CN112420759B - Complementary Metal Oxide Semiconductor (CMOS) image sensor pixel structure based on bionic vision - Google Patents
Complementary Metal Oxide Semiconductor (CMOS) image sensor pixel structure based on bionic vision Download PDFInfo
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Abstract
The invention relates to the technical field of CMOS image sensors, and provides a pixel structure of a CMOS image sensor based on bionic vision, which comprises the following components: a color signal collecting unit, a black-and-white signal collecting unit, a third transfer transistor TG3, a reset transistor RST, a source follower SF, and a row select transistor RS; the black-and-white signal collection unit includes: a first clamp photodiode PPD1, a first transfer transistor TG1, and a first floating diffusion capacitor FD1; the color signal collecting unit includes: a second clamp photodiode PPD2, a second transfer transistor TG2, and a second floating diffusion capacitance FD2. The invention can respectively obtain the black-white image signal and the color image signal with high sensitivity in the same CMOS image sensor.
Description
Technical Field
The invention relates to the technical field of CMOS image sensors, in particular to a pixel structure of a CMOS image sensor based on bionic vision.
Background
With the rapid development of semiconductor technology, the application range of CMOS image sensors has been expanded to the fields of intelligent automobiles, monitoring security, machine vision, consumer products, and the like. Especially in low-light imaging applications, parameters such as full well capacity, noise, dynamic range, sensitivity and signal-to-noise ratio will directly affect the imaging effect. In order to improve the imaging performance of a camera in a low-light environment, an image processing technology for realizing dark field enhancement by performing weighted synthesis on a dark field black-and-white image and a dark field color image is generated.
Currently, in order to obtain a black-and-white image with high responsiveness and a color image, a combination scheme of a color camera and a black-and-white camera is generally adopted. The current CMOS image sensor pixel adopts a 4T pixel structure, so that the signal can be read out and the exposure of the next frame can be carried out, but the structure can only realize the acquisition of one image, namely a black-and-white image or a color image, and can not acquire two images at the same time in the same pixel.
Disclosure of Invention
The invention mainly solves the technical problem that a black-and-white image signal and a color image signal cannot be obtained simultaneously on a CMOS image sensor in the prior art, and provides a pixel structure of the CMOS image sensor based on bionic vision, so that the black-and-white image signal and the color image signal with high sensitivity are respectively obtained in the same CMOS image sensor.
The invention provides a CMOS image sensor pixel structure based on bionic vision, which comprises: a color signal collecting unit, a black-and-white signal collecting unit, a third transfer transistor TG3, a reset transistor RST, a source follower SF, and a row select transistor RS;
the black-and-white signal collection unit includes: a first clamp photodiode PPD1, a first transfer transistor TG1, and a first floating diffusion capacitor FD1; the first clamping photodiode PPD1 has no color filter; the first clamping photodiode PPD1 is reversely biased, and the anode of the first clamping photodiode PPD1 is grounded, and the cathode of the first clamping photodiode PPD1 is connected with the drain electrode of the first transfer transistor TG 1; the source electrode of the first transfer transistor TG1 is connected with the first terminal of the first floating diffusion capacitor FD1; a second terminal of the first floating diffusion capacitor FD1 is grounded;
the color signal collecting unit includes: a second clamp photodiode PPD2, a second transfer transistor TG2, and a second floating diffusion capacitor FD2; the second clamping photodiode PPD2 is provided with a color filter; the second clamping photodiode PPD2 is reversely biased, and the anode of the second clamping photodiode PPD2 is grounded, and the cathode of the second clamping photodiode PPD2 is connected with the drain electrode of the second transfer transistor TG2; the source electrode of the second transfer transistor TG2 is connected with the first terminal of the second floating diffusion capacitor FD2; a first terminal of the floating diffusion capacitor FD2 is connected to the drain of the third transfer transistor TG 3;
the source electrode of the transfer transistor TG3 is connected to the first terminal of the first floating diffusion FD1 and to the source electrode of the reset transistor RST and the gate electrode of the source follower SF;
the drain electrode of the reset transistor RST is connected with a power supply voltage VDD;
the drain electrode of the source follower SF is connected with a power supply voltage VDD; the source of the source follower SF is connected to the drain of the row select transistor RS.
Preferably, the source of the row select transistor RS is connected to a readout circuit.
Preferably, the first floating diffusion FD1 has a capacitance of 5 to 10fF.
Preferably, the second floating diffusion FD2 has a capacitance of 700 to 1000fF.
Preferably, the working time sequence control process of the pixel structure of the CMOS image sensor based on bionic vision comprises the following steps:
the method comprises the steps of firstly, before a pixel structure of a CMOS image sensor starts to be exposed, pulling a reset Signal reset of a reset transistor RST to a high level, starting the reset transistor RST, simultaneously pulling a control Signal TX3 of a third transfer transistor TG3 to the high level, combining a first floating diffusion capacitor FD1 and a second floating diffusion capacitor FD2, pulling a first sampling Signal Samp1 high, reading a first reading Signal Signal1, and pulling a first sampling Signal Samp1 low after reading is finished; the first readout Signal1 is a charge Signal in a combined capacitor of the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2;
the second step, pull the control Signal TX3 of the third transfer transistor TG3 to a low level, split the combining capacitor into a first floating diffusion capacitor FD1 and a second floating diffusion capacitor FD2, pull the second sampling Signal Samp2 high, read the second read Signal2, and pull the second sampling Signal Samp2 low after the reading is completed; the second readout Signal2 is a charge Signal in the first floating diffusion capacitor FD1;
thirdly, exposing the pixel structure of the CMOS image sensor, and collecting photo-generated electrons in the first clamping photodiode PPD1 and the second clamping photodiode PPD 2;
fourth, after the exposure period is ended, the control signal TX1 of the first transfer transistor TG1 and the control signal TX2 of the second transfer transistor TG2 are pulled to high level, respectively, and photo-generated electrons are transferred to the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2, respectively; then, the third sampling Signal Samp3 is pulled up, the third read Signal3 of the first floating diffusion capacitor FD1 is read, and the third sampling Signal Samp3 is pulled down after the reading is finished, wherein the third read Signal3 is a charge Signal in the first floating diffusion capacitor FD1;
fifth, the control signal TX1 of the first transfer transistor TG1 and the control signal TX2 of the second transfer transistor TG2 are pulled to a low level, turning off the first transfer transistor TG1 and the second transfer transistor TG2; pulling the control signal TX3 of the third transfer transistor TG3 to a high level, mixing the charges in the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2; pulling up the fourth sampling Signal Samp4, reading a fourth read Signal4 of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2, and pulling down the fourth sampling Signal Samp4 after the reading is finished, wherein the fourth read Signal4 is a charge Signal of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2;
sixth, repeating the first step to start the next exposure.
The invention provides a CMOS image sensor pixel structure based on bionic vision, which is designed based on a bionic vision principle of matching and imaging human eye cone cells and video rod cells, and adopts two clamping photodiodes PPD to share the same readout circuit; in the first sampling period, reading out a first read Signal1 of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2 in the reset state; in the second sampling period, the third transfer transistor TG3 is turned off, and the second read Signal2 of the first floating diffusion FD1 in the reset state is read out; then turning on the first transfer transistor TG1 and the second transfer transistor TG2 to respectively derive photo-generated electrons collected in the first clamp photodiode PPD1 of the achromatic color filter to the first floating diffusion capacitor FD1, and derive photo-generated electrons collected in the second clamp photodiode PPD2 of the chromatic color filter to the second floating diffusion capacitor FD2, and reading out a third read Signal3 of the first floating diffusion capacitor FD1 in a third sampling period; the third transfer transistor TG3 is turned on, and the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2 are combined; in the fourth sampling period, the fourth read Signal4 of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2 is read out. And removing the reset noise signal through a correlated double sampling circuit to obtain a black-and-white image signal and a color image signal respectively.
The invention adopts the pixel structure design that the double PPDs share the same readout circuit, the first clamping photodiode PPD1 without the coverage of the color filter improves the sensitivity to incident light, can obtain clear black and white images, simultaneously improves the noise resistance of the pixels with high gain, and enhances the imaging capability of the image sensor under weak light. The second clamping photodiode PPD2 is provided with a color filter, so that a color image can be obtained, and meanwhile, the second clamping photodiode PPD2 is provided with a second floating diffusion capacitor FD2 which is larger than the achromatic filter PPD, so that the full-well capacity is improved, and the imaging capability of the image sensor under strong light is enhanced. Under the condition of low light level, the pixel structure of the CMOS image sensor can simultaneously obtain a color image and a black-and-white image for dark field enhancement, and compared with the prior double-lens scheme, the pixel structure of the CMOS image sensor further reduces the size of a camera, indicates the direction for miniaturization of the camera with the dark field enhancement technology, and has high research value and development prospect. In addition, the pixel structure of the invention supports the traditional correlated double sampling read-out circuit, can eliminate the reset noise caused by the reset operation, does not need extra read-out circuit design, and can directly adopt the traditional read-out mode.
Drawings
FIG. 1 is a schematic representation of the distribution of cone cells and rod cells in the human eye;
fig. 2 is a schematic structural diagram of a pixel structure of a CMOS image sensor based on bionic vision according to the present invention;
FIG. 3 is a schematic illustration of an achromatic color filter pixel;
FIG. 4 is a schematic diagram of a color filter pixel;
FIG. 5 is a working timing diagram of a pixel structure of a CMOS image sensor based on bionic vision provided by the invention;
fig. 6 is a schematic diagram of the working principle of the pixel structure of the CMOS image sensor based on bionic vision provided by the invention;
fig. 7 is a schematic diagram of a pixel array of a pixel structure of a CMOS image sensor based on bionic vision according to the present invention.
Detailed Description
In order to make the technical problems solved by the invention, the technical scheme adopted and the technical effects achieved clearer, the invention is further described in detail below with reference to the accompanying drawings and the embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the matters related to the present invention are shown in the accompanying drawings.
The pixel structure of the CMOS image sensor based on the bionic vision provided by the embodiment of the invention is designed based on the bionic vision principle, and the human eye can be regarded as an image sensor with up to 5.76 hundred million pixels. As shown in fig. 1, the human eye perceives external light signals through both cone cells and rod cells. The cone cells are mainly distributed in the central concave part of retina, are responsible for sensing strong light and color, and have higher resolution capability for strong light and color. The rod cells are mainly distributed at the edge of retina, and have no ability to distinguish colors, but have higher sensitivity and are more sensitive to dark light.
As shown in fig. 2, the CMOS image sensor pixel structure based on bionic vision according to the embodiment of the present invention includes: a color signal collecting unit, a black-and-white signal collecting unit, a third transfer transistor TG3, a reset transistor RST, a source follower SF, and a row select transistor RS;
the black-and-white signal collection unit includes: a first clamp photodiode PPD1, a first transfer transistor TG1, and a first floating diffusion capacitor FD1; the first clamping photodiode PPD1 has no color filter; the first clamping photodiode PPD1 is reversely biased, and the anode of the first clamping photodiode PPD1 is grounded, and the cathode of the first clamping photodiode PPD1 is connected with the drain electrode of the first transfer transistor TG 1; the source electrode of the first transfer transistor TG1 is connected with the first terminal of the first floating diffusion capacitor FD1; a second terminal of the first floating diffusion capacitor FD1 is grounded;
the color signal collecting unit includes: a second clamp photodiode PPD2, a second transfer transistor TG2, and a second floating diffusion capacitor FD2; the second clamping photodiode PPD2 is provided with a color filter; the second clamping photodiode PPD2 is reversely biased, and the anode of the second clamping photodiode PPD2 is grounded, and the cathode of the second clamping photodiode PPD2 is connected with the drain electrode of the second transfer transistor TG2; the source electrode of the second transfer transistor TG2 is connected with the first terminal of the second floating diffusion capacitor FD2; a first terminal of the second floating diffusion capacitor FD2 is connected to the drain of the third transfer transistor TG 3;
the source electrode of the transfer transistor TG3 is connected to the first terminal of the first floating diffusion FD1 and to the source electrode of the reset transistor RST and the gate electrode of the source follower SF;
the drain electrode of the reset transistor RST is connected with a power supply voltage VDD;
the drain electrode of the source follower SF is connected with a power supply voltage VDD; the source of the source follower SF is connected to the drain of the row select transistor RS.
The source of the row select transistor RS is connected to a readout circuit.
The pixel structure of the present invention is mainly composed of a clamp photodiode (pinned photodiode, PPD), a transfer Transistor (TG), a reset transistor (RST), a Source Follower (SF), a floating diffusion capacitor (floating diffusion capacitor, FD), and a row selection transistor (row select transistor, RS). As shown in fig. 3, the first clamp photodiode PPD1 has no color filter structure, and when incident light is emitted, all of the light can enter the first clamp photodiode PPD1 to generate photo-generated electrons, thereby generating an image signal. Therefore, the first clamping photodiode PPD1, the first transfer transistor TG1 and the first floating diffusion capacitor FD1 constitute a pixel structure for acquiring a black and white image signal, and since there is no color filter, PPD1 can only distinguish black and white signals and does not have the ability to distinguish colors, but at the same time, light loss due to the color filter is reduced, and the pixel structure has higher sensitivity to light. In addition, the first floating diffusion FD1 has a small capacitance of about 5 to 10fF, and can achieve a high conversion factor (Cvg), thereby improving sensitivity. As shown in fig. 4, the second clamping photodiode PPD2 has a color filter structure, and when incident light is emitted, light is filtered by the filter, and only light with a specific wavelength can enter the second clamping photodiode PPD2, so as to generate a wide-range electron generated image signal. Accordingly, the second clamp photodiode PPD2, the second transfer transistor TG2, and the second floating diffusion capacitor FD2 constitute a pixel structure that acquires color image signals, which result in fewer collected image signals due to reflection of light by the color filter and filtering out incident light of non-designated wavelengths. The second floating diffusion capacitor FD2 has a larger capacitance, about 700-1000 fF, and can accommodate more photo-generated electrons in a strong light environment, with a larger full well capacity.
Fig. 5 is a timing diagram of the operation of a CMOS image sensor pixel structure based on bionic vision. The pixel structure of the CMOS image sensor based on bionic vision comprises the following steps of:
the method comprises the steps of firstly, before a pixel structure of a CMOS image sensor starts to be exposed, pulling a reset Signal reset of a reset transistor RST to a high level, starting the reset transistor RST, simultaneously pulling a control Signal TX3 of a third transfer transistor TG3 to the high level, combining a first floating diffusion capacitor FD1 and a second floating diffusion capacitor FD2, pulling a first sampling Signal Samp1 high, reading a first reading Signal Signal1, and pulling a first sampling Signal Samp1 low after reading is finished; the first readout Signal1 is a charge Signal in a combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2.
The second step, pull the control Signal TX3 of the third transfer transistor TG3 to a low level, split the combining capacitor into a first floating diffusion capacitor FD1 and a second floating diffusion capacitor FD2, pull the second sampling Signal Samp2 high, read the second read Signal2, and pull the second sampling Signal Samp2 low after the reading is completed; the second readout Signal2 is a charge Signal in the first floating diffusion FD 1.
Third, the CMOS image sensor pixel structure starts to be exposed, and photo-generated electrons are collected in the first clamp photodiode PPD1 and the second clamp photodiode PPD 2.
Fourth, the exposure period is ended, the control signal TX1 of the first transfer transistor TG1 and the control signal TX2 of the second transfer transistor TG2 are pulled to high level, respectively, and photo-generated electrons are transferred into the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2, respectively. Then, the third sampling Signal Samp3 is pulled up, the third read Signal3 of the first floating diffusion capacitor FD1 is read, and the third sampling Signal Samp3 is pulled down after the reading is completed, wherein the third read Signal3 is the charge Signal in the first floating diffusion capacitor FD 1.
Fifth, the control signal TX1 of the first transfer transistor TG1 and the control signal TX2 of the second transfer transistor TG2 are pulled to a low level, turning off the first transfer transistor TG1 and the second transfer transistor TG2. The control signal TX3 of the third transfer transistor TG3 is pulled to a high level, and charges in the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2 are mixed. The fourth sampling Signal Samp4 is pulled up, the fourth readout Signal4 of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2 is read, and the fourth sampling Signal Samp4 is pulled down after the reading is completed, wherein the fourth readout Signal4 is the charge Signal of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2.
Sixth, repeating the first step to start the next exposure.
The specific working principle of the pixel of the CMOS image sensor is shown in fig. 6. The broken line in the figure indicates a high level; arrows indicate electron transfer directions; wherein the lengths and widths of the first clamp photodiode PPD1, the second clamp photodiode PPD2, the first floating diffusion capacitor FD1, and the second floating diffusion capacitor FD2 do not represent the size of the space charge region and the capacitor; the first transfer transistor TG1, the second transfer transistor TG2, and the third transfer transistor TG3 have two control levels, and the control signal TX1 of the first transfer transistor TG1, the control signal TX2 of the second transfer transistor TG1, and the control signal TX3 of the third transfer transistor TG1 control the turning on of the three transfer transistors, respectively, at high levels, and the turning off of the three transfer transistors, respectively, at low levels. When the pixel works, the first transfer transistor TG1, the second transfer transistor TG2 and the third transfer transistor TG3 are all in an off state, and the first clamping photodiode PPD1 and the second clamping photodiode PPD2 collect photo-generated electrons in an integrating way under illumination; after the integration period is finished, the first transfer transistor TG1 and the second transfer transistor TG2 are turned on, and photo-generated electrons in the first clamp photodiode PPD1 and the second clamp photodiode PPD2 are transferred into the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2 respectively through transfer processes of transfer1 and transfer 2; after the transfer period is ended, the level in the first floating diffusion FD1, that is, the black-and-white image signal is read out; after the reading period 1 is finished, the third transfer transistor TG3 is turned on, the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2 are combined, and the charges stored in the two capacitors are also combined; the read period 2 starts and the level of the combining capacitance, i.e., the color image signal, is read. After the read period 2 is received, the pixel resumes its original state, waiting for the next read operation.
The pixel image sensor pixel of the present invention has four readout signals in one working period, which are respectively a first readout Signal1 of a combined capacitor of the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2 in a reset state, a second readout Signal2 of the first floating diffusion capacitor FD1 in a reset state, a third readout Signal3 of the first floating diffusion capacitor FD1 in a working state, and a fourth readout Signal4 of a combined capacitor of the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2 in a working state. The first readout Signal1 includes reset noise in the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2, the fourth readout Signal4 includes reset noise and an image Signal in the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2, and a color image Signal from which the reset noise is eliminated can be obtained by making a difference between the fourth readout Signal4 and the first readout Signal 1. Similarly, the second read Signal2 contains the reset noise in the first floating diffusion capacitor FD1, the third read Signal3 contains the reset Signal and the image Signal in the first floating diffusion capacitor FD1, a black-and-white image Signal from which reset noise is eliminated can be obtained by making a difference between the third read Signal3 and the second read Signal 2.
In the present embodiment, the gates of the first transfer transistor TG1, the second transfer transistor TG2, and the third transfer transistor TG3 are controlled in their on and off states by signals TX1, TX2, and TX3, respectively; the gate voltage signal of the row selection transistor RS controls four readout operations by the first sampling signal Samp1, the second sampling signal Samp2, the third sampling signal3, and the fourth sampling signal Samp4, respectively; the gate voltage signal reset of the reset transistor RST controls the reset operation of the first floating diffusion capacitance FD1; the gate voltage signal reset of the reset transistor RST and the gate voltage TX3 of the third transfer transistor TG1 commonly control the reset operation of the second floating diffusion FD2.
Through the above readout process, readout operations for the reset signal, the black-and-white image signal, and the color image signal can be realized, respectively, and since the inventive pixel structure supports the correlated double sampling circuit, the influence of reset noise can be removed by the subtractor. When the black-white image signal is read out, the influence of noise on the signal can be reduced by the higher Cvg, and when the color image signal is read out, the image sensor can still normally work under stronger light rays due to the larger floating diffusion capacitance, so that high dynamic range imaging is realized.
Correspondingly, the present embodiment provides a pixel array layout of alternating achromatic color filter pixels and chromatic color filter pixels, as shown in fig. 7. In this pixel array layout, pixels with color filters are placed adjacent to each other and a conventional RGB layout is used to obtain a color image. On the basis of ensuring the unchanged pixel performance parameters, the dynamic range and the signal-to-noise ratio of the CMOS image sensor are improved, and the dark field imaging effect is greatly optimized.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments is modified or some or all of the technical features are replaced equivalently, so that the essence of the corresponding technical scheme does not deviate from the scope of the technical scheme of the embodiments of the present invention.
Claims (4)
1. A CMOS image sensor pixel structure based on bionic vision, comprising: a color signal collecting unit, a black-and-white signal collecting unit, a third transfer transistor TG3, a reset transistor RST, a source follower SF, and a row select transistor RS;
the black-and-white signal collection unit includes: a first clamp photodiode PPD1, a first transfer transistor TG1, and a first floating diffusion capacitor FD1; the first clamping photodiode PPD1 has no color filter; the first clamping photodiode PPD1 is reversely biased, and the anode of the first clamping photodiode PPD1 is grounded, and the cathode of the first clamping photodiode PPD1 is connected with the drain electrode of the first transfer transistor TG 1; the source electrode of the first transfer transistor TG1 is connected with the first terminal of the first floating diffusion capacitor FD1; a second terminal of the first floating diffusion capacitor FD1 is grounded;
the color signal collecting unit includes: a second clamp photodiode PPD2, a second transfer transistor TG2, and a second floating diffusion capacitor FD2; the second clamping photodiode PPD2 is provided with a color filter; the second clamping photodiode PPD2 is reversely biased, and the anode of the second clamping photodiode PPD2 is grounded, and the cathode of the second clamping photodiode PPD2 is connected with the drain electrode of the second transfer transistor TG2; the source electrode of the second transfer transistor TG2 is connected with the first terminal of the second floating diffusion capacitor FD2; a first terminal of the floating diffusion capacitor FD2 is connected to the drain of the third transfer transistor TG 3;
the source electrode of the transfer transistor TG3 is connected to the first terminal of the first floating diffusion FD1 and to the source electrode of the reset transistor RST and the gate electrode of the source follower SF;
the drain electrode of the reset transistor RST is connected with a power supply voltage VDD;
the drain electrode of the source follower SF is connected with a power supply voltage VDD; the source electrode of the source follower SF is connected with the drain electrode of the row selection transistor RS;
the working time sequence control process of the pixel structure of the CMOS image sensor based on bionic vision comprises the following steps:
the method comprises the steps of firstly, before a pixel structure of a CMOS image sensor starts to be exposed, pulling a reset Signal reset of a reset transistor RST to a high level, starting the reset transistor RST, simultaneously pulling a control Signal TX3 of a third transfer transistor TG3 to the high level, combining a first floating diffusion capacitor FD1 and a second floating diffusion capacitor FD2, pulling a first sampling Signal Samp1 high, reading a first reading Signal Signal1, and pulling a first sampling Signal Samp1 low after reading is finished; the first readout Signal1 is a charge Signal in a combined capacitor of the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2;
the second step, pull the control Signal TX3 of the third transfer transistor TG3 to a low level, split the combining capacitor into a first floating diffusion capacitor FD1 and a second floating diffusion capacitor FD2, pull the second sampling Signal Samp2 high, read the second read Signal2, and pull the second sampling Signal Samp2 low after the reading is completed; the second readout Signal2 is a charge Signal in the first floating diffusion capacitor FD1;
thirdly, exposing the pixel structure of the CMOS image sensor, and collecting photo-generated electrons in the first clamping photodiode PPD1 and the second clamping photodiode PPD 2;
fourth, after the exposure period is ended, the control signal TX1 of the first transfer transistor TG1 and the control signal TX2 of the second transfer transistor TG2 are pulled to high level, respectively, and photo-generated electrons are transferred to the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2, respectively; then, the third sampling Signal Samp3 is pulled up, the third read Signal3 of the first floating diffusion capacitor FD1 is read, and the third sampling Signal Samp3 is pulled down after the reading is finished, wherein the third read Signal3 is a charge Signal in the first floating diffusion capacitor FD1;
fifth, the control signal TX1 of the first transfer transistor TG1 and the control signal TX2 of the second transfer transistor TG2 are pulled to a low level, turning off the first transfer transistor TG1 and the second transfer transistor TG2; pulling the control signal TX3 of the third transfer transistor TG3 to a high level, mixing the charges in the first floating diffusion capacitor FD1 and the second floating diffusion capacitor FD2; pulling up the fourth sampling Signal Samp4, reading a fourth read Signal4 of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2, and pulling down the fourth sampling Signal Samp4 after the reading is finished, wherein the fourth read Signal4 is a charge Signal of the combined capacitance of the first floating diffusion capacitance FD1 and the second floating diffusion capacitance FD2;
sixth, repeating the first step to start the next exposure.
2. The CMOS image sensor pixel structure based on the bionic vision according to claim 1, wherein the source of the row select transistor RS is connected to a readout circuit.
3. The CMOS image sensor pixel structure based on the bionic vision according to claim 1, wherein the capacitance of the first floating diffusion capacitance FD1 is 5 to 10fF.
4. The CMOS image sensor pixel structure based on the bionic vision according to claim 1, wherein the capacitance of the second floating diffusion capacitance FD2 is 700 to 1000fF.
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