Method for improving adaptability of CCD imaging system to strong and weak light environments

Abstract

The invention discloses a method for improving strong and weak light environment adaptability of a CCD (charge coupled device) imaging system, which is based on a CCD structure with an on-chip signal shunting function and is realized by the following steps of: firstly, non-destructively sensing the size of a charge signal representing light intensity in real time in the CCD; then, the sensed signal intensity is compared with a preset threshold value, and whether the current environment is in a weak light environment or a strong light environment is judged according to the comparison result; and finally, based on a judgment result, adaptively shunting the charge signal to an electron multiplication channel for gain amplification through an on-chip selection mechanism to improve low-light sensitivity, or shunting the charge signal to a non-electron multiplication channel to maintain a high dynamic range and anti-halo capability under strong light. According to the on-chip adaptive shunting method, the single CCD imaging system can obtain high-quality images under the large-range illumination change from sunlight to starlight without external intervention, and the environmental adaptability of the system is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of image sensor technology, and specifically to a method for improving the adaptability of CCD imaging systems to strong and weak lighting environments, particularly a method based on on-chip signal strength judgment and splitting technology that enables a single CCD camera to adaptively image under extremely dynamic range lighting conditions. Background Technology

[0002] Charge-coupled devices (CCDs), as high-performance image sensors, are widely used in scientific imaging, industrial inspection, and other fields. However, traditional CCDs have inherent limitations when dealing with imaging scenarios with a wide dynamic range of illumination, such as day-night cycles and indoor-outdoor transitions: their signal-to-noise ratio is insufficient in low light, while they are prone to saturation in strong light, resulting in a limited dynamic range.

[0003] Electron-multiplying CCDs (EMCCDs) significantly improve low-light sensitivity through internal gain, but their electron-multiplying structure is prone to saturation under strong light and typically sacrifices key characteristics such as anti-blooming and global shutter performance. Conversely, conventional CCDs possess excellent anti-blooming and dynamic range, making them suitable for strong light conditions, but their readout noise limits their imaging capabilities in low light. Existing solutions, such as dual-camera systems or external mechanical filter switching devices, suffer from system complexity, high cost, large size, and slow response.

[0004] Therefore, the purpose of this invention is to solve how to enable a single CCD camera to adaptively balance high sensitivity in low light and high dynamic range in strong light without external mechanical or electronic intervention by means of a method integrated inside the chip, thereby significantly improving its environmental adaptability. Summary of the Invention

[0005] In view of this, the purpose of this invention is to overcome the shortcomings of existing technologies where single CCDs cannot simultaneously achieve high sensitivity in low light and high dynamic range in strong light, and to provide a method for improving the adaptability of CCD imaging systems to varying light environments. This method integrates intelligent signal judgment and diversion processes within the CCD chip to achieve adaptive processing of strong and weak light signals during a single exposure, significantly expanding the working illumination range of the imaging system.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] A method for improving the adaptability of a CCD imaging system to varying light conditions includes the following steps:

[0008] Non-destructive signal strength sensing step: Using a non-destructive sensing unit integrated on the CCD signal transmission path, the intensity of charge packets from the photosensitive area is sensed, and a sensing signal related to the amount of charge is output.

[0009] Signal strength judgment step: comparing the sensing signal with a preset threshold signal to generate a path selection control signal indicating whether the charge packet belongs to a weak light signal or a strong light signal;

[0010] Signal path adaptive selection step: according to the path selection control signal, the charge packet is adaptively routed to an electron multiplication channel for gain amplification or to a non-electron multiplication channel for regular readout through a selection mechanism;

[0011] Dual-channel signal readout and image synthesis step: reading out the signals processed through different channels respectively and synthesizing them into a high dynamic range image.

[0012] Preferably, the signal strength non-destructive sensing step is implemented by a floating gate amplifier; the charge packet passes below the floating gate, changes the floating gate potential through capacitive coupling, and the charge packet itself is completely preserved.

[0013] Preferably, the preset threshold signal is established by injecting a known reference charge packet into the non-destructive sensing unit.

[0014] Further, it also includes a potential reset step: using a reset gate to reset the potential of the floating gate to a known, fixed initial level at the beginning of each measurement period.

[0015] Further, it also includes a charge bleeding step: using a bleeding gate to guide the reference charge and signal charge after sensing to a preset bleeding area for removal.

[0016] Preferably, the signal path adaptive selection step is completed within a single exposure period, realizing single-frame high dynamic range imaging.

[0017] Preferably, the selection mechanism is implemented by a selection gate: if it is judged to be a weak signal, the selection gate directs the charge packet to the electron multiplication channel; the charge obtains avalanche multiplication gain in this channel through a high electric field, and is finally read out by an amplifier, realizing high signal-to-noise ratio imaging in low light; if it is judged to be a strong signal, the selection gate continues to direct the charge packet to the regular output amplifier.

[0018] The present application has the following beneficial effects:

[0019] 1. Excellent environmental adaptability: through adaptive signal processing inside the chip, a single CCD camera can obtain high-quality images in a very large illumination range from starlight-level low light to noon strong light without any external movable parts or complex control systems.

[0020] 2. True single-exposure high dynamic range: strong and weak signals are processed simultaneously within a single exposure, avoiding the motion artifact problem caused by multi-frame synthesis HDR technology, and being very suitable for dynamic scene imaging.

[0021] 3. Performance maximization: cleverly integrate the high gain advantage of EMCCD and the high dynamic range advantage of regular CCD in a single chip, and intelligently invoke according to signal strength, so that the performance of the system under various lighting conditions is close to optimal.

[0022] 4. System simplification and reliability improvement: avoid the problems of system complexity, calibration difficulty, large size and reliability risk caused by the use of double cameras or mechanical filters. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure diagram of the CCD chip based on the method.

[0024] Figure 2 The structure diagram of the non-destructive floating gate amplifier for realizing the core signal judgment function.

[0025] Among them, 31-floating gate, 32-reset gate, 33-reference charge injection gate, 34-signal sensing gate, 35-drain gate, 36-output amplifier. DETAILED DESCRIPTION

[0026] As shown in Figure 1 , the photosensitive area 1 of the CCD imaging system chip will transfer the photo-generated charge packets to the lower non-electron multiplication channel 2 (i.e. regular horizontal readout register) in parallel after exposure ends, and the charge packets are transmitted in this channel.

[0027] Implementation of signal strength sensing and judgment step: this function is completed by the non-destructive floating gate amplifier 3 core. As shown in Figure 2 , the key elements of the amplifier 3 are precisely arranged in sequence above the non-electron multiplication channel 2 along the charge transmission direction, including floating gate 31, reset gate 32, reference charge injection gate 33, signal sensing gate 34, drain gate 35 and output amplifier 36.

[0028] Floating gate 31: the core of the entire structure. It is a conductor suspended above the charge transmission channel and electrically isolated. Its directly below is the transmission path of the charge packet. When the charge packet passes from below, it will induce a voltage on the floating gate through capacitive coupling, and the voltage is proportional to the charge amount. This induction process is non-destructive, because the charge packet itself continues to advance intact.

[0029] Reset gate 32: located on the left side (upstream) of floating gate 31. Its function is to reset the potential of floating gate 31 to a known, fixed initial level at the beginning of each measurement period, ensuring that the starting point of each sensing is consistent and eliminating the influence of the last measurement.

[0030] Reference charge injection gate 33: located immediately to the left of reset gate 32. It is used to control the injection of a known and constant amount of "reference charge packet" and to pass it underneath floating gate 31. This reference charge packet induces a reference voltage on floating gate 31, which is used as a threshold for the subsequent signal strength determination.

[0031] Signal sensing gate 34: located to the right (downstream) of floating gate 31. It is used to control the passage of the signal charge packet from the photosensitive region underneath floating gate 31. At this point, the signal charge packet induces a second voltage signal on floating gate 31.

[0032] Drain gate 35: located at the far right (downstream) of the entire sensing region. After the reference and signal charge packets have completed their sensing tasks, they are no longer useful for imaging. Drain gate 35 is used to open and direct these "used" charge packets to a drain area (similar to a drain) for removal, preventing them from interfering with the subsequent routing of the actual imaging charge packets.

[0033] Output amplifier 36: it is typically connected directly to floating gate 31 through a capacitor (located above the floating gate structure in the figure). Its function is to sequentially read the reference and signal voltages on floating gate 31 and convert the difference between these two voltage values into a logic level signal. This determination result is used to control the downstream signal channel selection gate 5.

[0034] The above non-destructive floating gate amplifier workflow is as follows (as shown in the figure): Figure 2 :

[0035] a) Reset: reset gate 32 is opened to reset floating gate 31 to an initial potential.

[0036] b) Set threshold: reference charge injection gate 33 is opened to inject a known and constant reference charge packet and pass it underneath floating gate 31, thereby establishing an accurate reference voltage on floating gate 31, which is used as the threshold for determining the intensity of light.

[0037] c) Signal sensing: the signal charge packet to be measured from the photosensitive region reaches signal sensing gate 34 under the clock drive, and also induces a voltage on floating gate 31.

[0038] d) Signal comparison: output amplifier 36 reads the reference and sensing voltages in sequence. By comparing the difference between the read reference and sensing voltages, the relative strength of the signal charge packet can be determined non-destructively. The determination result is converted into a logic level signal.

[0039] e) Charge drain: the reference and signal charges after sensing are directed to the drain area by drain gate 35 for removal, without affecting the subsequent transfer and processing of the charge packets.

[0040] Implementation of signal path adaptive selection step: After a short delay, the sensed charge packet reaches the signal channel selection gate 5. At this time, the logic control signal from the non-destructive floating gate amplifier 3 has reached the control end of the selection gate 5 in advance:

[0041] If it is judged to be a weak signal, the selection gate 5 directs the charge packet to the electron multiplication channel 7. The charge obtains avalanche multiplication gain in the channel through a high electric field, and is finally read out by the amplifier, realizing high signal-to-noise ratio imaging under micro-light.

[0042] If it is judged to be a strong signal, the selection gate 5 continues to direct the charge packet to the conventional output amplifier 6. The signal is directly read out without gain, completely retaining the high linearity and anti-halation ability of the standard CCD, effectively preventing strong light saturation.

[0043] Implementation of dual-channel parallel readout and image synthesis step: The signals from the two channels are converted into digital values respectively. The subsequent image processing system fuses the image data according to the channel information (weak light channel / strong light channel) of each pixel signal source. For example, the signal from the weak light channel is multiplied by a coefficient corresponding to the EM gain for restoration, and is seamlessly spliced or weighted fused with the signal from the strong light channel, finally generating a high dynamic range image with rich details and no overexposure.

[0044] In summary, the present application realizes the self-adaptation of ambient light at the chip level through the above method steps, greatly improving the practicality and performance boundary of the CCD imaging system.

[0045] The above specific embodiments only describe the design principles of the present application, and the shapes and names of the components in the description can be different and are not limited. Therefore, those skilled in the art of the present application can modify or equivalently replace the technical solutions described in the foregoing embodiments; and these modifications and replacements do not deviate from the purpose and technical solutions of the present application, and should all belong to the protection scope of the present application.

Claims

1. A method for improving the adaptability of a CCD imaging system to varying light conditions, characterized in that, Includes the following steps: Non-destructive signal strength sensing step: Using a non-destructive sensing unit integrated on the CCD signal transmission path, the intensity of charge packets from the photosensitive area is sensed, and a sensing signal related to the amount of charge is output. Signal strength determination step: Compare the sensed signal with a preset threshold signal to generate a path selection control signal that indicates whether the charge packet belongs to a weak light signal or a strong light signal; Signal path adaptive selection step: According to the path selection control signal, the charge packet is adaptively routed to the electron multiplication channel for gain amplification or to a non-electron multiplication channel for conventional readout through the selection mechanism; Dual-channel signal readout and image synthesis steps: Read out the signals processed by different channels respectively, and synthesize them into a high dynamic range image.

2. The method for improving the adaptability of a CCD imaging system to varying light conditions according to claim 1, characterized in that, The non-destructive signal strength sensing step is implemented through a floating gate amplifier; the charge packet passes under the floating gate and changes the floating gate potential through capacitive coupling, while the charge packet itself is completely preserved.

3. The method for improving the adaptability of a CCD imaging system to varying light conditions according to claim 1 or 2, characterized in that, The preset threshold signal is established by injecting a known reference charge packet into the non-destructive sensing unit.

4. The method for improving the adaptability of a CCD imaging system to varying light conditions according to claim 2, characterized in that, It also includes a potential reset step: using a reset gate, the potential of the floating gate is reset to a known, fixed initial level at the beginning of each measurement cycle.

5. The method for improving the adaptability of a CCD imaging system to varying light conditions according to claim 4, characterized in that, It also includes a charge discharge step: using a discharge gate, the reference charge and signal charge after induction are guided to a preset discharge area for removal.

6. The method for improving the adaptability of a CCD imaging system to varying light conditions according to claim 1, characterized in that, The adaptive signal path selection step is completed within a single exposure cycle, enabling high dynamic range imaging in a single frame.

7. The method for improving the adaptability of a CCD imaging system to varying light conditions according to claim 1, characterized in that, The selection mechanism is implemented using a selection gate: if the signal is determined to be weak, the selection gate guides the charge packet to the electron multiplication channel; the charge gains avalanche multiplication gain in the channel through a high electric field, and is finally read out by the amplifier to achieve high signal-to-noise ratio imaging in low light; if the signal is determined to be strong, the selection gate continues to guide the charge packet to the conventional output amplifier.

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