Global exposure pixel and image sensor

Abstract

The invention discloses a global exposure pixel and an image sensor, and relates to the technical field of image sensors, and the global exposure pixel comprises a photosensitive unit, a transmission unit, a reset unit, an amplification unit, a pre-charging unit, a storage unit and a switch unit. According to the global exposure pixel, a second-stage amplification transistor and a selection tube in a traditional 8T pixel structure are omitted, only one path of amplification unit and one path of pre-charging unit are arranged, and the multiplexing amplification unit can achieve the functions of a first-stage amplification transistor and the second-stage amplification transistor in the 8T pixel structure; the multiplexing pre-charging unit can realize the functions of a pre-charging tube and a selection tube in the 8T pixel structure, so that the number of devices in the global exposure pixel can be reduced, the area of a photodiode is increased, the sensitivity of the global exposure pixel is improved, or the size of the global exposure pixel is reduced under the condition that the sensitivity is kept unchanged.

Description

Technical Field

[0001] The present application relates to the technical field of image sensors, and in particular to a global exposure pixel; and also to an image sensor. Background Art

[0002] An image sensor is a sensor that can convert light signals reflecting image information into electrical signals. It is divided into two categories: CCD structure and CMOS structure. In order to meet the needs of shooting high-speed moving objects, a global exposure pixel is required that can store the electrical signal generated by itself after exposure and wait for the peripheral signal readout circuit to read it out. The global exposure pixel is the global exposure pixel that meets this need.

[0003] like Figure 1 As shown in FIG. 1 , a conventional global exposure pixel includes eight NMOS transistors (Q0 to Q7), which is usually referred to as an 8T pixel structure. The 8T pixel structure includes two stages of amplification transistors. Figure 1 Q2 is the first-stage amplifier transistor, Q6 is the second-stage amplifier transistor, Q3 is the pre-charge tube, and Q7 is the selection tube. The final effective voltage signal is divided by two compared to the output of the first-stage amplifier transistor in the global exposure pixel, and the voltage signal amplitude is reduced by half, which will cause the sensitivity of the entire image sensor to be reduced by half, and also reduce the signal-to-noise ratio. The general method to improve the sensitivity is to increase the area of ​​the photosensitive diode, but because the size of the global exposure pixel is small and some other devices need to be placed in it, the area of ​​the photosensitive diode is limited and often cannot be increased. If you want to increase the area of ​​the photosensitive diode, you need to reduce the number of other devices in the global exposure pixel. Therefore, how to reduce the number of devices in the global exposure pixel has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0004] The purpose of the present application is to provide a global exposure pixel, which can reduce the number of devices in the global exposure pixel, so as to increase the area of ​​the photosensitive diode and improve the sensitivity of the global exposure pixel, or reduce the size of the global exposure pixel while keeping the sensitivity unchanged. Another purpose of the present application is to provide an image sensor, which also has the above technical effects.

[0005] In order to solve the above technical problems, the present application provides a global exposure pixel, including:

[0006] A photosensitive unit, a transmission unit, a reset unit, an amplifying unit, a pre-charging unit, a storage unit and a switch unit; the input end of the storage unit is connected to the amplifying unit, the output end of the storage unit is connected to one end of the switch unit, the other end of the switch unit is connected to a floating diffusion node, and the amplifying unit is also connected to the floating diffusion node and the pre-charging unit;

[0007] The photosensitive unit is used to sense light and generate charges;

[0008] The transfer unit is used to transfer the charges to the floating diffusion node;

[0009] The reset unit is used to reset the global exposure pixel;

[0010] The storage unit is used to store the reset voltage and the exposure voltage;

[0011] The amplification unit is used to amplify and output the voltage of the floating diffusion node;

[0012] The pre-charge unit is used to pre-charge the amplification unit at the frame head time;

[0013] The switch unit is used to connect the output end of the storage unit to the floating diffusion node when the switch unit is turned on.

[0014] Optionally, the storage unit includes:

[0015] A first transistor, a second transistor, a first capacitor and a second capacitor; the third end of the first transistor serves as the input end of the storage unit, the second end of the first transistor is connected to the first end of the first capacitor and the third end of the second transistor, the first end of the first transistor inputs a first control signal, the second end of the first capacitor is grounded, the second end of the second transistor is connected to the first end of the second capacitor, the first end of the second transistor inputs a second control signal, and the second end of the second capacitor is grounded.

[0016] Optionally, the first end of the second capacitor serves as the output end of the storage unit and is connected to one end of the switch unit, and the other end of the switch unit is connected to the floating diffusion node.

[0017] Optionally, the first end of the first capacitor serves as the output end of the storage unit and is connected to one end of the switch unit, and the other end of the switch unit is connected to the floating diffusion node.

[0018] Optionally, the switch unit includes:

[0019] A third transistor; the third end of the third transistor is connected to the floating diffusion node, the second end of the third transistor is connected to the output end of the storage unit, and the first end of the third transistor inputs a third control signal.

[0020] Optionally, the photosensitive unit includes:

[0021] A photodiode; the anode of the photodiode is grounded, and the cathode of the photodiode is connected to the transfer unit.

[0022] Optionally, the transmission unit includes:

[0023] A fourth transistor; a third terminal of the fourth transistor is connected to the floating diffusion node, a second terminal of the fourth transistor is connected to the photosensitive unit, and a first terminal of the fourth transistor inputs a transmission control signal.

[0024] Optionally, the reset unit includes:

[0025] A fifth transistor; a third terminal of the fifth transistor is connected to a preset potential, a second terminal of the fifth transistor is connected to the floating diffusion node, and a first terminal of the fifth transistor inputs a reset control signal.

[0026] Optionally, the amplification unit includes a sixth transistor; the pre-charge unit includes a seventh transistor; a first terminal of the sixth transistor is connected to the floating diffusion node, a second terminal of the sixth transistor is connected to an input terminal of the storage unit and a third terminal of the seventh transistor, a third terminal of the sixth transistor is connected to a preset potential, a second terminal of the seventh transistor serves as an output terminal of the global exposure pixel, and a first terminal of the seventh transistor inputs a pre-charge control signal.

[0027] To solve the above technical problems, the present application also provides an image sensor including the global exposure pixel as described above.

[0028] The global exposure pixel provided by the present application includes: a photosensitive unit, a transmission unit, a reset unit, an amplification unit, a pre-charge unit, a storage unit, and a switch unit; an input terminal of the storage unit is connected to the amplification unit, an output terminal of the storage unit is connected to one end of the switch unit, the other end of the switch unit is connected to the floating diffusion node, and the amplification unit is further connected to the floating diffusion node and the pre-charge unit; the photosensitive unit is configured to sense light to generate charges; the transmission unit is configured to transmit the charges to the floating diffusion node; the reset unit is configured to reset the global exposure pixel; the storage unit is configured to store a reset voltage and an exposure voltage; the amplification unit is configured to amplify and output the voltage of the floating diffusion node; the pre-charge unit is configured to pre-charge the amplification unit at the head time of a frame; the switch unit is configured to connect the output terminal of the storage unit to the floating diffusion node when the switch unit is turned on.

[0029] It can be seen that, compared with the traditional 8T pixel structure, the global exposure pixel provided by the present application removes the second-stage amplification transistor and the selection transistor in the 8T pixel structure, and only sets one path of amplification unit and one path of pre-charge unit. The multiplexing amplification unit can realize the functions of the first-stage amplification transistor and the second-stage amplification transistor in the 8T pixel structure, and the multiplexing pre-charge unit can realize the functions of the pre-charge transistor and the selection transistor in the 8T pixel structure. In this way, the number of devices in the global exposure pixel can be reduced.

[0030] The image sensor provided by the present application also has the above technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the prior art and the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0032] Figure 1 Schematic diagram of a traditional global exposure pixel;

[0033] Figure 2 Schematic diagram of a global exposure pixel provided by an embodiment of the present application;

[0034] Figure 3 Schematic diagram of another global exposure pixel provided by an embodiment of the present application;

[0035] Figure 4 Schematic diagram of yet another global exposure pixel provided by an embodiment of the present application;

[0036] Figure 5 Timing diagram provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The core of the present application is to provide a global exposure pixel, which can reduce the number of devices in the global exposure pixel, so as to increase the area of the photosensitive diode and improve the sensitivity of the global exposure pixel, or reduce the size of the global exposure pixel while maintaining the sensitivity unchanged. Another core of the present application is to provide an image sensor, which also has the above technical effects.

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without creative efforts fall within the scope of protection of this application.

[0039] Please refer to Figure 2 , Figure 2 which is a schematic diagram of a global exposure pixel provided by an embodiment of this application. As shown in Figure 2 , this global exposure pixel includes:

[0040] a photosensitive unit 10, a transmission unit 20, a reset unit 30, an amplification unit 40, a pre-charge unit 50, a storage unit 60, and a switch unit 70; the input end of the storage unit 60 is connected to the amplification unit 40, the output end of the storage unit 60 is connected to one end of the switch unit 70, the other end of the switch unit 70 is connected to a floating diffusion node, and the amplification unit 40 is also connected to the floating diffusion node and the pre-charge unit 50;

[0041] The photosensitive unit 10 is used for photosensing to generate charges;

[0042] The transmission unit 20 is used for transmitting charges to the floating diffusion node;

[0043] The reset unit 30 is used for resetting the global exposure pixel;

[0044] The storage unit 60 is used for storing the reset voltage and the exposure voltage;

[0045] The amplification unit 40 is used for amplifying and outputting the voltage of the floating diffusion node;

[0046] The pre-charge unit 50 is used for pre-charging the amplification unit 40 at the frame head time;

[0047] The switch unit 70 is used for connecting the output end of the storage unit 60 to the floating diffusion node when the switch unit 70 is turned on.

[0048] Different from the traditional 8T pixel structure, only one amplification unit 40 and one pre-charge unit 50 are provided for the global exposure pixel in this embodiment. Among them, in some embodiments, the amplification unit 40 includes a sixth transistor M6; the pre-charge unit 50 includes a seventh transistor M7; a first end of the sixth transistor M6 is connected to the floating diffusion node, a second end of the sixth transistor M6 is connected to an input end of the storage unit and a third end of the seventh transistor M7, a third end of the sixth transistor M6 is connected to a preset potential, a second end of the seventh transistor M7 serves as an output end of the global exposure pixel, and a first end of the seventh transistor M7 inputs a pre-charge control signal. The sixth transistor M6 and the seventh transistor M7 may specifically be NMOS transistors. A first end of the sixth transistor M6 and the seventh transistor M7 is a gate of the NMOS transistor, a second end of the sixth transistor M6 and the seventh transistor M7 is a source of the NMOS transistor, and a third end of the sixth transistor M6 and the seventh transistor M7 is a drain of the NMOS transistor.

[0049] The frame header time is the FOT. The full English name of FOT is Frame overhead time. The frame header time is a time state between exposure and readout. This period of time is used to store the exposed signal on the storage node in the pixel at the same time, and then read out the stored signal during the readout time.

[0050] One storage unit 60 is provided for the global exposure pixel in this embodiment. An input end of the storage unit 60 is connected to a second end of the amplification unit 40, an output end of the storage unit 60 is connected to one end of a switch unit 70, and the other end of the switch unit 70 is connected to the floating diffusion node. During the frame header time, the amplification unit 40 is used to implement the function of the first-stage amplification transistor in the 8T pixel structure, and the pre-charge unit 50 is used to implement the function of the pre-charge transistor in the 8T pixel structure. During the readout stage, the amplification unit 40 is used to implement the function of the second-stage amplification transistor in the 8T pixel structure, and the pre-charge unit 50 is used to implement the function of the selection transistor in the 8T pixel structure.

[0051] During the readout stage, the reset voltage and the exposure voltage stored in the storage unit 60 are output via the switch unit 70, the amplification unit 40, and the pre-charge unit 50.

[0052] In some embodiments, the storage unit 60 includes:

[0053] The first transistor M1, the second transistor M2, the first capacitor C1 and the second capacitor C2; the third terminal of the first transistor M1 serves as the input terminal of the storage unit 60, the second terminal of the first transistor M1 is connected to the first terminal of the first capacitor C1 and the third terminal of the second transistor M2, the first terminal of the first transistor M1 inputs a first control signal, the second terminal of the first capacitor C1 is grounded, the second terminal of the second transistor M2 is connected to the first terminal of the second capacitor C2, the first terminal of the second transistor M2 inputs a second control signal, and the second terminal of the second capacitor C2 is grounded.

[0054] The first capacitor C1 is used to store the reset voltage, and the second capacitor C2 is used to store the exposure voltage.

[0055] Wherein, in some embodiments, the first terminal of the second capacitor C2 serves as the output terminal of the storage unit 60 and is connected to one end of the switch unit 70, and the other end of the switch unit 70 is connected to the floating diffusion node.

[0056] Reference Figure 3 As shown, in this embodiment, the first terminal of the second capacitor C2 serves as the output terminal of the storage unit 60 and is connected to one end of the switch unit 70, and the other end of the switch unit 70 is connected to the floating diffusion node.

[0057] In the case where the first terminal of the second capacitor C2 serves as the output terminal of the storage unit 60, during the readout phase, the switch unit 70 is always closed, turning off the second transistor M2. The first terminal of the second capacitor C2 is connected to the floating diffusion node, and the voltage of the floating diffusion node is the reset voltage Vrst stored on the second capacitor C2. The global exposure pixel post-stage circuit samples the reset voltage VOUT1 = Vrst - V gs,M6 -V ds,M7 . Where V gs,M6 is the voltage difference between the gate and source of the amplification unit 40, and V ds,M7 is the voltage difference between the drain and source of the pre-charge unit 50. Then, the second transistor M2 is turned on, and the first terminal of the first capacitor C1, the first terminal of the second capacitor C2, and the floating diffusion node are connected. The voltage of the floating diffusion node becomes (Vrst * C2 + Vsig * C1) / (C1 + C2). The global exposure pixel post-stage circuit samples the voltage VOUT2 = (Vrst * C2 + Vsig * C1) / (C1 + C2) - V gs,M6 -V ds,M7 output from the output terminal of the global exposure pixel. Vsig is the exposure voltage stored in the first capacitor C1. Finally, the effective voltage output by the global exposure pixel is:

[0058] Veff = VOUT1 - VOUT2 = (Vrst - Vsig) * C1 / (C1 + C2).

[0059] When C1 = C2, Veff = (Vrst - Vsig) / 2, which is the same as the effective voltage output by the traditional 8T global exposure pixel structure.

[0060] In addition, in some embodiments, the first end of the first capacitor C1 is used as the output end of the storage unit 60 and is connected to one end of the switch unit 70, and the other end of the switch unit 70 is connected to the floating diffusion node.

[0061] Reference Figure 4 As shown, in this embodiment, the first end of the second transistor M2 is used as the output end of the storage unit 60 and is connected to one end of the switch unit 70, and the other end of the switch unit 70 is connected to the floating diffusion node.

[0062] When the first end of the first capacitor C1 is used as the output end of the storage unit 60, in the read stage, the switch unit 70 is always closed, the second transistor M2 is turned off, the first end of the first capacitor C1 is connected to the floating diffusion node, and the voltage of the floating diffusion node is the exposure voltage Vsig stored on the first capacitor C1. The global exposure pixel post-stage circuit samples the exposure voltage VOUT1 = Vsig - V gs,M6 -V ds,M7 output at the output end of the global exposure pixel. Then the second transistor M2 is turned on, the first end of the first capacitor C1 and the first end of the second capacitor C2 are connected to the floating diffusion node, and the voltage of the floating diffusion node becomes (Vrst*C2 + Vsig*C1) / (C1 + C2). The global exposure pixel post-stage circuit samples the voltage VOUT2 = (Vrst*C2 + Vsig*C1) / (C1 + C2) - V gs,M6 -V ds,M7 .

[0063] Finally, the effective voltage output by the global exposure pixel is:

[0064] Veff = VOUT2 - VOUT1 = (Vrst - Vsig)*C1 / (C1 + C2).

[0065] When C1 = C2, Veff = (Vrst - Vsig) / 2, which is the same as the effective voltage output by the traditional 8T global exposure pixel structure.

[0066] In some embodiments, the switch unit 70 includes: a third transistor M3; the third end of the third transistor M3 is connected to the floating diffusion node, the second end of the third transistor M3 is connected to the output end of the storage unit 60, and the first end of the third transistor M3 inputs a third control signal.

[0067] The photosensitive unit 10 includes: a photodiode PD; the anode of the photodiode PD is grounded, and the cathode of the photodiode PD is connected to the transmission unit 20.

[0068] The transmission unit 20 includes: a fourth transistor M4; the third terminal of the fourth transistor M4 is connected to the floating diffusion node, the second terminal of the fourth transistor M4 is connected to the photosensitive unit 10, and the first terminal of the fourth transistor M4 inputs a transmission control signal.

[0069] The reset unit 30 includes: a fifth transistor; the third terminal of the fifth transistor is connected to a preset potential, the second terminal of the fifth transistor is connected to the floating diffusion node, and the first terminal of the fifth transistor inputs a reset control signal.

[0070] As Figure 3 And Figure 4 shown, each transistor can specifically be an NMOS transistor. The first terminal of the transistor is the gate of the NMOS transistor, the second terminal of the transistor is the source of the NMOS transistor, and the third terminal of the transistor is the drain of the NMOS transistor.

[0071] Combined with Figure 5 the timing diagram shown, the working principle of the global exposure pixel structure shown below is described. Figure 3 The working principle of the global exposure pixel structure shown:

[0072] Figure 5 In the figure, RST represents the reset control signal, TX represents the transmission control signal, PC represents the pre-charge control signal, S1 represents the first control signal, S2 represents the second control signal, S3 represents the third control signal, FOT_CTR represents the signal for controlling the switch in the readout circuit outside the global exposure pixel, one end of the switch is connected to the output terminal of the global exposure pixel, and the other end of the switch is grounded.

[0073] The period from time t0 to time t1 is the exposure stage T_exp, the period from time t1 to time t7 is the FOT stage, and the period from t7 to t10 is the readout stage T_rd. Before time t0, both the transfer control signal TX and the reset control signal RST are at high level, and the global exposure pixel is in the reset state. At time t0, the transfer control signal TX changes to low level, and the global exposure pixel starts to expose. At time t1, the precharge control signal PC, the first control signal S1, and the second control signal S2 change from low level to high level, and the signal FOT_CTR changes from low level to high level, and the FOT stage begins. At time t2, the reset control signal RST changes from high level to low level. At time t3, the second control signal S2 changes from high level to low level, and the reset voltage Vrst output from the source of the amplification unit 40 of the global exposure pixel is sampled onto the second capacitor C2. At time t4, the transfer control signal TX changes from low level to high level, and the charge accumulated in the photosensitive diode PD starts to be transferred to the floating diffusion node FD. At time t5, the transfer control signal TX changes from high level to low level, and the charge transfer time ends. At time t6, the first control signal S1 changes from high level to low level, and the exposure voltage Vsig output from the source of the amplification unit 40 of the global exposure pixel is sampled onto the first capacitor C1.

[0074] The function of the signal FOT_CTR is to ground the source of the precharge unit 50 in the global exposure pixel during the FOT stage to implement the function of the precharge tube and precharge the amplification unit 40. The reset control signal RST and the transfer control signal TX remain at low level at time t7 when the FOT stage ends. The third control signal S3 remains at low level during both the exposure stage and the FOT stage.

[0075] Starting from time t7, the readout stage T_rd of the global exposure pixel begins. At this time, the precharge control signal PC and the signal FOT_CTR change from high level to low level, and the precharge control signal PC is used as a selection signal during the readout stage T_rd. At time t8, the precharge control signal PC and the third control signal S3 change from low level to high level, the third transistor M3 conducts, and the first end of the second capacitor C2 is connected to the floating diffusion node FD. At this time, the voltage of the floating diffusion node FD becomes the reset voltage Vrst stored on the second capacitor C2. The subsequent circuit of the global exposure pixel samples the reset voltage VOUT1 = Vrst - V gs,M6 -V ds,M7 output from the output terminal of the global exposure pixel from time t8 to time t9. Among them, V gs,M6 is the voltage difference between the gate and the source of the amplification unit 40, and V ds,M7is the voltage difference between the drain and source of the pre-charge unit 50. At time t9, the second control signal S2 changes from low level to high level, the second transistor M2 conducts, the first end of the first capacitor C1 is connected to the first end of the second capacitor C2 and the floating diffusion node FD, and the voltage of the floating diffusion node FD becomes (Vrst*C2 + Vsig*C1) / (C1 + C2). At this time, the global exposure pixel post-stage circuit samples the voltage VOUT2 = (Vrst*C2 + Vsig*C1) / (C1 + C2) - V output from the output terminal of the global exposure pixel. gs,M6 -V ds,M7 . Then at time t10, the read phase T_rd ends, the second control signal S2, the third control signal S3, and the pre-charge control signal PC change from high level to low level, and the reset control signal RST and the transfer control signal TX change from low level to high level.

[0076] Finally, the effective voltage output by the global exposure pixel is:

[0077] Veff = VOUT1 - VOUT2 = (Vrst - Vsig)*C1 / (C1 + C2).

[0078] When C1 = C2, Veff = (Vrst - Vsig) / 2, which is the same as the effective voltage output by the traditional 8T global exposure pixel structure.

[0079] Combined with Figure 5 the timing diagram shown below, the working principle of the global exposure pixel structure shown Figure 4 is described as follows:

[0080] Before time t0, both the transfer control signal TX and the reset control signal RST are at high level, and the global exposure pixel is in the reset state. At time t0, the transfer control signal TX changes to low level, and the global exposure pixel starts to expose. At time t1, the pre-charge control signal PC, the first control signal S1, and the second control signal S2 change from low level to high level, and the signal FOT_CTR changes from low level to high level, and starts to enter the FOT stage. At time t2, the reset control signal RST changes from high level to low level. At time t3, the second control signal S2 changes from high level to low level, and samples the reset voltage Vrst output from the source of the amplification unit 40 of the global exposure pixel onto the second capacitor C2. At time t4, the transfer control signal TX changes from low level to high level, and starts to transfer the charge accumulated by the photosensitive diode PD to the floating diffusion node FD. At time t5, the transfer control signal TX changes from high level to low level, and the charge transfer time ends. At time t6, the first control signal S1 changes from high level to low level, and samples the exposure voltage Vsig output from the source of the amplification unit 40 of the global exposure pixel onto the first capacitor C1.

[0081] The function of the signal FOT_CTR is to ground the source of the pre-charge unit 50 in the global exposure pixel during the FOT phase, so as to realize the function of the pre-charge tube and pre-charge the amplification unit 40. The reset control signal RST and the transmission control signal TX remain low at the moment t7 when the FOT phase ends. The third control signal S3 remains low during both the exposure phase and the FOT phase.

[0082] Starting from the moment t7, the global exposure pixel enters the readout phase T_rd. At this time, the pre-charge control signal PC and the signal FOT_CTR change from high level to low level, and the pre-charge control signal is used as a selection signal during the readout phase T_rd. At the moment t8, the pre-charge control signal PC and the third control signal S3 change from low level to high level, the third transistor M3 conducts, and the first end of the first capacitor C1 is connected to the floating diffusion node FD. At this time, the voltage of the floating diffusion node FD becomes the exposure voltage Vsig stored on the first capacitor C1. The subsequent circuit of the global exposure pixel samples the exposure voltage VOUT1 = Vsig - V output from the output terminal of the global exposure pixel during the time from t8 to t9. gs,M6 -V ds,M7 At the moment t9, the second control signal S2 changes from low level to high level, the second transistor M2 conducts, the first end of the first capacitor C1 is connected to the first end of the second capacitor C2 and the floating diffusion node FD, and the voltage of the floating diffusion node FD becomes (Vrst * C2 + Vsig * C1) / (C1 + C2). At this time, the subsequent circuit of the global exposure pixel samples the voltage VOUT2 = (Vrst * C2 + Vsig * C1) / (C1 + C2) - V output from the output terminal of the global exposure pixel. gs,M6 -V ds,M7 Then at the moment t10, the read phase T_rd ends, the second control signal S2, the third control signal S3, and the pre-charge control signal PC change from high level to low level, and the reset control signal RST and the transmission control signal TX change from low level to high level.

[0083] Finally, the effective voltage output by the global exposure pixel is:

[0084] Veff = VOUT2 - VOUT1 = (Vrst - Vsig) * C1 / (C1 + C2).

[0085] When C1 = C2, Veff = (Vrst - Vsig) / 2, which is the same as the effective voltage output by the traditional 8T global exposure pixel structure.

[0086] Figure 3 And Figure 4The global exposure pixel structure shown can also be used as a pixel in the rolling shutter mode. The pre-charge unit 50 serves as a selection transistor, the pre-charge control signal serves as a selection signal, the first control signal S1, the second control signal S2, the third control signal S3, and the signal FOT_CTR are kept at a constant low level, that is, the first transistor M1, the second transistor M2, the third transistor M3, and the switch controlled by the signal FOT_CTR in the readout circuit outside the global exposure pixel are kept off, which is equivalent to a 4T global exposure pixel structure for the rolling shutter mode.

[0087] Assume that the parasitic capacitance of the floating diffusion node FD is Cfd. At this time, the conversion gain of the global exposure pixel is determined by Cfd. On this basis, if the third control signal S3 is kept at a constant high level, that is, the third transistor M3 is always on, the total capacitance of the equivalent floating diffusion node FD is Cfd + C2. At this time, the conversion gain of the global exposure pixel is determined by Cfd + C2. If the third control signal S3 and the second control signal S2 are kept at a constant high level, that is, the second transistor M2 and the third transistor M3 are always on, the total capacitance of the equivalent floating diffusion node FD is Cfd + C2 + C1. At this time, the conversion gain of the global exposure pixel is determined by Cfd + C2 + C1. In this way, the global exposure pixel structure can easily configure three different conversion gains in the rolling shutter mode, thus supporting more flexible applications.

[0088] In summary, compared with the traditional 8T pixel structure, the global exposure pixel provided in this application removes the second-stage amplification transistor and the selection transistor in the 8T pixel structure, and only sets one amplification unit and one pre-charge unit. The multiplexed amplification unit can realize the functions of the first-stage amplification transistor and the second-stage amplification transistor in the 8T pixel structure, and the multiplexed pre-charge unit can realize the functions of the pre-charge transistor and the selection transistor in the 8T pixel structure, which can reduce the number of devices in the global exposure pixel.

[0089] This application also provides an image sensor, which includes the global exposure pixel described in the above embodiments. For the image sensor provided in this application, reference can be made to the introduction of the global exposure pixel in the above embodiments, which will not be elaborated here.

[0090] Because the situation is complex and cannot be listed one by one for elaboration, those skilled in the art should be able to realize that there can be multiple examples under the basic principle of the embodiments provided in this application in combination with the actual situation. Without sufficient creative labor, they should all be within the scope of this application.

[0091] The embodiments in the specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0092] The above has introduced in detail the global exposure pixel and the image sensor provided by the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

[0093] It should also be noted that in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the element.

Claims

1. A global exposure pixel, characterized in that, Comprising: A photosensitive unit, a transfer unit, a reset unit, an amplification unit, a pre-charge unit, a storage unit, and a switch unit; The input end of the storage unit is connected to the amplification unit, the output end of the storage unit is connected to one end of the switch unit, the other end of the switch unit is connected to a floating diffusion node, and the amplification unit is also connected to the floating diffusion node and the pre-charge unit; The photosensitive unit is used for photosensing to generate charges; The transfer unit is used for transferring charges to the floating diffusion node; The reset unit is used for resetting a global exposure pixel; The storage unit is used for storing a reset voltage and an exposure voltage; The amplification unit is used for amplifying and outputting the voltage of the floating diffusion node; The pre-charge unit is used for pre-charging the amplification unit at the frame head time; The switch unit is used for connecting the output end of the storage unit to the floating diffusion node when the switch unit is turned on.

2. The global exposure pixel according to claim 1, wherein, The storage unit includes: A first transistor, a second transistor, a first capacitor, and a second capacitor; the third end of the first transistor serves as the input end of the storage unit, the second end of the first transistor is connected to the first end of the first capacitor and the third end of the second transistor, the first end of the first transistor inputs a first control signal, the second end of the first capacitor is grounded, the second end of the second transistor is connected to the first end of the second capacitor, the first end of the second transistor inputs a second control signal, and the second end of the second capacitor is grounded.

3. The global exposure pixel according to claim 2, wherein, The first end of the second capacitor serves as the output end of the storage unit and is connected to one end of the switch unit, and the other end of the switch unit is connected to the floating diffusion node.

4. The global exposure pixel according to claim 2, wherein, The first end of the first capacitor serves as the output end of the storage unit and is connected to one end of the switch unit, and the other end of the switch unit is connected to the floating diffusion node.

5. The global exposure pixel according to claim 1, wherein The switch unit includes: A third transistor; the third end of the third transistor is connected to the floating diffusion node, the second end of the third transistor is connected to the output end of the storage unit, and the first end of the third transistor inputs a third control signal.

6. The global exposure pixel according to claim 1, wherein The photosensitive unit includes: A photodiode; the anode of the photodiode is grounded, and the cathode of the photodiode is connected to the transfer unit.

7. The global exposure pixel according to claim 1, wherein The transfer unit includes: A fourth transistor; the third end of the fourth transistor is connected to the floating diffusion node, the second end of the fourth transistor is connected to the photosensitive unit, and the first end of the fourth transistor inputs a transfer control signal.

8. The global exposure pixel according to claim 1, wherein The reset unit includes: A fifth transistor; the third end of the fifth transistor is connected to a preset potential, the second end of the fifth transistor is connected to the floating diffusion node, and the first end of the fifth transistor inputs a reset control signal.

9. The global exposure pixel according to claim 1, wherein The amplifying unit includes a sixth transistor; the pre-charging unit includes a seventh transistor; a first end of the sixth transistor is connected to the floating diffusion node, a second end of the sixth transistor is connected to an input end of the storage unit and a third end of the seventh transistor, a third end of the sixth transistor is connected to a preset potential, a second end of the seventh transistor serves as an output end of the global exposure pixel, and a first end of the seventh transistor inputs a pre-charging control signal.

10. An image sensor, characterized in that, It includes the global exposure pixel according to any one of claims 1 to 9.

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