阅读说明：本技术 高动态范围图像传感器像素电路及其操作方法 (High dynamic range image sensor pixel circuit and method of operating the same ) 是由 郭同辉 于 2021-09-16 设计创作，主要内容包括：一种高动态范围图像传感器像素电路及其操作方法,属于传感器领域,光电转换元件在曝光周期内接收光信号以产生电荷；电荷存储转移电路根据电荷调制信号对电荷进行存储以生成积分电荷信号,并根据控制选择信号将积分电荷信号输出；电荷调制信号与曝光时间之间成基数大于1的对数关系；释放电路至少在生成积分电荷信号的过程中根据弱关闭信号释放光电转换元件产生的部分电荷；电信号读出电路根据像素选择控制信号将积分电荷信号转换为电信号,以得到图像信号；故增加了高动态范围图像传感器像素电路感光动态范围,增加了高动态范围图像传感器像素电路感光动态范围调节的灵活性。(A high dynamic range image sensor pixel circuit and its operation method, in the field of sensor, a photoelectric conversion element receives optical signal in exposure period to generate charge; the charge storage and transfer circuit stores the charges according to the charge modulation signal to generate an integral charge signal and outputs the integral charge signal according to the control selection signal; the logarithm relation of the base number between the charge modulation signal and the exposure time is more than 1; the release circuit releases part of the charges generated by the photoelectric conversion element according to the weak off signal at least in the process of generating the integrated charge signal; the electric signal reading circuit converts the integrated charge signal into an electric signal according to the pixel selection control signal to obtain an image signal; therefore, the photosensitive dynamic range of the pixel circuit of the high dynamic range image sensor is increased, and the flexibility of adjusting the photosensitive dynamic range of the pixel circuit of the high dynamic range image sensor is increased.)

1. A high dynamic range image sensor pixel circuit, comprising:

a photoelectric conversion element configured to receive a light signal to generate electric charges during an exposure period;

a charge storage transfer circuit connected to the photoelectric conversion element, configured to store the charge to generate an integrated charge signal, and output the integrated charge signal according to a control selection signal;

wherein the charge storage transfer circuit stores the charge in accordance with a charge modulation signal to generate the integrated charge signal, the charge modulation signal having a logarithmic relationship with an exposure time having a base number greater than 1;

a discharging circuit connected to the photoelectric conversion element and an input terminal of the charge storage transfer circuit, and configured to discharge a part of charges generated by the photoelectric conversion element according to a weak off signal at least in a process of generating the integrated charge signal;

and the electric signal reading circuit is connected with the output end of the charge storage and transfer circuit and is configured to convert the integrated charge signal into an electric signal according to a pixel selection control signal so as to obtain an image signal.

2. The high dynamic range image sensor pixel circuit of claim 1, wherein the electrical signal readout circuit is further configured to clear at least the charge in the photoelectric conversion element in accordance with a clear signal.

3. The high dynamic range image sensor pixel circuit of claim 2, wherein when the electrical signal readout circuit clears at least the charge in the photoelectric conversion element, the release circuit is further configured to transfer the charge in the photoelectric conversion element in accordance with an anti-charge crosstalk control signal;

and the control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to the weak turn-off signal when part of charges generated by the photoelectric conversion element are released.

4. The high dynamic range image sensor pixel circuit of claim 1, wherein said electrical signal readout circuit comprises a reset transistor, a source follower transistor, and a pixel select transistor;

the source electrode of the reset transistor and the grid electrode of the source following transistor are connected to the input end of the electric signal reading circuit together, and the input end of the electric signal reading circuit is used as the integrated charge signal input end;

the grid electrode of the reset transistor is connected to a reset signal control line to serve as an input end of a reset control signal of the electric signal reading circuit;

the drain electrode of the reset transistor is connected to a first power supply, the drain electrode of the source follower transistor is connected to a second power supply, and the first power supply and the second power supply are the same or different power supplies;

the source electrode of the source following transistor is connected with the drain electrode of the pixel selection transistor, the source electrode of the pixel selection transistor is connected to the output end of the electric signal reading circuit, and the output end of the electric signal reading circuit is used as the output end of the electric signal;

the gate of the pixel selection transistor is connected to a pixel selection signal control line to serve as an input terminal of a pixel selection control signal of the electric signal readout circuit.

5. The high dynamic range image sensor pixel circuit of any of claims 1-4, wherein the charge storage transfer circuit comprises a charge transfer transistor, a charge storage control device;

the source electrode of the charge transmission transistor and the first end of the charge storage control device are connected to the charge input end of the charge storage transfer circuit, and the drain electrode of the charge transmission transistor is connected to the integrated charge signal output end of the charge storage transfer circuit;

the grid electrode of the charge transfer transistor is connected to a control selection signal control line to serve as the control selection signal input end;

the second terminal of the charge storage control device is connected to the charge modulation signal control line as an input terminal of a charge modulation signal.

6. The high dynamic range image sensor pixel circuit of claim 5, wherein said charge storage control device comprises a capacitance modulation transistor; the grid electrode of the capacitance modulation transistor is the second end of the charge storage device, and the source electrode of the capacitance modulation transistor and the drain electrode of the capacitance modulation transistor are the first end of the charge storage device;

wherein the base number of the electric potential of the grid of the capacitance modulation transistor and the exposure time is more than 1.

7. The high dynamic range image sensor pixel circuit of claim 6, wherein in a layout of the high dynamic range image sensor pixel circuit, a gate of the capacitance modulation transistor is located above the photoelectric conversion element and between the charge transfer transistor and the release circuit.

8. The high dynamic range image sensor pixel circuit of claim 5, wherein the release circuit comprises a charge crosstalk resistant transistor, a source of the charge crosstalk resistant transistor is connected to the output of the photoelectric conversion element, a drain of the charge crosstalk resistant transistor is connected to a control power supply, and a gate of the charge crosstalk resistant transistor is connected to a charge crosstalk resistant transistor control line.

9. The high dynamic range image sensor pixel circuit of claim 8, wherein said photoelectric conversion element comprises a photodiode; wherein the channel potential of the anti-charge crosstalk transistor is controlled to be less than a full depletion potential of the photodiode and greater than a channel potential of the charge transfer transistor based on the anti-charge crosstalk transistor control line to discharge the partial charge.

10. A method of operating a high dynamic range image sensor pixel circuit as claimed in any one of claims 1 to 9, comprising:

inputting the charge modulation signal in the exposure process, and storing the charge by a charge storage conversion circuit according to the charge modulation signal to generate an integral charge signal; a logarithmic relationship with a radix greater than 1 between the charge modulation signal and the exposure time;

inputting the weak off signal during inputting the charge modulation signal to cause a release circuit to release a part of the charge generated by the photoelectric conversion element in accordance with the weak off signal at least during generating the integrated charge signal;

and inputting a control selection signal to enable the charge storage transfer circuit to output the integrated charge signal according to the control selection signal so as to obtain an image signal.

11. The method of operating a high dynamic range image sensor pixel circuit as claimed in claim 10, wherein in generating said integrated charge signal:

the grid voltage of the transmission transistor is less than 0 and less than the grid voltage of the anti-charge crosstalk transistor corresponding to the weak turn-off signal of the release circuit and less than the positive voltage of the power supply; or the grid voltage of the transmission transistor is less than the grid voltage of the anti-charge crosstalk transistor corresponding to the weak closing signal of the release circuit and less than 0 and less than the positive voltage of the power supply; or the grid voltage of the transmission transistor is more than 0 and less than the grid voltage of the anti-charge crosstalk transistor corresponding to the weak closing signal of the release circuit and less than the positive voltage of the power supply.

12. The method of operating a high dynamic range image sensor pixel circuit as recited in claim 10, further comprising, prior to generating the integrated charge signal:

inputting a clear signal before starting exposure, and clearing the charges in the photoelectric conversion element by the electric signal readout circuit according to the clear signal; the input of the clear signal is stopped, and the exposure is started.

13. The method of operating a high dynamic range image sensor pixel circuit according to claim 12, wherein an anti-charge crosstalk control signal is input during the input of the clear signal, the discharging circuit clears the charge in the photoelectric conversion element in accordance with the anti-charge crosstalk control signal;

and the control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to the weak turn-off signal when part of charges generated by the photoelectric conversion element are released.

14. The method of operating a high dynamic range image sensor pixel circuit as claimed in claim 10, wherein inputting said control select signal causes a charge storage transfer circuit to output said integrated charge signal, further comprising, before said integrated charge signal is output and after an end of exposure:

stopping exposure, inputting a charge release signal, and clearing the charges in the photoelectric conversion element by the release circuit according to the charge release signal; wherein the charge release signal remains input during the outputting of the integrated charge signal.

15. The method of operating a high dynamic range image sensor pixel circuit of any of claims 10-14, further comprising, before the charge storage transfer circuit outputs the integrated charge signal and after generating the integrated charge signal:

and inputting a reset control signal, and outputting a reset signal by the electric signal reading circuit according to the reset control signal.

16. The method of operating a high dynamic range image sensor pixel circuit of any of claims 10-14, wherein in generating the integrated charge signal:

channel potential of the charge transfer transistor < channel potential when the anti-charge crosstalk transistor in the release circuit is in a weak off state < potential when the photoelectric conversion element is fully depleted < channel potential of the capacitance modulation transistor < reset potential of the floating diffusion region < power supply anode potential.

Technical Field

The present application relates to the field of sensors, and more particularly, to a high dynamic range image sensor pixel circuit and a method of operating the same.

Background

Image sensors have been widely used in digital cameras, mobile phones, medical devices, automobiles, and other applications. In particular, the rapid development of the technology for manufacturing a Complementary Metal Oxide Semiconductor (CMOS) image sensor has made people have higher requirements for the quality of an output image of the image sensor.

The pixel circuit of the image sensor generally adopts the working principle that a photodiode is adopted to convert a received optical signal into a photoelectric charge signal, the maximum amount of photoelectric charge which can be collected by the photodiode in the exposure process is called charge saturation capacity, and the higher the charge saturation capacity is, the higher the dynamic range of object information collected by the pixel is. In the pixel circuit of the image sensor in the related art, the photo response of the photodiode is generally linear, and is called a linear image sensor; the photodiode reaches a saturation state quickly along with the increase of the exposure, image information of a strong light environment is difficult to collect, and the dynamic range of the collected image information is generally lower than 80 dB. In nature, human eyes are sensitive to weak light, namely the sensitivity is high when the weak light is perceived; but is not sensitive to strong light, namely the sensitivity is low when strong light is sensed. The human eyes can perceive the light rays in a logarithmic curve relationship, the relationship effectively improves the capability of the eyes to perceive the light rays, and the dynamic range of the relationship can reach more than 100 dB. It follows that the above-described linear image sensor is clearly less capable of capturing images than the human eye.

Disclosure of Invention

The present application aims to provide a high dynamic range image sensor pixel circuit and an operation method thereof, and aims to solve the defect of low photosensitive dynamic range of the conventional high dynamic range image sensor pixel circuit.

The embodiment of the application provides a high dynamic range image sensor pixel circuit, including:

a photoelectric conversion element configured to receive a light signal to generate electric charges during an exposure period;

a charge storage transfer circuit connected to the photoelectric conversion element, configured to store the charge to generate an integrated charge signal, and output the integrated charge signal according to a control selection signal;

wherein the charge storage transfer circuit stores the charge in accordance with a charge modulation signal to generate the integrated charge signal, the charge modulation signal having a logarithmic relationship with an exposure time having a base number greater than 1;

a discharging circuit connected to the photoelectric conversion element and an input terminal of the charge storage transfer circuit, and configured to discharge a part of charges generated by the photoelectric conversion element according to a weak off signal at least in a process of generating the integrated charge signal;

and the electric signal reading circuit is connected with the output end of the charge storage and transfer circuit and is configured to convert the integrated charge signal into an electric signal according to a control selection signal so as to obtain an image signal.

The embodiment of the present application further provides an operating method of the pixel circuit of the high dynamic range image sensor, including:

inputting the charge modulation signal in the exposure process, and storing the charge by a charge storage conversion circuit according to the charge modulation signal to generate an integral charge signal; a logarithmic relationship with a radix greater than 1 between the charge modulation signal and the exposure time;

inputting the weak off signal during inputting the charge modulation signal to cause a release circuit to release a part of the charge generated by the photoelectric conversion element in accordance with the weak off signal at least during generating the integrated charge signal;

and inputting a control selection signal to enable the charge storage transfer circuit to output the integrated charge signal according to the control selection signal so as to obtain an image signal.

Compared with the prior art, the embodiment of the invention has the following beneficial effects: a discharging circuit for discharging a part of the electric charges generated by the photoelectric conversion element according to the weak off signal at least in the process of generating the integrated electric charge signal; the charge in the photoelectric conversion element irradiated by strong light is released by the release circuit, and the logarithmic relation of which the base number is more than 1 is formed between the charge modulation signal and the exposure time, the photosensitive capability of the pixel irradiated by the strong light is suppressed, the photosensitive sensitivity is reduced, and the photosensitive capability and the sensitivity of the pixel irradiated by weak light are kept unchanged, so that the photosensitive dynamic range of the pixel circuit of the high dynamic range image sensor is increased, and the flexibility of adjusting the photosensitive dynamic range of the pixel circuit of the high dynamic range image sensor is increased.

Drawings

In order to more clearly illustrate the technical invention in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts.

Fig. 1 is a schematic structural diagram of a pixel circuit of a high dynamic range image sensor according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of an exemplary circuit for a pixel circuit of a high dynamic range image sensor according to an embodiment of the present disclosure;

FIG. 3 is a partial layout of a pixel circuit corresponding to the high dynamic range image sensor of FIG. 2;

FIG. 4 is a schematic diagram illustrating a configuration of a transistor gate voltage during an exposure period for a pixel circuit of a high dynamic range image sensor according to an embodiment of the present application;

FIG. 5 is a schematic diagram of a potential well of a pixel circuit of a high dynamic range image sensor according to an embodiment of the present application when the pixel circuit is operated under strong light;

fig. 6 is a schematic diagram of charges and potentials of a photodiode in a pixel circuit of a high dynamic range image sensor during an exposure period according to an embodiment of the present application.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.

It will be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, refer to an orientation or positional relationship illustrated in the drawings for convenience in describing the present application and to simplify description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present application.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.

In a related art image sensor pixel circuit, in order to improve the dynamic range of the collected image information, a method of high-dose implantation of impurity ions is generally adopted in a photodiode, so as to increase the charge saturation capacity of the photodiode, but the defects are that the full depletion potential of the photodiode is increased, image smear is easily generated, and dark current is also increased. Another related technique for improving the dynamic range of the collected image information is to set two modes of high conversion gain and low conversion gain in the pixel to respectively deal with the image collection in the low-light environment and the high-light environment, although the two modes can be switched back and forth according to the illumination environment, only one of the two modes can be used at the same time in the working process of the pixel, so that the detail information of the low-light and high-light illumination images cannot be simultaneously obtained.

Fig. 1 shows a schematic structural diagram of a pixel circuit of a high dynamic range image sensor according to a preferred embodiment of the present application, and for convenience of description, only the parts related to the embodiment are shown, and detailed descriptions are as follows:

the high dynamic range image sensor pixel circuit described above includes a photoelectric conversion element 11, a charge storage transfer circuit 12, a discharge circuit 13, and an electric signal readout circuit 14.

A photoelectric conversion element 11 configured to receive a light signal to generate electric charges during an exposure period;

a charge storage transfer circuit 12 connected to the photoelectric conversion element 11, configured to store the charge to generate an integrated charge signal, and output the integrated charge signal according to a control selection signal;

the charge storage and transfer circuit 12 stores the charges according to the charge modulation signal to generate an integral charge signal, and the base number between the charge modulation signal and the exposure time is more than 1 in logarithmic relation;

a discharge circuit 13 connected to the photoelectric conversion element 11 and an input terminal of the charge storage transfer circuit 12, and configured to discharge a part of the charges generated by the photoelectric conversion element 11 in accordance with a weak off signal at least in a process of generating an integrated charge signal;

and an electrical signal readout circuit 14 connected to the output end of the charge storage transfer circuit 12 and configured to convert the integrated charge signal into an electrical signal according to the control selection signal to obtain an image signal.

Here, the output end of the photoelectric conversion element 11 may be a cathode of the photoelectric conversion element 11, for example, the photoelectric conversion element 11 is selected to be a photodiode. Accordingly, the photoelectric conversion element 11 receives a light signal in the exposure period and generates a negative charge, thereby improving the mobility of the charge.

In a specific implementation, the electrical signal readout circuit 14 is further configured to clear the charges in the photoelectric conversion element 11 according to the clear signal.

The electric charges in the photoelectric conversion elements 11 are cleared by the electric signal readout circuit 14 in accordance with the clear signal, so that the electric charges in the photoelectric conversion elements 11 are cleared each time an image signal is acquired, improving the acquisition accuracy of the image signal.

The discharge circuit 13 is also configured to transfer the electric charges in the photoelectric conversion element 11 in accordance with the anti-electric-charge-crosstalk control signal when the electric-signal readout circuit 14 clears at least the electric charges in the photoelectric conversion element 11; wherein the control voltage corresponding to the charge crosstalk resistant control signal is equal to the control voltage corresponding to the weak off signal when part of the charges generated by the photoelectric conversion element 11 are released.

The electric charges in the photoelectric conversion elements 11 are cleared by the discharge circuits 13, and the electric charges in the photoelectric conversion elements 11 are further cleared, improving the acquisition accuracy of the image signals. The control voltage corresponding to the anti-electric-charge crosstalk control signal is equal to the control voltage corresponding to when a part of the electric charges generated by the photoelectric conversion element 11 is discharged according to the weak off signal, so that the discharge circuit 13 is prevented from potential variation causing ground interference.

The embodiment of the invention also provides an operation method of the pixel circuit of the high dynamic range image sensor, which comprises the steps 101a and 101b and the step 102.

Step 101 a: inputting a charge modulation signal in an exposure process, and storing charges by a charge storage conversion circuit according to the charge modulation signal to generate an integral charge signal; the logarithm relation of the base number between the charge modulation signal and the exposure time is more than 1;

step 101 b: inputting a weak off signal in the course of inputting the charge modulation signal to cause the discharging circuit 13 to discharge a part of the charges generated by the photoelectric conversion element 11 in accordance with the weak off signal at least in the course of generating the integrated charge signal;

step 102: the control selection signal is input to cause the charge storage transfer circuit 12 to output the integrated charge signal in accordance with the control selection signal to obtain an image signal.

By way of example and not limitation, step 101a and step 101b may be preceded by step 100 a.

Step 100 a: inputting a clear signal before starting exposure, and the electric signal readout circuit 14 clears the electric charge in the photoelectric conversion element 11 in accordance with the clear signal; the exposure is started.

In performing step 100a, the method of operating a high dynamic range image sensor pixel circuit further includes step 100 b.

Step 100 b: inputting an anti-charge crosstalk control signal, and clearing the charges in the photoelectric conversion element 11 by the release circuit 13 according to the anti-charge crosstalk control signal;

wherein the control voltage corresponding to the charge crosstalk resistant control signal is equal to the control voltage corresponding to the weak off signal when part of the charges generated by the photoelectric conversion element 11 are released.

In particular implementations, step 102 may include steps a1 through a 2.

Step A1: inputting a control selection signal, outputting an integrated charge signal by the charge storage transfer circuit 12 according to the control selection signal, and outputting the charge in the photoelectric conversion element 11 by the photoelectric conversion element 11 according to the control selection signal;

step A2: the electric signal readout circuit 14 outputs an electric signal from the integrated charge signal and the charge in the photoelectric conversion element 11.

In particular implementations, step a1 may be preceded by step a 0.

Step A0: a reset control signal is input, and the electric signal readout circuit 14 outputs a reset signal in accordance with the reset control signal.

In a specific implementation, in the step 102, the method for operating the pixel circuit of the high dynamic range image sensor further includes the step 102 b:

step 102 b: stopping exposure, inputting a charge release signal, and outputting and clearing the charges in the photoelectric conversion element 11 by the release circuit 13 according to the charge release signal; wherein the input charge-release signal is maintained during the outputting of the integrated charge signal. The potential of the charge release signal may be a potential of a weak off signal or a channel potential when the anti-charge crosstalk transistor is in an on state.

By removing the electric charges in the photoelectric conversion element 11 before exposure and after stopping exposure, the acquisition accuracy of the image signal is improved.

In a specific implementation, the reset control signal, the charge crosstalk control signal, the charge modulation signal, the control selection signal, and the charge release signal may be output by the control logic.

In one embodiment, in generating the integrated charge signal:

the grid voltage of the transmission transistor is less than 0 and less than the grid voltage of the anti-charge crosstalk transistor corresponding to the weak turn-off signal of the release circuit and less than the positive voltage of the power supply; or the grid voltage of the transmission transistor is less than the grid voltage of the anti-charge crosstalk transistor corresponding to the weak closing signal of the release circuit and less than 0 and less than the positive voltage of the power supply; or the grid voltage of the anti-charge crosstalk transistor corresponding to the weak turn-off signal of the release circuit is less than 0 and less than the grid voltage of the power supply positive electrode voltage.

In a further example, in generating the integrated charge signal:

channel potential of the charge transfer transistor < channel potential when the anti-charge crosstalk transistor in the release circuit is in a weak off state < potential when the photoelectric conversion element is completely depleted < channel potential of the capacitance modulation transistor < reset potential of the floating diffusion region < power supply positive electrode potential.

Fig. 2 shows an exemplary circuit structure of a pixel circuit of a high dynamic range image sensor provided by an embodiment of the present invention, and for convenience of description, only the parts related to the embodiment of the present invention are shown, and detailed as follows:

the electric signal readout circuit 14 includes a reset transistor 103, a source follower transistor 104, and a pixel selection transistor 105.

The source of the reset transistor 104 and the gate of the source follower transistor 105 are commonly connected to the input end of the electrical signal readout circuit 14, and the input end of the electrical signal readout circuit 14 serves as an integrated charge signal input end;

the gate of the reset transistor 104 is connected to a reset signal control line to serve as an input terminal of a reset control signal of the electric signal readout circuit 14; the drain of the reset transistor 104 is connected to a first power supply VDD, the drain of the source follower transistor 105 is connected to a second power supply, and the first power supply VDD and the second power supply are the same or different power supplies; the source of the source follower transistor 105 is connected to the drain of the pixel selection transistor 106, the source of the pixel selection transistor 106 is connected to the output end of the electric signal readout circuit 14, and the output end of the electric signal readout circuit 14 serves as the output end of the electric signal; the gate of the pixel selection transistor is connected to a pixel selection signal control line as an input terminal of a pixel selection control signal of the electric signal readout circuit.

The charge storage transfer circuit 12 includes a charge transfer transistor 102 and a charge storage control device 107.

The source of the charge transfer transistor 102 and the first terminal of the charge storage control device 107 are connected to the charge input terminal of the charge storage transfer circuit 12, the charge input terminal is connected to the output terminal of the photoelectric conversion element 11, and the drain of the charge transfer transistor 102 is connected to the integrated charge signal output terminal of the charge storage transfer circuit 12; the gate of the charge transfer transistor 102 is connected to a control selection signal control line as a control selection signal input terminal. A second terminal of the charge storage device 108 is connected to the charge input signal control line as a charge modulated signal input terminal.

The discharging circuit 1313 includes the charge discharging transistor 107. The source electrode of the charge interference resisting transistor is connected with the output end of the photoelectric conversion element 11, the drain electrode of the charge interference resisting transistor is connected with the control power supply, and the grid electrode of the charge interference resisting transistor is connected with the control line of the charge interference resisting transistor. In one example, the charge discharging transistor 107 is input with a weak off signal through a control line during an exposure phase, input with an anti-crosstalk control signal before exposure, and output with a charge discharging signal during a readout phase. The control voltage corresponding to the anti-crosstalk control signal is equal to the control voltage corresponding to the weak turn-off signal and is smaller than the control voltage corresponding to the charge release signal.

The photoelectric conversion element 1111 includes, but is not limited to, a buried Photodiode (Pinned Photodiode), a polysilicon gate Photodiode (photo diode), a Current assisted Photodiode (Current Assistance Photodiode); charge storage devices include, but are not limited to, MOS transistor type capacitors, polysilicon gate-insulator-polysilicon gate type capacitors, metal-insulator-metal type capacitors. Wherein the channel potential of the anti-charge crosstalk transistor is controlled to be less than a fully depleted potential of the photodiode and greater than a channel potential of the charge transfer transistor based on the anti-charge crosstalk transistor control line to release a part of the charges.

The charge storage control device comprises a capacitance modulation transistor; the grid electrode of the capacitance modulation transistor is the second end of the charge storage control device, and the source electrode of the capacitance modulation transistor and the drain electrode of the capacitance modulation transistor are the first end of the charge storage control device;

wherein, the electric potential of the grid of the capacitance modulation transistor and the exposure time have a logarithmic relation with a base number larger than 1.

As shown in fig. 3, in the layout of the high dynamic range image sensor pixel circuit, the gate of the capacitance modulation transistor is located above the photodiode and between the charge transfer transistor 102 and the release circuit 13.

The following further description of fig. 2 and 3 is made in conjunction with the working principle:

the one-frame operation process for collecting photoelectric signals by the pixel circuit of the high dynamic range image sensor comprises three stages: a pixel reset phase, a photoelectric charge collection phase and a photoelectric signal output phase.

The pixel reset phase is the first phase in the operation of collecting a photoelectric signal by a pixel circuit of the high dynamic range image sensor in one frame, specifically, the reset transistor 103 and the charge transfer transistor 102 give a high potential pulse operation to clear the charge in the photodiode 101, and then the gate of the charge release transistor 106 is set to a low potential Vanti (i.e., a weak off signal is input, and set to a weak off state), and exposure is started.

In the second stage photoelectric charge collection stage, the gate potentials of the charge transfer transistor 102, the charge discharging transistor 106, and the capacitance modulating transistor 107 are arranged such that the vertical axis represents a potential value, the horizontal axis represents an exposure time T, and the exposure period represents T, as shown in fig. 4. In fig. 4, during the exposure period T, the charge transfer transistor 102 is kept in an off state with its gate potential configured to Vtx, as shown at 203 in fig. 4; the charge-discharge transistor 106 is kept in a weakly off state with its gate potential configured as Vanti, as shown at 202 in fig. 2; during the exposure period T, the gate terminal potential VSG of the capacitance modulation transistor 107 is gradually raised from 0V to the power supply positive electrode voltage Vdd as shown by the curve 201 in fig. 2; the gate terminal potential VSG of the capacitance modulation transistor 107 has a logarithmic relationship with a base number larger than 1 with the exposure time t. The relationship among the gate terminal potential Vtx of the charge transfer transistor 102, the gate terminal potential Vanti of the charge discharging transistor 106, the power ground 0V, and the power positive voltage Vdd is as follows:

vtx <0< Vanti < Vdd (1) or

Vtx < Vanti <0< Vdd (2) or

0<Vtx<Vanti<Vdd (3)

The photodiode 101 receives a light signal during an exposure period and converts it into an electrical charge, which is collected in the photodiode 101 and the capacitance modulation transistor 107.

In the third stage of outputting the photoelectric signal, after the photoelectric charge collecting stage is completed, the pixel selecting transistor 105 is turned on, the charge transmitting transistor 102 gives a high potential pulse operation (inputs a control selection signal), charges in the photodiode 101 and the capacitance modulating transistor 107 are transferred to the floating diffusion active region FD, and then the source follower transistor 104 reads the photoelectric signal in the floating diffusion active region FD to output the photoelectric signal through the signal output line output. Here, the floating diffusion active region FD is connected to the source of the charge transfer transistor 102, the source of the reset transistor 104, and the gate of the source follower transistor 105.

In the photoelectric charge collection stage, the potential well of the pixel under strong light irradiation is schematically shown in fig. 5, and the potential well state of the device marked with the dashed line AB in fig. 3 is shown in fig. 5. The charge discharging transistor 106 is kept in a weakly off state, the gate potential is Vanti, and the channel potential thereof is Vanti _ off; the fully depleted potential in the photodiode 101 is shown as Vpin; the gate terminal potential of the capacitance modulation transistor 107 is VSG, the channel potential thereof is VSG _ channal, the capacitance contributed by the charge storage control device 107 is CSG, and the capacitance contributed by the photodiode 101 is CPD; the gate terminal of the charge transfer transistor 102 is at Vtx, and the channel potential is at Vtx _ off; the reset potential of the floating diffusion active region FD is Vrst and the power supply positive electrode potential is Vdd. The magnitude relationship of the above potentials is shown by the following formula:

Vtx_off<Vanti_off<Vpin<VSG_channal<Vrst<Vdd (4)

since Vanti _ off is greater than Vtx _ off, the photodiode 101 generates excessive charge under strong light illumination that overflows to the power supply positive terminal Vdd through the channel of the charge discharging transistor 106. In the pixel exposure period T, the potential of the gate terminal VSG of the capacitance modulation transistor 107 is gradually increased from 0V to the power supply positive electrode voltage Vdd, and the potential change of the gate terminal VSG of the capacitance modulation transistor 107 has a logarithmic relationship with the base number larger than 1 with respect to the exposure time T.

In the photoelectric charge collection stage, under strong light irradiation, the relationship between the electric potential and the photoelectric charge amount and the exposure time T shown in fig. 5 is shown in fig. 6. In fig. 6, the left vertical axis represents the charge amount, the horizontal axis represents the exposure time t, the right vertical axis represents the potential, 401 represents the total photoelectric charge amount Qpd collected by the photodiode 101 and the capacitance modulation transistor 107 as a function of the exposure time t, 402 represents the VSG _ channal as a function of the exposure time t, and 403 represents the photoelectric charge amount Qleak of the photodiode 101 overflowing to the power supply positive electrode Vdd through the channel of the charge discharging transistor 106.

Qpd _ max is the sum of the maximum amounts of photoelectric charges that the photodiode 101 and the capacitance modulation transistor 107 can collect, Qleak _ max is the maximum amount of photoelectric charges that the photodiode 101 overflows to the power supply positive electrode Vdd through the channel of the charge discharging transistor 106, VSG _ channal _ max is the highest potential of the channel of the capacitance modulation transistor 107, and Vpin is the fully depleted potential of the photodiode 101.

When the number of photons received by the photodiode 101 in a unit time is n, the photoelectric conversion efficiency of the photodiode 101 is k, and the photoelectric charge Q generated by the photodiode 101 is expressed as:

Q＝knt(t<＝T) (5)

the amount of charge Qpd that the photodiode 101 and the capacitance modulation transistor 107 can collect is expressed as:

Qpd＝CPD*(Vpin-Vanti_off)+CSG*(VSG_channal-Vpin) (6)

the quantity Qleak of the photoelectric charge overflowing the photodiode 101 to the power supply positive electrode Vdd through the channel of the charge discharging transistor 106 is expressed as:

Qleak＝Q-Qpd (7)

because there is a logarithmic relationship between VSG and exposure time t with a base greater than 1, and VSG _ channal is proportional to VSG, there is a similar logarithmic relationship between VSG _ channal and exposure time t with a base greater than 1, as shown at 402 in fig. 6; as can be seen from equations 6 and 7, curves 401 and 403 in fig. 6 are non-linear curves, and curve 401 is a logarithmic relationship curve with a similar base number greater than 1.

As can be seen, the photodiode 101 and the capacitance modulation transistor 107 collectively collect the photoelectric charges, and the total effective photoelectric charge amount Qpd is the sum of both; under strong light irradiation, the total effective photoelectric charge quantity Qpd and the exposure time t have a logarithmic relation with a similar base number larger than 1. As a result, the sensitivity of the photodiode 101 is suppressed under strong light irradiation, and the sensitivity is lowered. The photoelectric response of the photodiode 101 is therefore in a non-linear mode, and such a sensor is referred to as a non-linear image sensor.

Therefore, the high dynamic range image sensor pixel circuit with the nonlinear photosensitive characteristic can effectively expand the signal acquisition of the strong light illumination intensity range, and effectively improve the pixel photosensitive dynamic range compared with the related technology.

In the embodiment of the invention, the photoelectric conversion element receives the optical signal in the exposure period to generate the electric charge; the charge storage and transfer circuit stores the charges according to the charge modulation signal to generate an integral charge signal and outputs the integral charge signal according to the control selection signal; the logarithm relation of the base number between the charge modulation signal and the exposure time is more than 1; the release circuit releases part of the charges generated by the photoelectric conversion element according to the weak off signal at least in the process of generating the integrated charge signal; the electric signal reading circuit converts the integrated charge signal into an electric signal according to the pixel selection control signal to obtain an image signal; the charge in the photoelectric conversion element irradiated by strong light is released by the release circuit, and the logarithmic relation of which the base number is more than 1 is formed between the charge modulation signal and the exposure time, the photosensitive capability of the pixel irradiated by the strong light is suppressed, the photosensitive sensitivity is reduced, and the photosensitive capability and the sensitivity of the pixel irradiated by weak light are kept unchanged, so that the photosensitive dynamic range of the pixel circuit of the high dynamic range image sensor is increased, and the flexibility of adjusting the photosensitive dynamic range of the pixel circuit of the high dynamic range image sensor is increased.

It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.