KR20020081656A - Image sensor having bad pixel replacement means - Google Patents

Abstract

PURPOSE: An image sensor having a bad pixel replacing element is provided to obtain good images by replacing bad pixel data to normal pixel data simply and effectively without any damage of image information. CONSTITUTION: An image sensor having a bad pixel replacing element includes a pixel array(10) formed of a plurality of pixels disposed in rows and columns, an analog/digital converter(20) for converting analog signals transmitted from the respective pixels of the pixel array to digital signals, a row-decoder(30) for selecting a row of the pixel array, and a bad pixel data replacement element(40) for replacing bad pixel data to normal pixel data by receiving pixel information from the analog/digital element.

Description

Image sensor having bad pixel replacement means

The present invention relates to an image sensor, and more particularly to an image sensor having a bad pixel replacement means.

A CMOS image sensor converts an optical image into an electrical signal using a CMOS manufacturing technology. The CMOS image sensor converts signal electrons generated in response to light into voltage and reproduces image information through a signal processing process. CMOS image sensor can be used in all fields of image signal reproduction such as various cameras, medical equipment, surveillance cameras, various industrial equipments for positioning and detection, toys, etc. The trend is expanding.

The CMOS image sensor adopts a switching method that makes MOS transistors as many as the number of pixels and uses them to sequentially detect the output. The CMOS image sensor is simpler to drive than the CCD image sensor, which is widely used as a conventional image sensor, and can realize various scanning methods, and can integrate a signal processing circuit into a single chip, thereby miniaturizing the product. The use of compatible CMOS technology reduces manufacturing costs and significantly lowers power consumption. 1 is a circuit diagram showing a unit pixel of a CMOS image sensor composed of four transistors and two capacitance structures, and a unit pixel of a CMOS image sensor composed of a photodiode (PD) as an optical sensing means and four NMOS transistors. . Of the four NMOS transistors, the transfer transistor Tx serves to transport the photocharges generated by the photodiode PD to the floating diffusion region, and the reset transistor Rx is stored in the floating diffusion region for signal detection. It serves to discharge the charge, the drive transistor (Dx) serves as a source follower (Source Follower), the select transistor (Sx) is for switching (Switching) and addressing (Addressing). In the drawing, "Cf" represents capacitance of the floating diffusion region, and "Cp" represents capacitance of the photodiode, respectively.

Operation of the image sensor unit pixel configured as described above is performed as follows. Initially, the unit pixel is reset by turning on the reset transistor Rx, the transfer transistor Tx, and the select transistor Sx. At this time, the photodiode PD starts to deplete, and carrier charging occurs in the photodiode, and the floating diffusion region is charged and stored in proportion to the supply voltage VDD.

The transfer transistor Tx is turned off, the select transistor Sx is turned on, and the reset transistor Rx is turned off. In such an operation state, after reading the first output voltage V1 from the unit pixel output terminal Out and storing the first output voltage V1 in the buffer, the transfer transistor Tx is turned on to float the charges of the photodiode changed according to the light intensity. After that, the second output voltage V2 is read again from the output terminal Out to convert analog data of the two voltage differences 'V1-V2' into digital data, thereby completing one operation cycle for the unit pixel.

Initially, the reset pixel Rx, the transfer transistor Tx, and the select transistor Sx are turned on to reset the unit pixel. At this time, the photodiode PD starts to deplete, and the capacitance Cp generates a carrier change, and the capacitance Cf of the floating diffusion region is charged up to the supply voltage VDD. The transfer transistor Tx is turned off, the select transistor Sx is turned on, and the reset transistor Rx is turned off. In this operation state, after reading the output voltage V1 from the unit pixel output terminal Out and storing it in the buffer, the transfer transistor Tx is turned on to move the carriers of the capacitance Cp changed according to the light intensity to the capacitance Cf. The output voltage V2 is read again from the output terminal, and the analog data for V1-V2 is converted into digital data, thereby completing one operation cycle for the unit pixel. As a technique of replacing defective pixels in a CMOS image sensor, a method of uniformly replacing a defective pixel using a vertical averaging method, a horizontal averaging method, a peripheral averaging method, or the like is used.

The vertical averaging method is a method of replacing the average value of normal pixels below and above a bad pixel, and has a weak point in horizontal high frequency components. In addition, the peripheral averaging method is a method of replacing the average value of normal pixels of the top, bottom, left, and right, and is more vulnerable to high frequency than the vertical and horizontal averaging methods because the average value is replaced when the bad pixel is at the edge.

On the other hand, if there is a bad pixel in the CMOS image sensor, since the pixel does not operate normally and cannot transmit image information, a spot appears on the screen, and thus, normal image display is impossible. In order to solve this problem, conventionally, all high frequency components are removed at a predetermined level, and this method has a problem in that even normal image information is lost.

The present invention for solving the above problems provides an image sensor that can obtain a good image by effectively replacing the defective pixels of the image sensor.

1 is a circuit diagram showing a unit pixel of a conventional CMOS image sensor having four transistors and two capacitance structures;

2 is a block diagram showing a schematic configuration of an image sensor according to the present invention;

3 is a block diagram showing the configuration of the bad pixel data exchanger according to the first embodiment of the present invention;

4 is a graph showing abnormal data of bad pixels;

5 is a block diagram showing the configuration of the bad pixel data exchanger according to the second embodiment of the present invention;

6 is a schematic diagram illustrating a case where a bad pixel is detected in an nth row when there is an oblique image;

Fig. 7 is a block diagram showing the configuration of the bad pixel data exchanger according to the third embodiment of the present invention.

8 is a block diagram showing the configuration of the bad pixel data exchanger according to the fourth embodiment of the present invention;

* Description of reference numerals for the main parts of the drawings *

10: pixel array 20: analog-to-digital converter

30: low-decoder 40: bad pixel data exchange

41: upper and lower limit setting memory 42: comparator

43: Interpreter

44A, 44B, 44C, 44D: Data processing unit 45: Detection unit

46: bad pixel address memory

The present invention for achieving the above object is a pixel array consisting of a plurality of pixels arranged in a row and a column; Analog-digital conversion means for exchanging an analog signal received from each pixel of the pixel array with a digital signal; A low-decoder for selecting a low portion of the pixel array; And bad pixel data exchange means for receiving pixel information from the analog-digital conversion means and replacing bad pixel data with normal pixel data.

The bad pixel data exchanging means includes: upper and lower limit setting memory means for a reference value; Comparison means for searching for a defective pixel from pixel data and data input from the upper and lower limit setting memories; Analyzing means for calculating which of a horizontal component and a vertical component is large in a block of a predetermined size among input pixel data; And data processing means for processing data input from the pixel data, the comparing means, and the analyzing means to output replacement data of the defective pixel.

In addition, the data processing means uses a vertical averaging method because the horizontal image information is large when the vertical component is large when the data for the bad pixel is input from the comparison means, and the horizontal averaging method is used because the vertical image information is large when the horizontal component is large. Normal pixel data corrected by replacing defective pixels is output, and normal pixel data is output as it is if there are no defective pixels.

The defective pixel data exchanging means may further include: an upper limit and a lower limit setting memory of a reference value; Comparison means for searching for a defective pixel from pixel data and data input from the upper and lower limit setting memories; A pre-lo memory for storing data of the n−1 th row immediately preceding the n th row currently read; And data processing means for processing the data input from the pixel data, the comparing means and the pre-lo memory to output replacement data of the defective pixel.

The data processing means, when data for a bad pixel is input from the comparator, replaces the bad pixel value input from the comparator with a data value of another column of the n-1 th row data input from the pre-lo memory. The corrected normal pixel data may be output, and if there is no bad pixel, the normal pixel data may be output as it is.

The defective pixel data exchanging means may further include: an upper limit and a lower limit setting memory of a reference value; Comparison means for searching for a defective pixel from pixel data and data input from the upper and lower limit setting memories; And data processing means for processing the pixel data and the data input from the comparing means to replace the data with data of surrounding pixels when a bad pixel occurs.

In addition, the data processing means outputs corrected normal pixel data by replacing bad pixel data with data of surrounding normal pixels when data for a bad pixel is input from the comparing means. You can also output data.

In addition, the bad pixel data exchange means, the detection means for receiving a pixel data to detect a bad pixel; A bad pixel address memory for storing a bad pixel address input from said detecting means; And data processing means for processing the data input from the pixel data and the bad pixel address memory to replace the data with data of surrounding pixels when a bad pixel occurs.

The present invention uses a horizontal averaging method when there are many horizontal components and a vertical averaging method when there are many horizontal components by setting a pixel block of a predetermined size instead of the conventional method of replacing a defective pixel. It is characterized by increasing the resilience of defective pixels.

In addition, the present invention has another feature of storing the data of the row and restoring the information by using the information when a bad pixel is detected.

In addition, the present invention has another feature to replace and restore the data of the bad pixel with the data value of the normal pixel around the bad pixel.

In addition, the present invention stores the address of the bad pixel deviated from the set value by adjusting the conditions at the initial setting of the image sensor, and in operation, the image is represented by replacing the data value of the bad pixel with the data value of the normal pixels around the There are other features.

FIG. 2 is a block diagram showing a schematic configuration of an image sensor according to the present invention. The pixel array 10 composed of a matrix of photodiodes and an analog signal received from each pixel of the pixel array 10 are digitally converted. The analog-to-digital converter 20 that exchanges the signal, a row decoder 30 that selects a row portion of the pixel array 10, and receives the pixel information from the analog-to-digital converter 20. An image sensor is shown that consists of a bad pixel replacement 40 that replaces bad pixels with surrounding normal pixel data. Fig. 3 is a block diagram showing the configuration of the bad pixel data exchanger 40A according to the first embodiment of the present invention, from the upper and lower limit setting memory 41, the pixel data and the upper and lower limit setting memory 41. A comparator 42 for retrieving bad pixels from the input data, an analyzer 43 for calculating which of the horizontal component and the vertical component is larger in a block of a predetermined size among the input pixel data, the pixel data, the comparator ( 42) and a data processor 44A for processing the data input from the analyzer 43 to output replacement data of the defective pixel.

The upper and lower limit setting memories 41 are places for storing values for discriminating bad pixels. For example, 8 bit pixel information having 256 levels from 0 to 255 is darker as it approaches 0, and brighter as 255. The lower limit is set as the lower limit for dark values of about 0 to 125, and the upper limit is set as upper limit for light values of about 130 to 255, and is stored in the upper and lower limit setting memories 41 and the values are output to the comparator 42. The comparator 42 compares the data received from the upper and lower limit setting memories 41 with the pixel data, searches for a bad pixel, and outputs the result to the data processor 44. That is, as shown in Fig. 4 showing the pixel signal, the pixel representing the signal exceeding the upper limit (or lower limit) is defined as a bad pixel.

The analyzer 43 calculates which of the horizontal component and the vertical component is large in a block of a predetermined size among the input pixel data, and outputs the result to the data processor 44.

The data processor 44A uses the vertical averaging method when the data for the bad pixel is input from the comparator 42, because the horizontal image information is large when the vertical component is large, and the horizontal averaging method is used because the vertical image information is large when the horizontal component is large. The normal pixel data is corrected by substituting the defective pixel, and the normal pixel data is output as it is. Fig. 5 is a block diagram showing the configuration of the bad pixel data exchanger 40B according to the second embodiment of the present invention, from the upper and lower limit setting memory 41, the pixel data and the upper and lower limit setting memory 41; A comparator 42 for retrieving bad pixels from the input data, a pre-row memory 43B for storing data of the n-1 th row immediately preceding the n th row currently read, the pixel data, the comparator And a data processor 44B which processes data input from the pre-lo memory 43B and outputs replacement data of the defective pixels.

The upper and lower limit setting memories 41 are places for storing values for discriminating bad pixels. For example, 8 bit pixel information having 256 levels from 0 to 255 is darker as it approaches 0, and brighter as 255. The lower limit is set as the lower limit for dark values of about 0 to 125, and the upper limit is set as upper limit for light values of about 130 to 255, and is stored in the upper and lower limit setting memories 41 and the values are output to the comparator 42.

The comparator 42 compares the data received from the upper and lower limit setting memories 41 with the pixel data, searches for a bad pixel, and outputs the result to the data processor 44. The pre-lo memory 43B stores the data of the n−1 th row immediately before the n th row that is currently read, and transfers the data to the data processor 44.

The data processor 44B, when data for a bad pixel is input from the comparator 42, stores the bad pixel value input from the comparator 42 among the n−1 th data input from the pre-lo memory 43B. The corrected normal pixel data is output by replacing the data value of another column, and if there is no bad pixel, the normal pixel data is output as it is. FIG. 6 illustrates a case where a bad pixel B is found in an nth row when there is an oblique image. Fig. 7 is a block diagram showing the configuration of the bad pixel data exchanger 40D according to the third embodiment of the present invention, from the upper and lower limit setting memory 41, the pixel data and the upper and lower limit setting memory 41. A comparator 42 for searching for bad pixels from the input data, and a data processor for processing the pixel data and data input from the comparator 42 and replacing the data with data of surrounding pixels when bad pixels are generated ( 44C).

The upper and lower limit setting memories 41 are places for storing values for discriminating bad pixels. For example, 8 bit pixel information having 256 levels from 0 to 255 is darker as it approaches 0, and brighter as 255. The lower limit is set as the lower limit for dark values of about 0 to 125, and the upper limit is set as upper limit for light values of about 130 to 255, and is stored in the upper and lower limit setting memories 41 and the values are output to the comparator 42. The comparator 42 compares the data received from the upper and lower limit setting memories 41 with the pixel data, searches for a bad pixel, and outputs the result to the data processor 44. That is, as shown in Fig. 4 showing the pixel signal, the pixel representing the signal exceeding the upper limit (or lower limit) is defined as a bad pixel.

When the data for the bad pixel is input from the comparator 42, the data processor 44C replaces the bad pixel data with the data of the surrounding normal pixel, and outputs corrected normal pixel data. Output pixel data.

FIG. 8 is a block diagram showing the configuration of the bad pixel data exchanger 40D according to the fourth embodiment of the present invention. The detector 45 detects a bad pixel by receiving pixel data, and is input from the detector 45. Processing the inputted data from the bad pixel address memory 46 and the pixel data and the bad pixel address memory 46 to store the bad pixel address, and when the bad pixel is generated, replaces the data with data of surrounding pixels and outputs the bad pixel address. It consists of the data processing part 44D.

In the case of dark defective pixels, the integration time is set to '0'. At this time, since no light enters the photodiode, all pixel data should be specified as '0', but in case of bad pixels, the value is larger than '0'. Is measured. In the case of the white bad pixel, the focusing time is set to infinity, and in this case, the data of the normal pixel is specified as '0'.

The data processor 44D receives the pixel data and the data from the bad pixel address memory 46 and, when a bad pixel occurs, replaces the data with data of surrounding pixels to output corrected normal pixel data. If none, normal pixel data is output as is.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

According to the present invention made as described above, a good image can be obtained by easily and effectively replacing defective pixels. In addition, unlike the conventional technology of removing data over a predetermined frequency to remove high frequency components, it is possible to prevent loss of image information by replacing only data of a specific bad pixel. In addition, the use of an image sensor chip with defective pixels can be expected to increase the actual production yield, thereby reducing the cost of the product.

Claims (9)

In the image sensor, A pixel array comprising a plurality of pixels arranged in rows and columns; Analog-digital conversion means for exchanging an analog signal received from each pixel of the pixel array with a digital signal; A low-decoder for selecting a low portion of the pixel array; And Bad pixel data exchange means for receiving pixel information from the analog-digital converting means and replacing bad pixel data with normal pixel data. Image sensor comprising a. The method of claim 1, The bad pixel data exchange means, Memory means for setting upper and lower limits of the reference value; Comparison means for searching for a defective pixel from pixel data and data input from the upper and lower limit setting memories; Analyzing means for calculating which of a horizontal component and a vertical component is large in a block of a predetermined size among input pixel data; And And data processing means for processing the data inputted from the pixel data, the comparing means and the analyzing means to output replacement data of the defective pixel. The method of claim 2, The data processing means, When the data about the bad pixels is input from the comparison means, the vertical average method is used because the horizontal image information is large when the vertical component is large, and the vertical average method is used because the vertical image information is large when the horizontal component is large. Normal pixel data, If there are no bad pixels, the image sensor characterized in that it outputs the normal pixel data as it is. The method of claim 1, The bad pixel data exchange means, Upper and lower limit setting memories of the reference value; Comparison means for searching for a defective pixel from pixel data and data input from the upper and lower limit setting memories; A pre-lo memory for storing data of the n−1 th row immediately preceding the n th row currently read; And And data processing means for processing data input from said pixel data, said comparing means and pre-lo memory to output replacement data of a bad pixel. The method of claim 4, wherein The data processing means, When the data for the bad pixel is input from the comparing means, the normal pixel data corrected by replacing the bad pixel value input from the comparator with the data value of another column among the n-1th low data input from the pre-lo memory is replaced. And normal pixel data as it is if there are no bad pixels. The method of claim 1, The bad pixel data exchange means, Upper and lower limit setting memories of the reference value; Comparison means for searching for a defective pixel from pixel data and data input from the upper and lower limit setting memories; And And data processing means for processing the pixel data and the data input from the comparing means to replace the data with data of surrounding pixels when a bad pixel occurs. The method of claim 6, The data processing means, When the data about the bad pixel is input from the comparing means, the corrected pixel data is output by replacing the bad pixel data with data of surrounding normal pixels, and If there are no bad pixels, the image sensor characterized in that it outputs the normal pixel data as it is. The method of claim 1, The bad pixel data exchange means, Detection means for receiving pixel data and detecting defective pixels; A bad pixel address memory for storing a bad pixel address input from said detecting means; And And data processing means for processing the inputted data from the pixel data and the bad pixel address memory and replacing the data with data of surrounding pixels when a bad pixel occurs. The method of claim 8, The data processing means, When data is received from the pixel data and the bad pixel address memory and a bad pixel occurs, the corrected pixel data is output by replacing the data with data of surrounding pixels, If there are no bad pixels, the image sensor characterized in that it outputs the normal pixel data as it is.