JPH09200621A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pickup device with which a dynamic range can be extended at low cost without degrading an S/N. SOLUTION: A solid-state imaging device 1 is driven at double speed by a driving pulse generating circuit 7, two pictures are outputted for one field period, a shutter operation is performed for one picture between these two pictures, a saturation nonuniformity component is removed through a white clip circuit 3 and converted to a digital signal by an A/D converter 4, and the outputs of two pictures are respectively stored in field memories 5 and 6 later. The outputs of these field memories 5 and 6 are synchronized by a vertical synchronizing pulse VD and added by an adder 8 so that the dynamic range can be extended corresponding to a shutter time ratio between two pictures without saturation unevenness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and more particularly to a solid-state image pickup device having an improved dynamic range by utilizing an electronic shutter.

[0002]

2. Description of the Related Art Due to advances in semiconductor technology, solid-state image pickup devices are becoming finer and higher in sensitivity. Along with this, dynamics for amplifying sensitivity and black level to high brightness level without saturating. The improvement has become an important point of development as the range decreases.

As one of the techniques for improving the dynamic range, there is a technique for giving a KNEE characteristic to the solid-state image pickup device itself or an image pickup apparatus using this device to artificially expand it. One example is JP-A-4-196776.
No., published in Japanese Unexamined Patent Publication No.

Referring to FIG. 6 which is a block diagram of the image pickup apparatus described in the above publication, this image pickup apparatus has a photographing lens 3
1. A half mirror 32 arranged on the same straight line with respect to the direction of the incident light, and an arbitrary shutter speed for receiving the light reflected and transmitted by the half mirror 32 and converting it into an electric signal. Charge-coupled devices (CCD) 33a and 73b with electronic shutters, C of these
Adder 34 for adding the outputs of the CDs 33a and 33b
The dynamic range control unit 35 is provided, and the incident light that has passed through the taking lens 31 is branched by the half mirror 32 into two systems, that is, the transmitted light and the reflected light, and the reflected light is the CCD 33a.
Then, the transmitted light is input to the CCD 33b.

The outputs of the CCDs 33a and 33b are added by the adder 34, and the added output is output as a video signal via the dynamic range control unit 35, so that the S / N ratio can be made smaller than before. Widening the dynamic range.

On the other hand, another example is described in Japanese Patent Application Laid-Open No. 2-87785. Referring to FIG. 7A showing a block diagram of an image pickup device in the image pickup device described in the publication, this image pickup device has a solid-state image pickup device 71, a light receiving section 72 for generating electric charges according to the amount of received light, A vertical transfer unit 73 that transfers the charges generated in the unit 72 in the vertical direction and a horizontal transfer unit 74 that transfers the charges from the vertical transfer unit 73 in the horizontal direction are provided, and the charges generated in the light receiving unit 72 are used as a light receiving unit. The dynamic range of the solid-state imaging device 71 is sufficiently utilized even in the high luminance region by reading out the data in a plurality of times according to the capacity of the vertical transfer unit and performing addition on the vertical transfer unit 73, and reading in a wide luminance range. I am getting the converted output.

[0007]

In the conventional image pickup apparatus described above, for example, in the case of the image pickup apparatus shown in FIG. 6, since it is a two-plate type using a half mirror, the scale of the apparatus becomes large, and images of two CCD outputs are obtained. Since the man-hours required for registration adjustment and the like for making the two coincide with each other increase, there is a drawback that the cost becomes high.

On the other hand, in the case of the image pickup device shown in FIG. 7A, since the outputs of the photodiodes are added, as shown in FIG. 7B showing the relationship between the photodiode and the light amount, the incident light amount is When the amount of light exceeds point b, the photodiode output is saturated by the overflow drain so that data does not overflow from the register of the vertical transfer unit. However, due to the structural variation, the saturated output varies from bit to bit, resulting in uneven saturation. Appears on the screen (hatched portion E in FIG. 7B). Therefore, the S / N ratio is greatly deteriorated above the point b, and the practical dynamic range is limited at the point b as before.

An object of the present invention is to solve the above-mentioned drawbacks, and it is an object of the present invention to provide a solid-state image pickup device which can expand the dynamic range at a low cost without deteriorating the S / N ratio.

[0010]

The solid-state image pickup device of the present invention is characterized in that at least two screens of image signals are output from the solid-state image pickup device in one field period, and the previous one of these two screens is output as it is. Then, the subsequent one screen is an output by an electronic shutter function that extracts the accumulated electrification of the solid-state imaging device by an overflow drain, and the image output of the one screen is white clipped to remove saturation unevenness at a high brightness level, and The image outputs of these two screens are held in different storage means respectively, and the image outputs of the two screens stored in these storage means are synchronized with a vertical synchronization pulse and added to eliminate the saturation unevenness. Moreover, it is to have a dynamic range expanding means for expanding the dynamic range.

The dynamic range expanding means clips the high-luminance level of the image signal of the n-screen and the solid-state image sensor for outputting the image signal of the n-screen (n is a natural number) to a predetermined saturation level. A white clip circuit, n field memories for storing the digital image signal for one field period for each of the n screens, a drive pulse generation circuit for driving the solid-state imaging device and controlling the field memory, and the field. An adder for adding digital image signals of a memory, and the drive pulse generation circuit drives the solid-state image pickup device at a speed of n times, so that the solid-state image pickup device reads out an image of n screens within one field. The first one of
The screen is directly output as the normal output and the remaining n-1
Responding to n-1 high voltage pulses for shutters supplied from the outside of the screen, the accumulated charges are extracted so as not to exceed the predetermined saturation level and output as shutter outputs. By passing through the white clipping circuit, only the high-intensity level of one screen of the normal output that exceeds the predetermined saturation level is clipped, and each of the n field memories corresponds to the corresponding screen for each screen. The image output of the n screens is stored in the memory, synchronized with the vertical synchronizing pulse supplied from the drive pulse generating circuit, and added by the adder to synthesize and output the image output of one field as an output image of one field.

Furthermore, the high voltage pulse for the shutter is set to n.
-1 is supplied to gradually reduce the output image level above the predetermined saturation level in the combined output, and obtain an image output with continuous gradation.

Furthermore, the adder is configured to add only the field memory outputs synchronized with the vertical synchronizing pulse.

Further, the drive pulse generation circuit generates a vertical transfer pulse, a horizontal transfer pulse, and a read gate pulse to control the n-fold speed read operation of the solid-state image pickup device, and generates the vertical synchronization signal to generate the vertical sync signal. The synchronization operation for matching the time lag between the screen for normal output and the screen for shutter output at the time of reading the field memory is controlled.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a solid-state imaging device 100 of the present invention.
FIG. 2 is a schematic diagram of the internal configuration of the solid-state imaging device 1. FIG.
Referring to, the solid-state imaging device 100 includes a solid-state imaging device 1 having a shutter function, and a buffer circuit 2 for sending a signal 21 output from the solid-state imaging device 1 to the next stage.
A white clipping circuit 3 for clipping the signal level of the output 22 of the buffer circuit 2, and an analog-digital converter (hereinafter referred to as an A / D converter) 4 for converting the clipped output signal 23 into a digital signal. , Field memories 5 and 6 for storing and holding the converted digital signal 24 in a time division manner, and an adder 8 for adding signals 26 and 28 read from these field memories 5 and 6 and outputting as an output signal 27. And a vertical synchronizing pulse VD to the field memories 5 and 6 and a horizontal transfer pulse HS and a vertical transfer pulse V to the solid-state image sensor 1.
It is provided with a drive pulse generation circuit 7 for supplying S and the read gate pulse VG, respectively.

The solid-state image pickup device 1 includes a photodiode 15 for accumulating charges proportional to the amount of incident light, and a vertical transfer register 10 for temporarily holding the charges of the photodiode 15 as an image signal in response to a vertical transfer pulse VS. A horizontal transfer register 11 that further transfers the image signal transferred from the vertical transfer register 10 to the output unit 15 in response to the horizontal transfer pulse HS, and an output that outputs the image signal transferred from the horizontal transfer register 11 to the buffer circuit 2. And part 14.

A high voltage pulse for shutter (hereinafter referred to as a shutter pulse) VP is externally supplied to the semiconductor substrate of the solid-state image pickup device 1 through a terminal 17, and is incident on a photodiode of this image pickup device. Electric charges are accumulated in proportion to the intensity of the light. For example, in a shutter using a vertical overflow drain, it is general to extract the accumulated electric charges by a high voltage pulse VP and control the shutter time.

That is, if the supply interval of the shutter pulse is shortened, the electric charge of the photodiode is emptied frequently, and therefore the overflow of the photodiode can be reduced, and therefore, the shutter output is saturated. The amount of light can be taken sufficiently to widen the dynamic range.

The operation of the solid-state image pickup device 100 will be described with reference to FIGS. 1 and 2 and FIG. 3 showing a timing chart for explaining the operation. If the number of field memories is n, an example of n = 2 is shown here as an example, and the same operation is performed even if the number is more than n.

Since there are two field memories, one vertical scanning period (hereinafter referred to as one field) is two.
The divided fields are scanned by the corresponding field memories. In order to correspond to the two-division scanning, the read gate pulse VG is applied to the read gate electrode 9 of the solid-state imaging device 1 twice in one field, that is, 1
/ 2 fields are supplied.

The charges accumulated in the photodiode 15 according to the amount of incident light are activated by the read gate pulse VP supplied to the read gate electrode 9 and immediately transferred to the vertical transfer register 10 as an image signal.

A vertical transfer pulse VS consisting of continuous pulses is supplied to the vertical transfer register 10 from the drive pulse generation circuit 7 through an input terminal 12 of the vertical transfer pulse VS, and a read gate pulse VG is supplied to this pulse. Superposed with positive polarity. The period from the trailing edge of the superimposed read gate pulse VG to the leading edge of the next gate pulse, which is ½ field period apart, is a normal accumulation period in which charges corresponding to the amount of incident light are accumulated in the photodiode 15. Vertical transfer pulse V consisting of continuous pulses during the period
Since S is supplied, the signal read from the photo register 15 in response to this pulse is transferred to the horizontal transfer register 11
Transfer to

The horizontal transfer pulse VH of positive polarity is supplied to the horizontal transfer register 11 from the drive pulse generation circuit 7 through the input terminal 13 of the horizontal transfer pulse HS, and the vertical transfer pulse VS is sandwiched in this pulse. There is a rest period that becomes low level for a predetermined width during the rest period, and between this rest period and the next rest period, that is, during a period when the vertical transfer pulse VS is at the high level, a data rate having a higher frequency than the vertical transfer pulse VH is set. Horizontal transfer pulse VH consisting of continuous pulses
Is set to occur. The signal transferred from the vertical transfer register 10 in response to this pulse is transferred to the output unit 14 at high speed.

Therefore, as can be seen from this operation, the drive pulse generating circuit 7 controls the vertical transfer register 10, the horizontal transfer register 11 and the output section 14 so as to operate at double speed.

The shutter pulse for controlling the electronic shutter is applied at any timing within the 1/2 field after the 1 field, and the accumulation time by the shutter can be varied from the 1/2 field to 0.

Here, the relationship between the amount of incident light and the output level of the solid-state image pickup device 1 will be described with reference to FIG. 7B again. In this figure, the amount of incident light is plotted on the X axis and the output voltage is plotted on the Y axis. The point a is the standard light quantity and the point b is the incident light quantity at the saturation point, and the corresponding outputs are shown as the standard output and the saturated output. The charge of 1 of the solid-state image pickup device linearly increases when the incident light amount a is a saturated standard, but linearly increases when the incident light amount is low. Since each of them is punched out by a low pressure (not shown), a saturation characteristic is exhibited. However, due to variations in the photodiodes 15 in the overflow drain, saturation unevenness occurs.

The dynamic range DL in this case is: dynamic range DL = (incident light quantity b at the saturation point) /
It can be expressed by (standard light amount a).

On the other hand, FIG. 4 showing the relationship between the image output before applying the white clip and the saturation output, and FIG. 5 showing the relationship between the shutter output and the saturation output after adding the image outputs of the field memory. Referring to FIG. 1, the dynamic range characteristic according to the block configuration of this embodiment shown in FIG. Although there is saturation unevenness, both the normal output A corresponding to the normal period after white clipping and the shutter output B corresponding to the shutter period have no saturation unevenness. As shown in the figure, even if the normal output A saturates at point b, there is no saturation unevenness, and the shutter output B causes c
It is shown that it is possible to obtain the addition output D which is expanded up to the point in a similar manner.

The term "simultaneous" as used herein means that the normal output A and the shutter output B are shifted from each other by a maximum of 1/2 field, as can be seen from the timing chart shown in FIG. To add the signals,
This means that the normal output A is delayed for a maximum of 1/2 field so that the output signals of the same pixel are simultaneously output.

The addition of these two image signals is controlled by synchronizing the two field memories 5 and 6 with a vertical synchronizing pulse VD for timing the two image signals supplied from the drive pulse generating circuit 7. After that, the adder 8 may add.

Since the ratio of the expansion of the dynamic range is determined by the ratio of the normal accumulation period and the shutter accumulation time, when a wider dynamic range is required, the light amount until the shutter output is saturated can be shortened by shortening the shutter accumulation period. Since it is sufficient, the dynamic range can be widened.

Although it has been conventionally performed to artificially widen the dynamic range by providing the KNEE characteristic, a bending point (KNEE point) between two shutter speeds, that is, a normal state and a shutter output state. There are only two points, point b and point c, and it is visually highlighted to give the impression that the contrast of the screen is sharply reduced. To prevent this, two or more types of shutters are set and finely controlled to obtain a smoothly continuous gradation image, and a more natural-looking image can be obtained.

In order to finely control the KNEE point, the number of field memories 5 and 6 may be set to three or more, and the vertical synchronizing pulse VD for matching the respective timings may be easily supplied.

That is, the solid-state image pickup device outputs an image signal for n screens in one field, and n field memories for storing the digital image signals output from the A / D converter 4 for one field period for every n screens. Set up.

The drive pulse generation circuit 7 drives the solid-state image pickup device 1 at a speed n times higher than that of the solid-state image pickup device 1.
Outputs the first one screen out of the read images of n screens within one field as it is as the normal output A.

On the other hand, in response to the n-1 shutter high-voltage pulses VP supplied from the outside at different timings, the remaining n-1 screens are withdrawn from the accumulated charges so as not to exceed the above-mentioned saturation level. Output as shutter output B.

By passing the output image of these n screens through the white clipping circuit 3, only the high brightness level of one screen of the normal output A which exceeds the saturation level is clipped to output C before white clipping, and A / Through the D converter 4, each screen is stored in the corresponding memory among the n field memories.

The outputs of these field memories are synchronized with the vertical synchronizing pulse VD supplied from the drive pulse generating circuit 7 and added by the adder 8 to synthesize and output the image output of n screens as an output image of one field. It may be configured as follows.

[0039]

As described above, according to the solid-state image pickup device of the present invention, the solid-state image pickup device is driven at a normal n-times speed, and n shutter pulses are supplied within one field to finely adjust the shutter accumulation period. Continuous grayscale image output can be obtained by controlling, and these image outputs are stored in the n field memories after white clipping is applied, and are stored in synchronization with the vertical synchronizing pulse VD, and then output by the adder. Since the addition is performed and the combined output is performed, it is possible to provide a solid-state imaging device having a wide dynamic range without saturation unevenness at low cost by using one solid-state imaging device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a solid-state image pickup device applied to an embodiment of the present invention.

FIG. 3 is a timing chart for explaining the operation of the block diagram of FIG.

FIG. 4 is a diagram showing a relationship between a shutter output and a saturation output before applying a white clip.

FIG. 5 is a diagram showing a relationship between a shutter output and a saturation output after adding the image outputs of the field memory.

FIG. 6 is a block diagram of an example of a conventional image pickup apparatus.

FIG. 7A is a block diagram of an example of another conventional imaging device. (B) It is the figure which showed the relationship between a photodiode and the amount of light.

[Explanation of symbols]

 1 solid-state image sensor 2 buffer circuit 3 white clip circuit 4 A / D converter 5, 6 field memory 7 drive pulse generation circuit 8 adder 9 readout gate electrode 10 vertical transfer register 11 horizontal transfer register 12 input terminal for vertical transfer pulse VS 13 Horizontal transfer pulse HS input terminal 14 Output section 15 Photodiode 16 Output terminal 17 Shutter high voltage pulse VP 21 Solid-state image sensor output 22 Buffer circuit output 23 White clip circuit output 24 A / D converter output 25 Vertical sync pulse VD 26, 28 Field memory output 27 Adder output 31 Imaging lens 32 Half mirror 33a, 33b CCD 34 Adder 35 Dynamic range control unit

Claims (5)

[Claims] 1. A solid-state image sensor outputs at least two screens of image signals in one field period, the first one of these two screens is output as it is, and the second one of the screens is output by an overflow drain. The output from the electronic shutter function is the same as the above 1
The image output of the screen is white clipped to remove the saturation unevenness of the high brightness level, and the image outputs of these two screens are held in different storage means respectively, and the two screens stored in these storage means are stored. A solid-state image pickup device having a dynamic range expansion means for expanding the dynamic range without causing the saturation unevenness by synchronizing and adding the image outputs of (1) with a vertical synchronization pulse. 2. The dynamic range expansion means is n
(N is a natural number) The solid-state imaging device that outputs an image signal of a screen, a white clip circuit that clips a high brightness level of the image signal of an n screen to a predetermined saturation level, and the digital image signal It has n field memories for storing one field period for each screen, a drive pulse generating circuit for driving the solid-state image pickup device and controlling the field memory, and an adder for adding digital image signals of the field memory. Then, the drive pulse generation circuit drives the solid-state image sensor at a speed n times higher, so that the solid-state image sensor outputs the first one screen of the n-screen read-out image within one field as the normal output. The remaining n-1 screens are responded to the n-1 shutter high voltage pulses supplied from the outside, respectively. The accumulated charge is extracted so as not to exceed a predetermined saturation level and output as a shutter output, and the image output of these n screens is passed through the white clip circuit to obtain one screen of the normal output that exceeds the predetermined saturation level. Of the n field memories, each of which is stored in a corresponding memory among the n field memories for each screen, and is synchronized with the vertical synchronizing pulse supplied from the drive pulse generating circuit to add the adder. 2. The solid-state image pickup device according to claim 1, wherein the image output of the n screen is combined and output as an output image of one field by adding. 3. An n-1 number of high voltage pulses for the shutters are supplied to gradually reduce an image output level above the predetermined saturation level of the combined output, thereby producing an image output of continuous gradation. The solid-state imaging device according to claim 2, wherein the solid-state imaging device is obtained. 4. The solid-state image pickup device according to claim 1, wherein the adder adds only the field memory outputs synchronized with the vertical synchronizing pulse. 5. The drive pulse generation circuit generates a vertical transfer pulse, a horizontal transfer pulse, and a read gate pulse to control an n-fold speed read operation of the solid-state imaging device,
2. The solid-state imaging device according to claim 1, wherein the vertical synchronizing signal is generated to control a synchronizing operation for matching a time lag between the screen of the normal output and the screen of the shutter output when the field memory is read.