Image sensor and image processing apparatus
By introducing a dual-conversion gain circuit and a gain mode switching unit into the image sensor and using the floating node voltage to control the state of the dual-conversion gain tube, the problem of 5T pixel circuit mode switching is solved, and high-quality image capture under different lighting conditions is achieved.
Patent Information
- Application Number
- CN202511044796.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-28
- Publication Date
- 2025-10-10
AI Technical Summary
In existing 5T pixel circuits, it is difficult to switch between a low conversion gain mode and a high conversion gain mode instantly, and the controller needs to output additional control timing.
By introducing a dual conversion gain circuit and a gain mode switching unit into the 4T pixel circuit, the on-off state of the dual conversion gain tube is controlled in real time by utilizing the voltage change of the floating node, thereby realizing automatic switching between low conversion gain mode and high conversion gain mode. The gain mode switching unit includes a comparator and a unidirectional conduction switch to control the on and off state of the dual conversion gain tube.
It realizes automatic switching of gain modes under different light intensities without the need for the controller to output additional timing, ensuring high-quality images in both strong and low-light environments.
Smart Images
Figure CN120769183A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of image processing technology, and in particular to an image sensor and an image processing device. Background Art
[0002] Traditional 4T pixel circuits can only meet basic signal transmission and reading functions. With the diversification of application scenarios, especially under different light intensities, the performance requirements for image sensors are constantly increasing.
[0003] Currently, by setting a dual conversion gain (DCG) circuit in a 4T pixel circuit, it is possible to ensure that high image quality can be obtained in both strong light and low light environments.
[0004] However, in the 5T pixel circuit with the addition of a dual conversion gain circuit, the controller is required to obtain the changes in light intensity in real time, and then output the corresponding control timing in real time to control the conduction and disconnection of the dual conversion gain tube DCG, thereby realizing switching between low conversion gain mode and high conversion gain mode.
[0005] In the prior art, it is difficult to implement the switch between the low conversion gain mode and the high conversion gain mode in real time, and the controller needs to output additional control timing. Summary of the Invention
[0006] An object of the present invention is at least to provide an image sensor that can switch between a low conversion gain mode and a high conversion gain mode in real time without requiring a controller to output additional control timing.
[0007] In a first aspect, the present invention provides an image sensor comprising: a 4T pixel circuit, a dual conversion gain circuit, and a gain mode switching unit, wherein: the dual conversion gain circuit comprises a dual conversion gain tube and a first capacitor, wherein: the drain of the dual conversion gain tube is coupled to the source of a reset tube in the 4T pixel circuit, and the source of the dual conversion gain tube is coupled to the drain of a transmission tube in the 4T pixel circuit; the first capacitor has a first end coupled to the drain of the dual conversion gain tube and a second end grounded; the gain mode switching unit is adapted to control the on / off state of the dual conversion gain tube based on the voltage of a floating node of the 4T pixel circuit; when the dual conversion gain tube is in the on state, it enters a low conversion gain mode; when the dual conversion gain tube is in the off state, it enters a high conversion gain mode.
[0008] The gain mode switching unit controls the on-off state of the double conversion gain tube based on the voltage of the floating node of the 4T pixel circuit. Since the voltage of the floating node is related to the light intensity collected by the image sensor, when the light intensity changes, the voltage of the floating node changes in real time, thereby being able to control the switching between the low conversion gain mode and the high conversion gain mode in real time without the need of an additional control timing output by the controller.
[0009] Optionally, the gain mode switching unit comprises a comparator, wherein: a first input end of the comparator is coupled with the floating node of the 4T pixel circuit, a second input end of the comparator inputs a reference voltage, and an output end of the comparator is coupled with the gate of the double conversion gain tube; when the reference voltage is greater than the voltage of the floating node, the double conversion gain tube is in an off state; and when the reference voltage is less than the voltage of the floating node, the double conversion gain tube is in an on state.
[0010] Optionally, the image sensor further comprises a unidirectional conduction switch coupled between the gate of the reset tube and the gate of the double conversion gain tube to block the connection between the output end of the comparator and the gate of the reset tube.
[0011] The unidirectional conduction switch is coupled between the gate of the reset tube and the gate of the double conversion gain tube. When the comparator outputs a comparison signal to control the on-off state of the double conversion gain tube, the unidirectional conduction switch can prevent the comparison signal from affecting the reset tube. When the gate of the reset tube inputs a reset signal, the unidirectional conduction switch is turned on, and the double conversion gain tube is also turned on under the action of the reset signal, so that synchronous reset can be realized.
[0012] Optionally, a first end of the unidirectional conduction switch is coupled with the output end of the comparator and the gate of the double conversion gain tube, and a second end of the unidirectional conduction switch is coupled with the gate of the reset tube in the 4T pixel circuit.
[0013] Optionally, the unidirectional conduction switch is a switching device with PN junction switching characteristics.
[0014] Optionally, the unidirectional conduction switch comprises a first diode, wherein: a cathode of the first diode is coupled with the output end of the comparator, and an anode of the first diode is coupled with the gate of the reset tube in the 4T pixel circuit.
[0015] Optionally, the image sensor further comprises a switching unit, a first end of the switching unit is coupled with the gate of the reset tube, a second end of the switching unit is coupled with the gate of the double conversion gain tube, and a control end of the switching unit is coupled with the gate of the reset tube; when the gate of the switching unit inputs the reset signal, a path is formed between the gate of the reset tube and the gate of the double conversion gain tube; and when the gate of the switching unit does not input the reset signal, the path between the gate of the reset tube and the gate of the double conversion gain tube is broken.
[0016] A switch unit is provided, coupled between the gate of the reset transistor and the gate of the dual-conversion-gain transistor. When a reset signal is input to the gate of the switch unit, a path is formed between the gates of the reset transistor and the dual-conversion-gain transistor. Therefore, when a reset signal is input to the gate of the reset transistor, the dual-conversion-gain transistor also turns on under the action of the reset signal, thereby achieving a synchronous reset.
[0017] Optionally, the 4T pixel circuit includes: the reset tube, the transmission tube, the source follower tube, the row selection tube, the second diode and the second capacitor, wherein: the reset tube, its gate inputs the reset signal, its drain is coupled to the preset voltage source, and its source is coupled to the drain of the dual conversion gain tube; the transmission tube, its gate inputs the transmission signal, its drain is coupled to the source of the dual conversion gain tube, and its source is coupled to the cathode of the second diode; the anode of the second diode is grounded; the source follower tube, its drain is coupled to the voltage source, its gate is coupled to the first end of the second capacitor and the drain of the transmission tube, and its source is coupled to the drain of the row selection tube; the row selection tube, its gate inputs the row selection signal, and its source is coupled to the output end of the 4T pixel circuit; the second capacitor, its first end is also coupled to the drain of the transmission tube, and its second end is grounded.
[0018] In a second aspect, the present invention provides an image processing device comprising any one of the above-mentioned image sensors. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 This is a schematic structural diagram of a 4T pixel circuit in the prior art;
[0020] Figure 2 1 is a schematic structural diagram of a 5T pixel circuit including a dual conversion gain circuit;
[0021] Figure 3 is a schematic structural diagram of an image sensor in an embodiment of the present invention;
[0022] Figure 4 Schematic diagram of the structure of another image sensor in an embodiment of the present invention. DETAILED DESCRIPTION
[0023] Reference Figure 1 , provides a schematic diagram of a 4T pixel circuit in the prior art. The 4T pixel circuit includes a reset transistor RST, a transmission transistor TX, a source follower transistor SF, a row select transistor RS, and a diode D2. Traditional 4T pixel circuits can only meet basic signal transmission and reading functions.
[0024] As application scenarios diversify, performance requirements for image sensors continue to increase, especially under varying light intensities. By incorporating a dual conversion gain (DCG) circuit into the 4T pixel circuit, high image quality can be achieved in both bright and low-light environments.
[0025] like Figure 2 As shown, a structural schematic diagram of a 5T pixel circuit including a dual conversion gain circuit is given.
[0026] Figure 2 In Figure 1 Based on the provided 4T pixel circuit, a dual conversion gain tube DCG and a capacitor C1 are added.
[0027] Specifically, the drain of the dual conversion gain transistor DCG is coupled to the source of the reset transistor RST, and the source of the dual conversion gain transistor DCG is coupled to the floating node (FD).
[0028] A first end of the capacitor C1 is coupled to the drain of the dual-conversion gain transistor DCG, and a second end of the capacitor C1 is grounded.
[0029] However, in the 5T pixel circuit with the addition of a dual conversion gain circuit, the controller is required to obtain the changes in light intensity in real time, and then output the corresponding control timing in real time to control the conduction and disconnection of the dual conversion gain tube DCG, thereby realizing switching between low conversion gain mode and high conversion gain mode.
[0030] In the prior art, it is difficult to implement the switch between the low conversion gain mode and the high conversion gain mode in real time, and the controller needs to output additional control timing.
[0031] In an embodiment of the present invention, a gain mode switching unit is provided to control the on / off state of the dual-conversion gain transistor based on the voltage of the floating node of the 4T pixel circuit. Because the voltage of the floating node is correlated to the light intensity captured by the image sensor, the voltage of the floating node changes in real time when the light intensity changes, thereby enabling real-time control of switching between low-conversion gain mode and high-conversion gain mode without requiring the controller to output additional control timing.
[0032] In order to make the above-mentioned objects, features and beneficial effects of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.
[0033] An embodiment of the present invention provides an image sensor, which is described in detail below.
[0034] In an embodiment of the present invention, an image sensor may include: a 4T pixel circuit, a dual conversion gain circuit, and a gain mode switching unit.
[0035] In a specific implementation, the structure of the 4T pixel circuit can correspond to the reference Figure 1 , including: a reset transistor RST, a transmission transistor TX, a source follower transistor SF, a row selection transistor RS, a second diode D2 and a second capacitor C2, wherein:
[0036] The gate of the reset tube RST can input a reset signal, the drain of the reset tube RST is coupled to a preset voltage source VDD, and the source of the reset tube RST is coupled to the drain of the transmission tube TX and the gate of the source follower;
[0037] The gate of the transmission tube TX can input a transmission signal, which can be a signal of a pixel to be output; the source of the transmission tube TX can be coupled to the cathode of the diode D2;
[0038] The drain of the source follower transistor SF may be coupled to a preset voltage source VDD, and the source of the source follower transistor SF may be coupled to the drain of the row select transistor RS;
[0039] The gate of the row select tube RS can input a selection signal to select a pixel for data output, and the source of the row select tube RS is connected to a preset bit line Bit-line; that is, the source of the row select tube RS is the output end of the 4T pixel circuit;
[0040] The anode of diode D2 is grounded;
[0041] A first terminal of the capacitor C2 is coupled to the gate of the source follower transistor SF and the floating node (FD), and a second terminal of the capacitor C2 is grounded.
[0042] In a specific implementation, the structure of the pixel circuit with the dual conversion gain circuit added can correspond to the following: Figure 2 .
[0043] Specifically, the dual conversion gain circuit includes a dual conversion gain transistor DCG and a first capacitor C1, wherein:
[0044] The drain of the dual conversion gain tube DCG is coupled to the source of the reset tube RST in the 4T pixel circuit, and the source of the dual conversion gain tube DCG is coupled to the drain of the transmission tube RX in the 4T pixel circuit;
[0045] A first end of the first capacitor C1 is coupled to the drain of the dual conversion gain transistor DCG, a second end of the first capacitor C1 is grounded, and a first end of the first capacitor C1 is connected to the second floating node FD'.
[0046] In an embodiment of the present invention, the gain mode switching unit is adapted to control the on / off state of the dual-conversion-gain transistor DCG based on the voltage of the floating node of the 4T pixel circuit. Specifically, when the dual-conversion-gain transistor DCG is in the on state, the circuit enters a low-conversion-gain mode; when the dual-conversion-gain transistor DCG is in the off state, the circuit enters a high-conversion-gain mode.
[0047] In a specific implementation, the gain mode switching unit can compare the voltage of the floating node FD with a preset reference voltage. When it is detected that the reference voltage is greater than the voltage of the floating node FD, the gain mode switching unit can output a corresponding signal to the gate of the dual-conversion gain transistor, thereby controlling the dual-conversion gain transistor to be in an off state. When it is detected that the reference voltage is not greater than the voltage of the floating node FD, the gain mode switching unit can output a corresponding signal to the gate of the dual-conversion gain transistor, thereby controlling the dual-conversion gain transistor to be in an on state.
[0048] In specific applications, it can be seen that the voltage of floating node FD is related to the light intensity collected by the image sensor. The greater the collected light intensity, the greater the voltage of floating node FD; the weaker the collected light intensity, the smaller the voltage of floating node FD. Therefore, the gain mode switching unit compares the reference voltage with the voltage of floating node FD, enabling the sensor to enter a low conversion gain mode when the light intensity is high and a high conversion gain mode when the light intensity is low, thereby achieving low read noise. This ensures high image quality in both bright and low light environments.
[0049] In a specific implementation, the gain mode switching unit can be a comparator, wherein: the first input terminal of the comparator is coupled to the floating node FD of the 4T pixel circuit, the second input terminal of the comparator inputs the reference voltage, and the output terminal of the comparator is coupled to the gate of the dual conversion gain tube.
[0050] When the reference voltage is greater than the voltage of the floating node FD, the output end of the comparator can output a low-level comparison signal, so that the dual conversion gain tube is in the disconnected state; when the reference voltage is not greater than the voltage of the floating node FD, the output end of the comparator can output a high-level comparison signal, so that the dual conversion gain tube is in the on state.
[0051] In some embodiments, the first input terminal of the comparator may be a positive input terminal of the comparator, and the second input terminal of the comparator may be an inverting input terminal of the comparator.
[0052] In a specific implementation, the reference voltage can be a fixed value or an adjustable value. The specific value of the reference voltage can be set according to the specific application scenario (such as the requirements for high conversion gain mode and low conversion gain mode).
[0053] In some embodiments, if the specific value of the reference voltage is adjustable, a reference voltage generation circuit can be provided in the image processing device, and the reference voltage generation circuit can output a reference voltage with an adjustable voltage value. Alternatively, the reference voltage output by the reference voltage generation circuit can be adjusted by a controller in the image processing device.
[0054] Reference Figure 3 , a structural schematic diagram of an image sensor in an embodiment of the present invention is given.
[0055] Figure 3 In the embodiment, the first input terminal of the comparator COMP is coupled to the floating node FD of the 4T pixel circuit, and its input voltage is V FD The second input terminal of the comparator COMP inputs the reference voltage V ref , the output end of the comparator COMP is coupled to the gate of the dual conversion gain tube DCG.
[0056] It is understandable that the gain mode switching unit may also be a device capable of implementing a comparison function and outputting a corresponding comparison result, such as a comparison chip or a comparison circuit module having a comparison function.
[0057] In specific implementation, Figure 3 In the image sensor shown, when the dual conversion gain transistor DCG needs to be reset, a reset signal can be input to its gate to reset the first capacitor C1.
[0058] In some embodiments, the dual conversion gain transistor DCG and the reset transistor RST can be reset using the same reset signal, thereby simplifying the circuit structure and achieving synchronous reset.
[0059] In other embodiments, the dual conversion gain transistor DCG may use a reset signal different from the reset signal of the reset transistor RST to perform a reset operation.
[0060] In an embodiment of the present invention, the image sensor may further include a unidirectional conduction switch. The unidirectional conduction switch may be coupled between the gate of the reset transistor RST and the gate of the dual conversion gain transistor DCG to block the connection between the output terminal of the comparator COMP and the gate of the reset transistor RST.
[0061] In a specific implementation, the first end of the unidirectional conduction switch can be coupled to the output end of the comparator COMP and the gate of the dual conversion gain tube DCG, and the second end of the unidirectional conduction switch is coupled to the gate of the reset tube RST in the 4T pixel circuit.
[0062] That is to say, through the above-mentioned unidirectional conduction switch, the comparison signal of the comparator COMP can only be output to the gate of the dual conversion gain tube DCG, and will not be input to the gate of the reset tube RST, so it will not affect the on-off state of the reset tube RST.
[0063] In a specific implementation, the unidirectional conducting switch may be a switching device having PN junction switching characteristics, specifically, a diode, a transistor, and the like.
[0064] In some embodiments, the unidirectional conduction switch may include a first diode D1, wherein: the cathode of the first diode D1 is coupled to the output terminal of the comparator COMP, and the anode of the first diode D1 is coupled to the gate of the reset transistor RST at the midpoint of the 4T pixel circuit.
[0065] Reference Figure 4 , a schematic structural diagram of another image sensor in an embodiment of the present invention is given.
[0066] Figure 4 In Figure 3 On the basis of, a first diode D1 is provided between the gate of the dual conversion gain tube DCG and the gate of the reset tube RST, and the first diode D1 is coupled between the gate of the reset tube RST and the gate of the dual conversion gain tube DCG.
[0067] Due to the unidirectional conduction characteristics of the first diode D1, the output signal of the comparator COMP can only be output to the gate of the dual-conversion gain tube DCG to control the on-off state of the dual-conversion gain tube DCG, but cannot be output to the gate of the reset tube RST to control the on-off state of the reset tube RST.
[0068] Therefore, by providing the first diode D1 , the output signal of the comparator COMP is prevented from affecting the on / off state of the reset tube RST.
[0069] By providing a unidirectional conduction switch, when the comparator outputs a comparison signal to control the on / off state of the dual-conversion gain transistor, the unidirectional conduction switch can prevent the comparison signal from affecting the reset transistor. When the reset signal is input to the gate of the reset transistor, the unidirectional conduction switch turns on, and the dual-conversion gain transistor also turns on under the action of the reset signal, thus achieving synchronous reset.
[0070] In an embodiment of the present invention, a structure for achieving simultaneous resetting of the dual conversion gain tube and the reset tube can also be: a switch unit is provided between the gate of the reset tube and the gate of the dual conversion gain tube, and the on-off state of the switch unit is controlled by a reset signal.
[0071] Specifically, the first end of the switch unit is coupled to the gate of the reset tube, the second end of the switch unit is coupled to the gate of the dual conversion gain tube, and the control end of the switch unit is coupled to the gate of the reset tube. When a high-level reset signal is input to the gate of the reset tube, the switch unit is turned on, and a path is formed between the gate of the reset tube and the gate of the dual conversion gain tube. Therefore, when a reset signal is input to the gate of the reset tube, the dual conversion gain tube is also turned on under the action of the reset signal, thereby achieving synchronous reset. When the gate of the reset tube is not input with a reset signal, the switch unit can be in an off state. In this scenario, the output signal of the comparator COMP can only be output to the gate of the dual conversion gain tube DCG to control the on-off state of the dual conversion gain tube DCG, but cannot be output to the gate of the reset tube RST to control the on-off state of the reset tube RST.
[0072] In some embodiments, the switch unit may be an NMOS transistor, the first end of the NMOS transistor is the drain of the NMOS transistor, the second end of the NMOS transistor is the source of the NMOS transistor, and the control end of the NMOS transistor is the gate of the NMOS transistor.
[0073] An embodiment of the present invention further provides an image processing device, comprising any one of the above-mentioned image sensors.
[0074] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.
Claims
1. An image sensor, characterized in that: include: 4T pixel circuit, dual conversion gain circuit and gain mode switching unit, wherein: The dual conversion gain circuit includes a dual conversion gain tube and a first capacitor, wherein: the drain of the dual conversion gain tube is coupled to the source of the reset tube in the 4T pixel circuit, and the source of the dual conversion gain tube is coupled to the drain of the transmission tube in the 4T pixel circuit; the first capacitor has a first end coupled to the drain of the dual conversion gain tube and a second end grounded; The gain mode switching unit is adapted to control the on / off state of the dual conversion gain tube based on the voltage of the floating node of the 4T pixel circuit; when the dual conversion gain tube is in the on state, the circuit enters a low conversion gain mode; and when the dual conversion gain tube is in the off state, the circuit enters a high conversion gain mode.
2. The image sensor according to claim 1, wherein The gain mode switching unit includes a comparator, wherein: The first input terminal of the comparator is coupled to the floating node of the 4T pixel circuit, the second input terminal of the comparator inputs a reference voltage, and the output terminal of the comparator is coupled to the gate of the dual conversion gain tube; when the reference voltage is greater than the voltage of the floating node, the dual conversion gain tube is in an off state; when the reference voltage is not greater than the voltage of the floating node, the dual conversion gain tube is in an on state.
3. The image sensor according to claim 1 or 2, wherein: Also includes: A unidirectional conduction switch is coupled between the gate of the reset tube and the gate of the dual-conversion gain tube to block the connection between the output end of the comparator and the gate of the reset tube.
4. The image sensor according to claim 3, wherein A first end of the unidirectional conduction switch is coupled to the output end of the comparator and the gate of the dual conversion gain tube, and a second end of the unidirectional conduction switch is coupled to the gate of the reset tube in the 4T pixel circuit.
5. The image sensor according to claim 4, wherein: The unidirectional conducting switch is a switching device having PN junction switching characteristics.
6. The image sensor according to claim 5, wherein: The unidirectional conducting switch comprises: a first diode, wherein: A cathode of the first diode is coupled to the output terminal of the comparator, and an anode of the first diode is coupled to the gate of the reset tube in the 4T pixel circuit.
7. The image sensor according to claim 1 or 2, wherein: Also includes: A switch unit, wherein a first end thereof is coupled to the gate of the reset tube, a second end thereof is coupled to the gate of the dual-conversion gain tube, and a control end thereof is coupled to the gate of the reset tube; when the reset signal is input to the gate of the switch unit, a path is formed between the gate of the reset tube and the gate of the dual-conversion gain tube; when the reset signal is not input to the gate of the switch unit, a circuit is disconnected between the gate of the reset tube and the gate of the dual-conversion gain tube.
8. The image sensor according to claim 1, wherein The 4T pixel circuit includes: the reset transistor, the transmission transistor, a source follower transistor, a row selection transistor, a second diode, and a second capacitor, wherein: The reset tube has a gate inputting a reset signal, a drain coupled to a preset voltage source, and a source coupled to the drain of the dual-conversion gain tube; The transmission tube has a gate for inputting a transmission signal, a drain coupled to the source of the dual-conversion gain tube, and a source coupled to the cathode of the second diode; The anode of the second diode is grounded; The source follower transistor has a drain coupled to the voltage source, a gate coupled to the first end of the second capacitor and the drain of the transmission transistor, and a source coupled to the drain of the row selection transistor; The row selection tube has a gate inputting a row selection signal and a source coupled to the output terminal of the 4T pixel circuit; The second capacitor has a first end coupled to the drain of the transmission tube, and a second end grounded.
9. An image processing device, characterized in that The method comprises the image sensor according to any one of claims 1 to 8.