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, a first reading control module, a second reading control module and a charge balancing unit. The light sensor is used to perform photoelectric conversion to generate charge. The first reading control module and the second reading control module are both connected to the light sensor, and are both used to perform reading control according to the charge. The charge balancing unit is connected to a first floating diffusion node of the first reading control module and a second floating diffusion node of the second reading control module, and is used to balance the charge of the first floating diffusion node and the second floating diffusion node after resetting. Therefore, the present invention can ensure that the voltages of several floating diffusion nodes in the TOF image sensor pixel are equal after resetting, thereby alleviating the fixed pattern noise in the pixel and improving the ranging accuracy of the image sensor.

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. Depending on the components, image sensors can be divided into two categories: CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors. CMOS image sensors have been widely used in various fields due to their advantages such as low power consumption, low cost, and easy standardized production.

[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 traditional TOF image sensor pixels, after the voltages of several floating diffusion nodes are reset, there will be differences in the voltages of several floating diffusion nodes, which will affect the ranging accuracy.

[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 ensure that the voltages of several floating diffusion nodes are equal after reset, thereby improving the ranging accuracy.

[0008] The present invention is achieved in that:

[0009] The present invention provides a TOF image sensor pixel structure, comprising a light sensor, a first reading control module, a second reading control module and a charge balancing unit. The light sensor is used for performing photoelectric conversion to generate charge. The first reading control module and the second reading control module are both connected to the light sensor and are both used for performing reading control according to the charge. The charge balancing unit is connected to a first floating diffusion node of the first reading control module and a second floating diffusion node of the second reading control module and is used for balancing the charge of the first floating diffusion node and the second floating diffusion node after reset.

[0010] Optionally, the charge balancing unit comprises a balancing control transistor.

[0011] Optionally, the first read control module also includes a first reset transistor, a first dual conversion gain control unit, a first transfer transistor, a first storage capacitor 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 also includes a second reset transistor, a second dual conversion gain control unit, a second transfer transistor, a second storage capacitor 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.

[0012] 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.

[0013] 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.

[0014] Optionally, the phase difference between the first transmission transistor of the first reading control module and the second transmission transistor of the second reading control module in which they are alternately turned on during the exposure process of the light sensor is π.

[0015] Optionally, an electric field generating gate is further included, and the light sensor includes an upper end and a lower end. The first reading control module and the second reading control module are both connected to the lower end of the light sensor. The electric field generating gate covers the upper end of the light sensor and is used to create a constant electric field when a negative pressure is applied to assist the transfer of charges generated by the light sensor to the first reading control module and / or the second reading control module.

[0016] Optionally, the electric field generating gate completely covers the top edge of the upper end of the photosensor.

[0017] Optionally, the light sensor includes at least two photosensitive regions with different doping concentrations, so that the light sensor itself can form a potential difference to further assist the charge transfer to the first read control module and / or the second read control module.

[0018] Optionally, the light sensor includes a first photosensitive region and a second photosensitive region, wherein the doping concentration of the first photosensitive region is lower than that of the second photosensitive region. The electric field generating gate covers the top edge of the first photosensitive region. The first reading control module and the second reading control module are both connected to the bottom edge of the second photosensitive region.

[0019] Optionally, the optical sensor is an axisymmetric structure. The shape of the lower end of the optical sensor is an inverted trapezoid, and the overall shape of the optical sensor is U-shaped. The first reading control module and the second reading control module are both connected to the short bottom side of the inverted trapezoid.

[0020] Optionally, the photosensor includes a first photosensitive area, a second photosensitive area and a third photosensitive area with gradually decreasing potentials, which are used to generate a potential difference to assist the charges generated by itself to flow to the first reading control module and / or the second reading control module connected to the third photosensitive area.

[0021] Optionally, the light sensor is an axisymmetric structure, 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. The first photosensitive area is located at the upper end of the light sensor, including at least two photosensitive parts, the at least two photosensitive parts are symmetrically arranged about the axis, and an opening area is provided between two adjacent photosensitive parts. The second photosensitive area and the third photosensitive area are both located at the lower end of the light sensor, and the third photosensitive area is located at the bottom of the lower end, wherein the doping concentration of the third photosensitive area is higher than the doping concentration of the second photosensitive area.

[0022] 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.

[0023] The TOF image sensor pixel structure and ranging system provided by the present invention include a TOF image sensor pixel structure, including a light sensor, a first reading control module, a second reading control module and a charge balancing unit. The light sensor is used to perform photoelectric conversion to generate charge. The first reading control module and the second reading control module are both connected to the light sensor, and are both used to perform reading control according to the charge. The charge balancing unit is connected to the first floating diffusion node of the first reading control module and the second floating diffusion node of the second reading control module, and is used to balance the charge of the first floating diffusion node and the second floating diffusion node after resetting. Therefore, the present invention can ensure that the voltages of several floating diffusion nodes in the TOF image sensor pixel are equal after resetting, thereby alleviating the fixed pattern noise (FPN) in the pixel and improving the ranging accuracy of the image sensor.

[0024] 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

[0025] Figure 1 4 is a first circuit diagram of a TOF image sensor pixel structure provided by the first embodiment of the present invention.

[0026] Figure 2 4 is a second circuit diagram of the TOF image sensor pixel structure provided by the first embodiment of the present invention.

[0027] Figure 3 Schematic diagram of a pixel structure of a first TOF image sensor provided by a second embodiment of the present invention.

[0028] Figure 4 Schematic diagram of a pixel structure of a second TOF image sensor provided by a second embodiment of the present invention.

[0029] Figure 5 It is a schematic diagram of the structure of a distance measurement system provided by the third embodiment of the present invention. DETAILED DESCRIPTION

[0030] 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.

[0031] Although the present invention uses the terms first, second, third, etc. to describe different reading control modules, output units, photosensitive areas, etc., these reading control modules, output units, photosensitive areas, etc. are not limited by these terms. These terms are only used to distinguish one reading control module, output unit, photosensitive area, etc. from another reading control module, output unit, photosensitive area, 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.

[0032] In the present invention, 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, the light sensor in the present invention may be a photodiode PD (hereinafter described as a photodiode PD).

[0033] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0034] First embodiment:

[0035] Figure 1 4 is a first circuit diagram of a TOF image sensor pixel structure provided by the first embodiment of the present invention. Figure 2 is a second circuit diagram of the TOF image sensor pixel structure provided by the first 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 and Figure 2 .

[0036] The pixel structure of a TOF image sensor provided by the first embodiment of the present invention includes a photodiode PD, a first reading control module M1, a second reading control module M2 and a charge balancing unit EQ.

[0037] The photodiode PD is used for performing photoelectric conversion to generate charges.

[0038] The first reading control module M1 and the second reading control module M2 are both connected to the photodiode PD, and are both used to perform reading control according to the charge.

[0039] 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 transmission transistor MIX1, a first storage capacitor C1, 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 a voltage source VDD, and the second end of the first reset transistor RST1 is coupled to a first floating diffusion node FD1 through the first dual conversion gain control unit. The first end of the first transmission transistor MIX1 is connected to the cathode of the photodiode PD, and the second end of the first transmission 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.

[0040] 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.

[0041] 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.

[0042] 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 DCG1 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.

[0043] 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.

[0044] 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 .

[0045] 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.

[0046] 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.

[0047] 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 transmission transistor MIX2, a second storage capacitor C2, 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 transmission transistor MIX2 is connected to the cathode of the photodiode PD, and the second end of the second transmission 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.

[0048] 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.

[0049] 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.

[0050] 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 DCG2 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.

[0051] 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.

[0052] 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 .

[0053] In one embodiment, the second transfer transistor MIX2 of the second read control unit and the first transfer transistor MIX1 of the first read control unit 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, respectively. 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 suitable for 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] The charge balancing unit EQ is connected to the first floating diffusion node FD1 of the first read control module M1 and the second floating diffusion node FD2 of the second read control module M2 to balance the charges of the first floating diffusion node FD1 and the second floating diffusion node FD2 after reset.

[0059] In one implementation, the charge balancing unit EQ may include a balancing control transistor.

[0060] See also Figure 2 In one implementation, the TOF image sensor pixel structure provided in this embodiment 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.

[0061] The TOF image sensor pixel structure provided by the first embodiment of the present invention includes a photodiode PD, a first reading control module M1, a second reading control module M2 and a charge balancing unit EQ. The photodiode PD is used to perform photoelectric conversion to generate charges. The first reading control module M1 and the second reading control module M2 are both connected to the photodiode PD, and are both used to perform reading control according to the charges. The charge balancing unit EQ is connected to the first floating diffusion node FD1 of the first reading control module M1 and the second floating diffusion node FD2 of the second reading control module M2, and is used to balance the charges of the first floating diffusion node FD1 and the second floating diffusion node FD2 after resetting. Therefore, this embodiment can ensure that the voltages of several floating diffusion nodes in the TOF image sensor pixel are equal after resetting, thereby improving the ranging accuracy of the image sensor.

[0062] Second embodiment:

[0063] Figure 3 is a schematic diagram of a first TOF image sensor pixel structure provided by the second embodiment of the present invention. In order to clearly describe the first TOF image sensor pixel structure provided by the second embodiment of the present invention, please refer to Figure 1 , Figure 2 and Figure 3 .

[0064] The first TOF image sensor pixel structure provided by the second embodiment of the present invention is different from the TOF image sensor pixel structure provided by the first embodiment of the present invention in that: it also includes an electric field generating gate G1, and the photodiode PD includes an upper end ( Figure 3The upper end is above the dotted line) and the lower end is Figure 3 The lower end is below the dotted line). The first read control module M1 and the second read control module M2 are both connected to the lower end of the photodiode PD. The electric field generating gate G1 covers the upper end of the photodiode PD and is used to generate a constant electric field when a negative voltage is applied to assist the transfer of the charge generated by the photodiode PD to the first read control module M1 and / or the second read control module M2.

[0065] In one embodiment, the electric field generating gate G1 completely covers the top edge of the upper end of the photodiode PD.

[0066] In one embodiment, the photodiode PD includes at least two photosensitive regions with different doping concentrations, so that the photodiode PD itself can form a potential difference to further assist the charge transfer to the first read control module M1 and / or the second read control module M2. Specifically, the photodiode PD includes at least two photosensitive regions with different doping concentrations to further improve the charge transfer efficiency.

[0067] In one embodiment, the photodiode PD includes a first photosensitive region B1 and a second photosensitive region B2, wherein the doping concentration of the first photosensitive region B1 is lower than that of the second photosensitive region B2. The electric field generating gate G1 covers the top edge of the first photosensitive region B1. The first reading control module M1 and the second reading control module M2 are both connected to the bottom edge of the second photosensitive region B2.

[0068] In one embodiment, the photodiode PD is a symmetrical structure with a central axis. The lower end of the photodiode PD is in an inverted trapezoidal shape, and the overall shape of the photodiode PD is U-shaped. The first read control module M1 and the second read control module M2 are both connected to the short bottom side of the inverted trapezoid. Specifically, the U-shaped photodiode PD has a faster flow speed of charge than a traditional rectangular photodiode, and thus can also improve the charge transmission efficiency.

[0069] In the first TOF image sensor pixel structure provided by the second embodiment of the present invention, the electric field generating gate G1 covers the upper end of the photodiode PD, and is used to create a constant electric field when a negative voltage is applied to assist the charge generated by the photodiode PD to be transferred to the first reading control module M1 and / or the second reading control module M2, thereby improving the charge transfer efficiency, so that the charge generated by the photodiode PD can be quickly transferred to the first storage capacitor C1 in the first reading control module M1 and / or the second storage capacitor C2 in the second reading control module M2, thereby improving the ranging accuracy. Therefore, the first TOF image sensor pixel structure provided by the second embodiment of the present invention can ensure that the voltages of several floating diffusion nodes in the TOF image sensor pixel are equal after reset, thereby alleviating the fixed pattern noise in the pixel and better improving the ranging accuracy of the image sensor.

[0070] Figure 4 is a schematic diagram of a second TOF image sensor pixel structure provided by the second embodiment of the present invention. In order to clearly describe the second TOF image sensor pixel structure provided by the second embodiment of the present invention, please refer to Figure 1 , Figure 2 and Figure 4 .

[0071] The difference between the second TOF image sensor pixel structure provided by the second embodiment of the present invention and the TOF image sensor pixel structure provided by the first embodiment of the present invention is that 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 first reading control module M1 and / or the second reading control module M2 connected to the third photosensitive area A3.

[0072] In one embodiment, the photodiode PD is a central axis symmetrical structure, the shape of the lower end of the photodiode PD includes an inverted trapezoid, and the overall shape of the photodiode PD is U-shaped.

[0073] In one embodiment, the first photosensitive region A1 is located at the upper end of the photodiode PD (eg, Figure 4 The first photosensitive area A1 of the photodiode PD marked by the dotted frame is the upper end, including at least two photosensitive parts A101, the at least two photosensitive parts A101 are symmetrically arranged about the central axis, and an opening area A102 is provided between two adjacent photosensitive parts A101.

[0074] In one embodiment, the second photosensitive area A2 (eg, Figure 4The 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.

[0075] In the second TOF image sensor pixel structure provided by the second embodiment of the present invention, 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 charge generated by itself to flow to the first reading control module M1 and / or the second reading control module M2 connected to the third photosensitive area A3, thereby improving the charge transmission efficiency, so that the charge generated by the photodiode PD can be quickly transmitted to the first storage capacitor C1 in the first reading control module M1 and / or the second storage capacitor C2 in the second reading control module M2, thereby improving the ranging accuracy. Therefore, the second TOF image sensor pixel structure provided by the second embodiment of the present invention can ensure that the voltages of several floating diffusion nodes in the TOF image sensor pixel are equal after reset, thereby alleviating the fixed pattern noise in the pixel and better improving the ranging accuracy of the image sensor.

[0076] 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.

[0077] Third embodiment:

[0078] Figure 5 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 5 .

[0079] 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 .

[0080] 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.

[0081] The control signal processing unit 11 is used to control the system working process and process the image data acquired by the pixel array.

[0082] 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.

[0083] The distance measurement system provided by the third embodiment of the present invention has a TOF image sensor pixel structure of its image sensor including at least a photodiode PD, a first reading control module M1, a second reading control module M2 and a charge balancing unit EQ. The photodiode PD is used to perform photoelectric conversion to generate charge. The first reading control module M1 and the second reading control module M2 are both connected to the photodiode PD, and are both used to perform reading control according to the charge. The charge balancing unit EQ is connected to the first floating diffusion node FD1 of the first reading control module M1 and the second floating diffusion node FD2 of the second reading control module M2, and is used to balance the charge of the first floating diffusion node FD1 and the second floating diffusion node FD2 after resetting. Therefore, the distance measurement system provided by the third embodiment of the present invention can ensure that the voltages of several floating diffusion nodes in the TOF image sensor pixel are equal after resetting, thereby improving the distance measurement accuracy.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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: It includes a light sensor, a first reading control module, a second reading control module and a charge balancing unit; The light sensor is used to perform photoelectric conversion to generate electric charge; The first reading control module and the second reading control module are symmetrically arranged in the substrate, and are both connected to the light sensor, and are both used to perform reading control according to the charge, and are alternately turned on during the exposure process of the light sensor to alternately transfer the charge accumulated by the light sensor to the corresponding floating diffusion node respectively; 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 light sensor comprises one of a photodiode, a grating or a photoconductor; The charge balancing unit includes a balancing control transistor.

3. The TOF image sensor pixel structure according to claim 1, wherein: The first read control module further includes a first reset transistor, a first dual conversion gain control unit, a first transmission transistor, a first storage capacitor and a first output unit; Wherein, a first terminal of the first reset transistor is connected to a voltage source, and a second terminal of the first reset transistor is coupled to the first floating diffusion node through the first dual conversion gain control unit; A first terminal of the first transfer transistor is connected to a cathode of the light sensor, and a second terminal 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 transmission transistor, a second storage capacitor and a second output unit; Wherein, a first terminal of the second reset transistor is connected to the voltage source, and a second terminal of the second reset transistor is coupled to the second floating diffusion node through the second dual conversion gain control unit; A first terminal of the second transfer transistor is connected to the cathode of the light sensor, and a second terminal 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.

4. The TOF image sensor pixel structure according to claim 3, characterized in that: 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; A first control terminal of the first source follower transistor is connected to the first floating diffusion node, a first terminal of the first source follower transistor is connected to the voltage source, and a second terminal of the first source follower transistor is connected to 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 selection transistor.

5. The TOF image sensor pixel structure according to claim 3, characterized in that: Also included are overflow-resistant transistors; A first terminal of the anti-overflow transistor is coupled to the 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.

6. The TOF image sensor pixel structure according to claim 3, characterized in that: The first transmission transistor of the first reading control module and the second transmission transistor of the second reading control module are alternately turned on in the exposure process of the light sensor with a phase difference of π.

7. The TOF image sensor pixel structure according to claim 1, wherein: Also comprising an electric field generating gate, the light sensor comprising an upper end and a lower end; The first reading control module and the second reading control module are both connected to the lower end of the optical sensor; The electric field generating gate covers the upper end of the light sensor and is used to generate a constant electric field when a negative voltage is applied to assist in transferring the charges generated by the light sensor to the first reading control module and / or the second reading control module.

8. The TOF image sensor pixel structure according to claim 7, wherein: The electric field generating gate completely covers a top edge of an upper end of the photosensor.

9. The TOF image sensor pixel structure according to claim 7, wherein: The light sensor includes at least two photosensitive regions with different doping concentrations, so that the light sensor itself can form a potential difference to further assist the charge transmission to the first reading control module and / or the second reading control module.

10. The TOF image sensor pixel structure according to claim 9, wherein: The light sensor comprises a first light-sensitive region and a second light-sensitive region, wherein the doping concentration of the first light-sensitive region is lower than that of the second light-sensitive region; The electric field generating gate covers the top edge of the first photosensitive area; The first reading control module and the second reading control module are both connected to the bottom edge of the second photosensitive area.

11. The TOF image sensor pixel structure according to claim 7, wherein: The optical sensor is of a central axis symmetrical structure; The shape of the lower end of the optical sensor is an inverted trapezoid, and the overall shape of the optical sensor is U-shaped; The first reading control module and the second reading control module are both connected to the short bottom side of the inverted trapezoid.

12. The TOF image sensor pixel structure according to claim 1, wherein: The light sensor includes a first photosensitive area, a second photosensitive area and a third photosensitive area with gradually decreasing potentials, and is used to generate a potential difference to assist the charges generated by itself to flow to the first reading control module and / or the second reading control module connected to the third photosensitive area.

13. The TOF image sensor pixel structure according to claim 12, wherein: The optical sensor is of a central axis symmetrical structure, 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; 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.

14. 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 13; 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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