JPH08237425A - Linear image sensor - Google Patents

Abstract

PURPOSE: To provide the linear image sensor whose resolution is improved without setting a transfer frequency higher. CONSTITUTION: Four picture element arrays 11-14 each comprising picture elements of, e g. 1/16 area with respect to an area of a reference picture element are arranged and a sensor section 10 is formed by providing vertical shift registers 15-18 corresponding to the picture element arrays 11-14, and a signal charge read from each picture element of the picture element arrays 11-14 to the vertical shift registers 15-18 is transferred to a common output section 20 via a horizontal shift register 19 for each array.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear image sensor, and more particularly to a CCD linear image sensor which converts one-dimensional image information into an analog electric signal while scanning in a direction perpendicular to a pixel array.

[0002]

2. Description of the Related Art The basic structure of a CCD linear image sensor is shown in FIG. In this CCD linear image sensor, the pixel row 31 integrated and formed on the chip is composed of a separated and formed pn photodiode. Then, in each of the photodiodes, a signal charge corresponding to the product of the intensity of light incident on the photodiode and time, that is, the exposure amount is accumulated. The signal charges accumulated in each of the photodiodes are simultaneously transferred to the CCD shift register 33 via the shift gate 32, transferred in the pixel arrangement direction, and supplied to the output section 34. Output unit 34
Has a floating diffusion configuration, for example, and detects the supplied signal charge and converts it into an analog electric signal.

By the way, conventionally, the resolution of a CCD linear image sensor can be increased by increasing the number of pixels. For example, considering the CCD linear image sensor (A) in FIG. 4 as a reference, the CCD linear image sensor (B) is set to double the resolution in each of the X and Y directions, and the CCD linear image sensor is set to four times the resolution.
This is a linear image sensor (C). In this case, the area of the pixel for the CCD linear image sensor (A) is 1 / for the CCD linear image sensor (B).
4, 1/16 in CCD linear image sensor (C).

[0004]

However, in the conventional CCD linear image sensor, if an attempt is made to increase the resolution under the same conditions, the operation cycle becomes shorter as the resolution increases, so that the transfer frequency increases. For example, the accumulation time of the CCD linear image sensor (A) is 200 μsec,
When the operation cycle is 200 μsec and the transfer frequency is 500 kHz, in the case of the CCD linear image sensor (B),
The accumulation time is 100 μsec, the operation cycle is 100 μsec, and the transfer frequency is 2 MHz. For the CCD linear image sensor (C), the accumulation time is 50 μsec, the operation cycle is 50 μsec, and the transfer frequency is 8 MHz. As described above, when the transfer frequency is increased, a problem occurs in transfer of signal charges such as transfer efficiency with the basic device structure (A).

The present invention has been made in view of the above problems, and its object is to improve the resolution without increasing the transfer frequency on the assumption that the basic device structure is used as it is. It is to provide a linear image sensor that enables the above.

[0006]

In the linear image sensor according to the present invention, a pixel array in which pixels each having an area of 1/2 ²ⁿ (n is a natural number) is one-dimensionally arranged with respect to the area of a reference pixel is 2n. A sensor unit which is arranged side by side and transfers the signal charge of each pixel in the pixel arrangement direction for each pixel column while scanning in the arrangement direction, and each pixel column provided at the end of the transfer destination side of each pixel column A configuration including a charge transfer unit that transfers the signal charges transferred for each of them in the arrangement direction of the pixel column, and an output unit that detects the signal charges transferred by the charge transfer unit, converts the signal charges into an analog electric signal, and outputs the analog electric signal. Has become.

[0007]

In the linear image sensor having the above structure, by arranging 2n pixel columns each having an area of 1/2 ²ⁿ with respect to the area of the reference pixel, the accumulation time is longer than that of the reference pixel. Although the 1 / 2n, the operation cycle is the same, therefore the transfer frequency is not a 2 ²ⁿ times may be 2n times. Therefore, the resolution can be improved without increasing the transfer frequency. In addition, the signal charge of each pixel column is sequentially transferred to the common output unit via the charge transfer unit for each column.
As a result, a signal having no relative level difference between the columns can be derived as an output for each column.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic block diagram showing an embodiment of the present invention. In FIG. 1, for example, four pixel columns 11 to 1
4 are arranged side by side. These four pixel columns 11
The basic unit cell forming each pixel of
The light receiving portion PD including a photodiode and a channel stop portion CS around the light receiving portion PD are shown in FIG.
When the pixel of the CD linear image sensor (A) is used as a reference, the area of the reference pixel is 1/16 (= 2 ⁴ ). As a result, the four pixel columns 11 to 1
A set of 4 pixels of 4 corresponds to one size of the reference pixel. A signal charge corresponding to the product of the intensity of incident light and time, that is, the amount of exposure is accumulated in each pixel. Four vertical Cs are provided corresponding to each of the four pixel columns 11 to 14.
CD shift registers (hereinafter, simply referred to as vertical shift registers) 15 to 18 are provided.

The signal charges accumulated in the respective pixels of the four pixel columns 11 to 14 are read out to the vertical shift registers 15 to 18 all at once via a shift gate (not shown). The vertical shift registers 15 to 18 are sequentially transferred and driven from the left side, so that the vertical shift register 15 is driven.
The signal charges read from 18 to 18 are transferred in the vertical direction (pixel arrangement direction) for each column. As a result, the signal charge for one column of the leftmost pixel column 11, the signal charge for one column of the second pixel column 12 from the left, and the signal charge of the third pixel column 13 next The signal charges of the fourth pixel column 14 are vertically transferred in order. The pixel section 11 to 14 and the vertical shift registers 15 to 18 form the sensor unit 10.

Horizontal CCD shift registers (hereinafter, referred to as
A horizontal shift register) 19 is provided. The horizontal shift register 19 transfers in the horizontal direction (arrangement direction of pixel columns) the signal charges sequentially transferred from the vertical shift registers 15 to 18 for each column. At the end of the transfer destination of the horizontal shift register 19, for example, an output unit 20 having a floating diffusion (FD) configuration is provided. When the signal charge flows into the FD region, the output section 20 changes the potential of the FD region according to the amount of the charge, thereby converting the signal charge into a voltage signal. This FD
The potential of the region is derived to the outside through impedance conversion by a source follower (not shown).

Next, the operation of the CCD linear image sensor having the above structure will be described in comparison with the conventional CCD linear image sensor (C) shown in FIG. 4 having the same pixel area with reference to FIG. First, in the case of the conventional CCD linear image sensor (C), as shown in FIG. 2A, all the information A, B, C, D, ... To be scanned must be handled in one array (one column). I don't get. Therefore, as described above, the operation cycle = accumulation time (50 μsec
), The vertical transfer frequency is as high as 8 MHz.

On the other hand, if the information A, B, C, D, ... To be scanned is handled in four arrays (four columns) as in the present embodiment, as shown in FIG. 1st array (pixel array 11) has information A, E, I, ..., 2nd array (pixel array 12) has information B, F, J, ..., 3rd array (pixel array 13) has information C, G , K, ... For the 4th array (pixel array 14), information D, H, L ,. The signal charges accumulated in each pixel of the four pixel columns 11 to 14 are transferred to the output section 20 through the horizontal shift register 19 in order for each column and combined, and the information A, B, C, D, and It is output in the order of …….

As a result, if one array is used, the storage time is 1 in the case of the CCD linear image sensor (A) of FIG.
/ 4 becomes a 50 .mu.sec, the operation period when equivalent 200μsec next of the sensor (A), may be 2 MH _Z where originally also vertical transfer frequency is 8MH _Z. As a result, the resolution can be improved without increasing the transfer frequency.

Although the storage time for one array is 50 μsec, for example, the 1st array (pixel array 11)
Paying attention to, the information B, the information B, the information C, and the information D are accumulated in addition to the information A during the operation period of 200 μsec.
Therefore, before the accumulation of the information E to be handled by the 1st array next to the information A, the process of discharging the signal charge accumulated in the pixel column 11 is executed. This signal charge discharging process can be realized by, for example, an electronic shutter operation in a 50 μsec accumulation mode.

By the way, for example, four pixel columns 11-14
In the case of using, it is possible to adopt a configuration in which four output sections are respectively arranged at the end portions on the transfer destination side of the shift registers 15 to 18 and the read information is taken out for each array. However, when an output section is provided for each array, if there is a gain variation among the output sections, a relative level is generated between the outputs of each array. However,
In the present invention, one output unit 20 is commonly used for each array.
And the signal charge of each array is provided in the horizontal shift register 19
Since the configuration is adopted in which the data is sequentially transferred to the output unit 20 via
The output of each array can be derived at a uniform level.

In the above embodiment, the CCD shown in FIG.
When the pixel of the linear image sensor (A) is used as a reference,
The case where the CCD linear image sensor is configured by using the four pixel columns 11 to 14 each having the area of 1/16 (= 2 ⁴ ) with respect to the area of the reference pixel has been described. Instead, it is sufficient if ²ⁿ pixel rows of pixels each having an area of 1/2 ²ⁿ (n is a natural number) with respect to the area of the reference pixel are arranged side by side.

[0018]

As described above, according to the present invention,
²ⁿ pixel columns each having a pixel area of 1/2 ²ⁿ with respect to the area of the reference pixel are arranged side by side, and the signal charges of each pixel column are sequentially transferred to the common output unit via the charge transfer unit. With this configuration, the accumulation time is 1 / 2n compared to that of the reference pixel, but the operation cycle is the same and the transfer frequency can be 2n times, so the resolution can be increased without increasing the transfer frequency. In addition to the improvement, it is possible to derive a signal having no relative level difference between the columns as an output for each column.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram for explaining an operation.

FIG. 3 is a basic configuration diagram of a CCD linear image sensor.

FIG. 4 is a schematic configuration diagram showing a conventional example.

[Explanation of Codes] 10 Sensor Units 11 to 1
4 pixel rows 15 to 18 vertical CCD shift register 19 horizontal CCD shift register 20 output unit

Claims (1)

[Claims] 1. An array of 2n pixel rows in which pixels each having an area of 1/2 ²ⁿ (n is a natural number) with respect to the area of a reference pixel are one-dimensionally arranged is arranged and scanning is performed in the arrangement direction. Meanwhile, a sensor unit that transfers the signal charge of each pixel in the pixel array direction for each pixel column, and the arrangement of the pixel charge that is provided at the transfer destination side end of each pixel column and that is transferred for each pixel column A linear image sensor, comprising: a charge transfer unit that transfers a charge in a direction; and an output unit that detects the signal charge transferred by the charge transfer unit, converts the signal charge into an analog electric signal, and outputs the analog electric signal.