KR100759869B1 - Cmos image sensor using vertical scan - Google Patents

Abstract

A CMOS(Complementary Metal Oxide Semiconductor) image sensor is provided to decrease the number of signal reading circuits or A/D converts, thereby reducing the entire size of chip. An image sensor comprises a pixel array consisting of one or more unit pixels for converting optical signals into electric signals. A timing control circuit(360) generates a control signal for controlling timing. A column decoder(320) selects a column of the pixel array according to the control signal. A row decoder(330) selects a row of the pixel array according to the control signal. A signal reading circuit(340) reads electric signals of respective unit pixels included in the selected column sequentially. A converter(350) converts the read electric signals into analog/digital signals and outputs the converted signals. The row decoder(330) selects unit pixels included in the column selected by the column decoder(320).

Description

CMOS image sensor using vertical scan

1 is a block diagram of a conventional CMOS image sensor of the horizontal scan method.

FIG. 2 is a view showing an example of an image photographed by a CMOS image sensor of a horizontal scan method shown in FIG. 1; FIG.

3 is a block diagram of a vertical type CMOS image sensor according to an embodiment of the present invention.

4 is an equivalent circuit diagram of a unit pixel and a signal read timing diagram.

5 is a configuration diagram of a signal reading circuit.

6 is a view showing an image of a moving subject photographed by a CMOS image sensor of a vertical scan method according to the present invention.

<Description of the symbols for the main parts of the drawings>

310: pixel array

320: thermal decoder

330: row decoder

340: signal reading circuit

350: A / D Converter

360: Timing Control Circuit

370 output buffer

The present invention relates to an image sensor, and more particularly to a CMOS image sensor (scanning in the vertical direction).

Image sensors are classified into CCD (charge coupled device) type and CMOS (Complementary Metal Oxide Semiconductor) type. CMOS image sensors are commonly referred to as CMOS image sensors (CIS).

The CCD-type image sensor moves electrons generated by light to the output unit by using a gate pulse. Therefore, there is external noise along the way, so the number of electrons does not change even if the voltage changes, so the noise does not affect the output signal. CMOS image sensors, on the other hand, convert electrons generated by light into voltage within each pixel and then output them through several CMOS switches. Therefore, the noise comes in the form of the original voltage, so the noise appears as it is in the output signal. In addition, the CCD image sensor has no difference between each pixel by passing the signal of all pixels through one output circuit. In the CMOS image sensor, since each pixel has an electronic-voltage conversion circuit, the unevenness of each pixel circuit It is reflected in the output signal as it is. Noise caused by such nonuniformity is called fixed pattern noise. Therefore, the CMOS image sensor is inferior to the CCD image sensor due to the noise of the fixed pattern and various noises.

On the other hand, the CMOS image sensor uses a standard process, but the CCD image sensor uses a special process, resulting in high wafer manufacturing costs. In addition, CCD type image sensor has various driving pulses such as 3.3V, 0V, -7V, 12V and so on, and the cost increases as the driving IC becomes special. CMOS type image sensor has a single power supply such as 0-3.3V. Can be driven by In addition, the CMOS image sensor can be digitally converted in a chip and can process image signals, but the CCD image sensor is difficult to make one-chip of circuits other than the image sensor.

CMOS image sensor has advantages such as low manufacturing cost, low power consumption, and integration with peripheral circuits compared to CCD image sensor.

1 is a block diagram of a conventional CMOS image sensor of a horizontal scan method.

Referring to FIG. 1, a CMOS image sensor includes a pixel array 110, a row decoder 120, a column decoder 130, a signal readout circuit 140, an A / D converter 150, and a timing control circuit 160. It includes.

The pixel array 110 includes one or more unit pixels 110-a. In this example, 4 × 6 unit pixels 110-a constitute the pixel array 110. The unit pixel 110-a has four rows and six columns.

The pixel array 110 is connected to a row decoder 130 so that any one row in the horizontal direction is selected sequentially or in a predetermined order. There are six unit pixels 110-1 to 110-6 for each selected row, and each unit pixel 110-1, 110-2, 110-3, 110-4, 110-5 or 110-6 Are selected sequentially by the column decoder 120 or in a predetermined order. Then, the signal reading circuit 140 reads an electric signal obtained by converting an optical signal from the selected unit pixels 110-1, 110-2, 110-3, 110-4, 110-5, or 110-6. Analog-to-digital conversion by the / D converter 150 outputs the digitized output signal to the outside of the chip.

When the portion (long side) of the pixel array 110 has a large number of unit pixels among the horizontal and the vertical is defined in the horizontal direction, in FIG. 1, the left and right directions become horizontal and the up and down direction become vertical. That is, the horizontal direction becomes a row and the vertical direction becomes a column. Since the scan is performed again on another row after the scanning of each unit pixel included in one row is completed, this is called a horizontal scan method.

Selection of the unit pixels 110-1, 110-2, 110-3, 110-4, 110-5 or 110-6 by the row decoder 130 and the column decoder 120 is carried out to the timing control circuit 160. It is controlled by the generated control signal.

FIG. 2 is a diagram illustrating an example of an image photographed by the CMOS image sensor of the horizontal scan type shown in FIG. 1. FIG. 2A is an image photographed when the subject is stationary, and FIG. 2B is an image photographed when the subject is rotated clockwise.

It can be seen that 'G' near the center of the screen has a rectangular shape (see 210 in FIG. 2A). However, when the subject is rotated, the 'G' in the photographed image has a parallelogram shape in which the lower side is biased to the right than the upper side (see 220 of FIG. 2B). This is a phenomenon that occurs in the case of a horizontal scan type CMOS image sensor because a scan is performed for each row based on a large number of rows of unit pixels included in the CMOS image sensor. That is, after the upper rows are all scanned, the lower rows are scanned. The distortion of the image of the moving subject as shown in FIG. 2 (b) due to the relationship between the number of unit pixels in each row is greater than the number of unit pixels in each column. There is a problem that occurs.

Accordingly, the present invention provides a CMOS image sensor that can reduce distortion of an image of a moving subject by adopting a vertical scan method instead of a horizontal scan method.

In addition, the present invention provides a CMOS image sensor that can reduce the overall chip size by reducing the number of signal reading circuits or A / D converters.

Other objects of the present invention will be readily understood through the following description.

In order to achieve the above objects, according to an aspect of the present invention, it comprises one or more unit pixels for converting an input optical signal into an electrical signal, and outputs the image data by combining the unit pixels in m rows and n columns A pixel array, where m and n are natural numbers and m is less than n; A timing control circuit for generating a control signal for controlling timing; A column decoder for selecting a column of the pixel array according to the control signal; A row decoder for selecting a row of the pixel array according to the control signal; A signal reading circuit for reading an electric signal of each unit pixel included in a column selected by the column decoder; And an A / D converter for analog-to-digital converting the electrical signal read out from the signal reading circuit and generating an output signal.

Preferably, the row decoder may select a row of each unit pixel included in a column selected by the column decoder. Here, the row decoder selects each row in accordance with the order in which the electrical signal is applied from the signal reading circuit to the A / D converter according to the control signal. The signal reading circuit is m, and the A / D converter has m input terminals, and thus may be connected to each signal reading circuit.

Alternatively, the row decoder selects each row in accordance with the order in which the output signal is applied from the A / D converter to the output buffer according to the control signal. The signal reading circuit and the A / D converters each have m, and the output buffer has m input terminals so that the signal reading circuit and the A / D converters can be connected to each of the A / D converters.

In order to achieve the above objects, according to another aspect of the present invention, a pixel array which combines one or more unit pixels into m rows and n columns to output image data, wherein m, n are natural numbers, and m is greater than n An image output method of a CMOS type image sensor comprising: (a) converting an input optical signal into an electrical signal; (b) a column decoder selecting a column of the pixel array; (c) the signal reading circuit reading the electrical signal of each unit pixel included in the selected column; And (d) the A / D converter may analog-digital convert the electrical signal and generate an output signal.

Preferably, the method may further include repeating steps (b) to (d) until all columns of the pixel array are selected.

Hereinafter, a preferred embodiment of a vertical scan type CMOS image sensor according to the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Numbers (eg, first, second, etc.) used in the description of the present specification are merely identification symbols for sequentially distinguishing identical or similar entities.

3 is a configuration diagram of a vertical type CMOS image sensor according to an exemplary embodiment of the present invention, FIG. 4 is an equivalent circuit diagram and a signal read timing diagram of a unit pixel, and FIG. 5 is a configuration diagram of a signal read circuit. .

Referring to FIG. 3, a vertical scan type CMOS image sensor includes a pixel array 310, a column decoder 320, a row decoder 330, a signal readout circuit 340, an A / D converter 350, and timing control. Circuit 360 and an output buffer 370.

The pixel array 310 includes m × n unit pixels 310-a. m is the number of rows in the pixel array 310 and n is the number of columns. In the present invention, m is preferably smaller than n. In the present invention, the row direction is the horizontal direction and the column direction is the vertical direction. That is, in the pixel array 310, the direction parallel to the short side is the column direction, and the direction parallel to the long side is the row direction.

The unit pixel 310-a converts an input optical signal into an electrical signal. The unit pixel 310-a may be a 1-transistor structure, a 3-transistor structure, a 4-transistor structure, a 5-transistor structure, or the like.

Referring to FIG. 4A, an equivalent circuit diagram of a unit pixel 310-a having a 4-transistor structure is shown. It consists of one photodiode (PD) and four transistors. The four transistors are transfer transistors (Tx) for transporting photocharges generated from the photodiode PD to a floating diffusion node (FD), which set the potential of the node to a desired value and discharge the charges to float. A reset transistor (Rx) for resetting the diffusion node (FD), a drive transistor (Dx) serving as a source follower buffer amplifier, and a select transistor for addressing by switching (Sx; Select Transistor). The other transistor is a load transistor LD to which a bias voltage Vb is applied.

Referring to FIG. 4B, the floating diffusion node FD is precharged by the reset signal Rx signal to have the reset data 410. Thereafter, the transfer transistor is turned on by the transmission signal (Tx signal), so that the photocharge generated in the photodiode PD is transferred to the floating diffusion node FD to generate a voltage drop, and the drive transistor Dx and the select transistor Sx The pixel data 420 is read.

The column decoder 320 selects unit pixels corresponding to any one column of each unit pixel of the pixel array 310. The column decoder 320 selects the next column after all of the electric signals of the unit pixels 310-1, 310-2, 310-3, and 310-4 included in the selected column have been read by the signal reading circuit 340. do. That is, the reading of the electrical signal is performed for each column.

The row decoder 330 selects a unit pixel corresponding to any one row of each unit pixel of the pixel array 310. In the present invention, column selection by the column decoder 320 is performed first, and then row selection by the row decoder 330 is performed. Therefore, the row decoder 330 selects each unit pixel 310-1, 310-2, 310-3, and 310-4 included in the column selected by the column decoder 320 sequentially or in a predetermined order. .

The signal readout circuit 340 reads out the electrical signal converted by the unit pixels 310-1, 310-2, 310-3, and 310-4 in the column selected by the column decoder 320.

The image sensor generates a fixed pattern noise due to an offset voltage due to a slight difference in the manufacturing process. To compensate for this, the image sensor uses a correlated double sampling (CDS) method that reads a reset signal from each pixel of the pixel array, reads a data signal, and outputs the difference.

The signal readout circuit 340 may include a CDS circuit for compensating fixed pattern noise. To compensate for the fixed pattern noise, the difference between the data in the reset state and the pixel data is output as a signal value. Referring to FIG. 5, the reset data 410 is stored in the first capacitor 530 by turning on the first switch 510, and the pixel data is stored in the second capacitor 540 by turning on the second switch 520. Save it. The reset data 410 stored in the first capacitor 530 and the pixel data stored in the second capacitor 540 are respectively input to the first input terminal and the second input terminal of the differential amplifier 550 to amplify the difference between the two data. do. The value is output to an automatic gain controller 560 to adjust gain. The gain-adjusted value is then output to the A / D converter 350.

It is preferable that the signal reading circuit 340 is m. Since the number of unit pixels located in the selected column is m equal to the number of rows, the signal readout circuit 340 may also be located in each row to read an electric signal. In the horizontal scan type CMOS image sensor, the number of signal readout circuits is n equal to the number of columns. In the vertical scan type CMOS image sensor, the signal readout circuit 340 is m equal to the number of rows. The number is small. This reduces the number of capacitors and amplifiers and reduces the chip size of CMOS-type image sensors.

The A / D converter 350 converts the electric signal read out from the signal readout circuit 340 into a digital signal that can be processed because it is an analog signal.

The A / D converter 350 may be one or m. When the A / D converter 350 is one, it has m input terminals, and each input terminal is connected to the m signal readout circuits 340, respectively. The A / D converter 350 receives an electrical signal read by the signal reading circuit 340 that is in charge of the row selected by the row decoder 330, converts the electrical signal into an output signal that is a digital signal, and outputs the output signal to the output buffer 370. Output Alternatively, when the A / D converter 350 is m, each of the A / D converters 350 is connected to the m signal readout circuits 340, respectively. Digital conversion generates m output signals. The m output signals are connected to an output buffer 370 having m input terminals, and an output signal of an input terminal corresponding to a row selected by the row decoder 330 is output to the outside of the chip through the output buffer 370. Is output.

Vertical type CMOS image sensor according to the present invention can be implemented on one chip.

6 is a view showing an image of a moving subject photographed by a CMOS image sensor of a vertical scan method according to the present invention. The image of the moving subject is captured by using the photographed subject in FIG.

Referring to FIG. 6A, it can be seen that the letter 'G' of the subject rotating clockwise (moving from right to left on the screen) has an almost rectangular shape 610. This difference is clear when compared with the parallelogram shape 220 of FIG.

Referring to FIG. 6B, it can be seen that the letter 'G' of the subject rotating clockwise (moving from left to right on the screen) also has a rectangular shape 620.

In the case of a CMOS image sensor of a vertical scanning method (that is, scanning in a direction parallel to a short side of a pixel array), distortion by an object moving in a horizontal direction is alleviated.

An output method of a CMOS image sensor according to an exemplary embodiment of the present invention is as follows. The CMOS image sensor includes a pixel array 310 for outputting image data by combining one or more unit pixels into m rows and n columns as shown in FIG. 3. Here, m and n are natural numbers, and it is preferable that m is smaller than n.

A unit pixel of a CMOS image sensor converts an input optical signal into an electrical signal. The column decoder 320 selects a column of the pixel array. The signal reading circuit 340 reads an electric signal of each unit pixel included in the selected column. The A / D converter 350 converts an electric signal into an analog / digital signal and generates an output signal. The output buffer 370 outputs an image by outputting an output signal to the outside of the chip.

Here, the column decoder 320 selects one column for the n columns of the pixel array sequentially or in a predetermined order. After each column is selected and the electric signals of the unit pixels of the selected column are all read out, a vertical scan is performed because the next column is selected.

In the present invention, the pixel array has a unit pixel in the column direction (i.e., the number of unit pixels m in a row) is smaller than the number of unit pixels in the row direction (i.e., the number of unit pixels n in a column). The distortion of the subject movement is less sensitive than the distortion caused by the subject movement in the row direction.

As described above, the vertical scan type CMOS image sensor according to the present invention can reduce distortion of an image of a moving subject.

In addition, the total chip size can be reduced by reducing the number of signal reading circuits or A / D converters.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be appreciated that modifications and variations can be made.

Claims (8)

delete A pixel array including one or more unit pixels for converting an input optical signal into an electrical signal, and outputting image data by combining the unit pixels into m rows and n columns, wherein m and n are natural numbers and m is less than n; A timing control circuit for generating a control signal for controlling timing; A column decoder for selecting a column of the pixel array according to the control signal; A row decoder for selecting a row of the pixel array according to the control signal; A signal reading circuit for reading an electric signal of each unit pixel included in a column selected by the column decoder sequentially or in a predetermined order; And Including an A / D converter for converting the electrical signal read by the signal reading circuit to analog / digital and generates an output signal, And the row decoder selects a row of each unit pixel included in a column selected by the column decoder. The method of claim 2, And the row decoder selects each row in accordance with the order in which the electrical signal is applied from the signal reading circuit to the A / D converter according to the control signal. The method of claim 3, And m signal reading circuits, and the A / D converter has m input terminals and is connected to each of the signal reading circuits. The method of claim 2, And the row decoder selects each row in accordance with the order in which the output signal is applied from the A / D converter to the output buffer according to the control signal. The method of claim 5, And each of the signal reading circuit and the A / D converter has m input terminals, and the output buffer has m input terminals and is connected to each of the A / D converters. delete In an image output method of a CMOS image sensor comprising a pixel array which combines one or more unit pixels into m rows and n columns to output image data, where m and n are natural numbers and m is less than n. , (a) converting the input optical signal into an electrical signal; (b) a column decoder selecting a column of the pixel array; (c) the signal reading circuit reading out an electrical signal of each unit pixel included in the selected column sequentially or in a predetermined order; (d) converting the electrical signal into an analog / digital signal and generating an output signal; And (e) repeating steps (b) to (d) until all columns of the pixel array are selected.

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