JPH0366164A - Color image sensor - Google Patents

Abstract

PURPOSE:To arrange light-shielding picture-element arrays at gaps of light-responsive picture- element arrays, to suppress a spike noise caused at a changeover operation of an access switch and to realize a contact-type color image sensor which is provided with a light- resistance property and a heat-resistant property at a low cost by a method wherein, while an interval between light-responsive picture element arrays is kept equal to an interval between picture elements in a main scanning direction, a light-responsive picture element size is reduced to a sub-scanning direction. CONSTITUTION:Phototransistors 3 as picture-element units are arranged in a matrix shape of n columns and five arrays; the phototransistors whose base is made blank are phototransistors as light-responsive picture elements; the phototransistors whose base is tinted black are phototransistors which have shielded light. Intervals between picture elements in a sub-scanning direction among a first array, a third row and a fifth array are constituted so as to be equal to intervals between picture elements in a main scanning direction. The intervals between the picture elements in the main scanning direction are equal to intervals between light-responsive picture elements in the sub-scanning direction; picture elements, which have shielded light, used to remove a spike noise caused by a changeover operation of an access switch are arranged among three light-responsive picture element arrays. Thereby, the picture elements, which have shielded light, used to suppress the spike noise can be arranged inside a chip face which substantially covers three arrays of picture elements; a good-quality image signal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an imaging device that reads video information, and more particularly to an inexpensive color image sensor that reads color video information.

Some conventional linear image sensors have a plurality of pixel rows mainly to enable color reading. In this case, stripe filters are provided so that different colors are read for each column. This type of sensor is less prone to moire and color shift than a sensor with a configuration in which pixels with filters of different colors are alternately arranged in a row, and the clock frequency of the scanning circuit and resolution in monochrome conversion are lower. It has the advantage of being low cost. Furthermore, if the scanning circuit is formed not from COD but from a bipolar transistor or MOS (MOS) run master, it is sufficient to have one row of scanning circuits, which is the same as in the case of a monochrome sensor, and a color image sensor with an extremely simple configuration is sufficient. can be realized. However, for the purpose of reducing spike noise and the like that occur when switching the access switch, it is desirable to further provide light-shielded pixel columns in parallel in order to obtain a differential output later.

Problems to be Solved by the Invention In a linear image sensor having a configuration in which multiple columns are arranged in parallel as described above, the interval between pixels in the sub-scanning direction, that is, the interval between columns, is an integral multiple of the inter-pixel interval in the main scanning direction. It is desirable that The reason for this is that moire and color shift can be suppressed as described above by easily matching the timing of the integration time of each row of sensors operating in the charge accumulation mode using a line buffer memory or the like. However, in order to miniaturize the device, contact image sensors with a short optical path length are
The pixel row section occupies a larger area within the sensor chip than the scanning circuit section. Therefore, if the inter-pixel interval in the sub-scanning direction is one time the inter-pixel interval in the main-scanning direction,
The increase in chip size can be suppressed compared to doubling or more.

However, as described above, adding an extra light-shielded pixel column in order to obtain an output with less spike noise generated when switching the access switch also directly leads to an increase in chip size, that is, an increase in chip cost.

Means to Solve the Problem Normally, the pixel resolution of a contact type image sensor for color reading is 400 dots/inch for each color when accurately reading originals with fine patterns such as letters, but when the document does not contain fine letters etc. For example, approximately 200 dots/inch for each color is practically sufficient as an inexpensive image-powered device for individuals.

For personal use, which is inexpensive at about 200 dots/inch for each color, the amount of light or integration time can be sufficiently large, so there is no problem even if the size of the pixel that detects the light is made somewhat smaller. Therefore, in view of the above problems, the image sensor of the present invention reduces the photosensitive pixel size in the sub-scanning direction while keeping the interval between the photosensitive pixel rows equal to the inter-pixel interval in the main scanning direction. It is characterized in that light-shielding pixel columns are arranged in gaps between pixel columns.

Effect of the Invention According to the above-described configuration, the present invention provides a light-shielding pixel array for suppressing spike noise generated when switching access switches without substantially increasing the area occupied on the chip, thereby achieving color reading with good S/N. This is to realize an inexpensive contact-type image sensor. Further, the arrangement of the light-shielding pixel rows between the photosensitive pixel rows increases the tolerance range for the stacking position accuracy of the stripe filters provided on the photosensitive pixel rows. In other words, there is a permissible margin of filter loading position error corresponding to the width of the light-shielded pixel row. Therefore, instead of using filter formation technology using lithography, which has high positional accuracy but is also expensive, it is possible to form a filter containing light- and heat-resistant pigments on the sensor using printing technology, which has slightly lower positional accuracy but is cheaper. . In this sense as well, the present invention realizes an inexpensive and high-performance color image sensor.

Embodiments Hereinafter, image sensors according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of the configuration of an image sensor for implementing the present invention. 1 is a scanning circuit that selects a row from which to read a video signal; 2 is an access switch array that switches the common line of the row selected by the scanning circuit so that it can be charged to a constant voltage when it is on; 3 is a pixel unit The phototransistors are arranged in a matrix of n rows and 5 columns. Among the phototransistors 3, those with white bases are phototransistors that are photosensitive pixels, and those with black bases are light-shielded phototransistors. 4 is an output terminal for obtaining video signals from the light-sensitive pixels belonging to the first column, 5 is an output terminal for obtaining video signals from the light-shielding pixels belonging to the second column, and 6 is an output terminal for obtaining video signals from the light-sensitive pixels belonging to the third column. An output terminal for obtaining a signal; 7 is an output terminal for obtaining a video signal from a shaded pixel belonging to the fourth column;
8 is an output terminal for obtaining a video signal from the photosensitive pixels belonging to the fifth column. Here, red, green, and blue stripe filters are arranged above the pixels in the first, third, and fifth columns to realize a sensor capable of color reading. The inter-pixel interval in the sub-scanning direction between the first, third and fifth columns is configured to be equal to the inter-pixel interval in the main-scanning direction. In a contact image sensor with a relatively low pixel resolution of about 200 DPI, the interval between pixels is large, so an increase or decrease in one pixel line has a large effect on the chip size. However, a large pixel interval means that the size of the light receiving portion of the pixel can be increased.

Further, in this case, since the amount of light is usually sufficient, there is no need to make the light receiving portion size very close to the inter-pixel interval value. In addition, in the case of the same pixel interval, if the shape of the light receiving part is square, the resolution in the sub-scanning direction will be about half of the resolution in the main scanning direction, so the length of the side along the sub-scanning direction will be The shorter the length, the more advantageous it is because it suppresses a decrease in resolution in the sub-scanning direction. Therefore, FIG. 2(a) shows a plan view and a cross-sectional view of the pixel structure in consideration of the above.
Each is shown in (b). FIG. 2(a) shows the portion surrounded by the dashed dotted line in FIG.

In Figures 2(a) and (b), 9.10.11. ,1
2.13 are output lines connected to output terminals 4.5, 6, and 7.8 in FIG. 1, respectively. 14 is the emitter of the phototransistor, and 15, shown with diagonal lines, is the base of the phototransistor, which serves as the main photoelectric conversion region. Pixels belonging to the same row have a structure in which they share a collector region, thereby achieving a common collector configuration as explained in FIG. 1 above. 16.17.18
is a line for accessing each collector, and outputs of pixels sharing the accessed collector are obtained from a common output terminal for each column. 19, 20, 21, and 22 are all made of the same type of semiconductor as the emitter as collectors, 19 has low resistance for connection with electrodes, and 20 has crosstalk of photogenerated carriers between each pixel in the same row. 21 is a buried layer of the collector and has low resistance, and 22 has high resistance to improve photoelectric conversion efficiency. 23 is a semiconductor substrate of the same type as the base. In FIG. 2(a), the interval between pixels in the main scanning direction and the interval between light-sensitive pixels in the sub-scanning direction are equal, and there are light-shielded pixels between the three light-sensitive pixel columns for removing spike noise that occurs when switching the access switch. are placed. In other words, when the resolution of a contact image sensor is not very high, it is possible to use light-shielded pixels for spike noise suppression without changing the interval between light-sensitive pixels and while ensuring the required sensitivity of the light-sensitive pixels. It can be placed between sensitive pixels. As a result, as shown in FIG. 2, light-shielded pixels for suppressing spike noise can be arranged within the chip surface for substantially three rows of pixels, and a high-quality image signal can be obtained. Furthermore, since there is always a light-shielding pixel row adjacent to the three rows of photosensitive pixels, the effect of suppressing spike noise during differential output is extremely large. Furthermore, when forming stripe filters on the first, third, and fifth photosensitive pixel rows, there is a light-shielding pixel row between each row, so the width corresponding to the width of this light-shielding pixel row is The margin for allowing the filter formation position shift is large. Therefore, instead of using filter formation technology using lithography, which has high positional accuracy but is also expensive, it is possible to form a filter containing light- and heat-resistant pigments on the sensor using printing technology, which has slightly lower positional accuracy but is cheaper. .

In this sense as well, an inexpensive and high-performance color image sensor can be realized.

If the balance between red, green, and red outputs is important, as shown in Figure 3, one of the two light-shielded pixel rows can be eliminated and the area of the light-sensitive pixel that should improve sensitivity can be reduced. It can also be increased by that amount. In this figure, 24.26.2
7 is the output line of the photosensitive pixel of each column, and 25 is the output line of the light-shielded pixel column. 28 is the emitter of the phototransistor, and 29, shown with diagonal lines, is the base of the phototransistor. Pixels belonging to the same row share a collector area, thereby providing a common collector configuration. 30.3L 32 is a line for accessing each collector, and outputs of pixels sharing the accessed collector are obtained from a common output terminal for each column. The interval between pixels in the main scanning direction and the interval between photosensitive pixels in the sub-scanning direction are equal, and light-shielded pixels for spike noise removal are arranged only between the two upper rows of photosensitive pixel columns. On the other hand, the light-receiving area of the photosensitive pixels in the bottom row is larger. The interval between pixels in the sub-scanning direction is kept constant. As a result, by configuring the pixel area that reads the color with the lowest sensitivity when the area is the same, as in the bottom row of pixels in this figure, it is possible to balance the outputs of the three color pixel rows. Also in this case,
Since there is no light-shielding pixel row between the second row of photosensitive pixel rows and the third row of photosensitive pixel rows, the margin for allowing formation position errors when forming filters using printing technology is somewhat small. However, by arranging the largest photosensitive pixel 1 2 row in the outermost row (the bottom row in this figure) and keeping the inter-pixel interval in the sub-scanning direction equal to the inter-pixel interval in the main-scanning direction, the output line 27 As can be seen from the width of the output lines 24 and 26, there is a margin for forming a filter that is larger than the widths of the other output lines 24 and 26. Therefore, a filter containing a pigment can be easily formed on the sensor using an inexpensive printing technique.

As described above, it consists of a light receiving section in which pixels made of phototransistors are arranged in a matrix, a scanning circuit that sequentially accesses each row of the matrix, and an access switch. The collectors of pixels belonging to the same row share a semiconductor isolation region of a different type with the substrate, and the common collectors are sequentially accessed to output video signals from the output lines of each column. and one row of the pixels arranged in the matrix is made up of light-shielded pixels, and the interval between the pixel rows sensitive to light is kept equal to the interval between pixels in the main scanning direction. A pixel column that is sensitive to light is placed between the output of the light-shielded pixel column and another light-sensitive pixel column, and a differential is established between the output of the light-shielded pixel column and the output of the light-shielded pixel column. Therefore, it is possible to obtain a video signal with less spike noise generated when switching the access switch without increasing the chip area. Furthermore, since the tolerance margin for misalignment when forming the filter on the sensor can be increased, inexpensive printing technology can be used to provide a color filter containing pigments with strong light and heat resistance, resulting in inexpensive and high-performance adhesion. It is possible to realize a type color image sensor.

Effects of the Invention As is clear from the above explanation, according to the present invention, a light-shielded pixel array can be provided within a sensor chip without increasing the effective chip area, thereby reducing the spike noise that occurs when switching access switches. It is possible to inexpensively realize a contact type color image sensor that suppresses heat and light resistance, and has great industrial effects.

3 4

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of the image sensor of the present invention, FIGS. 2(a) and (b) are a plan view and a sectional view of the pixel structure of the image sensor in the embodiment shown in FIG. 1, and FIG. FIG. 2 is a plan view of a pixel structure of an image sensor in an example. 1...Scanning circuit, 2...Access switch row, 3...Phototransistor, 4, 5,
6,7.8...Video signal output terminal, 14.28
Emitter region of phototransistor, 15.29...
...Base region of phototransistor.

Claims (5)

[Claims] (1) It consists of a light receiving section in which pixels made up of phototransistors are arranged in a matrix, a scanning circuit that sequentially accesses each row of the matrix, and an access switch, and the emitters of pixels belonging to the same column are commonly connected to the output line. is formed in each column, the collectors of the pixels belonging to the same row share a semiconductor isolation region of a different type with the substrate, and the common collector is sequentially accessed to obtain a video signal from the output line of each column. and one of the columns arranged in the matrix is a column consisting of light-shielded pixels, and the difference between the output of this light-shielded pixel column and the output of other light-sensitive pixel columns is taken. In an image sensor that obtains a video signal with less spike noise, the light-shielded pixel row is arranged so as to be between other light-sensitive pixel rows, and the intervals between the light-sensitive pixel rows are set in the main scanning direction. A color image sensor characterized in that the interval between pixels in the direction is equal to the interval between pixels. (2) There are three light-sensitive pixel rows, and a total of two light-shielded pixel rows are arranged, one row between each light-sensitive pixel row,
2. The color image sensor according to claim 1, wherein stripe filters having different colors are arranged for each row above the light-sensitive pixel rows to enable reading of color originals. (3) There are three light-sensitive pixel rows, and only one light-shielded pixel row is arranged in one of the two light-sensitive pixel rows, and above the light-sensitive pixel row. Stripe filters of different colors are arranged in each column to enable reading of color documents, while keeping the interval between light-sensitive pixels equal to the interval between pixels in the main scanning direction.
According to claim (1), the areas of the phototransistor light-receiving portions of the two photosensitive pixel columns that do not sandwich the light-shielded pixels are increased, and these are used as pixel columns that read light in a wavelength region with a small amount of light. color image sensor. (4) The color image sensor according to claim (2), wherein a filter containing a pigment is formed on the photosensitive pixel array by a printing technique. (5) The color image sensor according to claim (3), wherein a filter containing a pigment is formed on the photosensitive pixel array by a printing technique.