CN111541853B - Method for evaluating dark current of large-area-array color CMOS image sensor after irradiation based on channel separation - Google Patents
Method for evaluating dark current of large-area-array color CMOS image sensor after irradiation based on channel separation Download PDFInfo
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- CN111541853B CN111541853B CN202010385562.8A CN202010385562A CN111541853B CN 111541853 B CN111541853 B CN 111541853B CN 202010385562 A CN202010385562 A CN 202010385562A CN 111541853 B CN111541853 B CN 111541853B
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- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
Abstract
The invention relates to a dark current evaluation method after irradiation of a large-area array color CMOS image sensor based on channel separation, which comprises a static test platform, a three-dimensional sample adjusting platform, a sample test board, a large-area array color CMOS image sensor sample, a direct current power supply and a computer. The invention has convenient and simple operation, and can visually find out the condition of dark current degradation of each channel of the device caused by irradiation. Therefore, theoretical basis and technical support are provided for the anti-radiation design of the large-area array color CMOS image sensor in space application.
Description
Technical Field
The invention belongs to the technical field of performance parameter detection of photoelectric imaging devices, and relates to a method for evaluating dark current of a color image sensor after irradiation based on channel separation.
Background
The photoelectric imaging device is a generic term for an information device that converts an optical radiation image into an image that can be observed, recorded, transmitted, stored, and processed by using the photoelectric effect. The photoelectric imaging device is widely applied to various space optical satellites and effective loads, and is an indispensable core device in space photoelectric systems such as ground remote sensing reconnaissance, target monitoring, star sensors and the like due to the fact that images can be obtained in real time. Compared with a charge coupled device, the CMOS image sensor has the obvious advantages of monolithic integration, high reliability, single voltage, low power consumption, low cost and the like, gradually occupies the field of medium and low-end imaging in space with strict requirements on small volume and light weight, and is widely applied to aspects of star sensors, sun sensors, micro-nano satellite remote sensing, satellite attitude control, airship visual systems, space visual monitoring and the like. With the progress of large-scale integrated circuit technology, the sensitivity and noise performance of some high-performance CMOS image sensors are approaching to the level of charge coupled devices, and charge coupled devices are gradually replaced in the high-end imaging field at home and abroad.
In the natural space radiation environment in which the spacecraft is located, radiation mainly originates from the galaxy cosmic rays, the solar cosmic rays and the terrestrial magnetism capture zone radiation surrounding the earth. The high energy charged particles in the radiation environment act on the CMOS image sensor to influence its performance parameters. The large-area array color CMOS image sensor mostly adopts 8T technology and a global electronic shutter, extra storage nodes are integrated in pixels, a corresponding reading function is realized, the synchronous exposure of all the pixels is guaranteed, the defect of shutter exposure is overcome, a high filling factor is provided, the photoresponse sensitivity and the signal-to-noise ratio are increased, and the chip can realize external triggering and exposure control. Since 8T CMOS image sensors are promoted, the 8T CMOS image sensors are popular with space optical camera designers, and 8T CMOS image sensors are adopted in a plurality of aerospace models in China, such as a staring camera for butt joint targets in the world of Tiangong II and Shenzhou elen, an auxiliary landing camera for Chang' e III and the like.
Taking a large-area-array color image sensor such as CMV12000-2E5C1PA as an example, an output image of the large-area-array color image sensor is an original image in a Bayer format, and when analyzing the change of performance parameters of the large-area-array color image sensor in a radiation environment, data of all channels of pixels R, GB, GR and B must be separated firstly, and then the change of the performance parameters before and after irradiation is calculated respectively according to the separated data. In addition to electrons generated by light, an image sensor also generates electron/hole pairs by thermal excitation, i.e., in the absence of light, the image sensor also generates electrons by thermal excitation, which is referred to as dark current. Dark current is a key parameter characterizing the performance of a CMOS image sensor and is also a sensitive parameter of spatial radiation damage. In the prior art, a large amount of documents research methods for calculating dark currents before and after irradiation of a black-and-white image sensor, but for the large-area-array color image sensor, parameter degradation degrees of output signals of all channels of all pixels after irradiation are different, so that signals of all channels need to be separated through a mathematical method according to the arrangement relation of all channels of a pixel unit of the large-area-array color image sensor, then the dark current of all channels is calculated, and finally, the mechanisms of different degradation degrees of different channels are compared and analyzed. The method for evaluating the dark current of the large-area array color CMOS image sensor based on channel separation after irradiation is not formed at present, but is necessary for radiation resistance and reinforcement of the large-area array color CMOS image sensor. Therefore, the dark current evaluation method after irradiation of the large-area array color CMOS image sensor based on channel separation is provided, the change trend of different channel signals along with irradiation can be mastered, the method has important significance for researching the radiation effect of a device, and theoretical basis and technical support can be provided for the radiation-resistant design of the large-area array color CMOS image sensor in space application.
Disclosure of Invention
The invention aims to solve the limitation of the prior testing technology and provides a dark current evaluation method after irradiation of a large-area array color CMOS image sensor based on channel separation, which relates to a device consisting of a static testing platform, a three-dimensional sample adjusting platform, a sample testing board, a large-area array color CMOS image sensor sample, a direct current power supply and a computer, wherein firstly, under the dark field condition, the integration time is selected, 10 frames of dark field images (RAW format) are obtained and stored by using the irradiated image sensor, then, 16-bit 2-system data of each pixel of the acquired original images are read and converted into 10-system data, corresponding data of different pixel units of the image sensor are classified and placed into gray value matrixes of R, GB, GR or B channels according to coordinates, the average gray value of all pixels of the R, GB, GR and B channels is respectively calculated, and changing the integration time to obtain the average gray values of all pixels of R, GB, GR and B channels under different integration times, finally drawing a curve of the average gray values of all pixels of each channel along with the change of the integration time under the dark field, wherein the slope of a fitting straight line of the curve is divided by the conversion gain of the image sensor to respectively obtain the dark current of each channel. The method is convenient and simple to operate, and can visually find out the specific condition of dark current degradation of each channel of the device caused by irradiation, thereby providing theoretical basis and technical support for the anti-radiation design of the large-area array color CMOS image sensor in space application.
The invention relates to a dark current evaluation method after irradiation of a large-area array color CMOS image sensor based on channel separation, which relates to a device consisting of a static test platform, a three-dimensional sample adjusting platform, a sample test board, a large-area array color CMOS image sensor sample, a direct current power supply and a computer, wherein the static test platform (1) is provided with the three-dimensional sample adjusting platform (2), the three-dimensional sample adjusting platform (2) is fixedly provided with the sample test board (3), the large-area array color CMOS image sensor sample (4) is placed on the sample test board (3), the sample test board (3) is connected with the direct current power supply (5), the static test platform (1) is connected with the computer (6), and the specific operation is carried out according to the following steps:
a. selecting integration time under the dark field condition, and acquiring and storing a RAW format of 10 frames of dark field images by using an irradiated image sensor;
b. reading out 16-bit 2-system data of each pixel of the RAW format original image acquired in the step a;
c. b, converting the 16-bit 2-system data of each pixel read out in the step b into 10-system data, wherein the 10-system data is the gray value of the pixel;
d. the four groups are taken as the abscissa 2m and the ordinate 2n of the circulating unit; abscissa 2m +1, ordinate 2 n; abscissa 2m, ordinate 2n + 1; the gray scale values of pixel units with an abscissa of 2M +1 and an ordinate of 2N +1 are respectively and sequentially read into gray scale value matrixes of R, GB, GR or B channels, wherein M is 0,1,2 … M, N is 0,1,2 … N, M is the width of a large-area-array color CMOS image sensor pixel array, and N is the height of the large-area-array color CMOS image sensor pixel array;
e. respectively calculating the average gray value of all pixels of R, GB, GR or B channels;
f. changing the integration time, and repeating the steps a to e to obtain the average gray values of all pixels of the R, GB, GR or B channels under different integration times;
g. drawing a curve of the average gray value of all pixels of the R channel along with the change of the integration time under a dark field, wherein the slope of a curve fitting line is divided by the conversion gain of the image sensor to obtain the dark current of the R channel;
h. and g, repeating the step g to obtain the dark current of the GB channel, the GR channel or the B channel respectively.
The invention relates to a channel separation-based evaluation method for dark current of a large-area array color CMOS image sensor after irradiation, which utilizes a formula (1) to calculate the average value of gray values of all pixel positions of an R channel under the dark field condition after irradiation, namely muR.dark：
Wherein M is the total row number of the R channel gray value matrix, and N is the total column number of the R channel gray value matrix;
the average of the gray values of all pixel positions of the GB, GR or B channel under dark field conditions is also calculated according to equation (1), M, N being exchanged for the total number of rows and the total number of columns of the corresponding channel gray value matrix.
The method for evaluating the dark current of the large-area array color CMOS image sensor based on channel separation after irradiation is suitable for the color CMOS image sensor with the pixel size of 5.5 mu m x 5.5.5 mu m or larger than the pixel size. The method has the advantages of high accuracy, simplicity, rapidness and strong practicability, and can provide theoretical basis and technical support for the anti-radiation design of a large-area array color CMOS image sensor in space application.
Therefore, the method is suitable for being used by device development units, scientific research institutions and aerospace load units needing to estimate or master the radiation damage degree of the large-area array color CMOS image sensor.
Drawings
FIG. 1 is a schematic diagram of a test system according to the present invention.
Detailed Description
The present invention is described in further detail below with reference to the attached drawing figures.
Examples
The invention relates to a dark current evaluation method after irradiation of a large-area array color CMOS image sensor based on channel separation, which relates to a device, and the method comprises a static test platform, a three-dimensional sample adjusting platform, a sample test board, a large-area array color CMOS image sensor sample, a direct current power supply and a computer, wherein the static test platform 1 is provided with the three-dimensional sample adjusting platform 2, the three-dimensional sample adjusting platform 2 is fixedly provided with the sample test board 3, the sample test board 3 is provided with the large-area array color CMOS image sensor sample 4, the sample test board 3 is connected with the direct current power supply 5, the static test platform 1 is connected with the computer 6, and the specific operation is carried out according to the following steps:
a. before dark field testing, inserting an irradiated large-area array color CMOS image sensor sample 4 (the model is CMV12000) on a sample test board 3, wherein the total dose accumulated after irradiation of the large-area array color CMOS image sensor sample 4 is 30krad (Si), fixing the large-area array color CMOS image sensor sample 4 by using a zero insertion force socket on the sample test board 3, connecting the sample test board 3 with a direct current power supply 5 and a computer 6 respectively, setting the voltage of the direct current power supply to be +28V and grounding, and setting the current limit to be 1A; the driving clock of the sample test board 3 is 125MHz, the resolution of the image output by the test software is 4096X 3072, the integration time is 5ms, the dark field test is started after the direct current power supply 5 and the computer 6 are set, all the illuminating light sources of the test room are required to be closed during the dark field test, the sample 4 of the large area array color CMOS image sensor is covered by an opaque black box, and 10 frames of dark field images (RAW format) are obtained and stored by utilizing the irradiated sample 4 of the large area array color CMOS image sensor;
b. reading out 16-bit 2-system data of each pixel of the acquired RAW format original image;
c. converting the read 16-bit 2-system data of each pixel into 10-system data, wherein the 10-system data is the gray value of the pixel;
d. sequentially reading the gray values of four groups of pixel units with a cyclic unit, wherein the abscissa of the cyclic unit is 2M, and the ordinate of the cyclic unit is 2N into a gray value matrix of an R channel, wherein M is 0,1,2 … M, N is 0,1,2 … N, M is the width of a large-area array color CMOS image sensor pixel array, and N is the height of the large-area array color CMOS image sensor pixel array;
sequentially reading the gray values of the pixel units with the abscissa of 2M +1 and the ordinate of 2N into a gray value matrix of a GB channel, wherein M is 0,1,2 … M, N is 0,1,2 … N, M is the width of a large-area array color CMOS image sensor pixel array, and N is the height of the large-area array color CMOS image sensor pixel array;
sequentially reading gray values of pixel units with the abscissa of 2M and the ordinate of 2N +1 into a gray value matrix of a GR channel, wherein M is 0,1,2 … M, N is 0,1,2 … N, M is the width of a large-area-array color CMOS image sensor pixel array, and N is the height of the large-area-array color CMOS image sensor pixel array;
sequentially reading the gray values of the pixel units with the abscissa of 2M +1 and the ordinate of 2N +1 into a gray value matrix of a B channel, wherein M is 0,1,2 … M, N is 0,1,2 … N, M is the width of a large-area array color CMOS image sensor pixel array, and N is the height of the large-area array color CMOS image sensor pixel array;
e. respectively calculating the average gray value of all pixels of an R channel, a GB channel, a GR channel or a B channel according to a formula (1);
m is the total row number of each channel gray value matrix, and N is the total column number of each channel gray value matrix;
the average gray value of all pixels of the R, GB, GR or B channel calculated according to the formula (1) is shown as data of 5ms of integration time in the table 1;
f. changing the integration time, respectively setting the integration time to be 10ms, 15ms, 20ms and 40ms, and repeating the steps a to e to obtain the average gray values of all pixels of the R, GB, GR or B channels under different integration times;
calculating the average gray value of all pixels of the R, GB, GR or B channel according to the formula (1), as shown by the data of the integration time of 10ms, 15ms, 20ms and 40ms in the table 1;
g. drawing a curve of the average gray value of all pixels of the R channel along with the change of the integration time under a dark field, wherein the slope of a fitted straight line is divided by the conversion gain of the image sensor to obtain the dark current of the R channel, and the dark current of the R channel is 197.9e/s/pix as shown in the table 1;
h. repeating the step g to obtain dark currents of a GB channel, a GR channel or a B channel respectively, wherein as shown in Table 1, the dark current of the GB channel is 199.8e/s/pix, the dark current of the GR channel is 201.1e/s/pix, and the dark current of the B channel is 196.5 e/s/pix;
TABLE 1 results of parameter calculation
It can be seen visually from the table that: with the increase of the integration time, the average gray values of all pixels of R, GB, GR or B channels under the same accumulated dose are gradually increased, and the magnitude of dark current of different channels under the same accumulated dose can be clearly compared, so that deeper mechanism analysis can be conveniently carried out.
The above description is only an embodiment of the method for estimating dark current after irradiation of a large area array color CMOS image sensor based on channel separation according to the present invention, but the scope of the present invention is not limited thereto, and any replacement or addition that can be understood by those skilled in the art within the scope of the present invention should be included in the scope of the present invention.
Claims (1)
1. The method is characterized in that the method relates to a device which comprises a static test platform, a three-dimensional sample adjusting platform, a sample test board, a large-area array color CMOS image sensor sample, a direct current power supply and a computer, wherein the static test platform (1) is provided with the three-dimensional sample adjusting platform (2), the three-dimensional sample adjusting platform (2) is fixedly provided with the sample test board (3), the large-area array color CMOS image sensor sample (4) is placed on the sample test board (3), the sample test board (3) is connected with the direct current power supply (5), the static test platform (1) is connected with the computer (6), and the specific operation is carried out according to the following steps:
a. selecting integration time under the dark field condition, and acquiring and storing a RAW format of 10 frames of dark field images by using an irradiated image sensor;
b. reading out 16-bit 2-system data of each pixel of the RAW format original image acquired in the step a;
c. b, converting the 16-bit 2-system data of each pixel read out in the step b into 10-system data, wherein the 10-system data is the gray value of the pixel;
d. the four groups are taken as the abscissa 2m and the ordinate 2n of the circulating unit; abscissa 2m +1, ordinate 2 n; abscissa 2m, ordinate 2n + 1; the gray values of the pixel units with the abscissa of 2M +1 and the ordinate of 2N +1 are respectively and sequentially read into gray value matrixes of R, GB, GR or B channels, wherein M =0,1,2 … M, N =0,1,2 … N, M is the width of the pixel array of the large-area array color CMOS image sensor, and N is the height of the pixel array of the large-area array color CMOS image sensor;
e. respectively calculating the average gray value of all pixels of R, GB, GR or B channels;
f. changing the integration time, and repeating the steps a to e to obtain the average gray values of all pixels of the R, GB, GR or B channels under different integration times;
g. drawing a curve of the average gray value of all pixels of the R channel along with the change of the integration time under a dark field, wherein the slope of a curve fitting line is divided by the conversion gain of the image sensor to obtain the dark current of the R channel;
h. and g, repeating the step g to obtain the dark current of the GB channel, the GR channel or the B channel respectively.
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