JPH02149082A - Imaging device - Google Patents

Abstract

PURPOSE:To obtain an image with a high picture quality by a low dark current while maintaining high antiblooming capacity by increasing clock frequency to an antiblooming gate only at the time of emitting a strobe, and at the time other than strobe emission, reducing the clock frequency. CONSTITUTION:A clock phiAB with an extremely low frequency f1 is applied in the antiblooming gate 18 of a solid-state image pickup element 3 simultaneously with the generation of a pulse phiSS1 or after a delay time expecting the delay of a shutter. Simultaneously when the shutter 2 reaches at a proposed stop diameter, a pulse phiSS2 is generated. When the pulse phiSS2 is obtained, a clock generating means is switched to the generation of a clock with frequency f0Hz prevented from generating blooming due to the reflected light of strobe light itself. When a pulse phiSS3 to be an instruction specifying the close of the shutter 2 after the emission of the strobe is generated, the clock phiAB to be applied to the antiblooming gate is switched to frequency f1Hz again by the pulse phiSS3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an imaging device that utilizes an electronic flash.

[Conventional technology]

2. Description of the Related Art In recent years, imaging devices that record still images of objects have been used as electronic still video cameras, industrial cameras, and the like. Such cameras are small,
Solid-state imaging devices are used as imaging devices because of the requirements for light weight and high reliability.

A drawback of solid-state image sensors is a phenomenon called pluming, where strong light enters a part of the image area, and the amount of charge generated in that area exceeds the charge storage capacity of the pixel and flows into an adjacent area with less incident light, resulting in false signals. There is a phenomenon that occurs, and as a method to protect against this phenomenon, there is a method of providing an anti-blooming gate in the pixel to remove excess charge due to electron/hole recombination. As such a solid-state image sensor, a frame transfer type plate phase CCD (Cha
2. Description of the Related Art A solid-state image sensor is known as an RG Coupled Device and has an anti-blooming gate.

The mechanism of this anti-blooming gate will be explained below.

FIG. 2(a) is a cross-sectional view in the transfer direction of a virtual phase CCD having an anti-blooming gate.

One transfer gate region and one virtual phase region constitute one pixel. The anti-blooming gate 18 is provided in the virtual phase region, which is located between the virtual barrier and the virtual well.

In addition, 16 is a transfer gate electrode, 17 is an N-type impurity layer, 1
9 is a P'' impurity layer. FIG. 2(b) is a diagram showing the potential distribution during the charge accumulation mode, and at this time, a clock having a frequency of 7@ is applied to the anti-blooming gate.

FIG. 3 shows the potential distribution in the depth direction under the anti-blooming gate 18, when the voltage level applied to the anti-blooming gate 18 is High. In this state, the signal charge, that is, the charge generated by photoelectric conversion during charge accumulation mode, is
When the capacitance exceeds the capacitance determined by the surface potential and the maximum channel potential, more charges overflow to the interface and are trapped in the surface levels. Here, when the potential level of the anti-blooming gate 18 is set to a low level such that the surface is in a pinning state, the surface is filled with holes using the P0 layer 19 in the channel stop region and the virtual gate region as a supply source, and the surface level is Trapped electrons recombine with holes. By repeating this operation during charge accumulation, the blooming phenomenon caused by excess charge can be prevented.

FIG. 4 is a diagram showing the configuration of a conventional electronic still video camera. In the figure, 1 is a lens, 2 is a half-open shutter, 3 is a solid-state image pickup device with an anti-blooming gate, 6 is a drive circuit that generates a gate pulse for the solid-state image pickup device 3, and 4 is a photometry circuit for determining appropriate exposure. , 5 is a color measurement circuit for determining white balance; 7 is a system control circuit that generates operation timing pulses for the entire apparatus and generates control signals; 8 is a color difference signal ( RY and B-Y) and a luminance signal plus a synchronization signal (y+5ync); 9 is a modulation circuit that FM-modulates No. 18 from the imaging signal processing circuit 8; a recording amplifier for amplifying the signal; 11 a magnetic head for electromagnetically converting the signal from the recording amplifier 10; 12 a magnetic head 1;
1 is a magnetic sheet for recording magnetic signals; 13 is a motor for rotating the magnetic sheet 12; 14 is a motor 13;
A servo circuit 15 controls the rotation of the camera, and 15 is an electronic flash (commonly called a strobe, henceforth referred to as a strobe) that illuminates the subject, and there are some built-in types in the camera and some that are detachable.

FIG. 5 is a time chart showing the operation of the electronic still camera shown in FIG. 4 during flash photography.

The operation of the conventional electronic still camera during strobe photography will be explained below with reference to FIGS. 5 and 4.

φSS1 is an opening command pulse for the half-open shutter 2. In response to this command, the half-open shutter 2 starts operating, and after a delay time due to the mechanical structure relative to the electric signal, the shutter 2 begins to open to an arbitrary aperture diameter. The anti-blooming gate 18 of the solid-state image sensor 3 has an fO that prevents blooming from occurring in the subject image when the strobe light is emitted, especially by the reflected light of the strobe light itself.
A clock φAB having a frequency of H, is applied at the same time as the φSSI pulse is generated or after a delay time that takes into account the delay of the shutter 2.

φSS2 is a pulse generated at the same time when the shutter 2 reaches a predetermined aperture diameter, and this pulse causes the shutter 2 to stop its opening operation so that the aperture diameter remains unchanged. At the same time as the aperture of the shutter 2 stops at a specified diameter, the strobe 15 is commanded to fire, and at the latest
It emits light with a flash duration of /1000 sec. After the strobe fires, shutter 2 receives φS, which is a close command.
S3 is issued and closing begins. After the shutter closes, the accumulated charge in the solid-state image sensor 3 is read out, and signal processing, modulation,
The signal is amplified and recorded on the magnetic sheet 12.

[Problem to be solved by the invention]

However, in the conventional example described above, there is a problem in that if a sufficient anti-blooming ability is to be obtained, the dark current becomes extremely high, causing deterioration of image quality.

The details will be explained below.

The operation of the anti-blooming gate to remove excess charge has already been explained, and one of the steps in its operation is the process in which holes return to their source, the channel stop region and virtual gate region of the P+ layer, after surface pinning. There is. Immediately after the bias of the anti-blooming gate changes from the level at which the surface potential under the gate becomes pinning to a positive bias, many of the holes remain under the gate. Thereafter, since the gate bias is High, a large fringing field forms between the edge of the anti-blooming gate region and the edge of the virtual gate region or the etch of the channel stop region. The holes remaining in the anti-blooming gate region return to the Po channel stop region and the virtual gate region along this field, but because the fringing field is large, the holes become hot holes and cause impact ionization. wake up The electrons generated by this are collected as false signals. The trtf current generated by such a mechanism is hereinafter referred to as hot hole dark current.

In a solid-state imaging device having such an anti-blooming gate, the amount of excess charge removed and the amount of false signals generated can be defined by the clock cycle of the anti-blooming gate. Therefore, if the storage time is constant, the anti-blooming ability and dark current can be said to be proportional to the clock frequency.

Now, in strobe photography, the flash duration of the discharge tube (xenon tube used) that generates the strobe light is very short, so the amount of light in a minute period of time is extremely high. As mentioned above, the anti-blooming ability of a solid-state image sensor with an anti-blooming gate is determined by the amount of excess charge removed in a very short period of time, so an extremely high frequency clock must be added to the anti-blooming gate during flash photography. Therefore, the dark current also becomes extremely large and the image quality deteriorates.

The present invention has been made under these circumstances, and it is an object of the present invention to provide an imaging device in which image quality is less likely to deteriorate due to activation of the anti-blooming gate when using a strobe.

[Means to solve the problem]

In the present invention, in order to achieve the above object, an imaging device is configured as shown in (1) and (2) below.

(1) A solid-state image pickup device having an anti-blooming gate and an electronic flash are provided, and a clock of a predetermined frequency is applied to the gate during the light emission period of the electronic flash.
A clock generating means is provided for applying a clock having a frequency lower than the predetermined frequency immediately before the flash is emitted and after the flash is completed.

(2) In the above (1), the clock generation means is capable of externally switching the frequency of the clock applied to the gate immediately before the electronic flash emits light and after the completion of light emission.

(Function) With the configurations (1) and (2) above, the dark current becomes small at times other than when the strobe is released, and furthermore, according to the configuration (2), when the strobe is not released, the dark current is reduced depending on the usage of the strobe. You can select the lock frequency.

(Example) The present invention will be explained below using examples.

FIG. 1 is a timing chart showing the operation of an electronic still video camera according to a first embodiment of the present invention. The configuration of this embodiment is almost the same as that shown in FIG. 4, but is different in that the system controller 7 is provided with clock generation means for generating a variable frequency clock as will be explained later.

Therefore, this embodiment will be explained with reference to FIG. 1 with reference to FIG. 4.

In FIG. 1, φSS1 is a command pulse for opening the half-open shutter 2. In FIG. This command pulse causes the half-open shutter 2 to start operating, and after a delay time due to the mechanical structure relative to the electrical signal, the shutter 2 begins to open to an arbitrary aperture diameter. The anti-blooming gate 18 of the solid-state image sensor 3 is supplied with a strobe light by the clock generation means of the system control 7 via the drive circuit 6, either with the generation of the φSSI pulse or after a delay that takes into account the shutter depth. Sometimes, the frequency f is extremely lower than the lock frequency fo so that blooming does not occur in the subject image, especially due to the reflected light of the strobe light itself.
A clock φAB of , is applied. The φSS2 pulse is generated at the same time when the shutter 2 reaches the predetermined aperture diameter. This pulse stops the opening operation of the shutter so that the aperture diameter is maintained. Further, when this pulse is obtained, the clock generating means uses a frequency f such that blooming does not occur in the subject image when the strobe light is emitted, especially by the reflected light of the strobe light itself. Switching to H2 clock generation. After the strobe light is emitted, a φSS3 pulse, which is a command to close the shutter 2, is issued. This pulse causes the shutter 2 to start its closing operation and eventually close completely. The clock φAB to the anti-blooming gate is switched again to the frequency f, )i by the pulse φSS3.

As mentioned above, the clock frequency of the anti-blooming gate is increased only when flashing with a high instantaneous amount of incident light.
In other cases, by lowering it, it is possible to maintain high anti-blooming ability as in the past, and also to reduce hot hole dark current and reduce deterioration in image quality.

Next, a second embodiment of the present invention will be described.

In this embodiment, the clock frequency to the gate in the first embodiment can be changed externally depending on how a strobe is used.

In other words, there are two ways to use a strobe: (a) to illuminate a subject in a dark place, and (b) to compensate for the exposure of a dark image due to backlighting. The frequencies of the blooming gate clock φAB are different, with the latter requiring a higher frequency.

Therefore, an external switch for specifying the use of the strobe should be provided, or the mode would be set to mode a above automatically when the amount of peripheral light decreases, and the conditions for the above could be selected by the photographer using an external switch, before and after the strobe fires. The clock frequency of the anti-blooming gate is changed depending on the purpose of the strobe.

(Effects of the Invention) As explained above, according to the present invention, the clock frequency to the anti-blooming gate is made high only when strobe light is emitted, and the clock frequency to the anti-blooming gate is made low except when strobe light is emitted. It is possible to obtain high-quality images with low dark current while maintaining high anti-blooming ability.

Furthermore, the clock frequency to the anti-blooming gate can be switched and selected from the outside depending on the purpose of the strobe, so deterioration in image quality can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a timing chart showing the operation of the first embodiment;
FIG. 2 shows a virtual phase C with an anti-blooming gate.
An explanatory diagram of OD, Fig. 3 is a potential distribution diagram in the depth direction under the anti-blooming gate, Fig. 4 is a block diagram showing the configuration of a conventional electronic still camera, and Fig. 5 is a timing chart showing the operation of the conventional example. It is. 3--Solid-state imaging device with anti-blooming gate 7--System control 15--Strobe

Claims (2)

[Claims] (1) A solid-state image pickup device having an anti-blooming gate and an electronic flash are provided, and a clock of a predetermined frequency is applied to the gate during the light emission period of the electronic flash.
An imaging device comprising a clock generating means for applying a clock having a frequency lower than the predetermined frequency until immediately before flash emission and after completion of flash emission. (2) The imaging device according to claim 1, wherein the clock generating means is capable of externally switching the frequency of the clock to be applied to the gate immediately before the electronic flash emits light and after the electronic flash completes light emission.