JP2004173132A - Solid-state image pickup device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a sufficient margin in a sampling frequency and to prevent colors from being mixed at the time of CDS processing, even when the formation of multiple pixels in an imaging area progresses. <P>SOLUTION: A solid-state image pickup device is provided with: a plurality of photoelectric converters 1 arrayed two-dimensionally in a matrix shape; vertical transfer registers 2 arranged for each column of the two-dimensional array and for transferring electric charge to the two-dimensional array vertically; one horizontal transfer register 3 for receiving the electric charge from the vertical transfer registers 2 and transferring the electric charge to the two-dimensional array horizontally; and color filters respectively provided in each of the photoelectric converters 1, wherein color filters corresponding to the same color component are arranged on the same row in the two-dimensional array. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charge transfer type solid-state imaging device represented by a CCD (Charge Coupled Device) image sensor and a driving method thereof.
[0002]
[Prior art]
In general, a solid-state imaging device for capturing a color image includes a plurality of photoelectric conversion elements arranged two-dimensionally in a matrix, and transfers charges accumulated in each photoelectric conversion element by a vertical transfer register and a horizontal transfer register. Is known. Each of the photoelectric conversion elements arranged two-dimensionally in a matrix has a color filter corresponding to each color component such as R (red), G (green), and B (blue) in order to enable a color image to be captured. (For example, an on-chip color filter).
[0003]
Conventionally, the arrangement of color filters on a two-dimensional array is such that, for example, as shown in FIG. 4, ones corresponding to G color components are arranged in a checkered pattern, and ones corresponding to R color components and B color components, respectively. A so-called Bayer method is used in which pixels are arranged every other pixel in the vertical direction and the horizontal direction (for example, see Patent Document 1). As a result, in the imaging region of the solid-state imaging device, the color filters of the respective color components are arranged with a repetition period of 2 × 2 pixels or 2 × 4 pixels in the horizontal and vertical directions. The reason that only the G color component is arranged in a checkered pattern is that the G color component is located substantially at the center in the spectral characteristics, and the G color component is a color component that serves as a reference when generating a luminance signal. That's why.
[0004]
A signal output from such a solid-state imaging device is usually subjected to a correlated double sampling (hereinafter abbreviated as “CDS”) process, and then subjected to a quantization process by analog / digital conversion or the like. (See, for example, Patent Document 2). The CDS process performs a phase adjustment by performing a second sampling with a time shift after the first sampling, and performs an arithmetic process using a correlation related to a plurality of sampling data. It is used for the purpose of, for example, suppression. For example, in the CDS process, a sample-and-hold signal SHP for precharge (Precharge) phase sampling is applied to a signal output CCD-out from the solid-state imaging device as shown in FIG. 5A (see FIG. 5B). And a sample hold signal SHD for data (Data) phase sampling (see FIG. 5C), and a CDS output S / H-out as shown in FIG. 6A is obtained from the result. .
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-307095 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-13811
[Problems to be solved by the invention]
By the way, in the solid-state imaging device based on the Bayer method as described above, since the color filters of each color component are arranged with a repetition period of 2 × 2 pixels or 2 × 4 pixels in the horizontal and vertical directions, the signal output CCD thereof is used. −out is modulated by repeating two pixels in the horizontal direction. This is because the color filters of the respective color components have different spectral transmission characteristics even in a situation where light of uniform color and brightness is irradiated. Therefore, when the signal output CCD-out undergoes the CDS processing, the signals of two consecutive pixels interfere with each other, and for example, as shown by a broken line in FIG. 6B, the color is mixed with the CDS output S / H-out. A state may occur, and as a result, a decrease in image quality called line crawl may be caused.
[0007]
In particular, in recent years, where the number of pixels in the imaging area is strongly required, the pixel size is reduced due to the increase in the number of pixels, and the signal frequency is increased with the increase in the number of pixels, so that color mixing may occur during CDS processing. Is high. As the number of pixels increases and the frequency increases, the sample-and-hold signals SHP and SHD used in the CDS processing also become shorter, but the level change of the signal output CCD-out cannot keep up with this.
[0008]
On the other hand, from the viewpoint of preventing color mixing, for example, providing an on-chip lens for controlling incident light to each photoelectric conversion element, or adjusting the arrangement of color filters in consideration of the light incident path. Is also conceivable. However, in these techniques, when the pixel size is reduced by increasing the number of pixels in the imaging region, it is difficult to arrange and adjust with sufficient accuracy, and a sufficient effect of preventing color mixing is not always obtained. Further, since the signal frequency is increased by increasing the number of pixels and the modulation degree of the color filter is increased from the complementary color to the primary color, no effect can be expected to improve the color mixture in the CDS processing.
[0009]
Therefore, the present invention provides a solid-state imaging device that can secure a sufficient margin for the sampling frequency even when the number of pixels in the imaging region has advanced, and is very effective in preventing color mixing during CDS processing. It is an object to provide a driving method thereof.
[0010]
[Means for Solving the Problems]
The present invention is a solid-state imaging device devised to achieve the above object, a plurality of photoelectric conversion elements two-dimensionally arranged in a matrix, and the two-dimensional array is arranged for each column of the two-dimensional array , A vertical transfer register that transfers charges in the vertical direction, a horizontal transfer register that receives charges from the vertical transfer registers and transfers the charges in the horizontal direction of the two-dimensional array, and a photoelectric conversion element. And a color filter arranged such that color filters corresponding to the same color component are arranged on the same row in the two-dimensional array.
[0011]
According to the solid-state imaging device having the above configuration and the method for driving the solid-state imaging device having the above-described procedure, the color filters of the same color component are arranged on the same row in the two-dimensional array, that is, in the horizontal direction of the two-dimensional array. When each of the vertical transfer registers receives the charge read from the photoelectric conversion element and transfers the charge in the horizontal direction, the transfer register continuously transfers the charges for the same color component by the number of the vertical transfer registers. Become. Therefore, even when, for example, the CDS process is performed on the signal output from the horizontal transfer register, since signals of the same color component are continuous, color mixing hardly occurs.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a solid-state imaging device according to the present invention will be described with reference to the drawings. Note that, needless to say, the present invention is not limited to the embodiments described below.
[0013]
Here, a solid-state imaging device mounted on a camera system that captures a color image (still image or moving image) will be described as an example. FIG. 1 is a schematic diagram illustrating an example of a schematic configuration of a solid-state imaging device according to the present invention. As shown in the example, the solid-state imaging device described here includes a plurality of photoelectric conversion elements 1 two-dimensionally arranged in a matrix in an imaging region thereof. Each photoelectric conversion element 1 is provided with a color filter (for example, an on-chip color filter) corresponding to each of the R, G, and B color components in order to enable a color image to be captured.
[0014]
FIG. 2 is a schematic diagram illustrating an example of the arrangement of color filters. The color filters are not arranged in the Bayer system as in the related art, but are arranged using a so-called horizontal stripe color arrangement arranged on different rows for each color component. Specifically, as shown in the figure, color filters corresponding to the G color component are arranged in the horizontal direction of the two-dimensional array, and a color filter corresponding to the R color component is located next to the color filter (for example, below the two-dimensional array). The color filters corresponding to the B color components are arranged in the horizontal direction of the two-dimensional array, and the color filters corresponding to the B color components are arranged in the horizontal direction of the two-dimensional array.
[0015]
Also, as shown in FIG. 1, a vertical transfer register 2 is provided in the imaging region of the solid-state imaging device for each column of the two-dimensional array of the photoelectric conversion elements 1. These vertical transfer registers 2 transfer charges accumulated in the photoelectric conversion elements 1 in a two-dimensional array in the vertical direction. For this purpose, the vertical transfer register 2 is provided with electrodes V1, V2, and V3, and by applying a voltage to these sequentially at a predetermined timing, electric charges are read from each photoelectric conversion element 1 and the read electric charges are read out. The transfer in the vertical direction can be performed. However, the electrode V2 is provided with electrodes V2R, V2G, and V2B for applying charges for each color component so that charges can be read for each color component of the color filter, that is, for each row of the two-dimensional array. .
[0016]
Further, the solid-state imaging device includes one horizontal transfer register 3 for receiving charges from each vertical transfer register 2 and transferring the charges in a two-dimensional array in the horizontal direction. The horizontal transfer register 3 is provided with electrodes H1 and H2. By sequentially applying voltages to these electrodes at a predetermined timing, charges received from each vertical transfer register 2 can be transferred in the horizontal direction. It has become. At the subsequent stage of the horizontal transfer register 3, a signal processing circuit (not shown) such as a CDS circuit or an A / D conversion circuit is provided, and the signal processing circuit outputs a signal charge output from the horizontal transfer register 3. Are subjected to signal processing such as CDS processing.
[0017]
In the solid-state imaging device having such a configuration, when electric charge is accumulated in each photoelectric conversion element 1, the electric charge is read out to the vertical transfer register 2 at a predetermined timing, and the vertical transfer registers 2 in each column are aligned vertically. The charge is transferred in the direction. Then, the horizontal transfer register 3 receives charges from each of the vertical transfer registers 2 and transfers the charges in the horizontal direction.
[0018]
At this time, in the imaging region, color filters of the same color component are arranged on the same row in the two-dimensional array, that is, in the horizontal direction of the two-dimensional array. Therefore, when the horizontal transfer register 3 receives charges from each of the vertical transfer registers 2 and transfers the charges in the horizontal direction, charges of the same color component are continuously transferred by the number of the vertical transfer registers 2. . For example, from each of the photoelectric conversion elements 1 in the row in which the color filters of the G color component are arranged, the accumulated charges are read out almost simultaneously to the corresponding vertical transfer registers 2. Then, each of the vertical transfer registers 2 receiving the charge for the G color component performs the charge transfer in the vertical direction in synchronization with each other. Therefore, the horizontal transfer register 3 receives the charges for the G color component from each vertical transfer register 2 substantially simultaneously. As a result, the horizontal transfer registers 3 continuously transfer charges of the same color component by the number of the vertical transfer registers 2.
[0019]
Thereafter, the processing circuit at the subsequent stage of the horizontal transfer register 3 performs a process on the signal charges output from the horizontal transfer register 3. At this time, signal charges for the same color component are continuously output from the horizontal transfer register 3 by the number of vertical transfer registers 2. Therefore, in the subsequent processing circuit, for example, even when the CDS circuit performs the CDS processing, color mixing hardly occurs.
[0020]
Specifically, for example, in the case of CDS processing, signal processing as shown in FIG. 3 is performed. FIG. 3 is a schematic diagram illustrating an example of signal processing for an output signal from the solid-state imaging device according to the present invention. As described above, the horizontal transfer registers 3 continuously output signal charges for the same color component by the number of the vertical transfer registers 2. That is, as shown in FIG. 3A, the signal output CCD-out from the horizontal transfer register 3 is for the G color component (see the solid line in the figure), or for the R color component or the B color component. (See the broken line in the figure) are continuous.
[0021]
Therefore, even if the signal output CCD-out is sampled using the sample-and-hold signal SHP (see FIG. 3B) and the sample-and-hold signal SHD (see FIG. 3C), the result is obtained from the result. The CDS output S / H-out having the same output level as shown in FIG. 3D can be obtained. That is, different output levels are not alternately repeated for each cycle of the sample and hold signals SHP and SHD as in the related art.
[0022]
Therefore, if the solid-state imaging device described in the present embodiment is used, it is possible to prevent a color mixture state from occurring in the CDS output S / H-out even if the sample hold signals SHP and SHD are shortened. As a result, a decrease in image quality called line crawl does not occur. That is, since the modulation of the signal output CCD-out is suppressed, the line crawl caused by the CDS circuit is reduced. In addition, since it is only necessary to arrange the color filters in the form of horizontal stripes, there is no need for arrangement with sufficient accuracy or special adjustment for preventing color mixing.
[0023]
For these reasons, in the solid-state imaging device according to the present embodiment, even when the solid-state imaging device is mounted on a camera system that captures a color image, a margin of a sampling frequency required for a CDS circuit included in the camera system can be provided. . Therefore, even if the number of pixels in the imaging area increases, a sufficient margin can be secured for the sampling frequency, which is very effective in preventing color mixing during CDS processing.
[0024]
Meanwhile, in the solid-state imaging device according to the present embodiment, as described above, the electrodes V2R, V2G, and V2B are provided for each color component arranged in a horizontal stripe. Therefore, for example, by applying a voltage to the electrodes V2R, V2G, and V2B substantially simultaneously and reading out all the charges for the R, G, and B color components to the vertical transfer register 2, it corresponds to so-called all-pixel reading. It becomes possible. Even in this case, the horizontal transfer register 3 continuously transfers the charges of the same color component by the number of the vertical transfer registers 2, so that the CDS output S / H-out has a mixed color state. This can be avoided.
[0025]
In addition, since the electrodes V2R, V2G, and V2B are provided for each color component, it is also possible to selectively apply a voltage to any of these. That is, the reading of the electric charge from the photoelectric conversion element 1 to the vertical transfer register 2 can be performed only for the row in which the color filter corresponding to the specific color component is arranged. In this case, since only the charges of the selected same color component are transferred, it is needless to say that the occurrence of a mixed color state can be avoided.
[0026]
In any case, the reading of the electric charge from the photoelectric conversion element 1 to the vertical transfer register 2 is independently controlled for each row corresponding to the same color component by the electrodes V2R, V2G, V2B for each color component. It is possible to do. That is, the imaging area is divided into a plurality of fields for each color component, and for example, the signal accumulation time is variably controlled in units of fields, or a predetermined signal processing is performed only on signal charges of a specific color component. Can be easily realized.
[0027]
Therefore, in the solid-state imaging device according to the present embodiment, it is possible to separate color signals for each field in a state of the solid-state imaging device alone. Therefore, for example, it is very suitable to be mounted on a camera system that extracts an image for each color without using signal processing.
[0028]
Furthermore, if the electric charges are read only from the rows corresponding to the specific color components, the electric charges can be mixed in the horizontal transfer register 3. Specifically, charge transfer by the horizontal transfer register 3 is performed for 1H (horizontal) lines for one line shift pulse normally given to the vertical transfer register 2. In this case, charge transfer by the horizontal transfer register 3 is performed for 1H lines. In this way, the function of mixing the charges in the horizontal transfer register 3 is realized, so that a variable output in which the sensitivity is improved and the number of output pixels is balanced can be realized.
[0029]
Therefore, in the solid-state imaging device according to the present embodiment, the readout is independently controlled for each color, and the addition is performed in the horizontal transfer register 3, so that the number of output pixels and the sensitivity can be appropriately balanced. Will be possible. Therefore, it is very suitable to be mounted on a high-speed imaging camera system in which the number of output data is reduced by, for example, charge mixing in a register.
[0030]
In the present embodiment, the case where the present invention is applied to a charge transfer type device represented by a CCD image sensor has been described as an example. However, the present invention is not limited to the CCD type solid-state imaging device, but may be a MOS type. The same applies to solid-state imaging devices and amplification-type solid-state imaging devices as long as they use color filters for color separation.
[0031]
【The invention's effect】
As described above, according to the solid-state imaging device and the method of driving the solid-state imaging device according to the present invention, even when the signal output from the horizontal transfer register is subjected to the CDS processing, the signal of the same color component is continuous. Therefore, it is possible to avoid the occurrence of the mixed color state, and it is possible to prevent the deterioration of the image quality called line crawl. Therefore, even if the number of pixels in the imaging area increases, a sufficient margin can be secured for the sampling frequency, which is very effective in preventing color mixing during CDS processing.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a schematic configuration of a solid-state imaging device according to the present invention.
FIG. 2 is a schematic diagram showing an example of the arrangement of color filters in the solid-state imaging device according to the present invention.
3A and 3B are schematic diagrams illustrating an example of signal processing on an output signal from a solid-state imaging device according to the present invention, in which FIG. 3A illustrates a signal output from a horizontal transfer register, and FIG. FIG. 3C is a diagram showing a sample hold signal for data phase sampling, FIG. 4C is a diagram showing a sample hold signal for data phase sampling, and FIG. 4D is a diagram showing a CDS output after CDS processing.
FIG. 4 is a schematic diagram illustrating an example of the arrangement of color filters in a conventional solid-state imaging device.
5A and 5B are schematic diagrams illustrating an example of an output signal from a conventional solid-state imaging device. FIG. 5A illustrates a signal output from a horizontal transfer register, and FIG. 5B illustrates a sample-hold signal for precharge phase sampling. FIG.
6A and 6B are schematic diagrams illustrating an example of signal processing on an output signal from a conventional solid-state imaging device. FIG. 6A is a diagram illustrating a CDS output after CDS processing, and FIG. 6B is a diagram in which color mixing occurs in the CDS output. It is a figure showing a state.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoelectric conversion element, 2 ... Vertical transfer register, 3 ... Horizontal transfer register

Claims (4)

A plurality of photoelectric conversion elements arranged two-dimensionally in a matrix,
A vertical transfer register arranged for each column of the two-dimensional array and transferring charges in a vertical direction of the two-dimensional array;
One horizontal transfer register for receiving charges from the vertical transfer register and transferring the charges in the horizontal direction of the two-dimensional array;
A solid-state imaging device, comprising: a color filter attached to each of the photoelectric conversion elements and arranged so that those corresponding to the same color component are arranged on the same row in the two-dimensional array. . 2. The solid-state imaging device according to claim 1, further comprising: a read electrode for reading charges from the photoelectric conversion element to the vertical transfer register for each row on which a color filter corresponding to the same color component is arranged. 3. apparatus. A plurality of photoelectric conversion elements arranged two-dimensionally in a matrix,
A vertical transfer register arranged for each column of the two-dimensional array and transferring charges in a vertical direction of the two-dimensional array;
One horizontal transfer register for receiving charges from the vertical transfer register and transferring the charges in the horizontal direction of the two-dimensional array;
A method for driving a solid-state imaging device, comprising: a color filter attached to each of the photoelectric conversion elements and arranged so that color filters corresponding to the same color component are arranged on the same row in the two-dimensional array. hand,
A method for driving a solid-state imaging device, comprising: reading charges from the photoelectric conversion element to the vertical transfer register for each row in which color filters corresponding to the same color component are arranged. 4. The method according to claim 3, wherein the electric charges received from the vertical transfer registers are mixed in the horizontal transfer registers.

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