JP2002271702A - Solid-state imaging device - Google Patents

Abstract

(57) [Problem] To provide a solid-state imaging device capable of eliminating a black level fluctuation when shifting from a partial reading scanning mode to a normal scanning mode and sufficiently increasing a frame rate. SOLUTION: In a solid-state imaging device in which a black level of an image output of a solid-state imaging device 1 is fixed by a clamp circuit 4 of a feedback clamp system, a pause pulse generator 6 and a clamp pulse pause circuit 7 are provided, and partial reading is performed. In the scanning mode, the supply of the clamp pulse to the clamp circuit 4 is prohibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device that obtains a black level value of an image signal from an optical black section provided in an imaging device, and more particularly to a solid-state imaging device that performs a partial reading scan.

[0002]

2. Description of the Related Art In recent years, the development of solid-state imaging devices has been remarkable, and the range of application has been steadily expanding. For this reason, various types of devices have been proposed. 2. Description of the Related Art A solid-state imaging device in which a specific element among a plurality of photoelectric conversion elements (light receiving units) constituting a unit is an optical black unit and thereby obtains a black level value of an image signal is conventionally known. .

FIG. 4 conceptually shows an example of a solid-state image pickup device having such an optical black section (hereinafter, referred to as an OB section) 23. Here, the OB section 23 is shown.
In the plurality of light receiving units (photoelectric conversion units) 24 arranged in a matrix, the light receiving units in a plurality of continuous columns including the first column on the output unit 27 side in the horizontal scanning direction are covered with a light shielding film. , Light-shielded.

Then, the electric charge accumulated in each light receiving section 24 by the image light is transferred to the vertical transfer section 25 once every frame period.
Then, the image signal is obtained from the output unit 27 by reading the image data from the output unit 27 line by line to the horizontal transfer unit 26. At this time, the level of the signal read from the OB unit 23 is changed to a black level voltage (black level). (A reference value that represents).

Next, FIG. 5 is a timing chart at the time of normal scanning of the image pickup device having such an OB section (referred to as a normal scanning mode).
As shown in the figure, during the vertical transfer period (period represented by the square in the figure) by the vertical transfer pulse, the horizontal transfer pulse is prevented from appearing. Then, the black level can be fixed and the image level can be stabilized by clamping the level of the first part of the image output, that is, the level of the part read from the OB section 23 with the clamp pulse.

FIG. 6 shows an example of a solid-state image pickup device according to the prior art. In FIG. 6, reference numeral 1 denotes a solid-state image pickup device, which is provided with an OB section 23 as shown in FIG. It is driven by a horizontal transfer pulse and a vertical transfer pulse (FIG. 5) supplied from 8 to generate an image output.

At this time, the horizontal and vertical transfer driving circuits 8
Is operated by a pulse supplied from the horizontal / vertical transfer pulse generator 12 of the timing generator 9, and generates a horizontal transfer pulse and a vertical transfer pulse.

[0008] The video output of the solid-state imaging device 1 is input to a correlated double sampling circuit 2 and output via an amplifier 3, a clamp circuit 4 and a video processing circuit 5. Here, the clamp circuit 4 is, for example, a circuit of a feedback clamp system controlled by a clamp pulse as shown in FIG. 7, and thereby, as described in FIG.
At the timing when the signal is read out from the device, the level of the signal is captured and held, and is output as a black level.

Incidentally, as for the reading of the image signal from the solid-state imaging device 1, there is a so-called partial scan mode (partial scan mode) in addition to the normal scan mode described with reference to FIG. This is a method used in a system called a machine vision, for example, in which the vertical scanning range for extracting an image signal for video display is limited to a part of the solid-state imaging device. For example, as shown in FIG. The vertical period is shortened by partially reading the image signal in the vertical period, and the number of images per unit time is increased,
This is a method for increasing the frame rate.

In the case of this partial readout scanning mode, since the imaging area in the vertical direction is reduced, the amount of the video signal is reduced. Will be partially displayed in the image,
A substantial increase in frame rate will be obtained.

In machine vision, for example, an object to be inspected, which is moving at a high speed, is continuously captured by a television conveyor at a factory or the like, and the image is processed by a computer. It is used as a system for performing inspections. Incidentally, the inspection target object at this time is an IC pattern identification inspection.

Here, in the case of the partial reading scanning mode,
Since a period in which image signals are transferred at high speed at short intervals is partially provided, vertical transfer in the image sensor is performed in three periods of A, B, and C within one vertical cycle as shown in FIG. The transfer is performed separately, the high-speed transfer is performed in the period A and the period C, and the normal speed is performed in the period B. The switching of the scanning mode at this time is as follows.
This is provided by controlling the horizontal and vertical transfer pulse generators 12 by a partial readout scanning mode selection circuit 13 in the timing generator 9 (FIG. 6).

At this time, even if the high-speed transfer is performed during the normal vertical transfer period, the speed does not increase so much. Therefore, the vertical transfer is continued even during the horizontal transfer period during which the image signal is still output. Accordingly, the timing chart in the case of the partial reading scanning mode is as shown in FIG. 10 because the vertical transfer is also performed during the horizontal transfer period. In this partial readout scanning mode, the vertical transfer pulse is called a high-speed vertical transfer pulse.

[0014]

The above prior art is based on the OB
When the partial reading scan mode is set in the solid-state imaging device having the section, no consideration is given to the fact that the black level becomes unstable in the normal transfer scanning period immediately after the high-speed vertical transfer scanning, and the frame by the partial reading scan is not used. There was a problem that the rate increase was dissatisfied. Hereinafter, this point will be described.

In the prior art, when partial reading scanning is performed, vertical transfer is also performed during the horizontal transfer period as shown in FIG. 10, and as a result, pixel (light receiving portion) signals are mixed. In this case, also in the OB section 23 (FIG. 4), this pixel signal is mixed, and the signal of the other light receiving section 24 is mixed with the signal of the OB section 23, and the level of the signal read out therefrom becomes Fluctuates depending on the level of the signal read from the light receiving unit receiving the light.

Then, apparently, the OB section 23 has sensitivity to light, and its signal level changes according to the amount of light, and the changed level is clamped. Fluctuates depending on
This leads to a misclamp operation, and thus the black level changes. This will be described with reference to FIG.

In FIG. 11, a high-speed transfer period (FIG. 9)
In the period A or the period C, the black level voltage fluctuates as shown in the figure due to the mixture of the pixel signals described above.
(B period), a level fluctuation occurs in the image signal, and an image output level fluctuation period appears. This period of change
Although it attenuates according to the time constant in the clamp circuit 4 (determined by the capacitor C1 and the resistor R1 in FIG. 7), in any case, the black level changes during this period.
The image signal becomes unstable.

Therefore, in the prior art, in consideration of this image output level fluctuation period, a blanking pulse is used as shown in the figure, and high-speed transfer periods A and C are included. As a result, in the related art, since the blanking period of the image due to the masking increases, the frame rate in the partial reading scan is restricted, and the increase in the frame rate remains unsatisfactory. is there.

An object of the present invention is to provide a solid-state imaging device which eliminates black level fluctuation when shifting from the partial readout scanning mode to the normal scanning mode, and can sufficiently increase the frame rate. .

[0020]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solid-state image pickup device in which a clamp level by a clamp circuit of a feedback clamp system is obtained from an optical black section provided in an image pickup device. This is achieved by prohibiting the supply of the clamp pulse to the clamp circuit.

Further, the object is to provide a solid-state imaging device in which a clamp level by a clamp circuit of a feedback clamp system is obtained from an optical black section provided in an image sensor, when a partial reading scan mode is selected. A pause pulse generating unit for generating a pulse; and a clamp pulse pause unit for inhibiting supply of a clamp pulse to the clamp circuit, wherein the clamp pulse pause unit clamps the clamp circuit when the pause pulse is supplied. This is also achieved by prohibiting the supply of pulses.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a solid-state imaging device according to the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention, in which the same parts as those of the prior art described with reference to FIG. 6 are denoted by the same reference numerals. Therefore, the embodiment of FIG. , A pause pulse generator 6 and a clamp pulse pause circuit 7 are added, and other configurations are the same.

Therefore, except for the pause pulse generator 6 and the clamp pulse pause circuit 7, the embodiment of FIG.
Since the operation is the same as that of the prior art, detailed description will be omitted, and the following description will be mainly given of the pause pulse generator 6 and the clamp pulse pause circuit 7.

First, when the pause pulse generator 6 enters the partial read scan mode, the partial read scan mode selection circuit 1
The signal is activated by the output of No. 3 and becomes "H" level only during the period A and period C, that is, during the high-speed transfer period in FIG. 9, and functions to generate a pause pulse which maintains the "L" level in other periods.

Next, the clamp pulse pause circuit 7 is a kind of gate operated by the pause pulse, and the pause pulse is "H".
Only when the level is at the level, the clamp pulse supplied from the clamp pulse generator 11 is passed and supplied to the clamp circuit 4 as it is. While the pause pulse is at the “L” level, it is supplied from the clamp pulse generator 11. The function is to prohibit the passage of the clamp pulse and to prevent the clamp pulse from being supplied to the clamp circuit 4.

Next, the operation of this embodiment will be described with reference to FIG.
This will be described with reference to the timing chart of FIG. First, in the period B, the pause pulse maintains the “L” level. Therefore, the clamp pulse output from the clamp pulse generator 11 is supplied to the clamp circuit 4 as it is,
As a result, the black level voltage is stably fixed by the output read out from the OB section 23 (FIG. 4), as shown, and the image signal is also stable.

Next, in the period A and the period C, the pause pulse goes to the "H" level as shown in the figure, and as a result, no clamp pulse is supplied to the clamp circuit 4.
Therefore, in the periods A and C, that is, in the high-speed transfer period, the clamp circuit 4 stops the feedback clamp operation, and holds the level held in the internal holding circuit (the capacitor C1 in FIG. 7) during the period B. ing.

Further, thereafter, when the period B is resumed, the pause pulse returns to the "L" level, and as a result, the clamp circuit 4
Are supplied with a clamp pulse again. As a result, the black level voltage is fixed again by the output read out from the OB unit 23 again.

Here, regarding the black level voltage at the first time when the period B is again entered,
This is because the output read from the OB unit 23 in the B period immediately before the A period and the C period immediately before is held in the clamp circuit 4 described above. Similarly, the black level voltage is almost the same as the black level voltage determined by the output read from the OB unit 23.

In this case, as shown in FIG.
Even during the normal transfer period immediately after the high-speed transfer period, the black level voltage maintains a sufficient continuity, and as a result, a sufficiently stable image signal can be obtained without masking by a blanking pulse. Is obtained.

Therefore, according to this embodiment, masking of the image signal can be made unnecessary, and as a result, the frame rate can be easily increased. This frame rate is substantially inversely proportional to the width of the partial readout scanning area. Here, FIG. 3 is a characteristic diagram showing the relationship between the partial readout scan area and the frame rate. It is the number.

In the case of the prior art, the image output level fluctuation period
Although there is a period (FIG. 11) substantially equal to the time constant of the clamp circuit, in the case of the present invention, the period equal to this time constant can be shortened. As a result, as is clear from this figure,
In the present invention and the prior art, there is not much difference in the frame rate while the partial readout scanning area is wide, but the difference becomes remarkable as the area becomes narrower.

[0033]

According to the present invention, it is possible to eliminate the image output level fluctuation period at the time of the partial readout scanning.
The frame rate can be sufficiently increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a timing chart for explaining the operation of one embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the performance of an embodiment of the present invention in comparison with a conventional technique.

FIG. 4 is a structural diagram illustrating an example of a solid-state imaging device including optical black.

FIG. 5 is a timing chart for explaining an operation during normal scanning.

FIG. 6 is a block diagram illustrating an example of a conventional solid-state imaging device.

FIG. 7 is a circuit diagram illustrating an example of a clamp circuit of a feedback clamp system.

FIG. 8 is an explanatory diagram schematically showing partial reading scanning.

FIG. 9 is another explanatory diagram schematically showing partial reading scanning.

FIG. 10 is a timing chart for explaining an operation of a partial reading scan in an example of a solid-state imaging device according to the related art.

FIG. 11 is a timing chart for explaining an operation at the time of partial read scanning.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solid-state imaging device 2 correlated double sampling circuit 3 amplifier 4 clamp circuit 5 video processing circuit 6 pause pulse generator 7 clamp pulse pause circuit 8 horizontal / vertical transfer drive circuit 9 timing generator 11 clamp pulse generator 12 horizontal / vertical transfer pulse Generator 13 Partial read scan mode selection circuit 23 Optical black section (OB section) 24 Light receiving section (photoelectric conversion section) 25 Vertical transfer section 26 Horizontal transfer section 27 Output section

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuhito Enomoto 32nd Miyukicho, Kodaira-shi, Tokyo F-term in Hitachi Kokusai Electric Koganei Factory (reference) 4M118 AA05 AA10 AB01 BA10 DB09 DD10 DD11 DD12 5C024 GZ39 HX10 HX50 JX08

Claims (3)

[Claims] 1. A solid-state imaging device in which a clamp level of a clamp circuit of a feedback clamp system is obtained from an optical black section provided in an image pickup device. A solid-state imaging device configured to prohibit supply of a clamp pulse. 2. A solid-state image pickup device in which a clamp level by a clamp circuit of a feedback clamp system is obtained from an optical black section provided in an image pickup device, wherein a pause pulse is generated during a high-speed transfer period in a partial reading scan mode. And a clamp pulse pause means for inhibiting supply of a clamp pulse to the clamp circuit. The clamp pulse pause means supplies a clamp pulse to the clamp circuit when the pause pulse is supplied. The solid-state imaging device is configured to prohibit the operation. 3. A plurality of photoelectric conversion elements, an optical black element formed by shielding a predetermined element of the plurality of photoelectric conversion elements from light, and a plurality of transfer elements for transferring charges obtained by the photoelectric conversion elements including the optical black element. A vertical transfer unit, and a solid-state imaging device including a horizontal transfer unit that transfers the charge transferred from the vertical transfer unit, and an output signal based on the charge obtained by the optical black element among output signals of the solid-state imaging device. A solid-state imaging device having a clamp circuit for clamping, and having a high-speed transfer period for performing an operation involving the horizontal transfer operation period of the horizontal transfer unit within the vertical transfer operation period of the vertical transfer unit. The clamp circuit stops the operation of clamping the output signal by the electric charge obtained by the optical black element. A solid-state imaging device.