JP2003198945A - Solid-state electronic imaging device and solid-state electronic image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain brightness of an obtained image even though the light reception area of a photodiode 2 is reduced. <P>SOLUTION: The light reception area of the photodiode 2, the area of a transfer electrode on a vertical transfer line 4, and the magnitude of a transfer pulse to be given to the vertical transfer line 4 are so determined that a potential well for storing 3-fold storage capacity of the photodiode 2 is formed. Signal electric charge is repeatedly stored in the photodiode 2 several times ((A), (C), and (E)) and is shifted to the vertical transfer line 4 at each time of storage ((B), (D), and (F)). Thus the storage capacity of the photodiode 2 can be practically increased though the storage capacity of the photodiode 2 (the light reception area) is small, and brightness of the obtained image is increased. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solid-state electronic image pickup device and a solid-state electronic image pickup device.

[0002]

Despite the demand for miniaturization of CCD, the number of pixels of CCD is increasing year by year. CCD is
It has a large number of photodiodes and transfer paths (vertical transfer paths, horizontal transfer paths) for transferring the signal charges accumulated in the photodiodes. In the area of 1 pixel of CCD, 1
Each photodiode and a transfer electrode corresponding to this one photodiode are included. Even if the number of pixels of the CCD increases, if the CCD becomes smaller, the CCD
The area for one pixel becomes smaller.

Since the signal charge accumulated in the photodiode is transferred by the potential well formed under the transfer path, the light receiving area of one photodiode and the area of one transfer electrode are almost equal. If the area for one pixel is reduced to reduce the size of the CCD, the light receiving area of the photodiode is also reduced. However, in order to maintain the quality of the obtained image, the light receiving area of the photodiode cannot be made very small. As a result, the area for one pixel cannot be made smaller, and the CCD itself cannot be made smaller.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to reduce the light receiving area of a photodiode (photoelectric conversion element).

In the solid-state electronic image pickup device according to the present invention, a large number of photoelectric conversion devices for accumulating signal charges corresponding to the amount of incident light, adjacent to the photoelectric conversion devices, and provided with transfer pulses to transfer electrodes are provided. A potential well is formed,
The photoelectric conversion element includes a transfer path for transferring the signal charge by the formed potential well, and a transfer gate for shifting the signal charge accumulated in the photoelectric conversion element to the transfer path when a shift pulse is applied. Is smaller than the area of the transfer electrode.

According to this invention, since the light receiving area of the photoelectric conversion element (light receiving area for one photoelectric conversion element) is less than the area of the transfer electrode (area of one transfer electrode), the area for one pixel is Can be made smaller. The solid-state electronic image sensor can be downsized.

A solid-state electronic image pickup device including the above-mentioned solid-state electronic image pickup device and a drive circuit for giving the above-mentioned transfer pulse to the above-mentioned transfer path can be constructed. In this case, when a shift pulse is applied to the transfer gate, the capacity of the potential well generated when the signal charge stored in the photoelectric conversion element is shifted to the transfer path is smaller than the storage capacity of the photoelectric conversion element. The area of the transfer electrode corresponding to the photoelectric conversion element and the level of the transfer pulse may be determined so as to be large.

Since the capacity of the potential well is larger than the storage capacity of the photoelectric conversion element, it is possible to store the signal charge in the potential well even if the signal charge accumulated during the exposure of the photoelectric conversion element is shifted to the transfer path at any time. it can. By shifting the signal charges accumulated in the photoelectric conversion element to the transfer path at any time during exposure, the storage capacity of the photoelectric conversion element is substantially increased. Even if the light receiving area of the photoelectric conversion element is small, a large amount of signal charges can be stored. It is possible to prevent a decrease in the brightness of the obtained image.

Within the exposure time of the photoelectric conversion element,
When a shift pulse is applied to the transfer gate a plurality of times, the capacitance of the potential well and the storage capacitance of the photoelectric conversion element generated when the signal charges accumulated in the photoelectric conversion element are shifted to the transfer path. The timing of the shift pulse applied to the transfer gate pulse is preferably determined based on the ratio.

A sweep pulse for giving an unnecessary charge pulse for sweeping unnecessary charges accumulated in the transfer path before the first timing of the field shift pulse (may be before starting exposure of the photoelectric conversion element). You may make it further provide an output means.

In the solid-state electronic image pickup device, a large number of the photoelectric conversion elements are arranged in the row direction and the column direction, and the transfer path is arranged adjacent to each column of the photoelectric conversion elements. It may be one.

In this case, the image generating means for generating an image of one frame based on the signal charges corresponding to the storage capacities of the photoelectric conversion elements of the first field and the second field, and the signal charges of the first field are read out, A shift pulse is applied to the transfer gates in the odd-numbered rows, and a shift pulse is applied to the transfer gates in the even-numbered rows when the signal charges in the second field are read. In one of the fields read out first, the timing of the shift pulse is determined based on the ratio of the capacity of the potential well to the storage capacity of the photoelectric conversion element. The brightness of the image generated by the image generating means is increased by using the signal charges obtained in excess of the storage capacity of the conversion element. It is a brightness adjusting means for adjusting comprises a solid-state electronic image sensing device.

When the photoelectric conversion elements of the first field and the second field are exposed at the same time, the signal charges accumulated in the photoelectric conversion elements of the previously read field are shifted to the transfer path at any time during the exposure. , Substantially more signal charges than the storage capacity of the photoelectric conversion element can be stored. On the other hand, the signal charge accumulated in the photoelectric conversion element of the subsequent field cannot be shifted to the transfer path in order to prevent it from being mixed with the signal charge accumulated in the photoelectric conversion element of the previous field. Therefore, it is not possible to substantially store a larger amount of signal charge than the storage capacity of the photoelectric conversion element in the subsequent field. Therefore, when the signal charges are not shifted to the transfer path, an image is generated using the signal charges accumulated in the photoelectric conversion elements of the first field and the second field. The signal charge that is equal to or larger than the storage capacity of the photoelectric conversion element that is read out first in the first field or the second field is used for adjusting the brightness of the generated image.
The obtained signal charge represents a high-luminance portion, and an image with good gradation in the high-luminance portion can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention and schematically shows the structure of a CCD.

The CCD 1 is provided with a plurality of photodiodes (photoelectric conversion elements) 2 arranged in columns and rows. Further, by applying the vertical transfer pulses φV1 to φV3, the vertical transfer paths 4 (shielded) for transferring the signal charges accumulated in the photodiodes 2 in the row direction are adjacent to each column of the photodiodes 2. It is provided. A shift gate 3 for shifting the signal charge accumulated in the photodiode 2 to the vertical transfer path 4 by forming a field shift pulse FS between the photodiode 2 and the vertical transfer path 4 is formed. Has been done. A horizontal transfer pulse φH is applied to the CCD 1 so that the signal charges transferred through the vertical transfer path 4 are transferred in the column direction (horizontal direction).
An amplifier circuit 7 for amplifying the video signal output from the horizontal transfer path 6 is provided.

The above-mentioned field shift pulse F
S, vertical transfer pulses φV1 to φV3, horizontal transfer pulse φH, etc. are output from the drive circuit 9 and given to the CCD 1. Further, the overflow / drain / pulse OFDP is also output from the drive circuit 9 and given to the CCD 1.
The overflow / drain / pulse OFDP is used when sweeping unnecessary residual signal charges from the substrate of the CCD 1.

One photodiode 2 of the CCD 1 is
It corresponds to one pixel of the image represented by the video signal obtained from the CCD 1. An area including a vertical transfer electrode formed on the vertical transfer path 4 corresponding to one photodiode 2, shift gate 3 and one photodiode 2 is referred to as one pixel area 5 (see FIG. 2 later). As will be described with reference to the CCD 1, an electrode 8 for applying each pulse to the vertical transfer electrode 4 and the like is formed corresponding to the photodiode 2. This electrode 8 is also included in one pixel region 5.) .

FIG. 2 is a plan view of the one pixel area 5.

In FIG. 2, compared with FIG.
The gate is not shown and the electrode 8 is shown.

Three vertical transfer electrodes V1, V2 and V3 are formed corresponding to one photodiode (PD) 2. These vertical transfer electrodes V1, V2 and V3
By applying the vertical transfer pulses φV1, φV2 and φV3 to, the potential wells are formed under the vertical transfer electrodes V1, V2 and V3. The signal charge is accumulated in the formed potential well and transferred.

In this embodiment, the light receiving area of one photodiode 2 is equal to that of one vertical transfer electrode V1, V2.
Alternatively, the photodiode 2 and the vertical transfer electrode are formed so as to be smaller than the area of V3. Also,
The area of the photodiode 2, the area of the vertical transfer electrodes V1, V2 or V3, and the vertical transfer pulses φV1 to φV3 are set so that the capacity of the potential well formed below one transfer electrode is larger than the storage capacity of the photodiode 2. The size of is fixed.

FIGS. 3A to 3F are potential profiles showing how the signal charges are shifted. It is shown that the signal charges accumulated in the photodiode 2 are shifted to the vertical transfer path (VCCD) 4.

In this example, with the driving of the vertical transfer path 4 stopped, the signal charges accumulated by exposing one photodiode 2 are repeatedly shifted three times during the exposure to the vertical transfer path 4. It is a thing. Photodiode 1
Since the signal charge accumulated in the vertical transfer path 4 is repeated three times and shifted to the vertical transfer path 4, it is necessary to prevent overflow in the vertical transfer path 4, and the storage capacity of the photodiode 2 and the potential formed in the vertical transfer path 4 are prevented. A certain relationship with the well capacity is required as described below.

In the case where the one pixel region 5 has the structure shown in FIG. 2, when the signal charges accumulated in all the photodiodes 2 of the CCD 1 are read in the same field (all pixel reading), they are adjacent in the vertical direction. If a barrier (potential barrier) cannot be formed between the potential wells, the signal charges will be mixed. Therefore, when reading out all pixels, the storage capacity of the potential well formed below one vertical transfer electrode is required to be three times as large as the storage capacity of the photodiode 2 since the shift is performed three times. When the photodiodes 2 in the odd rows and the photodiodes 2 in the even rows are read in different fields (called interlaced reading), they are formed below the three vertical transfer electrodes V1 to V3 corresponding to one photodiode 2. The storage capacity of the potential well may be three times the storage capacity of the photodiode 2. Thus, the light receiving area of the photodiode 2
Area of vertical transfer electrodes V1 to V3, vertical transfer pulse φV1
~ ΦV3 is determined respectively.

In either all-pixel reading or interlaced reading, the photodiode 2 is exposed as shown in FIG.
The signal charge is accumulated for the second time.

As shown in (B), a field shift pulse is applied to the shift gate during exposure, and the signal charge accumulated in the photodiode 2 by the first exposure is shifted to the vertical transfer path 4. (First signal charge shift).

Exposure of the photodiode 2 is continued, and signal charges are accumulated in the photodiode 2 as shown in (C). As shown in (D), the field shift is applied to the shift gate as in the first time.
A pulse is applied, and the signal charge accumulated in the photodiode 2 by the second exposure is shifted to the vertical transfer path 4.

When the second accumulation of the signal charges in the photodiode 2 and the shift to the vertical transfer path 4 are completed,
The third exposure is performed on the photodiode 2 as shown in (E), and the third shift to the vertical transfer path 4 is performed as shown in (F).

As described above, the shift of the signal charges accumulated in the photodiode 2 to the vertical transfer path 4 is
Is repeatedly performed three times during the exposure while the driving of is stopped. At least the storage capacitance of the photodiode 3 (even if the light receiving area of the photodiode 2 is small) can shift substantially a large amount of signal charge to the vertical transfer path 4. The number of pixels can be increased while maintaining the miniaturization of the CCD 1. Further, even if the light receiving area of the photodiode 2 is reduced, the amount of signal charge obtained per photodiode 2 does not substantially decrease, so that it is possible to prevent deterioration of the image quality of the obtained image. .

FIG. 4 is a potential profile of the vertical transfer path, and FIG. 5 is a time chart of the pulse given to the CCD 1, which corresponds to FIG.

In this example, the signal charges accumulated in the photodiode 2 are read out by all pixel readout. In addition, the signal charge accumulated in the first field in the interlaced reading can be transferred by the same reading method.

The exposure time for the photodiode 2 is from time t2 to time t6. During this exposure time, the signal charges are transferred to the vertical transfer path 4 three times.

At time t1 before the start of exposure, vertical transfer pulses φV1 and φ are applied to the vertical transfer electrodes V1 and V2.
V2 is applied, and potential wells are formed below the vertical transfer electrodes V1 and V2. In this potential well, unnecessary charges S
Is left.

At time t2, an overflow / drain pulse OFDP is applied to the photodiode 2, and unnecessary charges remaining on the vertical transfer path 4 are swept out from the substrate of the CCD 1. However, the vertical transfer path 4 may be transferred without sweeping unnecessary charges from the substrate. Overflow / drain / pulse O
When the FDP is applied and is swept out from the substrate, it must be performed before the exposure of the photodiode 2 is started (before the time t2), but when the unnecessary charges are transferred from the vertical transfer path 4, the photodiode 2 is used. It may be performed before shifting the signal charges accumulated in the vertical transfer path 4 (before the rise of the first field shift pulse FS1). In addition, in order to easily sweep out the unnecessary charges S remaining in the vertical transfer paths 4 from the substrate of the CCD 1, the vertical transfer electrodes V1
And V2 applied to the vertical transfer electrodes φV1 and φV
The voltage of 2 may be changed and the depth of the potential well may be made shallow as shown by arrow A in FIG.

At time t3 before the signal charge accumulated in the photodiode 2 is shifted to the vertical transfer path 4, the unnecessary charge 5 is removed and empty in the potential well formed in the vertical transfer path 4. It is in a state.

At time t4, the first shift gate
When the field shift pulse FS1 for the second time is applied, the signal charge S1 accumulated in the photodiode 2 from time t2 to time t4 is shifted to the potential well below the vertical transfer electrodes V2 and V1. Photodiode 2
Is continuously exposed, and signal charges are accumulated. The second field shift at time t5
The pulse FS2 is applied to the shift gate, and the signal charge S2 accumulated in the photodiode 2 between time t4 and time t5 is shifted to the potential well (S1 + S2) below the vertical transfer electrodes V2 and V1. Further, the photodiode 2 is continuously exposed. The third field shift pulse FS is applied to the shift gate at time t6.
By applying 3, the signal charge S3 accumulated in the photodiode 2 from time t5 to time t6 is shifted to the potential well below the vertical transfer electrodes V2 and V1.

In this way, even the signal charges S1 + S2 + S3 having a larger amount than the storage capacitance of the photodiode 2 are shifted and stored in the potential wells below the vertical transfer electrodes V2 and V1.

At time t7, the vertical transfer pulse φV1 is applied to the vertical transfer electrode V1, so that the potential well is formed below the vertical transfer electrode V1. At time t8, the vertical transfer electrodes V1 and V3 are supplied with the vertical transfer pulses φV1 and φV3, whereby the vertical transfer electrodes V1 and V3 are applied.
And a potential well is formed under V3. The signal charges S1 + S2 + S3 shifted from the photodiode 2 are transferred in the vertical transfer path 4.

A large amount of signal charge is accumulated in the storage capacity of the photodiode 2 by at least one exposure, and a bright image can be obtained.

6 to 8 show an application example.

When interlaced reading is performed,
A mechanical shutter (for shading) is needed to control the exposure time. By opening the mechanical shutter, the first field photodiode 2 (odd row photodiode 2) and the second field photodiode 2 (even row photodiode 2) are simultaneously exposed. The signal charges accumulated in the photodiode 2 of the first field, which is previously read, can be repeatedly shifted to the vertical transfer path 4 as described above. However,
When the signal charge accumulated in the photodiode 2 of the second field is shifted to the vertical transfer path 4, since the mechanical shutter is closed, the first shift of the signal charge to the vertical transfer path 4 is performed. Then, the photodiode 2 becomes empty and no signal charge is stored. Therefore, it is not possible to repeatedly accumulate the signal charges in the photodiode 2 and repeat the shift to the vertical transfer path 4.

In the application example described below, in the photodiode 2 of the first field, the signal charge is accumulated three times and shifted to the vertical transfer path 4 as described above,
In the photodiode 2 of the field, signal charges are accumulated once and shifted to the vertical transfer path 4. In such a case, the signal charge obtained by the first accumulation in the photodiode 2 of the first field and the signal charge obtained by the accumulation (first accumulation) in the photodiode 2 of the second field An image is generated using the video signal obtained by. And the first
The first accumulation in the photodiode 2 of the field,
The image of the high-luminance image portion of the generated image is replaced by using the image represented by the video signal based on the signal charges obtained by the second accumulation and the third accumulation. An image with good gradation can be generated without being saturated in an image part with high brightness.

FIG. 6 is a graph showing the relationship between the amount of light incident on the CCD 1 and its output signal.

In the photodiode 2 of the second field from which the signal charge is read out later, since the signal charge can be stored only once as described above, the threshold value L1
Incident light Ai up to can be accumulated,
Even if the incident light Bi that exceeds the threshold L1 is incident, CC
It cannot be obtained as a video signal from D1. Only the Ao part is obtained as a video signal. Therefore, the first
An image of one frame is formed by using the video signal of the Ao portion obtained by the accumulation of the signal charge in the photodiode 2 of the field and the video signal of the Ao portion obtained by the accumulation of the signal charge in the photodiode 2 of the second field. Is generated.

In the photodiode 2 of the first field, since the signal charge can be accumulated and shifted to the vertical transfer path 4 three times as described above, the incident light quantity exceeds the threshold value L1 and the threshold value L2. Up to the signal charges corresponding to the amount of incident light can be stored. Therefore, in the first field, a video signal in the range of Bo exceeding Ao can be obtained from the CCD 1. Since the accumulation of the first field in the photodiode 2 is repeated three times, the maximum value of the Bo video signal is three times the maximum value of the Ao video signal.

FIG. 7 shows the relationship between the amount of incident light on the CCD 1 and the image data after gamma correction.

In a digital still camera,
Gamma correction is performed. When the gamma correction is performed, the gamma correction circuit is set so that the image data after the gamma correction is not saturated up to the incident light amount Ai as described above.
However, the incident light Bi that exceeds the threshold L1 is saturated. For this reason, the high-intensity part of the image is all white as shown by the chain line.

Since the signal charges can be repeatedly stored in the photodiode 2 of the first field three times, the incident light Bi exceeding the threshold value L1 can be used. The image data obtained based on the portion of the incident light Bi is replaced with the image data of the corresponding portion of the image data representing the generated image of one frame. As shown by the solid line in FIG. An image in which the brightness is displayed relatively accurately can be obtained.

FIG. 8 is a block diagram showing a part of the electrical construction of the digital still camera.

The digital still camera has a CPU 10
The whole operation is controlled by.

A mechanical shutter 11 is provided, and the mechanical shutter 11 controls the exposure of the CCD 1. The opening and closing of the mechanical shutter 11 is controlled by the shutter control circuit 12.

The CCD 1 is driven on the basis of various pulses given from the driving circuit 9 so that the interlaced reading is performed as described above. The video signal output from the CCD 1 is converted into digital image data in the analog / digital conversion circuit 13. The digital image data is input to the signal processing circuit 14.

As described above, the signal processing circuit 14 generates image data representing one frame of image from the image data of the first field and the image data of the second field, gamma correction,
For the generated image data representing the high-intensity part, each process such as replacement with high-intensity image data obtained by the incident light having the threshold value L1 or more obtained as described above is performed. . The signal-processed image data is output from the signal processing circuit 14.

In the image represented by the image data output from the signal processing circuit 14, the brightness of the high-luminance portion is displayed relatively accurately without being saturated in white.

In the above embodiment, the two-dimensional CC
Although D has been described, it can be applied to a line sensor.

[Brief description of drawings]

FIG. 1 shows the configuration of a CCD.

FIG. 2 shows one pixel area.

3A to 3F show a state in which the accumulation of signal charges in a photodiode and the shift to a vertical transfer path are repeated a plurality of times.

FIG. 4 is a potential profile showing shift and transfer of signal charges to a vertical transfer path.

FIG. 5 is a time chart showing various pulses given to a CCD.
It is a chart.

FIG. 6 is a graph showing a relationship between a CCD incident light amount and a CCD output.

FIG. 7 is a graph showing a relationship between a CCD incident light amount and image data after gamma correction.

FIG. 8 is a block diagram showing a part of an electrical configuration of a digital still camera.

[Explanation of symbols]

1 CCD 2 photodiode 3 shift gates 4 Vertical transfer path 5 1 pixel area 9 drive circuit 10 CPU 11 Mechanical shutter 14 Signal processing circuit V1, V2, V3 Vertical transfer electrodes

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4M118 AA10 AB01 BA10 CA03 DB01                       DB03 DB07 DB09 FA06 FA08                       FA17                 5C024 CX47 CX55 GX03 GY04 HX29                       HX50                 5C051 AA01 BA03 DA02 DB01 DB04                       DB07 DC02 DC03 DC07 DE03

Claims (3)

[Claims] 1. A large number of photoelectric conversion elements for accumulating a signal charge of an amount of electric charge according to the amount of incident light, a potential well is formed by being provided with a transfer pulse adjacent to the photoelectric conversion element and being applied to a transfer electrode. A transfer path for transferring the signal charge by the potential well formed and a transfer gate for shifting the signal charge accumulated in the photoelectric conversion element to the transfer path by applying a shift pulse to the transfer path. A solid-state electronic image sensor having a light-receiving area less than the area of the transfer electrode. 2. The solid-state electronic image pickup device according to claim 1, and a drive circuit for applying the transfer pulse to the transfer path, wherein a shift pulse is applied to the transfer gate to accumulate in the photoelectric conversion device. The area of the transfer electrode corresponding to the photoelectric conversion element and the level of the transfer pulse so that the capacity of the potential well generated when the stored signal charge is shifted to the transfer path becomes larger than the storage capacity of the photoelectric conversion element. Solid-state electronic imaging device that has been decided. 3. The solid-state electronic image pickup device, wherein a large number of the photoelectric conversion elements are arranged in a row direction and a column direction, and the transfer path is arranged adjacent to each column of the photoelectric conversion elements. Image generating means for generating an image of one frame based on the signal charges corresponding to the storage capacities of the photoelectric conversion elements in the first field and the second field, and when reading the signal charges in the first field, A shift pulse is applied to the transfer gates in odd rows,
At the time of reading the signal charge of the second field, a shift pulse is applied to the transfer gates of the even-numbered rows, and one of the signal charge read of the first field and the signal charge read of the second field is read first. , The timing of the shift pulse is determined based on the ratio of the capacity of the potential well to the storage capacity of the photoelectric conversion element, and the signal charge obtained above the storage capacity of the photoelectric conversion element is used. 3. The solid-state electronic imaging device according to claim 2, further comprising brightness adjusting means for adjusting the brightness of the image generated by the image generating means.