A pixel circuit, an image sensor, and a camera

Abstract

The application provides a pixel circuit, an image sensor and a camera, and relates to the technical field of pixel circuits.The pixel circuit comprises a photodiode, a first switching device, a first capacitor, a second switching device, a second capacitor, a third switching device, a third capacitor and an output module.The photo-generated electrons of the photodiode overflow to the first capacitor after the photodiode is saturated, overflow to the second capacitor after the first capacitor is saturated, and overflow to the third capacitor after the second capacitor is saturated, forming a pixel circuit with three conversion gains, and without using MOS tubes as capacitors in the pixel circuit, the stability of the capacitance value of the capacitor in the pixel circuit is improved, and the dynamic range stability of the pixel circuit is improved, thereby solving the problem of poor dynamic range stability of the pixel circuit in the prior art, because the pixel circuit uses MOS tubes as capacitors to receive the photo-generated electrons of the photodiode, and the capacitance value of the MOS tube changes with the working state of the MOS tube.

Description

Technical Field

[0001] This application belongs to the field of pixel circuit technology, specifically relating to a pixel circuit, an image sensor, and a camera. Background Technology

[0002] High dynamic range (HDR) complementary metal-oxide-semiconductor (CMOS) image sensors can adapt to scenes under different lighting conditions and often use pixel circuits with triple conversion gain (TCG).

[0003] It should be noted that the dynamic range of a pixel circuit is positively correlated with the capacitance value in the pixel circuit.

[0004] In prior art, the pixel circuit with three-conversion gain uses a MOS transistor (Metal-Oxide-Semiconductor Field-Effect Transistor) as a capacitor to receive photogenerated electrons from a photodiode.

[0005] In the process of developing this application, the inventors discovered that the prior art has at least the following problems: since the pixel circuit uses a MOS transistor as a capacitor to receive photogenerated electrons from the photodiode, and the capacitance value of the MOS transistor changes with the working state of the MOS transistor, the dynamic range stability of the pixel circuit is poor. Summary of the Invention

[0006] This application aims to provide a pixel circuit, an image sensor, and a camera, at least to solve the problem in the prior art where the pixel circuit uses a MOSFET as a capacitor to receive photogenerated electrons from a photodiode, and the capacitance value of the MOSFET changes with the operating state of the MOSFET, resulting in poor dynamic range stability of the pixel circuit.

[0007] To solve the above-mentioned technical problems, this application is implemented as follows:

[0008] In a first aspect, embodiments of this application provide a pixel circuit, including: a photodiode, a first switching device, a first capacitor, a second switching device, a second capacitor, a third switching device, a third capacitor, and an output module;

[0009] The photodiode, the first switching device, the second switching device, and the third switching device are electrically connected in sequence;

[0010] The first pin of the first capacitor is electrically connected between the first switching device and the second switching device, and the second pin of the first capacitor is grounded; the output module is electrically connected between the first switching device and the second switching device.

[0011] The first pin of the second capacitor is electrically connected between the second switching device and the third switching device, and the second pin of the second capacitor is grounded;

[0012] The first pin of the third capacitor is electrically connected to the third switching device, and the second pin of the third capacitor is grounded or used to receive externally input voltage signals.

[0013] Optionally, the first switching device, the second switching device, and the third switching device are all transistors.

[0014] Optionally, the anode of the photodiode is grounded, the first pin of the first switching device is electrically connected to the cathode of the photodiode, the second pin of the first switching device is electrically connected to the first pin of the second switching device and the first pin of the first capacitor respectively; the first pin of the second switching device is electrically connected to the first pin of the first capacitor, the second pin of the second switching device is electrically connected to the first pin of the second capacitor and the first pin of the third switching device respectively; the second pin of the third switching device is electrically connected to the first pin of the third capacitor; the control pin of the first switching device is used to receive a first control signal input from an external source, the control pin of the second switching device is used to receive a second control signal input from an external source, and the control pin of the third switching device is used to receive a third control signal input from an external source.

[0015] Optionally, the pixel circuit further includes a reset device, which is electrically connected to the third switching device.

[0016] Optionally, the reset device is a transistor; the first pin of the reset device is electrically connected to an external power supply, the second pin of the reset device is electrically connected to the third switching device, and the control pin of the reset device is used to receive an externally input reset signal.

[0017] Optionally, the output module includes a signal amplification device and a fourth switching device; the signal amplification device is electrically connected to the first switching device, the first capacitor, the second switching device, and the fourth switching device, respectively.

[0018] Optionally, both the signal amplification device and the fourth switching device are transistors; the control pin of the signal amplification device is electrically connected to the first switching device, the first capacitor, and the second switching device, respectively; the first pin of the signal amplification device is used to be electrically connected to an external power supply; the second pin of the signal amplification device is electrically connected to the first pin of the fourth switching device; the second pin of the fourth switching device is the signal output terminal of the pixel circuit; and the control pin of the fourth switching device is used to receive externally input pixel row scanning signals.

[0019] Optionally, the first capacitor, the second capacitor, and the third capacitor are all plate capacitors.

[0020] Secondly, embodiments of this application provide an image sensor, including the pixel circuit described in the first aspect.

[0021] Thirdly, embodiments of this application provide a camera, including the image sensor described in the second aspect.

[0022] In this embodiment, the pixel circuit includes a photodiode, a first switching device, a first capacitor, a second switching device, a second capacitor, a third switching device, a third capacitor, and an output module. Photogenerated electrons from the photodiode overflow to the first capacitor after the photodiode saturates, overflow to the second capacitor after the first capacitor saturates, and overflow to the third capacitor after the second capacitor saturates. When the second switching device is off, the output signal of the pixel circuit represents the amount of photogenerated electrons (charge) stored in the first capacitor. When the second switching device is on and the third switching device is off, the output current of the pixel circuit represents the amount of photogenerated electrons stored in the first and second capacitors. When both the second and third switching devices are on, the output current of the pixel circuit represents the amount of photogenerated electrons stored in the first, second, and third capacitors, thus forming a pixel circuit with three-conversion gain. Furthermore, it eliminates the need to use a MOSFET as the capacitor for receiving photogenerated electrons in the pixel circuit, improving the stability of the capacitance value in the pixel circuit and thus improving the dynamic range stability of the pixel circuit. This solves the problem in the prior art where the pixel circuit uses a MOSFET as the capacitor to receive photogenerated electrons from the photodiode, and the capacitance value of the MOSFET changes with the operating state of the MOSFET, resulting in poor dynamic range stability of the pixel circuit. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0024] Figure 1 This is a schematic diagram of a pixel circuit provided in an embodiment of this application;

[0025] Figure 2 This is a control timing diagram of a pixel circuit provided in an embodiment of this application;

[0026] Figure 3 This is a schematic diagram showing the charge quantities of the photodiode, first capacitor, second capacitor, and third capacitor in the pixel circuit provided in this application embodiment.

[0027] Figure label:

[0028] 10-Photodiode; 20-First switching device; 30-Second switching device; 40-Third switching device; 50-First capacitor; 60-Second capacitor; 70-Third capacitor; 80-Output module; 81-Signal amplification device; 82-Fourth switching device; 90-Reset device. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0031] Reference Figure 1This application provides a pixel circuit, including: a photodiode 10, a first switching device 20, a first capacitor 50, a second switching device 30, a second capacitor 60, a third switching device 40, a third capacitor 70, and an output module 80; the photodiode 10, the first switching device 20, the second switching device 30, and the third switching device 40 are electrically connected in sequence; the first pin of the first capacitor 50 is electrically connected between the first switching device 20 and the second switching device 30, and the second pin of the first capacitor 50 is grounded; the output module 80 is electrically connected between the first switching device 20 and the second switching device 30; the first pin of the second capacitor 60 is electrically connected between the second switching device 30 and the third switching device 40, and the second pin of the second capacitor 60 is grounded; the first pin of the third capacitor 70 is electrically connected to the third switching device 40, and the second pin of the third capacitor 70 is either grounded or used to receive an externally input voltage signal.

[0032] It should be noted that the photodiode 10 is used to receive external light signals and convert the electrons in the light signals into photogenerated electrons. The first capacitor 50, the second capacitor 60, and the third capacitor 70 all have stable capacitance values. The externally input voltage signal is used to adjust the charge of the third capacitor 70.

[0033] In some embodiments, the capacitance value of the third capacitor 70 is greater than the sum of the capacitance values ​​of the first capacitor 50 and the second capacitor 60.

[0034] In related technologies, pixel circuits with three-conversion gain use MOSFETs as capacitors to receive photogenerated electrons from photodiodes. It should be noted that the capacitance of a MOSFET is the capacitance between its source and drain. Because the capacitance of a MOSFET changes with its operating state—specifically, with the voltage difference between its source and gate voltages—it suffers from poor capacitance stability. Furthermore, the capacitance occupies area of ​​the MOSFET's active region, making it prone to leakage.

[0035] In this embodiment, the pixel circuit includes a photodiode 10, a first switching device 20, a first capacitor 50, a second switching device 30, a second capacitor 60, a third switching device 40, a third capacitor 70, and an output module 80. Photogenerated electrons from the photodiode 10 overflow to the first capacitor 50 after the photodiode 10 saturates; overflow to the second capacitor 60 after the first capacitor 50 saturates; and overflow to the third capacitor 70 after the second capacitor 60 saturates. When the second switching device 30 is off, the output signal of the pixel circuit represents the amount of photogenerated electrons (charge) stored in the first capacitor 50. When the second switching device 30 is on and the third switching device 40 is off, the output current of the pixel circuit represents the amount of charge stored in the first capacitor 50. The amount of photogenerated electrons stored in the second capacitor 60, when both the second switch device 30 and the third switch device 40 are turned on, the output current of the pixel circuit represents the amount of photogenerated electrons stored in the first capacitor 50, the second capacitor 60 and the third capacitor 70, thus forming a pixel circuit with three-conversion gain. Moreover, it eliminates the need to use a MOS transistor as the capacitor in the pixel circuit to receive photogenerated electrons, thereby improving the stability of the capacitance value in the pixel circuit and thus improving the dynamic range stability of the pixel circuit. This solves the problem in the prior art where the pixel circuit uses a MOS transistor as the capacitor to receive photogenerated electrons from the photodiode 10, and the capacitance value of the MOS transistor changes with the operating state of the MOS transistor, resulting in poor dynamic range stability of the pixel circuit.

[0036] Optionally, the first switching device 20, the second switching device 30, and the third switching device 40 are all transistors.

[0037] Specifically, the first switching device 20, the second switching device 30, and the third switching device 40 are NMOS transistors, namely negative channel metal oxide semiconductor transistors, and the first switching device 20, the second switching device 30, and the third switching device 40 have three working states: on, half-on, and off.

[0038] When the first switching device 20, the second switching device 30, and the third switching device 40 are all in a semi-conducting state, the photogenerated electrons of the photodiode 10 overflow to the first capacitor 50 after the photodiode 10 is saturated, overflow to the second capacitor 60 after the first capacitor 50 is saturated, and overflow to the third capacitor 70 after the second capacitor 60 is saturated.

[0039] Optionally, the anode of the photodiode 10 is grounded, the first pin of the first switching device 20 is electrically connected to the cathode of the photodiode 10, the second pin of the first switching device 20 is electrically connected to the first pin of the second switching device 30 and the first pin of the first capacitor 50, respectively; the first pin of the second switching device 30 is electrically connected to the first pin of the first capacitor 50, the second pin of the second switching device 30 is electrically connected to the first pin of the second capacitor 60 and the first pin of the third switching device 40, respectively; the second pin of the third switching device 40 is electrically connected to the first pin of the third capacitor 70; the control pin of the first switching device 20 is used to receive a first control signal input from an external source, the control pin of the second switching device 30 is used to receive a second control signal input from an external source, and the control pin of the third switching device 40 is used to receive a third control signal input from an external source.

[0040] Specifically, the first switching device 20, the second switching device 30, and the third switching device 40 are NMOS transistors. The source of the first switching device 20 is electrically connected to the cathode of the photodiode 10, and the drain of the first switching device 20 is electrically connected to the source of the second switching device 30 and the first pin of the first capacitor 50, respectively. The source of the second switching device 30 is electrically connected to the first pin of the first capacitor 50, and the drain of the second switching device 30 is electrically connected to the first pin of the second capacitor 60 and the source of the third switching device 40, respectively. The drain of the third switching device 40 is electrically connected to the first pin of the third capacitor 70. The gate of the first switching device 20 is used to receive a first control signal input from the outside, the gate of the second switching device 30 is used to receive a second control signal input from the outside, and the gate of the third switching device 40 is used to receive a third control signal input from the outside.

[0041] It should be noted that when the voltage value of the first control signal is the first voltage value, the first switching device 20 is turned off; when the voltage value of the first control signal is the second voltage value, the first switching device 20 is semi-conducting; and when the voltage value of the first control signal is the third voltage value, the first switching device 20 is turned on. The first voltage value is less than the second voltage value, and the second voltage value is less than the third voltage value.

[0042] Similarly, when the voltage value of the second control signal is the first voltage value, the second switching device 30 is off; when the voltage value of the second control signal is the second voltage value, the second switching device 30 is half-conducting; when the voltage value of the second control signal is the third voltage value, the second switching device 30 is on. When the voltage value of the third control signal is the first voltage value, the third switching device 40 is off; when the voltage value of the third control signal is the second voltage value, the third switching device 40 is half-conducting; when the voltage value of the third control signal is the third voltage value, the third switching device 40 is on.

[0043] Optionally, the pixel circuit further includes a reset device 90, which is electrically connected to the third switching device 40.

[0044] It should be noted that the reset device 90 is used to reset the first capacitor 50, the second capacitor 60, and the third capacitor 70, that is, to consume the photogenerated electrons stored in the first capacitor 50, the second capacitor 60, and the third capacitor 70, so that the charge of the first capacitor 50, the second capacitor 60, and the third capacitor 70 is zero.

[0045] Optionally, the reset device 90 is a transistor; the first pin of the reset device 90 is used to be electrically connected to an external power supply, the second pin of the reset device 90 is electrically connected to the third switching device 40, and the control pin of the reset device 90 is used to receive an externally input reset signal.

[0046] Specifically, the reset device 90 is an NMOS transistor. The drain of the reset device 90 is electrically connected to an external power supply, the source of the reset device 90 is electrically connected to the drain of the third switching device 40, and the gate of the reset device 90 is used to receive an externally input reset signal.

[0047] It should be noted that when the reset signal is high, the reset device 90 is turned on, and when the reset signal is low, the reset device 90 is turned off. When the reset device 90, the first switching device 20, the second switching device 30, and the third switching device 40 are all turned on, the photogenerated electrons in the photodiode 10, the first capacitor 50, the second capacitor 60, and the third capacitor 70 all flow to the positive terminal of the power supply electrically connected to the reset device 90, making the charge in the photodiode 10, the first capacitor 50, the second capacitor 60, and the third capacitor 70 zero, thereby resetting the photodiode 10, the first capacitor 50, the second capacitor 60, and the third capacitor 70.

[0048] Optionally, the output module 80 includes a signal amplification device 81 and a fourth switching device 82; the signal amplification device 81 is electrically connected to the first switching device 20, the first capacitor 50, the second switching device 30, and the fourth switching device 82, respectively.

[0049] It should be noted that when the second switching device 30 is off, the signal amplifier device 81 is used to amplify the current generated by the first capacitor 50; when the second switching device 30 is on and the third switching device 40 is off, the signal amplifier device 81 is used to amplify the current generated by the first capacitor 50 and the second capacitor 60 together; and when both the second switching device 30 and the third switching device 40 are on, the signal amplifier device 81 is used to amplify the current generated by the first capacitor 50, the second capacitor 60 and the third capacitor 70 together.

[0050] When the fourth switching device 82 is turned on, the pixel circuit outputs a pixel signal; when the fourth switching device 82 is turned off, the pixel circuit stops outputting a pixel signal. The pixel signal is the output signal of the pixel circuit.

[0051] Optionally, both the signal amplification device 81 and the fourth switching device 82 are transistors; the control pin of the signal amplification device 81 is electrically connected to the first switching device 20, the first capacitor 50, and the second switching device 30, respectively; the first pin of the signal amplification device 81 is used to be electrically connected to an external power supply; the second pin of the signal amplification device 81 is electrically connected to the first pin of the fourth switching device 82; the second pin of the fourth switching device 82 is the signal output terminal of the pixel circuit; and the control pin of the fourth switching device 82 is used to receive externally input pixel row scanning signals.

[0052] Specifically, both the signal amplification device 81 and the fourth switching device 82 are NMOS transistors. The gate of the signal amplification device 81 is electrically connected to the drain of the first switching device 20, the first pin of the first capacitor 50, and the source of the second switching device 30, respectively. The drain of the signal amplification device 81 is used to connect to an external power supply, and the source of the signal amplification device 81 is electrically connected to the drain of the fourth switching device 82. The source of the fourth switching device 82 is the signal output terminal of the pixel circuit, and the gate of the fourth switching device 82 is used to receive the externally input pixel row scanning signal.

[0053] It should be noted that when the pixel row scan signal is high, the source of the fourth switching device 82 outputs a pixel signal, and when the pixel row scan signal is low, the source of the fourth switching device 82 stops outputting a pixel signal.

[0054] Optionally, the first capacitor 50, the second capacitor 60, and the third capacitor 70 are all plate capacitors.

[0055] It should be noted that a plate capacitor consists of two metal plates with opposite charges, separated by an insulator. The capacitance value of a plate capacitor is stable.

[0056] Figure 2 This is a control timing diagram of a pixel circuit provided in an embodiment of this application. Waveform curve A is the timing waveform curve of the pixel row scanning signal, waveform curve B is the timing waveform curve of the first control signal, waveform curve C is the timing waveform curve of the reset signal, waveform curve D is the timing waveform curve of the third control signal, waveform curve E is the timing waveform curve of the second control signal, and waveform curve F is the timing waveform curve of the pixel signal output from the signal output terminal of the pixel circuit.

[0057] At time t0, the pixel row scan signal is low, the voltage value of the first control signal is the second voltage value, the voltage value of the reset signal is the second voltage value, the voltage value of the third control signal is the second voltage value, the voltage value of the second control signal is the second voltage value, and the pixel signal is low.

[0058] During time period T1, the reset device 90, the first switching device 20, the second switching device 30, and the third switching device 40 are all in a semi-conducting state. After the photodiode 10 is saturated, the photogenerated electrons overflow to the first capacitor 50, then to the second capacitor 60, then to the third capacitor 70, and finally to the positive terminal of the external power supply electrically connected to the reset device 90.

[0059] At time t1, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the first voltage value, the voltage value of the second control signal is the third voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50 and the second capacitor 60.

[0060] At time t2, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the first voltage value, the voltage value of the second control signal is the first voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50.

[0061] At time t3, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the first voltage value, the voltage value of the second control signal is the first voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50.

[0062] At time t4, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the first voltage value, the voltage value of the second control signal is the third voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50 and the second capacitor 60.

[0063] At time t5, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the third voltage value, the voltage value of the second control signal is the third voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50, the second capacitor 60, and the third capacitor 70.

[0064] At time t6, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the third voltage value, the voltage value of the second control signal is the third voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50, the second capacitor 60, and the third capacitor 70.

[0065] To increase the dynamic range of the pixel circuit, an exposure process with a time interval T2 (photodiode 10 collects the light signal) is added, where time interval T1 is 60 to 100 times longer than time interval T2, which can improve the dynamic range by 35 dB to 40 dB. The exposure process in time interval T1 meets the requirements for LED flicker mitigation (LFM).

[0066] During time period T2, the reset device 90, the first switching device 20, the second switching device 30, and the third switching device 40 are all in a semi-conducting state. After the photodiode 10 is saturated, the photogenerated electrons overflow to the first capacitor 50, then to the second capacitor 60, then to the third capacitor 70, and finally to the positive terminal of the external power supply electrically connected to the reset device 90.

[0067] At time t7, the pixel row scanning signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the first voltage value, the voltage value of the second control signal is the third voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50 and the second capacitor 60.

[0068] At time t8, the pixel row scan signal is high, the voltage value of the first control signal is the first voltage value, the voltage value of the reset signal is the first voltage value, the voltage value of the third control signal is the third voltage value, the voltage value of the second control signal is the third voltage value, the pixel signal is high, and the pixel signal represents the amount of photogenerated electrons stored in the first capacitor 50, the second capacitor 60, and the third capacitor 70.

[0069] In the above process, refer to Figure 3 In (a), at time t0, the charge Q1 of photodiode 10, the charge Q2 of the first capacitor 50, the charge Q3 of the second capacitor 60, and the charge Q4 of the third capacitor 70 are all 0; (Refer to...) Figure 3 In (b), during time period T1, the charge Q1 of photodiode 10, the charge Q2 of the first capacitor 50, and the charge Q3 of the second capacitor 60 are all saturated and overflow, while the charge Q4 of the third capacitor 70 is not saturated; (Refer to...) Figure 3 (c) At time t1, the charge Q1 of photodiode 10 is not saturated, the total charge Q2+Q3 of the first capacitor 50 and the second capacitor 60 is not saturated, and the charge Q4 of the third capacitor 70 is not saturated; refer to Figure 3 At time t2, the charge Q1 of photodiode 10 is not saturated, the charge Q2 of the first capacitor 50 is not saturated, the charge Q3 of the second capacitor 60 is not saturated, and the charge Q4 of the third capacitor 70 is not saturated; (refer to...) Figure 3 (e) At time t3, the charge Q1 of photodiode 10 is not saturated, the charge Q2 of the first capacitor 50 is saturated, the charge Q3 of the second capacitor 60 is not saturated, and the charge Q4 of the third capacitor 70 is not saturated; refer to Figure 3 At time t4, the charge Q1 of photodiode 10 is not saturated, the total charge Q2 of first capacitor 50 and Q3 of second capacitor 60 is saturated (Q2 + Q3), and the charge Q4 of third capacitor 70 is not saturated; (Refer to...) Figure 3 At time t5, the charge Q1 of photodiode 10 is 0, and the total charge Q2+Q3+Q4 of the first capacitor 50, the second capacitor 60, and the third capacitor 70 is not saturated; (refer to...) Figure 3 At time t6, the charge Q1 of photodiode 10 is 0, and the total charge Q2+Q3+Q4 of the first capacitor 50, the second capacitor 60, and the third capacitor 70 is 0.

[0070] In summary, in this embodiment, the pixel circuit includes a photodiode 10, a first switching device 20, a first capacitor 50, a second switching device 30, a second capacitor 60, a third switching device 40, a third capacitor 70, and an output module 80. After the photodiode 10 is saturated, the photogenerated electrons overflow to the first capacitor 50, then to the second capacitor 60, and finally to the third capacitor 70. When the second switching device 30 is off, the output signal of the pixel circuit represents the amount of photogenerated electrons (charge) stored in the first capacitor 50. When the second switching device 30 is on and the third switching device 40 is off, the output current of the pixel circuit represents the amount of photogenerated electrons (charge) stored in the first capacitor 50. The amount of photogenerated electrons stored in the first capacitor 50 and the second capacitor 60, when both the second switching device 30 and the third switching device 40 are turned on, the output current of the pixel circuit represents the amount of photogenerated electrons stored in the first capacitor 50, the second capacitor 60 and the third capacitor 70, thus forming a pixel circuit with three conversion gains. Moreover, it eliminates the need to use a MOSFET as a capacitor to receive photogenerated electrons in the pixel circuit, improving the stability of the capacitance value in the pixel circuit, and thus improving the dynamic range stability of the pixel circuit. This solves the problem in the prior art where the pixel circuit uses a MOSFET as a capacitor to receive photogenerated electrons from the photodiode 10, and the capacitance value of the MOSFET changes with the operating state of the MOSFET, resulting in poor dynamic range stability of the pixel circuit.

[0071] Secondly, embodiments of this application provide an image sensor, including the aforementioned pixel circuit.

[0072] In some embodiments, the image sensor is a CMOS image sensor.

[0073] The specific implementation process of the pixel circuit in the image sensor is similar to that of the aforementioned pixel circuit, and will not be repeated here.

[0074] Since the pixel circuit of the present application embodiment has better dynamic range stability compared with the pixel circuit in the related art, the image sensor using the pixel circuit of the present application embodiment has better dynamic range stability compared with the image sensor using the pixel circuit in the related art.

[0075] Thirdly, embodiments of this application provide a camera, including the aforementioned image sensor.

[0076] The implementation process of the pixel circuit in the image sensor of the camera is similar to that of the aforementioned pixel circuit, and will not be repeated here.

[0077] Since the image sensor using the pixel circuit of the present application has better dynamic range stability compared to the image sensor using the pixel circuit in the related art, the camera using the image sensor of the present application has better dynamic range stability compared to the camera using the image sensor in the related art.

[0078] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0079] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A pixel circuit, characterized in that, include: A photodiode, a first switching device, a first capacitor, a second switching device, a second capacitor, a third switching device, a third capacitor, and an output module; The photodiode, the first switching device, the second switching device, and the third switching device are electrically connected in sequence. The first switching device, the second switching device, and the third switching device have three operating states: on, half-on, and off. The operating state is determined based on the voltage values ​​of the control signals received by the first switching device, the second switching device, and the third switching device, respectively. The voltage value corresponding to the half-on state is greater than the voltage value corresponding to the off state and less than the voltage value corresponding to the on state. When the first switching device, the second switching device, and the third switching device are all in the half-on state, the photogenerated electrons of the photodiode overflow to the first capacitor after the photodiode is saturated, overflow to the second capacitor after the first capacitor is saturated, and overflow to the third capacitor after the second capacitor is saturated. The first pin of the first capacitor is electrically connected between the first switching device and the second switching device, and the second pin of the first capacitor is grounded; the output module is electrically connected between the first switching device and the second switching device. The first pin of the second capacitor is electrically connected between the second switching device and the third switching device, and the second pin of the second capacitor is grounded; The first pin of the third capacitor is electrically connected to the third switching device, and the second pin of the third capacitor is grounded or used to receive an externally input voltage signal; the first capacitor, the second capacitor, and the third capacitor are all plate capacitors; the capacitance value of the third capacitor is greater than the sum of the capacitance values ​​of the first capacitor and the second capacitor.

2. The pixel circuit according to claim 1, characterized in that, The first switching device, the second switching device, and the third switching device are all transistors.

3. The pixel circuit according to claim 2, characterized in that, The anode of the photodiode is grounded, the first pin of the first switching device is electrically connected to the cathode of the photodiode, and the second pin of the first switching device is electrically connected to the first pin of the second switching device and the first pin of the first capacitor, respectively. The first pin of the second switching device is electrically connected to the first pin of the first capacitor, and the second pin of the second switching device is electrically connected to the first pin of the second capacitor and the first pin of the third switching device, respectively. The second pin of the third switching device is electrically connected to the first pin of the third capacitor; The control pin of the first switching device is used to receive a first control signal input from an external source; the control pin of the second switching device is used to receive a second control signal input from an external source; and the control pin of the third switching device is used to receive a third control signal input from an external source.

4. The pixel circuit according to claim 1, characterized in that, The pixel circuit also includes a reset device, which is electrically connected to the third switching device.

5. The pixel circuit according to claim 4, characterized in that, The reset device is a transistor; The first pin of the reset device is used to be electrically connected to an external power supply, the second pin of the reset device is electrically connected to the third switching device, and the control pin of the reset device is used to receive an externally input reset signal.

6. The pixel circuit according to claim 1, characterized in that, The output module includes a signal amplification device and a fourth switching device; The signal amplification device is electrically connected to the first switching device, the first capacitor, the second switching device, and the fourth switching device, respectively.

7. The pixel circuit according to claim 6, characterized in that, Both the signal amplification device and the fourth switching device are transistors; The control pins of the signal amplification device are electrically connected to the first switching device, the first capacitor, and the second switching device, respectively. The first pin of the signal amplification device is used to be electrically connected to an external power supply, and the second pin of the signal amplification device is electrically connected to the first pin of the fourth switching device. The second pin of the fourth switching device is the signal output terminal of the pixel circuit, and the control pin of the fourth switching device is used to receive externally input pixel row scanning signals.

8. An image sensor, characterized in that, Includes the pixel circuit as described in any one of claims 1 to 7.

9. A camera, characterized in that, Including the image sensor as described in claim 8.

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