JPH07121087B2 - Solid-state imaging device - Google Patents

Description

The present invention relates to a solid-state imaging device capable of exposure control.

[Outline of Invention]

In the present invention, the overflow drain current of the solid-state image sensor is detected, and the aperture is controlled in accordance with the detected output, so that the exposure amount is accurately controlled.

[Conventional technology]

BACKGROUND ART Conventionally, a television camera (TV camera) that captures a moving image and a still camera that captures a still image using a solid-state imaging device such as a charge-coupled device (hereinafter abbreviated as CCD) are known.

First, a conventional TV camera will be described with reference to FIGS. 2 and 3.

FIG. 2 shows a configuration example of a conventional TV camera.

In FIG. 2, the incident light that has passed through the lens (1) and the diaphragm (2) is guided to the CCD image sensor (3) and converted into an electric signal. Since the output of the CCD image pickup device (3) includes an unnecessary component generated when each device is reset, it is supplied to the signal separation circuit (4) to separate only a desired data component and sample-hold. The output of the signal separation circuit (4) is supplied to the image signal processing circuit (5) and converted into an NTSC TV signal by appropriate processing. This TV signal is supplied to a monitor and a VTR (both not shown).

The output of the signal separation circuit (4) is supplied to the detection circuit (7) via the clamp circuit (6). Normal,
The detection circuit (7) performs detection as if the peak detection and the average value detection were mixed. Further, the target signal is often weighted, for example, in the central portion of the screen or the lower 3/4 of the screen.

The DC output of the detection circuit (7) is supplied to the inverting input terminal of the operational amplifier (8) and compared with the voltage of the adjustable voltage source Ea connected to the non-inverting input terminal. The reference voltage source Er is connected to the output terminal of the operational amplifier (8) via the coil (9c) of the diaphragm drive mechanism (9).

In this diaphragm drive mechanism (9), a movable coil (9c) is arranged in the magnetic field of a permanent magnet (not shown), and the output voltage of the operational amplifier (8) is large relative to the reference voltage of the reference voltage source Er. The diaphragm (2) is configured to open and close depending on the smallness. As a result, the amount of light incident on the image sensor (3) is controlled to be constant.

[Problems to be solved by the invention]

By the way, for simplification, in the conventional example shown in FIG. 2, it is assumed that the detection circuit (7) performs weighted average value detection.

In this case, the incident light from a low-contrast subject as shown in FIG. 3A is equal to the total light amount as shown in FIG. 3B, and the highlight portion is the saturation level Ls of the CCD image sensor (3). The output of the detection circuit (7) is at the same level and the diaphragm (2) is controlled to the same F value with respect to incident light from a high-contrast subject that reaches 0. As a result, the CCD image sensor (3) in the highlighted portion of FIG.
Is saturated (overloaded), and a blooming phenomenon occurs in which the image size of the subject apparently increases.

Further, as shown in FIG. 3C, even for a subject having a higher contrast and partially exceeding the saturation level Ls, as long as the total light amount is constant, the conventional example of FIG.
The diaphragm (2) is controlled to the same F value.

Therefore, in order to avoid saturation in the case of a high-contrast subject as shown in FIG. 3C by lowering the aperture setting level by the adjustable voltage source Ea, in the case of a low-contrast subject as shown in FIG. However, there is a problem that the output signal level of the image pickup device (3) decreases and the S / N deteriorates.

On the other hand, in the case of a low-contrast subject, if the aperture setting level is increased in order to improve the S / N, the image sensor (3) will be completely removed even in the case of a critical subject as shown in FIG. There was a problem of saturation.

As a means for solving the problems of the conventional solid-state image pickup device using the output signal of the image pickup device for aperture control as described above, for example, as shown in JP-A-58-154974, photometry is separately performed. There is known an "electrophotographic apparatus" in which a system is provided and the exposure is determined according to incident light.

Next, another conventional example will be described with reference to FIGS. 4 and 5. This electrophotographic apparatus will be described.

FIG. 4 shows the configuration of another conventional example. In FIG. 4, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and duplicate description will be omitted.

In FIG. 4, (11) is a quick return mirror,
A shutter (12) is provided between the lens (1) and the image pickup device (3) together. (13) is a CCD image sensor, and as shown in FIG.
Is provided, and the image signal from the terminal (13a) and the terminal (13a
The overflow output from d) is supplied to the exposure control circuit (14). A proper exposure control signal from the exposure control circuit (14) is supplied to the shutter control mechanism (15), and the shutter (12) is opened and closed at a shutter speed that provides proper exposure.

When the image sensor (13) is driven in TV mode, the switching signals VG ₁ and VG ₂ of the transfer gate TG are
Generated at 1/30 second intervals, the signal accumulation time corresponding to the shutter speed of a conventional still camera is 1/30 second. Then, when strong light is incident, excess signal charge generated in the light receiving portion R flows into the overflow drain OD, and blooming is controlled by this.

During still shooting, the image sensor (13) is used as a photometric element to determine the proper exposure amount and control the shutter speed, but in that case, the light receiving part becomes saturated within 1/30 seconds or less. Can happen. In such a case, the exposure cannot be determined only from the signal charge. Therefore, when the subject is too bright and a high-speed shutter is used, the signal obtained by adding the signal output and the overflow output is the exposure control circuit (1
4) is supplied to determine the exposure.

However, in the case of the still photography, the electrophotographic apparatus of FIG. 4 can control the proper exposure, but since the CCD image pickup element (13) is used as the photometric element, the cost is significantly increased. was there.

Further, there is a problem that the saturation information of the image pickup device (3) actually picked up cannot be obtained accurately.

In view of these points, an object of the present invention is to provide a fixed image pickup device capable of obtaining reliable saturation information from the image pickup device itself and performing appropriate exposure control while suppressing an increase in cost. is there.

[Means for solving problems]

In order to solve the above-mentioned problems, according to the present invention, a first detecting means for detecting an overflow drain current of a solid-state image sensor for extracting image information as an electric signal, and the electrical device extracted from the solid-state image sensor. The aperture of the solid-state image sensor is controlled by the second detection means for detecting the DC component of the signal, and the output signal obtained by adding the output signal from the first detection means and the output signal from the second detection means. There is provided a solid-state image pickup device comprising:

[Action]

According to such a configuration, the saturation information from the solid-state imaging device itself can be used, and the exposure amount can be controlled appropriately.

〔Example〕

An embodiment of the solid-state imaging device according to the present invention will be described below with reference to FIG.

The configuration of one embodiment of the present invention is shown in FIG. In FIG. 1, parts corresponding to those in FIGS. 2 and 4 are designated by the same reference numerals, and redundant description will be omitted.

In FIG. 1, a signal output is supplied to a signal separation circuit (4) from a terminal (13s) of a CCD image pickup device (13). The output of the detection circuit (7) supplied with the output of the signal separation circuit (14) via the clamp circuit (6) is the emitter follower (16).
Is supplied to the inverting input terminal of the operational amplifier (8). The slider of the variable resistor (17) is connected to the non-inverting input terminal of the operational amplifier (8), and the variable resistor (17) is connected to the slider.
Has one end connected to the power supply terminal (18) and the other end grounded.

(20) is an overflow drain current detection circuit,
This transistor (2) including pnp type transistor (21)
The base of 1) and the terminal (13d) of the CCD image sensor (13) are connected. The base and emitter of the transistor (21) are connected to the power supply terminal (18) via the resistors (22) and (23), respectively, and the collector of the transistor (21) is connected via the resistor (24). It is connected to the inverting input terminal of the operational amplifier (8). The remaining structure is similar to that of the conventional example shown in FIG.

The operation of this embodiment is as follows.

When strong light enters the image sensor (13), as described above,
Excess signal charge flows into the overflow drain (see FIG. 5). Since this signal charge has a negative polarity, the overflow drain current flows from the power supply terminal (18) through the resistor (22) to the terminal (13d). As a result, the base potential drops, the transistor (21) becomes conductive, and the potential of the inverting input terminal of the operational amplifier (8) rises. Therefore, the potential of the output terminal of the operational amplifier (8) drops, and a current flows from the reference voltage source Er to the operational amplifier (8) in the coil (9c), and as described above, the diaphragm (2). Is closed, the saturation state is eliminated, and an appropriate exposure state is obtained.

By appropriately setting the ratio of the resistors (22) and (23), it is possible to control the overflow drain current detection point at which the transistor (21) is turned on.

Further, in order to simplify the configuration, when the diaphragm is manually controlled, the overflow drain current may be detected and the warning light may be turned on.

〔The invention's effect〕

As described above in detail, according to the present invention, by detecting the overflow drain current of the image pickup device itself, the saturation information of the image pickup device can be surely obtained, and therefore, the solid-state image pickup device capable of performing appropriate exposure control. Is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a solid-state imaging device according to the present invention, FIG. 2 is a block diagram showing a configuration example of a conventional solid-state imaging device, and FIG. 3 is an operation of the conventional example of FIG. FIG. 4 is a block diagram showing another configuration example of a conventional solid-state imaging device, and FIG. 5 is a block diagram showing a configuration of a main part of the conventional example of FIG. (2) is a diaphragm, (9) is a diaphragm drive mechanism, (13) is a CCD image sensor, (20) is an overflow drain current detection circuit,
OD is the overflow drain.

Claims (1)

[Claims] 1. A first detecting means for detecting an overflow drain current of a solid-state image pickup device for extracting image information as an electric signal, and a second detection for detecting a DC component of the electric signal taken out of the solid-state image pickup device. Means, and control means for controlling the aperture of the solid-state imaging device by an output signal obtained by adding the output signal from the first detection means and the output signal from the second detection means. Solid-state imaging device.