CN114339086B - TOF image sensor pixel structure and ranging system - Google Patents
TOF image sensor pixel structure and ranging system Download PDFInfo
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Abstract
本发明属于图像传感器技术领域，涉及一种TOF图像传感器像素结构及测距系统，其中，TOF图像传感器像素结构，包括光传感器及传输电路。光传感器包括电位逐级递减的第一感光区域、第二感光区域及第三感光区域，用于产生电位差，协助自身产生的电荷流向与第三感光区域连接的传输电路。因此，本发明通过电位从高到低的第一感光区域、第二感光区域及第三感光区域能够将光传感器产生电荷快速的传输至传输电路，从而能够使得该电荷快速的传输到存储单元(例如存储节点或存储电容)，故而提高了光电二极管产生的电荷的传输效率，进而能够提高测距精度。
The present invention belongs to the technical field of image sensors, and relates to a TOF image sensor pixel structure and a ranging system, wherein the TOF image sensor pixel structure includes a light sensor and a transmission circuit. The light sensor includes a first photosensitive area, a second photosensitive area, and a third photosensitive area with a gradually decreasing potential, which are used to generate a potential difference and assist the charge generated by itself to flow to the transmission circuit connected to the third photosensitive area. Therefore, the present invention can quickly transmit the charge generated by the light sensor to the transmission circuit through the first photosensitive area, the second photosensitive area, and the third photosensitive area with a potential from high to low, so that the charge can be quickly transmitted to a storage unit (such as a storage node or a storage capacitor), thereby improving the transmission efficiency of the charge generated by the photodiode, and then improving the ranging accuracy.
Description
Technical Field
The present invention relates to the field of image sensors, and in particular, to a pixel structure of a TOF image sensor and a ranging system.
Background
Image sensors are important components constituting digital cameras, and can be classified into two major types, CCD (Charge Coupled Device ) image sensors and CMOS (Complementary Metal Oxide Semiconductor ) image sensors, according to the elements. The CMOS image sensor has the advantages of low power consumption, low cost, easy standardized production and the like, and is widely applied to various fields.
With rapid development of three-dimensional imaging information technology, especially building measurement, indoor positioning and navigation, stereoscopic imaging and assisted living environment application, urgent demands are placed on Time-of-Flight (TOF) imaging, and pixel structures of CMOS image sensors applied to the Time-of-Flight imaging system are rapidly developed. TOF image sensors can be classified into dTOF image sensors and iTOF image sensors. Wherein dTOF is an image sensor that directly measures the time of flight, i.e., the time interval between the transmitted light pulse and the received light pulse. Wherein iTOF image sensors, which measure time of flight indirectly, typically employ a method of measuring phase shift, i.e., measuring the phase difference between the transmitted sine wave/square wave and the received sine wave/square wave. For all types of TOF image sensors, ranging accuracy is an important parameter, and the higher the ranging accuracy, the more accurate the three-dimensional image detection of the target.
In the pixel of the TOF image sensor, the transmission efficiency of the charges generated by the photodiode directly affects the ranging accuracy, so how to improve the transmission efficiency of the charges generated by the photodiode is considered.
In view of the above problems, those skilled in the art have sought solutions.
The foregoing description is provided for general background information and does not necessarily constitute prior art.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a pixel structure of a TOF image sensor and a ranging system aiming at the defects of the prior art so as to achieve the purpose of improving the transmission efficiency of charges generated by a photodiode and further improve the ranging precision.
The invention is realized in the following way:
The invention provides a pixel structure of a TOF image sensor, which comprises a light sensor and a transmission circuit. The optical sensor comprises a first photosensitive area, a second photosensitive area and a third photosensitive area, the electric potential of which is gradually decreased, and the first photosensitive area, the second photosensitive area and the third photosensitive area are used for generating potential difference and assisting the generated electric charge to flow to a transmission circuit connected with the third photosensitive area.
Optionally, the shape of the lower end of the light sensor includes an inverted trapezoid, and the overall shape of the light sensor is U-shaped.
Optionally, the light sensor has a axisymmetric structure. The first photosensitive area is positioned at the upper end of the optical sensor and comprises at least two photosensitive parts which are symmetrically arranged with a central axis, and an opening area is arranged between the two adjacent photosensitive parts. The second photosensitive region and the third photosensitive region are both positioned at the lower end of the optical sensor, and the third photosensitive region is positioned at the bottom of the lower end, wherein the doping concentration of the third photosensitive region is higher than that of the second photosensitive region. The third photosensitive area is of a axisymmetric structure.
Alternatively, the number of at least two photosensitive portions is 3, and the number of opening areas is 2.
Optionally, the opening area is rectangular with a width in the range of 0.2-0.8um.
Optionally, the width of the opening area is 0.4um.
Optionally, the light sensor is obtained by patterning the upper end of the complete U-shaped light sensor to form a first light sensing region, and doping material adding treatment is performed on the bottom of the lower end of the complete U-shaped light sensor to form a third light sensing region.
Optionally, the patterning process includes punching the upper end of the complete U-shaped photosensor to form a filling region, and filling the P-type material in the filling region to form an opening region. The doping material increasing process includes increasing the concentration of N-type material to the bottom of the lower end of the completed U-shaped photosensor.
Optionally, the shape of the open area comprises at least one of a rectangular shape or a top-bottom shape. Inverted trapezium, inverted triangle, inverted semicircle or shape which becomes smaller from top to bottom.
Optionally, the photosensor and the transmission circuit form a complete TOF pixel circuit. The complete TOF pixel circuit includes one of a 2T pixel circuit, a 3T pixel circuit, a 4T pixel circuit, and a 5T pixel circuit.
Optionally, the transmission circuit includes a first read control module and a second read control module. The first reading control module and the second reading control module are connected with the light sensor and are used for carrying out reading control according to the electric charges.
Optionally, the first read control module further includes a first reset transistor, a first dual conversion gain control unit, a first pass transistor, a first storage capacitor, a first floating diffusion node, and a first output unit. The first end of the first reset transistor is connected to a voltage source, and the second end of the first reset transistor is coupled to the first floating diffusion node through the first dual conversion gain control unit. The first end of the first transmission transistor is connected to the cathode of the light sensor, and the second end of the first transmission transistor is connected with the first storage capacitor and the first floating diffusion node. The first output unit is connected with the first floating diffusion node. The second read control module further includes a second reset transistor, a second dual conversion gain control unit, a second transfer transistor, a second storage capacitor, a second floating diffusion node, and a second output unit. The first end of the second reset transistor is connected to the voltage source, and the second end of the second reset transistor is coupled to the second floating diffusion node through the second dual conversion gain control unit. The first end of the second transmission transistor is connected to the cathode of the light sensor, and the second end of the second transmission transistor is connected to the second storage capacitor and the second floating diffusion node. The second output unit is connected with the second floating diffusion node.
Optionally, the first output unit includes a first source follower transistor and a first row select transistor, and the second output unit includes a second source follower transistor and a second row select transistor. The first control end of the first source following transistor is connected with the first floating diffusion node, the first end of the first source following transistor is connected with a voltage source, and the second end of the first source following transistor is connected with a first data output line through the first row selection transistor. The second control terminal of the second source follower transistor is connected to the second floating diffusion node, the first terminal of the second source follower transistor is connected to the voltage source, and the second terminal of the second source follower transistor is connected to the second data output line through the second row select transistor.
Optionally, a charge balancing unit is also included. The charge balancing unit is connected with the first floating diffusion node of the first read control module and the second floating diffusion node of the second read control module and used for balancing charges of the first floating diffusion node and the second floating diffusion node after reset.
Optionally, an anti-overflow transistor is also included. The first end of the anti-overflow transistor is coupled to a voltage source, and the second end of the anti-overflow transistor is connected to the photosensor for removing charges generated by the photosensor due to background light when the modulated light is not turned on.
The invention also provides a ranging system comprising an image sensor comprising a plurality of arrays of pixels arranged in rows and columns, each pixel comprising a TOF image sensor pixel structure as described above. And the control signal processing unit is used for controlling the working process of the system and processing the image data acquired by the pixel array. The light source can be modulated, and is used for generating a modulated light signal after receiving the modulated signal and feeding the received modulated signal back to the pixel array.
The invention provides a TOF image sensor pixel structure and a ranging system, wherein the TOF image sensor pixel structure comprises a light sensor and a transmission circuit. The optical sensor comprises a first photosensitive area, a second photosensitive area and a third photosensitive area, the electric potential of which is gradually decreased, and the first photosensitive area, the second photosensitive area and the third photosensitive area are used for generating potential difference and assisting the generated electric charge to flow to a transmission circuit connected with the third photosensitive area. Therefore, the first photosensitive region, the second photosensitive region and the third photosensitive region with the potential from high to low can quickly transmit charges generated by the photosensor to the transmission circuit, so that the charges can be quickly transmitted to the storage unit (such as a storage node or a storage capacitor), the transmission efficiency of the charges generated by the photodiode is improved, and the ranging precision is further improved.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments, as illustrated in the accompanying drawings.
Drawings
FIG. 1 is a first schematic diagram of a pixel structure of a TOF image sensor according to a first embodiment of the present invention;
FIG. 2 is a second schematic diagram of a pixel structure of a TOF image sensor according to the first embodiment of the present invention;
FIG. 3 is a schematic diagram of a pixel structure of a TOF image sensor according to a second embodiment of the present invention;
FIG. 4 is a first schematic circuit diagram of a pixel structure of a TOF image sensor according to a second embodiment of the present invention;
FIG. 5 is a second circuit schematic of a pixel structure of a TOF image sensor according to a second embodiment of the present invention;
fig. 6 is a schematic structural diagram of a ranging system according to a third embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the described embodiments are merely some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Although the present invention uses the terms of first, second, third, etc. to describe different photosensitive regions, read control modules, reset transistors, output units, etc., these photosensitive regions, read control modules, reset transistors, output units, etc. are not limited by these terms. These terms are only used to distinguish one photosensitive region, read control module, reset transistor, output unit, etc. from another photosensitive region, read control module, reset transistor, output unit, etc. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
First embodiment:
Fig. 1 is a first schematic diagram of a pixel structure of a TOF image sensor according to a first embodiment of the present invention. Fig. 2 is a second schematic diagram of a pixel structure of a TOF image sensor according to a first embodiment of the present invention. For a clear description of the pixel structure of the TOF image sensor provided in the first embodiment of the present invention, please refer to fig. 1 and 2.
The pixel structure of the TOF image sensor provided by the first embodiment of the invention comprises a light sensor and a transmission circuit.
In an embodiment, the photosensor may be any photosensitive structure for converting visible light into electrons (or charge, photo-generated charge), such as any of a photodiode PD, a grating, or a photoconductor. Preferably, the light sensor in the present embodiment may be a photodiode PD (hereinafter described using the photodiode PD).
Referring to fig. 1 or 2, the photodiode PD includes a first photosensitive area A1, a second photosensitive area A2, and a third photosensitive area A3 with gradually decreasing potential, and is configured to generate a potential difference to assist the generated charge to flow to a transmission circuit connected to the third photosensitive area A3.
In an embodiment, the first photosensitive area A1, the second photosensitive area A2 and the third photosensitive area A3, which are gradually decreased in potential, can form a constant electric field through the generated potential difference, so that the photo-generated charges of the photodiode PD are rapidly transferred to the transmission circuit, and thus are rapidly transferred to the storage unit (such as the storage node or the storage capacitor), and further the ranging accuracy is improved.
In one embodiment, the shape of the lower end of the photodiode PD includes an inverted trapezoid (see fig. 1 or 2, the area of the photodiode PD below the dashed line frame is the lower end), and the overall shape of the photodiode PD is U-shaped. Specifically, the above-described U-shaped photodiode PD has a faster flow rate of charges than the conventional rectangular photodiode, and thus can also improve the charge transfer efficiency.
In one embodiment, the photodiode PD is of a symmetrical configuration with respect to the central axis Z-Z'. The first photosensitive area A1 is located at the upper end of the photodiode PD (see fig. 1 or 2, the area of the photodiode PD within the dashed frame is the upper end), and includes at least two photosensitive portions a101 (e.g., three photosensitive portions a101 in fig. 1 or two photosensitive portions a101 in fig. 2), at least two photosensitive portions a101 are symmetrically disposed with a central axis Z-Z', and an opening area a102 is provided between two adjacent photosensitive portions a 101.
In an embodiment, the shape of the opening area A102 may include at least one of a rectangular shape (see, for example, A102 in FIG. 1) or a shape that is the same as above and below, an inverted trapezoid shape (see, for example, A102' in FIG. 2), an inverted triangle shape, an inverted semicircle shape, or a shape that becomes smaller from top to bottom.
In an embodiment, the number of the at least two photosensitive portions a101 is 3, and the number of the opening areas a102 is 2. In one embodiment, the opening area a102 is rectangular, and has a width ranging from 0.2 um to 0.8um, and preferably, the width of the opening area a102 is 0.4um.
In an embodiment, the second photosensitive region A2 (for example, a region below the dashed line frame of fig. 1 or fig. 2 except the third photosensitive region A3 is the second photosensitive region A2) and the third photosensitive region A3 are both located at the lower end of the photodiode PD, and the third photosensitive region A3 is located at the bottom of the lower end, where the doping concentration of the third photosensitive region A3 is higher than the doping concentration of the second photosensitive region A2, and the third photosensitive region is in a axisymmetric structure. .
In one embodiment, the photodiode PD is obtained by patterning the upper end of the complete U-shaped photosensor to form the first photosensitive region A1, and doping material adding process to the bottom of the lower end of the complete U-shaped photosensor to form the third photosensitive region A3. The complete U-shaped photo sensor may be directly formed by the photodiode PD forming process, or may be formed by forming photo sensors of other shapes (e.g., rectangular photo sensors) and then performing patterning.
In one embodiment, the patterning process may include punching the upper end of the complete U-shaped photosensor to form a fill region, and filling P-type material in the fill region to form the opening region a102. The doping material adding process includes adding a layer of N-type material to the bottom of the lower end of the completed U-shaped photosensor.
In one embodiment, the photodiode PD and the transmission circuit form a complete TOF pixel circuit. The complete TOF pixel circuit includes one of a 2T pixel circuit, a 3T pixel circuit, a 4T pixel circuit, and a 5T pixel circuit.
In an embodiment, the transmission circuit may be symmetrically disposed on the substrate about a central axis Z-Z' of the photodiode PD.
The pixel structure of the TOF image sensor provided by the first embodiment of the invention comprises a photodiode PD and a transmission circuit. The photodiode PD includes a first photosensitive area A1, a second photosensitive area A2, and a third photosensitive area A3 with gradually decreasing potential, and is configured to generate a potential difference to assist the generated charge to flow to a transmission circuit connected to the third photosensitive area A3. Therefore, in the pixel structure of the TOF image sensor according to the first embodiment of the present invention, the charges generated by the photodiode PD can be quickly transferred to the transfer circuit through the first photosensitive area A1, the second photosensitive area A2 and the third photosensitive area A3 from high to low, so that the charges can be quickly transferred to the storage unit (such as the storage node or the storage capacitor), so that the transfer efficiency of the charges generated by the photodiode PD is improved, and the ranging accuracy is further improved.
Second embodiment:
Fig. 3 is a schematic diagram of a pixel structure of a TOF image sensor according to a second embodiment of the present invention. Fig. 4 is a first circuit schematic of a pixel structure of a TOF image sensor according to a second embodiment of the present invention. Fig. 5 is a second circuit schematic of a pixel structure of a TOF image sensor according to a second embodiment of the present invention. For a clear description of the pixel structure of the TOF image sensor provided in the first embodiment of the present invention, please refer to fig. 1, 2, 3, 4 and 5.
The TOF image sensor pixel structure provided by the second embodiment of the present invention exemplifies the transmission circuit in the TOF image sensor pixel structure provided by the first embodiment.
Referring to fig. 3, 4 or 5, the transmission circuit includes a first read control module M1 and a second read control module M2. The first read control module M1 and the second read control module M2 are both connected to the photodiode PD, and are both used for performing read control according to the electric charges.
Referring to fig. 3 and 4, in an embodiment, the first read control module M1 further includes a first reset transistor RST1, a first dual conversion gain control unit (e.g., a first dual conversion gain control transistor DCG 1), a first pass transistor MIX1, a first storage capacitor C1, a first floating diffusion node FD1, and a first output unit (e.g., a first source follower transistor SF1 and a first row select transistor RS 1). Wherein, a first end of the first reset transistor RST1 is connected to the voltage source VDD, and a second end of the first reset transistor RST1 is coupled to the first floating diffusion node FD1 through the first dual conversion gain control unit. A first terminal of the first transfer transistor MIX1 is connected to the cathode of the photodiode PD, and a second terminal of the first transfer transistor MIX1 is connected to the first storage capacitor C1 and the first floating diffusion node FD1. The first output unit is connected to the first floating diffusion node FD1.
In an embodiment, the first reset transistor RST1 in the first read control module M1 may be used to reset the voltage of the first floating diffusion node FD1 according to a reset control signal.
In an embodiment, the first dual conversion gain control unit in the first read control module M1 may be used to implement gain control and charge storage.
In an embodiment, the first dual conversion gain control unit in the first read control module M1 may include a first dual conversion gain control transistor DCG1 and a first dual conversion gain capacitor Cdcg, the first dual conversion gain control transistor DCG1 is coupled between the second terminal of the first reset transistor RST1 and the corresponding first floating diffusion node FD1, the first terminal of the first dual conversion gain capacitor Cdcg is coupled between the first dual conversion gain control transistor and the first reset transistor RST1, and the second terminal of the first dual conversion gain capacitor Cdcg1 is connected to the voltage source VDD.
In other embodiments, the first dual conversion gain capacitor Cdcg is a parasitic capacitance of the connection point of the first reset transistor RST1 and the first dual conversion gain control transistor DCG1 to ground.
In one embodiment, the first transfer transistor MIX1 in the first read control module M1 is used to transfer the accumulated charge of the photodiode PD to the first floating diffusion node FD1.
In one embodiment, the first output unit in the first read control module M1 is configured to amplify and output the voltage signal of the first floating diffusion node FD 1.
In an embodiment, the first output unit in the first read control module M1 may include a first source follower transistor SF1 and a first row select transistor RS1. The first control terminal of the first source follower transistor SF1 is connected to the first floating diffusion node FD1, the first terminal of the first source follower transistor SF1 is connected to the voltage source VDD, and the second terminal of the first source follower transistor SF1 is connected to the first data output line BL1 through the first row select transistor RS1.
Referring to fig. 3 and 4, in an embodiment, the second read control module M2 further includes a second reset transistor RST2, a second dual conversion gain control unit (e.g., a second dual conversion gain control transistor DCG 2), a second pass transistor MIX2, a second storage capacitor C2, a second floating diffusion node FD2, and a second output unit (e.g., a second source follower transistor SF2 and a second row select transistor RS 2). Wherein, the first end of the second reset transistor RST2 is connected to the voltage source VDD, and the second end of the second reset transistor RST2 is coupled to the second floating diffusion node FD2 through the second dual conversion gain control unit. A first terminal of the second transfer transistor MIX2 is connected to the cathode of the photodiode PD, and a second terminal of the second transfer transistor MIX2 is connected to the second storage capacitor C2 and the second floating diffusion node FD2. The second output unit is connected to the second floating diffusion node FD2.
In an embodiment, the second reset transistor RST2 in the second read control module M2 may be used to reset the voltage of the second floating diffusion node FD2 according to the reset control signal.
In an embodiment, a second dual conversion gain control unit in the second read control module M2 may be used to implement gain control and charge storage.
In an embodiment, the second dual conversion gain control unit in the second read control module M2 may include a second dual conversion gain control transistor DCG2 and a second dual conversion gain capacitor Cdcg2, the second dual conversion gain control transistor DCG2 is coupled between a second terminal of the second reset transistor RST2 and the corresponding second floating diffusion node FD2, a second terminal of the second dual conversion gain capacitor Cdcg2 is coupled between the second dual conversion gain control transistor and the second reset transistor RST2, and a second terminal of the second dual conversion gain capacitor Cdcg2 is connected to the voltage source VDD.
In other embodiments, the second dual conversion gain capacitor Cdcg is a parasitic capacitance to ground of the connection point of the second reset transistor RST2 and the second dual conversion gain control transistor DCG 2.
In one embodiment, the second transfer transistor MIX2 in the second read control module M2 is configured to transfer the accumulated charge of the photodiode PD to the second floating diffusion node FD2.
In an embodiment, the second transfer transistor MIX2 of the second read control unit M2 and the first transfer transistor MIX1 of the first read control unit M1 are alternately turned on during the exposure of the photodiode PD to alternately transfer the charge accumulated by the photodiode PD to the second floating diffusion node FD2 or the first floating diffusion node FD1, respectively. Specifically, in this embodiment, by providing the first read control module M1 and the second read control module M2 respectively coupled to the photodiodes PD and controlling the first transfer transistor MIX1 and the second transfer transistor MIX2 to be alternately turned on during the exposure of the photodiodes PD to alternately transfer the charges accumulated by the photodiodes PD to the corresponding floating diffusion nodes, the flight time of the light pulse can be determined by calculating the effective light signals accumulated by the floating diffusion nodes corresponding to the first read control module M1 and the second read control module M2, so that the pixel structure can be applied to the image sensor of the TOF technology. And, since the first read control module M1 and the second read control module M2 are coupled to the photodiode PD and the corresponding floating diffusion node by using the transfer transistor, the charge accumulated by the photodiode PD is transferred to the floating diffusion node by the transfer transistor, so that the pixel structure can support the rolling exposure mode.
In one embodiment, the second pass transistor MIX2 of the second read control module M2 is out of phase pi with the first pass transistor MIX1 of the first read control module M1, which is alternately turned on during the exposure of the photodiode PD.
In an embodiment, the second output unit in the second read control module M2 is configured to amplify and output the voltage signal of the second floating diffusion node FD 2.
In an embodiment, the second output unit in the second read control module M2 includes a second source follower transistor SF2 and a second row select transistor RS2. The second control terminal of the second source follower transistor SF2 is connected to the second floating diffusion node FD2, the first terminal of the second source follower transistor SF2 is connected to the voltage source VDD, and the second terminal of the second source follower transistor SF2 is connected to the second data output line BL2 through the second row select transistor RS2.
In an embodiment, the second read control module M2 and the first read control module M1 may be symmetrically disposed in the substrate of the pixel structure of the TOF image sensor provided in this embodiment.
Referring to fig. 3 and 4, in an implementation manner, the pixel structure of the TOF image sensor provided by the second embodiment of the present invention may further include a charge balancing unit EQ. The charge balancing unit EQ is connected to the first floating diffusion node FD1 of the first read control module and the second floating diffusion node FD2 of the second read control module for balancing charges of the first floating diffusion node FD1 and the second floating diffusion node FD2 after reset.
In one embodiment, the charge balance unit EQ may include a balance control transistor.
Referring to fig. 5, in an implementation manner, the TOF image sensor pixel structure provided by the second embodiment of the present invention may further include an anti-overflow transistor AB. The first terminal of the anti-overflow transistor AB is coupled to the voltage source VDD, and the second terminal of the anti-overflow transistor AB is connected to the photodiode PD for removing charges generated by the photodiode PD due to the background light when the modulated light is not turned on. Specifically, when the modulated light is not transmitted, the anti-overflow transistor AB is turned on to eliminate an unwanted background light signal, and the background light charge is prevented from being transmitted to the floating diffusion node, so that the background light is suppressed, and the ranging accuracy can be improved.
According to the pixel structure of the TOF image sensor provided by the second embodiment of the invention, charges generated by the photodiode PD can be quickly transmitted to the first storage capacitor C1 and/or the second storage capacitor C2, so that the transmission efficiency of charges generated by the photodiode PD is improved, and further the ranging precision can be improved.
Third embodiment:
fig. 6 is a schematic structural diagram of a ranging system according to a third embodiment of the present invention. For a clear description of the ranging system provided by the third embodiment of the present invention, please refer to fig. 6.
A third embodiment of the present invention provides a ranging system comprising an image sensor 10, a control signal processing unit 11 and a modulatable light source 12.
Wherein the image sensor 10 comprises a plurality of arrays of pixels arranged in rows and columns, each pixel comprising a TOF image sensor pixel structure as described in the first and/or second embodiments.
The control signal processing unit 11 is used for controlling the working process of the system and processing the image data acquired by the pixel array.
The light source 12 is configured to receive the modulated signal, generate a modulated light signal, and feed back the received modulated signal to the pixel array.
In the ranging system provided by the third embodiment of the present invention, the pixel structure of the TOF image sensor at least includes a first photosensitive area A1, a second photosensitive area A2 and a third photosensitive area A3 with gradually decreasing electric potential in the photodiode PD, which are used for generating a potential difference to assist the generated electric charges to flow to a transmission circuit connected to the third photosensitive area A3. Therefore, the ranging system provided by the third embodiment of the present invention can enable the charges generated by the photodiode PD to be rapidly transferred to the memory cell, so as to improve the transfer efficiency of the charges generated by the photodiode, and further achieve the purpose of improving the ranging accuracy.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, element, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, element, or apparatus. Without further limitation, the element(s) defined by the phrase "comprising one does not exclude the presence of other like elements in a process, method, article, element or apparatus that comprises a list of elements does not include only those elements but may include other like elements, features, elements, and may have the same meaning as may be expressed in different embodiments of the application, the particular meaning of which is to be determined by its interpretation in this particular embodiment or by further incorporation of the context of that particular embodiment.
It should be understood that although the terms first, second, third, etc. may be used herein to describe various information, these information should not be limited by these terms. These terms are only used to distinguish one type of information from another. The term "if" as used herein may be interpreted as "at..once" or "when..once" or "in response to a determination", depending on the context. Furthermore, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including" specify the presence of stated features, steps, operations, elements, components, items, categories, and/or groups, but do not preclude the presence, presence or addition of one or more other features, steps, operations, elements, components, items, categories, and/or groups. The terms "or" and/or "as used herein are to be construed as inclusive, or meaning any one or any combination. Thus, "A, B or C" or "A, B and/or C" means "any of A, B, C, A and B, A and C, B and C, A, B and C". An exception to this definition will occur only when a combination of elements, functions, steps or operations are in some way inherently mutually exclusive.
The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, or alternatives falling within the spirit and principles of the application.
Claims (12)
1. A TOF image sensor pixel structure is characterized by comprising a light sensor and a transmission circuit;
the optical sensor comprises a first photosensitive area, a second photosensitive area and a third photosensitive area, the electric potential of which is gradually decreased, and the first photosensitive area, the second photosensitive area and the third photosensitive area are used for generating potential difference and assisting the self-generated electric charge to flow to the transmission circuit connected with the third photosensitive area;
the transmission circuit comprises a first reading control module, a second reading control module and a charge balance unit;
The first reading control module and the second reading control module are connected with the photosensor, and are alternately conducted in the exposure process of the photosensor so as to alternately transfer charges accumulated by the photosensor to corresponding floating diffusion nodes respectively, so as to carry out reading control on the charges;
The charge balancing unit is connected with a first floating diffusion node of the first read control module and a second floating diffusion node of the second read control module, and is used for balancing charges of the first floating diffusion node and the second floating diffusion node after reset.
2. The TOF image sensor pixel structure of claim 1, wherein the shape of the lower end of the photosensor comprises an inverted trapezoid, and the overall shape of the photosensor is U-shaped.
3. The TOF image sensor pixel structure of claim 1 or 2, wherein the light sensor is axisymmetric;
The first photosensitive area is positioned at the upper end of the optical sensor and comprises at least two photosensitive parts, the at least two photosensitive parts are symmetrically arranged with the central axis, and an opening area is arranged between the two adjacent photosensitive parts;
The second photosensitive region and the third photosensitive region are both positioned at the lower end of the optical sensor, and the third photosensitive region is positioned at the bottom of the lower end, wherein the doping concentration of the third photosensitive region is higher than that of the second photosensitive region;
the third photosensitive area is of a axisymmetric structure.
4. The TOF image sensor pixel structure of claim 3, wherein the number of the at least two photosensitive portions is 3 and the number of the open areas is 2.
5. The TOF image sensor pixel structure of claim 4, wherein the opening region is rectangular with a width in the range of 0.2-0.8um.
6. The TOF image sensor pixel structure of claim 5, wherein the width of the opening region is 0.4um.
7. The TOF image sensor pixel structure of claim 3, wherein the photosensor is obtained by patterning an upper end of a complete U-shaped photosensor to form the first photosensitive region and doping material addition to a bottom of a lower end of the complete U-shaped photosensor to form the third photosensitive region.
8. The TOF image sensor pixel structure of claim 7, wherein the patterning process includes a punching process of the complete U-shaped photosensor upper end to form a fill region and filling P-type material in the fill region to form the open region;
The doping material increasing process includes increasing the concentration of N-type material to the bottom of the lower end of the complete U-shaped photosensor.
9. The TOF image sensor pixel structure of claim 3, wherein the shape of the open area comprises at least one of:
rectangular or top-bottom like shape;
inverted trapezium, inverted triangle, inverted semicircle or shape which becomes smaller from top to bottom.
10. The TOF image sensor pixel structure of claim 1, wherein the photosensor and the transmission circuit form a complete TOF pixel circuit;
the complete TOF pixel circuit includes one of a 2T pixel circuit, a 3T pixel circuit, a 4T pixel circuit, and a 5T pixel circuit.
11. The TOF image sensor pixel structure of claim 1, further comprising an anti-blooming transistor;
The first end of the anti-overflow transistor is coupled to a voltage source, and the second end of the anti-overflow transistor is connected to the photosensor for removing charges generated by the photosensor due to background light when the modulated light is not on.
12. A ranging system, comprising:
an image sensor comprising a plurality of arrays of pixels arranged in rows and columns, each pixel comprising the TOF image sensor pixel structure of any one of claims 1-11;
The control signal processing unit is used for controlling the working process of the system and processing the image data acquired by the pixel array;
the light source can be modulated, and is used for generating a modulated light signal after receiving the modulated signal and feeding the received modulated signal back to the pixel array.
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