Image sensor exposure control method and image sensor

Abstract

The present application provides an image sensor exposure control method and an image sensor, which divides the exposure stage of each frame of image into a pre-reading time period and a subsequent effective exposure time period. In the pre-reading time period, each pixel unit is controlled to perform pre-exposure, and its voltage signal is read at the end of the pre-exposure. By comparing the voltage signal with a plurality of preset threshold voltages, the current brightness interval of each pixel unit is determined, and a corresponding shutter channel and shutter control parameter are assigned to it accordingly. After the end of the pre-reading time period, the charge of each pixel unit is emptied, and in the effective exposure time period, the effective exposure of the pixel unit is controlled based on the assigned shutter control parameter, thereby realizing pixel-level dynamic exposure control for different brightness intervals. The present embodiment can simultaneously obtain effective exposure data of different brightness intervals within a single frame, realize high dynamic range imaging, avoid multi-frame synthesis, and thus reduce the amount of redundant image acquisition and stored data.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of image processing, and in particular to an image sensor exposure control method and an image sensor. BACKGROUND

[0002] With the increasing requirements of image acquisition quality and real-time performance in application scenarios such as autonomous driving, industrial detection, and biological imaging, image sensors have exposed significant bottlenecks in dynamic range, response speed, noise resistance, and local detail capture.

[0003] Traditional exposure control schemes usually use a global shutter or a rolling shutter method to control the exposure of all pixels with a unified exposure time. This method is difficult to capture details in both bright and dark areas in high dynamic range scenes (such as strong light and dark light coexisting), resulting in image distortion or increased noise, limiting the versatility of the sensor in complex environments.

[0004] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to provide an image sensor exposure control method and an image sensor, which overcome the difficulties of the prior art and can solve the technical problem of limited application range of related art image sensors.

[0006] The present disclosure provides an image sensor exposure control method, which comprises:

[0007] In a pre-reading time period from the start of the current frame image exposure stage, each pixel unit is controlled to pre-expose, and the voltage signal of each pixel unit is pre-read at the end of the pre-exposure, the voltage signal reflecting the degree of illumination response of the current scene brightness to the pixel unit;

[0008] According to the comparison result of the voltage signal of each pixel unit and the plurality of threshold voltages, the current brightness interval corresponding to each pixel unit is determined;

[0009] According to the current brightness interval of each pixel unit, a corresponding shutter channel is allocated, wherein at least two pixel units with different current brightness intervals are respectively allocated different shutter channels, and the shutter control parameters of different shutter channels are different;

[0010] After the end of the pre-reading time period, the charges of each pixel unit are cleared, and in an effective exposure time period, the shutter channel allocated to each pixel unit is scheduled, and the corresponding pixel unit is controlled to effectively expose based on the shutter control parameter, to obtain a current frame image.

[0011] Optionally, the corresponding shutter channel is assigned according to the current brightness interval of each pixel unit, comprising:

[0012] According to the current brightness interval of each pixel unit, a corresponding shutter channel number is assigned and written into a register array, and each pixel unit corresponds to one or more register fields;

[0013] The shutter channel assigned by scheduling each pixel unit comprises:

[0014] Based on the shutter channel number stored in the register array, the shutter channel corresponding to each pixel unit is scheduled by row and column selection signals.

[0015] Optionally, the shutter channel is triggered in an interleaved manner within a plurality of clock cycles to control the exposure of each pixel unit based on a corresponding shutter control parameter.

[0016] Optionally, the shutter control parameter includes an effective exposure time, and the effective exposure processes of different pixel units partially overlap in the effective exposure time.

[0017] Optionally, the voltage signal of each pixel unit is pre-read, comprising: pre-reading the voltage signal of the pixel unit inside the pixel unit.

[0018] Optionally, each pixel unit includes a source follower, a selection transistor, and a lateral overflow integration capacitor; the voltage signal of the pixel unit is pre-read inside the pixel unit, comprising:

[0019] The voltage on the floating diffusion node or the lateral overflow integration capacitor is converted into the voltage signal output by the selection transistor by the source follower.

[0020] Optionally, the current brightness interval corresponding to each pixel unit is determined according to the comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages, comprising:

[0021] A plurality of threshold voltages arranged from low to high and their corresponding plurality of brightness intervals are obtained, a step-by-step comparison or parallel comparison method is used to determine the threshold voltage level corresponding to the voltage signal of each pixel unit, and the current brightness interval corresponding to the threshold voltage level is determined.

[0022] Optionally, the pixel unit includes a photodiode, a transfer transistor, a reset transistor, and a lateral overflow integration capacitor; the charge of each pixel unit is emptied, comprising:

[0023] The charge in the photodiode is transferred to the floating diffusion node by the transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied by the reset transistor.

[0024] Optionally, the image sensor further comprises a pre-read reset transistor and a pre-read transfer transistor, each of the pre-read reset transistor being coupled to a reset transistor in the same row of pixel units, and each of the pre-read transfer transistor being coupled to a transfer transistor in the same row of pixel units; and the emptying of the charge of each of the pixel units comprises:

[0025] The charge in the photodiode is transferred to the floating diffusion node by the transfer transistor in the same row of pixel units by controlling the pre-read transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied by the reset transistor in the same row of pixel units by controlling the pre-read reset transistor.

[0026] The second aspect of the present disclosure provides an image sensor, comprising:

[0027] a pixel array comprising a plurality of pixel units;

[0028] an exposure control logic module connected to the pixel array and configured to:

[0029] pre-expose each pixel unit in a pre-read time period starting from the beginning of an exposure phase of a current frame image, and pre-read a voltage signal of each pixel unit at the end of the pre-exposure, the voltage signal reflecting a degree of illumination response of a current scene brightness to the pixel unit;

[0030] determine a current brightness interval corresponding to each pixel unit according to a comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages;

[0031] assign a corresponding shutter channel to each of the pixel units according to the current brightness interval of each of the pixel units, wherein at least two of the pixel units with different current brightness intervals are assigned different shutter channels, and shutter control parameters of the different shutter channels are different;

[0032] empty the charge of each of the pixel units after the end of the pre-read time period, and control the effective exposure of the corresponding pixel unit based on the shutter control parameters of the shutter channel assigned to each of the pixel units in an effective exposure time period by scheduling the shutter channel, to obtain a current frame image.

[0033] Optionally, the image sensor adopts a stacked chip structure, comprising a main chip integrating the pixel array and a second chip comprising the exposure control logic module.

[0034] Optionally, the pixel unit comprises a photodiode, a transfer transistor, a reset transistor and a lateral overflow integration capacitor; the exposure control logic module is further configured to empty the charge of each pixel unit in the following manner:

[0035] The charge in the photodiode is transferred to the floating diffusion node through the transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied through the reset transistor.

[0036] Optionally, the image sensor further comprises a pre-reading reset transistor and a pre-reading transfer transistor, each pre-reading reset transistor is coupled to each reset transistor in the same row of pixel units, and each pre-reading transfer transistor is coupled to each transfer transistor in the same row of pixel units; the exposure control logic module is specifically configured to:

[0037] The charge in the photodiode is transferred to the floating diffusion node through each transfer transistor in the same row of pixel units by controlling the pre-reading transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied through each reset transistor in the same row of pixel units by controlling the pre-reading reset transistor.

[0038] The image sensor exposure control method and the image sensor provided by the embodiments of the present disclosure have the following advantages:

[0039] In the present embodiment, the exposure stage of each frame of image is divided into a pre-reading time period and a subsequent effective exposure time period. In the pre-reading time period, each pixel unit is controlled to perform pre-exposure, and its voltage signal is read at the end of the pre-exposure, which represents the response degree of the pixel unit to the current incident light intensity and can be used to determine the light response level thereof. By comparing the voltage signal with a plurality of preset threshold voltages, the current brightness interval of each pixel unit is determined, and the corresponding shutter channel and shutter control parameter are assigned to it accordingly. After the end of the pre-reading time period, the charge of each pixel unit is emptied, and in the effective exposure time period, the effective exposure of the pixel unit is controlled based on the assigned shutter control parameter, thereby realizing pixel-level dynamic exposure control for different brightness intervals.

[0040] Compared with the related art, the present embodiment can simultaneously obtain effective exposure data of different brightness intervals within a single frame, realize high dynamic range imaging, avoid multi-frame synthesis, thereby reducing the amount of redundant image acquisition and stored data, and can significantly enhance the imaging adaptability of the image sensor under high brightness difference, high speed motion or complex lighting conditions. The present method is suitable for image sensor systems that need to realize precise exposure control in complex lighting and high-speed changing environment, such as automatic driving, high-speed detection, biological imaging, etc.

[0041] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0042] Other features, objects, and advantages of the application will become more apparent from a reading of the detailed description in conjunction with the drawings.

[0043] Figure 1 One of flowcharts of image sensor exposure control methods provided by embodiments of the present disclosure;

[0044] Figure 2 A circuit architecture diagram of an image sensor provided by embodiments of the present disclosure is shown;

[0045] Figures 3-6 A schematic diagram of four exposure process principles of the image sensor exposure control method shown in Figure 1

[0046] Figure 7 A schematic diagram of one exposure process of the image sensor exposure control method shown in Figure 1

[0047] Figure 8 A schematic diagram of a pixel array in an image sensor and corresponding working timing is shown;

[0048] Figure 9 A schematic diagram of a pixel array in an image sensor and corresponding working timing is shown; Figure 10 Figure 1 A schematic diagram of multiple shutter channel timings of the image sensor exposure control method shown in

[0049] Figure 11 A schematic diagram of one shutter channel timing is shown;

[0050] Figure 12 An architecture diagram of an image sensor provided by embodiments of the present disclosure is shown;

[0051] Figure 13 A schematic diagram of an exposure control logic module in the image sensor shown in Figure 12 DETAILED DESCRIPTION

[0052] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations may, however, be implemented in many different forms and should not be construed as limited to the implementations set forth herein; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example implementations to those skilled in the art. Features described in the description, structures, or characteristics may be combined in any suitable manner in one or more implementations.

[0053] ​​​​In addition, the accompanying drawings are only schematic and are non-limiting. Identical components have been given the same reference numerals in the various drawings and have not been repeatedly described. Some embodiments are shown by way of example in the drawings and will be described in detail below. It goes without saying that the elements and features of the various embodiments described herein can be combined with each other, unless specifically stated otherwise.

[0054] In the related art, part of the image sensor generates a high dynamic range imaging (HDR) image through multi-frame image fusion, but multiple exposures and data processing are required, which increases power consumption and delay, and it is difficult to balance the frame rate requirement and dynamic range performance.

[0055] To improve the dynamic range performance of the image sensor, the related art proposes various optimization paths:

[0056] Dual Conversion Gain (DCG): reading signals of two different gain paths in a single exposure to cover a wider dynamic range;

[0057] Multiple Exposure High Dynamic Range (ME-HDR): by collecting multiple images with different exposure times in one frame or multiple frames and fusing them, the dynamic range performance of the image is improved. The dynamic range represents the adaptability of the image sensor to the intensity of light. The higher the value, the more the sensor can capture bright areas and dark details at the same time, and it is suitable for imaging environments with strong contrast and high brightness difference.

[0058] These schemes have made technical progress in improving the dynamic range, but still have the following technical problems:

[0059] Data redundancy and processing burden: especially for fusion schemes such as Staggered High Dynamic Range (Stagger HDR), multiple frame image output and storage are required, which greatly increases the data throughput and computing burden of the system. Moreover, the current exposure control is based on the whole row or frame image, which is difficult to optimize the local overexposure or underexposure area of the complex scene.

[0060] Therefore, while improving the dynamic range, the existing schemes face problems such as large amount of data, low response accuracy, and insufficient pixel control ability, which limits their application adaptability in complex lighting conditions.

[0061] The image sensor exposure control method and the image sensor provided by the embodiments of the present disclosure combine a pixel-level pre-reading voltage analysis mechanism and a multi-channel exposure signal distribution strategy, can dynamically adjust the exposure path of a single pixel between each frame of image, and realize true pixel-level exposure adaptive control. The technical solution of the embodiments of the present disclosure can reduce data redundancy and improve frame rate through efficient data scheduling, and is particularly suitable for imaging tasks in high-brightness difference, high-speed and complex lighting environments.

[0062] Figure 1 A flowchart of the image sensor exposure control method provided by the embodiments of the present disclosure is shown. The execution subject of the method is an exposure control logic (ESL) module or a chip integrated with the exposure control logic module, as shown in FIG. 1. The image sensor exposure control method provided by the embodiments of the present disclosure includes but is not limited to the following steps: Figure 1

[0063] Step 110: controlling pre-exposure of each pixel unit in a pre-reading time period starting from the beginning of the current frame image exposure stage, and pre-reading a voltage signal of each pixel unit at the end of the pre-exposure, the voltage signal reflecting the degree of illumination response of the current scene brightness to the pixel unit;

[0064] Step 120: determining the current brightness interval corresponding to each pixel unit according to the comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages;

[0065] Step 130: assigning a corresponding shutter channel to each of the pixel units according to the current brightness interval of the pixel unit, wherein at least two of the pixel units with different current brightness intervals are respectively assigned different shutter channels, and the shutter control parameters of the different shutter channels are different;

[0066] Step 140: emptying the charge of each of the pixel units after the end of the pre-reading time period, and controlling effective exposure of the corresponding pixel unit based on the shutter control parameters of the shutter channel assigned to each of the pixel units in an effective exposure time period, to obtain a current frame image.

[0067] ​In the embodiment, the exposure stage of each frame of image is divided into a pre-reading time period and a subsequent effective exposure time period. In the pre-reading time period, each pixel unit is controlled to perform pre-exposure, and a voltage signal of the pixel unit is read at the end of the pre-exposure, the voltage signal representing a degree of response of the pixel unit to a current incident light intensity and being used to determine a light response level of the pixel unit. By comparing the voltage signal with a plurality of preset threshold voltages, a current brightness interval of each pixel unit is determined, and a corresponding shutter channel and shutter control parameter are assigned to the pixel unit according to the brightness interval. After the end of the pre-reading time period, the charge of each pixel unit is emptied, and in the effective exposure time period, the pixel unit is controlled to perform effective exposure based on the assigned shutter control parameter, so as to realize pixel-level dynamic exposure control for different brightness intervals.

[0068] Compared with related technologies, the embodiment can simultaneously acquire effective exposure data of different brightness intervals in a single frame, realize high dynamic range imaging, avoid multi-frame synthesis, thereby reducing the amount of redundant image acquisition and stored data, and can significantly enhance the imaging adaptability of an image sensor under high brightness difference, high-speed motion or complex lighting conditions. The method is suitable for image sensor systems that need to realize accurate exposure control in complex lighting and high-speed changing environments, such as automatic driving, high-speed detection, biological imaging and the like.

[0069] In the embodiment of the present disclosure, to evaluate a current scene brightness, in a pre-reading time period starting from the beginning of the exposure stage of a current frame of image, each pixel unit is controlled to perform pre-exposure, and a voltage signal of the pixel unit is acquired at the end of the pre-exposure. For example, the pre-reading time period can be 10 microseconds or other time intervals between the end of pre-exposure and the beginning of effective exposure.

[0070] In an embodiment, the voltage signal of the pixel unit can be directly pre-read in the pixel unit, the voltage signal reflecting a degree of light response of the pixel unit to the current scene brightness and being used to represent a brightness interval (such as low brightness, medium brightness or high brightness) of the incident light intensity received by the pixel unit. The pre-reading is completed in the pixel unit, which can avoid interference caused by long-distance transmission of an analog signal, improve the reliability of signal sampling, and complete brightness determination without outputting the voltage signal through an external analog-digital conversion path.

[0071] Combined reference Figure 2As shown, it displays four pixel units Pixel 1, Pixel 2, Pixel 3 and Pixel 4 of the same column, taking Pixel 1 as an example, the pixel circuit in the pixel unit includes a photodiode PD, a transfer transistor TX, a floating diffusion node (FD), a switch transistor DCG, a reset transistor RST, a lateral overflow integration capacitor (LOFIC) Cs, a first power supply Vddrst, a second power supply Vddsf, a source follower SF, a selection transistor SEL and a column output bus OUT. Among them, the anode of the photodiode PD is connected to the ground, the cathode of the photodiode PD is connected to the source of the transfer transistor TX, the drain of the transfer transistor TX is connected to the floating diffusion node FD and the source of the switch transistor DCG, the drain of the switch transistor DCG is connected to the upper plate of the lateral overflow integration capacitor Cs, and the drain of the reset transistor RST is connected to the first power supply Vddrst; the lower plate of the lateral overflow integration capacitor Cs is connected to the ground.

[0072] In Figure 2 As shown in the pixel circuit based on the LOFIC structure, the floating diffusion node FD has an associated floating diffusion capacitor Cfd for temporarily storing the voltage signal converted from the photo-generated charge. After the current frame image exposure starts, enter the pre-reading time period, control the pixel unit to pre-expose in the pre-reading time period, and turn on the transfer transistor TX at the end of the pre-reading time period, transfer the charge accumulated in the photodiode PD to the floating diffusion node FD or the lateral overflow integration capacitor Cs, and through the pre-reading operation, the source follower SF buffers the voltage of the floating diffusion node FD or the lateral overflow integration capacitor Cs node as an analog voltage signal, and outputs to the column bus after turning on the selection transistor SEL, forming a pre-reading voltage signal Vpix_pre. Vpix_pre is controlled by the column selection signal ColSel to enter the column register array for temporary storage, and is read by the exposure setting logic ESL module, compared with multiple threshold voltages to determine the brightness interval, and assigned to the corresponding shutter channel and shutter control parameters.

[0073] The introduction of LOFIC helps to guide the excess charge to the additional capacitor in the high light scene, prevent charge overflow and expand the charge capacity of the pixel unit, so as to maintain the linear response of Vpix_pre in the high light condition, and improve the accuracy of brightness interval determination.

[0074] In addition, as Figure 2As shown, after the end of the effective exposure phase, it enters the image readout phase. The FD node stores the photo-generated charges generated by the effective exposure and converts them into effective voltage signals, which are then output to the column bus through SF and SEL to obtain the formal output data Vout of this frame of image.

[0075] In an alternative embodiment, the column circuit or the row buffer stage can also be used to pre-read the voltage signal and perform brightness judgment, and specific optimization design can be carried out according to the application scenario and system integration.

[0076] After obtaining the voltage signal, perform step 120 above, and use the voltage signal of each pixel unit to determine its current brightness interval. The brightness interval is the brightness level range divided according to multiple threshold voltages (representing the light intensity), and each brightness interval corresponds to a range of light intensity, which can be preset according to the specific scenario. Figure 3 As shown, Vrst represents the reset voltage and Vsat represents the saturation voltage. Taking the time before the trigger of shutter channel 0 as an example, the exposure control logic module compares the pre-read Vpix_pre with multiple preset threshold voltages (exemplarily, Vref1, Vref2, Vref3), determines the current brightness interval of each pixel unit, and assigns the corresponding shutter channel and shutter control parameters according to this. The shutter control parameters of different shutter channels can include different exposure times.

[0077] Taking Figure 3 as an example, after the pre-read time period T0, at the termination time point of T0, the pre-read voltage signal Vpix_pre is greater than the first threshold voltage Vref1 (Vpix_pre > Vref1), and Vref1 corresponds to the low brightness interval, then Figure 3 the pixel unit shown corresponds to the low brightness interval;

[0078] Before Figure 4 the shown Shutter 1, after the pre-read time period T0, the voltage signal Vpix_pre is between the second threshold voltage Vref2 and the first threshold voltage Vref1 (Vref2 < Vpix_pre ≤ Vref1), corresponding to the medium-low brightness interval;

[0079] Before Figure 5 the shown Shutter 2, after the pre-read time period T0, the voltage signal Vpix_pre is between the third threshold voltage Vref3 and the second threshold voltage Vref2 (Vref3 < Vpix_pre ≤ Vref2), corresponding to the medium-high brightness interval;

[0080] Before Figure 6Before the shutter 3 is shown, the voltage signal Vpix_pre is less than Vref3 (Vpix_pre≤Vref3) for a pre-reading time period T0, corresponding to the high brightness interval.

[0081] As described above Figures 3-6 Four threshold voltages and corresponding four brightness intervals are shown, which is an example. In actual applications, the number of threshold voltages and the number of corresponding brightness intervals can be designed as needed.

[0082] In the above embodiment, a plurality of threshold voltages arranged from low to high and a plurality of corresponding brightness intervals are obtained, and a step-by-step comparison or parallel comparison method is used to determine the threshold voltage level corresponding to the voltage signal of each pixel unit, and the current brightness interval corresponding to the threshold voltage level is determined.

[0083] The step-by-step comparison method refers to sequentially comparing Vpix_pre with a plurality of threshold voltages arranged from low to high, and if Vpix_pre meets the set condition (for example, greater than a certain threshold voltage), it is determined that the corresponding current brightness level is determined, and its belonging threshold voltage level is determined. The parallel comparison method refers to comparing Vpix_pre with all threshold voltages at the same time through a comparator array, which significantly improves the processing speed. According to the comparison result, the brightness interval number (such as 0: low brightness, 1: medium brightness, 2: high brightness) is output, and the number is mapped to the corresponding shutter channel number for exposure control logic module to allocate shutter control parameters.

[0084] In the embodiment of the present disclosure, after determining the current brightness interval corresponding to each pixel unit, step 130 is performed, and each pixel unit is assigned a corresponding shutter channel based on its current brightness interval, and corresponding shutter control parameters are provided through each shutter channel.

[0085] Optionally, the shutter channel can correspond to a combination of a hardware trigger signal (such as EXRST) and a logic port, which is used to schedule the corresponding shutter control parameters. There can be a mapping relationship between the current brightness interval, the shutter channel and the shutter control parameter, wherein the pixel units with the same current brightness interval can share the shutter channel to reduce the resource occupation of the shutter channel.

[0086] In some embodiments, the shutter control parameters can include:

[0087] Exposure time control strategy: different effective exposure times are allocated for different brightness intervals to avoid overexposure or underexposure, for example, long exposure time is allocated for low brightness interval and short exposure time is allocated for high brightness interval;

[0088] Gain control strategy: different analog gain or digital gain levels are assigned to pixel units, which can be used alone or in combination with exposure time control strategy to achieve a wider dynamic range, for example, high conversion gain (HCG) and low conversion gain (LCG) switching is adopted;

[0089] Exposure mode switching strategy: select the integration path of the pixel unit, for example, switch between the main capacitor path and the lateral overflow integration capacitor (LOFIC) path, which can enable LOFIC shunt to improve charge capacity when in high brightness interval.

[0090] Optionally, the shutter channel allocation can be batch configured by row, column or pixel group within the pixel array, or independently configured for a single pixel; the channel allocation mode can adopt different implementation modes such as hardware register writing, lookup table mapping or firmware algorithm dynamic calculation.

[0091] During the effective exposure time period, the exposure control logic module can activate each shutter channel according to a preset scheduling strategy, output corresponding trigger signals and control parameters, thereby implementing differentiated exposure control on pixel units in different brightness intervals and achieving pixel-level dynamic exposure adjustment.

[0092] In some embodiments, to implement the shutter channel allocation based on brightness intervals described above, the following register array-based implementation mode can be adopted:

[0093] According to the current brightness interval of each pixel unit, a corresponding shutter channel number is assigned and written into a register array, with each pixel unit corresponding to one or more register fields. In this way, the exposure control logic module can schedule the corresponding shutter channel based on the shutter channel number stored in the register array through row and column signal, and control the exposure of the corresponding pixel unit based on the corresponding shutter control parameter, thereby generating a single frame image.

[0094] In one example, as Figures 3-6 shown, Te represents the effective exposure time, and the mapping relationship between the brightness interval and the shutter channel (e.g. Shutter0~Shutter3) can be: low brightness interval is assigned Shutter0 (corresponding to the longest exposure time), medium-low brightness interval is assigned Shutter1, medium-high brightness interval is assigned Shutter2, and high brightness interval is assigned Shutter3 (corresponding to the shortest exposure time). This mapping relationship can be adjusted according to specific application scenarios.

[0095] Each pixel unit occupies one or more fields in the register array for storing shutter channel number (e.g. binary 00 represents Shutter0, 01 represents Shutter1, 10 represents Shutter2, and so on). The exposure control logic module can write shutter channel number into the register array through the data bus, and also can update synchronously with the system master through the I2C interface to ensure the real-time and accuracy of the allocation result. The efficient storage structure of the register array supports fast batch reading, row or column access, and multiplexing between multiple frames of images, thereby optimizing the system performance.

[0096] In the embodiment of the present disclosure, when performing step 140, the shutter channels are triggered in an interleaved manner within multiple clock cycles, and the interleaved triggering is activated in turn with the same or different intervals in each clock cycle to control the exposure of each pixel unit based on the corresponding shutter control parameter. By interleaving the shutter mode to stagger the triggering timing of the corresponding shutter channel, the exposure control of the corresponding pixel unit is realized.

[0097] In combination with Figure 2 and Figure 7 As shown, the exposure control logic module sends an EXRST (Extended Reset) signal to the corresponding row of pixel units as a reset control signal for resetting the floating diffusion node (FD) or other charge storage node to Vddrst. Figure 7 In the embodiment, EXRST1 to EXRST4 correspond to Figures 3 to 6 In the embodiment, the reset control signals (shutter0~shutter3) of the pixel units in different exposure intervals.

[0098] In the embodiment, the reset control signals (shutter0~shutter3) of the pixel units in different exposure intervals. Figure 7 In the embodiment, the shutter stage is used to clear the previous frame signal and start the current frame exposure. The pre-read (Pre-read) time period is the preparation stage of the current frame exposure. After the pre-read time period ends, the effective exposure (EffectiveExpo) time period is entered. The pre-read time period selects the pixel row through the SEL, TXread, RSTread signals to complete the voltage signal pre-sampling. In the effective exposure time period, the ΦExpo signal is pulled high, and EXRST1~EXRST4 are pulled high in turn, respectively starting the exposure window of the corresponding shutter channel to form an interleaved shutter strategy.

[0099] Further reference is made to Figure 8In the pixel array shown, Row Address represents the row address, EXRST1-EXRST4 are reset control signals corresponding to four types of pixel units respectively, different pixel units in the same row respond to different EXRST signals to achieve classified triggering. For example, taking the first row Row Address=0 as an example, in response to the EXRST1 signal, three same type pixel units are triggered synchronously; in response to the EXRST2 signal, two same type pixel units are triggered synchronously, and the three same type pixel units corresponding to the EXRST1 signal and the two same type pixel units corresponding to the EXRST2 signal are triggered alternately. In this way, EXRST1-EXRST4 correspond to four types of pixel units, realizing classification and staggered triggering of pixel units in the same row.

[0100] Figure 2 The pixel circuit shown includes a pre-reading reset transistor RSTread and a pre-reading transfer transistor TXread, the control ends of which are coupled to the reset transistor RST and the transfer transistor TX in the same row of pixel units. In this embodiment, the timing switching of the RSTread and TXread signals is controlled by the ΦExpo pulse, and the exposure start and charge processing of each row of pixel units are managed. The EXRST<1:4> pulse is applied through column address decoding logic to activate the corresponding shutter path, thereby realizing the sequential opening of exposure by row and by type.

[0101] The specific timing is as follows:

[0102] In the shutter stage of the previous frame signal, the DCG, TXread, and RSTread gates are all pulled high, keeping the pixels in the same row reset, preparing for pre-reading. The ΦExpo remains low, and the effective exposure has not yet begun.

[0103] In the pre-reading (Pre-read) period, the SEL is pulled high for a short time to select the corresponding row of pixel circuits, and the TXread is pulled low and then pulled high for a short time to transfer the charges in the PD to the FD. The SF buffers the analog voltage and outputs it to the column bus through the SEL, forming a voltage signal Vpix_pre that reflects the current light intensity. No reset operation is performed in this stage to ensure that the sampled data truly reflects the current brightness. The TXread is then pulled low, and the RSTread remains pulled low to prevent the pre-reading signal from being emptied.

[0104] In the effective exposure period, the ΦExpo is pulled high, and the shutter channels EXRST1-EXRST4 corresponding to the pixel units in the same row are pulled high alternately, respectively allocating different shutter channels and opening the exposure in time sequence to form a staggered exposure strategy (Staggered Shutter). After the effective exposure ends, the ΦExpo returns to low, the TXread, RSTread, and SEL are pulled high, and the image reading (Readout) stage is entered.

[0105] The present embodiment adopts a phased exposure control timing, divides the current frame exposure into a pre-reading and an effective exposure phase, and optimizes the trade-off between exposure accuracy and system frame rate. In the pre-reading phase, the pixels are selected through ΦExpo and SEL, TXread and RSTread are respectively turned on to control the transmission and reset channels, the charge emptying before voltage signal pre-sampling is completed, and pre-sampling is performed to provide accurate brightness input for effective exposure.

[0106] In the effective exposure period, different shutter channels (EXRST1~EXRST4) are sequentially pulled up to control the exposure start time of the corresponding pixels, realizing pixel-level exposure control and adaptive exposure time adjustment. This scheme effectively reduces the instantaneous bandwidth pressure of the column bus, improves the frame rate, enhances the dynamic range, and optimizes the image fusion delay, which is suitable for high-speed and high-brightness difference acquisition tasks.

[0107] The present embodiment works cooperatively through row and column selection signals, so that different pixels in a two-dimensional pixel array can be set to different exposure times even if they are in the same row or column, supporting pixel-level fine-grained exposure control and adapting to high-brightness gradient and complex lighting environment. After exposure, the Readout timing is consistent with the traditional double conversion gain (DCG) pixel structure.

[0108] The traditional non-interlaced shutter method needs to sequentially complete various shutter exposures and readouts, and due to the large number of pixel array rows, the overall exposure period is long, which limits the system frame rate. The interlaced exposure of the present embodiment uses different exposure paths for different columns in the same clock cycle without interfering with each other, reducing column bus conflicts and improving the maximum frame rate.

[0109] In combination with the above, the row and column selection signals include a row selection signal (RowSel, ΦExpo pulse) and a column selection signal (ColSel). RowSel activates the pixel array row by row, and ColSel decodes the shutter channel number stored in the register array column to realize the scheduling of each pixel shutter channel. The scheduling is completed within a single row processing period to ensure efficiency. The trigger adopts an interlaced shutter mechanism, and the shutter channel trigger times are staggered (e.g., Shutter0 at T0+0ns, Shutter1 at T0+10ns, Shutter2 at T0+20ns), and the ΦExpo pulse is generated by a logic control module to control the exposure start.

[0110] There are three specific schemes for interlaced triggering:

[0111] Scheme 1 ( Figure 9 ): shutter0 is triggered again after shutter0 in the array is triggered, and so on. The start points of different exposure channels do not coincide, avoiding EXRST column interference, but the effective exposure time design is limited.

[0112] Scheme 2 (Figure 10 ): Compared with scheme 1, each shutter is staggered and selected, and the exposure time is overlapped, so that the design flexibility is improved, and various scenes are adapted.

[0113] Scheme 3: Further improve the coincidence degree of triggering of different shutter channels, compress the shutter triggering window, and improve the upper limit of frame rate. Through the optimization of the hardware architecture by the double-column ADC structure, the parallel readout capability is improved, the readout time is shortened, and the frame rate is improved.

[0114] Compared with the traditional Stagger HDR scheme which only outputs one frame of image, the present embodiment supports pixel-level exposure time control, can independently adjust the pixel exposure time, improves the exposure flexibility, simplifies the data transmission and subsequent processing, and reduces the system bandwidth occupation and image fusion delay.

[0115] Compared with schemes 2 and 3, by compressing the shutter channel triggering interval, the effective exposure processes of different pixel units are partially overlapped in the effective exposure time, the frame period is shortened, and the system frame rate is improved.

[0116] In combination with Figure 11 , in a high frame rate application, a pre-reading (pre-read) operation is allowed to be introduced in a normal pixel reading (Readout) process, such as the introduction of pre-read in the left Readout process, to realize a "sliding window type" staggered design. This design is similar to staggered exposure, improves the exposure design flexibility and the highest frame rate, and increases the upper limit of the effective exposure time, reduces the signal loss caused by charge overflow.

[0117] The present disclosure also provides an image sensor, referring to Figure 12 , the image sensor can include:

[0118] a pixel array 1 including a plurality of pixel units 11;

[0119] an exposure control logic module 2 connected with the pixel array 1 and configured to:

[0120] pre-expose each pixel unit 11 in a pre-reading time period starting from the beginning of the current frame image exposure stage, and pre-read the voltage signal of each pixel unit at the end of the pre-exposure, the voltage signal reflecting the degree of illumination response of the current scene brightness to the pixel unit 11;

[0121] determine the current brightness interval corresponding to each pixel unit 11 according to the comparison result of the voltage signal of each pixel unit 11 and a plurality of threshold voltages;

[0122] According to the current brightness interval of each pixel unit 11, a corresponding shutter channel is allocated, wherein at least two pixel units with different current brightness intervals are respectively allocated different shutter channels, and the shutter control parameters of different shutter channels are different;

[0123] After the end of the pre-reading time period, the charges of each pixel unit 11 are cleared, and during the effective exposure time period, the shutter channel allocated to each pixel unit 11 is scheduled to control the effective exposure of the corresponding pixel unit 11 based on the corresponding shutter control parameter, thereby obtaining a current frame image.

[0124] Based on the image sensor of the embodiment, the pixel-level pre-reading voltage analysis mechanism and the multi-channel exposure signal allocation strategy are combined, the shutter channel of each pixel unit can be dynamically adjusted during the effective exposure of each frame image, and the adaptive adjustment of the shutter control parameter at the pixel level is realized. Through efficient data scheduling, the data redundancy is significantly reduced, the system frame rate is improved, and the imaging task in a high brightness difference, high-speed motion and complex lighting environment is especially suitable.

[0125] The exposure control logic module 2 is connected to the pixel array 1 through a high-speed data bus to perform the exposure control function. The exposure control logic module 2 specifically realizes the following functions: comparing Vpix_pre of each pixel unit with each threshold voltage to determine the corresponding current brightness interval. According to the current brightness interval, a shutter channel number (such as Shutter0~Shutter3 above) is allocated, and the shutter channel number is written into a register array. Subsequently, during the effective exposure time period of the current frame image, based on the shutter channel number in the register array, each shutter channel is scheduled through a row selection signal (RowSel, corresponding to ΦExpo signal) and a column selection signal (ColSel, decoding EXRST signal), and is activated one by one in a staggered trigger mode, realizing multi-shutter channel staggered exposure, and finally generating a single-frame HDR image.

[0126] This scheme not only improves the flexibility and precision of pixel-level exposure control, but also reduces the instantaneous bandwidth pressure of the column bus through staggered triggering, effectively improves the overall frame rate and dynamic range, and greatly enhances the imaging performance of the image sensor in complex environments.

[0127] In this embodiment, as shown in Figure 13 The exposure control logic module 2 can specifically include the following modules:

[0128] The pre-reading module 1310 is configured to control the pre-exposure of each pixel unit during a pre-reading time period starting from the beginning of the exposure phase of the current frame image, and pre-read the voltage signal of each pixel unit at the end of the pre-exposure;

[0129] The voltage comparison module 1320 is configured to determine the current brightness interval corresponding to each pixel unit according to a comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages.

[0130] The distribution module 1330 is configured to distribute a corresponding shutter channel to each pixel unit according to the current brightness interval of the pixel unit, wherein at least two pixel units with different current brightness intervals are respectively distributed with different shutter channels, and the shutter control parameters of the different shutter channels are different.

[0131] The exposure module 1340 is configured to clear the charge of each pixel unit after the pre-reading time period ends, and control the effective exposure of the corresponding pixel unit based on the shutter control parameter of the shutter channel distributed to the pixel unit during the effective exposure time period, to obtain a current frame image.

[0132] In the embodiment, the pixel-level exposure control is realized by introducing the above program module in the exposure control logic module 2.

[0133] In an optional embodiment, the shutter channel is triggered in an interleaved manner in a plurality of clock cycles to control the exposure of each pixel unit based on the corresponding shutter control parameter.

[0134] In an optional embodiment, the shutter control parameter includes an effective exposure time, and the effective exposure time intervals of different pixel units partially overlap, so as to compress the overall exposure time and be compatible with the exposure requirements of different types of pixel units.

[0135] In an optional embodiment, the exposure control logic module 2 is specifically configured to pre-read the voltage signal of the pixel unit in the pixel unit.

[0136] In an optional embodiment, in combination with Figure 2 As shown in the figure, each pixel unit includes a source follower SF, a selection transistor SEL, and a lateral overflow integration capacitor Cs; and the exposure control logic module 2 is configured to:

[0137] convert the voltage on the floating diffusion node FD or the lateral overflow integration capacitor Cs into the voltage signal output by the selection transistor SEL through the source follower SF.

[0138] In an optional embodiment, the exposure control logic module 2 is configured to:

[0139] In an optional embodiment, a plurality of threshold voltages arranged from low to high and a plurality of brightness intervals corresponding to the threshold voltages are obtained, a step-by-step comparison or a parallel comparison is used to determine the threshold voltage level corresponding to the voltage signal of each pixel unit 11, and the current brightness interval corresponding to the threshold voltage level is determined.

[0140] In an optional embodiment, the pixel unit includes a photodiode PD, a transfer transistor TX, a reset transistor RST, and a lateral overflow integration capacitor Cs; the exposure control logic module 2 is further configured to clear the charge of each pixel unit in the following manner:

[0141] The charge of the photodiode PD is transferred to the floating diffusion node FD through the transfer transistor TX, and the charge of the floating diffusion node FD or the lateral overflow integration capacitor Cs is immediately cleared through the reset transistor RST after the pre-reading is completed.

[0142] In an alternative embodiment, reference Figure 2 As shown, the image sensor includes a pre-read reset transistor RSTread and a pre-read transfer transistor TXread, wherein the control terminal of each pre-read reset transistor RSTread is coupled to the control terminal of each reset transistor RST in the same row of pixel units, and the control terminal of each pre-read transfer transistor TXread is coupled to the control terminal of each transfer transistor TX in the same row of pixel units; the exposure control logic module 2 is further configured as follows:

[0143] By controlling the pre-read transfer transistor TXread, each transfer transistor TX in the same row of pixel units transfers the charge in the photodiode PD to the floating diffusion node, and by controlling the pre-read reset transistor RSTread, each reset transistor RST in the same row of pixel units clears the charge of the floating diffusion node FD or the lateral overflow integration capacitor Cs.

[0144] Combine Figure 2 As shown, during the pre-read period after the current frame image exposure phase begins, the pixel unit converts the voltage on the floating diffusion node FD or the lateral overflow integration capacitor Cs into a voltage signal Vpix_pre through the source follower SF. This voltage signal is then selected by ColSel via the column output bus OUT and stored in the column register. The reset operation transfers the charge of PD to FD via TX, and then clears the charge of FD or Cs via RST. The pre-read transfer transistor TXread and the pre-read reset transistor RSTread control the reset of the pixel units in the same row. Multiple rows of pixel units share the pre-read transfer transistor and pre-read reset transistor, optimizing the chip layout area.

[0145] In this embodiment, the image sensor utilizes a stacked chip structure, comprising a main chip integrating the pixel array and a second chip comprising the exposure control logic module. The main chip is configured to lay out the pixel array and specifically pre-read the voltage signal for each pixel unit. The exposure control logic module can perform voltage signal pre-reading operations via the main chip. For example, the main chip can perform pre-reading operations under the instructions of the second chip.

[0146] Through the above-mentioned stacked chip structure, decoupling between functional modules and optimized configuration of system resources are achieved. Through the above-mentioned division mechanism, the following technical advantages are obtained:

[0147] By setting the exposure control logic module in the second chip, the scale of the main chip is significantly reduced, the chip area is easier to control, and it is suitable for high pixel density layout; at the same time, the logic power consumption is reduced, which helps to meet the needs of mobile terminals or power sensitive scenarios. And the exposure control logic module and the pixel array are physically and functionally decoupled, so that different exposure control logic modules can be flexibly replaced or upgraded according to the scene requirements, improving the design flexibility and maintainability. This ultimately enables the image sensor of the present case to support system-level expansion for large-scale image arrays or special control requirements (such as high-speed linear array exposure control). In addition, the stacked chip structure can flexibly deploy higher computing power or parallel control logic to solve the control resource bottleneck problem under the traditional single-chip architecture.

[0148] Other embodiments of the present disclosure will be apparent to those skilled in the art with the consideration of the specification and practice of the disclosure disclosed herein. The present disclosure is intended to cover any variations, uses, or adaptive changes of the present disclosure that follow the general principles of the present disclosure and include common knowledge or conventional technical means in the art that are not disclosed by the present disclosure. The specification and examples are only considered as exemplary, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. An image sensor exposure control method, characterized by, The method comprises: controlling each pixel unit to pre-expose during a pre-reading period starting from the beginning of the current frame image exposure stage, and pre-reading the voltage signal of each pixel unit at the end of the pre-exposure, the voltage signal reflecting the degree of light response of the current scene brightness to the pixel unit; determining the current brightness interval corresponding to each pixel unit according to the comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages; allocating a corresponding shutter channel to each pixel unit according to the current brightness interval of each pixel unit, wherein at least two different shutter channels are allocated to different pixel units with different current brightness intervals, and the shutter control parameters of different shutter channels are different, wherein the shutter channels are triggered in an interleaved manner in a plurality of clock cycles to control the exposure of each pixel unit based on the corresponding shutter control parameters, and the shutter control parameters include an effective exposure time, so that the effective exposure processes of different pixel units partially overlap in the effective exposure time; after the pre-reading period ends, emptying the charge of each pixel unit, and during the effective exposure period, controlling the effective exposure of the corresponding pixel unit based on the shutter control parameters of the shutter channel allocated to each pixel unit by scheduling the shutter channel, to obtain the current frame image.

2. The image sensor exposure control method according to claim 1, characterized by, The method further comprises: allocating a corresponding shutter channel number to each pixel unit according to the current brightness interval of each pixel unit, and writing the shutter channel number into a register array, each pixel unit corresponding to one or more register fields; The method further comprises: scheduling the shutter channel corresponding to each pixel unit by row and column selection signals based on the shutter channel number stored in the register array.

3. The image sensor exposure control method according to claim 1, characterized by, The pre-reading of the voltage signal of each pixel unit comprises pre-reading the voltage signal of the pixel unit inside the pixel unit.

4. The image sensor exposure control method according to claim 3, characterized by, Each pixel unit comprises a source follower, a selection transistor, and a lateral overflow integration capacitor; and the pre-reading of the voltage signal of the pixel unit inside the pixel unit comprises: converting the voltage on the floating diffusion node or the lateral overflow integration capacitor into the voltage signal output by the selection transistor through the source follower.

5. The image sensor exposure control method of claim 1, wherein determining the current brightness interval corresponding to each pixel unit according to the comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages comprises: obtaining a plurality of threshold voltages arranged from low to high and a plurality of brightness intervals corresponding to the threshold voltages, determining the threshold voltage level corresponding to the voltage signal of each pixel unit by using a step-by-step comparison or parallel comparison method, and determining the current brightness interval corresponding to the threshold voltage level.

6. The image sensor exposure control method according to claim 1, characterized by, The pixel unit comprises a photodiode, a transfer transistor, a reset transistor, and a lateral overflow integration capacitor; and the emptying of the charge of each pixel unit comprises: The charge in the photodiode is transferred to a floating diffusion node through the transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied through the reset transistor.

7. The image sensor exposure control method according to claim 6, characterized by, The image sensor further comprises a pre-reading reset transistor and a pre-reading transfer transistor, each of the pre-reading reset transistor is coupled to each of the reset transistor in the same row of pixel units, and each of the pre-reading transfer transistor is coupled to each of the transfer transistor in the same row of pixel units. The method further comprises: The charge in the photodiode is transferred to a floating diffusion node through the transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied through the reset transistor.

8. An image sensor, comprising: The method further comprises: An image sensor comprises: A pixel array comprising a plurality of pixel units; An exposure control logic module connected to the pixel array and configured to: In a pre-reading period starting from the beginning of the current frame image exposure stage, control each pixel unit to pre-expose, and read the voltage signal of each pixel unit at the end of the pre-exposure, the voltage signal reflecting the degree of illumination response of the current scene brightness to the pixel unit; Determine the current brightness interval corresponding to each pixel unit according to the comparison result of the voltage signal of each pixel unit and a plurality of threshold voltages; Assign a corresponding shutter channel to each of the pixel units according to the current brightness interval thereof, wherein at least two of the pixel units with different current brightness intervals are assigned different shutter channels, and the shutter control parameters of different shutter channels are different, wherein the shutter channels are triggered in an interleaved manner in a plurality of clock cycles to control the exposure of each pixel unit based on the corresponding shutter control parameters, and the shutter control parameters include an effective exposure time, so that the effective exposure processes of different pixel units partially overlap in the effective exposure time.

9. The image sensor of claim 8, wherein, After the pre-reading period ends, empty the charge of each pixel unit, and in an effective exposure period, control the effective exposure of the corresponding pixel unit based on the shutter control parameters of the shutter channel assigned to each pixel unit by scheduling the shutter channel, to obtain the current frame image.

10. The image sensor of claim 8, wherein, The image sensor adopts a stacked chip structure, comprising a main chip integrating the pixel array and a second chip comprising the exposure control logic module. The pixel unit comprises a photodiode, a transfer transistor, a reset transistor and a lateral overflow integration capacitor; and the exposure control logic module is further configured to empty the charge of each pixel unit in the following manner: The charge in the photodiode is transferred to a floating diffusion node through the transfer transistor, and the charge of the floating diffusion node or the lateral overflow integration capacitor is emptied through the reset transistor.

11. The image sensor of claim 10, wherein, The image sensor further comprises a pre-read reset transistor and a pre-read transfer transistor, each of the pre-read reset transistor is coupled to each of the reset transistor in the same row of pixel units, and each of the pre-read transfer transistor is coupled to each of the transfer transistor in the same row of pixel units; the exposure control logic module is specifically configured to: by controlling the pre-read transfer transistor, each of the transfer transistor in the same row of pixel units transfers the charge in the photodiode to the floating diffusion node, and by controlling the pre-read reset transistor, each of the reset transistor in the same row of pixel units empties the charge of the floating diffusion node or the lateral overflow integration capacitor.

Images