controls the whole still video camera.

The imaging optical system includes a lens 11, a stop 12, and an optical filter 13.
Guided to CD14. CCD 14 is a VCCD driver 1
5 and a timing generation circuit 17, whereby a video signal corresponding to the subject image formed on the CCD 14 is output from the CCD 14 and supplied to the correlated double sampling (CDS) circuit 16.

The video signal input to the CDS circuit 16 is
After the reset noise is removed, predetermined processing such as gamma correction is performed in a pre-processing circuit (not shown). The video signal is converted into a digital signal by the A / D converter 21 and stored in the image memory 22. The address of the image memory 22 where the video signal is stored is controlled via the system control circuit 10 and the address control circuit 23. The CDS circuit 16 and the A / D
The operation of converter 21 is controlled by a pulse signal output from timing generation circuit 17.

The image processing circuit 24 performs a predetermined process on the image signal stored in the image memory 22, and outputs an R signal, a G signal and a B signal. These R signal, G signal and B signal are input to the recording device 25 and recorded on a recording medium such as an IC memory card.

A manual switch group 26 connected to the system control circuit 10 operates the present still video camera, and a display element 27 displays the contents of operation by various switches of the manual switch group 26, and the like. Each is provided.

Next, referring to FIG. 1 and FIG.
A configuration of the CCD 14 and a configuration for driving the CCD 14 will be described.

The photodiodes 31 are provided corresponding to the respective pixels. In the photodiodes 31, signal charges are formed in accordance with the amount of incident light. The vertical transfer CCD 32
It is provided adjacent to the photodiode 31 along the vertical direction (vertical direction in the figure), and transfers the charge generated in the photodiode 31 to the horizontal transfer CCD 33. An FDA (floating diffusion amplifier) 34 is connected to the horizontal transfer CCD 33, and this FDA
In the DA 34, the electric charge transferred by the horizontal transfer CCD 33 is converted into a voltage and output to the outside.

The VCCD driver 15 receives a / V1 signal (sign / means that the polarity is inverted) from the timing generation circuit 17 and a / Vsub signal from the system control circuit 10, respectively. Is output to the CCD 14. For example, when the / V1 signal to / V4 signal is "L" (low), the φV1 signal to φV4 signal (drive signal) are output as "H" (high). / Vsub
Similarly, a φVsub signal having the opposite polarity is output.

In the synchronizing signal generating circuit 41, a vertical synchronizing signal VD and a horizontal synchronizing signal HD are generated under the control of the system control circuit 10 based on the clock signal fck output from the timing generating circuit 17. In the timing generation circuit 17, the / V1 signal to the / V4 signal, the / TG1 signal and / T
G2 signals are generated, and these signals are input to the VCCD driver 15.

In the CCD 14, the transfer of the vertical transfer CCD from the photodiode and the vertical transfer in the vertical transfer CCD are performed by the drive signal output from the VCCD driver 15, and the horizontal transfer operation is performed by the drive signal output from the timing generation circuit 17. Done. That is, in the vertical transfer CCD 32, four-phase φV1 to φV supplied from the VCCD driver 15 via the terminals 35a to 35d.
Charge transfer from the photodiode and charge transfer in the vertical direction are performed by four signals (drive signals). In the horizontal transfer CCD 33, φH1 and φH2 supplied from the timing generation circuit 17 through terminals 36a and 36b are used.
The transfer of electric charge in the horizontal direction is performed by a signal (drive signal). The φVsub signal supplied from the VCCD driver 15 via the terminal 37 is for sweeping out unnecessary charges accumulated in the CCD 14 toward the substrate of the CCD 14 immediately before the exposure period. These signals control the transfer of the signal charge, the accumulation time of the signal charge, the determination of the electronic shutter speed, and the sweeping of the excess charge.

FIGS. 3 and 4 show an image pickup device driving method according to a first embodiment of the present invention.
5 is a timing chart of an operation of outputting a video signal detected by D14 from a CCD 14.

In FIG. 3, before the exposure period, the aperture 12 is opened (reference F1). The FLD signal indicates an image field, and switches between “H” and “L” according to the field. That is, it becomes "H" in the first field and "L" in the second field. / V
The sub signal is normally "H", but is set to "L" at a predetermined timing based on the operation of a release switch (not shown) in the manual switch group 26. When the / Vsub signal becomes "L", that is, the φVsub signal (see FIG. 2)
Becomes "H", unnecessary charges accumulated in the photodiode 31 up to that point are swept toward the substrate. Since all charges generated in the photodiode during this sweeping period are swept out, charge accumulation of the photodiode is started from the time when the sweeping operation is completed, and thereafter, when the aperture 12 is closed (reference F2), the exposure is completed. I do. The exposure period is from the end of the unnecessary charge sweeping to the closing of the aperture 12, during which the charge corresponding to the subject image is accumulated in the photodiode 31 of the CCD.

On the other hand, the / V1 signal to / V4 signal are repeatedly turned on and off at a predetermined timing. That is, the signals φV1 to φV4 applied to the first to fourth electrodes of the vertical transfer CCD 32 always repeat “H” and “L” at a predetermined timing. This φV1 signal to φ
The V4 signal is a drive signal for vertically transferring charges in the vertical transfer CCD 32.

At the end of the exposure period, the FLD signal is switched, and during the period corresponding to one field (sweep period), vertical transfer and horizontal transfer are performed, and the charge remaining in the vertical transfer CCD 32 is removed. It is swept out through the horizontal transfer CCD 33. The charge remaining in the vertical transfer CCD 32 is due to excess charge leaked from the photodiode 31 or dark current.

The operation of sweeping out the excess charge is performed at the same speed as when the video signal is read. This sweeping operation will be described with reference to FIG. 4. During the period in which the HD signal is "L", that is, during the blanking period, the signals φV1 to φV1
The V4 signal changes continuously, and the charge remaining in the vertical transfer CCD 32 is transferred to the horizontal transfer CCD 33 by two pixels. That is, the first to fourth of the vertical transfer CCD 32
For example, a photodiode 31 of an odd field is connected to the first electrode, and a photodiode 31 of the even field is connected to the third electrode. For example, the photodiode 31 remains at a portion corresponding to the first electrode. Charge is
The data is transferred to a portion corresponding to the next first electrode by one vertical transfer operation.

After such a vertical transfer operation, the HD signal goes to "H" and a horizontal transfer period is started. During this horizontal transfer period, the horizontal transfer CCD 33 outputs the φH1 signal and φ
The charge is transferred by the H2 signal repeating “H” and “L” at a predetermined timing, and the charge corresponding to one horizontal scanning period is swept out from the horizontal transfer CCD 33.

By the repetition of the vertical transfer and the horizontal transfer, the electric charge remaining in the vertical transfer CCD 32 becomes 1
The same time as reading the video signal for the field (1/6
(0 second), and is swept out of the vertical transfer CCD 32 (first
3), as shown in FIG. 3, the / TG1 signal and / TG2 signal are output immediately after the switching of the FLD signal. Thereby, the charges corresponding to the images of the first and second fields stored in the photodiode 31,
That is, the charge accumulated in the photodiode 31 by the exposure is transferred to the vertical transfer CCD 32 (second step).

The charges are transferred to the horizontal transfer CCD 33 by two pixels by the action of the signals / V1 to / V4, that is, the signals φV1 to φV4.
H1 signal and φH2 signal cause horizontal transfer CC.
The signal for one horizontal scanning line in D33 is transferred to the FDA 34 (FIG. 2) (third step). In this way, the electric charge (video signal) accumulated in the photodiode 31 is output from the CCD 14 by one horizontal scanning line via the vertical transfer CCD 32 and the horizontal transfer CCD 33 (reference C1).

As described above, in the first embodiment, the charge remaining in the vertical transfer CCD 32 is swept to the outside via the horizontal transfer CCD 33 before the charge stored in the photodiode 31 is read out after the exposure period. Is configured. Therefore, even if excess charge leaks from the photodiode to the vertical transfer CCD during the exposure period, or if a dark current is generated, the excess charge and the like are not mixed with the signal charge stored in the photodiode. Therefore, occurrence of smear or the like, that is, deterioration of image quality is prevented. Further, in this embodiment, the vertical transfer CCD 3
2 does not sweep out the excess charge at a high speed, but transfers at the same speed as the read operation of the video signal. Therefore, no transfer error occurs, and it is necessary to provide a circuit for high-speed driving. Absent.

FIGS. 5 and 6 show a second embodiment. In this embodiment, only the portions different from the first embodiment will be described. The end of the exposure period is after the switching of the FLD signal. That is, the output of the / V1 signal to / V4 signal is started before the end of the exposure period by a period indicated by reference F3 (hereinafter, referred to as a preceding sweep period). Other operations are the same as in the first embodiment.

The length of the preceding sweep period F3 will be described with reference to FIG. This figure shows the light receiving surface 44 of the CCD 14.
And the horizontal transfer CCD 33. The light receiving surface 44 includes an effective pixel area 44a to which light is actually irradiated, and an optical black area 44b formed around the effective pixel area 44a. Optical black area 44
b is a portion where light is not irradiated, that is, a portion where effective signal charges are not formed.

The pre-sweep period F3 corresponds to the portion A which is the optical black area 44b and is close to the horizontal transfer CCD 33, and the number of pixels of this portion A in the vertical direction (vertical direction in the figure) × 1 horizontal scanning Line read time x 1/2,
That is, it is time to read the electric charges for one field of the portion A. In other words, the exposure has been completed before the sweeping out of the charges remaining in the vertical transfer CCD 32 (FIG. 2) connected to the photodiode 31 (FIG. 2) in this part A is completed. Therefore, after the exposure is completed, the charge remaining in the vertical transfer CCD 32 connected to the photodiode in the effective pixel area 44a is swept out, and the time of the sweeping operation can be minimized.

Other functions and effects are the same as those of the first embodiment.

As described above, the first and second embodiments have an effect that the image quality can be improved without providing a particularly complicated circuit.

In each of the above embodiments, the video signal is recorded in the field mode. However, it is needless to say that the present invention can be applied to the frame mode.

[0034]

As described above, according to the present invention, there is obtained an effect that unnecessary charges remaining in the vertical transfer CCD can be reliably discharged to the outside without providing a circuit for high-speed driving. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of a still video camera to which an embodiment of the present invention has been applied.

FIG. 2 is a diagram showing a configuration of a CCD.

FIG. 3 is a timing chart of the operation of the CCD according to the first embodiment of the present invention.

FIG. 4 is a timing chart of an operation of sweeping out excess charges of a vertical transfer CCD.

FIG. 5 is a timing chart of the operation of the CCD according to the second embodiment of the present invention.

FIG. 6 is a diagram showing an effective pixel area and an optical black area of the CCD.

[Description of Signs] 14 CCD 31 Photodiode 32 Vertical transfer CCD 33 Horizontal transfer CCD 44 Light receiving surface 44a Effective pixel area 44b Optical black area

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/335

Claims (2)

(57) [Claims] 1. An electric charge remaining in a vertical transfer CCD is reduced by 1
A first step of sweeping out to the outside via the horizontal transfer CCD over a period corresponding to the field, and a second step of transferring the charge accumulated in the photodiode by exposure to the vertical transfer CCD after the first step is completed. And after the completion of the second step, a third step of outputting the electric charge accumulated in the photodiode via the vertical transfer CCD and the horizontal transfer CCD to the outside, and after the aperture starts closing. And before closing completely
And the horizontal transfer CCD is an optical black area where effective signal charges are not formed in the first step.
The exposure is completed before the sweeping out of the charge remaining in the vertical transfer CCD connected to the photodiode in the portion close to the photodiode is completed, and the sweeping out of the charge in the first step is the transfer of the charge in the third step. An image pickup device driving method, wherein the operation is performed at the same speed as the operation. 2. The electric charge remaining in the vertical transfer CCD is reduced by 1
Means for sweeping out to the outside via the horizontal transfer CCD over a period corresponding to the field, means for transferring the charge accumulated in the photodiode by exposure to the vertical transfer CCD, and vertical transfer after the transfer by the transfer means is completed. CCD
And means for outputting the charge accumulated in the photodiode to the outside via a horizontal transfer CCD, and after the aperture starts to be closed and before the aperture is completely closed, the sweeping operation of the charge by the sweeping means is started. An optical black area where effective signal charges are not formed in the sweeping operation and a horizontal transfer CCD
The exposure is completed before the sweeping out of the charge remaining in the vertical transfer CCD connected to the photodiode in a portion close to the photodiode is completed, and the sweeping operation is performed at the same speed as the charge transfer operation by the output unit. An image pickup device driving device, comprising: