CN111263089B

CN111263089B - Pixel, image sensor and electronic device

Info

Publication number: CN111263089B
Application number: CN202010374086.XA
Authority: CN
Inventors: 林奇青; 杨富强
Original assignee: Shenzhen Goodix Technology Co Ltd
Current assignee: Shenzhen Goodix Technology Co Ltd
Priority date: 2020-05-06
Filing date: 2020-05-06
Publication date: 2020-10-16
Anticipated expiration: 2040-05-06
Also published as: CN111263089A

Abstract

A pixel (P11) includes an optical sensor (PD) and a pixel circuit (200). The optical sensor has a cathode and an anode, the anode being coupled to a first voltage source (V1). The optical sensor is used for sensing an optical Signal (SL) in a sensing phase and generating a Sensing Signal (SS) at a floating diffusion region (FD). The pixel circuit is arranged on the non-epitaxial substrate. The pixel circuit is coupled to the cathode of the optical sensor and a second voltage source (V2). Wherein the pixel circuit comprises a reset circuit (202) and an operational amplifier (OP). The reset circuit is coupled between the cathode and the floating diffusion region, wherein the reset circuit is used for resetting the sensing signal of the floating diffusion region in a reset stage. The operational amplifier has a positive terminal (+), a negative terminal (-) and an output terminal, wherein the positive terminal is coupled to the second voltage source (V2), the negative terminal is coupled to the cathode, and the output terminal is coupled to the floating diffusion region. The operational amplifier is used for fixing the voltage difference between the cathode and the anode of the optical sensor. An optical sensor (PD) is disposed over the pixel circuit (200).

Description

Pixel, image sensor and electronic device

Technical Field

The present disclosure relates to pixels, and more particularly, to a pixel including a pixel circuit disposed on a non-epitaxial substrate, and related image sensor and electronic device.

Background

Increasing the sensing area of the optical sensor in a pixel without increasing the area of the pixel relatively reduces the area available for pixel circuitry other than the optical sensor. In addition, the optical sensor has the problem of linearity of a sensing signal due to the change of the cross voltage in the sensing stage. Furthermore, the current pixels are generally implemented by using an epitaxial substrate, which is relatively high in cost, and if the pixels implemented by using a non-epitaxial substrate are implemented, the cost can be far lower than that of the pixels implemented by using an epitaxial substrate, but the pixels implemented by using a non-epitaxial substrate have the problem of increased leakage current. Therefore, the structure of the existing pixel needs to be further improved to overcome the above problems.

Disclosure of Invention

An objective of the present application is to disclose a pixel, a related image sensor and an electronic device, so as to solve the above problems.

An embodiment of the present application discloses a pixel including an optical sensor and a pixel circuit. The optical sensor has a cathode and an anode, and the anode is coupled to a first voltage source. The optical sensor is used for sensing an optical signal in a sensing stage and generating a sensing signal in the floating diffusion region. The pixel circuit is arranged on the non-epitaxial substrate. The pixel circuit is coupled between the cathode of the optical sensor, the second voltage source and the floating diffusion region. The pixel circuit includes a reset circuit and an operational amplifier. The reset circuit is coupled between the cathode of the optical sensor and the floating diffusion region. In the reset phase, the reset circuit is used for resetting the sensing signal on the floating diffusion region. The operational amplifier has a positive terminal, a negative terminal and an output terminal. The positive terminal is coupled to a second voltage source, the negative terminal is coupled to the cathode of the optical sensor, and the output terminal is coupled to the floating diffusion region. The operational amplifier is used for fixing the voltage difference between the cathode and the anode of the optical sensor. The optical sensor is disposed on the pixel circuit.

An embodiment of the present application discloses an image sensor including a pixel array. The pixel array includes a plurality of the pixels.

An embodiment of the application discloses an electronic device, which comprises an image sensor and a display screen.

Specifically, the pixel, the related image sensor and the electronic device disclosed by the application can increase the light sensing area, improve the filling factor, reduce the cost and ensure the performance of the pixel, and further, the pixel disclosed by the application does not increase the leakage current of a circuit besides improving the linearity of the optical sensor.

Drawings

Fig. 1 is a schematic diagram of an embodiment of an image sensor of the present application.

Fig. 2 is a schematic diagram of an embodiment of a pixel of the present application.

Fig. 3 is a schematic diagram of another embodiment of a pixel of the present application.

Fig. 4 is a timing diagram illustrating operation of the pixel.

Fig. 5 is a schematic diagram of an embodiment of an electronic device according to the present application.

Detailed Description

In a pixel conventionally implemented by using an epitaxial substrate, an optical sensor and a pixel circuit except the optical sensor are all manufactured on the same plane. That is, the optical sensor and the pixel circuit share a fixed area. Increasing the area of the optical sensor without changing the area of the pixel tends to reduce the area available for the pixel circuitry. The pixel disclosed by the application is realized by utilizing a layered structure, and is different from the traditional pixel in that the optical sensor and the pixel circuit in the pixel are arranged on different planes, so that the area of the photosensitive area of the optical sensor can not be limited by the area required by the pixel circuit, and the area of the photosensitive area of the optical sensor is increased, thereby increasing the filling factor. Here, the fill factor is defined as a ratio of an area of a photosensitive region of the optical sensor to a total area of the pixels, and when the total area of the pixels is not changed, increasing the area of the photosensitive region of the optical sensor increases the fill factor. In addition, the pixel of the present application uses a novel pixel circuit to control the voltage across the cathode and the anode of the optical sensor when sensing the optical signal, thereby increasing the linearity of the sensing signal. In addition, in order to provide the optical sensor with good electronic characteristics, the conventional pixel is implemented using an epitaxial substrate. However, the cost of the non-epitaxial substrate is lower than that of the epitaxial substrate, and the pixel of the present application replaces the epitaxial substrate with the non-epitaxial substrate to implement a pixel circuit other than the optical sensor, thereby reducing the manufacturing cost and changing the circuit structure to overcome the physical disadvantages of the non-epitaxial substrate (e.g., higher leakage current). The following describes the pixel, the related image sensor and the electronic device in detail with reference to a plurality of embodiments and drawings.

Fig. 1 is a schematic diagram of an embodiment of an image sensor 100 of the present application. The image sensor 100 includes a pixel array 101 and a read circuit structure 103. The pixel array 101 includes an array of at least one pixel, only the pixels P11, P21, P12, P22 are illustrated in fig. 1, and actually the pixel array 101 includes, for example, n rows by m columns of the pixel array 101, where n and m are integers greater than 0. The reading circuit structure 103 includes a plurality of columns of reading circuits, such as the reading circuits 103_1, 103_2, etc., which are respectively coupled to the plurality of columns of pixels in the pixel array 101.

The operation of the image sensor 100 has a reset phase, a sensing phase, and a readout phase. Each pixel in the pixel array 101 resets the sensing signal in the reset phase, regenerates the sensing signal in the sensing phase, and outputs the sensing signal to the corresponding reading circuit in the reading circuit structure 103 in the readout phase. In this embodiment, the pixel array 101 can output a plurality of sensing signals corresponding to an entire row of pixels to corresponding reading circuits in the reading circuit structure 103 row by row. For example, the charges of the pixel P11 and the pixel P12 are output to the read circuits 103_1 and 103_2 in the read circuit structure 103 through the bit line BL1 and the bit line BL2, respectively, and then the charges of the pixel P21 and the pixel P22 are output to the read circuits 103_1 and 103_2 in the read circuit structure 103 through the bit line BL1 and the bit line BL2, respectively. The read circuits 103_1 and 103_2 output read results SO1 and SO2, respectively.

Fig. 2 is a schematic diagram of an embodiment of a pixel P11 of the present application. The pixel P11 is coupled to the readout circuit 103_1, wherein the pixel P11 includes the optical sensor PD and the pixel circuit 200. In the sensing phase, when the light signal SL is irradiated to the pixel P11, the optical sensor PD is used to convert the light signal SL into electric charges, the pixel circuit 200 accumulates the electric charges and induces the sensing signal SS in the floating diffusion FD (also referred to as a sensing node), and then in the readout phase, the output signal SO is generated to the readout circuit 103_1 according to the sensing signal SS and the selection signal SE.

In the pixel P11, the optical sensor PD is disposed on a different plane from the pixel circuit 200. For example, the pixel circuit 200 is disposed on a non-epitaxial substrate and the optical sensor PD1 is disposed above the pixel circuit 200. The present application does not limit how to implement the optical sensor PD, for example, the optical sensor PD may be implemented by a thin film photodiode or a Complementary Metal-Oxide-Semiconductor (CMOS) photodiode. In some embodiments, the optical sensor PD overlies the pixel circuit 200, and the optical signal SL encounters the optical sensor PD first, as viewed from the direction in which the optical signal SL is incident. As such, even if the pixel circuit 200 and the optical sensor PD overlap, the pixel circuit 200 does not block the optical sensor PD from receiving the light signal SL. Therefore, without increasing the area of the pixel P11, the optical sensor PD can increase the photosensitive area without occupying the area of the pixel circuit 200 below, thereby increasing the fill factor of the pixel P11.

In the embodiment of fig. 2, the optical sensor PD is a photodiode, which includes a cathode and an anode. As shown in fig. 2, the cathode and the anode of the optical sensor PD are connected across the pixel circuit 200, and the anode is further coupled to the voltage source V1.

The pixel circuit 200 is coupled between the optical sensor PD and the readout circuit 103_ 1. The pixel circuit 200 includes an operational amplifier OP, a capacitor C, a reset circuit 202 and a pixel readout circuit 204, wherein the operational amplifier OP, the capacitor C and the reset circuit 202 are respectively coupled between the optical sensor PD and the floating diffusion FD, and the pixel readout circuit 204 is coupled between the floating diffusion FD and the readout circuit 103_ 1.

In the reset phase, the reset circuit 202 is used to reset the sensing signal SS on the floating diffusion FD according to at least one control signal. In the sensing phase, the operational amplifier OP is used to control the voltage difference between the cathode and the anode of the optical sensor PD, and the capacitor C is used to accumulate the charges generated by the optical sensor PD sensing the optical signal SL, and generate the sensing signal SS at the floating diffusion FD. In the readout stage, the pixel readout circuit 204 is configured to generate an output signal SO to the readout circuit 103_1 according to the sense signal SS and the select signal SE.

In the present embodiment, the reset circuit 202 includes a transistor T1, a transistor T2, and a transistor T3. The gates of the transistors T1, T2, and T3 respectively receive the control signals CS1, CS2, and CS3, so that the conduction and non-conduction of the transistors T1, T2, and T3 can be controlled by the control signals CS1, CS2, and CS3, respectively. As shown in fig. 2, the drain of the transistor T1 is coupled to the cathode of the optical sensor PD, the first terminal of the capacitor C and the negative terminal (-) of the operational amplifier OP, the source of the transistor T1 is coupled to the drain of the transistor T2 and the drain of the transistor T3, the source of the transistor T2 is coupled to the second terminal of the capacitor C, the output terminal of the operational amplifier OP and the floating diffusion FD, and the source of the transistor T3 is coupled to the base of the transistor T3, the positive terminal (+), the anode of the operational amplifier OP, the anode of the optical sensor PD and the voltage source V1.

The pixel readout circuit 204 includes a transistor T4 and a source follower transistor SF. The gate of the transistor T4 receives the select signal SE, so that the conduction and non-conduction of the transistor T4 can be controlled by the select signal SE. As shown in FIG. 2, the source of the source follower transistor SF is coupled to the drain of the transistor T4, and the drain of the source follower transistor SF and the source of the transistor T4 are coupled to the read circuit structure 103_ 1.

In this embodiment, the transistors T1, T2 and T3 are P-type transistors, and the transistor T4 and the source follower transistor SF are N-type transistors. However, the implementation of the transistor is not limited thereto.

Please refer to fig. 4 together. In the reset phase, the control signal CS1 and the control signal CS2 have the system low voltage, and the control signal CS3 has the system high voltage. The transistor T1 is conductive with the transistor T2 and the transistor T3 is non-conductive. In this configuration, the cathode of the optical sensor PD is electrically connected to the floating diffusion FD. The sensing signal SS is reset by turning on the optical sensor PD from the floating diffusion FD so that the cathode of the optical sensor PD and the floating diffusion FD have the same potential.

In the sensing phase, the control signal CS1 and the control signal CS2 have the system high level, and the control signal CS3 has the system low level. The transistor T1 and the transistor T2 are non-conductive, and the transistor T3 is conductive. With this configuration, an open circuit is formed between the floating diffusion FD and the cathode of the optical sensor PD. After the optical sensor PD senses the optical signal SL, the optical sensor PD senses the generated charges accumulated at the first end of the capacitor C and induces the sensing signal SS at the second end of the capacitor C. In addition, the operational amplifier OP has a characteristic of an imaginary short circuit between the positive terminal and the negative terminal, and since the optical sensor PD is connected across the positive terminal and the negative terminal of the operational amplifier OP, the cross voltage between the cathode and the anode of the optical sensor PD is controlled to be about zero by the operational amplifier OP. When the voltage across the optical sensor PD is controlled to be about zero, the optical sensor PD is operated in the photovoltaic mode of the photodiode, and the linearity of the optical sensor PD is higher than that in other operation modes. The pixel P11 provided herein operates with a higher linearity of the optical sensor PD than conventional pixels that operate the optical sensor PD in the photoconductive mode. Here, the photovoltaic mode is defined when the cross-bias of the optical sensor PD is operated at zero, and the photoconductive mode is defined when the cross-bias of the optical sensor PD is operated at a negative bias, that is, the potential of the cathode is higher than the potential of the anode.

When the optical sensor PD is operated in the photovoltaic mode, the dark current of the optical sensor PD is minimal, when the optical sensor PD is relatively sensitive to other currents in the pixel circuit 200. For example, if a leakage current having a magnitude corresponding to a dark current of the optical sensor PD flows to the optical sensor PD in the pixel circuit 200, the operation of the optical sensor PD is affected. In other words, with this configuration, the tolerance of the optical sensor PD to the leakage current of the pixel circuit 200 decreases. Thus. The non-conduction of the transistors T1 and T2 is also used to reduce the leakage current flowing to the optical sensor PD. Furthermore, the turning on of the transistor T3 transmits the voltage of the voltage source V1 to the source of the transistor T1, and transmits the voltage of the voltage source V1 from the positive terminal to the negative terminal and from the negative terminal to the drain of the transistor T1 through the virtual short circuit characteristic of the operational amplifier OP, in this case, the source and drain of the transistor T1 have the same potential, so that the transistor T1 does not have the leakage current flowing through the channel of the transistor T1 during the sensing phase.

In the present embodiment, the pixel circuit 200 is disposed on a non-epitaxial substrate, i.e., the components of the pixel circuit 200 are not implemented in any epitaxial layer structure. The transistor realized by using the non-epitaxial substrate has the advantage that the leakage current from the base to the source/drain of the transistor in a non-conducting state is higher because the lattice arrangement of the non-epitaxial substrate material per se is irregular compared with that of the epitaxial substrate material. In some embodiments, the source of the transistor T3 is further coupled to the voltage source V1, the positive terminal of the operational amplifier OP and the base of the transistor T1, and the voltage of the voltage source V1 at the positive terminal is equivalent to the negative terminal by the virtual short circuit characteristic of the operational amplifier OP, wherein the negative terminal is coupled to the drain of the transistor T1, so that the drain of the transistor T1 has the same potential as the voltage of the voltage source V1. In such a connection relationship, since the base and drain potentials of the transistor T1 are equal, there is no voltage difference from the base to the drain of the transistor T1, and thus the leakage current flowing from the base to the drain of the transistor T1 approaches zero. With such an arrangement, the control of the leakage current flowing to the optical sensor PD by the pixel circuit 200 in the sensing phase can be enhanced.

In the present embodiment, the reset circuit 202 makes the transistors T1 and T2 non-conductive and the transistor T3 conductive during the sensing phase to prevent the leakage current from flowing to the optical sensor PD. However, when the reset circuit 202 uses a larger number of transistors to prevent the leakage current from flowing to the optical sensor PD, it has a better effect, that is, the leakage current is smaller. In other words, for suppression of the leakage current, the more transistors used, the better the effect. For ease of illustration, the embodiment is exemplified by only three transistors T1, T2 and T3, but the application does not limit the number of transistors in the reset circuit 202, i.e. the number of transistors may be more than three or less than three. For example, in one embodiment, the reset circuit 202 only uses the transistor T1 and the transistor T2 to prevent leakage current from flowing to the optical sensor PD. Also or for example, in other embodiments, the reset circuit 202 prevents leakage current from flowing to the optical sensor PD using only the transistor T1. In other examples, the reset circuit 202 uses an additional transistor to prevent leakage current from flowing to the optical sensor PD. The drain of the additional transistor is coupled to the source of the transistor T2, the source of the additional transistor is coupled to the second terminal of the capacitor C, the output terminal and the floating diffusion FD, and the gate of the additional transistor receives an additional control signal.

From the reset phase to the sensing phase, the transistors T1 and T2 are switched from a conductive state to a non-conductive state, and the transistor T3 is switched from a non-conductive state to a conductive state. Referring to fig. 4 again, from the reset phase to the sensing phase, the control signal CS1, the control signal CS2 and the control signal CS3 sequentially change from the system low level to the system high level or from the system high level to the system low level, that is, the transistor T1, the transistor T2 and the transistor T3 sequentially switch to a conducting state or a non-conducting state. From the potentials of the control signal CS1, the control signal CS2, and the control signal CS3, at the beginning of the reset phase, the control signal CS1, the control signal CS2, and the control signal CS3 change from the system high potential to the system low potential or from the system high potential to the system low potential at the same time. Before the sensing period begins, the control signal CS1 changes from the system low voltage to the system high voltage, after a time interval, the control signal CS2 changes from the system low voltage to the system high voltage, and after a time interval, the control signal CS3 changes from the system high voltage to the system low voltage. Therefore, in the reset phase, the on time of the transistor T2 is longer than the on time of the transistor T1, and the off time of the transistor T3 is longer than the on time of the transistor T2.

In the read-out phase, the select signal SE has a system high potential. The transistor T4 is turned on. In this configuration, the source follower transistor SF outputs the sensing signal SS received at the gate as the output signal SO, which is transmitted to the read circuit 103_1 through the turned-on transistor T4.

FIG. 3 is a diagram of another embodiment of a pixel P11. Pixel P11 in FIG. 3 is similar to pixel P11 in FIG. 2, and therefore like numbers and associated descriptions are not repeated here. In comparison with the embodiment of fig. 2, the positive terminal of the operational amplifier OP of the pixel P11 of fig. 3 and the anode of the optical sensor PD are not coupled to each other, specifically, in comparison with fig. 2, the positive terminal of the operational amplifier OP and the source of the transistor T3 of fig. 3 are coupled to the voltage source V2 instead.

In the present embodiment, also because of the characteristic of the virtual short of the operational amplifier OP, the voltage difference between the cathode and the anode of the optical sensor PD is equal to the voltage difference between the voltage of the voltage source V1 and the voltage of the voltage source V2. When the voltage of the voltage source V1 is not equal to the voltage of the voltage source V2, the operation of the optical sensor PD deviates from the photovoltaic mode. In this embodiment, the voltage of the voltage source V2 is greater than the voltage of the voltage source V1, that is, the optical sensor PD operates in the light guide mode. The quantum efficiency of the optical sensor PD is related to the voltage difference between the cathode and the anode, that is, the voltage difference between the voltage of the voltage source V2 and the voltage of the voltage source V1, and the quantum efficiency of the optical sensor PD is higher when the voltage of the voltage source V2 is more than the voltage of the voltage source V1. When the quantum efficiency of the optical sensor PD is higher, the optical sensor PD can generate more charges to induce a larger sensing signal SS for the same optical signal SL. However, the dark current of the optical sensor PD increases as the voltage of the voltage source V2 is greater than the voltage of the voltage source V1. When the dark current increases, the offset (offset) of the sensing signal SS caused by the dark current also increases, thereby reducing the dynamic range of the sensing signal SS. Therefore, in the present embodiment, the voltage of the voltage source V1 and the voltage of the voltage source V2 are adjustable, that is, the voltage difference between the cathode and the anode of the optical sensor PD can be optimized according to the quantum efficiency of the optical sensor PD and the actual condition of the dark current.

In some embodiments, the voltage of the voltage source V2 is a system reference potential, which has a fixed value, such as ground potential. The pixel P11 adjusts only the voltage of the voltage source V1 to control the quantum efficiency and the dark current of the optical sensor PD.

By configuring the pixel circuit 200 and the optical sensor PD in different layers, that is, the pixel circuit 200 is on a semiconductor substrate, and the optical sensor PD is on the pixel circuit 200, the photosensitive area of the pixel P11 per unit area is increased, that is, the fill factor is increased, the linearity of the optical sensor PD is increased without increasing the leakage current, and the novel pixel circuit 200 is realized by using a non-epitaxial substrate without affecting the quality of the sensing signal SS, so as to reduce the manufacturing cost.

Fig. 5 is a schematic diagram of an embodiment of an electronic device according to the present application. For example, the electronic device 500 may be used for optical off-screen/on-screen fingerprint sensing to sense a fingerprint of a particular object. The electronic device 500 includes a display screen 502 and the image sensor 100, when a finger approaches the display screen 502, light emitted from the display screen 502 irradiates the finger and is reflected back to the electronic device 500 by the finger, and is received by the image sensor 100, and the image sensor 100 generates a sensing signal accordingly for fingerprint recognition, and optionally, the image sensor 100 may be disposed below the display screen 502 to implement an off-screen optical fingerprint sensing.

Claims

1. A pixel, comprising:

an optical sensor having a cathode and an anode, the anode being coupled to a first voltage source, wherein the optical sensor is used for sensing an optical signal in a sensing phase and generating a sensing signal in a floating diffusion region; and

a pixel circuit disposed on a non-epitaxial substrate, the pixel circuit coupled to the cathode of the optical sensor and a second voltage source, wherein the pixel circuit comprises:

a reset circuit coupled between the cathode and the floating diffusion region, wherein the reset circuit is used for resetting the sensing signal of the floating diffusion region in a reset phase; and

an operational amplifier having a positive terminal coupled to the second voltage source, a negative terminal coupled to the cathode, and an output terminal coupled to the floating diffusion region, the operational amplifier being configured to fix a voltage difference between the cathode and the anode of the optical sensor,

wherein the reset circuit includes:

a first transistor; and

a second transistor for controlling the output voltage of the transistor,

wherein a drain of the first transistor is coupled to the cathode and the negative terminal, a source of the first transistor is coupled to a drain of the second transistor, a source of the second transistor is coupled to the output terminal and the floating diffusion region, and

wherein the optical sensor is disposed above the pixel circuit.

2. The pixel of claim 1 wherein said optical sensor is a thin film photodiode and overlies said pixel circuit.

3. The pixel of claim 1 wherein the optical sensor is a cmos photodiode and overlies the pixel circuit.

4. The pixel of claim 1, wherein the pixel circuit further comprises:

a capacitor having a first terminal coupled to the cathode of the optical sensor and a second terminal coupled to the floating diffusion region,

wherein in a sensing phase, the capacitance is used to accumulate a charge to generate the sensing signal at the floating diffusion region, wherein the charge is generated in response to the optical sensor sensing the light signal.

5. The pixel of claim 1, wherein a gate of the first transistor receives a first control signal and a gate of the second transistor receives a second control signal, the first and second control signals respectively rendering the first and second transistors conductive during the reset phase, and the first and second control signals rendering the first and second transistors non-conductive during the sensing phase.

6. The pixel of claim 5, wherein the reset circuit further comprises:

a third transistor, wherein a drain of the third transistor is coupled to a source of the first transistor and a drain of the second transistor, and a source of the third transistor is coupled to a base of the third transistor, the second voltage source, and the positive terminal.

7. The pixel of claim 6, wherein the source of the third transistor is further coupled to the base of the first transistor.

8. The pixel of claim 6, wherein a gate of the third transistor receives a third control signal, the third control signal rendering the third transistor non-conductive during the reset phase, and the third control signal rendering the third transistor conductive during the sense phase.

9. The pixel of claim 6, wherein a length of on time of the second transistor is greater than a length of on time of the first transistor in the reset phase.

10. The pixel of claim 9, wherein a length of time that the third transistor is non-conductive is greater than a length of time that the second transistor is conductive during the reset phase.

11. The pixel of claim 1 or claim 6, wherein the voltage of the first voltage source is equal to the voltage of the second voltage source and the voltage difference is zero.

12. The pixel of claim 11, wherein the positive terminal is more directly coupled to the anode of the optical sensor.

13. The pixel of claim 1, wherein the voltage of the first voltage source is not equal to the voltage of the second voltage source, and the voltage difference is not zero.

14. The pixel of claim 13, wherein the voltage of the second voltage source is higher than the voltage of the first voltage source.

15. The pixel of claim 1 wherein the pixel circuit further comprises:

and the pixel reading circuit is coupled to the floating diffusion region and used for outputting an output signal according to the sensing signal and the selection signal in a reading-out stage.

16. The pixel of claim 15, wherein the pixel readout circuit comprises a source follower transistor and a fourth transistor, wherein a gate of the source follower transistor is coupled to the floating diffusion region, a source of the source follower transistor is coupled to a drain of the fourth transistor, and a gate of the fourth transistor receives a select signal.

17. An image sensor, comprising:

a pixel array comprising a plurality of pixels as claimed in any one of claims 1 to 16.

18. An electronic device, comprising:

the image sensor of claim 17; and

a display screen.