JP2660596B2 - Imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging apparatus in which a charge-coupled solid-state imaging device is applied to an image sensor, and in particular, to effectively capture a high-brightness subject optical image. It relates to device technology and circuit technology.

[Prior Art] A conventional image pickup apparatus is described as a still image pickup apparatus such as an electronic still camera. A charge-coupled solid-state image pickup device is applied as an image sensor, and an aperture mechanism is provided in front of a light receiving area of the solid-state image pickup device. An image pickup optical system such as a shutter mechanism and an image pickup lens is arranged, and a plurality of photoelectric conversion elements arranged and formed in a matrix in the light receiving area receive an object optical image passing through these image pickup optical systems. It is configured.

Further, a charge transfer path is formed adjacent to the plurality of photoelectric conversion elements formed in the light receiving region, and scans and reads pixel signals integrated in the photoelectric conversion element by exposure through the charge transfer path.

The aperture mechanism and the shutter mechanism control the aperture amount of the aperture and the shutter speed so as to obtain an optimal imaging state with respect to the brightness and the moving speed of the subject.

[Problems to be Solved by the Invention] However, in the conventional imaging apparatus, when the high-luminance subject is imaged, there is a problem that the imaging accuracy is reduced for the following reasons.

That is, the mechanical aperture mechanism has a mechanical problem that the aperture accuracy decreases as the aperture amount is reduced, and the mechanical shutter mechanism has a limitation in a high-speed shutter opening / closing operation. Therefore, it has been difficult to realize high-precision exposure control.

The present invention has been made in view of such problems of the related art, and in particular, has as its object to provide an imaging apparatus capable of imaging a high-luminance subject without depending on the accuracy of a mechanical diaphragm mechanism. And

Means for Solving the Problems In order to achieve such an object, the present invention provides an image pickup apparatus that performs image pickup using a charge-coupled solid-state image pickup device, in an exposure period during which the shutter mechanism opens. A means for supplying a drive signal for reading out a smear component mixed into the charge transfer path as a pixel signal after the shutter mechanism is closed is provided. That is, for example, charges generated in the P well where the photoelectric conversion element is formed and leaked into the charge transfer path, and smear components leaked by irregular reflection or the like into the charge transfer path for transferring the signal charge are read out as pixel signals. Realize imaging.

[Operation] According to the present invention having such a control means, the amount of charge of the smear component leaking into the transfer channel is extremely small compared to the amount of signal charge generated in the photoelectric conversion element during the exposure period. The shutter time can be opened for a long time or the aperture diameter can be increased in accordance with the magnification of the signal charge amount and the charge amount generated from components other than the photoelectric conversion element, and the mechanical accuracy is not affected. Accordingly, it is possible to perform low-speed shutter imaging of a high-luminance subject and highly accurate exposure control.

Embodiment An embodiment of an imaging device according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a charge-coupled solid-state imaging device, FIG. 2 is a partial plan view of a light-receiving region, FIG.
The figure is a schematic vertical sectional view for explaining the control of the potential level, and FIG. 5 is a schematic configuration diagram of the electronic still camera.

A feature of the present embodiment is that a signal charge generated in a photoelectric conversion element corresponding to a pixel is not used as a video signal, and a video signal is obtained using a snare component generated in a region other than the photoelectric conversion element. However, for convenience of explanation, the first
The overall configuration of the charge-coupled solid-state imaging device will be described with reference to the drawings, and then the circuit configuration and operation will be described.

This charge-coupled solid-state imaging device is an interline device, and receives a subject optical image formed through an imaging optical system of an electronic still camera, for example, in a light receiving region 1. Then, signal charges generated in a group of optical conversion elements such as photodiodes arranged and formed in a matrix in the light receiving region 1 are converted into four-phase driving signals φ1, φ2, φ3, The charge transfer path is configured to read out in synchronization with φ4.

Reference numeral 3 denotes a horizontal charge transfer path, which converts a signal charge transferred from the charge transfer path in the light receiving region 1 into a two-phase driving signal φ1.
1, and serially transferred to the output terminal 4 in synchronization with φ12.

Further, the structure of the light receiving region 1 will be described in detail with reference to FIG. 2. The P-type impurity layer (P
By forming a plurality of n-type impurity layers in a matrix in a well, a plurality of photodiodes Pd11 to Pd1n,
Pd21 to Pd2n, Pd31 to Pd3n... Are formed.

These photodiodes (hereinafter collectively referred to as Pdij)
In between, multiple charge transfer paths for transferring signal charges
L1, L2, L3 ... (hereinafter collectively referred to as Lj) are formed. Also, each photodiode Pdij and charge transfer path
A hatched portion surrounded by a dotted line in the drawing except for Lj is a channel stopper.

On the upper surface of the charge transfer path Lj, a plurality of transfer electrodes G1, G2, G3 consisting of a polysilicon layer extending in the horizontal direction (hereinafter, Gj
Are collectively arranged, and drive signals φ1 to φ4 based on a four-phase drive method at a predetermined timing described later are applied as a set of four transfer electrodes adjacent to each other. That is, photodiodes (for example, Pd11, Pd12, Pd
13 Two transfer electrodes (for example, G1 and G2) for Pd1n)
The transfer electrodes adjacent to each other are partially overlapped so that an unnecessary potential barrier is not formed. The signal charges generated in each photodiode Pdij are transferred to transfer gates Tg11, Tg12, Tg13,.
Through the corresponding charge transfer path Lj.

Next, a sectional structure of the light receiving region 1 will be described with reference to FIG.

That is, a P-type diffusion region 12 (hereinafter referred to as P-type
Well). A photodiode Pd is formed in the P well 12, and a reverse bias voltage is applied between the P well 12 and the n-type substrate 11 to deplete the P well 12.

Further, the charge transfer path Lj is formed in the P well 12,
The transfer electrode Gj made of a polysilicon layer and the aluminum shielding plate 13 are formed on the upper portion. A transfer gate TG is formed between the photodiode Pd and the charge transfer path Lj, and is configured to transfer signal charges generated in the photodiode Pd to the charge transfer path Lj.
In FIG. 3, channel stops 14 are formed on the left side of the photodiode Pd and on the right side of the charge transfer path Lj, respectively.

Next, the potential well at the time of light reception will be described.
When light hν, which is an optical object image, enters the photodiode Pd, signal charges accumulate on the photodiode Pd.
At the time of normal photographing, the accumulated signal charges are transferred to the charge transfer path Lj via the transfer gate TG. And
After controlling the potential well of the charge transfer path Lj from the depth indicated by the dotted line in FIG. 3 to the depth indicated by the solid line to accumulate the signal charges, the drive signals φ1 to φ1 as described with reference to FIG.
The data is sequentially transferred and read in the horizontal charge transfer path 3 direction by φ4.

Light reception and charge transfer as described below are performed at the time of imaging a high-precision and high-luminance subject, as compared with the normal imaging.

That is, when imaging a high-brightness subject, the potential well of the charge transfer path Lj is set in advance to a desired depth as shown by a solid line in FIG. However, this setting is not performed over the entire charge transfer path Lj, but is set intermittently as shown in FIG.

At the time of light reception, light hν is incident on the photodiode Pd, and leakage light is incident on the charge transfer path Lj. Although a signal charge is generated in the photodiode Pd, the transfer gate Tg is not driven, so that the signal charge generated in the photodiode Pd is not transferred to the charge transfer path Lj. On the other hand, if there is incident light on the photodiode Pd, the photodiode Pd
Unnecessary charges are generated in the P well 12 below the P well. Further, the leakage light incident on the charge transfer path Lj causes the vertical charge transfer path Lj
Unwanted charges are also generated inside. These unnecessary charges correspond to charges other than the signal charges according to the present invention, and are conventionally discharged to the n-type substrate 11 as a cause of smear.

However, in the present embodiment, it is possible to image a high-brightness subject with high exposure accuracy by positively using the unnecessary charges that have been swept out, in other words, charges other than the signal charges.

If the shutter speed is 1/60 sec, F5.6, light intensity 400
Unnecessary charge (smear component) is 0.1% of the signal charge of the solid-state imaging device which can obtain 100% output image under 0Lux condition.
%, The signal charge is 1000 times the unnecessary charge. Therefore, the shutter speed for obtaining an image from unnecessary charges is determined by 1/60 sec × 1000, and a long shutter of 16.7 sec can be performed for a long time.
Similarly, the aperture may be opened. Similarly, in a solid-state imaging device in which unnecessary charges are 0.01% of signal charges,
The shutter speed is 000 times faster, and a long shutter time of 167 seconds is possible. Similarly, the aperture may be opened.
As described above, in the present embodiment, high-precision exposure and high-luminance subject photographing are performed using unnecessary charges. This can be achieved by controlling the potential well of the charge transfer path Lj.

That is, by fixing the levels of the drive signals φ1 to φ4, the potential well of the charge transfer channel Lj is intermittently deepened as shown in FIG. 4, and the transfer gate Tg is set to the high level. As a result, the light hν is applied to the photodiode Pd with the aperture mechanism and the shutter mechanism opened.
Does not transfer the signal charges accumulated in the photodiode Pd to the charge transfer path Lj.

On the other hand, during the exposure period, the charge generated in the P well 12 flows to the charge transfer path Lj, and the charge transfer path Lj corresponds to the leak incident light.
And is accumulated together with the electric charge generated at the time.

However, unless the phases of the drive signals φ1 to φ4 are changed,
Since the charge transfer path Lj does not perform charge transfer, the charge transfer path Lj
The amount of charge stored in the memory gradually increases. When the shutter mechanism is closed after a predetermined time has elapsed, the drive signal φ
1 to φ4 sequentially change in level in the form of a pulse. Referring to FIG. 4, among the charge transfer paths Lj, the potential wells under the electrodes to which the drive signals φ2 and φ4 are applied are deeply controlled, and the drive signals φ1 and φ3 are The charge accumulated under the applied electrode is transferred. Such charge transfer is performed for each charge transfer path Lj, and transferred to the horizontal charge transfer path 3 as described with reference to FIG.

The signal charge stored in the photodiode Pd is applied to the n-type substrate 11 by a VOD structure known to those skilled in the art.
To be swept out. That is, a higher level voltage is applied to the n-type substrate 11 than in the normal operation, and the same structure as the npn transistor is realized by the n-layer, the P-well 12, and the n-type substrate 11 constituting the photodiode Pd, and the signal charge is increased. To the n-type substrate 11. At this time, the potential under the photodiode Pd is around it, that is, the channel stop.
The signal charge does not flow into the charge transfer channel Lj because it is higher than the potential of the region 14 and the lower part of the charge transfer path Lj.

Next, an example of an electronic still camera having a function of obtaining an image of the high-brightness subject will be described.

 FIG. 5 is a schematic configuration diagram of an electronic still camera.

In the electronic still camera, the image sensor 21 having the above configuration is provided. The charge-coupled solid-state imaging device 21 receives the subject light that has passed through the imaging lens 23, the aperture mechanism 24, and the beam splitter 25 while the shutter mechanism 22 opens and closes, converts an optical image into an electric signal, and converts the image into a video signal processing circuit. Output to 30.

The shutter mechanism 22 and the aperture mechanism 24 are provided to adjust the amount of exposure to the charge-coupled solid-state imaging device 21. In order to determine the amount of exposure, a part of the subject light extracted by the beam splitter 25 is guided to the light receiving element 26, and the output from the light receiving element 26 is input to the exposure control circuit 27. The exposure control circuit 27 calculates an aperture value corresponding to the subject brightness and the shutter speed based on the signal output from the light receiving element 26, and controls the driving of the aperture mechanism 24 and the shutter mechanism 22. The operation of the exposure control circuit 27 is controlled by a system controller 28 composed of a microcomputer.

Here, high-luminance subject photography will be described. In the charge-coupled solid-state imaging device 21, the ratio between the signal charge generated in each photodiode and the charge generated from the P well 12 and the charge transfer path Lj is constant. Therefore, if the exposure control circuit 27 and the system controller 28 that controls the exposure control circuit switch between high-brightness subject shooting, if the amount of charge is 1000 times as in the previous example, the shutter is controlled based on the signal output from the light receiving element 26. Set the time to 1000 times. At this time, an aperture value that may be opened by setting the shutter time shorter than the above is also set, but may be the same aperture value as in normal shooting.

The electronic still camera also incorporates a finder optical system including a quick return mirror and a pentaprism, but these are not shown in order to avoid complication of the drawing.

The system controller 28 includes a CC in addition to the exposure control circuit 12.
The operation of the D drive circuit 29, the video signal processing circuit 30, and the recording control circuit 31 is controlled. That is, the half-press signal of the release button 32a is transmitted from the release operation detection circuit 32 to the system controller.
When supplied to the exposure controller 28, the system controller 28 outputs a photometry timing signal to the exposure control circuit 27. Thus, the exposure control circuit 27 takes in the subject luminance information from the light receiving element 26 and calculates the aperture value and the shutter time. This calculation is similarly performed during a long shutter.

Further, when a signal that the release button 32a is pressed is input from the release operation detection circuit 32 to the system controller 28, the aperture value calculated by the exposure control circuit 27, the aperture 24 and the shutter 22 are driven according to the shutter time, The subject light is irradiated onto the charge-coupled solid-state imaging device 21 with an appropriate exposure amount.

The CCD drive circuit 29 drives the charge-coupled solid-state imaging device 21 in synchronization with a timing clock TP from the system controller 28. This timing clock has a period equal to 1/60 second, that is, one vertical scanning period (one field period; 1 V) in the standard television system.

In this electronic still camera, the CCD driving circuit 29 transmits a first field pulse FSA to the charge-coupled solid-state imaging device 21 in order to capture a video signal by a frame imaging method.
A second field pulse FSB, a vertical transfer pulse φv (corresponding to the drive signals φ1 to φ4), and a horizontal transfer pulse φH (corresponding to the drive signals φ11 to φ12) are supplied. Each of the first field pulse FSA and the second field pulse FSB is equal to twice the cycle of the timing clock TP, and their phases are shifted from each other by a half cycle. Each of the vertical transfer pulse φv and the horizontal transfer pulse φH sends out a video signal for each field from the charge-coupled solid-state imaging device 21 during one cycle (1 V) of the timing clock TP.

The video signal processing circuit 30 is a charge-coupled solid-state imaging device.
Video signals output serially from 21
Converts to an output signal conforming to the SC system. The output signal thus obtained is supplied to the recording device 34 via the buffer circuit 33 controlled by the recording control circuit 31. Recording device
The device 34 includes, for example, a device that digitally converts an output signal supplied from the buffer circuit 33 and writes the converted signal into a card-type semiconductor memory, so that video data of a still image can be recorded. . Incidentally, as the recording device 34, a disk device for magnetically recording the output signal on a still video floppy may be used.

Note that the present invention can be applied to an appropriate charge-coupled solid-state imaging device. Also, in order to obtain the effect of photographing only by the charges of the smear component, it is preferable to reduce the influence of the dark current from the semiconductor substrate side. Therefore, the charge transfer path should be formed on the surface layer of the semiconductor substrate as much as possible. It is effective.

The present invention can be applied to a charge-coupled solid-state imaging device that performs color imaging.

[Effects of the Invention] As described above, the imaging apparatus according to the present invention performs imaging using charges of smear components other than signal charges generated at a predetermined ratio with respect to signal charges generated in the photoelectric conversion element of the image sensor. It is like that. Therefore, the shutter time can be extended corresponding to the predetermined ratio without strictly adjusting the light reception of the image sensor by the mechanically configured aperture mechanism, so that high-precision, high-luminance subject shooting becomes possible. Multipurpose use of the imaging device can be achieved.

[Brief description of the drawings]

1 to 5 show an embodiment of an image pickup apparatus to which the present invention is applied, FIG. 1 is a schematic configuration diagram of an image sensor, FIG. 2 is a plan view of a main part of a light receiving area, 3 is a longitudinal sectional view of a light receiving region of the image sensor, FIG. 4 is a schematic sectional view showing control of a potential well of a charge transfer path, and FIG. 5 is a schematic configuration diagram of an electronic still camera. Reference numerals in the drawing: 1 ... light receiving area, 2 ... scanning circuit, 3 ... horizontal charge transfer path, 4 ... output terminal, 11 ... n-type substrate, 12 ... P well, 13 ... shield plate , 14 ... Channel stopper, 21 ... Charge-coupled solid-state imaging device, 22 ... Shutter mechanism, 23 ... Aperture mechanism, 27 ... Exposure control circuit, 28 ... System controller, Pd ... Photodiode, Lj ... ... Charge transfer path, φv, φH ... Drive signal, hν ... Incoming light.

Claims (1)

(57) [Claims] 1. A subject optical image passing through a shutter mechanism and an aperture mechanism is imaged by a plurality of photoelectric conversion elements formed in a light receiving region of a charge-coupled solid-state imaging device, and pixels generated in these photoelectric conversion elements are captured. In an image pickup apparatus that scans and reads a signal through a charge transfer path, an exposure period during which the shutter mechanism is opened, for reading a smear component mixed into the charge transfer path as a pixel signal after the shutter mechanism is closed. A digital electronic still camera comprising means for supplying a drive signal.