WO2007067013A1

WO2007067013A1 - Capteur d'image cmos utilisant un balayage vertical

Info

Publication number: WO2007067013A1
Application number: PCT/KR2006/005354
Authority: WO
Inventors: Jung-Bum Chun
Original assignee: Mtekvision Co., Ltd.
Priority date: 2005-12-09
Filing date: 2006-12-08
Publication date: 2007-06-14
Also published as: WO2007067013A8; KR100759869B1

Abstract

La présente invention concerne un capteur d'image CMOS utilisant un balayage vertical. Cette invention concerne un capteur d'image CMOS comprenant un réseau de pixels, lequel comprend un ou plusieurs pixels unité qui transforment des signaux optiques entrés en signaux électriques et produit en sortie des données d'image par combinaison des pixels unité en m colonnes et en n rangs, m et n étant des nombres entiers et m étant inférieur à n, un circuit de commande de synchronisation qui génère des signaux de commandes qui commande la synchronisation, un décodeur de colonne qui sélectionne une colonne du réseau de pixels en fonction des signaux de commande, un décodeur de rang qui sélectionne une rangée du réseau de pixels en fonction des signaux de commande, un circuit de lecture de signaux qui lit des signaux électriques de chaque pixel unité sur les colonnes sélectionnées par le décodeur de colonne et, un convertisseur A/N qui convertit les signaux électriques lus par le circuit de lecture de signaux en signaux de sortie via une conversion analogique/numérique. La distorsion de l'image d'un objet mobile peut être réduite.

Description

[DESCRIPTION]

[Invention Title]

CMOS IMAGE SENSOR USING VERTICAL SCAN

[Technical Field]

The present invention is related to an image sensor, more specifically, a CMOS image sensor using vertical scan.

[Background Art]

Image sensor are divided by a CCD(charge coupled device) type and a CMOS(complementary metal oxide semiconductor) type. Usually the CMOS image sensor is called a CIS(CMOS Image sensor). A CCD Image sensor shifts electrons generated from light to an output unit using gate pulse. Because the number of the electrons doesn't change even though the voltage changes in the middle of the process from outside noise, the noise doesn't influence the output signal. Otherwise a CMOS image sensor outputs the voltage through many CMOS switches after converging the electrons that are generated from light into the voltage in each pixel. The noises appear on output signals as the noises are added, because the noises are inputted as a form of voltage. And compared to the case of the CCD image sensor that has few differences between one pixel and another pixel, the case of CMOS image sensor, because each pixel has an electron-voltage converging circuit, the unevenness of each circuit of each pixel is reflected in output signals. The noises from such

unevenness are called fixed pattern noise. So the image quality of the CMOS image sensor is inferior to the image quality of the CCD image sensor because of many noises including the fixed pattern noise.

In contrast to the CMOS image sensor which is produced by a standard process, the CCD image sensor is produced by a specific process which renders high costs for producing wafer. Further, since the CCD image sensor needs many kinds of driving pulses of 3.3 V, OV, -TW, 12V and so on, production costs of the CCD image sensor grows higher for specialization of driving IC. On the other hand the CMOS image sensor needs one power source of 0-3.3 V etc. for driving. And in the case of the CMOS image sensor, digitization and image signal processing is possible in a chip, but in the case of CCD image sensor, it is difficult to unify circuits besides the image sensor into one-chip.

The CMOS image sensor has many merits of lower manufacturing cost, less power consumption and easier in integration with neighbored circuits, compared to the CCD image sensor. Fig.l shows a related art CMOS image sensor using horizontal scan.

Referring to Fig.l, the CMOS image sensor includes an pixel array 110, a row decoder 130, a column decoder 120, a signal reading circuit 140, an A/D converter 150 and a timing control circuit 160.

The pixel array 110 includes more than one unit pixels 110a. In present embodiment, 4x6 unit pixels 110a composes the pixel array 110. The unit pixel 110a is arranged, in 4 rows and 6 columns.

The pixel array 110 is connected to the row decoder 130 and one horizontal row of the pixel array is selected according to a sequential or predetermined order. In a selected row 6 unit pixels 110-1 to 110-6 are exist, each unit pixel 110-1, 110-2, 110-3, 110-4, 110-5 or 110-6 is selected according to a sequential or predetermined order for the column decoder 120. The signal reading circuit 140 reads electric signals converted from optical signals in the selected unit pixel(l 10-1, 110-2, 110-3, 110-4, 110-5 or 110- 6) and the A/D converter 150 outputs digitalized output signals by an analog/digital conversion to outside the chip.

If the part that has more unit pixels(longer side) of the width and the length is defined as a horizontal direction in the pixel array 110, a left-to-right direction may be a horizontal one and up-to-down direction a vertical one in Fig. 1. That is, the horizontal direction is a row and the vertical direction is a column. After scanning of all unit pixels in one row is completed, scanning of another row is followed, so that this method of scanning is called as horizontal scan.

Selection of the unit pixel 110-1, 110-2, 110-3, 110-4, 110-5 or 110-6 by the row decoder 130 and the column decoder 120 may be controlled by a control signal generated by the timing control circuit 160.

Fig.2 and Fig. 3 show examples of images photographed by the CMOS image sensor using horizontal scan shown in Fig. 1. Fig.2 shows the image photographed when an object halts and Fig. 3 shows the image photographed when an object spins clockwise.

It is certain that 'G' near the center of the image has a shape of rectangle (See 210 of Fig. 2). But when the object spins, 'G' in the image photographed has a shape of parallelogram of which bottom side leans more to the right than upper side (see 220 of Fig. 3). This phenomenon comes from the CMOS image sensor scanning since scanning is performed according to the row in order of which has more unit pixels. Namely, the bottom row is scanned after all the upper row is scanned, because the number of unit pixels of each row is larger than the number of unit pixels of each column, which causes the image distortion of an object. [Disclosure] [Technical Problem]

The present invention provides a CMOS image sensor that can reduce the image distortion of a moving object by employing vertical scanning method, instead of horizontal scanning method.

The present invention further provides a CMOS image sensor that can make a whole size of chips be smaller by reducing signal reading circuits or the number of AJO converters.

[Technical Solution]

To achieve the above objects, an aspect of the present invention features, a

CMOS image sensor, including: a pixel array that includes one or more unit pixels that convert inputted optical signals into electrical signals and output image data by combining the unit pixels into m columns and n rows- wherein m and n are natural numbers and m is smaller than n-; a timing control circuit that generates control signals that control timing; a column decoder that selects a column of the pixel array according to the control signals; a row decoder that selects a row of the pixel array according to the control signals; a signal reading circuit that reads electric signals of each unit pixel on the column selected by the column decoder; and an A/D converter that converts the electric signals read by the signal reading circuit into output signals through an analog/digital conversion. The row decoder can select a row corresponding to each unit pixel in the column selected by the column decoder. Herein, the row decoder selects each row in correspondence with the order in which the electric signal is applied to the A/D converter from the signal reading circuit according to the control signal. And the number of the signal reading circuits is m, and the A/D converter has an m number of input terminals that can be connected to the m number of the signal reading circuits, respectively.

Or the row decoder selects each row in correspondence with the order in which the output signal is applied to an output buffer from the A/D converter according to the control signal. And the number of the signal reading circuits is m, the number of the A/D converters is m, and the output buffer has an m number of input terminals that can be connected to the m number of A/D converters, respectively.

To achieve the above objects, an aspect of the present invention features, a method of outputting image of the CMOS image sensor which includes a pixel array outputting image data by combining one or more unit pixels into m rows and n columns -wherein m and n are natural numbers and m is smaller than n- including; the pixel array converting inputted optical signals into electric signals; a column decoder selecting a column of the pixel array; a signal reading circuit reading electric signals of each unit pixel included in the selected column; and an A/D converter converting the electric signals into output signals through analog/digital conversion. The method of outputting image may further include repeating the step of a column decoder selecting a column of the pixel array through the step of an A/D converter converting the electric signals into output signals through analog/digital conversion till all the columns of the pixel array are selected.

The objects, specified advantages and new features will become more apparent through the below description and desirable embodiments with reference to the accompanying drawings.

[Description of Drawings]

Fig.l shows a related art CMOS image sensor using horizontal scan.

Fig.2 and Fig.3 show examples of images photographed with the CMOS image sensor shown in Fig. 1.

Fig.4 shows a CMOS image sensor using vertical scan according to an embodiment of the present invention.

Fig.5 shows an equivalent circuit diagram of a unit pixel.

Fig 6 shows a timing diagram of signal reading.

Fig 7 shows a diagram of signal reading circuit.

Fig 8 and fig 9 show images photographed of a moving object with the CMOS image sensor using vertical scan according to the present invention [Mode for Invention]

The above objects, features and advantages will become more apparent through the below description with reference to the accompanying drawings.

Since there can be a variety of permutations and embodiments of the present invention, certain embodiments will be illustrated and described with reference to the accompanying drawings. This, however, is by no means to restrict the present invention to certain embodiments, and shall be construed as including all permutations, equivalents and substitutes covered by the spirit and scope of the present invention.

Terms such as "first" and "second" can be used in describing various elements, but the above elements shall not be restricted to the above terms. The above terms are used only to distinguish one element from the other. For instance, the first element can be named the second element, and vice versa, without departing the scope of claims of the present invention. The term "and/or" shall include the combination of a plurality of listed items or any of the plurality of listed items.

The terms used in the description are intended to describe certain embodiments only, and shall by no means restrict the present invention. Unless clearly stated otherwise, expressions in the singular include the plural meaning. In the present description, an expression such as "including" or "stored ", "loaded or mounted", "inserted" is intended to designate a characteristic, a number, a step, an operation, an element, a part or combinations thereof, and shall not be construed to preclude any presence or possibility of one or more other characteristics, numbers, steps, operations, elements, parts or combinations thereof.

Unless otherwise defined specifically, all terms, including technical terms and scientific terms, used herein have the same meaning as how they are generally understood by those of ordinary skill in the art to which the invention pertains. Any term that is defined in a general dictionary shall be construed to have the same meaning in the context of the relevant art, and, unless otherwise defined explicitly, shall not be interpreted to have an idealistic or excessively formalistic meaning. FIG.4 shows a CMOS image sensor of vertical scan type in accordance with an embodiment of the present invention, FIG.5 shows an equivalent circuit diagram of a unit pixel, Fig 6 shows a timing diagram of signal reading and Fig 7 shows a diagram of signal reading circuit.

Referring to FIG. 4, the CMOS mage sensor using vertical scan may include a pixel array 310, an column decoder 320, a row decoder 330 a signal reading circuit 340, a A/D converter 350, a timing control circuit 360, and a output buffer 370.

The pixel array 310 includes mxn number of unit pixels 310a. M is the number of rows of the pixel array 310 and n is the number of columns of the pixel array 310. In present invention, m is smaller than n. A row direction is referred to as a horizontal direction, and a column direction is referred to as a vertical direction. The direction parallel to a short side of the pixel array 310 is referred to as a column direction, and the direction parallel to a long side of the pixel array 310 is referred to as a row direction.

The Unit Pixel 310a converts inputted optical signals to electric signals. The Unit Pixel 310a can have a 1-trasistor structure, a 3-trasistor structure, a 4-trasistor structure, a 5-trasistor structure, and the like.

Fig. 5 shows an equivalent circuit diagram of the unit pixel having a 4- transistor structure. One unit pixel is composed of one photo diode PD and 4 trnasistors. The 4 transistors are a transfer transistor Tx for transferring photocharges generated from the photo diode to a floating diffusion FD node, a reset transistor Rx for resetting the floating diffusion FD node by setting the electric potential of a node to have a desired value and emitting electrons, a drive transistor Dx playing a role of a source follower buffer amplifier, and a select transistor Sx allowing to address by switching. The other transistor is a load transistor LD being applied bias voltage Vb.

Referring to Fig 6, the floating diffusion FD node is precharged and gets reset data 410 by a reset signal. And then when the transfer transistor is turned on by a transfer signal, photocharges generated at the photo diode PD are transferred to the floating diffusion node to drop the voltage, pixel data 420 is read by the drive transistor and the select transistor.

The column decoder 320 selects unit pixels corresponding to one of the columns of the pixel array. The column decoder 320 selects a next column after all the electric signals of each unit pixel 310-1, 310-2, 310-3, 310-4 included in the selected column are read by the signal reading circuit 340. In other words, the column decoder 320 makes electric signal reading be processed in each column.

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

The signal reading circuit 340 reads electric signals converted by the unit pixels(310-l, 310-2, 310-3, 310-4) on the column that was selected by the column decoder 320.

The fixed pattern noise is caused by offset voltage generated from delicate differences during the manufacturing process. To compensate the difference, the image sensor uses a CDS(correlated double sampling) method outputting the difference between reset signals of each pixel of the pixel array and data signals after reset.

The signal reading circuit 340 may include a CDS circuit to compensate the fixed pattern noise. To compensate the fixed pattern noise the difference between data in reset mode and pixel data is outputted as a signal value. Referring to FIG. 5, the circuit saves reset data 410 in a 1st capacitor 530 by turning on a 1st switch 510, and saves pixel data in a 2nd capacitor 540 by turning on a 2nd switch 520. The signal reading circuit 340 amplifies the difference between the reset data 410 and the pixel data by inputting the reset data 410 saved in the 1st capacitor 530 and the pixel data saved in the 2nd capacitor 540 into a 1 st input terminal and a 2nd input terminal in the differential amplifier 550, respectively. And the signal reading circuit 340 can adjust the gain by outputting the value of difference to an automatic gain controller 560. And the adjusted gain is then output to A/D Converter 350.

The number of the signal reading circuit 340 is m. The number of unit pixels in the selected row and the number of rows are the same, m, so that the signal reading circuit 340 may be placed at each row to read electricsignals. In case of the CMOS image sensor using horizontal scan, the number of signal reading circuits is the same as the number of columns which is n. But, in case of the CMOS image sensor using vertical scan of the present invention, the number of signal reading circuits 340 is the same as that of rows which is m and smaller than that in case of the CMOS image sensor using horizontal scan. As a result, the number of capacitors and amplifiers may be reduced and the chip size of the CMOS image sensor may become smaller.

The A/D converter 350 may convert the electric signals read from the signal reading circuit 340, which are analog signals, into digital signals which can be processed. The number of the A/D converters 350 may be 1 or m. If the number is 1, the A/D converter 350 has m input terminals and each input terminal is connected with m signal reading circuits 340. The A/D converter 350 receives the electric signals, which are read by the signal reading circuit 340 corresponding to the row selected by the row decoder 330, converts the electric signals into output signals which are digital signals, and outputs the output signals through an output buffer 370. If the number is m, each A/D converter 350 is connected with m signal reading circuits 340 and converts the electric signals from the connected signal reading circuits into m output signals through analog-digital conversion. And the m output signals are connected with the output buffer 370 having m input terminals through which the output signals of the input terminal corresponding to the row selected by the row decoder 330 is output outside the chip.

The CMOS image sensor using vertical scan of the present invention may be embodied in one chip

Fig. 8 and Fig. 9 show images of a moving object that are photographed by the CMOS image sensor using vertical scan of the present invention. Images of a moving object are photographed by using the object photographed in Fig.2

Referring to Fig. 8, 'G' letter on the object spinning clockwise (shown as moving right to left) has a shape of rectangle 610. It is apparent that the shape is significantly different from the shape 220 of parallelogram in Fig. 3

Referring to Fig. 9, the letter 'G' on the object spinning clockwise (shown as moving left to right) also has a shape of a rectangle 620.

The CMOS image sensor using vertical scan (method of scanning in the parallel direction to a short side of the pixel array) reduces distortion by the moving object caused with the object moving in the horizontal direction.

An output method of the CMOS image sensor according to an embodiment of the present invention is as follows. The CMOS image sensor includes the pixel array 310 that outputs image data combined one or more unit pixels into m rows and n columns as shown in FIG. 4, wherein m and n are natural numbers and m is smaller than n.

The unit pixel of the CMOS image sensor converts inputted optical signals into electric signals and selects a column of the pixel array using the column decoder 320. The signal reading circuit 340 reads electric signals of each unit pixel included by the selected column. The A/D converter 350 converts the electric signals into output signals through the analog-digital conversion. The output buffer 370 outputs images through the process of outputting the output signals outside the chip

Herein, the column decoder 320 selects a column one by one in a sequential or predetermined order among n columns of the pixel array. After each column is selected and all electric signals of the unit pixels of the selected column are read, a next column is selected, so that the vertical scanning can be performed.

In present invention, the pixel array has less unit pixels in the column direction( m - the number of unit pixels in one row) than unit pixels in the row direction (n - the number of unit pixels in one column). Therefore, the distortion by an object's movement in the column direction is less sensitive than that by the object's movement in the row direction.

While the invention has been described with reference to the disclosed embodiments, it is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the invention or its equivalents as stated below in the claims.

[Industrial Applicability]

As described earlier, the CMOS image sensor using vertical scan in accordance with the present invention can reduce the image distortion of a moving object.

And by reducing the number of signal reading circuits or A/D converters, a total size of chips can be smaller.

Claims

[CLAIMS]

[Claim 1]

A CMOS image sensor, comprising;

a pixel array that includes one or more unit pixels that converts inputted optical signals into electrical signals and outputs image data by combining the unit pixels into m columns and n rows- wherein m and n are natural numbers and m is smaller than n-; a timing control circuit that generates control signals that control timing;

a column decoder that selects a column of the pixel array according to the control signals;

a row decoder that selects a row of the pixel array according to the control signals;

a signal reading circuit that reads electric signals of each unit pixel on the columns selected by the column decoder ;

an A/D converter that converts the electric signals read by the signal reading circuit into output signals through an analog/digital conversion.

[Claim 2]

The CMOS image sensor of claim 1, wherein the row decoder selects a row of each unit pixel included in the column selected by the column decoder.

[Claim 3]

The CMOS image sensor of Claim 2, wherein the row decoder selects each row in correspondence with the order in which the electric signals are applied to the A/D converter from the signal reading circuit according to the control signals.

[Claim 4]

The CMOS image sensor of claim 3, wherein the number of the signal reading circuits is m, and the A/D converter has m number of input terminals that are connected to the m number of the signal reading circuits, respectively.

[Claim 5]

The CMOS image sensor of Claim 2, wherein the row decoder selects each row in correspondence with the order in which the output signals are applied to an output buffer from the A/D converter according to the control signals.

[Claim 6]

The CMOS image sensor of claim 5, wherein the number of the signal reading circuits is m, the number of the A/D converters is m, and the output buffer has m number of input terminals that are connected to the m number of the A/D converters, respectively.

[Claim 7]

A method of image output of a CMOS image sensor which comprises a pixel array outputting image data by combining one or more unit pixels into m rows and n columns -wherein m and n are natural numbers and m is smaller than n-;

the pixel array converting the inputted optical signals into electric signals; a column decoder selecting a column of the pixel array;

a signal reading circuit reading the electric signals of each unit pixel included in the selected column; and

an A/D converter converting the electric signals into output signals through an analog/digital conversion.

[Claim 8]

The method of image output of claim 7, wherein the step of a column decoder selecting a column of the pixel array through the step of an A/D converter converting the electric signals into output signals through an analog/digital conversion is repeated till all the columns of the pixel array are selected.