JPH08102893A - Image pickup device - Google Patents

Abstract

PURPOSE: To enable stable black reference level clamp in a video device using a solid-state image pickup element. CONSTITUTION: Among image pickup cells arrayed two-dimensionally in the solid-state image pickup element 1, image pickup cells for a prescribed horizontal scanning lines from an edge are light-shielded by a light shielding part. The video signal outputted from the solid-state image pickup element 1 is provided for a black reference level clamp circuit 5 through a sample/hold circuit 2, an amplifier circuit 3 and a low pass filter 4. The black reference level clamp circuit 5 sample/holds a signal outputted from the image pickup cells for a specified one horizontal scanning line among the image pickup cells light- shielded by the light shielding part among the provided video signals in accordance with a clamp pulse cp the pulse width of which is longer than a period corresponding to a horizontal retrace line period and clamps the video signal in accordance with the difference between the level of the sample/held signal and a reference level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus using a solid-state image pickup device such as a CCD image pickup device, and more particularly, to a stable black reference level clamp for a video signal output from the solid-state image pickup device. The present invention relates to an image pickup device.

[0002]

2. Description of the Related Art In an image pickup apparatus using a solid-state image pickup element, a black reference level clamp is performed on a video signal in order to compensate for a change in the level of the video signal due to a temperature change.

By the way, in order to perform the black reference level clamp, it is necessary to obtain the black level of the video signal output from the solid-state image sensor. Conventionally, for example, as shown in FIG. Among the image pickup cells arranged two-dimensionally in the image pickup area 103 of 100, a plurality of image pickup cells corresponding to the front porch in the horizontal blanking period are provided in the light shielding unit 10.
The light level is blocked by 2 and the black level is obtained by sample-holding the signal output from the image pickup cell blocked by the light-blocking section 102 in accordance with the sample-hold pulse (for example, Japanese Patent Laid-Open No. 58-346).
No. 80). That is, as shown in FIG. 6, a black level is obtained by sample-holding a signal output from the image pickup cell shielded by the light-shielding section in the front porch during the horizontal blanking period by the sample-hold pulse. There is. In FIG. 5, reference numeral 101 denotes an effective image pickup area.

Then, the clamp control means clamps the video signal so that the black level of the video signal obtained as described above is equal to the black reference level.

[0005]

By the way, in order to obtain an accurate black level by the above-mentioned method, it is desired that the number of image pickup cells shielded by the light shielding portion is large and the sample time is long. However, if an attempt is made to increase the number of image pickup cells shielded by the light shielding unit, the total number of image pickup cells of the solid-state image pickup element will increase or the effective image pickup area will decrease.
In addition, the sample time cannot be set too long because it is limited by the number of imaging cells in the horizontal direction, the time of the horizontal blanking period, and the like. As described above, conventionally, it is necessary to obtain a black level within a very spatially and temporally limited range.

As described above, since there is conventionally no room in space and time, as shown in FIG. 7 which is a horizontal sectional view of the solid-state image sensor 100 shown in FIG. 5, diffuse reflection of excess light is performed. In the case where unnecessary leakage charge is generated in the image pickup cell 104 of the light shielding unit 102 due to the light b incident on the image pickup cell 104 due to a defect of the light shielding unit 102 such as a or a pinhole, or FIG.
As shown in, due to the horizontal transfer failure of the solid-state image sensor,
When unnecessary leak charges are generated during the horizontal blanking period of the video signal, the average value of the signal level during the sampling period increases. As a result, as shown in FIG. 9, when the above-mentioned unnecessary leak charge is generated in a certain horizontal blanking period, the black level used for clamping during the horizontal blanking period is increased. It becomes higher than the black level used for clamping in other horizontal blanking periods.

When the black level becomes high, the clamp level control means works so as to lower the level of the entire video signal output from the solid-state image pickup device in order to make the level equal to the reference level. The black level becomes lower than the black levels of other horizontal scanning lines. As a result, in the reproduced image, the signal level of the horizontal scanning line becomes lower than the other horizontal scanning lines as a whole, so that the horizontal striping occurs as a black band and the image quality is deteriorated.

An object of the present invention is to make it possible to perform stable black reference level clamping in an image device using a solid-state image pickup device.

[0009]

In order to achieve the above-mentioned object, the present invention achieves the above-mentioned object, and among the two-dimensionally arranged image pickup cells, the image pickup cells for a predetermined horizontal scanning line from the end are shielded by the light shielding portion. A solid-state image pickup device, and of the signals output from the solid-state image pickup device, the level of the signal output from the image pickup cell shielded by the light shielding unit is sample-held according to a clamp pulse, and the level of the sample-held signal and the reference A signal is output from an image pickup cell for a specific one horizontal scanning line of a black reference level clamp circuit that clamps a signal output from the solid-state image pickup element according to a level difference and an image pickup cell shielded by the light shielding unit. While being output, a clamp pulse having a pulse width longer than the period corresponding to the horizontal blanking period is output and is shielded by the light shielding unit. It is obtained by a synchronizing signal generator for a signal output period from the image cells in a part of the vertical blanking interval.

[0010]

In the vertical blanking period, the signal of the image pickup cell shielded by the light shielding portion is output from the solid-state image sensor.
Further, while the signal of the image pickup cell for one specific horizontal scanning line among the image pickup cells shielded by the light shielding unit from the solid-state image pickup device is being output, a clamp pulse is output from the synchronization signal generator.

When a clamp pulse is output from the synchronizing signal generator, the black reference level clamp circuit samples and holds the level of the signal output from the image pickup cell shielded by the light shield unit according to the clamp pulse, and the sampled and held signal. The signal output from the solid-state image pickup device is clamped according to the difference between the level of 1 and the reference level. Here, the pulse width of the clamp pulse is set to be longer than the period corresponding to the horizontal blanking period, and the level of the signal output from the image pickup cell shielded with high precision can be sampled and held, and thus stable. The black reference level clamp can be performed.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a solid-state image pickup device 1 used in the embodiment of the present invention.

The solid-state image pickup device 1 includes a plurality of image pickup cells 11
Are arranged two-dimensionally, and the image pickup cells 11 of a predetermined horizontal scanning line are shielded by the light shielding portion 15 from the upper end portion thereof. Further, the signal charges obtained by the image pickup cells 11 arranged in the effective image pickup area 16 and the image pickup cells 11 shielded by the light shielding unit 15 are output to the outside via the vertical register 12, the horizontal register 13, and the output amplifier 14. It

FIG. 2 is a block diagram of an embodiment of the present invention. The solid-state image pickup device 1 having the structure shown in FIG. 1, a sample hold circuit 2, an amplifier circuit 3, a low pass filter 4, and a black reference level. It is composed of a clamp circuit 5, a signal processing circuit 6, and a synchronization signal generator 7.

FIG. 3 is a circuit diagram showing a configuration example of the black reference level clamp circuit 5, which is an amplifier circuit 51, a sample hold circuit 52, an error amplifier 53, and resistors R, Ri, R.
f and.

Next, the operation of this embodiment will be described.

The synchronizing signal generator 7 synchronizes a drive pulse to the solid-state image pickup device 1, a sample and hold pulse to the sample and hold circuit 2, a clamp pulse cp to the black reference level clamp circuit 5, and a horizontal and vertical synchronization to the signal processing circuit 6. Supply a signal. Here, the synchronization signal generator 7 is configured to make the period during which the image signal corresponding to the image pickup cell 11 shielded by the light shielding unit 15 is output from the solid-state image sensor 1 to be part of the vertical blanking period. A predetermined one horizontal scanning line (preferably 1 to 2 horizontal from the end of the light-shielding portion) of the plurality of horizontal scanning-line image-capturing cells 11 that output the synchronization signal and are shielded by the light-shielding portion 15. While the signal corresponding to the imaging cell 11 corresponding to the horizontal scanning line separated by the scanning line) is output from the solid-state imaging device 1, the clamp pulse cp having a predetermined pulse width is output. In this embodiment,
The pulse width of the clamp pulse cp is made longer than the period corresponding to the horizontal blanking period, and the supply timing of the clamp pulse cp is set to 1 to 1 from the boundary between the light shielding unit 15 and the effective imaging region 16.
The timing is set to have a margin for two imaging cells.

The solid-state image pickup device 1 outputs a video signal according to the drive pulse supplied from the synchronization signal generator 7.

The sample and hold circuit 2 samples and holds the video signal output from the solid-state image pickup device 1 in accordance with the sample and hold pulse supplied from the synchronizing signal generator 7, and extracts and outputs only the signal component in the video signal.

The output signal of the sample-hold circuit 2 is amplified by the amplifier circuit 3, further noise-removed by the low-pass filter 4, and then input to the black reference level clamp circuit 5.

The black reference level clamp circuit 5 having the structure shown in FIG. 3 amplifies the video signal from the low pass filter 4 by the amplifier circuit 51. The output signal of the amplifier circuit 51 is output to the signal processing circuit 6 and also to the sample hold circuit 52 in the black reference level clamp circuit 5.

The sample and hold circuit 52 samples and holds the video signal output from the amplifier circuit 51 in accordance with the clamp pulse cp supplied from the sync signal generator 7. Here, as shown in FIG. 4, the clamp pulse cp is within a vertical blanking period and is a predetermined one of the image pickup cells 11 shielded by the light shielding unit 15.
Since the signal corresponding to the imaging cell 11 of the horizontal scanning line is output during the period in which the solid-state imaging device 1 is outputting, the sample hold circuit 52 outputs from the imaging cell 11 shielded by the light shielding unit 15. The output signal will be sample-held.

The level sampled and held by the sample and hold circuit 52 is supplied to the reference voltage V by the error amplifier 53.
It is compared with ref, and the error is amplified and fed back to the amplifier circuit 51 via the resistor R in the direction of canceling the error with the reference voltage Vref.

The signal processing circuit 6 receives the video signal from the black reference level clamp circuit 5 and the horizontal signal from the sync signal generator 7.
The vertical synchronizing signal is combined and output as a decoded video signal to a monitor or the like.

In the above-described embodiment, the light-shielding portion is provided above the solid-state image pickup element, but it may be provided below. Also, in the embodiment, the clamp pulse is output for each vertical blanking period, that is, for each field, and the sample hold is performed for one field period immediately after the black reference level clamp circuit outputs the clamp pulse. Although the signal output from the solid-state image sensor is clamped according to the level, the clamp pulse is output every two fields, that is, every frame, and the black reference level clamp circuit outputs the clamp pulse in the two fields immediately after the clamp pulse is output. The signal output from the solid-state imaging device may be clamped according to the level sampled and held during the period.

[0027]

As described above, according to the present invention, among the image pickup cells arranged in the solid-state image pickup device, the image pickup cells for a predetermined horizontal scanning line from the end are shielded by the light shield portion and are shielded. The period during which the signal is output from the image pickup cell is set to the period within the vertical blanking period, and further, one specific horizontal scan line segment of the predetermined horizontal scan line segment that is shielded from light is provided. During the period when the signal is being output from the image pickup cell, the clamp level is output to output a clamp pulse that is longer than the period corresponding to the horizontal blanking period to sample the black level of the video signal for performing the black reference level clamp. Therefore, it is possible to obtain a sufficient spatial and temporal margin as compared with the conventional example in which the black level is sampled during the horizontal blanking period.

Therefore, even if a part of the image pickup cell shielded by irregular reflection or a pinhole is irradiated with light, the black level should be sampled for a sufficiently long time longer than the horizontal blanking period. Therefore, the influence can be reduced as compared with the conventional example.
That is, sample holding can be performed by a sample hold circuit having a large capacitance and a long time constant, so that the influence of irregular reflection and pinholes can be reduced. Further, the sampled black level can be held for a long time by using the sample hold circuit as described above. Further, even if a part of the light shielding portion is irradiated with light due to irregular reflection, it is hardly affected by the light, so that the area of the light shielding portion can be made small.

Further, in the present invention, since the signal output from the image pickup cell on a certain horizontal scanning line which is wholly shielded by the light shielding portion is sampled for a certain period, immediately before and immediately after the sample period. The signal also becomes black level. Therefore, even if a transfer failure occurs during the horizontal transfer of signal charges, the sampling result is not affected, and an accurate black level can be sampled and held. In addition,
Since the transfer speed of the signal charges in the vertical direction is much slower than that in the horizontal direction, a transfer failure hardly occurs.
Therefore, the specific horizontal scanning line is installed on the side opposite to the signal extraction side, and therefore, even if the vertical transfer distance becomes long, no transfer failure occurs during vertical transfer, so there is no problem.

As described above, according to the present invention, the black level of the video signal output from the solid-state image pickup device can be accurately sampled and held, so that there is an effect that a stable black reference level clamp can be performed. . .

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a solid-state imaging device 1 used in an embodiment of the present invention.

FIG. 2 is a block diagram of an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration example of a black reference level clamp circuit 5.

FIG. 4 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a solid-state imaging device which has been conventionally used.

FIG. 6 is an operation explanatory diagram of a conventional technique.

FIG. 7 is a diagram for explaining a problem of the conventional technique.

FIG. 8 is a diagram for explaining a problem of the conventional technique.

FIG. 9 is a diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Solid-state image sensor 11 ... Imaging cell 12 ... Vertical register 13 ... Horizontal register 14 ... Output amplifier 15 ... Shading part 16 ... Effective imaging area 2 ... Sample hold circuit 3 ... Amplification circuit 4 ... Low pass filter 5 ... Black reference level clamp circuit 6 ... Signal processing circuit 7 ... Synchronous signal generator 51 ... Amplification circuit 52 ... Sample hold circuit 53 ... Error amplification circuit

Claims (3)

[Claims] 1. A solid-state image sensor in which a predetermined horizontal scanning line segment from an end of a two-dimensionally arranged image cell is shielded by a light-shielding portion, and the solid-state image sensor outputs the image. The signal output from the solid-state image sensor according to the difference between the level of the sample-held signal and the reference level is sampled and held according to the clamp pulse of the level of the signal output from the imaging cell shielded by the light-shielding unit A black reference level clamp circuit that clamps a signal, and a period corresponding to a horizontal blanking period while a signal is output from a specific one horizontal scanning line of the image pickup cells among the image pickup cells shielded by the light shielding unit. A clamp pulse having a longer pulse width is output, and a signal output period from the image pickup cell shielded by the light shielding unit is part of the vertical blanking period. Imaging apparatus characterized by comprising a synchronizing signal generator for. 2. The synchronizing signal generator outputs the clamp pulse in each vertical blanking period, and the black reference level clamp circuit outputs the clamp pulse in the one field period immediately after the clamp pulse is output. The image pickup apparatus according to claim 1, wherein a signal output from the solid-state image pickup element is clamped according to a level sampled and held according to a pulse. 3. The sync signal generator outputs the clamp pulse every one vertical blanking period, and the black reference level clamp circuit outputs the clamp pulse for a period of two fields immediately after a clamp pulse is output. 2. The image pickup apparatus according to claim 1, wherein the signal output from the solid-state image pickup element is clamped according to the level sampled and held according to the above.