Pixel and image sensor
By introducing three capacitance configurations and switch control into the pixels, the pixels with multiple conversion gains are realized, solving the problem of limited dynamic range of existing pixels and significantly improving image quality and signal-to-noise ratio.
Patent Information
- Application Number
- CN202311847593.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-28
- Publication Date
- 2025-07-01
AI Technical Summary
The dynamic range of existing pixels is limited, resulting in lower image quality, especially in low-signal and noise.
By introducing three different capacitance configurations into the pixel, corresponding to three conversion gains, and controlling the on states of the first switching unit, the second switching unit and the third switch, the capacitance at the floating diffusion node has three different situations, thereby improving the dynamic range of the pixel.
This greatly improves the dynamic range of pixels and improves image quality, especially in low-light environments, and the signal-to-noise ratio is significantly improved.
Smart Images
Figure CN120238767A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical field of image sensors, and particularly relates to a pixel; it also relates to an image sensor. Background Art
[0002] A common structure of a pixel is the 4T structure as shown in Figure 1 In the 4T structure, a photodiode is used to collect the photo-generated electrons generated in the silicon substrate. During the exposure process, the potential of the photodiode continuously decreases, and at this time, the charge transfer tube is closed. When entering the readout stage, the reset tube is turned on, and after the charge accumulated in the floating diffusion node FD is drained, the reset tube is closed. Then the charge transfer tube is opened, and the electrons in the photodiode will transfer to the floating diffusion node. Subsequently, the charge transfer tube is closed. The electrons transferred to the floating diffusion node complete the conversion from charge to voltage through the parasitic capacitance Cfd of the floating diffusion node itself, and finally output. In a single readout stage, the reset voltage and the signal voltage are read out, and the signal actually output via the analog-to-digital converter is the difference between the reset voltage and the signal voltage.
[0003] The fully depleted voltage of the photodiode is about 1.5V. Once the floating diffusion node is lower than this potential, the electrons in the photodiode cannot be completely transferred to the floating diffusion node, and the remaining electrons will enter the next frame of the image, forming an afterimage and reducing the image quality. At the same time, due to the fixed 3.3V power supply voltage, the voltage swing Vswing of the floating diffusion node is limited. At this time, the maximum charge amount Qmax that the floating diffusion node can read out is Qmax = Vswing * Cfd. Although the dynamic range of the image sensor can be increased by increasing Cfd, the increase in Cfd corresponds to a decrease in the conversion gain of FD, thereby reducing the signal-to-noise ratio in low-light environments. Therefore Figure 1 the dynamic range of the pixel shown is generally not more than 80dB.
[0004] In order to increase the dynamic range that a pixel can achieve, the pixel structures that can be adopted include logarithmic pixels, large and small PDs, dual conversion gains, etc. However, the dynamic range that the above pixel structures can achieve is limited, which in turn limits the application of the pixel. Therefore, how to significantly increase the dynamic range of the pixel has become a technical problem that those skilled in the art urgently need to solve. Summary of the Invention
[0005] The purpose of this application is to provide a pixel that can significantly increase the dynamic range. Another purpose of this application is to provide an image sensor that also has the above technical effect.
[0006] To solve the above technical problems, this application provides a pixel, including:
[0007] A photosensitive unit, a transmission unit, a first switch unit, a second switch unit, a third switch unit, a first capacitor, a second capacitor, and an output unit; one end of the transmission unit is connected to the photosensitive unit, the other end of the transmission unit is connected to a floating diffusion node, one end of the first switch unit is connected to one end of the second switch unit, the other end of the first switch unit is connected to the floating diffusion node, the other end of the second switch unit is connected to a preset potential, one end of the third switch unit is connected to one end of the second capacitor, the other end of the third switch is connected to the preset potential, the other end of the second capacitor is connected to the end where the first switch unit and the second switch unit are connected, and the first capacitor is connected in parallel across the two ends of the first switch unit; when the first switch unit, the second switch unit, and the third switch unit are all turned off, the first capacitor and the second capacitor do not introduce to the floating diffusion node; when the first switch unit and the third switch unit are turned on and the second switch unit is turned off, the second capacitor introduces to the floating diffusion node; when the first switch unit and the third switch unit are turned off and the second switch unit is turned on, the first capacitor introduces to the floating diffusion node;
[0008] The photosensitive unit is configured to sense light and generate charges;
[0009] The transmission unit is configured to transmit charges to the floating diffusion node;
[0010] The output unit is configured to output the voltage of the floating diffusion node.
[0011] Optionally, the photosensitive unit includes:
[0012] A photodiode; the anode of the photodiode is grounded, and the cathode of the photodiode is connected to the transmission unit.
[0013] Optionally, the transmission unit includes:
[0014] A first transistor; the first end of the first transistor is connected to the photosensitive unit, the second end of the first transistor is connected to the floating diffusion node, and the third end of the first transistor inputs a transmission control signal.
[0015] Optionally, the first switch unit includes:
[0016] A second transistor; the first end of the second transistor is connected to the floating diffusion node, the second end of the second transistor is connected to the second switch unit, and the third end of the second transistor inputs a conversion gain control signal.
[0017] Optionally, the second switch unit includes:
[0018] A third transistor; a first end of the third transistor is connected to the first switching unit, a second end of the third transistor is connected to a preset potential, and a third end of the third transistor inputs a reset control signal.
[0019] Optionally, the third switching unit includes:
[0020] A fourth transistor; a first end of the fourth transistor is connected to one end of the second capacitor, a second end of the fourth transistor is connected to a preset potential, and a third end of the fourth transistor inputs a conversion gain control signal.
[0021] Optionally, the output unit includes:
[0022] A fifth transistor and a sixth transistor; a first end of the fifth transistor is connected to a second end of the sixth transistor, a second end of the fifth transistor is connected to a preset potential, a third end of the fifth transistor is connected to the floating diffusion node, a first end of the sixth transistor serves as an output end of the output unit, and a third end of the sixth transistor inputs a selection signal.
[0023] Optionally, it further includes:
[0024] A fourth switching unit; one end of the fourth switching unit is connected to one end where the photosensitive unit is connected to the transmission unit, and the other end of the fourth switching unit is connected to a preset potential.
[0025] Optionally, the third switching unit includes:
[0026] A seventh transistor; a first end of the seventh transistor is connected to a preset potential, a second end of the seventh transistor is connected to one end where the photosensitive unit is connected to the transmission unit, and a third end of the seventh transistor inputs a control signal.
[0027] To solve the above technical problems, the present application further provides an image sensor including the pixel as described above.
[0028] The pixel provided by this application includes: a photosensitive unit, a transmission unit, a first switch unit, a second switch unit, a third switch unit, a first capacitor, a second capacitor, and an output unit; one end of the transmission unit is connected to the photosensitive unit, the other end of the transmission unit is connected to a floating diffusion node, one end of the first switch unit is connected to one end of the second switch unit, the other end of the first switch unit is connected to the floating diffusion node, the other end of the second switch unit is connected to a preset potential, one end of the third switch unit is connected to one end of the second capacitor, the other end of the third switch is connected to the preset potential, the other end of the second capacitor is connected to the end where the first switch unit is connected to the second switch unit, and the first capacitor is connected in parallel across the two ends of the first switch unit; when the first switch unit, the second switch unit, and the third switch unit are all turned off, the first capacitor and the second capacitor do not introduce the floating diffusion node; when the first switch unit and the third switch unit are turned on and the second switch unit is turned off, the second capacitor introduces the floating diffusion node; when the first switch unit and the third switch unit are turned off and the second switch unit is turned on, the first capacitor introduces the floating diffusion node; the photosensitive unit is used for photosensing to generate charges; the transmission unit is used for transmitting the charges to the floating diffusion node; the output unit is used for outputting the voltage of the floating diffusion node.
[0029] It can be seen that for the pixel provided by this application, by controlling the conduction states of the first switch unit, the second switch unit, and the third switch, there can be three different situations for the capacitors at the floating diffusion node, so that the pixel has three conversion gains, greatly improving the dynamic range of the pixel.
[0030] The image sensor provided by this application also has the above technical effects. Description of the Drawings
[0031] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for use in the prior art and the embodiments. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.
[0032] Figure 1 It is a schematic diagram of a traditional pixel;
[0033] Figure 2 It is a schematic diagram of a pixel provided by an embodiment of this application;
[0034] Figure 3 It is a schematic diagram of a structure in which a switch tube is connected in parallel with a capacitor provided by an embodiment of this application;
[0035] Figure 4 Schematic diagram of a specific embodiment of a pixel provided by an embodiment of the present application;
[0036] Figure 5 The first timing diagram provided by an embodiment of the present application;
[0037] Figure 6 The second timing diagram provided by an embodiment of the present application;
[0038] Figure 7 Schematic diagram of another pixel provided by an embodiment of the present application;
[0039] Figure 8 Schematic diagram of a specific embodiment of another pixel provided by an embodiment of the present application;
[0040] Figure 9 Another timing diagram provided by an embodiment of the present application. Detailed implementation manners
[0041] The core of the present application is to provide a pixel that can greatly improve the dynamic range. Another core of the present application is to provide an image sensor that also has the above technical effects.
[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.
[0043] Please refer to Figure 2 , Figure 2 Schematic diagram of a pixel provided by an embodiment of the present application. Referring to Figure 2 as shown, the pixel includes:
[0044] A photosensitive unit 10, a transmission unit 20, a first switch unit 30, a second switch unit 40, a third switch unit 50, a first capacitor C1, a second capacitor C2, and an output unit 60; one end of the transmission unit 20 is connected to the photosensitive unit 10, the other end of the transmission unit 20 is connected to a floating diffusion node, one end of the first switch unit 30 is connected to one end of the second switch unit 40, the other end of the first switch unit 30 is connected to the floating diffusion node, the other end of the second switch unit 40 is connected to a preset potential, one end of the third switch unit 50 is connected to one end of the second capacitor C2, the other end of the third switch is connected to the preset potential, the other end of the second capacitor C2 is connected to the end where the first switch unit 30 is connected to the second switch unit 40, and the first capacitor C1 is connected in parallel across the two ends of the first switch unit 40; when the first switch unit 30, the second switch unit 40, and the third switch unit 50 are all turned off, the first capacitor C1 and the second capacitor C2 do not introduce to the floating diffusion node; when the first switch unit 30 and the third switch unit 50 are turned on and the second switch unit 40 is turned off, the second capacitor C2 introduces to the floating diffusion node; when the first switch unit 30 and the third switch unit 50 are turned off and the second switch unit 40 is turned on, the first capacitor C1 introduces to the floating diffusion node;
[0045] The photosensitive unit 10 is configured to sense light to generate charges;
[0046] The transmission unit 20 is configured to transmit the charges to the floating diffusion node;
[0047] The output unit 60 is configured to output the voltage of the floating diffusion node.
[0048] Reference Figure 3 to the schematic diagram of the structure where a switching transistor is connected in parallel with a capacitor. When the switching transistor SW1, the switching transistor SW2, and the switching transistor SW3 are all turned off, the capacitance C between point A and point C AC = 0. When the switching transistor SW2 is turned off and the switching transistors SW1 and SW3 are turned on, C AC = C2. When the switching transistor SW2 is turned on and the switching transistors SW1 and SW3 are turned off, C AC = C1. By changing the switching states of the switching transistors SW1, SW2, and SW3 and the voltage at point C, three different capacitance values: 0, C2, and C1 can be introduced to point A.
[0049] Based on this, this embodiment provides a pixel including a photosensitive unit 10, a transmission unit 20, a first switch unit 30, a second switch unit 40, a third switch unit 50, a first capacitor C1, a second capacitor C2, and an output unit 60. The first switch unit 30, the second switch unit 40, the third switch unit 50, the first capacitor C1, and the second capacitor C2 form a structure as shown in Figure 3 shown.
[0050] When the first switch unit 30, the second switch unit 40, and the third switch unit 50 are all turned off, the first capacitor C1 and the second capacitor C2 do not introduce the floating diffusion node, and the capacitance value at the floating diffusion node is the capacitance value of the parasitic capacitance of the floating diffusion node itself. When the first switch unit 30 and the third switch unit 50 are turned on and the second switch unit 40 is turned off, the second capacitor C2 introduces the floating diffusion node, and the capacitance value of the capacitance at the floating diffusion node is approximately equal to the capacitance value of the second capacitor C2 (because the capacitance value of the second capacitor C2 is much larger than the capacitance value of the parasitic capacitance of the floating diffusion node itself); when the first switch unit 30 and the third switch unit 50 are turned off and the second switch unit 40 is turned on, the first capacitor C1 introduces the floating diffusion node, and the capacitance value of the capacitance at the floating diffusion node is approximately equal to the capacitance value of the first capacitor C1 (because the capacitance value of the first capacitor C1 is much larger than the capacitance value of the parasitic capacitance of the floating diffusion node itself). Cfd is the parasitic capacitance of the floating diffusion node. The capacitance values of the first capacitor C1 and the second capacitor C2 are not equal.
[0051] The photosensitive unit 10 is connected to the transmission unit 20, the transmission unit 20 is connected to the floating diffusion node, and the output unit 60 is connected to the floating diffusion node. The photosensitive unit 10 is used for photosensing to generate charges. The control signal corresponding to the transmission unit 20 has three levels: high, medium, and low. At the beginning of exposure, the control signal of the transmission unit 20 switches from high level to medium level, and electrons start to accumulate in the photosensitive unit 10. When the electron potential of the photosensitive unit 10 is higher than the channel of the transmission unit 20, the electrons in the photosensitive unit 10 start to overflow to the floating diffusion node. After entering the readout time, the control signal of the transmission unit 20 switches from medium level to low level, and the photosensitive unit 10 stops overflowing electrons to the floating diffusion node. The output unit 60 outputs the voltage of the floating diffusion node.
[0052] Referring to Figure 4 shown, in some embodiments, 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.
[0053] The transmission unit 20 includes: a first transistor M1; a first end of the first transistor M1 is connected to the photosensitive unit 10, a second end of the first transistor M1 is connected to the floating diffusion node, and a third end of the first transistor M1 inputs a transmission control signal.
[0054] The first switching unit 30 includes: a second transistor M2; a first end of the second transistor M2 is connected to the floating diffusion node, a second end of the second transistor M2 is connected to the second switching unit 40, and a third end of the second transistor M2 inputs a conversion gain control signal.
[0055] The second switching unit 40 includes: a third transistor M3; a first end of the third transistor M3 is connected to the first switching unit 30, a second end of the third transistor M3 is connected to a preset potential, and a third end of the third transistor M3 inputs a reset control signal.
[0056] The third switching unit 50 includes: a fourth transistor M4; a first end of the fourth transistor M4 is connected to one end of the second capacitor C2, a second end of the fourth transistor M4 is connected to a preset potential, and a third end of the fourth transistor M4 inputs a conversion gain control signal.
[0057] The output unit 60 includes: a fifth transistor M5 and a sixth transistor M6; a first end of the fifth transistor M5 is connected to a second end of the sixth transistor M6, a second end of the fifth transistor M5 is connected to a preset potential, a third end of the fifth transistor M5 is connected to the floating diffusion node, a first end of the sixth transistor M6 serves as an output end of the output unit 60, and a third end of the sixth transistor M6 inputs a selection signal.
[0058] Each of the above transistors may be an NMOS transistor. The gate of the NMOS transistor is the third end of the transistor, the source of the NMOS transistor is the first end of the transistor, and the drain of the NMOS transistor is the second end of the transistor.
[0059] When the capacitance value of the first capacitor is greater than the capacitance value of the second capacitor, combined with Figure 5 the timing diagram shown, Figure 4 the working principle of the pixel shown is as follows:
[0060] Figure 5In the exp stage, it is the exposure stage, and in the read stage, it is the read stage. T1 is the first conversion gain time, T2 is the second conversion gain time, and T3 is the third conversion gain time. The conversion gain control signals input to the second transistor M2 and the fourth transistor M4 are the same signal. At the starting moment, the transmission control signal TX is set low, and the exposure of the photodiode PD starts. During the exposure process, the first transistor M1 is half-open. When the electron potential accumulated in the photodiode PD is higher than the channel of the first transistor M1, the excess electrons will overflow to the floating diffusion node FD. At time T1, the first transistor M1 is completely turned off, and the voltage of the electrons accumulated in the floating diffusion node FD during the exposure period is read, that is, V 2cg1 , at this time, the reset control signal RST is at a high level, the conversion gain control signal CG is at a low level, the second transistor M2 and the fourth transistor M4 are turned off, the third transistor M3 is turned on, and the capacitance C FD ≈C1 at the floating diffusion node FD, and the conversion gain is the first conversion gain. Then, after the conversion gain control signal CG changes from a low level to a high level and then to a low level, that is, after the second transistor M2 and the fourth transistor M4 are turned on and then turned off, the floating diffusion node FD is reset, and the reset voltage V 1cg1 under the first conversion gain is read.
[0061] At time T2, the reset control signal RST and the conversion gain control signal CG are set to a low level. The second transistor M2, the third transistor M3, and the fourth transistor M4 are all turned off. The capacitance C FD at the floating diffusion node = Cfd, that is, the capacitance of the floating diffusion node is equal to its own parasitic capacitance, and the conversion gain is the second conversion gain. Before and after the first transistor M1 is turned on, the reset voltage V 1cg2 under the second conversion gain and the signal voltage V 2cg2 are read.
[0062] At time T3, the reset control signal RST is set to a low level, and the conversion gain control signal CG is set to a high level, that is, the second transistor M2 and the fourth transistor M4 are turned on, and the third transistor M3 is turned off. At this time, the capacitance C FD ≈C2 at the floating diffusion node FD, and the conversion gain is the third conversion gain. Before and after the first transistor M1 is turned on, the reset signal V 1cg3 under the third conversion gain and the signal voltage V 2cg3 are read.
[0063] When the capacitance value of the first capacitor is less than the capacitance value of the second capacitor, combined with Figure 6 the timing diagram shown, Figure 4 the working principle of the pixel shown is as follows:
[0064] Figure 6In the exp stage, it is the exposure stage, and in the read stage, it is the read stage. T1 is the first conversion gain time, T2 is the second conversion gain time, and T3 is the third conversion gain time. The conversion gain control signals input to the second transistor M2 and the fourth transistor M4 are the same signal. At the starting moment, the transmission control signal TX is set low, and the exposure of the photodiode PD starts. During the exposure process, the first transistor M1 is half-open. When the electron potential accumulated in the photodiode PD is higher than the channel of the first transistor M1, the excess electrons will overflow to the floating diffusion node FD. At time T1, the first transistor M1 is completely turned off, and the voltage of the electrons accumulated at the floating diffusion node FD during the exposure period is read, that is, V 2cg1 , at this time, the reset control signal RST is at a low level, the conversion gain control signal CG is at a high level, the second transistor M2 and the fourth transistor M4 are turned on, and the third transistor M3 turns off the capacitor C at the floating diffusion node FD FD ≈C2, and the conversion gain is the first conversion gain. Turn on the third transistor to complete the reset of the floating diffusion node FD, and read the reset voltage V at the first conversion gain 1cg1 .
[0065] At time T2, the reset control signal RST and the conversion gain control signal CG are set to a low level. The second transistor M2, the third transistor M3, and the fourth transistor M4 are all turned off. The capacitance C at the floating diffusion node FD =Cfd, that is, the capacitance of the floating diffusion node is equal to its own parasitic capacitance. The conversion gain is the second conversion gain. Before and after the first transistor M1 is turned on, the reset voltage V at the second conversion gain and the signal voltage V 1cg2 are read 2cg2 .
[0066] At time T3, the reset control signal RST is set to a high level, and the conversion gain control signal CG is set to a low level, that is, the second transistor M2 and the fourth transistor M4 are turned off, and the third transistor M3 is turned on. At this time, the capacitance C of the floating diffusion node FD FD ≈C1, and the conversion gain is the third conversion gain. Before and after the first transistor M1 is turned on, the reset signal V1cg3 at the third conversion gain and the signal voltage V 2cg3 are read
[0067] Reference Figure 7 As shown, in some embodiments, it further includes:
[0068] A fourth switch unit 70; one end of the fourth switch unit 70 is connected to one end where the photosensitive unit 10 is connected to the transmission unit 20, and the other end of the fourth switch unit 70 is connected to a preset potential
[0069] Based on Figure 3For the structure shown, in this embodiment, a pixel is provided that includes a photosensitive unit 10, a transfer unit 20, a first switch unit 30, a second switch unit 40, a third switch unit, a fourth switch unit 70, a first capacitor C1, a second capacitor C2, and an output unit 60.
[0070] Among them, one end of the fourth switch unit 70 is connected to the end where the photosensitive unit 10 is connected to the transfer unit 20, and the other end of the fourth switch unit 70 is connected to a preset potential. By turning on both the fourth switch unit 70 and the transfer unit 20, the voltage of the floating diffusion node FD can be pulled to the full depletion voltage of the photodiode PD. When the transfer unit 20 is turned off, no electrons flow back into the floating diffusion node. In this way, it is not necessary to separately read out the reset voltage at the first conversion gain. This embodiment supports signal readout at three conversion gains. The swing of the readout signal increases at the first conversion gain, and only the signal voltage is read out, avoiding the influence of the reset voltage of the floating diffusion node. At the same time, the signal readout time is shortened, and the frame rate can be increased.
[0071] In some embodiments, the fourth switch unit 70 includes:
[0072] A seventh transistor M7; a first end of the seventh transistor M7 is connected to a preset potential, a second end of the seventh transistor M7 is connected to the end where the photosensitive unit 10 is connected to the transfer unit 20, and a control signal is input to a third end of the seventh transistor M7.
[0073] The seventh transistor M7 can be an NMOS transistor. The gate of the NMOS transistor is the third end of the seventh transistor M7, the source of the NMOS transistor is the first end of the seventh transistor M7, and the drain of the NMOS transistor is the second end of the seventh transistor M7. Referring to Figure 8 shown, the drain of the seventh transistor M7 is connected to the cathode of the photodiode PD and the source of the first transistor M1, the source of the seventh transistor M7 is connected to a preset potential, and a control signal AB is input to the gate of the seventh transistor M7. The third transistor M3 and the fourth transistor M4 are both connected to the potential RSTD. The fourth transistor M4 can also be connected to a preset unit VDDP.
[0074] When the capacitance value of the first capacitor C1 is greater than the capacitance value of the second capacitor C2, combined with Figure 9 the timing diagram shown, Figure 8 the working principle of the pixel shown is as follows:
[0075] Set the control signal AB and the transmission control signal TX to high level, turn on the first transistor M1 and the seventh transistor M7, so as to pull the voltage of the floating diffusion node FD to the full depletion voltage of the photodiode PD. Set the control signal AB and the transmission control signal TX to low level, the reset of the floating diffusion node FD ends, and the exposure starts. The drain of the second transistor M2 is initially at a low potential. After the reset control signal RST is set to high level, it will raise the potential of the floating diffusion node, and increase the output swing of the voltage at the first conversion gain. During the exposure process, the first transistor M1 is half-open, and the photodiode PD generates excess electrons and transfers them to the floating diffusion node. At time T1, the first transistor M1 is completely turned off, and the voltage V of the electrons accumulated at the floating diffusion node FD during the exposure period is read out. cg1 The reset voltage is not read out.
[0076] At time T2, the reset control signal RST and the conversion gain control signal CG are at low level, the second transistor M2, the third transistor M3 and the fourth transistor M4 are all turned off, and the capacitance C of the floating diffusion node FD = Cfd, that is, the capacitance of the floating diffusion node is equal to its own parasitic capacitance, and the conversion gain is the second conversion gain. The reset voltage V at the second conversion gain is read out before and after the first transistor M1 is turned on. 1cg2 and the signal voltage V 2cg2 .
[0077] At time T3, set the reset control signal RST to low level and the conversion gain control signal CG to high level, that is, turn on the second transistor M2 and the fourth transistor M4, and turn off the third transistor M3. At this time, the capacitance C of the floating diffusion node FD FD ≈ C2. Before and after the first transistor M1 is turned on, the reset signal V at the third conversion gain and the signal voltage V 1cg3 and 2cg3 are read out.
[0078] At time T4, the conversion gain control signal CG is set to low level, the reset control signal RST is set to high level, the potential RSTD is set to low, pulling down the drain of the second transistor M2 and the potential of the floating diffusion node FD to complete the reset of the drain of the second transistor M2. Then the reset control signal RST is set to low level, the third transistor M3 is turned off, and the potential RSTD is set to high. At the end of the readout, the first transistor M1 and the seventh transistor M7 are turned on simultaneously to complete the reset of the floating diffusion node FD.
[0079] In summary, for the pixel provided by the present application, by controlling the conduction states of the first switch unit, the second switch unit and the third switch, the capacitance at the floating diffusion node can have three different situations, so that the pixel has three conversion gains, greatly improving the dynamic range of the pixel.
[0080] The present application also provides an image sensor, which includes the pixels described in the above embodiments. For the image sensor provided by the present application, reference may be made to the introduction of the pixels, which will not be elaborated herein.
[0081] Due to the complex situation and inability to list and elaborate one by one, those skilled in the art should be able to realize that there can be multiple examples under the basic principle of the embodiments provided by the present application in combination with the actual situation. Without sufficient creative labor, they should all fall within the scope of the present application.
[0082] The various 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 various embodiments can be referred to each other.
[0083] The pixels and the image sensor provided by the present application have been introduced in detail above. Specific examples are used herein to elaborate 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 in this technical field, 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.
[0084] 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 expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including an..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.
Claims
1. A pixel, characterized in that, Comprising: A photosensitive unit, a transmission unit, a first switch unit, a second switch unit, a third switch unit, a first capacitor, a second capacitor, and an output unit; one end of the transmission unit is connected to the photosensitive unit, the other end of the transmission unit is connected to a floating diffusion node, one end of the first switch unit is connected to one end of the second switch unit, the other end of the first switch unit is connected to the floating diffusion node, the other end of the second switch unit is connected to a preset potential, one end of the third switch unit is connected to one end of the second capacitor, the other end of the third switch is connected to the preset potential, the other end of the second capacitor is connected to the end where the first switch unit is connected to the second switch unit, and the first capacitor is connected in parallel across the two ends of the first switch unit; when the first switch unit, the second switch unit, and the third switch unit are all turned off, the first capacitor and the second capacitor do not introduce to the floating diffusion node; when the first switch unit and the third switch unit are turned on and the second switch unit is turned off, the second capacitor introduces to the floating diffusion node; when the first switch unit and the third switch unit are turned off and the second switch unit is turned on, the first capacitor introduces to the floating diffusion node; 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 output unit is configured to output the voltage of the floating diffusion node.
2. The 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 transmission unit.
3. The pixel according to claim 1, wherein The transmission unit includes: A first transistor; the first end of the first transistor is connected to the photosensitive unit, the second end of the first transistor is connected to the floating diffusion node, and the third end of the first transistor inputs a transmission control signal.
4. The pixel according to claim 1, characterized in that, The first switch unit includes: A second transistor; the first end of the second transistor is connected to the floating diffusion node, the second end of the second transistor is connected to the second switch unit, and the third end of the second transistor inputs a conversion gain control signal.
5. The pixel according to claim 1, characterized in that, The second switch unit includes: A third transistor; the first end of the third transistor is connected to the first switch unit, the second end of the third transistor is connected to the preset potential, and the third end of the third transistor inputs a reset control signal.
6. The pixel according to claim 1, wherein The third switch unit includes: A fourth transistor; the first end of the fourth transistor is connected to one end of the second capacitor, the second end of the fourth transistor is connected to the preset potential, and the third end of the fourth transistor inputs a conversion gain control signal.
7. The pixel according to claim 1, characterized in that, The output unit includes: A fifth transistor and a sixth transistor; the first end of the fifth transistor is connected to the second end of the sixth transistor, the second end of the fifth transistor is connected to the preset potential, the third end of the fifth transistor is connected to the floating diffusion node, the first end of the sixth transistor serves as the output end of the output unit, and the third end of the sixth transistor inputs a selection signal.
8. The pixel according to any one of claims 1 to 7, characterized in that, Further comprising: A fourth switching unit; one end of the fourth switching unit is connected to one end where the photosensitive unit is connected to the transmission unit, and the other end of the fourth switching unit is connected to a preset potential.
9. The pixel according to claim 8, wherein The third switching unit includes: A seventh transistor; a first end of the seventh transistor is connected to a preset potential, a second end of the seventh transistor is connected to one end where the photosensitive unit is connected to the transmission unit, and a control signal is input to a third end of the seventh transistor.
10. An image sensor, characterized in that, Comprising a pixel according to any one of claims 1 to 9.