JPS6362479A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To securely obtain the saturation information of an image pickup element and to attain a suitable exposure-control by detecting the over flow drain current of the solid-state image pickup element and controlling a diaphragm in accordance with the detected output. CONSTITUTION:An image pickup signal from a CCD image pickup element 13 is supplied to a signal separation circuit 4. An output from said circuit 4 is added to a detection circuit 7 through a clamping circuit 6 and transmitted to an operation amplifier 8. If strong light beams are made incident on the image pickup element 13, excess signal loads flow in an overflow drain. The loads flow into a terminal 13d through a resistor 22 from a source terminal 18. Thus, the base potential of a transistor 21 drops and the transistor 21 comes to a conductive state, whereby the potential of the inversion input terminal of the operation amplifier 8 is rised. Consequently, the output from the amplifier 8 is decreased, the current of a coil 9a is limited and the diaphragm 2 is adjusted so that an exposure state is set appropriate.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a solid-state imaging device capable of controlling exposure.

[Summary of the invention]

According to the present invention, the overflow drain current of a solid-state image sensor is detected, and the aperture is controlled according to the detected output, thereby accurately controlling the exposure amount.

[Conventional technology]

BACKGROUND ART Conventionally, television cameras (TV cameras) that capture moving images and still cameras that capture still images are known using solid-state image sensors such as charge-coupled devices (hereinafter abbreviated as COD).

While referring to Figures 2 and 3, the conventional 'r■
Let me explain about the camera.

An example of the configuration of a conventional TV camera is shown in FIG.

In Fig. 2, the incident light that has passed through the lens (11) and the aperture (2) is guided to the CCD image sensor (3) and converted into an electrical signal.The output of the CCD image sensor (3) is transmitted to each element. Since the data contains unnecessary components generated at the time of resetting, the data is supplied to the signal separation circuit (4), where only the desired data components are separated and sampled and held.

The output of the signal dividing circuit (4) is supplied to the image signal processing circuit (5), and through appropriate processing, the output of the NTSC system is
The signal is converted twice. This TV signal is supplied to a monitor and a VTR, both of which are not shown.

In addition, the output of the signal separation circuit (4) is connected to the clamp circuit (6).
) is supplied to the detection circuit (7). Normally, this detection circuit (7) performs detection that is a mixture of peak detection and average value detection. Also, if the target signal is in the center of the screen or the bottom 3/4 of the screen, for example,
Often weighted.

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. Operational amplification '5 (8)
The coil (9c) of the aperture drive mechanism (9) is connected to the output terminal of
A reference voltage source Er is connected thereto.

This diaphragm drive mechanism (9) has a moving coil (9c) disposed within the magnetic field of a permanent magnet (not shown), and the output voltage of the operational amplifier (8) with respect to the reference voltage of the reference heavy pressure source Er. The diaphragm (2) is configured to open or close depending on the size. Thereby, the amount of light incident on the image sensor (3) is controlled to be constant.

[Problem that the invention seeks to solve]

For simplicity, it is assumed that in the conventional example shown in FIG. 2, the detection circuit (7) performs average value detection without weighting.

In this case, the incident light from a low-contrast object as shown in FIG. 3A is equal to the total amount of light as shown in FIG. The output of the detection circuit (7) is at the same level as the incident light from the subject with high contrast reaching , and the aperture (2) is controlled to the same F value. As a result, the CCD image sensor (3) becomes saturated (overloaded) in the highlighted portion of FIG.

Furthermore, as shown in FIG. 3C, even for a subject with high -layer contrast that partially exceeds the saturation level Ls, as long as the total amount of light is constant, the conventional example shown in FIG.
The aperture (2) is controlled to the same F number.

Therefore, if you lower the aperture setting level using the adjustable tortoise pressure @ E a to avoid saturation in the case of a high-contrast subject as shown in Figure 3C, it will result in a low-contrast subject as shown in Figure 3A. There has been a problem in that the output signal level of the image sensor (3) in the case of a subject decreases and the S/N ratio deteriorates.

Conversely, in the case of a low-contrast subject, increasing the aperture setting level to improve the S/N will reduce the loss @2 elements (3) even in the case of a critical subject as shown in Figure B. There was a problem of complete saturation.

To solve the above-mentioned problems of conventional solid-state imaging devices that use the output signal of the image sensor for aperture control, for example, as shown in Japanese Patent Application Laid-open No. 154974/1983, a separate photometering method is proposed. 2. Description of the Related Art An "electrophotographic apparatus" is known in which a system is provided to determine exposure according to incident light.

Next, this electrophotographic apparatus, which is another conventional example, will be explained with reference to FIGS. 4 and 5.

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 redundant explanation will be omitted.

In Figure 4, (11) is a quick return mirror;
(12) is a shutter, which is disposed between the lens (11) and the image sensor (3). (13) is a CCD image sensor, and as shown in FIG. 5, the overflow drain OD is The image signal from the terminal (13s) and the overflow output from the terminal (13d) are supplied to the exposure control circuit (14).The appropriate exposure control signal from the exposure control circuit (14) is sent to the shutter control mechanism. (15), 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, l.
Transfer gate TG switching signal VG□, V
G2 is generated at intervals of 1/30 seconds each, resulting in a signal accumulation time of 1/30 seconds, which corresponds to the shutter speed of a conventional still camera. Then, when strong light is incident, excess signal charges generated in the light receiving portion R flow into the overflow drain OD, thereby controlling blooming.

During still photography, the image sensor (13) is used as a photometric element to determine the appropriate exposure amount and control the shutter speed, but in this case, the light receiving section may become saturated in 1730 seconds or less. obtain. In such a case, exposure cannot be determined from the signal charge alone. Therefore, when the subject is too bright and a high-speed shutter is used, a signal that is the sum of the signal output and the overflow output is sent to the exposure control circuit (14). exposure is determined.

However, although the electrophotographic device shown in FIG. 4 is capable of proper exposure control in the case of still photography, it uses a separate CCD image sensor (13) as a photometric element, which poses the problem of a significant increase in cost. was there.

Furthermore, there is a problem in that it is not always possible to accurately obtain saturation information of the image sensor (3) that is actually capturing an image.

In view of the above, an object of the present invention is to provide a fixed imaging device that can obtain reliable saturation information from the imaging device itself and perform consistent exposure control while suppressing increases in cost. be.

[Means for solving problems]

The present invention is a solid-state imaging device that detects an overflow drain current of a solid-state imaging device that extracts image information as an electrical signal, and controls an aperture according to this detection output.

[Effect]

According to such a configuration, saturation information from the solid-state image sensor itself can be used, and the exposure amount can be reduced to 'i! precisely controlled.

〔Example〕

Hereinafter, an embodiment of the solid-state imaging device according to the present invention will be described with reference to FIG.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, portions corresponding to °ζ, FIG. 2, and FIG. 4 are designated by the same reference numerals, and redundant explanation will be omitted.

In FIG. 1, the terminal (13) of the CCD i-sensor (13)
A signal output from s) is supplied to a signal separation circuit (4).

The output of the detection circuit (7), which is supplied with the output of the signal separation circuit (14) via the clamp circuit (6), is supplied to the inverting input terminal of the operational amplifier (8) via the emitter follower (16). Ru. A slider of a variable resistor (17) is connected to the non-inverting input terminal of this operational amplifier (8), one end of this variable resistor (17) is connected to a power supply terminal (18), and the other end is grounded. be done.

(20) is an overflow drain current detection circuit, which includes a pnp type transistor (21), and the base of this transistor (21) and the ccc++Ji & image element (13).
) is connected to the image width element (13d). Transistor (2
The base and emitter of 1) are each resistor (22)
and (23), connected to the power terminal (18),
The collector of the transistor (21) is connected to the inverting input terminal of the operational amplifier (8) via a resistor W (24). The rest of the structure is the same as the conventional example shown in FIG.

The operation of this embodiment is as follows.

When strong light enters the image sensor (13), as mentioned above, excessive signal charges flow into the overflow drain (see Figure 5).Since this signal charge has negative polarity, the overflow drain current is reversely It flows from the power supply terminal (18) through the resistor W (22) to the terminal (13d). As a result, the base potential drops and the transistor (21
) becomes conductive, and the potential at the inverting input terminal of the operational amplifier (8) rises. Therefore, the potential at the output terminal of the operational amplifier (8) decreases, and a current flows through the coil (9c) from the reference voltage source Er to the operational amplifier (8), and as described above, the aperture (2) is closed and the saturation state is resolved,
Appropriate exposure conditions can be obtained.

Note that 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) becomes conductive.

Further, in order to simplify the configuration, when manually controlling the aperture, an overflow drain current may be detected and a warning light may be turned on.

〔Effect of the invention〕

As detailed above, according to the present invention, saturation information of the image sensor can be reliably obtained by detecting the overflow drain current of the image sensor itself, so that the solid-state image sensor can perform appropriate exposure control. is obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the solid-state imaging device according to the present invention, FIG. 2 is a block diagram showing an example of the configuration of a conventional solid-state imaging device, and FIG. 3 is the operation of the conventional example shown in FIG. 2. FIG. 4 is a block diagram showing another example of the configuration of a conventional solid-state imaging device, and FIG. 5 is a block diagram showing the configuration of main parts of the conventional example shown in FIG. 4. (2) is the aperture, (9) is the aperture drive mechanism, (13) is C0
DJi@! The element, (20) is an overflow drain current detection circuit, and ○D is an overflow drain.

Claims (1)

[Claims] A solid-state imaging device characterized in that an overflow drain current of a solid-state imaging device that extracts image information as an electrical signal is detected, and an aperture is controlled according to this detection output.