KR100771117B1 - Image sensor and control method therefor - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor and a control method thereof. According to the present invention, there is provided an image sensor for preventing distortion of a still image, comprising: a photodiode that accumulates charge generated by photoelectric conversion; A pixel array in which a plurality of unit pixels including at least one transistor for transferring charge accumulated in a diode to a floating diffusion region are two-dimensionally arranged; And in the still image capture mode, supply a pulse for simultaneously resetting the photodiodes included in the plurality of unit pixels, and simultaneously transmitting a pulse for transmission to the floating diffusion region to the plurality of unit pixels after a preset time. An image sensor is provided that includes a timing generator for supplying. According to the present invention, it is possible to prevent distortion of a still image and to increase frame transmission rate when capturing a video.

Still Image, Pixel, Reset, Transfer, Timing Generator

Description

Image sensor and its control method {IMAGE SENSOR AND CONTROL METHOD THEREFOR}

1 is a block diagram of a typical CMOS image sensor.

2 is a circuit diagram of each pixel of a typical CMOS image sensor.

Figure 3 is a timing diagram showing the operation of the image sensor in the rolling shutter system according to the prior art.

4 is a block diagram of a camera apparatus including an image sensor according to an exemplary embodiment of the present invention.

5 is a diagram illustrating a pixel array driving mode of an image sensor during image capturing according to an exemplary embodiment of the present invention.

Fig. 6 is a timing chart showing pixel array driving during still image pick-up according to the preferred embodiment of the present invention.

The present invention relates to an image sensor and a control method thereof, and more particularly, to an image sensor and a control method thereof capable of providing an image without distortion during still image capturing.

In the past, analog cameras were generally used. However, in recent years, digital cameras are rapidly being used as digital cameras due to the development of digital processing technology and high pixel integration of image sensors.

A digital camera converts a light signal of a subject into a digital signal, and one of the most necessary is an image sensor. Currently, an image sensor mainly includes a Charged Coupled Device (CCD) and a Complementary Metal Oxide Semiconductor (CMOS) image sensor. It is used.

The dual CMOS image sensor uses metal oxide semiconductors as many as the number of pixels, and uses them as a switching method that sequentially detects the signals output from each pixel. In addition, since signal processing circuits can be integrated on a single chip, they are mainly used for small digital camera devices.

In addition, CMOS has advantages in low manufacturing cost and greatly reducing power consumption.

1 is a block diagram of a general CMOS image sensor, and FIG. 2 is a circuit diagram of each pixel of a general CMOS image sensor.

Referring to FIG. 1, a CMOS image sensor includes a pixel array 110, a row decoder 130, a CDS and a correlated double sampling & analog digital converter 150, and a column decoder 170. do.

In the pixel array 110, unit pixels as illustrated in FIG. 2 are arranged, and a row decoder 130 for designating a row address is disposed in one direction of the pixel array 110, and the pixel data is perpendicular to the pixel array 110. And a column decoder 170 to specify column addresses of the pixels.

The low decoder includes a plurality of low decoder cells including a plurality of gates. The low decoder cell receives an input signal through an address lead line, a transmission signal lead line, a selection signal lead line, and a reset signal lead line, and is input through a reset signal lead line. A reset gate signal output unit for outputting a reset gate signal generated according to an address signal incoming through a reset signal and an address signal lead-in, a selection signal incoming through a selection signal lead-in and an address signal incoming through an address signal lead-in An output signal is output through a selection gate signal output unit for outputting a selection gate signal and a transmission signal output line for outputting a transmission signal input through the transmission signal lead line.

More specifically, the process of extracting data from the CMOS image sensor may be performed by selecting a specific pixel row in the raw decoder 130 and extracting data for each pixel in the selected row in the column decoder 170 and then extracting each pixel. Amplify the data. In this way, data is extracted for the entire pixel of the pixel array.

The extracted pixel data is analog data and is converted into digital data by the CDS and ADC unit 140 and sampled to obtain a high quality image.

The pixel data extraction process will be described with reference to FIG. 2. As shown in FIG. 2, a unit pixel includes a photo diode (PD) for performing photoelectric conversion and a reset for resetting the photo diode by a reset gate signal. Transistor (Rx), transfer transistor (Tx) that transfers the electrons charged in the photodiode to the floating diffusion region in response to the transmission signal, changes the current of the source follower circuit according to the change of the electrode voltage of the floating diffusion region And a select transistor Sx for analogly outputting the output voltage of the unit pixel generated by the voltage change of the floating diffusion region according to the selection gate signal.

Currently, a digital camera having an image sensor such as a CMOS captures a subject by a rolling shutter method. The rolling shutter method sequentially exposes a plurality of pixels arranged in two dimensions in a row unit, and advances them. After the set exposure time, data in each pixel row is sequentially output and read out.

3 is a timing diagram illustrating an operation of an image sensor in a rolling shutter method according to the related art.

Referring to FIG. 3, when a specific row is first selected by the selection gate signal SG, the rolling shutter method resets a specific pixel row by the reset gate signal RG.

Accordingly, the pixel is exposed to light, and the charge accumulated in the photodiode by the transfer gate signal TG is transferred to the floating diffusion region after a preset exposure time (time difference between the reset pulse and the transfer pulse).

In Figure 3, Vout represents the voltage in the i-th row, where a level is the initial voltage of the output node by the selection gate signal, b level is the output node voltage after being reset by the reset gate signal, and c level is the transmission. The voltage level after the transfer to the floating diffusion region is performed by the gate signal, and the voltage difference between the b and c levels means actual pixel data.

 In this manner, pixel data in the i + 1 th row is collected. As shown in FIG. 3, in the rolling shutter method, the reset and the transfer gate signals are sequentially generated for each pixel row, thereby exposing each pixel row. There will be a difference in time.

Therefore, when capturing a still image by a conventional rolling shutter method, there is a problem that image distortion occurs as if an object extending vertically is inclined horizontally.

To solve this problem, a mechanical shutter is used to capture still images, which can apply the same exposure time to each pixel and prevent distorted images even in a situation requiring a short exposure time. Although it can be, this is a separate mechanical device is added, there is a problem in the design problem and the manufacturing cost increase in that it requires a control device for driving it.

In addition, although the mechanical shutter can prevent distortion of still images, the frame transfer rate is remarkably high since the next frame can be transmitted after reset and transfer of all pixels constituting one frame. There was a declining issue.

In the present invention, to solve the problems of the prior art as described above, an image sensor and a control method thereof that can prevent distortion of the image when capturing a still image.

Another object of the present invention is to provide an image sensor and a control method thereof capable of obtaining a still image without distortion in a short exposure time without adding a separate mechanical configuration and control device.

Another object of the present invention is to provide an image sensor and a method of controlling the same, which does not reduce the frame transmission rate related to moving pictures.

In order to achieve the above object, according to a preferred embodiment of the present invention, an image sensor for preventing the distortion of the still image, a photodiode that accumulates the charge generated by the photoelectric conversion, the reset of the photodiode and A pixel array in which a plurality of unit pixels including at least one transistor for transferring charges accumulated in the photodiode to a floating diffusion region are two-dimensionally arranged; And in the still image capture mode, supply a pulse for simultaneously resetting the photodiodes included in the plurality of unit pixels, and simultaneously transmitting a pulse for transmission to the floating diffusion region to the plurality of unit pixels after a preset time. An image sensor is provided that includes a timing generator for supplying.

When the timing generator is in the video capture mode, it is preferable to sequentially supply pulses for the reset and the transmission to each pixel row of the pixel array, wherein the unit pixel resets the potential of the photodiode. A reset transistor, a transfer transistor for transferring charge accumulated in the photodiode, and a selection transistor for outputting a signal corresponding to the potential of the floating diffusion region after the pulse for the transfer is supplied.

According to the present invention, the timing generator is configured to output a signal corresponding to the potential of the floating diffusion region after the selection transistor of each unit pixel for the nth row of the pixel array is turned on. A pulse SHD may be supplied, and the timing generator supplies a pulse for resetting the floating diffusion region of each unit pixel for the nth row of the pixel array, and a signal corresponding to the potential of the reset floating diffusion region. The second sample hold pulse SHR may be supplied to output the second sample hold pulse SHR.

According to another aspect of the invention, a plurality of comprising a photodiode accumulating charge generated by photoelectric conversion, at least one transistor for resetting the photodiode and transferring the charge accumulated in the photodiode to a floating diffusion region. A method for preventing still image distortion in an image sensor including a pixel array in which unit pixels of 2D are arranged, the method comprising: determining a current image capture mode; Supplying a pulse for simultaneously resetting the photodiodes included in the plurality of unit pixels when the current image capture mode is still image capture; And simultaneously supplying pulses for transmission to the floating diffusion region to the plurality of unit pixels after a predetermined time elapses.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of an image sensor and a control method thereof according to the present invention.

4 is a diagram illustrating a camera apparatus including an image sensor according to an exemplary embodiment of the present invention.

As shown in FIG. 4, the camera apparatus according to the present invention includes a lens unit 400, an image sensor 402, an image signal processor 404, a memory controller 406, a codec 408, and a memory. 410 and the CPU 412.

Referring to Figure 4 will be described in detail the image capture process according to the present invention.

Light rays incident through the lens unit 400 are collected in the pixel array of the image sensor 402.

The image sensor 402 may be a CMOS image sensor, and includes a pixel array in which a plurality of unit pixels are arranged in two dimensions, a row decoder assigning addresses in a row direction of the pixel array, and a column in a column direction of each pixel row. It may include a column decoder for assigning an address.

In addition, the unit pixel may include a photodiode that accumulates the charge generated by the photoelectric conversion, a floating diffusion region where the charge accumulated in the photodiode is transferred, and a select / reset / transfer transistor as shown in FIG. 2. These transistors are turned on / off by a select / reset / transmit gate signal, and the gate signal is generated by a pulse supplied by a timing generator (not shown).

Therefore, in the image sensor 402, the driving of the pixel array is controlled by the timing generator. In the timing generator according to the present invention, as shown in FIG. 5, in the continuous capture mode, the general pixel array is rolled. While controlling to operate in a rolling mode (rolling shutter method), it is controlled to operate in a transfer mode in the case of a single capture mode.

When capturing an image, the timing generator supplies a pulse for resetting the photodiode to the pixel array and supplies a pulse for transferring the charge accumulated in the photodiode to the floating diffusion region after a predetermined time elapses.

The preset time difference between reset and transfer corresponds to the exposure (exposure) time of the pixels.When capturing a video, the timing generator sequentially supplies pulses for reset to each pixel row, and the preset exposure for each pixel row. After the elapse of time, the pulse for transmission is also sequentially supplied.

When capturing a video, the pixel array is driven by the rolling capture method, and thus, the frame rate may be increased since the pixel data collection process for the next frame may be performed even before the pixel data collection for one frame is completed. .

However, as described above, when the still image capture is performed by the rolling capture method, distortion of the image may occur. In the case of the still image capture, the timing generator according to the present invention determines the current image capture mode. The same exposure time can be applied to all the pixel rows by simultaneously supplying the pulses for the reset to the pixel rows and simultaneously supplying the pulses for the transmission to all the pixel rows after a predetermined time elapses.

As described above, in the case of the still image capturing, the switching of the driving method of the pixel array requires the transmission to be completed in every pixel row for one frame when the pulses for reset and transmission are simultaneously supplied as described above. This is because there is a problem that it takes a considerable time to obtain a moving picture because the transmission is performed in the next frame.

The pixel data for the still image or the moving image is collected by the above-described reset and transmission process, which is output to the image signal processor 404 shown in FIG.

The image signal processor 404 converts the collected pixel data (RGB data) into actual color data, and converts the RGB data into YUV (YIQ) data including luminance and chromaticity information.

The data converted by the image signal processor 404 is input to the memory controller 406, and after being compressed by the codec 408, is stored in the memory 410.

The controller (CPU) 412 according to the present invention performs the overall control process of each means shown in FIG. 4, and in particular, may control the timing generator to supply pulses in a different manner in a still image or video capture mode.

6 is a timing diagram illustrating an operation of an image sensor during still image capturing according to an exemplary embodiment of the present invention.

Fig. 6 shows the pixel array driving in the case of capturing still images.

Referring to FIG. 6, when capturing a still image, the timing generator supplies a pulse for resetting all unit pixels so that the reset gate signal RG-all is introduced into the reset transistors of all unit pixels.

After a predetermined time has elapsed, i.e., after applying the same exposure time, the timing generator supplies a pulse for transferring charges accumulated in the photodiodes of all the unit pixels to the floating diffusion region and thus transfer gate signal TG-all. ) Is introduced into the transfer transistors of all the unit pixels.

On the other hand, as described above, after the same exposure time is applied to all the unit pixels, and after the transmission gate signal is introduced, the timing generator sequentially selects the selection gate signal (for the pixel row) to collect pixel data stored in each unit pixel. SG-n th) supply the pulse for generation.

After the select gate signal is introduced into a particular pixel row, the timing generator supplies a first sample hold pulse, thereby reading the potential value in the floating diffusion region before reset for the selected pixel row.

The first sample hold pulse may be supplied to the column decoder of FIG. 2, which allows the potential value for the selected pixel row to be output analogously.

As described above, since the potential difference in the floating diffusion region before and after the reset for each pixel row corresponds to the actual pixel data, the timing generator according to the present invention supplies a pulse for resetting the selected pixel row, and thus floating diffusion. The area is reset.

The timing generator then supplies a second sample hold pulse to the column decoder, which allows the potential value of the reset floating diffusion region to be output analogously.

The CDS and the ADC digitally output the value obtained by subtracting the potential value of the floating diffusion region before and after the reset (actual data for the first pixel row) as described above.

After the pixel data of the selected pixel row is collected, the same process is performed on the next pixel row, thereby collecting all pixel data of the still image.

According to the present invention, when the still image and the moving image are captured, the pixel array is driven in different ways, thereby preventing distortion of the still image and increasing the frame transfer rate of the moving image.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit and scope of the present invention. Additions should be considered to be within the scope of the following claims.

As described above, according to the present invention, when capturing a still image, there is an advantage of preventing distortion of the image even when capturing a moving object.

In addition, according to the present invention, when capturing a still image and a video, instead of one capture mode, a different mode is applied to increase the frame transmission rate when capturing a video.

In addition, according to the present invention, when capturing still images, there is an advantage that an image without distortion can be obtained without a separate mechanical configuration and control means.

Claims (10)

An image sensor that prevents distortion of still images, A plurality of unit pixels including a photodiode for accumulating charge generated by photoelectric conversion, at least one transistor for resetting the photodiode and transferring the charge accumulated in the photodiode to a floating diffusion region are arranged in two dimensions. Pixel arrays; And In the still image capture mode, a pulse for simultaneously resetting the photodiodes included in the plurality of unit pixels is supplied, and a pulse for transmission to the floating diffusion region is simultaneously supplied to the plurality of unit pixels after a preset time. Include timing generators, The unit pixel outputs a signal corresponding to a potential of the floating diffusion region after a reset transistor for resetting a potential of the photodiode, a transfer transistor for transferring charge accumulated in the photodiode, and a pulse for the transfer are supplied. An image sensor comprising a selection transistor. The method of claim 1, The timing generator is configured to supply pulses for the reset and transmission sequentially for each pixel row of the pixel array when in the video capture mode. delete The method of claim 1, The timing generator generates a first sample hold pulse SHD for outputting a signal corresponding to the potential of the floating diffusion region after the selection transistor of each unit pixel for the nth row of the pixel array is turned on. Supplying image sensor. The method of claim 4, wherein The timing generator supplies a pulse for resetting the floating diffusion region of each unit pixel for the nth row of the pixel array, and outputs a signal corresponding to the potential of the reset floating diffusion region. Image sensor supplying (SHR). A plurality of unit pixels including a photodiode for accumulating charge generated by photoelectric conversion, at least one transistor for resetting the photodiode and transferring the charge accumulated in the photodiode to a floating diffusion region are arranged in two dimensions. A method of preventing still image distortion in an image sensor including a pixel array, the method comprising: Determining a current image capture mode; Supplying a pulse for simultaneously resetting the photodiodes included in the plurality of unit pixels when the current image capture mode is still image capture; And And simultaneously supplying pulses for transmission to the floating diffusion region to the plurality of unit pixels after a predetermined time elapses. The unit pixel outputs a signal corresponding to a potential of the floating diffusion region after a reset transistor for resetting a potential of the photodiode, a transfer transistor for transferring charge accumulated in the photodiode, and a pulse for the transfer are supplied. An image sensor control method comprising a selection transistor. The method of claim 6, And supplying a pulse for the reset and transmission sequentially for each pixel row of the pixel array when in the video capture mode. delete The method of claim 6, Supplying a first sample hold pulse (SHD) to output a signal corresponding to the potential of the floating diffusion region after the selection transistor of each unit pixel for the nth row of the pixel array is turned on Image sensor control method further comprising. The method of claim 9, Supplying a pulse to reset the floating diffusion region of each unit pixel for the nth row of the pixel array; And And supplying a second sample hold pulse (SHR) to output a signal corresponding to the potential of the reset floating diffusion region.

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