JPH0779438B2 - Solid-state imaging device - Google Patents

Description

The present invention relates to a solid-state imaging device including an optical diaphragm device.

[Conventional technology]

FIG. 2 shows a block diagram of a conventional solid-state image pickup device.

In the figure, 1 is a lens, 2 is an optical diaphragm device, 3 is a solid-state image sensor, 4 is a clamp circuit, 5 is a timing generation circuit, 6 is a diaphragm control device, 9 is an adder circuit, and 10 is an output terminal.

Before explaining the operation, a leak current called dark current is generally generated in a solid-state image sensor even if no light is applied to it.If this false signal increases, a large object will be captured when a black object is imaged. In order to solve this, the solid-state image sensor has a pixel called an optical black period (optical black) that is optically shielded. Then, the optical black video signal level is clamped by a clamp circuit, and the level is set as the black level of the video signal, thereby preventing the influence of the dark current.

The operation will be described with reference to FIG. An image of a subject is formed on the image pickup surface of the solid-state image pickup device 3 by the lens 1. The solid-state image sensor 3 is driven by the drive signal of the timing generation circuit 5, the signals of each pixel are sequentially read, and a video signal as shown in FIG. 3A is output. In the video signal of (a),
The period (A) is a video signal period corresponding to optical black. This video signal is clamped by the clamp circuit 4 by the pulse signal of FIG. Then, the addition circuit 9 adds the horizontal and vertical synchronization signals from the timing generation circuit 5 shown in FIG.
The composite video signal shown in is output from the output terminal 10. On the other hand, the aperture control device 6 controls the voltage level difference from the optical black level of the video signal reproduced by the clamp circuit 4 in FIG. 3B to the average level of the video signal in FIG. Compare the figure (d) with the reference level, and if the video signal level is lower than the reference level,
A high voltage is output and a high voltage is applied to the optical diaphragm device 2 to operate the optical diaphragm device 2 in the opening direction. Also,
When the average voltage level of the video signal reproduced by the clamp circuit 4 is higher than the reference level, the aperture control device 6 outputs a low voltage and applies a low voltage to the optical aperture device 2 to output the optical aperture device. 2 is moved in the closing direction. As described above, by continuously changing the optical diaphragm device 2 from the opening to the closing, the amount of light incident on the solid-state imaging device 3 is made constant, and the output terminal 10 does not change even if the illuminance of the subject changes greatly. The average level of the composite video signal obtained from is constant.

[Problems to be Solved by the Invention]

However, the above-mentioned conventional technique has the following problems. The optical black of the solid-state image sensor is, in particular, because it shields ordinary effective pixels with a thin metal material such as aluminum, so it is particularly sufficient when light containing a large amount of infrared rays with a long wavelength is incident. In reality, it is impossible to block light, and optical black does not operate unless the incident light amount is limited to a specified value or less in an optical diaphragm device or the like.

On the other hand, the output of the solid-state image sensor does not exceed the voltage applied to the solid-state image sensor, and the maximum output level of the solid-state image sensor is limited by factors other than the amount of incident light.

Here, a case where the solid-state imaging device 3 is suddenly exposed to strong light will be considered with reference to FIG. In the figure, (a) is the maximum output level of the solid-state image sensor 3. In such a case, the optical black image signal level (b) of the solid-state image pickup device 3 before the optical diaphragm device 2 limits the amount of light incident on the solid-state image pickup element 3 to a prescribed light amount is shown in FIG. As described above, the optical black video signal level (b) approaches the maximum output level (b) of the solid-state image sensor 3. Then, since the level difference (d) from the optical black image signal level (b) to the average level (c) of the image signal becomes small, the aperture control device 6
Judges that the video signal level is lower than the reference level and applies a high voltage to the optical diaphragm device 2 to operate the optical diaphragm device 2 in the opening direction. Then, the video signal level (b) in optical black further rises as shown in FIG. 4 (b) and approaches the maximum output level (b) of the solid-state image sensor 3. Then, the aperture control device 6 further operates the optical aperture device 2 in the opening direction. That is, the servo loop becomes a positive feedback, and the optical diaphragm device 2 remains open. Then, there is a problem that the video signal obtained from the output terminal 10 becomes an overexposed video as shown in FIG. 4 (c).

In view of the above problems, it is an object of the present invention to provide a solid-state image sensor that prevents malfunction due to positive feedback of aperture control when strong light enters.

[Means for Solving the Problems]

A solid-state image pickup device of the present invention is a first solid-state image pickup device which captures image data through an optical diaphragm device and which has a black pixel which is optically shielded, and a pedestal clamp output of a video signal output of the solid-state image pickup device. A clamp circuit, a second clamp circuit that clamps and outputs the signal pedestal clamped by the first clamp circuit, and a second clamp circuit that is clamped by the output of the second clamp circuit.
An adder circuit for adding a clamp signal and a synchronization signal, connected to the solid-state image sensor and the second clamp circuit, and clamps the clamp timing of the second clamp circuit during a period for capturing the output of the black pixel, A first timing generation circuit that controls to prevent the influence of dark current; and a second timing that controls the clamp timing of the first clamp circuit to perform pedestal clamp during a period when the pixel output of the solid-state image sensor does not exist. The level difference between the pedestal level clamped by the first clamp circuit and the video signal average level and a reference level are compared with the generation circuit and the period when the pixel output does not exist, and the aperture of the optical aperture device is adjusted. And a diaphragm control device for controlling.

〔Example〕

FIG. 1 is a block diagram of a solid-state image pickup device according to an embodiment of the present invention. In the figure, 1 is a lens, 2 is an optical diaphragm device, 3 is a solid-state image pickup device, 4 is a first clamp circuit, 5
Is a first timing generation circuit, 6 is a diaphragm control device, 7 is a second clamp circuit, 8 is a second timing generation circuit,
Reference numeral 9 is an adder circuit, and 10 is an output terminal. The operation will be described with reference to FIG.

An image of a subject is formed on the image pickup surface of the solid-state image pickup device 3 by the lens 1. The solid-state image sensor 3 is driven by the drive signal of the first timing generation circuit 5, and the signals of each pixel are sequentially output to output the video signal of FIG. 5 (a). This video signal from the solid-state image sensor 3 is supplied to the first clamp circuit 4
Then, the second timing generation circuit 8 is clamped by the timing pulse of FIG. Further, in the second clamp circuit 7, the video signal is clamped and the DC level of the video signal is reproduced by the timing pulse of FIG. 5 (b) of the first timing generation circuit. Then, in the adder circuit 9, the horizontal and vertical synchronizing signals from the first timing generating circuit 5 (c) and the video signal reproduced by direct current are added together to form a composite video signal of FIG. 5 (e). , Is output from the output terminal 10. On the other hand, the aperture control device 6
As in the case of FIG. 3, the aperture is opened and closed so that the average video level of the video signal clamped by the first clamp circuit 4 becomes the same as the reference level. However, unlike the case of FIG. 2, the timing of clamping is different from that of FIG.
The difference is that sampling is performed at the timing shown in FIG. 7D, that is, the timing at which no pixel exists. Here, a case where the solid-state image sensor 3 is exposed to strong light will be described with reference to FIG. The video signal from the solid-state image sensor 3 is as shown in FIG. 6 as in the case of FIG. Since the video signal is clamped by the first clamp circuit 4 at the timing shown in FIG. 5 (d), the average level (c) of the video signal is changed from the level (b) clamped by the first clamp circuit 4. The level difference (d) up to 1 tends to increase unlike the case of FIG. Therefore, the aperture control device 6
Operates the optical diaphragm device 2 in the closing direction and adjusts the optical diaphragm device 2 until it becomes equal to the reference level. And
In the second clamp circuit 7, the video signal from the first clamp circuit 4 is clamped by the clamp pulse having the same timing as in FIG. 3 to prevent the influence of the dark current.

〔The invention's effect〕

As described above, according to the present invention, the aperture control signal includes the reference level and the level difference between the pedestal level clamped by the first clamp circuit and the video signal average level during the period when no pixel output is present. Therefore, when an excessive level is suddenly input to the solid-state image sensor, even if the optical black level with poor shading rises, it is not adversely affected and the level difference between the pedestal level and the video signal average level becomes large. You can immediately stop down the aperture.

Further, since the video signal is clamped at the optical black timing by the second clamp circuit, it is possible to prevent dark current and increase the contrast.

[Brief description of drawings]

FIG. 1 is a block diagram of a solid-state imaging device according to the present invention. FIG. 2 is a block diagram of a conventional solid-state image pickup device. FIGS. 3A to 3D are signal diagrams showing the operation of the solid-state imaging device. FIGS. 4A to 4C are signal diagrams showing the operation of the solid-state imaging device. FIGS. 5A to 5E are signal diagrams showing the operation of the solid-state imaging device. FIG. 6 is a signal diagram showing the operation of the solid-state imaging device.

Claims (1)

[Claims] 1. A solid-state image pickup device having black pixels that are optically shielded by taking in image data through an optical diaphragm device, and a first clamp circuit for outputting a video signal output of the solid-state image pickup device as a pedestal clamp. A second clamp circuit that clamps and outputs a signal pedestal clamped by the first clamp circuit, and a second clamp circuit that is clamped by the output of the second clamp circuit.
An adder circuit for adding a clamp signal and a synchronization signal, connected to the solid-state image sensor and the second clamp circuit, and clamps the clamp timing of the second clamp circuit during a period for capturing the output of the black pixel, A first timing generation circuit that controls to prevent the influence of dark current; and a second timing that controls the clamp timing of the first clamp circuit to perform pedestal clamp during a period when the pixel output of the solid-state image sensor does not exist. The level difference between the pedestal level clamped by the first clamp circuit and the video signal average level and a reference level are compared with the generation circuit and the period when the pixel output is not present, and the aperture of the optical aperture device is adjusted. A solid-state imaging device comprising: a diaphragm control device for controlling.