TOF image sensor pixel structure and ranging system

Abstract

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

[0001] The present invention relates to the technical field of image sensors, and in particular to a TOF image sensor pixel structure and a distance measurement system. Background Art

[0002] Image sensors are an important part of digital cameras. According to different components, image sensors can be divided into two categories: CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors. Due to the advantages of CMOS image sensors such as low power consumption, low cost, and easy standardized production, they have been widely used in various fields.

[0003] With the rapid development of three-dimensional imaging information technology, especially the application of building measurement, indoor positioning and navigation, stereoscopic imaging and assisted living environment, Time-of-Flight (TOF) imaging has been urgently needed, and the pixel structure of CMOS image sensors used in time-of-flight imaging systems has also developed rapidly. TOF image sensors can be divided into dTOF image sensors and iTOF image sensors. Among them, dTOF image sensors directly measure the time of flight, that is, measure the time interval between the emitted light pulse and the received light pulse. Among them, iTOF image sensors indirectly measure the time of flight, usually using a method of measuring phase shift, that is, measuring the phase difference between the emitted sine wave / square wave and the received sine wave / square wave. For all types of TOF image sensors, ranging accuracy is an important parameter. The higher the ranging accuracy, the more accurate the three-dimensional image detection of the target.

[0004] In the TOF image sensor pixels, the transmission efficiency of the charge generated by the photodiode will directly affect the ranging accuracy. Therefore, how to improve the transmission efficiency of the charge generated by the photodiode is what we need to consider.

[0005] In view of the above problems, those skilled in the art have been seeking solutions.

[0006] The preceding description is intended to provide general background information and does not necessarily constitute prior art. Summary of the invention

[0007] The technical problem to be solved by the present invention is that, in view of the defects of the above-mentioned prior art, a TOF image sensor pixel structure and a ranging system are provided to achieve the purpose of improving the transmission efficiency of the charges generated by the photodiode, thereby improving the ranging accuracy.

[0008] The present invention is achieved in that:

[0009] The present invention provides a TOF image sensor pixel structure, including 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 is used to generate a potential difference to assist the charge generated by itself to flow to the transmission circuit connected to the third photosensitive area.

[0010] Optionally, the shape of the lower end of the optical sensor includes an inverted trapezoid, and the overall shape of the optical sensor is U-shaped.

[0011] Optionally, the light sensor is of a central axis symmetrical structure. The first photosensitive region is located at the upper end of the light sensor, and includes at least two photosensitive parts, at least two photosensitive parts are arranged symmetrically about the central axis, and an opening area is provided between two adjacent photosensitive parts. The second photosensitive region and the third photosensitive region are both located at the lower end of the light sensor, and the third photosensitive region is located at the bottom of the lower end, wherein the doping concentration of the third photosensitive region is higher than the doping concentration of the second photosensitive region. The third photosensitive region is of a central axis symmetrical structure.

[0012] Optionally, the number of the at least two photosensitive portions is three, and the number of the opening areas is two.

[0013] Optionally, the opening area is rectangular, and its width ranges from 0.2 to 0.8 um.

[0014] Optionally, the width of the opening area is 0.4 um.

[0015] Optionally, the light sensor is obtained by patterning the upper end of the complete U-shaped light sensor to form a first photosensitive area, and adding doping material to the bottom of the lower end of the complete U-shaped light sensor to form a third photosensitive area.

[0016] Optionally, the patterning process includes drilling a hole on the upper end of the complete U-shaped optical sensor to form a filling area, and filling the filling area with a P-type material to form an opening area. The doping material addition process includes increasing the concentration of the N-type material at the bottom of the lower end of the complete U-shaped optical sensor.

[0017] Optionally, the shape of the opening area includes at least one of the following: a rectangle or a shape that is the same from top to bottom, an inverted trapezoid, an inverted triangle, an inverted semicircle, or a shape that becomes smaller from top to bottom.

[0018] Optionally, the optical sensor 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.

[0019] Optionally, the transmission circuit includes a first reading control module and a second reading control module. The first reading control module and the second reading control module are both connected to the light sensor and are used to perform reading control according to the charge.

[0020] Optionally, the first read control module further includes a first reset transistor, a first dual conversion gain control unit, a first transfer 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 transfer transistor is connected to the negative electrode of the light sensor, and the second end of the first transfer transistor is connected to the first storage capacitor and the first floating diffusion node. The first output unit is connected to 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 transfer transistor is connected to the negative electrode of the light sensor, and the second end of the second transfer transistor is connected to the second storage capacitor and the second floating diffusion node. The second output unit is connected to the second floating diffusion node.

[0021] Optionally, the first output unit includes a first source follower transistor and a first row selection transistor, and the second output unit includes a second source follower transistor and a second row selection transistor. The first control terminal of the first source follower transistor is connected to the first floating diffusion node, the first terminal of the first source follower transistor is connected to the voltage source, and the second terminal of the first source follower transistor is connected to the 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 selection transistor.

[0022] Optionally, a charge balancing unit is further included. The charge balancing unit is connected to the first floating diffusion node of the first read control module and the second floating diffusion node of the second read control module, and is used to balance the charges of the first floating diffusion node and the second floating diffusion node after reset.

[0023] Optionally, an anti-overflow transistor is further included. A first terminal of the anti-overflow transistor is coupled to a voltage source, and a second terminal of the anti-overflow transistor is connected to the light sensor, so as to remove the charge generated by the background light in the light sensor when the modulated light is not turned on.

[0024] The present invention also provides a distance measurement system, comprising: an image sensor, the image sensor comprising a plurality of pixel arrays arranged in rows and columns, each pixel comprising the TOF image sensor pixel structure described above; a control signal processing unit, used to control the system operation process and process the image data acquired by the pixel array; a modulated light source, used to generate a modulated light signal after receiving a modulation signal, and feed the received modulation signal back to the pixel array.

[0025] The TOF image sensor pixel structure and ranging system provided by the present invention, 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 to 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 the 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 can improve the ranging accuracy.

[0026] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a first schematic diagram of a pixel structure of a TOF image sensor provided by a first embodiment of the present invention;

[0028] Figure 2 is a second schematic diagram of the pixel structure of the TOF image sensor provided by the first embodiment of the present invention;

[0029] Figure 3 is a schematic diagram of a pixel structure of a TOF image sensor provided by a second embodiment of the present invention;

[0030] Figure 4 is a first circuit schematic diagram of a TOF image sensor pixel structure provided by a second embodiment of the present invention;

[0031] Figure 5 is a second circuit schematic diagram of a TOF image sensor pixel structure provided by a second embodiment of the present invention;

[0032] Figure 6 It is a schematic diagram of the structure of a distance measurement system provided by the third embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] Although the present invention uses the terms first, second, third, etc. to describe different photosensitive areas, read control modules, reset transistors, output units, etc., these photosensitive areas, read control modules, reset transistors, output units, etc. are not limited by these terms. These terms are only used to distinguish one photosensitive area, read control module, reset transistor, output unit, etc. from another photosensitive area, read control module, reset transistor, output unit, etc. Unless otherwise defined, all terms (including technical terms and scientific terms) used in the present invention have the meanings commonly understood by ordinary technicians in the field to which the present invention belongs.

[0035] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0036] First embodiment:

[0037] Figure 1 4 is a first schematic diagram of a pixel structure of a TOF image sensor provided by the first embodiment of the present invention. Figure 2 is a second schematic diagram of the pixel structure of the TOF image sensor provided by the first embodiment of the present invention. In order to clearly describe the pixel structure of the TOF image sensor provided by the first embodiment of the present invention, please refer to Figure 1 and Figure 2 .

[0038] A TOF image sensor pixel structure provided by a first embodiment of the present invention includes a light sensor and a transmission circuit.

[0039] In one embodiment, the light sensor may be any photosensitive structure for converting visible light into electrons (or charges, photogenerated charges), such as any one of a photodiode PD, a grating, or a photoconductor. Preferably, in this embodiment, the light sensor may be a photodiode PD (hereinafter described as a photodiode PD).

[0040] Among them, see Figure 1 or Figure 2 The photodiode PD includes a first photosensitive area A1, a second photosensitive area A2 and a third photosensitive area A3 with gradually decreasing potentials, which are used to generate a potential difference to assist the charges generated by itself to flow to the transmission circuit connected to the third photosensitive area A3.

[0041] In one embodiment, the first photosensitive area A1, the second photosensitive area A2 and the third photosensitive area A3 included in the photodiode PD, whose potentials decrease step by step, can form a constant electric field through the generated potential difference, so that the photogenerated charges of the photodiode PD are quickly transmitted to the transmission circuit, and then quickly transmitted to the storage unit (such as a storage node or a storage capacitor), thereby improving the ranging accuracy.

[0042] In one embodiment, the shape of the lower end of the photodiode PD includes an inverted trapezoid (see Figure 1 or Figure 2 , the area of ​​the photodiode PD below the dotted box is the lower end), and the overall shape of the photodiode PD is U-shaped. Specifically, the U-shaped photodiode PD has a faster flow rate of charge than the traditional rectangular photodiode, so it can also improve the charge transfer efficiency.

[0043] In one embodiment, the photodiode PD is a symmetrical structure with respect to the central axis Z-Z'. The first photosensitive region A1 is located at the upper end of the photodiode PD (see Figure 1 or Figure 2 , the area of ​​the photodiode PD in the dotted frame is the upper end), including at least two photosensitive parts A101 (for example Figure 1 The three photosensitive parts A101, or Figure 2 At least two photosensitive portions A101 are symmetrically arranged about the central axis ZZ', and an opening area A102 is provided between two adjacent photosensitive portions A101.

[0044] In one embodiment, the shape of the opening area A102 may include at least one of the following: a rectangle (for example, see Figure 1 A102 in) or the same shape up and down; inverted trapezoid (for example, see Figure 2 A102' in the figure), an inverted triangle, an inverted semicircle, or a shape that becomes smaller from top to bottom.

[0045] In one embodiment, the number of the at least two photosensitive parts A101 is 3, and the number of the opening areas A102 is 2. In one embodiment, the opening area A102 is rectangular, and its width ranges from 0.2 to 0.8 um, and preferably, the width of the opening area A102 is 0.4 um.

[0046] In one embodiment, the second photosensitive area A2 (eg, Figure 1 or Figure 2The area below the dotted frame except the third photosensitive area A3 is the second photosensitive area A2) and the third photosensitive area A3 are both located at the lower end of the photodiode PD, and the third photosensitive area A3 is located at the bottom of the lower end, wherein the doping concentration of the third photosensitive area A3 is higher than the doping concentration of the second photosensitive area A2, and the third photosensitive area is a central axis symmetrical structure.

[0047] In one embodiment, the photodiode PD is obtained by patterning the upper end of the complete U-shaped light sensor to form a first photosensitive area A1, and adding doping material to the bottom of the lower end of the complete U-shaped light sensor to form a third photosensitive area A3. The complete U-shaped light sensor can be directly formed by the photodiode PD formation process, or can be obtained by first forming a light sensor of other shapes (such as a rectangular light sensor) and then patterning it.

[0048] In one embodiment, the patterning process may include drilling a hole on the upper end of the complete U-shaped optical sensor to form a filling area, and filling the filling area with a P-type material to form an opening area A102. The doping material addition process includes adding a layer of N-type material to the bottom of the lower end of the complete U-shaped optical sensor.

[0049] 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.

[0050] In one implementation, the transmission circuit may be disposed on the substrate symmetrically with respect to the center axis ZZ′ of the photodiode PD.

[0051] The pixel structure of the TOF image sensor provided by the first embodiment of the present invention includes a photodiode PD and a transmission circuit. Among them, the photodiode PD includes a first photosensitive area A1, a second photosensitive area A2 and a third photosensitive area A3 with a gradually decreasing potential, which is used to generate a potential difference to assist the charge generated by itself to flow to the transmission circuit connected to the third photosensitive area A3. Therefore, the pixel structure of the TOF image sensor provided by the first embodiment of the present invention can quickly transmit the charge generated by the photodiode PD to the transmission circuit through the first photosensitive area A1, the second photosensitive area A2 and the third photosensitive area A3 with a potential from high to low, so that the charge can be quickly transmitted to the storage unit (such as a storage node or a storage capacitor), thereby improving the transmission efficiency of the charge generated by the photodiode PD, and then improving the ranging accuracy.

[0052] Second embodiment:

[0053] Figure 3 Schematic diagram of a pixel structure of a TOF image sensor provided by a second embodiment of the present invention. Figure 4 4 is a first circuit diagram of a TOF image sensor pixel structure provided by a second embodiment of the present invention. Figure 5 is a second circuit diagram of a TOF image sensor pixel structure provided by the second embodiment of the present invention. In order to clearly describe the TOF image sensor pixel structure provided by the first embodiment of the present invention, please refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 .

[0054] The pixel structure of the TOF image sensor provided in the second embodiment of the present invention is an example of the transmission circuit in the pixel structure of the TOF image sensor provided in the first embodiment.

[0055] Among them, see Figure 3 , Figure 4 or Figure 5 The transmission circuit includes a first reading control module M1 and a second reading control module M2. The first reading control module M1 and the second reading control module M2 are both connected to the photodiode PD and are used for performing reading control according to the charge.

[0056] See also Figure 3 and Figure 4 In one 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 DCG1), a first transfer transistor MIX1, a first storage capacitor C1, a first floating diffusion node FD1, and a first output unit (e.g., including a first source follower transistor SF1 and a first row selection transistor RS1). The first end of the first reset transistor RST1 is connected to the voltage source VDD, and the 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. The first end of the first transfer transistor MIX1 is connected to the cathode of the photodiode PD, and the second end 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.

[0057] In one implementation, 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.

[0058] In one implementation, the first dual conversion gain control unit in the first read control module M1 may be used to implement gain control and charge storage.

[0059] In one 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 Cdcg1, the first dual conversion gain control transistor DCG1 is coupled between the second end of the first reset transistor RST1 and the corresponding first floating diffusion node FD1, the first end of the first dual conversion gain capacitor Cdcg1 is coupled between the first dual conversion gain control transistor and the first reset transistor RST1, and the second end of the first dual conversion gain capacitor Cdcg1 is connected to the voltage source VDD.

[0060] In other embodiments, the first dual conversion gain capacitor Cdcg1 is a parasitic capacitance between a connection point between the first reset transistor RST1 and the first dual conversion gain control transistor DCG1 and ground.

[0061] In one embodiment, the first transfer transistor MIX1 in the first read control module M1 is used to transfer the charges accumulated by the photodiode PD to the first floating diffusion node FD1 .

[0062] In one embodiment, the first output unit in the first read control module M1 is used to amplify and output the voltage signal of the first floating diffusion node FD1.

[0063] In one 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. A first control terminal of the first source follower transistor SF1 is connected to the first floating diffusion node FD1, a first terminal of the first source follower transistor SF1 is connected to a voltage source VDD, and a 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.

[0064] See also Figure 3 and Figure 4 In one 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 DCG2), a second transfer transistor MIX2, a second storage capacitor C2, a second floating diffusion node FD2, and a second output unit (e.g., including a second source follower transistor SF2 and a second row selection transistor RS2). 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. The first end of the second transfer transistor MIX2 is connected to the cathode of the photodiode PD, and the second end 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.

[0065] In one implementation, 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 a reset control signal.

[0066] In one implementation, the second dual conversion gain control unit in the second read control module M2 may be used to implement gain control and charge storage.

[0067] In one 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 the second end of the second reset transistor RST2 and the corresponding second floating diffusion node FD2, the second end 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 the second end of the second dual conversion gain capacitor Cdcg2 is connected to the voltage source VDD.

[0068] In other embodiments, the second dual conversion gain capacitor Cdcg2 is a parasitic capacitance between a connection point between the second reset transistor RST2 and the second dual conversion gain control transistor DCG2 and ground.

[0069] In one embodiment, the second transfer transistor MIX2 in the second read control module M2 is used to transfer the charges accumulated by the photodiode PD to the second floating diffusion node FD2 .

[0070] In one 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 process of the photodiode PD to alternately transfer the charge accumulated in the photodiode PD to the second floating diffusion node FD2 or the first floating diffusion node FD1. Specifically, in this embodiment, by setting the first read control module M1 and the second read control module M2 to be coupled to the photodiode PD respectively, and controlling the first transfer transistor MIX1 and the second transfer transistor MIX2 to be alternately turned on during the exposure process of the photodiode PD to alternately transfer the charge accumulated in the photodiode PD to the corresponding floating diffusion node, the effective light signal accumulated in the floating diffusion node corresponding to the first read control module M1 and the second read control module M2 can be determined, so that the pixel structure can be applied to the image sensor of TOF technology. And because the first read control module M1 and the second read control module M2 use transfer transistors to couple the photodiode PD with the corresponding floating diffusion node, the charge accumulated in the photodiode PD is transferred to the floating diffusion node through the transfer transistor, so that the pixel structure can support the rolling exposure mode.

[0071] In one embodiment, the phase difference between the second transfer transistor MIX2 of the second read control module M2 and the first transfer transistor MIX1 of the first read control module M1 during the exposure process of the photodiode PD is π.

[0072] In one embodiment, the second output unit in the second read control module M2 is used to amplify and output the voltage signal of the second floating diffusion node FD2.

[0073] In one 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.

[0074] In one implementation, the second reading control module M2 and the first reading control module M1 may be symmetrically arranged in the substrate of the TOF image sensor pixel structure provided in this embodiment.

[0075] See also Figure 3 and Figure 4 In one implementation, the TOF image sensor pixel structure provided in 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, and is used to balance the charges of the first floating diffusion node FD1 and the second floating diffusion node FD2 after reset.

[0076] In one implementation, the charge balancing unit EQ may include a balancing control transistor.

[0077] See also Figure 5 In one implementation, the TOF image sensor pixel structure provided in the second embodiment of the present invention may further include an anti-overflow transistor AB. The first end of the anti-overflow transistor AB is coupled to the voltage source VDD, and the second end of the anti-overflow transistor AB is connected to the photodiode PD, so as to remove the charge 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 on, the anti-overflow transistor AB is turned on to eliminate the unwanted background light signal, and prevent the background light charge from being transferred to the floating diffusion node, thereby suppressing the background light, so as to improve the ranging accuracy.

[0078] The pixel structure of the TOF image sensor provided in the second embodiment of the present invention can enable the charge generated by the photodiode PD to be quickly transmitted to the first storage capacitor C1 and / or the second storage capacitor C2, thereby improving the transmission efficiency of the charge generated by the photodiode PD, and further improving the ranging accuracy. In addition, a charge balancing unit can be provided to balance the charge of the first floating diffusion node FD1 and the second floating diffusion node FD2 after resetting, thereby further improving the ranging accuracy. In addition, an anti-overflow transistor AB can be provided to suppress background light, thereby further improving the ranging accuracy.

[0079] Third embodiment:

[0080] Figure 6 is a schematic diagram of the structure of the distance measurement system provided by the third embodiment of the present invention. In order to clearly describe the distance measurement system provided by the third embodiment of the present invention, please refer to Figure 6 .

[0081] The distance measurement system provided by the third embodiment of the present invention includes: an image sensor 10 , a control signal processing unit 11 and a modulatable light source 12 .

[0082] The image sensor 10 includes a plurality of pixel arrays arranged in rows and columns, and each pixel includes the TOF image sensor pixel structure as described in the first embodiment and / or the second embodiment.

[0083] The control signal processing unit 11 is used to control the system working process and process the image data acquired by the pixel array.

[0084] The modulated light source 12 is used to generate a modulated light signal after receiving a modulation signal, and feed back the received modulation signal to the pixel array.

[0085] The distance measurement system provided by the third embodiment of the present invention, wherein the pixel structure of the TOF image sensor includes at least a first photosensitive area A1, a second photosensitive area A2 and a third photosensitive area A3 in the photodiode PD, where the potential decreases step by step, for generating a potential difference to assist the charge generated by itself to flow to the transmission circuit connected to the third photosensitive area A3. Therefore, the distance measurement system provided by the third embodiment of the present invention can enable the charge generated by the photodiode PD to be quickly transmitted to the storage unit, improve the transmission efficiency of the charge generated by the photodiode, and thus achieve the purpose of improving the distance measurement accuracy.

[0086] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] It should be noted that, in this article, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, component or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article, component or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other identical elements in the process, method, article, component or device including the element. In addition, components, features, and elements with the same name in different embodiments of the present application may have the same meaning or different meanings, and their specific meanings need to be determined by their explanation in the specific embodiment or further combined with the context of the specific embodiment.

[0088] It should be understood that, although the terms first, second, third, etc. may be used to describe various information in this article, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. Depending on the context, the word "if" as used herein can be interpreted as "at the time of..." or "when..." or "in response to determination". Moreover, as used in this article, the singular forms "one", "one" and "the" are intended to also include plural forms, unless there is an opposite indication in the context. It should be further understood that the terms "comprising", "including" indicate that there are the described features, steps, operations, elements, components, projects, kinds, and / or groups, but do not exclude the existence, occurrence or addition of one or more other features, steps, operations, elements, components, projects, kinds, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or mean any one or any combination. Therefore, "A, B or C" or "A, B and / or C" means "any of the following: 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 inherently mutually exclusive in some manner.

[0089] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A TOF image sensor pixel structure, characterized in that: including a light sensor and a transmission circuit; The light sensor comprises a first light-sensitive region, a second light-sensitive region and a third light-sensitive region with gradually decreasing potentials, and is used to generate a potential difference to assist the charges generated by the light-sensitive region to flow to the transmission circuit connected to the third light-sensitive region; The transmission circuit includes a first read control module, a second read control module and a charge balancing unit; The first reading control module and the second reading control module are both connected to the light sensor, and are alternately turned on during the exposure process of the light sensor to alternately transfer the charges accumulated by the light sensor to the corresponding floating diffusion nodes, respectively, so as to perform reading control on the charges; The charge balancing unit is connected to the first floating diffusion node of the first read control module and the second floating diffusion node of the second read control module, and is used to balance the charges of the first floating diffusion node and the second floating diffusion node after reset.

2. The TOF image sensor pixel structure according to claim 1, wherein: The shape of the lower end of the optical sensor includes an inverted trapezoid, and the overall shape of the optical sensor is U-shaped.

3. The TOF image sensor pixel structure according to claim 1 or 2, characterized in that: The optical sensor is of a central axis symmetrical structure; The first photosensitive area is located at the upper end of the light sensor, and includes at least two photosensitive parts, the at least two photosensitive parts are symmetrically arranged about the central axis, and an opening area is provided between two adjacent photosensitive parts; The second photosensitive region and the third photosensitive region are both located at the lower end of the light sensor, and the third photosensitive region is located at the bottom of the lower end, wherein the doping concentration of the third photosensitive region is higher than the doping concentration of the second photosensitive region; The third photosensitive area is an axisymmetric structure.

4. The TOF image sensor pixel structure according to claim 3, characterized in that: The number of the at least two photosensitive parts is three, and the number of the opening areas is two.

5. The TOF image sensor pixel structure according to claim 4, characterized in that: The opening area is rectangular, and its width ranges from 0.2 to 0.8 um.

6. The TOF image sensor pixel structure according to claim 5, characterized in that: The width of the opening area is 0.4 um.

7. The TOF image sensor pixel structure according to claim 3, characterized in that: The optical sensor is obtained by patterning the upper end of the complete U-shaped optical sensor to form the first photosensitive area, and adding doping material to the bottom of the lower end of the complete U-shaped optical sensor to form the third photosensitive area.

8. The TOF image sensor pixel structure according to claim 7, wherein: The patterning process includes punching a hole on the upper end of the complete U-shaped optical sensor to form a filling area, and filling the filling area with a P-type material to form the opening area; The doping material adding process includes increasing the N-type material concentration at the bottom of the lower end of the complete U-shaped optical sensor.

9. The TOF image sensor pixel structure according to claim 3, characterized in that: The shape of the opening area includes at least one of the following: Rectangular or top-to-bottom shapes; An inverted trapezoid, inverted triangle, inverted semicircle, or a shape that becomes smaller from top to bottom.

10. The TOF image sensor pixel structure according to claim 1, wherein: The optical sensor and the transmission circuit constitute 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 according to claim 1, wherein: Also included are overflow-resistant transistors; A first terminal of the anti-overflow transistor is coupled to a voltage source, and a second terminal of the anti-overflow transistor is connected to the light sensor for removing charges generated by background light from the light sensor when the modulated light is not turned on.

12. A distance measurement system, characterized in that: include: An image sensor, the image sensor comprising a plurality of pixel arrays arranged in rows and columns, each pixel comprising a TOF image sensor pixel structure as claimed in any one of claims 1 to 11; A control signal processing unit, used to control the system working process and process the image data acquired by the pixel array; The modulated light source is used to generate a modulated light signal after receiving a modulation signal, and feed back the received modulation signal to the pixel array.

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