KR20070070991A - Automatic arm current compensation method of image sensor considering temperature and noise compensation - Google Patents

Abstract

The present invention relates to a dark current compensation method of an image sensor capable of effectively compensating a dark current acting as a noise of the image sensor. According to an embodiment of the present invention, a pixel pixel array unit including a plurality of pixels for receiving an image signal and a black line for forming a dark current generated in a state in which light is not collected is formed around the pixel pixel array unit. A dark current compensation method of an image sensor comprising: a first step of forming a dark current compensation value by sampling an image signal from both the pixel array unit and a black line in an idle state in which an integration time is 0; A second step of sampling an image signal from the black line during image sensing to form a dark current value in normal operation; And a third step of compensating the dark current value of the second step by reflecting the dark current compensation value of the first step.

Description

Method for compensating dark current in image sensor in consideration of temperature and noise}

1 is a diagram showing a configuration of a general image sensor.

2 is a diagram illustrating a configuration of an image sensor according to an exemplary embodiment.

3 is a diagram illustrating a configuration of an image sensor according to another exemplary embodiment.

4 is a table showing time control of an image pixel portion and a blackline pixel portion according to the present invention;

5 is a schematic diagram illustrating a method of calculating a dark current value in a black line and a sampled pixel portion in an image pixel portion according to the present invention.

* Explanation of symbols for the main parts of the drawings

30: pixel array unit 33: analog line buffer unit

32a: low decoder 32b: column decoder

51: sum and average block 52: dark current calculation unit

The present invention relates to a dark current compensation method of an image sensor that can prevent degradation of characteristics regardless of the use environment, in particular, a dark current compensation method of an image sensor that can effectively compensate for the dark current acting as noise of the image sensor It is about.

In general, image sensors have specific pixel portions to compensate for dark currents and use metal protected pixel portions to measure only dark currents. This is called a black line, and the pixel array portion that already generates data is called an image pixel portion. Referring to FIG. 1, a conventional image sensor may be digitally programmed through correlated-double sampling (CDS) of signals transmitted from pixels located in the image pixel array unit 11 under control of the control signal generator 10. Signal amplification is performed by the analog amplifier 12, and image data is processed by an ISP (Image Signal Processor) 14 through an ADC converter 13. In addition, the image pixel unit generates fixed pattern noise that degrades the image quality due to the inflow of an analog path or sub-noise, and the black line 15 that blocks the light source inflow to remove the fixed pattern noise. Will be used.

The conventional technique for compensating for dark current in an image sensor is that the black line 15 measures the pure dark current in a pixel in a metal-protected area for blocking light sources and generates the image data in the image pixel portion. By compensating for the dark current value obtained in, the deterioration of image characteristics can be minimized.

However, the black line should be spaced a certain distance from the image pixel portion to block the inflow of the light source, and the pixel array generating the image data because the reference number of the black lines does not accurately represent the dark current compensation value for the entire pixel. There was a problem that the correct compensation for the noise increase due to the dark current compensation and the temperature rise for the parts was problematic.

Meanwhile, US Patent Publication No. 2003 / 0184666A1 discloses a method of adjusting the timing of an updated offset value, which will be described in more detail with reference to FIG. 2.

First, the first pixel group 20 which detects information about an image coming from the outside by arranging pixels horizontally and vertically M (N and M are natural numbers) so as to maximize the response to light. That is, the core pixel array unit and the second pixel group 21 and the light blocking are arranged on one side and the other side in the column direction of the first pixel group 20 to calculate an offset value of the black level with respect to the constituent pixels. The pixel array unit 30 including the third pixel group 22 for changing the offset value of the second pixel group 30 according to the offset value of the black level to remove the offset change caused by the black level. It is comprised with the offset adjustment part 31.

In detail, the analog line buffer unit 33 receives and buffers a signal from the pixel array unit 30, an output of the analog line buffer unit 33, that is, an amplifier 34 for amplifying pixel data and an ADC ( 35 and a row decoder 32a and a column decoder 32b for controlling the rows and columns of the pixel array unit 30 and the pixel array unit 30, respectively, and the offset adjustment unit 31 includes an offset value of the calculated black level and an initial set value. A timing controller 31a for applying to the timing of the updated ADC offset for each of the colors R (red), G (green), and B (blue) according to the difference between the offset values (Initial offset), And an adder 31b for adding the updated offset value provided by the timing controller 31a and the analog pixel data from the first pixel group 20 to compensate for the analog data. The analog line buffer unit 33 serves to sense and store the voltage of the selected one row of pixels, and the amplifier 34, for example, the PGA, amplifies the pixel voltage stored in the analog line buffer unit 33 when it is small. The analog data passed through the amplifier 34 can adjust the gain of RGB for color interpolation and color correction, and is converted into a digital value through the ADC 35 and output.

However, the conventional timing adjustment also has a problem in that it is impossible to calculate an accurate dark current value because it only refers to a black line of a specific region.

Meanwhile, referring to US Patent Publication No. 2005 / 0024502A1, a method of considering an offset through a black line in analog amplification before converting a pixel value to an ADC is disclosed. Specifically, referring to FIG. 3, when the output of the ADC converter and the reference signal (not shown) from the black line are input to generate a correction (error) signal in the digital block, the computing means and The DAC generates an offset voltage that adjusts the gain of the analog amplifier.

However, since the black line does not accurately represent the dark current value used in the image pixel part according to the number and position of the reference pixel, there is a problem in that the accurate dark current value cannot be calculated.

The present invention devised to solve the above problems is to provide a dark current compensation method of the image sensor that can calculate a more accurate dark current value by using the additional dark current compensation value obtained from the pixel portion as well as the black line.

Another object of the present invention is to provide a dark current compensation method of an image sensor capable of obtaining accurate image data by generating a dark current that can effectively compensate for noise of an entire pixel while minimizing additional black lines.

According to an aspect of the present invention, a pixel pixel array unit including a plurality of pixels for receiving an image signal and generating an image signal and a pixel pixel array unit formed around the pixel pixel array unit are generated in a state where light is not collected. A dark current compensation method of an image sensor having a black line for forming a dark current, wherein the dark current compensation value is formed by sampling an image signal from both the pixel array unit and the black line in an idle state of zero integration time. First step; A second step of sampling an image signal from the black line during image sensing to form a dark current value in normal operation; And a third step of compensating the dark current value of the second step by reflecting the dark current compensation value of the first step.

The present invention also provides a pixel pixel array unit including a plurality of pixels for receiving an image signal and forming a dark current generated in a state in which light is not collected by being formed around the pixel pixel array unit. A method of compensating for a dark current of an image sensor having a black line, the method comprising: sampling an image signal from both the pixel array unit and the black line in an idle state with an integration time of 0 to sum and average the sampled signals step; A second step of sampling and averaging the sampled signal from the black line during image sensing; And a third step of compensating the average value of the second step by reflecting the average value of the first step when the average value of the first step is equal to or greater than a specific reference value.

Since the present invention does not accurately represent the dark current value used in the image pixel portion according to the number and position of pixels referring to the black line, the more accurate dark current value is calculated by using the additional dark current compensation value obtained in the image pixel portion.

Hereinafter, the most preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. 4 is a table illustrating time control of an image pixel unit and a black line pixel unit according to the present invention, and FIG. 5 illustrates a method of calculating a dark current value in a black line according to the present invention, and a sampled pixel unit in the image pixel unit. It is a schematic diagram to make.

First, the present invention obtains a dark current in each of the black line and the image pixel portion. According to an embodiment of the present invention, the black line of the structure for generating two dark current compensation values, forming a metal layer to prevent the inflow of the light source to block the light source inlet of the black line determined in the design, the image pixel portion Maintaining a distance from the image pixel portion to the upper and lower sides of the image pixel portion is composed of a total of four black lines, if the area is separated from the image pixel portion by a certain distance to block the light may be arranged in other ways.

The black line of the present invention operates by applying the set value when the image pixel unit normally operates. Therefore, the dark current compensation value of the black line is calculated while the condensing time is not applied and the condensing time is set to zero. In order to calculate the dark current compensation value of the image pixel unit, a blank time in which the sensor does not process image data is used during the sensor control time. Since the pixel parts sampled from the image pixel part can not calculate the dark current compensation value due to the light source flowing in the normal pixel operation state, the light source inflow blocking state is set by setting the condensing time of the pixel part to zero to block the inflow of the light source. . In this state, the dark current compensation value for each pixel of the RGB sampled image pixel portion is obtained. By comparing the dark current compensation value obtained in the black line with the dark current compensation value of a specific sampled image pixel part, a difference in the dark current compensation value due to temperature characteristics and other factors in actual pixels can be obtained.

The difference value is different from the black line dark current compensation value according to temperature and other noise characteristics, and the difference value increases as the temperature increases. The dark current compensation value calculated above calculates the compensation time point and value based on a reference value set by the user to the dark current value of the black line calculated by applying the same setting as the actual pixel part.

Figure 4 shows the time for one frame of image, IDLE SLOT (Time) is the time when the sensor does not perform any operation internally for the external device, the line in the CMOS image sensor using the line scan method in the HBLANK section It is the time to initialize the line before reading, and the section to get the data of actual pixels becomes the HSYNC section. In addition, it consists of HOLD SLOT (Time) for adjusting the condensing time and pixel scan time under specific circumstances in the sensor operation, and VSYNC which informs the external device of the end of one frame.

Referring to FIG. 5, the pixel data is read to obtain a dark current compensation value from the sampled line of the black line and the image pixel unit with the light collection time set to zero on the IDLE time when the sensor does not operate. Calculate the average value. In this case, pixels having a predetermined level are determined to be bad pixels so as not to contribute bad D pixels to the dark current compensation value and are excluded from the average value calculation. That is, the dark current compensation value is formed from each pixel in the black line and the image pixel array unit at the IDLE time (integration time = 0). In the drawing, the area indicated by the dark color sums and averages the signals of all pixels except the bad pixel at the time when the integration time is zero, and is then provided to the dark current calculator 52.

Among the two dark current compensation values calculated as described above, the average value of the dark current compensation value from the black line is used as a reference and compared with the dark current compensation value of the current image pixel unit. The comparison value thus formed may measure the amount of actual flow into the pixel portion due to temperature and other incident noise in the current image pixel portion. Meanwhile, when the comparison value is equal to or greater than a predetermined reference value preset by the user, the comparison value may be reflected in the dark current value or the dark current compensation value.

Subsequently, in order to obtain the dark current value of the black line, the condensing time is set to be the same as when the image pixels operate normally in a total of four lines of black lines, and the dark current value of the black line is obtained in the sum and average block 51. . Among the calculated dark current values and the above-described dark current compensation values, the black line dark current value after the normal operation setting is basically used, but the dark current compensation values contribute to the dark current value when the reference value determined by the user is higher than or equal to.

Although the technical spirit of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

According to the present invention as described above, an accurate dark current value can be calculated by applying a dark current compensation value to the image pixel unit without using only the dark current value of the black line calculated to remove the fixed pattern noise of the pixel. Therefore, it is possible to accurately measure the distance error current value between the black line and the image pixel part, and to reflect the noise effect due to the temperature rise inside the module, and to remove and calculate the noise component flowing into the substrate of the image pixel part, thereby calculating and correcting the image data. There is a great effect in improving the quality of.

Claims (5)

 A pixel pixel array unit having a plurality of pixels for receiving an image signal and forming a video signal, and a black line formed around the pixel pixel array unit to form a dark current generated when no light is collected; In the dark current compensation method of the image sensor, A first step of forming a dark current compensation value by sampling an image signal from both the pixel array unit and the black line in an idle state in which an integration time is 0;  A second step of sampling an image signal from the black line during image sensing to form a dark current value in normal operation; And And a third step of compensating the dark current value of the second step by reflecting the dark current compensation value of the first step. The method of claim 1, The first step includes a fourth step of removing an image of a bad pixel to form the dark current compensation value. The method of claim 1, The first step may include a fifth step of forming a comparison value by comparing the dark current compensation value of the image pixel part based on the average value of the dark current compensation value from the black line. . The method of claim 1, The method, And providing a reference value for compensating for the dark current when the dark current compensation value is within a range of a predetermined specific value. A pixel pixel array unit having a plurality of pixels for receiving an image signal and forming a video signal, and a black line formed around the pixel pixel array unit to form a dark current generated when no light is collected; In the dark current compensation method of the image sensor, A first step of sampling an image signal from both the pixel array unit and the black line in an idle state having an integration time of 0 to sum and average the sampled signals;  A second step of sampling an image signal from the black line and adding and averaging the sampled signal during image sensing; And And a third step of compensating the average value of the second step by reflecting the average value of the first step when the average value of the first step is equal to or greater than a specific reference value.

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