JPH10200687A - Solid-state image-pickup element and image reader provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a magnification color aberration and to read images of high quality with high color registration accuracy by providing photosensitive pixel columns for photoelectrically converting incident light, microlenses arrayed corresponding to the incident angle of the incident light with respect to photosensitive pixel columns and a color filter for passing through specified color lights. SOLUTION: For the respective photosensitive pixel columns 11R, 11G and 11B of R, G and B, plural photosensitive pixels 12R, 12G and 12B composed of the photoelectric conversion element of a photodiode or the like for photoelectrically converting the incident light are successively arrayed at equal pitches. By forming the color filter for passing selectively through the incident light by a color component on a chip on a light-receiving surface, a photosensor provided with sensitivity with respect to red, green and blue light is formed. For the photosensitive pixels 12R, 12G and 12B, microlens arrays 14R, 14G and 14B for which microlenses 13R, 13G and 13B in a cylindrical shape, which are not provided with a convergence action in a sub-scanning direction are arrayed, so that orthogonally crossed with a main scanning direction, are formed.

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 an image reading apparatus having the same, and more particularly to a color solid-state image pickup device for reading a color image and a color image scanner or digital color copier equipped with the same. The present invention relates to a color image reading device.

[0002]

2. Description of the Related Art In a color image reading apparatus, a three-line type color image sensor having three (R), G (green) and B (blue) photosensitive pixel arrays on one chip is widely used. I have. FIG. 6 shows a schematic configuration of a color image reading apparatus provided with a color image sensor of this type.

In FIG. 6, image information of a document 100 placed on a platen glass 101 is transmitted to a light source 10 such as a lamp.
Obtained as reflected light based on the irradiation light from No. 2. This original image information is converted into an image forming lens 103 constituting a reduction image forming optical system.
The main scanning image information for one line is read by reducing and projecting the image on the imaging surface of the three-line type color image sensor 104, and the optical system moving means such as the total reflection mirror 105 and the semi-reflection mirrors 106 and 107 The reading in the sub-scanning direction is sequentially performed by mechanically changing the positional relationship between the formed image and the sensor 104.

FIG. 7 is a plan view schematically showing the configuration of a three-line type color image sensor. In FIG. 7, R,
G, B photosensitive pixel rows 111R, 111G, 111B
Represents a plurality of photosensitive pixels 112 sequentially arranged at the same pitch.
R, 112G, and 112B, and are formed on the same plane with an interval of about 1 to 12 lines. Each photosensitive pixel row 111R, 111G, 111
On B, a color filter (not shown) for selectively passing an optical image in color components is formed on-chip so as to read different color information.

The photosensitive pixel rows 111R, 111G, 111B
, Transfer registers 113Ro, 113R
e, 113Go, 113Ge, 113Bo, 113Be
Is arranged. A shift gate 1 is provided between the photosensitive pixel column 111R and the transfer registers 113Ro and 113Re.
14Ro and 114Re are provided with a shift gate 1 between the photosensitive pixel row 111G and the transfer registers 113Go and 113Ge.
14Go and 114Ge are shift gates 1 between the photosensitive pixel column 111B and the transfer registers 113Bo and 113Be.
14Bo and 114Be are provided, respectively.

The shift gate 114Ro is connected to the photosensitive pixel row 11
The signal charge of the odd (odd) pixel in 1R is shifted to the transfer register 113Ro, and the shift gate 114Re transfers the signal charge of the even (even) pixel to the transfer register 113Re.
Shift to Similarly, shift gate 114Go,
114Ge transfers the signal charges of the odd-numbered pixels and the even-numbered pixels of the photosensitive pixel row 111G to the transfer registers 113Go and 113Ge.
The shift gates 114Bo and 114Be shift the signal charges of the odd-numbered pixels and the even-numbered pixels of the photosensitive pixel column 111B to the transfer registers 113Bo and 113Be, respectively. Transfer registers 113Ro, 113Re, 113Go, 11
3Ge, 113Bo, and 113Be correspond to the photosensitive pixel row 111.
The signal charges of the odd-numbered pixels and the signal charges of the even-numbered pixels of R, 111G, and 111B are horizontally transferred in parallel.

The original image information is formed on the chip plane of the color image sensor having the above-described configuration by the above-described reduced image forming optical system, and the respective photosensitive pixel rows 111R and 111 are provided for each color.
G, 111B, but due to the presence of chromatic aberration of magnification of the reduction imaging optical system, an image is read at a different magnification for each color. , Abbreviated as a color register).
Here, the chromatic aberration of magnification refers to a difference in image size due to a difference in imaging magnification between an image of one color and an image of another color in aberration of a lens.

In recent years, as the density of read images has increased, the pixel pitch of a read sensor has become smaller, and the problem of color registration misregistration has become an increasingly serious problem. At present, even if a design is made with careful attention to the reduction of the chromatic aberration of magnification, the design of an imaging lens with a configuration of about 6 to 8 sheets used for an image reading apparatus usually requires 0.2 pixels. A degree of lateral chromatic aberration remains. Increasing the number of components causes an adjustment error at the time of assembling the lens system, and other aberrations such as curvature of field deteriorate when chromatic aberration is reduced by using an extraordinary dispersion glass material. Problems arise. Furthermore, these chromatic aberration countermeasures
This leads to an increase in the cost of the imaging lens.

The presence of the chromatic aberration of magnification of the imaging lens leads to a phenomenon that when a black character in a document is read, the edge of the black character of the read image is colored, and the black character in the color image data cannot be recognized as such. This causes a recognition error as a color image reading apparatus such as a digital color copying machine. The amount of the chromatic aberration of magnification of 0.2 pixels is R
The read image data of the GB system is converted into the read image data of the L ^* a ^* b ^* system by the image processing unit, and the gray reference (a ^* = 0, b ^* = 0) on the chromaticity coordinate data a ^* b ^* plane. Distance c from
^* (C ^* = (a ^{* 2} + b ^{* 2} ) ^1/2 : 10 for the brightest color
(Equivalent to 0), which is equivalent to slightly less than 20, which is a bottleneck in improving black character recognition performance.

Conventionally, various methods have been proposed to prevent the color registration error. As one prior art, as shown in FIG. 8, a three-line type color image sensor 121 is arranged such that a perpendicular line of the sensor surface is inclined with respect to an optical axis O according to chromatic aberration of magnification caused by an imaging lens 122. By changing the optical path length for each color,
A method of correcting an imaging magnification has been proposed (for example, see Japanese Patent Application Laid-Open No. 6-6516).

[0011]

However, since the image magnification of each color due to the chromatic aberration of magnification of the imaging lens is not always proportional to the arrangement of each color of the photosensitive pixel rows 111R, 111G, 111B, As in the prior art described above, the three-line type color image sensor 121
Is arranged with its sensor surface inclined with respect to the optical axis O,
The center photosensitive pixel row (in this example, the G photosensitive pixel row 111
G) has a problem that the chromatic aberration of magnification of the photosensitive pixel rows 111R and 111B on both sides cannot be adjusted independently.

In recent years, in order to increase the tolerance to vibration during reading scanning, the photosensitive pixel rows 111R, 111G, 1
The structure is such that the distance between 11B is reduced to about 1 to 4 line intervals. In this case, for example, the image magnification of the other photosensitive pixel row is ±
In order to adjust 0.2 pixels, it is necessary to tilt the sensor greatly, or the distance between the photosensitive pixel rows is not equal to the integer of the pixel pitch, and registration in the sub-scanning direction due to line delay becomes difficult. There was a problem.

As another prior art, as shown in FIG. 9, in the structure of a three-line type color image sensor, the arrangement of the respective pixels of the three photosensitive pixel columns 131, 132, and 133 is changed to a different pixel pitch P1. , P2, and P3 to cope with the chromatic aberration of magnification has been proposed (for example, see JP-A-7-58908). However, in a three-line color image sensor, arranging pixels at different pixel pitches for each of the photosensitive pixel columns 131, 132, and 133 results in a different positional relationship and structure between adjacent photosensitive pixel columns. There is a problem that wiring of the wiring inside the sensor is difficult and complicated,
In addition, it is disadvantageous in that inductive noise from other channels is easily mixed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a solid-state imaging device capable of correcting chromatic aberration of magnification caused by an imaging lens with a simple configuration.
Another object of the present invention is to provide an image reading apparatus capable of reading a high-quality image with high color registration accuracy.

[0015]

According to the present invention, there is provided a solid-state imaging device comprising: a photosensitive pixel array in which photosensitive pixels for photoelectrically converting incident light are sequentially arranged; It is arranged corresponding to the incident angle of light,
A microlens for condensing the incident light on the photosensitive pixel row and a color filter for passing a specific color light of the incident light condensed by the microlens are provided.

In the solid-state image pickup device having the above-described structure, if the microlenses are arranged corresponding to the incident angles of the incident light with respect to the respective photosensitive pixels in the arrangement direction of the photosensitive pixels, the incident angle is different for each color of the incident light Is different, the incident light is always focused on the photosensitive pixel row on a pixel-by-pixel basis under the same incident condition for each color.

An image reading apparatus according to the present invention comprises a solid-state image pickup device having photosensitive pixels arranged in the main scanning direction and an image pickup device which optically scans a document in the sub-scanning direction and outputs the image light by the solid-state image pickup device. And an optical system for projecting the image on a plane.

In the image reading apparatus having the above configuration, the image light formed on the imaging surface of the solid-state imaging device through the imaging lens of the optical system has a different magnification for each color due to chromatic aberration of magnification of the imaging lens. However, the same incident condition is always given to each color by the micro lens, and all the color lights are read at the same magnification.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic plan view showing an embodiment of the present invention, and FIG. 2 is a perspective view conceptually showing a main part (microlens array) thereof.

In FIGS. 1 and 2, each of the R, G, B photosensitive pixel rows 11R, 11G, 11B has a plurality of photosensitive pixels 12R, 12G, 12B are sequentially arranged at the same pitch, and selectively transmit the incident light in the color component, that is, a color filter (not shown) having different light transmission characteristics is formed on a light receiving surface on a chip. As a result, a three-line color image sensor having sensitivity to red light, green light, and blue light is obtained.

In this color image sensor, each of the unit photosensitive pixels 12R, 12G, and 12B has a dimension (for example, 8 μm) in a direction (sub-scanning direction) perpendicular to the arrangement direction (main-scanning direction) and main scanning. In the direction, 7,500 effective photosensitive pixels are arranged at a pitch of, for example, 8 μm via a channel stopper (not shown) for limiting a photosensitive aperture (diameter) between the pixels. Each photosensitive pixel row 11R,
11G and 11B are arranged in parallel at an interval of, for example, 64 μm. Note that the numerical values shown here are merely examples, and the present invention is not limited to these. FIG. 1 shows each photosensitive pixel row 11R, 11G, 11B for simplicity.
Indicates the case of 33 pixels.

In each of the photosensitive pixel rows 11R, 11G, and 11B, above the on-chip color filter, the respective photosensitive pixels 12R, 12G, and 12B have no light condensing action (light condensing rate) in the sub-scanning direction. A microlens array 14 in which cylindrical microlenses 13R, 13G, and 13B are arranged so as to be orthogonal to the main scanning direction.
R, 14G, and 14B are formed on-chip.

Here, as is particularly clear from FIG. 2, among the microlens arrays 14R, 14G and 14B,
On each of the G and B photosensitive pixel columns 11B and 11G, all the photosensitive pixels 12B and 12G are
B and 12G are arranged directly above the photosensitive pixels 12B and 12G at the same pitch of 8 μm as the pitch in the main scanning direction. On the other hand, on the R photosensitive pixel row 11R,
The configuration in which the pitch in the main scanning direction of each microlens 13R when forming the microlens array 14R is changed for each position in the main scanning direction is adopted.

That is, as an example, the R photosensitive pixel row 1
Each of the 1R photosensitive pixels 12R is divided into a plurality of pixels in the main scanning direction, for example, 90 pixels in a 7500-pixel photosensitive pixel row, and the pitch in the main scanning direction is set to 7.9 μm once for every 90 pixels. And the photosensitive pixel row 11R
With reference to the center (arrow O in the figure), the microlenses 13R on the photosensitive pixels 12R move outward from the left and right sides.
The microlens array 14R is formed such that the center in the main scanning direction is smaller than the center of the photosensitive pixel row 11R.

By the way, depending on the relative positional relationship between the micro lens and the photosensitive pixels, the photosensitive pixel rows 11R, 11G, 11
It is possible to relatively adjust the positional relationship of B on the imaging surface (hereinafter, referred to as a sensor surface). That is, FIG.
As shown in (1), there are a portion where the imaging light flux is condensed on the sensor surface to be fine and a portion where it is rough due to the action of the microlens. In a range where the portion where the light flux becomes coarse corresponds to the boundary between the photosensitive pixels, as shown in (a) → (b) → (c) of FIG. 3, the relative positional relationship between the microlens and the photosensitive pixel is changed. , It is possible to adjust which part of the imaging light flux enters the center of the three photosensitive pixels shown in the figure.

FIG. 4 shows the relationship between the shift amount of the microlens and the shift of the incident light beam. If the characteristics of the micro-lens are such that the incident light is completely condensed at one point, the shift amount of the micro-lens and the shift amount of the incident light become equal to each other, as shown by the dashed line in FIG. When the pixel is shifted by more than .5 pixels, the phase has a periodic characteristic in which the phase goes around. Depending on the formation conditions of the microlens, the light condensing state on the sensor surface becomes broad, and the rate of change of the shift amount of the incident light beam with respect to the shift amount of the microlens becomes small.

The amount of displacement of the microlens in the main scanning direction;
The shift amount of the range of the light beam incident on the corresponding photosensitive pixel changes depending on the formation condition of the microlens. The parameters that determine the characteristics of the microlens include the height of the microlens from the photosensitive pixel surface, the curvature of the lens surface, the optical refractive index of the lens forming material, and the like. Here, in order to facilitate the design of the pitch correction amount of the micro lens, as shown in FIG. 3, the shift amount of the light beam incident on the corresponding photosensitive pixel is compared with the shift amount of the micro lens in the main scanning direction. The height of the microlens from the surface of the photosensitive pixel, the curvature of the lens surface, and the optical refractive index of the lens forming material were set so that was reduced by half.

In the microlens array thus designed, the relationship between the shift amount of the microlens in the main scanning direction and the shift amount of the light beam incident on the corresponding photosensitive pixel is shown by a solid line in FIG. It becomes like. Here, by setting the shift amount of the microlens in the main scanning direction to within ± 0.4 pixels with respect to the center line of the photosensitive pixel, the range of the light beam incident on the corresponding photosensitive pixel is almost directly proportional. It is possible to adjust the shift amount.

On the other hand, consider the case where the three-line color image sensor according to the present embodiment is used as the image sensor 104 of the image reading apparatus having the configuration shown in FIG. As shown in FIG. 5, the imaging lens 103 used here has a red light imaging magnification of 1.00007 times the green / blue light imaging magnification. Therefore, FIG.
In the above, when the optical system is adjusted with respect to the image forming magnification of green light / blue light with reference to the center O of the photosensitive pixel rows 11R, 11G, and 11B in the main scanning direction, the center on the R photosensitive pixel row 11R is 3750 pixels from the photosensitive pixel, ie, 30 m
On the outermost photosensitive pixels separated by m (= 8 μm × 3750), a shift of the imaging position occurs by about 2.1 μm on the outer side.

Here, as described above, the pitch of the microlenses 13R is 90 on the R photosensitive pixel row 11R.
Since it is 7.9 μm for each pixel, the position of the micro lens 13R is 4.1 μm on the outermost photosensitive pixel 3750 pixels away from the central photosensitive pixel.
(≒ 0.1 μm × (3750/90) times) inward. As a result, it is possible to correct inward the spread of about 2.1 μm, which is the amount of chromatic aberration of magnification of the imaging light incident on each photosensitive pixel 12R of the R photosensitive pixel row 11R.

However, in the case of the present embodiment, since the pitch correction of the microlens is performed once every 90 pixels, all the photosensitive pixels 12R of the R photosensitive pixel row 11R are corrected.
Are not necessarily optimized. However, the deviation of the pitch correction amount from the optimum value is at most 0.0 / 2 of 1/2 of the unit correction amount of 0.1 μm.
5 μm, and the effect of the shift correction is 0.025 μm, which is a half of that, which is not a problem because it is extremely small for a pixel pitch of 8 μm.

As described above, in a color image reading apparatus using a three-line type color image sensor as a reading sensor, the R, G, B photosensitive pixel rows 11R, 11G,
Microlens arrays 14R, 14G, 14B are arranged above the respective color filters 11B, and among these microlens arrays 14R, 14G, 14B, for example, the microlenses 13R of the microlens array 14R are placed on the corresponding photosensitive pixels 12R. Is shifted in the main scanning direction in accordance with the incident angle of the incident light, the chromatic aberration of magnification of the imaging lens can be accurately corrected.

That is, even when the image light formed on the image sensor through the imaging lens is different for each color due to the chromatic aberration of magnification of the imaging lens, it is shifted in the main scanning direction with respect to the corresponding photosensitive pixel. Image light of all colors can be read at the same magnification by the position correcting action of the microlens. Thus, for example, a small black character or a thin black line is not erroneously read as a color character or a thin thin line, and the accuracy of image reading is improved.

The micro lens arrays 14R, 14
G, 14B microlenses 13R, 13G, 13B
Is formed in a cylindrical shape having no light condensing function (light condensing rate) in the sub-scanning direction, so that the imaging magnification in the sub-scanning direction becomes the same as that of the conventional image sensor without a microlens. However, there is no problem associated with the provision of the micro lens. That is, the provision of the microlens does not degrade the resolution of the read image in the sub-scanning direction.

In the above embodiment, the chromatic aberration of magnification of the imaging lens is shifted by shifting the pitch of the microlenses 13R only on the R photosensitive pixel rows 11R with respect to the pixel pitch in accordance with the characteristics of the imaging lens. Although it was possible to correct, depending on the design of the imaging lens, red, green, and blue light may all have different imaging magnifications.In this case, for example, the green light imaging magnification is used as a reference. , R, B
Lens 13 on photosensitive pixel rows 11R and 11B
By shifting the pitches of R and 13B inward or outward in accordance with the respective imaging magnifications, the reading magnifications of the three colors R, G and B can be matched.

In the above embodiment, each photosensitive pixel in the photosensitive pixel row is divided into a plurality of pixels in the main scanning direction, and the shift amount of the pitch of the microlenses is set to be shifted by a fixed amount at fixed intervals. However, this is not necessarily the case, and chromatic aberration can be corrected by performing a pitch shift of the microlens by a fixed amount or a different amount at different intervals in accordance with the characteristics of the imaging lens.

Further, in the above embodiment, R,
The microlens arrays 14R, 14G, and 14B are arranged for all the G and B photosensitive pixel rows 11R, 11G, and 11B.
Since R, 14G, and 14B are used to correct the imaging magnification, the microlens array can be omitted for a photosensitive pixel row that does not need to correct the imaging magnification.

[0038]

As described above, in the solid-state imaging device according to the present invention, the microlenses arranged above the color filters of the photosensitive pixel array are arranged so that the incident light is incident on the corresponding photosensitive pixels in the arrangement direction. With the arrangement corresponding to the angle, even if the incident angle is different for each color of the incident light, the incident light can always be condensed on the photosensitive pixel row under the same incident condition for each color. However, the accuracy of color image reading can be improved with a simple configuration in which micro lenses different from each other are formed.

In the image reading apparatus according to the present invention, since the solid-state imaging device is used as a reading sensor, image light formed on the imaging surface of the solid-state imaging device through an imaging lens of an optical system can be obtained. Even if the magnification differs for each color due to the chromatic aberration of magnification of the imaging lens, the chromatic aberration of magnification of the imaging lens can be precisely corrected by the microlens, enabling high-quality image reading with high color registration accuracy. Becomes In addition, since the allowable amount of the correction accuracy of the chromatic aberration of the imaging lens alone increases, the degree of freedom of the glass material used for the lens increases, and the number of lenses can be reduced, thereby contributing to the cost reduction of the apparatus. .

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an embodiment of the present invention.

FIG. 2 is a perspective view conceptually showing a microlens array.

FIG. 3 is a diagram illustrating the operation of a microlens.

FIG. 4 is a diagram illustrating a relationship between a shift amount of a microlens and a shift amount of a light beam incident on a corresponding photosensitive pixel.

FIG. 5 is a diagram illustrating chromatic aberration of magnification of the imaging lens.

FIG. 6 is a schematic configuration diagram illustrating an example of a color image reading device.

FIG. 7 is a plan view schematically showing a configuration of a three-line color image sensor.

FIG. 8 is a configuration diagram showing a conventional technique.

FIG. 9 is a configuration diagram showing another conventional technique.

[Explanation of symbols]

 11R, 11G, 11B Photosensitive pixel array 12R, 12G, 12B Photosensitive pixel 13R, 13G, 13B Micro lens 14R, 14G, 14B Micro lens array

Claims (3)

[Claims] 1. A photosensitive pixel array in which photosensitive pixels for photoelectrically converting incident light are sequentially arranged; and a photosensitive pixel array is arranged corresponding to an incident angle of the incident light with respect to each photosensitive pixel in an arrangement direction of the photosensitive pixels. A solid-state imaging device comprising: a microlens for condensing incident light on the photosensitive pixel row; and a color filter for passing a specific color light of the incident light condensed by the microlens. 2. The solid-state imaging device according to claim 1, wherein the microlens does not have a light condensing function in a direction perpendicular to an arrangement direction of the photosensitive pixels. 3. The solid-state imaging device according to claim 1, wherein the photosensitive pixels are arranged in the main scanning direction, and the image light is optically scanned on the imaging surface of the solid-state imaging device while scanning the original in the sub-scanning direction. An image reading device comprising: an optical system for projecting.