Pixel circuit, control method thereof and image sensor

Abstract

The invention provides a pixel circuit, a control method thereof and an image sensor. The pixel circuit comprises an exposure module, a control module and an output module, a floating node is formed at the joint of the output end of the control module and the input end of the output module; the control module comprises a first reset tube and a capacitor; a source electrode of the first reset tube is connected with the floating node, and a grid electrode accesses a first reset signal; the first end of the capacitor is connected with the floating node, and the second end accesses a transmission control signal. The photosensitive signal is stored by the capacitor, so that the photosensitive signal can be amplified and the sensitivity of the pixel circuit can be improved by utilizing the energy storage characteristic of the capacitor, and the photosensitive signal can be subjected to noise suppression and the quality of the photosensitive signal can be improved, and therefore, the pixel circuit can be used for improving the sensitivity of the pixel circuit under the condition that the pixel circuit has fewer transistors and control signals. The pixel circuit can still realize more functions, has higher imaging quality, and solves the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuit design, and in particular to a pixel circuit and a control method thereof, and an image sensor. Background Art

[0002] CMOS (complementary metal oxide semiconductor) image sensor is a photoelectric conversion device that is widely used in security monitoring, intelligent driving, aerospace, industrial production and consumer electronics. There are two main exposure methods for commonly used image sensors: rolling shutter and global shutter. The rolling shutter method exposes and reads the pixel array of the image sensor row by row, while the global shutter method exposes the entire pixel array of the image sensor first and then reads it row by row.

[0003] At present, the pixel circuit structure of image sensors using rolling exposure generally contains 4 transistors, which is called 4T structure. For image sensors using global exposure, in order to ensure the performance of the image sensor and realize functions such as correlated double sampling (CDS), antiblooming and parasitic light suppression, the pixel circuit structure used generally contains 8 to 9 transistors, that is, 8T or 9T structure.

[0004] Although the global exposure method allows the images captured by the image sensor to maintain a high degree of consistency in time and space, and is very suitable for capturing dynamic scenes and high-speed moving objects, and has imaging advantages that rolling exposure does not have, in the global exposure image sensor, the number of transistors in the pixel circuit is large, which makes the working timing and manufacturing process of the image sensor more complicated, which not only leads to increased costs, but also causes poor performance of the image sensor due to factors such as timing control delays and process limitations. Summary of the invention

[0005] The object of the present invention is to provide a pixel circuit and a control method thereof, and an image sensor, so as to at least solve the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0006] In order to solve the above technical problems, the present invention provides a pixel circuit, comprising an exposure module, a control module and an output module; the exposure module is used for exposure to generate a photosensitive signal; the control module is used for transmitting the photosensitive signal under the control of a control signal; the output module is used for outputting the photosensitive signal under the control of a selection signal; the output end of the control module is connected to the input end of the output module to form a floating node at the connection point; Among them, the control module includes a first reset tube and a capacitor; the source of the first reset tube is connected to the floating node, the drain is connected to the power supply, and the gate is connected to the first reset signal; the first end of the capacitor is connected to the floating node, and the second end is connected to the transmission control signal; the control signal includes the first reset signal and the transmission control signal.

[0007] Optionally, in the pixel circuit, the exposure module includes a photosensitive diode and a first transmission tube; the anode of the photosensitive diode is grounded, and the cathode is connected to the source of the first transmission tube; the gate of the first transmission tube is connected to the first transmission signal, and the drain is connected to the floating node.

[0008] Optionally, in the pixel circuit, the control module also includes a second reset tube; the drain of the second reset tube is connected to the power supply, the gate is connected to the second reset signal, and the source is connected to the second end of the capacitor to input the transmission control signal to the capacitor; the control signal also includes the second reset signal.

[0009] Optionally, in the pixel circuit, the control module further includes a second transmission tube; a source of the second transmission tube is connected to the first end of the capacitor, and a drain is connected to the input end of the output module.

[0010] Optionally, in the pixel circuit, the control module further includes a second transmission tube; a source electrode of the second transmission tube is connected to a source electrode of the first reset tube, and a drain electrode is connected to a first end of the capacitor.

[0011] Optionally, in the pixel circuit, the output module includes a source follower tube and a gate tube; the drain of the source follower tube is connected to a power supply, the gate serves as the input end of the output module, and the source is connected to the drain of the gate tube; the source of the gate tube serves as the output end of the output module to output a photosensitive signal, and the gate is connected to a selection signal.

[0012] In order to solve the above technical problems, the present invention further provides a control method of a pixel circuit, which is applied to the pixel circuit as described in any one of the above items, and the control method comprises: In the first time period, the pixel circuit is in a reset state; In the second time period, the exposure module performs continuous exposure to generate a light-sensitive signal; In the third time period, the exposure is finished, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the floating node is in a reset state; In the fifth time period, the pixel circuit outputs light-sensing signals in sequence.

[0013] Optionally, in the control method of the pixel circuit, the exposure module receives a first transmission signal; when the control module further includes a second reset tube and the control signal further includes a second reset signal, the control method includes: In the first time period, the first reset signal, the second reset signal and the first transmission signal are valid, the selection signal is invalid, and the pixel circuit is in a reset state; In the second time period, when the first transmission signal is invalid, the exposure module starts to continuously expose to generate a light-sensitive signal until the first transmission signal becomes valid, and the exposure module stops exposing; In a third time period, the first reset signal is invalid, the first transmission signal and the second reset signal are valid, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the second reset signal is invalid, then the first reset signal and the first transmission signal are valid, and the floating node is in a reset state; In the fifth time period, the first reset signal and the first transmission signal are invalid, and when the selection signal is valid, the pixel circuit outputs the light-sensing signal in sequence.

[0014] Optionally, in the control method of the pixel circuit, the exposure module receives a first transmission signal; when the control module further includes a second transmission tube, and the source of the second transmission tube is connected to the first end of the capacitor, and the drain is connected to the input end of the output module, and the control signal further includes a second transmission signal, the control method includes: In the first time period, the first reset signal, the transmission control signal, the first transmission signal and the second transmission signal are valid, the selection signal is invalid, and the pixel circuit is in a reset state; In the second time period, when the first transmission signal is invalid, the photosensitive diode starts to continuously expose to generate a light-sensitive signal, until the first transmission signal becomes valid and the photosensitive diode stops exposing; In the third time period, the first reset signal and the second transmission signal are invalid, the first transmission signal and the transmission control signal are valid, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the transmission control signal and the second transmission signal are invalid, then the first reset signal and the first transmission signal are valid, and the floating node is in a reset state; In the fifth time period, the first reset signal and the first transmission signal are invalid, the second transmission signal is valid, and when the selection signal is valid, the pixel circuit outputs the light-sensing signal in sequence.

[0015] Optionally, in the control method of the pixel circuit, the exposure module receives a first transmission signal; when the control module further includes a second transmission tube, and the source of the second transmission tube is connected to the source of the first reset tube, and the drain is connected to the first end of the capacitor, and the control signal further includes a second transmission signal, the control method includes: In the first time period, the first reset signal, the transmission control signal, the first transmission signal and the second transmission signal are valid, the selection signal is invalid, and the pixel circuit is in a reset state; In the second time period, when the first transmission signal is invalid, the exposure module starts to continuously expose to generate a light-sensitive signal until the first transmission signal becomes valid, and the exposure module stops exposing; In a third time period, the first reset signal is invalid, the first transmission signal, the second transmission signal and the transmission control signal are valid, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the transmission control signal is invalid, then the first reset signal and the first transmission signal are valid, and the floating node is in a reset state; In the fifth time period, the first reset signal and the first transmission signal are invalid, the second transmission signal remains valid, and when the selection signal is valid, the pixel circuit outputs the light-sensing signal in sequence.

[0016] In order to solve the above technical problem, the present invention further provides an image sensor, comprising a pixel circuit as described in any one of the above items.

[0017] The pixel circuit and its control method, and image sensor provided by the present invention include an exposure module, a control module and an output module; the exposure module is used for exposure to generate a photosensitive signal; the control module is used for transmitting the photosensitive signal under the control of a control signal; the output module is used for outputting the photosensitive signal under the control of a selection signal; the output end of the control module is connected to the input end of the output module to form a floating node at the connection point; wherein the control module includes a first reset tube and a capacitor; the source of the first reset tube is connected to the floating node, the drain is connected to a power supply, and the gate is connected to a first reset signal; the first end of the capacitor is connected to the floating node, and the second end is connected to a transmission control signal; the control signal includes the first reset signal and the transmission control signal. By storing the photosensitive signal at the floating node through the capacitor, not only can the energy storage characteristics of the capacitor be used to amplify the photosensitive signal and improve the sensitivity of the pixel circuit and the signal transmission accuracy, but the noise of the photosensitive signal can also be suppressed to improve the quality of the photosensitive signal, thereby simplifying the circuit structure and signal control of the control module, so that the pixel circuit can still achieve more functions with fewer transistors and control signals, and thus have higher imaging quality, solving the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A structural block diagram of a pixel circuit provided in this embodiment; Figure 2 A flowchart of a method for controlling a pixel circuit provided in this embodiment; Figure 3 A circuit structure schematic diagram of a first pixel circuit provided in this embodiment; Figure 4 A timing diagram of a first pixel circuit provided in this embodiment; Figure 5 A circuit structure schematic diagram of a second pixel circuit provided in this embodiment; Figure 6 A timing diagram of a second pixel circuit provided in this embodiment; Figure 7 A circuit structure schematic diagram of a third pixel circuit provided in this embodiment; Figure 8 A circuit structure schematic diagram of a fourth pixel circuit provided in this embodiment; Fig. 9 A timing diagram of a fourth pixel circuit provided in this embodiment; Fig.10 A circuit structure schematic diagram of a fifth pixel circuit provided in this embodiment; Fig.11 A circuit structure schematic diagram of a sixth pixel circuit provided in this embodiment; Fig.12 This is a timing diagram of the sixth pixel circuit provided in this embodiment. DETAILED DESCRIPTION

[0019] The pixel circuit and its control method, and the image sensor proposed in the present invention are further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the accompanying drawings is often part of the actual structure. In particular, the emphasis that each drawing needs to show is different, and sometimes different proportions are used.

[0020] It should be noted that the terms "first", "second", etc. in the specification, claims and drawings of the present invention are used to distinguish similar objects in order to describe the embodiments of the present invention, rather than to describe a specific order or sequence. It should be understood that the structures used in this way can be interchanged under appropriate circumstances. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0021] This embodiment provides a pixel circuit such as Figure 1 As shown, it includes an exposure module, a control module and an output module; the exposure module is used for exposure to generate a photosensitive signal; the control module is used for transmitting the photosensitive signal under the control of the control signal; the output module is used for outputting the photosensitive signal in sequence under the control of the selection signal; the output end of the control module is connected to the input end of the output module to form a floating node FD at the connection point.

[0022] Among them, the control module includes a first reset tube Mrst1 and a capacitor C; the source of the first reset tube Mrst1 is connected to the floating node FD, the drain is connected to the power supply VDD, and the gate is connected to the first reset signal RX1; the first end of the capacitor C is connected to the floating node FD, and the second end is connected to the transmission control signal CL; the control signal includes the first reset signal RX1 and the transmission control signal CL.

[0023] The pixel circuit provided in this embodiment stores the photosensitive signal at the floating node through a capacitor, which can not only utilize the energy storage characteristics of the capacitor to amplify the photosensitive signal and improve the sensitivity and signal transmission accuracy of the pixel circuit, but also suppress the noise of the photosensitive signal and improve the quality of the photosensitive signal, thereby simplifying the circuit structure and signal control of the control module, so that the control module contains at least one transistor and one capacitor, and at least two control signals are used to achieve output control of the photosensitive signal, thereby enabling the pixel circuit to achieve more functions and higher imaging quality with fewer transistors and control signals, thereby solving the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0024] Correspondingly, this embodiment further provides a method for controlling a pixel circuit, which is applied to the pixel circuit provided by this embodiment, such as Figure 2 As shown, the control method includes: In the first time period t1, the pixel circuit is in a reset state; In the second time period t2, the exposure module performs continuous exposure to generate a light-sensitive signal; In the third time period t3, the exposure ends, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period t4, the floating node is in a reset state; In the fifth time period t5, the pixel circuits output light sensing signals in sequence.

[0025] The state changes of the pixel circuits in each time period are all controlled by various control signals.

[0026] Specifically, in this embodiment, if Figure 3 As shown, the exposure module includes a photosensitive diode PD and a first transmission tube Mtg1; the anode of the photosensitive diode PD is grounded, and the cathode is connected to the source of the first transmission tube Mtg1; the gate of the first transmission tube Mtg1 is connected to the first transmission signal TX1, and the drain is connected to the floating node FD.

[0027] And, in this embodiment, the output module includes a source follower tube Msf and a gate tube Msel; the drain of the source follower tube Msf is connected to the power supply VDD, the gate serves as the input end, and the source is connected to the drain of the gate tube Msel; the source of the gate tube Msel serves as the output end to output the photosensitive signal PIX_OUT, and the gate is connected to the selection signal SEL.

[0028] The pixel circuit provided in this embodiment has the following working principle: the photosensitive diode PD is sensitive to light and generates photoelectrons proportional to the light intensity; the function of the first transmission tube Mtg1 is to transfer the photoelectrons in the photosensitive diode PD. When the first transmission signal TX1 is at a high level (valid), the first transmission tube Mtg1 is turned on, and the photoelectrons in the photosensitive diode PD are transferred to the floating node FD, and there is a floating voltage Vfd at the floating node FD; the function of the first reset tube Mrst1 is to reset the floating node FD when the reset signal RX1 is at a high potential; Msf is a source follower tube. When the selection signal SEL is at a high potential and the gate tube Msel is turned on, the source follower tube Msf, the gate tube Msel and the current source to the ground form a path. At this time, the source follower tube Msf follows the change of the potential of the floating node FD and finally outputs the light-sensitive signal PIX_OUT.

[0029] Correspondingly, this embodiment provides Figure 3 The control method of the pixel circuit shown in FIG. Figure 4 See Figure 4 ,illustrate Figure 3 The control method of the pixel circuit shown includes: In the first time period t1, the first reset signal RX1, the transmission control signal CL and the first transmission signal TX1 are valid (high level), and the selection signal SEL is invalid (low level), so that the first reset tube Mrst1, the second reset tube Mrst2, and the first transmission tube Mtg1 are changed from the off state to the on state, the gate tube Msel is in the off state, and the pixel circuit is in the reset state; In the second time period t2, when the first transmission signal TX1 changes from a high level to a low level (invalid), the first transmission tube Mtg1 is turned off, and the photosensitive diode PD starts to expose until the first transmission signal TX1 becomes valid (high level), and the photosensitive diode PD stops exposing; wherein, when the first transmission signal TX1 changes to a low level, after a certain amount of photoelectrons are accumulated, the first reset signal RX1 also changes to a low level (invalid), so that the first reset tube Mrst1 is turned off later than the first transmission tube Mtg1, ensuring that the voltage at the floating node FD is the reset voltage; thereafter, the first reset signal RX1 maintains a low level state, and the transmission control signal CL maintains a high level (valid) state; In the third time period t3, the first reset signal RX1 remains invalid, the transmission control signal CL remains valid, the first transmission signal TX1 changes from a low level (invalid) to a high level (valid), the first transmission tube Mtg1 is turned on, and the photogenerated electrons (photosensitive signals) accumulated by the photodiode PD are transmitted to the floating node FD and stored on the capacitor C; when the electron transmission is completed, the first transmission signal TX1 changes from a high level to a low level (invalid) again; In the fourth time period t4, the transmission control signal CL is invalid, and then the first reset signal RX1 and the first transmission signal TX1 change from a low level (invalid) to a high level (valid), so that the second reset tube Mrst2 is turned off first. At this time, the charge stored on the capacitor C remains unchanged because the second end of the capacitor C is floating. After that, the first reset tube Mrst1 and the first transmission tube Mtg1 are turned on at the same time, so that the photosensitive diode PD and the floating node FD are always in a reset state, thereby effectively preventing the photosensitive diode PD from overflowing charge (Blooming), that is, having an anti-charge overflow (Antiblooming) function, and effectively suppressing the parasitic light effect at the floating node FD; From the first time period t1 to the fourth time period t4 , the selection signal SEL always maintains a disabled (low level) state, and this stage belongs to the global exposure stage.

[0030] In the fifth time period t5, the first transmission signal TX1 first becomes invalid (low level), so that the first transmission tube Mtg1 is turned off, and then the first reset signal RX1 becomes invalid (low level), so that the first reset tube Mrst1 is turned off. Similar to the t2 stage, the voltage at the floating node FD is guaranteed to be the reset voltage. At this time, the floating node FD reset is completed; then, the transmission control signal CL is maintained invalid, and when the selection signal SEL is valid, the gate tube Msel is turned on, and the photosensitive signal (reset signal) is read out. The photosensitive signal read out at this time can be recorded as V1; then, in the sixth time period t6, the transmission control signal CL is changed from invalid (low level) to valid (high level), the first transmission signal TX1 and the first reset signal RX1 are maintained in an invalid state, and when the selection signal SEL is valid, the gate tube Msel is turned on, and the photosensitive signal is read out. The photosensitive signal read out at this time can be recorded as V2. In this way, in the fifth time period t5 and the sixth time period t6, the reading of a row of photosensitive signals is completed.

[0031] The pixel circuit provided in this embodiment includes a photosensitive diode PD, four transistors (a first transmission tube Mtg1, a first reset tube Mrst1, a source follower tube Msf and a selection tube Msel) and a capacitor C, including four control signals (a first transmission signal TX1, a first reset signal RX1, a transmission control signal CL and a selection signal SEL). In this way, the photosensitive signal at the floating node is stored by the capacitor C, which can not only utilize the energy storage characteristics of the capacitor to amplify the photosensitive signal and improve the sensitivity and signal transmission accuracy of the pixel circuit, but also suppress the noise of the photosensitive signal and improve the quality of the photosensitive signal, so that the circuit structure and signal control of the control module can be simplified, so that while minimizing the number of transistors and control signals in the circuit, not only can the output of the photosensitive signal be realized, but also more functions can be realized, with higher imaging quality, and the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor is solved.

[0032] based on Figure 3 The pixel circuit shown in the figure, this embodiment also provides a pixel circuit, such as Figure 5 As shown, the control module further includes a second reset tube Mrst2; the drain of the second reset tube Mrst2 is connected to the power supply VDD, the gate is connected to the second reset signal RX2, and the source is connected to the second end of the capacitor C to input the transmission control signal to the capacitor; the control signal also includes the second reset signal RX2. That is, the second reset tube Mrst2 provides the transmission control signal CL to the capacitor C.

[0033] In this way, only one transistor (the second reset transistor Mrst2) is added, and the transmission control signal CL is changed to the second reset signal RX2. Compared with the prior art, Figure 5 The pixel circuit shown has only 5 transistors, but it can output photosensitivity signals, realize more functions, and have higher imaging quality. It solves the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0034] Correspondingly, this embodiment provides Figure 5 The control method of the pixel circuit shown in FIG. Figure 6 See Figure 6 ,illustrate Figure 5 The control method of the pixel circuit shown includes: In the first time period t1, the first reset signal RX1, the second reset signal RX2 and the first transmission signal TX1 are valid (high level), and the selection signal SEL is invalid (low level), so that the first reset tube Mrst1, the second reset tube Mrst2 and the first transmission tube Mtg1 are changed from the off state to the on state, the gate tube Msel is in the off state, and the pixel circuit is in the reset state; In the second time period t2, when the first transmission signal TX1 changes from a high level to a low level (invalid), the first transmission tube Mtg1 is turned off, and the photosensitive diode PD starts to expose until the first transmission signal TX1 becomes valid (high level), and the photosensitive diode PD stops exposing; wherein, after the first transmission signal TX1 changes to a low level, the first reset signal RX1 changes to a low level (invalid) again, so that the first reset tube Mrst1 is turned off later than the first transmission tube Mtg1, ensuring that the voltage at the floating node FD is the reset voltage; thereafter, the first reset signal RX1 maintains a low level state; and the second reset signal RX2 maintains a high level (valid) state; In the third time period t3, the first reset signal RX1 remains invalid, the second reset signal RX2 remains valid, the first transmission signal TX1 changes from a low level (invalid) to a high level (valid), the first transmission tube Mtg1 is turned on, and the photogenerated electrons (photosensitive signals) accumulated by the photodiode PD are transmitted to the floating node FD and stored on the capacitor C; when the electron transmission is completed, the first transmission signal TX1 changes from a high level to a low level (invalid) again; In the fourth time period t4, the second reset signal RX2 is invalid, and then the first reset signal RX1 and the first transmission signal TX1 change from low level (invalid) to high level (valid), so that the second reset tube Mrst2 is turned off first. At this time, the charge stored on the capacitor C remains unchanged because the second end of the capacitor C is floating. After that, the first reset tube Mrst1 and the first transmission tube Mtg1 are turned on at the same time, so that the photosensitive diode PD and the floating node FD are always in a reset state, thereby effectively preventing the photosensitive diode PD from charge overflow (Blooming), that is, having an anti-charge overflow (Antiblooming) function, and effectively suppressing the parasitic light effect at the floating node FD; From the first time period t1 to the fourth time period t4 , the selection signal SEL always maintains a disabled (low level) state, and this stage belongs to the global exposure stage.

[0035] In the fifth time period t5, the first transmission signal TX1 first becomes invalid (low level), so that the first transmission tube Mtg1 is turned off, and then the first reset signal RX1 becomes invalid (low level), so that the first reset tube Mrst1 is turned off. Similar to the t2 stage, the voltage at the floating node FD is guaranteed to be the reset voltage. At this time, the floating node FD reset is completed; then, the second reset signal RX2 is maintained invalid, and when the selection signal SEL is valid, the gate tube Msel is turned on, and the photosensitive signal (reset signal) is read out. The photosensitive signal read out at this time can be recorded as V1; then, in the sixth time period t6, the second reset signal RX2 is changed from invalid (low level) to valid (high level), the first transmission signal TX1 and the first reset signal RX1 are maintained in an invalid state, and when the selection signal SEL is valid, the gate tube Msel is turned on, and the photosensitive signal is read out. The photosensitive signal read out at this time can be recorded as V2. In this way, in the fifth time period t5 and the sixth time period t6, the reading of a row of photosensitive signals is completed.

[0036] based on Figure 3 The pixel circuit shown in the figure, this embodiment also provides a pixel circuit, the control module further includes a second transmission tube Mtg2, wherein, Figure 7 As shown, the source of the second transmission tube Mtg2 is connected to the first end of the capacitor C, and the drain is connected to the input end of the output module (the gate of the source follower tube Msf).

[0037] In this way, only one transistor (the second transmission transistor Mtg2) and a control signal (the second transmission signal TX2) need to be added to realize the output of the photosensitive signal, and more functions can be realized with higher imaging quality, thus solving the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0038] Of course, in practical applications, Figure 5 Based on the pixel circuit structure shown in FIG. 1 , a second transmission tube Mtg2 is added, wherein Figure 8 As shown, the source of the second transmission tube Mtg2 is connected to the first end of the capacitor C, and the drain is connected to the input end of the output module (the gate of the source follower tube Msf).

[0039] In this way, the pixel circuit contains only 6 transistors and uses 5 control signals to achieve the output of photosensitive signals. It can also realize more functions and have higher imaging quality, solving the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0040] Correspondingly, this embodiment provides Figure 8 The control method of the pixel circuit shown in FIG. Fig. 9 See Fig. 9 ,illustrate Figure 8 The control method of the pixel circuit shown includes: In the first time period t1, the first reset signal RX1, the second reset signal RX2, the first transmission signal TX1 and the second transmission signal TX2 are valid (high level), and the selection signal SEL is invalid (low level), so that the first reset tube Mrst1, the second reset tube Mrst2, the first transmission tube Mtg1 and the second transmission tube Mtg2 are changed from the off state to the on state, the gate tube Msel is in the off state, and the pixel circuit is in the reset state; In the second time period t2, when the first transmission signal TX1 changes from a high level to a low level (invalid), the first transmission tube Mtg1 is turned off, and the photosensitive diode PD starts to expose, until the first transmission signal TX1 becomes valid (high level), and the photosensitive diode PD stops exposing; wherein, after the first transmission signal TX1 changes to a low level, the first reset signal RX1 and the second transmission signal TX2 also change to a low level (invalid) in sequence, so that the first transmission tube Mtg1, the first reset tube Mrs1, and the second transmission tube Mtg2 are turned off in sequence, ensuring that the voltage at the floating node FD is the reset voltage; thereafter, the first reset signal RX1 and the second transmission signal TX2 maintain a low level state, and the second reset signal RX2 maintains a high level (valid) state; In the third time period t3, the first reset signal RX1 and the second transmission signal TX2 remain invalid, the second reset signal RX2 remains valid, the first transmission signal TX1 changes from a low level (invalid) to a high level (valid), the first transmission tube Mtg1 is turned on, and the photogenerated electrons (photosensitive signals) accumulated by the photodiode PD are transmitted to the floating node FD and stored on the capacitor C; when the electron transmission is completed, the first transmission signal TX1 changes from a high level to a low level (invalid) again, and the first transmission tube Mtg1 is turned off; In the fourth time period t4, the second reset signal RX2 is invalid, and then the first reset signal RX1 and the first transmission signal TX1 change from low level (invalid) to high level (valid), and the second transmission signal TX2 remains invalid, so that the second reset tube Mrst2 is turned off first. At this time, the charge stored on the capacitor C remains unchanged due to the floating of the second end of the capacitor C. After that, the first reset tube Mrst1 and the first transmission tube Mtg1 are turned on at the same time, so that the photosensitive diode PD and the floating node FD are always in a reset state, thereby effectively preventing the photosensitive diode PD from overflowing charge (Blooming), that is, having an anti-charge overflow (Antiblooming) function, and effectively suppressing the parasitic light effect at the floating node FD; From the first time period t1 to the fourth time period t4 , the selection signal SEL always maintains a disabled (low level) state, and this stage belongs to the global exposure stage.

[0041] In the fifth time period t5, the first transmission signal TX1 first becomes invalid (low level), and the second transmission signal TX2 becomes valid (high level) at the same time, so that the first transmission tube Mtg1 is turned off and the second transmission tube Mtg2 is turned on. Then, the first reset signal RX1 becomes invalid (low level), so that the first reset tube Mrs1 is turned off, ensuring that the voltage at the floating node FD is the reset voltage. At this time, the resetting of the floating node FD is completed; then, the second reset signal RX2 is maintained invalid, and when the selection signal SEL is valid, the selection tube Msel is turned on, and the photosensitive signal (reset signal) is read out. The photosensitive signal read out at this time can be recorded as V1; then, in the sixth time period t6, the second reset signal RX2 is changed from invalid (low level) to valid (high level), the first transmission signal TX1, the second transmission signal TX2 and the first reset signal RX1 maintain the previous state, and when the selection signal SEL is valid, the selection tube Msel is turned on, and the photosensitive signal is read out. The photosensitive signal read out at this time can be recorded as V2. In this way, in the fifth time period t5 and the sixth time period t6, the reading of one line of light-sensing signals is completed.

[0042] Figure 7 The pixel circuit shown in the figure has a timing control Figure 8 The timing control of the pixel circuit shown is similar, and only the second reset signal RX2 needs to be adjusted to the transmission control signal CL. The method of adjusting the signal is well known to those skilled in the art, and will not be described in detail in this application.

[0043] exist Figure 7 The pixel circuit structure shown in FIG. 1 is modified by adjusting the position and connection relationship of the second transmission tube Mtg2 to obtain the following Fig.10 The pixel circuit shown. Fig.10 The second transmission signal corresponding to the second transmission tube Mtg2 is recorded as TX2. Fig.10 As shown, the source of the second transmission tube Mtg2 is connected to the source of the first reset tube Mrst1, and the drain is connected to the first end of the capacitor C.

[0044] Of course, in practical applications, Figure 8 The pixel circuit structure shown in FIG. 1 is modified by adjusting the position and connection relationship of the second transmission tube Mtg2 to obtain the following Fig.11 The pixel circuit shown. Fig.11 The second transmission signal corresponding to the second transmission tube Mtg2 is recorded as TX2. Fig.11 As shown, the source of the second transmission tube Mtg2 is connected to the source of the first reset tube Mrst1, and the drain is connected to the first end of the capacitor C.

[0045] In this way, the pixel circuit also contains only 6 transistors and uses 5 control signals to achieve the output of photosensitive signals. It can also realize more functions and have higher imaging quality, solving the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0046] Correspondingly, this embodiment provides Fig.11 The control method of the pixel circuit shown in FIG. Fig.12 See Fig.12 ,illustrate Fig.11 The control method of the pixel circuit shown includes: In the first time period t1, the first reset signal RX1, the second reset signal RX3, the first transmission signal TX1 and the second transmission signal TX2 are valid (high level), and the selection signal SEL is invalid (low level), so that the first reset tube Mrst1, the second reset tube Mrst2, the first transmission tube Mtg1 and the second transmission tube Mtg2 are changed from the off state to the on state, the gate tube Msel is in the off state, and the pixel circuit is in the reset state; In the second time period t2, when the first transmission signal TX1 changes from a high level to a low level (invalid), the first transmission tube Mtg1 is turned off, and the photosensitive diode PD starts to expose, until the first transmission signal TX1 becomes valid (high level), and the photosensitive diode PD stops exposing; wherein, after the first transmission signal TX1 changes to a low level, the first reset signal RX1 and the second transmission signal TX2 also change to a low level (invalid) in sequence, so that the first transmission tube Mtg1, the first reset tube Mrs1, and the second transmission tube Mtg2 are turned off in sequence, ensuring that the voltage at the floating node FD is the reset voltage; thereafter, the first reset signal RX1 and the second transmission signal TX2 maintain a low level state, and the second reset signal RX2 maintains a high level (valid) state; In the third time period t3, the first reset signal RX1 remains invalid, the second reset signal RX2 remains valid, the first transmission signal TX1 and the second transmission signal TX2 change from low level (invalid) to high level (valid), the first transmission tube Mtg1 and the second transmission tube Mtg2 are turned on, and the photogenerated electrons (photosensitive signals) accumulated by the photodiode PD are transmitted to the floating node FD and stored on the capacitor C; when the electron transmission is completed, the first transmission signal TX1 changes from high level to low level (invalid) again, the first transmission tube Mtg1 is turned off, and the second transmission signal TX2 maintains a high level (valid); In the fourth time period t4, the second reset signal RX2 is invalid, and then the first reset signal RX1 and the first transmission signal TX1 change from low level (invalid) to high level (valid), and the second transmission signal TX2 remains valid, so that the second reset tube Mrst2 is turned off first. At this time, the charge stored on the capacitor C remains unchanged due to the floating of the second end of the capacitor C. After that, the first reset tube Mrst1 is turned on and the first transmission tube Mtg1 is turned on at the same time, so that the photosensitive diode PD and the floating node FD are always in a reset state, thereby effectively preventing the photosensitive diode PD from overflowing charge (Blooming), that is, having an anti-charge overflow (Antiblooming) function, and effectively suppressing the parasitic light effect at the floating node FD; From the first time period t1 to the fourth time period t4 , the selection signal SEL always maintains a disabled (low level) state, and this stage belongs to the global exposure stage.

[0047] In the fifth time period t5, the second transmission signal TX2 remains valid (high level), and the first transmission signal TX1 becomes invalid (low level) first, so that the first transmission tube Mtg1 is turned off and the second transmission tube Mtg2 is turned on. Then, the first reset signal RX1 becomes invalid (low level), so that the first reset tube Mrs1 is turned off, ensuring that the voltage at the floating node FD is the reset voltage. At this time, the resetting of the floating node FD is completed; then, the second reset signal RX2 is maintained invalid, and when the selection signal SEL is valid, the selection tube Msel is turned on, and the photosensitive signal (reset signal) is read out. The photosensitive signal read out at this time can be recorded as V1; then, in the sixth time period t6, the second reset signal RX2 is changed from invalid (low level) to valid (high level), the first transmission signal TX1, the second transmission signal TX2 and the first reset signal RX1 maintain the previous state, and when the selection signal SEL is valid, the selection tube Msel is turned on, and the photosensitive signal is read out. The photosensitive signal read out at this time can be recorded as V2. In this way, in the fifth time period t5 and the sixth time period t6, the reading of one line of light-sensing signals is completed.

[0048] Fig.10 The pixel circuit shown in the figure has a timing control Fig.11The timing control of the pixel circuit shown is similar, and only the second reset signal RX2 needs to be adjusted to the transmission control signal CL. The method of adjusting the signal is well known to those skilled in the art, and will not be described in detail in this application.

[0049] In practical applications, the voltage of the power source VDD is adjustable. Specifically, it can be externally controlled to provide different voltages for the pixel circuit to adapt to different circuit structures and transistor requirements.

[0050] In addition, this embodiment also provides an image sensor, comprising any of the above described pixel circuits.

[0051] The image sensor provided in this embodiment has a pixel circuit that has an anti-blooming function under the action of fewer transistors and control signals, and can suppress the parasitic light effect at the floating node FD, thereby meeting the imaging requirements of the global exposure method, simplifying the working timing and manufacturing process, while ensuring the performance of the global exposure method of the image sensor and improving the image quality.

[0052] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other. In addition, the different parts between the various embodiments can also be used in combination with each other, and the present invention is not limited to this.

[0053] The pixel circuit and its control method, and image sensor provided in this embodiment include an exposure module, a control module and an output module; the exposure module is used for exposure to generate a photosensitive signal; the control module is used for transmitting the photosensitive signal under the control of a control signal; the output module is used for outputting the photosensitive signal under the control of a selection signal; the output end of the control module is connected to the input end of the output module to form a floating node at the connection point; wherein the control module includes a first reset tube and a capacitor; the source of the first reset tube is connected to the floating node, the drain is connected to the power supply, and the gate is connected to the first reset signal; the first end of the capacitor is connected to the floating node, and the second end is connected to the transmission control signal; the control signal includes the first reset signal and the transmission control signal. By storing the photosensitive signal at the floating node through the capacitor, not only can the energy storage characteristics of the capacitor be used to amplify the photosensitive signal and improve the sensitivity of the pixel circuit and the signal transmission accuracy, but the noise of the photosensitive signal can also be suppressed to improve the quality of the photosensitive signal, thereby simplifying the circuit structure and signal control of the control module, so that the pixel circuit can still achieve more functions with fewer transistors and control signals, and thus have higher imaging quality, solving the problem of how to reduce the number of transistors in the pixel circuit while ensuring the performance of the image sensor.

[0054] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A pixel circuit, characterized in that: The invention comprises an exposure module, a control module and an output module; the exposure module is used for exposure to generate a photosensitive signal; the control module is used for transmitting the photosensitive signal under the control of the control signal; the output module is used for outputting the photosensitive signal under the control of the selection signal; the output end of the control module is connected to the input end of the output module to form a floating node at the connection point; Among them, the control module includes a first reset tube and a capacitor; the source of the first reset tube is connected to the floating node, the drain is connected to the power supply, and the gate is connected to the first reset signal; the first end of the capacitor is connected to the floating node, and the second end is connected to the transmission control signal; the control signal includes the first reset signal and the transmission control signal.

2. The pixel circuit according to claim 1, characterized in that: The exposure module includes a photosensitive diode and a first transmission tube; the anode of the photosensitive diode is grounded, and the cathode is connected to the source of the first transmission tube; the gate of the first transmission tube is connected to the first transmission signal, and the drain is connected to the floating node.

3. The pixel circuit according to claim 1, characterized in that: The control module also includes a second reset tube; the drain of the second reset tube is connected to the power supply, the gate is connected to the second reset signal, and the source is connected to the second end of the capacitor to input the transmission control signal to the capacitor; the control signal also includes the second reset signal.

4. The pixel circuit according to claim 1 or 3, characterized in that: The control module further includes a second transmission tube; a source of the second transmission tube is connected to the first end of the capacitor, and a drain is connected to the input end of the output module.

5. The pixel circuit according to claim 1 or 3, characterized in that: The control module further includes a second transmission tube, a source of the second transmission tube is connected to the source of the first reset tube, and a drain of the second transmission tube is connected to the first end of the capacitor.

6. The pixel circuit according to claim 1, characterized in that: The output module includes a source follower tube and a gate tube; the drain of the source follower tube is connected to the power supply, the gate serves as the input end of the output module, and the source is connected to the drain of the gate tube; the source of the gate tube serves as the output end of the output module to output the photosensitive signal, and the gate is connected to the selection signal.

7. A method for controlling a pixel circuit, applied to the pixel circuit according to any one of claims 1 to 6, characterized in that: The control method comprises: In the first time period, the pixel circuit is in a reset state; In the second time period, the exposure module performs continuous exposure to generate a light-sensitive signal; In the third time period, the exposure is finished, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the floating node is in a reset state; In the fifth time period, the pixel circuit outputs light-sensing signals in sequence.

8. The method for controlling a pixel circuit according to claim 7, characterized in that: The exposure module receives a first transmission signal; when the control module further includes a second reset tube and the control signal further includes a second reset signal, the control method includes: In the first time period, the first reset signal, the second reset signal and the first transmission signal are valid, the selection signal is invalid, and the pixel circuit is in a reset state; In the second time period, when the first transmission signal is invalid, the exposure module starts to continuously expose to generate a light-sensitive signal until the first transmission signal becomes valid, and the exposure module stops exposing; In a third time period, the first reset signal is invalid, the first transmission signal and the second reset signal are valid, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the second reset signal is invalid, then the first reset signal and the first transmission signal are valid, and the floating node is in a reset state; In the fifth time period, the first reset signal and the first transmission signal are invalid, and when the selection signal is valid, the pixel circuit outputs the light-sensing signal in sequence.

9. The method for controlling a pixel circuit according to claim 7, characterized in that: The exposure module receives a first transmission signal; when the control module further includes a second transmission tube, and the source of the second transmission tube is connected to the first end of the capacitor, and the drain is connected to the input end of the output module, and the control signal further includes a second transmission signal, the control method includes: In the first time period, the first reset signal, the transmission control signal, the first transmission signal and the second transmission signal are valid, the selection signal is invalid, and the pixel circuit is in a reset state; In the second time period, when the first transmission signal is invalid, the photosensitive diode starts to continuously expose to generate a light-sensitive signal, until the first transmission signal becomes valid and the photosensitive diode stops exposing; In the third time period, the first reset signal and the second transmission signal are invalid, the first transmission signal and the transmission control signal are valid, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the transmission control signal and the second transmission signal are invalid, then the first reset signal and the first transmission signal are valid, and the floating node is in a reset state; In the fifth time period, the first reset signal and the first transmission signal are invalid, the second transmission signal is valid, and when the selection signal is valid, the pixel circuit outputs the light-sensing signal in sequence.

10. The method for controlling a pixel circuit according to claim 7, wherein: The exposure module receives a first transmission signal; when the control module further includes a second transmission tube, and the source of the second transmission tube is connected to the source of the first reset tube, and the drain is connected to the first end of the capacitor, and the control signal further includes a second transmission signal, the control method includes: In the first time period, the first reset signal, the transmission control signal, the first transmission signal and the second transmission signal are valid, the selection signal is invalid, and the pixel circuit is in a reset state; In the second time period, when the first transmission signal is invalid, the exposure module starts to continuously expose to generate a light-sensitive signal until the first transmission signal becomes valid, and the exposure module stops exposing; In a third time period, the first reset signal is invalid, the first transmission signal, the second transmission signal and the transmission control signal are valid, and the light-sensing signal is transmitted to the floating node and stored on the capacitor; In the fourth time period, the transmission control signal is invalid, then the first reset signal and the first transmission signal are valid, and the floating node is in a reset state; In the fifth time period, the first reset signal and the first transmission signal are invalid, the second transmission signal remains valid, and when the selection signal is valid, the pixel circuit outputs the light-sensing signal in sequence.

11. An image sensor, characterized in that: Comprising the pixel circuit as described in any one of claims 1 to 6.

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