Device for testing charge transfer efficiency of time delay integral CMOS image sensor after irradiation

Abstract

The invention relates to a device for testing charge transfer efficiency of a time delay integral CMOS image sensor after irradiation. The device is composed of a support, an LED strip-shaped light source, a digital light source controller, a signal amplifier, a neutral dimmer, the time delay integral CMOS image sensor, a test board, a direct-current power source and a computer. When a light field image is collected, the sensor is firstly in a regional mode so that pixels can be exposed, then the sensor is switched into a time delay integral mode, the light source is synchronously closed so as to read the pixel array, and the LED strip-shaped light source is driven through an external trigger port of the digital light source controller. In order to meet a pixel gray value required by a light field test, the invention provides a multi-stage light intensity regulation and control mechanism: the distance of a light source is changed by regulating the height of a bracket, dimming is realized by utilizing a digital light source controller, and neutral density optical filters with different attenuation coefficients are selected for optical modulation. The device has the remarkable technical advantages of being high in measurement precision, good in result repeatability, simple in structure, convenient to construct, high in operation practicability and the like.

Description

Technical Field

[0001] The present invention relates to the field of image sensor performance testing, and in particular to a device for testing the charge transfer efficiency of a time delay integration (TDI) CMOS image sensor after irradiation. Background Art

[0002] Time Delay Integration (TDI) CMOS image sensors utilize time delay integration technology, primarily for accurately capturing objects in high-speed motion. Their basic operating principle is to incorporate multiple memory cells within the image sensor to acquire and store image data line by line, effectively accumulating information from adjacent lines and thus improving image quality. This technology has broad application prospects in fields such as satellite remote sensing, medical imaging, and industrial inspection, attracting considerable attention for its high sensitivity, low noise, and high-speed imaging.

[0003] When used as imaging components in space cameras for remote sensing missions, time-delay integration (TDI) CMOS image sensors are susceptible to the effects of various particles in the space radiation environment, causing performance degradation. Charge transfer efficiency, a key parameter for measuring sensor performance, refers to the ratio of charge successfully transferred from one pixel to the next during vertical charge transfer in a TDI CMOS image sensor. Space radiation introduces various defects, causing some charge to be retained, thereby reducing charge transfer efficiency.

[0004] To address the shortcomings of existing device testing equipment, such as high complexity, low efficiency, poor reliability, and limited portability, and considering the need for rapid and accurate testing between different dose / fluence points after irradiation, the overall structure of the device has been improved and the testing procedures have been simplified. This test device can efficiently and accurately test charge transfer efficiency, is easy to set up and carry, and provides strong support for the reliability evaluation of space cameras. Summary of the Invention

[0005] The present invention addresses the shortcomings of existing testing devices and proposes a device for testing the charge transfer efficiency of a time-delayed integration (TDI) CMOS image sensor after irradiation. The device comprises a bracket, an LED bar light source, a digital light source controller, a signal amplifier, a neutral density filter (NDF), a TDI CMOS image sensor, a test board, a DC power supply, and a computer. The charge transfer efficiency test requires simultaneous acquisition of light-field and dark-field images. During light-field image acquisition, the sensor is first placed in area mode to expose pixels, then switched to TDI mode with the light source turned off to read the pixel array. The light source is switched on and off by a square wave signal from the test board. The square wave signal is amplified by the signal amplifier and externally triggered by the digital light source controller to drive the LED bar light source. Light intensity is controlled by varying the bracket height, adjusting the digital light source controller, and the NDF, ensuring that pixel grayscale values ​​reach approximately 50% of the full well capacity. This device is suitable for testing the charge transfer efficiency of TDI CMOS image sensors after irradiation and offers advantages such as ease of construction, high accuracy, good repeatability, and strong practicality.

[0006] The present invention discloses a device for testing the charge transfer efficiency of a time-delayed integration CMOS image sensor after irradiation. The device comprises a bracket (1), an LED strip light source (2), a neutral light reduction film (3), a time-delayed integration CMOS image sensor (4), a test board (5), a signal amplifier (6), a computer (7), a digital light source controller (8), a first DC power supply (9), and a second DC power supply (10); the bracket (1) fixes the LED strip light source (2), and the neutral light reduction film (3) is placed directly above the time-delayed integration CMOS image sensor (4); the square wave signal output port of the test board (5) is connected to the signal amplifier (6), and the data output transmission port is connected to the computer (7); the LED strip light source (2) is connected to the digital light source controller (8); the first DC power supply (9) supplies power to the test board (5), and the second DC power supply (10) supplies power to the signal amplifier (6). The specific operation is performed according to the following steps:

[0007] a. Based on the on-orbit operating environment of a push-broom space camera, the parameters of the equivalent ground irradiation experiment are determined for the dose / fluence rate and cumulative dose / fluence in its typical space radiation environment, and the irradiation effect experiment of the time-delayed integration CMOS image sensor (4) under the corresponding cumulative total dose / fluence is carried out;

[0008] b. Open the charge transfer efficiency mode on the computer (7) software, set the line frequency to 5kHz, turn off the LED strip light source (2), prepare to start the dark field test in the dark room, and cover the time delay integration CMOS image sensor (4) with an opaque black box; select the maximum integration level of 256 and the minimum integration level of 4 in the dark field, respectively, to collect 20 frames of images and save them;

[0009] c. Turn on the LED strip light source (2) and remove the opaque black box. Set the light intensity to 50% of the full well capacity of the time-delayed integration CMOS image sensor (4). Start the light field test. The computer (7) controls the test board (5) to output a square wave signal. After amplification by the signal amplifier (6), the signal is sent to the digital light source controller (8). The digital light source controller (8) turns on and off the LED strip light source (2) through an external trigger function. The uniform light passes through the neutral light reduction film (3) and reaches the time-delayed integration CMOS image sensor (4). Under the light field, select the maximum integration level of 256 and the minimum integration level of 4 to collect 20 frames of images for storage.

[0010] d. Divide the light field and dark field images collected at the maximum integration level of 256 and the minimum integration level of 4 into three areas: the original signal area, the trailing area, and the background area. Calculate the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area.

[0011] According to the image sensor performance test standard, the average grayscale value of each pixel position μ y The calculation formula is as follows:

[0012]

[0013] Where m and n represent the position of a grayscale pixel in the 20-frame image, 1≤m≤9288, 1≤n≤2800;

[0014] The average gray value μ of the pixel position in the specified area y The calculation formula is as follows:

[0015]

[0016] Where M and N represent the number of columns and rows in the specified area, 1≤M≤9288, 1≤N≤2800.

[0017] e. The grayscale value calculation formula of the trailing area is:

[0018] Trailing area = 50 lines of trailing area - 50 lines of background area (3)

[0019] Subtract the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area in the light field under the maximum integration level of 256 and the minimum integration level of 4 from the grayscale values ​​of the same areas in the dark field to obtain the average grayscale value of the original signal area, the average grayscale value of the trailing area with the maximum integration level of 256, and the average grayscale value of the trailing area with the minimum integration level of 4;

[0020] f. The calculation formula of charge transfer efficiency is as follows:

[0021]

[0022] Repeat steps a to f to complete data collection and calculation for each dose / fluence point after irradiation.

[0023] The present invention describes a device for testing the charge transfer efficiency of a time delay integration (TDI) CMOS image sensor after irradiation. This device addresses the shortcomings of existing device testing devices, such as high complexity, low efficiency, poor reliability, and limited portability. Taking into account the need for rapid and accurate testing between different dose / fluence points after irradiation, the device improves its overall architecture and simplifies the testing procedures. This device can efficiently and accurately test charge transfer efficiency, is easy to build, and is portable, providing strong support for the reliability assessment of space cameras.

[0024] The present invention proposes a test device for the charge transfer efficiency of a time delay integration (TDI) CMOS image sensor after irradiation. The test device comprises a bracket, an LED bar light source, a digital light source controller, a signal amplifier, a neutral density filter (NDF), a TDI CMOS image sensor, a test board, a DC power supply, and a computer. When measuring the charge transfer efficiency of a TDI CMOS image sensor, its photosensitive area easily reaches saturation. To overcome this problem, a neutral density filter is used to attenuate the incident light intensity. Furthermore, when using a pulse-width modulation-based digital light source controller to adjust the brightness level of the LED bar light source, this can cause uneven brightness between rows (bright and dark rows) in the sensor output image. By adding a neutral density filter between the light source and the sensor, this inter-row unevenness can be effectively eliminated. In the test system, the DC power supply powering the LED bar light source has an output voltage set to the rated drive voltage of the light source. Furthermore, light intensity can be adjusted by adjusting the vertical height (axial distance) of the LED bar light source on the mounting bracket relative to the sensor under test.

[0025] The present invention provides the following beneficial effects: The signal amplifier can amplify the amplitude of square wave signals according to the driving requirements of LED strip light sources, thereby adapting to light sources of varying specifications. To meet the pixel grayscale values ​​required for light field testing (approximately 50% of the full well capacity), the present invention provides a multi-level light intensity control mechanism: adjusting the light source distance by adjusting the height of the bracket, dimming using a digital light source controller, and optical modulation using neutral density filters with different attenuation coefficients. This complex adjustment scheme efficiently and accurately meets the light intensity requirements of the desired test scenario. The core design of the device significantly reduces system complexity and manufacturing costs. Its construction primarily utilizes widely available and readily available standard commercial electronic components and universal modules. The optimized overall structure of the device boasts a high degree of integration and compactness, significantly enhancing its portability and enabling easy deployment and operation in various laboratory environments or field conditions. This self-contained system efficiently and reliably characterizes and accurately evaluates the key performance parameter of TDI CMOS devices, charge transfer efficiency, without relying on large or expensive specialized testing equipment, providing an economical, convenient, and practical solution for post-irradiation device performance testing. The present invention belongs to the field of image sensor testing technology. Its device and technical solution have the characteristics of convenient deployment, high measurement accuracy, good result repeatability, and strong practicality. It can provide solid technical support for the reliability verification of the core imaging components of push-broom space cameras. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A block diagram showing the connection relationship between the components of the device of the present invention;

[0027] Figure 2 Schematic diagram of the composition and working principle of the device of the present invention;

[0028] Figure 3 Flow chart of the charge transfer efficiency test steps of the present invention;

[0029] Figure 4 This is a schematic diagram of the working time of regional mode;

[0030] Figure 5 Schematic diagram of the original signal area, tailing area, and background area;

[0031] Figure 6 is the change of charge transfer efficiency under different irradiation doses.

[0032] In the figure, (1) bracket, (2) LED strip light source, (3) neutral density filter, (4) TDI CMOS image sensor, (5) test board, (6) signal amplifier, (7) computer, (8) digital light source controller, (9) first DC power supply, and (10) second DC power supply. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0034] Example

[0035] The present invention discloses a device for testing the charge transfer efficiency of a time-delayed integration CMOS image sensor after irradiation. The device comprises a bracket 1, an LED bar light source 2, a neutral light reduction filter 3, a time-delayed integration CMOS image sensor 4, a test board 5, a signal amplifier 6, a computer 7, a digital light source controller 8, a first DC power supply 9, and a second DC power supply 10. The bracket 1 fixes the LED bar light source 2, and the neutral light reduction filter 3 is placed directly above the time-delayed integration CMOS image sensor 4. The square wave signal output port of the test board 5 is connected to the signal amplifier 6, and the data output transmission port is connected to the computer 7. The LED bar light source 2 is connected to the digital light source controller 8. The first DC power supply 9 supplies power to the test board 5, and the second DC power supply 10 supplies power to the signal amplifier 6. The specific operation is performed according to the following steps:

[0036] a. Based on the on-orbit operating environment of a push-broom space camera, determine the parameters of an equivalent ground irradiation experiment for the dose / fluence rate and cumulative dose / fluence in a typical space radiation environment, and conduct an irradiation effect experiment on a time-delayed integration CMOS image sensor 4 under the corresponding cumulative total dose / fluence;

[0037] b. Enable the charge transfer efficiency mode on the computer 7 software, set the line frequency to 5 kHz, turn off the LED strip light source 2, and prepare to begin a dark field test in a dark room. Cover the time-delayed integration CMOS image sensor 4 with an opaque black box. Select the maximum integration level of 256 and the minimum integration level of 4 in the dark field, and capture 20 frames of images for storage.

[0038] c. Turn on the LED bar light source 2 and remove the opaque black box. Set the light intensity to 50% of the full well capacity of the time-delayed integration CMOS image sensor 4, and begin the light field test. Computer 7 controls the test board 5 to output a square wave signal, which is amplified by signal amplifier 6 and then transmitted to the digital light source controller 8. The digital light source controller 8 uses an external trigger function to turn the LED bar light source 2 on and off. Uniform light passes through the neutral light reduction filter 3 and reaches the time-delayed integration CMOS image sensor 4. Under the light field, select the maximum integration level of 256 and the minimum integration level of 4, respectively, to collect and save 20 frames of images;

[0039] d. Divide the light field and dark field images collected at the maximum integration level of 256 and the minimum integration level of 4 into three areas: the original signal area, the trailing area, and the background area. Calculate the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area.

[0040] According to the image sensor performance test standard, the average grayscale value of each pixel position μ y The calculation formula is as follows:

[0041]

[0042] Where m and n represent the position of a grayscale pixel in the 20-frame image, 1≤m≤9288, 1≤n≤2800;

[0043] The average gray value μ of the pixel position in the specified area y The calculation formula is as follows:

[0044]

[0045] Where M and N represent the number of columns and rows in the specified area, 1≤m≤9288, 1≤N≤2800;

[0046] e. The grayscale value calculation formula of the trailing area is:

[0047] Trailing area = 50 lines of trailing area - 50 lines of background area (3)

[0048] Subtract the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area in the light field under the maximum integration level of 256 and the minimum integration level of 4 from the grayscale values ​​of the same areas in the dark field to obtain the average grayscale value of the original signal area, the average grayscale value of the trailing area with the maximum integration level of 256, and the average grayscale value of the trailing area with the minimum integration level of 4;

[0049] f. The calculation formula of charge transfer efficiency is as follows:

[0050]

[0051] Repeat steps a to f to complete data collection and calculation at each dose / fluence point after irradiation;

[0052] like Figure 1 and Figure 2As shown, a device for testing the charge transfer efficiency of a time-delayed integration CMOS image sensor after irradiation according to the present invention comprises a bracket 1, an LED bar light source 2, a neutral light reduction filter 3, a time-delayed integration CMOS image sensor 4, a test board 5, a signal amplifier 6, a computer 7, a digital light source controller 8, a first DC power supply 9, and a second DC power supply 10. The bracket 1 fixes the LED bar light source 2, and the neutral light reduction filter 3 is placed directly above the time-delayed integration CMOS image sensor 4. The square wave signal output port of the test board 5 is connected to the signal amplifier 6, and the data output transmission port is connected to the computer 7. The LED bar light source 2 is connected to the digital light source controller 8. The first DC power supply 9 supplies power to the test board 5, and the second DC power supply 10 supplies power to the signal amplifier 6. The specific operation is performed according to the following steps:

[0053] The GLT5009BSI is a back-illuminated, time-delayed, and charge-domain CMOS image sensor with a 5μm pixel size and 9072 effective resolution. This sensor utilizes a dual-band design (256 and 32 levels) and leverages advanced back-illuminated scientific-grade CMOS technology to maximize sensitivity across the ultraviolet to near-infrared spectrum. It is specifically developed to meet the demands of high-speed and low-light applications. The cumulative gamma-ray dose points are 11.25 krad(Si), 22.5 krad(Si), 33.75 krad(Si), 45 krad(Si), and 70 krad(Si), with a dose rate of 50 rad(Si) / s. During irradiation, the device pins are shorted and unpowered.

[0054] b. Before the test begins, insert the time-delayed integration CMOS image sensor 4 onto the test board 5 and secure it. Then, connect the test board 5 to the first DC power supply 9 and the computer 7. Set both circuits of the first DC power supply 9 to +12V, set the current limit of the first circuit to 3A, and the current limit of the second circuit to 2A. The configuration parameters and timing of the test board 5 are provided by Gpixel Optoelectronics Technology Co., Ltd. The 12-bit mode with a maximum line frequency of 300kHz was used in this test. Open the software on the computer 7 to enable the charge transfer efficiency mode, set the line frequency to 5kHz, and the number of image acquisition frames to 20. The dark field test was conducted in a darkroom at 25°C. Before the test began, turn off the LED bar light source 2 and other light sources, and cover the time-delayed integration CMOS image sensor 4 with an opaque black box. Under dark field conditions, select a maximum integration level of 256 and a minimum integration level of 4 to capture and save 20 frames of images.

[0055] c. Turn on the LED strip light source 2 and remove the opaque black box. The light intensity is controlled by changing the bracket height, adjusting the digital light source controller, and the neutral density filter. The intensity is set to approximately 50% of the full well capacity of the time-delayed integration CMOS image sensor 4, and then a light field test is initiated. A computer 7 controls the test board 5 to output a square wave signal, which is amplified by a signal amplifier 6 and then transmitted to the digital light source controller 8. The light source controller 8 uses an external trigger function to turn the LED strip light source 2 on and off. Uniform light passes through the neutral density filter 3 and reaches the time-delayed integration CMOS image sensor 4. Under the light field, a maximum integration level of 256 and a minimum integration level of 4 are selected. Twenty frames of images are collected and saved.

[0056] d. Divide the light field and dark field images collected at the maximum integration level of 256 and the minimum integration level of 4 into three areas: the original signal area, the trailing area, and the background area. Calculate the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area.

[0057] According to the image sensor performance test standard, the average grayscale value of each pixel position μ y The calculation formula is as follows:

[0058]

[0059] Where m and n represent the position of a grayscale pixel in the 20-frame image, 1≤m≤9288, 1≤n≤2800;

[0060] The average gray value μ of the pixel position in the specified area y The calculation formula is as follows:

[0061]

[0062] Where M and N represent the number of columns and rows in the specified area, 1≤M≤9288, 1≤N≤2800;

[0063] e. The grayscale value calculation formula of the trailing area is:

[0064] Trailing area = 50 lines of trailing area - 50 lines of background area (3)

[0065] The grayscale values ​​of the original signal area, 50 lines of the tailing area, and 50 lines of the background area in the light field under the maximum integration level of 256 and the minimum integration level of 4 are subtracted from the grayscale values ​​of the same areas in the dark field; the average grayscale value of the original signal area, the average grayscale value of the tailing area with the maximum integration level of 256, and the average grayscale value of the tailing area with the minimum integration level of 4 are obtained; taking a cumulative dose of 70 krad (Si) as an example, the average grayscale value of the original signal area calculated by the above formula is 967.64, the average grayscale value of the tailing area with the maximum integration level of 256 is 116.92, and the average grayscale value of the tailing area with the minimum integration level of 4 is 8.58;

[0066] f. The calculation formula of charge transfer efficiency is as follows:

[0067]

[0068] Substituting the formula into the calculation, the charge transfer efficiency of the time-delayed integration CMOS image sensor 4 is 99.9851901%, while the charge before irradiation is 99.9962%, indicating that the defects introduced by γ-ray irradiation cause some charges to be retained, and the charge transfer efficiency is significantly reduced. The changes in charge transfer efficiency at each dose point after irradiation are shown in the figure below. Figure 6 As shown in the figure, this device can reflect the impact of defects introduced by irradiation on the charge transfer efficiency of time delay integration (TDI) CMOS image sensors. Compared with other devices, it has the advantages of convenient deployment, high measurement accuracy, good result repeatability, and strong practicality. It can provide a solid technical guarantee for the reliability verification of the core imaging components of push-broom space cameras.

[0069] The above is merely a specific embodiment of a device for testing the charge transfer efficiency of a time delay integration (TDI) CMOS image sensor after irradiation according to the present invention. However, the scope of protection of the present invention is not limited thereto. Any substitutions, additions, or deletions that can be understood by anyone familiar with the technology within the technical scope disclosed by the present invention should be included within the scope of the present invention.

Claims

1. A device for testing the charge transfer efficiency of a time-delayed integration CMOS image sensor after irradiation, characterized in that: The device is composed of a bracket (1), an LED strip light source (2), a neutral light reduction film (3), a time-delayed integration CMOS image sensor (4), a test board (5), a signal amplifier (6), a computer (7), a digital light source controller (8), a first DC power supply (9), and a second DC power supply (10); the bracket (1) fixes the LED strip light source (2), and the neutral light reduction film (3) is placed directly above the time-delayed integration CMOS image sensor (4); the square wave signal output port of the test board (5) is connected to the signal amplifier (6), and the data output transmission port is connected to the computer (7); the LED strip light source (2) is connected to the digital light source controller (8); the first DC power supply (9) supplies power to the test board (5), and the second DC power supply (10) supplies power to the signal amplifier (6). The specific operation is carried out according to the following steps: a. Based on the on-orbit operating environment of a push-broom space camera, the parameters of the equivalent ground irradiation experiment are determined for the dose / fluence rate and cumulative dose / fluence in its typical space radiation environment, and the irradiation effect experiment of the time-delayed integration CMOS image sensor (4) under the corresponding cumulative total dose / fluence is carried out; b. Open the charge transfer efficiency mode on the computer (7) software, set the line frequency to 5kHz, turn off the LED strip light source (2), prepare to start the dark field test in the dark room, and cover the time delay integration CMOS image sensor (4) with an opaque black box; select the maximum integration level of 256 and the minimum integration level of 4 in the dark field, respectively, to collect 20 frames of images and save them; c. Turn on the LED strip light source (2) and remove the opaque black box. Set the light intensity to 50% of the full well capacity of the time-delayed integration CMOS image sensor (4). Start the light field test. The computer (7) controls the test board (5) to output a square wave signal. After amplification by the signal amplifier (6), the signal is sent to the digital light source controller (8). The digital light source controller (8) turns on and off the LED strip light source (2) through an external trigger function. The uniform light passes through the neutral light reduction film (3) and reaches the time-delayed integration CMOS image sensor (4). Under the light field, select the maximum integration level of 256 and the minimum integration level of 4 to collect 20 frames of images for storage. d. Divide the light field and dark field images collected at the maximum integration level of 256 and the minimum integration level of 4 into three areas: the original signal area, the trailing area, and the background area. Calculate the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area. According to the image sensor performance test standard, the average grayscale value of each pixel position μ y The calculation formula is as follows: Where m and n represent the position of a grayscale pixel in the 20-frame image, 1≤m≤9288, 1≤n≤2800; The average gray value μ of the pixel position in the specified area y The calculation formula is as follows: Where M and N represent the number of columns and rows in the specified area, 1≤M≤9288, 1≤N≤2800; e. The grayscale value calculation formula of the trailing area is: Trailing area = 50 lines of trailing area - 50 lines of background area (3) Subtract the grayscale values ​​of the original signal area, 50 lines of the trailing area, and 50 lines of the background area in the light field under the maximum integration level of 256 and the minimum integration level of 4 from the grayscale values ​​of the same areas in the dark field to obtain the average grayscale value of the original signal area, the average grayscale value of the trailing area with the maximum integration level of 256, and the average grayscale value of the trailing area with the minimum integration level of 4; f. The calculation formula of charge transfer efficiency is as follows: Repeat steps a to f to complete data collection and calculation for each dose / fluence point after irradiation.

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