A TOF image sensor pixel structure and ranging system

Abstract

The present invention relates to a TOF image sensor pixel structure and a distance measurement system, comprising a light sensor, a first reading control unit, a second reading control unit and an anti-overflow transistor respectively coupled to the light sensor; the first reading control unit and the second reading control unit respectively comprise a reset transistor, a transmission transistor and an output unit; the reset transistor is used to reset the voltage of a floating diffusion node; the transmission transistor couples the light sensor to the corresponding floating diffusion node; the output unit is coupled to the corresponding floating diffusion node; the first channel end of the anti-overflow transistor is coupled to a voltage source, and the second channel end of the anti-overflow transistor is coupled to the light sensor. The pixel structure can eliminate background light signals when the modulated light is not turned on, avoid background light charges from being transmitted to the floating diffusion node, improve distance measurement accuracy, and has a high dynamic range characteristic.

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 3D imaging information technology, especially building measurement, indoor positioning and navigation, stereo imaging and assisted living environment applications, 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. For TOF image sensors, ranging accuracy is an important parameter. The higher the ranging accuracy, the more accurate the 3D image detection of the target.

[0004] In the TOF image sensor pixels, the charges generated by the background light are not helpful for measuring distance information. Instead, the background light charges are transferred to the floating diffusion nodes in the TOF image sensor pixels, thus affecting the distance measurement accuracy. Summary of the invention

[0005] In view of this, the present invention provides a TOF image sensor pixel structure and a ranging system, which can effectively eliminate background light signals, avoid background light charges from being transmitted to floating diffusion nodes, improve ranging accuracy, and have high dynamic range characteristics.

[0006] To achieve the above-mentioned purpose, a first aspect of an embodiment of the present invention provides a TOF image sensor pixel structure. As one implementation method thereof, the TOF image sensor pixel structure includes a light sensor, a first read control unit, a second read control unit and an anti-overflow transistor respectively coupled to the light sensor; wherein,

[0007] The light sensor is used to accumulate charges generated by the photoelectric effect in response to applied light;

[0008] The first read control unit and the second read control unit each include a reset transistor, a transmission transistor and an output unit, and the output unit includes a source follower transistor; wherein,

[0009] The first path end of the reset transistor is coupled to a voltage source, the second path end of the reset transistor is coupled between corresponding floating diffusion nodes, and the reset transistor is used to reset the voltage of the floating diffusion node according to a reset control signal;

[0010] The transfer transistor couples the photosensor to the corresponding floating diffusion node to transfer the charge accumulated by the photosensor to the corresponding floating diffusion node;

[0011] The output unit includes a source follower transistor coupled to the corresponding floating diffusion node to amplify and output the voltage signal of the corresponding floating diffusion node;

[0012] A first channel terminal of the anti-overflow transistor is coupled to the voltage source, and a second channel terminal of the anti-overflow transistor is coupled to the light sensor for removing charges generated by background light from the light sensor when the modulated light is not turned on.

[0013] As one implementation manner, the transfer transistor of the first read control unit and the transfer transistor of the second read control unit are alternately turned on during the exposure process of the photosensor to alternately transfer the charges accumulated in the photosensor to the corresponding floating diffusion nodes.

[0014] As one implementation manner, the phase difference between the alternate conduction of the transmission transistor of the first read control unit and the transmission transistor of the second read control unit during the exposure process of the light sensor is π.

[0015] As one embodiment, the first read control unit and the second read control unit further include a storage control unit, respectively, which is coupled between the light sensor and the transfer transistor to store the charge generated by the light sensor before the charge is read out.

[0016] As one embodiment, the storage control unit includes a storage control transistor and a storage capacitor, the light sensor is coupled to the corresponding floating diffusion node through the storage control transistor and the transfer transistor, the first end of the storage capacitor is coupled to the node between the storage control transistor and the transfer transistor, and the second end of the storage capacitor is connected to the ground or to a fixed voltage value.

[0017] As one implementation manner, the storage capacitor is a device capacitor.

[0018] As one implementation manner, the first read control unit, the second read control unit and the anti-overflow transistor are all located on one side of the light sensor, and the first read control unit and the second read control unit are mirror-symmetrically arranged along a center line of a column direction of the light sensor.

[0019] As one implementation manner, the anti-overflow transistor is disposed between the storage control transistors of the first read control unit and the second read control unit.

[0020] As one implementation manner, the output unit further includes a row selection transistor, and the source follower transistor is coupled to the corresponding column output line through the row selection transistor; the row selection transistor, the source follower transistor and the reset transistor are arranged adjacent to each other in sequence along the same direction.

[0021] As one embodiment, the TOF image sensor pixel structure also includes a balancing control transistor, wherein the first channel end and the second channel end of the balancing control transistor are respectively connected to the corresponding floating diffusion nodes in the first read control unit and the second read control unit, so as to balance the charges of the two floating diffusion nodes after resetting.

[0022] To achieve the above-mentioned purpose, a second aspect of an embodiment of the present invention provides a ranging system. As one implementation mode, the ranging system includes: an image sensor, the image sensor includes a plurality of pixel arrays arranged in rows and columns, each pixel includes the TOF image sensor pixel structure described in any of the above-mentioned implementation modes; a control signal processing unit, used to control the system working 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 back the received modulation signal to the pixel array.

[0023] In summary, the TOF image sensor pixel structure and ranging system provided by the present invention include a light sensor, a first read control unit, a second read control unit and an anti-overflow transistor respectively coupled to the light sensor; wherein the light sensor is used to accumulate charges generated by the photoelectric effect in response to the applied light; the first read control unit and the second read control unit respectively include a reset transistor, a dual conversion gain control unit, a transmission transistor and an output unit; wherein the first channel end of the reset transistor is coupled to a voltage source, the dual conversion gain control unit is coupled between the second channel end of the reset transistor and the corresponding floating diffusion node, the reset transistor is used to reset the voltage of the floating diffusion node according to a reset control signal, and the dual conversion gain control unit is used to achieve gain control and charge storage; the transmission transistor is coupled to the light sensor to the corresponding floating diffusion node to transfer the accumulated charge of the light sensor to the corresponding floating diffusion node; the output unit is coupled to the corresponding floating diffusion node to amplify and output the voltage signal of the corresponding floating diffusion node; the first channel end of the anti-overflow transistor is coupled to the voltage source, and the second channel end of the anti-overflow transistor is coupled to the light sensor to remove the charge generated by the light sensor due to background light when the modulated light is not turned on. Therefore, the TOF image sensor pixel structure provided by the present invention can eliminate the background light signal when the modulated light is not turned on, avoid the charge generated by the background light from being transmitted to the floating diffusion node, improve the ranging accuracy, and have a high dynamic range characteristic. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A circuit diagram of a TOF image sensor pixel structure provided by an embodiment of the present invention is shown.

[0025] Figure 2 A circuit diagram showing a pixel structure of a TOF image sensor provided by another embodiment of the present invention is shown.

[0026] Figure 3 A schematic diagram showing the layout structure of a TOF image sensor pixel structure provided by an embodiment of the present invention is shown.

[0027] Figure 4 A basic block diagram of a distance measurement system provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments, and are only used to explain the present invention, not to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In this patent specification, "one embodiment" or "an implementation method" refers to the specific features, structures or characteristics described in the example included in at least one embodiment of the present invention.

[0029] Please refer to Figure 1 , Figure 1 FIG. 1 is a circuit diagram showing a pixel structure of a TOF image sensor provided by an embodiment of the present invention. Figure 1 As shown, the pixel structure of the TOF image sensor includes a light sensor (PD), a first read control unit, a second read control unit and an anti-overflow transistor AB respectively coupled to the light sensor; wherein the light sensor is used to accumulate the charge generated by the photoelectric effect in response to the applied light. The light sensor can be any photosensitive structure used to convert visible light into electrons (photocharges), such as any one of a photodiode, a grating or a photoconductor. As a preferred embodiment, the light sensor in this embodiment is a photodiode. Figure 1 As shown in the figure, the light sensor is a photodiode PD, which has a first end and a second end, wherein the second end is grounded, and the first end is respectively connected to the first reading control unit and the second reading control unit; specifically, the first end is the cathode end of the photodiode PD, and the second end is the anode end of the photodiode PD.

[0030] The first read control unit and the second read control unit each include a reset transistor, a dual conversion gain control unit, a transmission transistor and an output unit; for convenience and clear description, Figure 1 The components of the first read control unit and the second read control unit are numbered and described as follows:

[0031] The first read control unit includes a first reset transistor RST1, a first dual conversion gain control unit, a first transmission transistor TX1, and a first output unit. Among them, the first channel end of the first reset transistor RST1 is coupled to the voltage source VDD, the first dual conversion gain control unit is coupled between the second channel end of the first reset transistor RST1 and the first floating diffusion node FDA, the first reset transistor RST1 is used to reset the voltage of the first floating diffusion node FDA according to the reset control signal, and the first dual conversion gain control unit is used to achieve gain control and charge storage. The first transmission transistor TX1 couples the photodiode to the first floating diffusion node FDA to transfer the charge accumulated by the photodiode PDA to the first floating diffusion node FDA. The first output unit is coupled to the first floating diffusion node FDA to amplify and output the voltage signal of the first floating diffusion node FDA.

[0032] The second read control unit includes a second reset transistor RST2, a second dual conversion gain control unit, a second transmission transistor TX2, and a second output unit. The second path end of the second reset transistor RST2 is coupled to the voltage source VDD, the second dual conversion gain control unit is coupled between the second path end of the second reset transistor RST2 and the second floating diffusion node FDB, the second reset transistor RST2 is used to reset the voltage of the second floating diffusion node FDB according to the reset control signal, and the second dual conversion gain control unit is used to achieve gain control and charge storage. The second transmission transistor TX2 couples the photodiode to the second floating diffusion node FDB to transfer the charge accumulated by the photodiode PD to the second floating diffusion node FDB. The second output unit is coupled to the second floating diffusion node FDB to amplify and output the voltage signal of the second floating diffusion node FDB.

[0033] The first channel end of the anti-overflow transistor AB is coupled to the voltage source VDD, and the second channel end of the anti-overflow transistor AB is coupled to the photodiode PD to remove the charge generated by the photodiode PD due to the background light when the modulated light is not turned on.

[0034] 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.

[0035] In one embodiment, the first transfer transistor TX1 of the first read control unit and the second transfer transistor TX2 of the second read control unit are alternately turned on during the exposure process of the photodiode PD to alternately transfer the charges accumulated in the photodiode PD to the first floating diffusion node FDA and the second floating diffusion node FDB, respectively.

[0036] In one embodiment, the first transfer transistor TX1 of the first read control unit and the second transfer transistor TX2 of the second read control unit are alternately turned on in the exposure process of the photodiode PD with a phase difference of π. For example, it is only necessary to control the control signal and phase of the first transfer transistor TX1 to be consistent with the modulated light source, and the control signal of the second transfer transistor TX2 and the control signal of the first transfer transistor TX1 only have a phase difference of π.

[0037] Specifically, in this embodiment, by setting a first read control unit and a second read control unit to be coupled to the photodiode PD respectively, and controlling the first transfer transistor TX1 and the second transfer transistor TX2 to be turned on alternately 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 unit and the second read control unit can be calculated to determine the flight time of the light pulse, so that the pixel structure can be suitable for the image sensor of TOF application. And because the first read control unit and the second read control unit use transfer transistors to couple the photodiode PD and 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.

[0038] In one embodiment, the first read control unit and the second read control unit further include a storage control unit, respectively, and the storage control unit is coupled between the photodiode PD and the transfer transistor to store the charge generated by the photodiode PD before the charge is read out.

[0039] Specifically, when the floating diffusion node is sampled as a storage node for charge, the conversion gain of the pixel is very small, resulting in readout noise affecting the ranging accuracy. In this embodiment, by setting a storage control unit, the function of the floating diffusion node can be separated, that is, the storage function and the readout function are separated, the storage control unit is used as a storage node, and the floating diffusion node is used as a readout node, thereby reducing the capacitance of the floating diffusion node, providing conversion gain, reducing readout noise, and achieving high-precision ranging.

[0040] Please refer to Figure 2 , Figure 2 FIG. 2 is a circuit diagram showing a pixel structure of a TOF image sensor provided by another embodiment of the present invention. Figure 2 As shown, in one embodiment, the storage control unit includes storage control transistors MIX1 and MIX2 and storage capacitors C1 and C2, the photodiode PD is coupled to the corresponding floating diffusion node through the storage control transistor and the transfer transistor, the first end of the storage capacitor is coupled to the node between the storage control transistor and the transfer transistor, and the second end of the storage capacitor is connected to the ground or to a fixed voltage value.

[0041] Specifically, the first read control unit and the second read control unit include a first storage control unit and a second storage control unit, respectively. The first storage control unit includes a first storage control transistor MIX1 and a first storage capacitor C1. The photodiode PD is coupled to the first floating diffusion node FDA through the first storage control transistor MIX1 and the first transfer transistor TX1. The first end of the first storage capacitor C1 is coupled to the node between the first storage control transistor MIX1 and the first transfer transistor TX1. The second end of the first storage capacitor C1 is connected to the ground or to a fixed voltage value. The second storage control unit includes a second storage control transistor MIX2 and a second storage capacitor C2. The photodiode PD is coupled to the second floating diffusion node FDB through the second storage control transistor MIX2 and the second transfer transistor TX2. The second end of the second storage capacitor C2 is coupled to the node between the second storage control transistor MIX2 and the second transfer transistor TX2. The second end of the second storage capacitor C2 is connected to the ground or to a fixed voltage value.

[0042] It is worth mentioning that since in the present embodiment, the first read control unit and the second read control unit respectively include a first storage control unit and a second storage control unit, the charge accumulated in the photodiode PD during the exposure process can be transferred to the storage capacitor for storage through the storage control transistor, and after the exposure is completed, the charge stored in the storage capacitor can be transferred to the corresponding floating diffusion node through the transfer transistor for reading, so that the pixel structure of the present embodiment supports the global exposure mode.

[0043] In one embodiment, the first storage capacitor and the second storage capacitor are device capacitors.

[0044] Specifically, the first storage capacitor and the second storage capacitor serve as storage nodes, and the photodiode PD or the photogate may be used as the storage node to store charges.

[0045] In one embodiment, the dual conversion gain control unit includes a dual conversion gain control transistor and a dual conversion gain capacitor, the dual conversion gain control transistor is coupled between the second end of the reset transistor and the corresponding floating diffusion node, the first end of the dual conversion gain capacitor is coupled to the node between the dual conversion gain transistor and the reset transistor, and the second end of the dual conversion gain capacitor is connected to a fixed level.

[0046] Specifically, the first read control unit and the second read control unit include a first dual conversion gain control unit and a second dual conversion gain control unit, respectively. The first dual conversion gain control unit includes a first dual conversion gain control transistor DCG1 and a first dual conversion gain capacitor (not shown in the figure), the first dual conversion gain control transistor DCG1 is coupled between the second end of the first reset transistor RST1 and the first floating diffusion node FDA, the first end of the first dual conversion gain capacitor is coupled to the node between the first dual conversion gain transistor DCG1 and the first reset transistor RST1, and the second end thereof is connected to a fixed level. The second dual conversion gain control unit includes a second dual conversion gain control transistor DCG2 and a second dual conversion gain capacitor (not shown in the figure), the second dual conversion gain control transistor DCG2 is coupled between the second end of the second reset transistor RST2 and the second floating diffusion node FDB, the first end of the second dual conversion gain capacitor is coupled to the node between the second dual conversion gain transistor DCG2 and the second reset transistor RST2, and the second end thereof is connected to a fixed level. The fixed level may be a low level, such as grounding, or other potential levels.

[0047] In one embodiment, the first dual conversion gain capacitor is a parasitic capacitor between a connection point between the first reset transistor and the first dual conversion gain control transistor and ground, and the second dual conversion gain capacitor is a parasitic capacitor between a connection point between the second reset transistor and the second dual conversion gain control transistor and ground.

[0048] In one embodiment, the output unit includes source follower transistors SF1 and SF2 and row select transistors RS1 and RS2 , and the source follower transistors are coupled to corresponding column output lines through the row select transistors.

[0049] Specifically, the first read control unit and the second read control unit include a first output unit and a second output unit, respectively; wherein the first output unit includes a first source follower transistor SF1 and a first row selection transistor RS1, the gate of the first source follower transistor SF1 is coupled to the first floating diffusion node FDA, the drain thereof is coupled to the voltage source VDD, and the source thereof is coupled to the first column output line BL through the first row selection transistor RS1. The second output unit includes a second source follower transistor SF2 and a second row selection transistor RS2, the gate of the second source follower transistor SF2 is coupled to the second floating diffusion node FDB, the drain thereof is coupled to the voltage source VDD, and the source thereof is coupled to the second column output line BLB through the second row selection transistor RS2.

[0050] It is worth mentioning that the first output unit and the second output unit may also only include source follower transistors, and other amplifier devices with different gains may be used to replace the source follower transistors.

[0051] In one embodiment, the TOF image sensor pixel structure also includes a balancing control transistor EQ, wherein the first channel end and the second channel end of the balancing control transistor EQ are respectively connected to corresponding floating diffusion nodes in the first read control unit and the second read control unit, so as to balance the charges of the two floating diffusion nodes after resetting.

[0052] Specifically, the balance control transistor EQ serves as a balancing circuit, and its two path ends are respectively connected to the first floating diffusion node FDA and the second floating diffusion node FDB, and are used to balance the charges of the first floating diffusion node FDA and the second floating diffusion node FDB after reset, so as to avoid the influence of uneven charges on the ranging accuracy after charge collection.

[0053] Please refer to Figure 3 , Figure 3 FIG. 1 is a schematic diagram showing the layout structure of a TOF image sensor pixel structure provided by an embodiment of the present invention. Figure 3 As shown, the first read control unit, the second read control unit and the anti-overflow transistor are all located on one side of the photodiode PD, and the first read control unit and the second read control unit are arranged in mirror symmetry along the center line of the column direction of the photodiode PD.

[0054] In one embodiment, the anti-overflow transistor AB is disposed between the storage control transistors ( MIX1 and MIX2 ) of the first read control unit and the second read control unit.

[0055] In one implementation, the row selection transistor, the source follower transistor and the reset transistor are arranged adjacent to each other in sequence along the same direction.

[0056] In one embodiment, the balancing transistor EQ is disposed at a midpoint of a line connecting the first floating diffusion node FDA and the second floating diffusion node FDB.

[0057] It should be noted that Figure 3 The schematic diagram of the layout structure of the pixel structure of the TOF image sensor provided by one embodiment of the present invention is only shown, and only a general description of the layout structure is given. The specific connection relationship between the components can be known by those skilled in the art according to the functions of the components and the relationship between the components. Figure 3 It is not shown in detail, for example Figure 3 The specific connection relationship between the transfer transistor and the storage node SD, the specific connection relationship between the floating diffusion node and the source follower transistor, etc. The storage node SD corresponds to Figure 2 C1 and C2 in the embodiment may be photogates, photodiodes or other capacitive devices.

[0058] The TOF image sensor pixel structure provided by the embodiment of the present invention includes a light sensor, a first read control unit, a second read control unit and an anti-overflow transistor respectively coupled to the light sensor; wherein the light sensor is used to accumulate charges generated by the photoelectric effect in response to the applied light; the first read control unit and the second read control unit respectively include a reset transistor, a dual conversion gain control unit, a transmission transistor and an output unit; wherein the first channel end of the reset transistor is coupled to a voltage source, the dual conversion gain control unit is coupled between the second channel end of the reset transistor and the corresponding floating diffusion node, the reset transistor is used to reset the voltage of the floating diffusion node according to a reset control signal, and the dual conversion gain control unit is used to achieve gain control and charge storage; the transmission transistor is coupled to the light sensor to the corresponding floating diffusion node to transfer the accumulated charge of the light sensor to the corresponding floating diffusion node; the output unit is coupled to the corresponding floating diffusion node to amplify and output the voltage signal of the corresponding floating diffusion node; the first channel end of the anti-overflow transistor is coupled to the voltage source, and the second channel end of the anti-overflow transistor is coupled to the light sensor to remove the charge generated by the light sensor due to background light when the modulated light is not turned on. Therefore, the TOF image sensor pixel structure provided by the present invention can eliminate the background light signal when the modulated light is not turned on, avoid the charge generated by the background light from being transmitted to the floating diffusion node, improve the ranging accuracy, and have a high dynamic range characteristic.

[0059] This application also provides a ranging system, please refer to Figure 4 , Figure 4 FIG. 2 shows a basic block diagram of a distance measurement system provided by an embodiment of the present invention. Figure 4 As shown, the ranging system includes: an image sensor 10, a control signal processing unit 11 and a modulated light source 12. The image sensor 10 includes a plurality of pixel arrays arranged in rows and columns, each pixel including the TOF image sensor pixel structure described in any one of the above embodiments; the control signal processing unit 11 is used to control the system working process and process the image data acquired by the pixel array; 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.

[0060] The distance measurement system provided by the embodiment of the present invention has a TOF image sensor pixel structure of an image sensor including a light sensor, a first reading control unit, a second reading control unit and an anti-overflow transistor respectively coupled to the light sensor; wherein the light sensor is used to accumulate charges generated by the photoelectric effect in response to the applied light; the first reading control unit and the second reading control unit respectively include a reset transistor, a dual conversion gain control unit, a transmission transistor and an output unit; wherein the first channel end of the reset transistor is coupled to a voltage source, the dual conversion gain control unit is coupled between the second channel end of the reset transistor and the corresponding floating diffusion node, the reset transistor is used to reset the voltage of the floating diffusion node according to a reset control signal, and the dual conversion gain control unit is used to achieve gain control and charge storage; the transmission transistor is coupled to the light sensor to the corresponding floating diffusion node to transfer the accumulated charges of the light sensor to the corresponding floating diffusion node; the output unit is coupled to the corresponding floating diffusion node to amplify and output the voltage signal of the corresponding floating diffusion node; the first channel end of the anti-overflow transistor is coupled to the voltage source, and the second channel end of the anti-overflow transistor is coupled to the light sensor to remove the charges generated by the light sensor due to background light when the modulated light is not turned on. Therefore, the ranging system provided by the present invention can eliminate the background light signal when the modulated light is not turned on, avoid the charge generated by the background light from being transmitted to the floating diffusion node, improve the ranging accuracy to obtain a high-precision image, and has a high dynamic range characteristic.

[0061] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, and these simple modifications all belong to the protection scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. The present invention will not further explain various possible combinations.

Claims

1. A TOF image sensor pixel structure, characterized in that: It includes a light sensor, a first read control unit, a second read control unit, an anti-overflow transistor and a balance control transistor respectively coupled to the light sensor; wherein, The light sensor is used to accumulate charges generated by the photoelectric effect in response to applied light; The first read control unit and the second read control unit each include a reset transistor, a transfer transistor and an output unit, wherein the transfer transistor of the first read control unit and the transfer transistor of the second read control unit 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, and the output unit includes a source follower transistor; wherein, The first channel end of the reset transistor is coupled to a voltage source, the second channel end of the reset transistor is coupled to a corresponding floating diffusion node, and the reset transistor is used to reset the voltage of the floating diffusion node according to a reset control signal; The transfer transistor couples the photosensor to the corresponding floating diffusion node to transfer the charge accumulated by the photosensor to the corresponding floating diffusion node; The source follower transistor is coupled to the corresponding floating diffusion node to amplify and output the voltage signal of the corresponding floating diffusion node; The first channel terminal of the anti-overflow transistor is coupled to the voltage source, and the second channel terminal of the anti-overflow transistor is coupled to the light sensor, so as to remove the charge generated by the background light from the light sensor when the modulated light is not turned on; The first channel end and the second channel end of the balancing control transistor are respectively connected to corresponding floating diffusion nodes in the first read control unit and the second read control unit, so as to balance the charges of the two floating diffusion nodes after resetting.

2. The TOF image sensor pixel structure according to claim 1, characterized in that: The phases of the transfer transistor of the first read control unit and the transfer transistor of the second read control unit being alternately turned on during the exposure process of the light sensor differ by π.

3. The TOF image sensor pixel structure according to claim 1, characterized in that: The first read control unit and the second read control unit further include a storage control unit, respectively, which is coupled between the light sensor and the transfer transistor to store the charge generated by the light sensor before the charge is read out.

4. The TOF image sensor pixel structure according to claim 3, characterized in that: The storage control unit includes a storage control transistor and a storage capacitor. The light sensor is coupled to a corresponding floating diffusion node through the storage control transistor and the transfer transistor. The first end of the storage capacitor is coupled to a node between the storage control transistor and the transfer transistor. The second end of the storage capacitor is connected to the ground or to a fixed voltage value.

5. The TOF image sensor pixel structure according to claim 4, characterized in that: The storage capacitor is a device capacitor.

6. The TOF image sensor pixel structure according to claim 4, characterized in that: The first read control unit, the second read control unit and the anti-overflow transistor are all located on one side of the light sensor, and the first read control unit and the second read control unit are arranged in mirror symmetry along a center line of a column direction of the light sensor.

7. The TOF image sensor pixel structure according to claim 6, characterized in that: The anti-overflow transistor is disposed between the storage control transistors of the first read control unit and the second read control unit.

8. The TOF image sensor pixel structure according to claim 6 or 7, characterized in that: The output unit further includes a row selection transistor, through which the source follower transistor is coupled to the corresponding column output line; the row selection transistor, the source follower transistor and the reset transistor are arranged adjacent to each other in sequence along the same direction.

9. A distance measurement system, characterized in that: The ranging system comprises: 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 8; 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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