Dark current pixel level suppression circuit and method for a cmos image sensor

Abstract

The application discloses a dark current pixel level suppression circuit and method of a CMOS image sensor, and belongs to the technical field of dark current pixel level suppression. The method comprises the following steps: without starting dark current calibration, scanning the temperature of the CMOS image sensor from high to low under dark light, measuring the corresponding dark current value at each temperature, and obtaining the corresponding relationship between the temperature and the dark current in the working temperature range; adjusting the voltage value of the dark current overflow gate step by step, so that the dark current is offset at the temperature value, and a temperature and overflow gate voltage corresponding relationship table is formed; when starting the dark current calibration, the CMOS image sensor first performs temperature detection to obtain the current working temperature; and based on the working temperature and the temperature and overflow gate voltage corresponding relationship table, the opening degree of the dark current overflow gate is adjusted to complete the dark current discharge. Through the temperature-dark current overflow matching technology and the intelligent pixel level suppression method of the dark current, the dark current occupying the full well capacity of the photodiode caused by the rapid growth of the dark current under high temperature is avoided.

Description

Technical Field

[0001] This invention belongs to the field of dark current pixel-level suppression technology, and relates to a dark current pixel-level suppression circuit and method for CMOS image sensors. Background Technology

[0002] Image sensors are widely used in airborne cameras, civilian surveillance, and automotive imaging, requiring them to maintain stable imaging under varying temperatures. The ambient temperature significantly impacts dark current in image sensors. Due to the unique properties of dark current, it exhibits an exponential trend with increasing temperature. Dark current increases with temperature, approximately doubling for every 9°C increase. If high-temperature dark current is not effectively suppressed, changes in the environment during chip application will cause the image sensor temperature to rise, leading to increased dark current and reduced image quality. This will limit the imaging quality of image sensors in various complex environments.

[0003] Traditional image sensors reduce dark current by improving processes, optimizing device isolation, reducing metal ion contamination, and improving oxide layer quality. Regarding process improvement, the silicon surface of photodiodes experiences high defect density due to multiple ion implantation and etching processes. Forming a P-type pin-doped layer on the photodiode surface creates a reverse-biased PN junction that isolates these defects, preventing the impact of multiple surface processes on the photodiode and effectively suppressing pixel dark current. Semiconductor etching typically uses plasma etching, which removes dielectric or metal layers by bombarding the silicon surface with plasma. This plasma etching can easily damage the silicon substrate surface, leading to increased leakage current in the photodiode, i.e., increased pixel dark current. To reduce plasma damage to the silicon surface, the etching process needs optimization, such as reducing the plasma energy during etching to suppress dark current. Ion implantation processes also suffer from implantation damage; therefore, optimizing the implantation process is necessary to reduce dark current. Figure 1 As shown, while meeting the requirements for implantation junction depth and concentration, it is necessary to minimize implantation damage and, in conjunction with subsequent annealing processes, repair lattice damage to reduce the resulting dark current. The photosensitive unit of the pixel, i.e., the photodiode, is isolated by STI and a well, such as... Figure 2As shown, the surface of the STI has a large number of interface states and defects, which easily lead to leakage current. Therefore, a P-type doped layer is needed between the N-type photodiode and the STI to prevent the depletion region of the photodiode from contacting the surface of the STI. The energy and dosage of this P-type doping layer need to be optimized to reduce dark current. Leakage in the gate oxide layer may come from the penetration effect of injected impurities, causing defect damage to the gate oxide layer itself, injection damage of hot carriers, etc. To reduce the dark current of the pixel, the growth process of the oxide layer, such as... Figure 3 As shown, the injection conditions related to the transmission transistor, especially the region closest to the photodiode, are optimized to reduce oxide layer defects and damage. By employing a pure dry oxidation process to form the gate oxide, or by increasing the gate oxide formation temperature or annealing temperature, defects such as interface states in the gate oxide layer can be reduced, effectively suppressing the generation of dark current under the transmission transistor of the pixel.

[0004] Existing dark current suppression techniques in the image processing stage employ frame subtraction. This involves subtracting multiple frames from the image stored at room temperature from the image stored at high temperature, thus suppressing dark current. However, this method fails to address the issue of dark current consuming the full-well capacity of the photodiode, leading to a decrease in full-well charge. Traditional image sensor circuits suppress dark current through process optimization. However, image sensor dark current is not only related to the manufacturing process but also closely related to the operating temperature. Once the chip is manufactured and enters the usage phase, its process factors are already determined, and therefore, dark current cannot be suppressed during use. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem that the storage space of effective photoelectric signals in photodiodes is reduced due to dark current occupation in the prior art, and to provide a dark current pixel-level suppression circuit and method for CMOS image sensors.

[0006] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention discloses a dark current pixel-level suppression circuit for a CMOS image sensor, comprising a photodiode disposed in a pixel, wherein the cathode of the photodiode PD is connected to a dark current overflow gate, the dark current overflow gate is connected to the output terminal of a digital-to-dark current overflow gate voltage converter (DAC), the input terminal of the DAC is connected to the output terminal of an analog-to-digital converter (ADC), and the input terminal of the ADC is connected to a temperature detection sensing unit; the photodiode is also connected to a transistor array.

[0007] Further improvements are made in the following aspects: The dark current overflow gate is transistor T2, the cathode of the photodiode PD is connected to the source of transistor T2, and the anode of the photodiode PD is grounded.

[0008] The transistor array includes the source of transistor T1 connected to the drain of transistor T2; the gate of transistor T1 is connected to the control signal TX, and its drain is connected to one end of capacitor C, the source of transistor T3 and transistor T5; the gate of transistor T3 is connected to the reset signal RST, and its drain is connected to the power supply VDD; the gate of transistor T5 is connected to the control signal FD, its drain is connected to VDD, and its source is connected to the drain of transistor T4; the gate of transistor T4 is connected to the input signal BIN, and its source is grounded; transistor T5 is connected to transistor T6, the gate of transistor T6 is connected to the control signal RS, and its drain serves as the circuit output terminal.

[0009] Secondly, this invention discloses a pixel-level dark current suppression method for a CMOS image sensor based on the above-described circuit, comprising: Without enabling dark current calibration, the CMOS image sensor is scanned from high to low temperature in low light, and the corresponding dark current value at each temperature is measured to obtain the relationship between temperature and dark current within the operating temperature range. The voltage value of the dark current overflow gate is adjusted step by step so that the dark current is canceled at the temperature value, forming a table of the correspondence between temperature and overflow gate voltage; When initiating dark current calibration, the CMOS image sensor first performs temperature detection to obtain the current operating temperature. Based on the operating temperature and the table showing the relationship between temperature and overflow gate voltage, the opening degree of the dark current overflow gate is adjusted to complete the dark current discharge.

[0010] The specific steps of scanning the CMOS image sensor from high to low temperature in low light are as follows: The CMOS image sensor is placed in a temperature-controlled high and low temperature dark chamber, and is illuminated by a light source through a collimator; the CMOS image sensor is connected to a computer to monitor and calculate the dark current and adjust the voltage of the dark current overflow gate.

[0011] After obtaining the current operating temperature, the method further includes temperature compensation algorithm optimization, which predicts the dark current change trend and dynamically adjusts the compensation strategy based on the correspondence between temperature and dark current and the current temperature change rate.

[0012] After the dark current discharge is completed, the method also includes real-time monitoring of the residual dark current and transmitting the monitoring signal back to the temperature probe to continue fine-tuning the voltage of the current overflow gate.

[0013] Humidity and air pressure sensors are placed around the CMOS image sensor to integrate the influence of environmental factors on dark current, establish a multi-factor coupling model, and optimize the dark current calibration strategy.

[0014] During the process of measuring the dark current value corresponding to each temperature, multiple dark current measurements are performed at each temperature point, and the average value of the multiple measurement results is calculated as the dark current value corresponding to that temperature to improve the accuracy of dark current measurement. At the same time, the standard deviation of the multiple measurement results is calculated, and when the standard deviation exceeds a preset threshold, the dark current measurement at that temperature point is repeated.

[0015] After forming the temperature and overflow gate voltage correspondence table, the table is subjected to data fitting processing to obtain a mathematical function relationship between temperature and overflow gate voltage. When starting dark current calibration, the voltage value required for dark current overflow gate is directly calculated based on the current operating temperature and the mathematical function relationship to quickly adjust the opening degree of dark current overflow gate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a pixel-level dark current suppression circuit for CMOS image sensors. By placing a photodiode within the pixel and cleverly connecting the photodiode's cathode to a dark current overflow gate, a highly efficient dark current suppression mechanism is constructed. A temperature sensing unit detects temperature changes in real time, and the detected signal is converted by an analog-to-digital converter (ADC). The corresponding voltage is then output by a digital-to-dark current overflow gate voltage converter (DAC) to control the opening degree of the dark current overflow gate. This real-time temperature response and dynamic adjustment of the overflow gate opening degree enable real-time discharge of dark current. Real-time discharge of dark current avoids its accumulation within the pixel, effectively reducing interference with the effective photoelectric signal, ensuring full utilization of the photodiode's full-well capacity, and reserving sufficient space for storing the effective photoelectric signal. This ensures that the image sensor can accurately capture and record high-quality optical information. At high temperatures, dark current generation often increases significantly, severely affecting the imaging quality of the image sensor. This circuit, through real-time temperature monitoring and precise control of the dark current overflow gate, can quickly and effectively address the dark current problem caused by high temperatures, significantly improving the imaging quality of the image sensor in high-temperature environments. This enables the sensor to stably output clear and accurate images under various complex temperature conditions, greatly expanding the application scenarios and scope of the image sensor.

[0017] This invention discloses a pixel-level dark current suppression method for CMOS image sensors. In a high-low temperature chamber, the temperature is scanned from low to high, and the dark current value corresponding to each temperature point is read and stored, forming a correspondence between temperature and dark current within the operating temperature range. The voltage value of the digital dark current overflow gate is adjusted so that the dark current cancels out at that temperature value; a temperature-overflow gate voltage correspondence table is formed in this way. The temperature (digitally represented) and overflow gate correspondence table covers temperature points within the operating range, achieving matching between dark current generation and overflow at different temperatures, and achieving the excellent characteristic of maintaining a basically constant and small dark current as the temperature rises. Based on the detected temperature changes, the opening degree of the photodiode overflow gate in the pixel is intelligently adjusted in real time. When the temperature is low, the photodiode overflow gate is weakly opened; when the temperature is high, the photodiode overflow gate is more fully opened, achieving real-time intelligent discharge of dark current. This ensures sufficient full-well capacity of the photodiode, reserving enough space for the storage of effective photoelectric signals, and significantly improving the imaging quality of the image sensor under high-temperature conditions. The present invention provides an intelligent pixel-level dark current suppression method for CMOS image sensors. By using temperature-dark current overflow matching technology and intelligent pixel-level dark current suppression method, the dark current generated in real time is discharged from the root cause at the pixel level. This avoids the dark current from occupying the full-well capacity of the photodiode due to the rapid growth of dark current at high temperatures, thereby improving the imaging quality under high-temperature conditions and greatly enhancing the flexibility of image sensors in multiple application scenarios. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 Optimize the injection process for dark current in existing technologies; Figure 2 Provides low dark current STI isolation in existing technologies; Figure 3 Optimize injection conditions for dark current in existing technologies; Figure 4 This is a schematic diagram illustrating how, in existing technologies, dark current gradually fills the full-well capacity of a photodiode as temperature increases. Figure 5 This invention relates to an automatic dark current calibration circuit structure for a pixel-level dark current suppression circuit in a CMOS image sensor. Figure 6 This is a timing diagram for automatic dark current calibration of a pixel-level dark current suppression method for a CMOS image sensor according to the present invention. Figure 7 (a) shows the relationship between temperature and temperature sensor output during dark current calibration in an embodiment of the present invention; Figure 7 (b) shows the relationship between the temperature sensor output and the ADC output during dark current calibration in this embodiment of the invention; Figure 7 (c) shows the relationship between ADC output and DAC output during dark current calibration in this embodiment of the invention; Figure 7 (d) shows the relationship between DAC output and photodiode (PD) electron overflow during dark current calibration in this embodiment of the invention; Figure 7 (e) shows the relationship between temperature during dark current calibration and the electron relationship between the dark current of the photodiode PD before calibration in this embodiment of the invention; Figure 7 (f) is the dark current after calibration during dark current calibration in this embodiment of the invention; Figure 8 This is an embodiment of the present invention; Figure 8 (a) is a schematic diagram showing the increase of dark current with increasing temperature in an embodiment of the present invention. Figure 8 (b) is a schematic diagram of the dark current overflow gate being turned on in an embodiment of the present invention. Figure 8 (c) is a schematic diagram of dark current overflow from the gate in an embodiment of the present invention. Figure 9 This is a hardware connection diagram for dark current calibration in this invention; Figure 10 This is a flowchart of the pixel-level dark current suppression method for CMOS image sensors in this invention.

[0020] Wherein: 1-Computer; 2-Temperature-controlled high and low temperature dark chamber; 3-CMOS image sensor; 4-Light source; 11-Dark current overflow gate; 12-Photodiode; 21-Temperature detection and sensing unit; 22-Analog-to-digital converter (ADC); 23-Digital-to-dark current overflow gate voltage converter (DAC); 31-Analog signal output; 32-Digital signal output; 33-Dark current overflow gate voltage output. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 5 This invention discloses a pixel-level dark current suppression circuit for a CMOS image sensor, including a photodiode 12 disposed in a pixel. The cathode of the photodiode 12 is connected to a dark current overflow gate 11, which is connected to the output of a digital-to-dark current overflow gate voltage converter (DAC) 23. The input of the DAC 23 is connected to the output of an analog-to-digital converter (ADC) 22, and the input of the ADC 22 is connected to a temperature sensing unit 21. The photodiode 12 is also connected to a transistor array. The dark current overflow gate 11 is a transistor T2, the cathode of the photodiode 12 is connected to the source of the transistor T2, and the anode of the photodiode 12 is grounded. The transistor array includes the source of transistor T1 connected to the drain of transistor T2; the gate of transistor T1 is connected to the control signal TX, and its drain is connected to one end of capacitor C, the source of transistor T3 and transistor T5; the gate of transistor T3 is connected to the reset signal RST, and its drain is connected to the power supply VDD; the gate of transistor T5 is connected to the control signal FD, its drain is connected to VDD, and its source is connected to the drain of transistor T4; the gate of transistor T4 is connected to the input signal BIN, and its source is grounded; transistor T5 is connected to transistor T6, the gate of transistor T6 is connected to the control signal RS, and its drain serves as the circuit output terminal.

[0025] See Figure 10 This invention discloses a pixel-level dark current suppression method for CMOS image sensors, comprising: Step 1: Without initiating dark current calibration, scan the CMOS image sensor under low light conditions from high to low temperature, measuring the corresponding dark current value at each temperature to obtain the correspondence between temperature and dark current within the operating temperature range. During the measurement of the dark current value at each temperature, perform multiple dark current measurements at each temperature point and calculate the average of the multiple measurement results as the corresponding dark current value at that temperature to improve the accuracy of dark current measurement. Simultaneously, calculate the standard deviation of the multiple measurement results. When the standard deviation exceeds a preset threshold, repeat the dark current measurement at that temperature point. Place the CMOS image sensor in a temperature-controlled high and low temperature dark chamber, with illumination provided by a light source through a collimator. The CMOS image sensor is connected to a computer to monitor and calculate the dark current and adjust the voltage of the dark current overflow gate 11.

[0026] In the dark chamber high and low temperature chamber, the temperature is scanned from low to high, and the dark current value corresponding to each temperature point is read and stored, forming a correspondence between temperature and dark current within the operating temperature range. The voltage value of the digital dark current overflow gate is adjusted so that the dark current cancels out at that temperature value; in this way, a correspondence table between temperature and overflow gate voltage is formed. The temperature (digitally represented) and overflow gate correspondence table covers temperature points within the operating range, achieving matching between dark current generation and dark current overflow at different temperatures, and realizing the excellent characteristic of maintaining a basically constant and small dark current as the temperature rises.

[0027] Step two: Gradually adjust the voltage value of the dark current overflow gate 11 so that the dark current cancels out at this temperature value, forming a table of correspondence between temperature and overflow gate voltage; perform data fitting processing on the table of correspondence between temperature and overflow gate voltage to obtain a mathematical function relationship between temperature and overflow gate voltage; when starting dark current calibration, directly calculate the voltage value required for the dark current overflow gate 11 based on the current operating temperature and the mathematical function relationship to quickly adjust the opening degree of the dark current overflow gate 11.

[0028] Step 3: When starting dark current calibration, the CMOS image sensor first performs temperature detection to obtain the current operating temperature. After obtaining the current operating temperature, it also includes temperature compensation algorithm optimization. Based on the correspondence between temperature and dark current and the current temperature change rate, it predicts the dark current change trend and dynamically adjusts the compensation strategy.

[0029] Step four involves adjusting the opening degree of the dark current overflow gate 11 based on the operating temperature and the temperature-overflow gate voltage correspondence table to complete dark current discharge. After dark current discharge, the process includes real-time monitoring of residual dark current and transmitting the monitoring signal back to the temperature detector for further fine-tuning of the voltage of the current overflow gate 11. Humidity and air pressure sensors are placed around the CMOS image sensor to comprehensively consider the influence of environmental factors on dark current, establishing a multi-factor coupling model to optimize the dark current calibration strategy. Real-time intelligent adjustment of the opening degree of the photodiode overflow gate in the pixel ensures sufficient full-well capacity of the photodiode, reserving enough space for effective photoelectric signal storage and significantly improving the imaging quality of the image sensor under high-temperature conditions.

[0030] The present invention provides an intelligent pixel-level dark current suppression method for CMOS image sensors. By using temperature-dark current overflow matching technology and intelligent pixel-level dark current suppression method, the dark current generated in real time is discharged from the root cause at the pixel level. This avoids the dark current from occupying the full-well capacity of the photodiode due to the rapid growth of dark current at high temperatures, thereby improving the imaging quality under high-temperature conditions and greatly enhancing the flexibility of image sensors in multiple application scenarios.

[0031] The working principle of this invention is as follows: This invention proposes an intelligent pixel-level dark current suppression method for CMOS image sensors, utilizing a temperature-dark current overflow matching technique. This technique gradually increases the temperature within the image sensor's operating temperature range. Figure 7 (a) The temperature sensing unit 21 converts the temperature into an analog signal. As the temperature rises, the analog signal Sensor_out increases; for example... Figure 7 (b) The analog-to-digital converter 22 further converts the analog temperature signal into a digital signal characterizing the temperature. As the analog signal Sensor_out increases, the digital signal ADC_out also increases; for example... Figure 7 (c) As the digital signal ADC_out increases, the dark current overflow gate voltage DAC_out increases; such as Figure 7 (d) As the dark current overflow gate voltage DAC_out increases, electrons overflow from photodiode 12 PD; such as Figure 7 (e) Before calibration, the dark current electrons in the photodiode (PD) increase with increasing temperature; such as Figure 7 (f) By adjusting and optimizing the gate voltage value of the dark current overflow DAC_out, the DAC_out in Figure 6It takes effect within the exposure time, achieving matching between dark current generation and overflow under this temperature condition, ensuring that the dark current remains constant and small with temperature after calibration. A table of correspondence between temperature (digital characterization) and overflow gate is generated and stored in the digital-to-dark current overflow gate voltage conversion unit 23. The table of correspondence between temperature (digital characterization) and overflow gate covers temperature points within the operating range, achieving matching between dark current generation and dark current overflow at different temperatures, and achieving the excellent characteristic of maintaining a basically constant and small dark current as the temperature rises.

[0032] Figure 8 The diagram shown illustrates the leakage of electrons from the dark current. Figure 8 (a) shows a schematic diagram of the increase of dark current with increasing temperature. As the temperature increases, the dark current gradually increases, occupying the full-well capacity of the photodiode and greatly limiting the storage space of effective photoelectrons. Figure 8 (b) shows a schematic diagram of dark current overflow gate opening. The higher the temperature, the greater the degree of overflow gate opening. Figure 8 (c) shows a schematic diagram of dark current overflow from the gate. As the temperature increases, the gate opening degree increases, and the dark current overflow increases. This fully guarantees the full-well capacity of the photodiode and ensures the effective storage space for photoelectrons.

[0033] For applications such as airborne cameras, civilian surveillance, and automotive imaging, which face long operating times and large temperature variations, the dark current of image sensors increases exponentially with increasing temperature. This dark current occupies the charge storage space of photodiodes, significantly suppressing the storage of effective photoelectric signals, resulting in a substantial decrease in image quality and even loss of image functionality, thus reducing the reliability of image sensor applications. This invention proposes an intelligent pixel-level dark current suppression method and a temperature-dark current overflow matching technology, which matches the increase in dark current with its overflow, significantly reducing the temperature sensitivity of image sensors and improving application reliability and image quality.

[0034] This invention proposes an intelligent pixel-level dark current suppression method for CMOS image sensors. It eliminates the need for traditional digital processing methods, such as outputting multiple images and performing subtraction to reduce dark current. Traditional methods cannot address the issue of reduced effective photoelectric signal storage space in photodiodes due to dark current occupancy. This invention, by detecting temperature and controlling the opening amplitude of the dark current overflow gate based on a temperature (digitally characterized) and overflow gate correspondence table, achieves pixel-level dark current discharge, ensuring the full-well charge of the photodiode and the imaging performance of the image sensor.

[0035] The specific work process is as follows: Figure 9 and Figure 10 As shown, where Figure 9 Here is the hardware connection diagram for dark current calibration. Figure 10Flowchart for dark current calibration and suppression. Figure 9 The image sensor shown is located in a temperature-controlled dark chamber, illuminated by a light source through a collimator. The computer monitors and calculates the dark current and can adjust the voltage of the overflow gate 11.

[0036] Figure 10 Here is a flowchart for dark current calibration and suppression. Figure 5 The temperature sensing unit 21 detects temperature in low light conditions. When dark current calibration is not initiated, the dark current overflow gate 11... Figure 6 The exposure stage shown is low, using Figure 9 The computer reads the dark current value of the image sensor; following this method... Figure 9 The dark chamber high and low temperature chamber is scanned from low to high, and the dark current value corresponding to each temperature point is read and stored, forming a correspondence between temperature and dark current within the operating temperature range. The voltage value of DAC_out in the digital-to-dark current overflow gate voltage conversion unit 23 is adjusted. Figure 6 The effect is achieved during the exposure time, which cancels out the dark current at that temperature. In this way, a table of correspondence between temperature and overflow gate voltage is formed, which can also eliminate the correspondence between ADC_out and DAC_out at each temperature point.

[0037] Once in normal operation, users can configure the image sensor to enable or disable dark current calibration to meet the needs of various application scenarios. If dark current calibration is not enabled, the dark current increases with rising temperature. If dark current calibration is enabled, the temperature detection sensing unit 21 detects the temperature and converts it into an analog signal. The analog-to-digital conversion unit 22 converts the analog temperature signal into a digital temperature signal. Based on the established temperature-overflow gate correspondence table, the digital-to-dark current overflow gate voltage conversion unit 23 performs DA conversion and outputs a voltage value DAC_out that suppresses dark current. The overflow gate is partially opened, releasing the dark current and achieving effective suppression of dark current.

[0038] The dark current suppression method of this image sensor releases the dark current generated in real time from the pixel level, avoiding the dark current from occupying the full-well capacity of the photodiode due to the rapid growth of dark current at high temperature, thus improving the imaging quality under high temperature environment.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pixel-level dark current suppression circuit for a CMOS image sensor, characterized in that, The device includes a photodiode (12) disposed in a pixel. The cathode of the photodiode (12) is connected to a dark current overflow gate (11). The dark current overflow gate (11) is connected to the output terminal of a digital-to-dark current overflow gate voltage converter (DAC) (23). The input terminal of the DAC (23) is connected to the output terminal of an analog-to-digital converter (ADC) (22). The input terminal of the ADC (22) is connected to a temperature sensing unit (21). The photodiode (12) is also connected to a transistor array. The dark current overflow gate (11) is transistor T2, the cathode of the photodiode PD (12) is connected to the source of transistor T2, and the anode of photodiode PD (12) is grounded.

2. The dark current pixel-level suppression circuit for a CMOS image sensor according to claim 1, characterized in that, The transistor array includes the source of transistor T1 connected to the drain of transistor T2; the gate of transistor T1 is connected to the control signal TX, and its drain is connected to one end of capacitor C, the source of transistor T3 and transistor T5; the gate of transistor T3 is connected to the reset signal RST, and its drain is connected to the power supply VDD; the gate of transistor T5 is connected to the control signal FD, its drain is connected to VDD, and its source is connected to the drain of transistor T4; the gate of transistor T4 is connected to the input signal BIN, and its source is grounded; transistor T5 is connected to transistor T6, the gate of transistor T6 is connected to the control signal RS, and its drain serves as the circuit output terminal.

3. A method for pixel-level dark current suppression in a CMOS image sensor based on the circuit described in claim 1 or 2, characterized in that, include: Without enabling dark current calibration, the CMOS image sensor is scanned from high to low temperature in low light, and the corresponding dark current value at each temperature is measured to obtain the relationship between temperature and dark current within the operating temperature range. The voltage value of the dark current overflow gate (11) is adjusted step by step so that the dark current is canceled at this temperature value, forming a table of the correspondence between temperature and overflow gate voltage; When initiating dark current calibration, the CMOS image sensor first performs temperature detection to obtain the current operating temperature. Adjust the opening degree of the dark current overflow gate (11) based on the operating temperature and the temperature-overflow gate voltage correspondence table to complete the dark current discharge.

4. The method for pixel-level dark current suppression of a CMOS image sensor according to claim 3, characterized in that, The specific steps of scanning the CMOS image sensor from high to low temperature in low light are as follows: The CMOS image sensor is placed in a temperature-controlled high and low temperature dark chamber, and is illuminated by a light source through a parallel light tube; the CMOS image sensor is connected to a computer to monitor and calculate the dark current and adjust the voltage of the dark current overflow gate (11).

5. The method for pixel-level dark current suppression of a CMOS image sensor according to claim 3, characterized in that, After obtaining the current operating temperature, the method further includes temperature compensation algorithm optimization, which predicts the dark current change trend and dynamically adjusts the compensation strategy based on the correspondence between temperature and dark current and the current temperature change rate.

6. The method for pixel-level dark current suppression of a CMOS image sensor according to claim 3, characterized in that, After the dark current discharge is completed, the method also includes real-time monitoring of the residual dark current and transmitting the monitoring signal back to the temperature detection, which is used to continue to fine-tune the voltage of the current overflow gate (11).

7. The method for pixel-level dark current suppression of a CMOS image sensor according to claim 3, characterized in that, Humidity and air pressure sensors are placed around the CMOS image sensor to integrate the influence of environmental factors on dark current, establish a multi-factor coupling model, and optimize the dark current calibration strategy.

8. The method for pixel-level dark current suppression of a CMOS image sensor according to claim 3, characterized in that, During the process of measuring the dark current value corresponding to each temperature, multiple dark current measurements are performed at each temperature point, and the average value of the multiple measurement results is calculated as the dark current value corresponding to that temperature to improve the accuracy of dark current measurement. At the same time, the standard deviation of the multiple measurement results is calculated, and when the standard deviation exceeds a preset threshold, the dark current measurement at that temperature point is repeated.

9. The method for pixel-level dark current suppression of a CMOS image sensor according to claim 3, characterized in that, After forming the temperature and overflow gate voltage correspondence table, the temperature and overflow gate voltage correspondence table is subjected to data fitting processing to obtain the mathematical function relationship between temperature and overflow gate voltage; when starting dark current calibration, the voltage value required for dark current overflow gate (11) is directly calculated based on the current operating temperature and the mathematical function relationship to quickly adjust the opening degree of dark current overflow gate (11).

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