High dynamic range image sensor pixel circuit and operation method thereof

Abstract

A high dynamic range image sensor pixel circuit and an operation method thereof belong to the field of sensors. A photoelectric conversion element receives a light signal during an exposure period to generate a charge; a charge storage transfer circuit stores the charge according to a charge modulation signal to generate an integrated charge signal, and outputs the integrated charge signal according to a control selection signal; the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1; a release circuit releases part of the charge generated by the photoelectric conversion element according to a weak shutdown signal at least during the process of generating the integrated charge signal; an electrical signal readout circuit converts the integrated charge signal into an electrical signal according to a pixel selection control signal to obtain an image signal; therefore, the photosensitivity dynamic range of the high dynamic range image sensor pixel circuit is increased, and the flexibility of adjusting the photosensitivity dynamic range of the high dynamic range image sensor pixel circuit is increased.

Description

Technical Field

[0001] The present application belongs to the field of sensors, and in particular, relates to a high dynamic range image sensor pixel circuit and an operation method thereof. Background Art

[0002] Image sensors have been widely used in digital cameras, mobile phones, medical devices, automobiles and other applications. In particular, the rapid development of complementary metal oxide semiconductor (CMOS) image sensor technology has led to higher requirements for the output image quality of image sensors.

[0003] The working principle of the pixel circuit of the image sensor is usually to use a photodiode to convert the received light signal into a photoelectric charge signal. The maximum amount of photoelectric charge that the photodiode can collect during the exposure process is called the charge saturation capacity. The higher the charge saturation capacity, the higher the dynamic range of the pixel to collect object information. In the image sensor pixel circuit of the related technology, the photoelectric response of the photodiode is usually a linear relationship, which is called a linear image sensor; as the exposure increases, the photodiode quickly reaches a saturated state, and it is difficult to collect image information in a strong light environment. The dynamic range of the collected image information is generally less than 80dB. In nature, the human eye is sensitive to weak light, that is, it has high sensitivity when perceiving weak light; and it is insensitive to strong light, that is, it has low sensitivity when perceiving strong light. The human eye's perception of light is characterized by a logarithmic curve relationship, which effectively improves the eye's ability to perceive light, and its dynamic range can reach more than 100dB. It can be seen that compared with the human eye, the ability of the above-mentioned linear image sensor to collect images is obviously poor. Summary of the invention

[0004] The purpose of the present application is to provide a high dynamic range image sensor pixel circuit and an operation method thereof, aiming to solve the defect of low photosensitivity dynamic range in traditional high dynamic range image sensor pixel circuits.

[0005] An embodiment of the present application provides a high dynamic range image sensor pixel circuit, comprising:

[0006] A photoelectric conversion element configured to receive a light signal to generate an electric charge during an exposure period;

[0007] 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;

[0008] Wherein, the charge storage transfer circuit stores the charge according to the charge modulation signal to generate the integrated charge signal, and the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1;

[0009] a release circuit connected to the photoelectric conversion element and an input end of the charge storage transfer circuit, and configured to release part of the charge generated by the photoelectric conversion element according to a weak shutdown signal at least during the process of generating the integrated charge signal;

[0010] The electric signal readout circuit is connected to the output end of the charge storage transfer circuit and is configured to convert the integrated charge signal into an electric signal according to a control selection signal to obtain an image signal.

[0011] The embodiment of the present application further provides an operating method of the above-mentioned high dynamic range image sensor pixel circuit, including:

[0012] The charge modulation signal is input during the exposure process, and the charge storage conversion circuit stores the charge according to the charge modulation signal to generate an integrated charge signal; the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1;

[0013] In the process of inputting the charge modulation signal, inputting the weak shutdown signal, so that the release circuit releases part of the charge generated by the photoelectric conversion element according to the weak shutdown signal at least in the process of generating the integrated charge signal;

[0014] A control selection signal is input to enable the charge storage transfer circuit to output the integrated charge signal according to the control selection signal to obtain an image signal.

[0015] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: since the release circuit releases part of the charge generated by the photoelectric conversion element according to the weak shutdown signal at least in the process of generating the integrated charge signal; the charge in the photoelectric conversion element irradiated with strong light is partially released through the release circuit, and the charge modulation signal and the exposure time are in a logarithmic relationship with a base greater than 1, the photosensitivity of the pixel irradiated with strong light is suppressed, and the photosensitivity sensitivity is reduced, while the photosensitivity and sensitivity of the pixel irradiated with weak light remain unchanged, thereby increasing the photosensitivity dynamic range of the pixel circuit of the high dynamic range image sensor, and increasing the flexibility of adjusting the photosensitivity dynamic range of the pixel circuit of the high dynamic range image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical invention in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A schematic diagram of a high dynamic range image sensor pixel circuit provided by an embodiment of the present application;

[0018] Figure 2 An exemplary circuit schematic diagram of a high dynamic range image sensor pixel circuit provided by an embodiment of the present application;

[0019] Figure 3 For the corresponding Figure 2 A partial layout of a high dynamic range image sensor pixel circuit;

[0020] Figure 4 A schematic diagram of transistor gate voltage configuration during an exposure period of a high dynamic range image sensor pixel circuit provided by an embodiment of the present application;

[0021] Figure 5 A schematic diagram of a potential well of a high dynamic range image sensor pixel circuit provided in an embodiment of the present application when operating under strong light irradiation;

[0022] Figure 6 A schematic diagram of the charge and potential of a photodiode in a high dynamic range image sensor pixel circuit during an exposure period provided by an embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or 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 indirectly connected to the other element.

[0025] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0026] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0027] In a related technology, in order to improve the dynamic range of image information acquisition, a high-dose impurity ion injection method is usually used in the photodiode to increase the charge saturation capacity of the photodiode. However, the disadvantage is that the photodiode is completely depleted. The potential is increased, which is prone to image smearing, and the dark current will also increase. Another related technology to improve the dynamic range of image information acquisition is to set two modes of high conversion gain and low conversion gain in the pixel to deal with image acquisition in weak light and strong light environments respectively. Although these two modes can be switched back and forth according to the lighting environment, only one of the two modes can be used at the same time during the operation of the pixel, so the detail information of weak light and strong light images cannot be obtained at the same time.

[0028] Figure 1 The schematic diagram of the structure of the high dynamic range image sensor pixel circuit provided by the preferred embodiment of the present application is shown. For the convenience of explanation, only the part related to the present embodiment is shown, which is described in detail as follows:

[0029] The high dynamic range image sensor pixel circuit includes a photoelectric conversion element 11 , a charge storage transfer circuit 12 , a release circuit 13 and an electrical signal readout circuit 14 .

[0030] The photoelectric conversion element 11 is configured to receive a light signal to generate electric charge during an exposure period;

[0031] The charge storage transfer circuit 12 is connected to the photoelectric conversion element 11 and is configured to store the charge to generate an integrated charge signal and output the integrated charge signal according to the control selection signal;

[0032] The charge storage transfer circuit 12 stores the charge according to the charge modulation signal to generate an integrated charge signal, and the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1;

[0033] a release circuit 13 connected to the photoelectric conversion element 11 and the input end of the charge storage transfer circuit 12, and configured to release part of the charge generated by the photoelectric conversion element 11 according to the weak shutdown signal at least in the process of generating the integrated charge signal;

[0034] The electric signal readout circuit 14 is connected to the output end of the charge storage transfer circuit 12 and is configured to convert the integrated charge signal into an electric signal according to the control selection signal to obtain an image signal.

[0035] The output end of the photoelectric conversion element 11 may be the cathode of the photoelectric conversion element 11. For example, the photoelectric conversion element 11 may be a photodiode. Thus, the charge generated by the photoelectric conversion element 11 when receiving the light signal during the exposure period is negative charge, which improves the mobility of the charge.

[0036] In a specific implementation, the electric signal readout circuit 14 is further configured to clear the charge in the photoelectric conversion element 11 according to the clear signal.

[0037] The electric signal readout circuit 14 clears the charge in the photoelectric conversion element 11 according to the clear signal, so that the charge in the photoelectric conversion element 11 is cleared every time an image signal is acquired, thereby improving the acquisition accuracy of the image signal.

[0038] When the electrical signal readout circuit 14 at least clears the charge in the photoelectric conversion element 11, the release circuit 13 is also configured to transfer the charge in the photoelectric conversion element 11 according to the anti-charge crosstalk control signal; wherein the control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to releasing part of the charge generated by the photoelectric conversion element 11 according to the weak shutdown signal.

[0039] The charge in the photoelectric conversion element 11 is cleared by the release circuit 13, and the charge in the photoelectric conversion element 11 is further cleared, thereby improving the acquisition accuracy of the image signal. The control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to when part of the charge generated by the photoelectric conversion element 11 is released according to the weak shutdown signal, thereby preventing the interference caused by the potential change of the release circuit 13.

[0040] An embodiment of the present invention further provides a method for operating a pixel circuit of a high dynamic range image sensor, comprising steps 101 a , 101 b and step 102 .

[0041] Step 101a: during the exposure process, a charge modulation signal is input, and the charge storage conversion circuit stores the charge according to the charge modulation signal to generate an integrated charge signal; the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1;

[0042] Step 101b: during the process of inputting the charge modulation signal, inputting a weak shutdown signal, so that the release circuit 13 releases part of the charge generated by the photoelectric conversion element 11 according to the weak shutdown signal at least during the process of generating the integrated charge signal;

[0043] Step 102: Input a control selection signal so that the charge storage transfer circuit 12 outputs the integrated charge signal according to the control selection signal to obtain an image signal.

[0044] As an example but not a limitation, step 100a is included before step 101a and step 101b.

[0045] Step 100a: before starting exposure, a clear signal is input, and the electric signal readout circuit 14 clears the charge in the photoelectric conversion element 11 according to the clear signal; exposure starts.

[0046] During the execution of step 100a, the operating method of the high dynamic range image sensor pixel circuit further includes step 100b.

[0047] Step 100b: inputting an anti-charge crosstalk control signal, and the release circuit 13 clears the charge in the photoelectric conversion element 11 according to the anti-charge crosstalk control signal;

[0048] The control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to releasing part of the charges generated by the photoelectric conversion element 11 according to the weak shutdown signal.

[0049] In a specific implementation, step 102 may include step A1 to step A2.

[0050] Step A1: input a control selection signal, the charge storage transfer circuit 12 outputs the integrated charge signal according to the control selection signal, and the photoelectric conversion element 11 outputs the charge in the photoelectric conversion element 11 according to the control selection signal;

[0051] Step A2 : The electric signal readout circuit 14 outputs an electric signal based on the integrated charge signal and the charge in the photoelectric conversion element 11 .

[0052] In a specific implementation, step A0 may be included before step A1.

[0053] Step A0: A reset control signal is input, and the electrical signal readout circuit 14 outputs a reset signal according to the reset control signal.

[0054] In a specific implementation, during the execution of step 102, the operating method of the high dynamic range image sensor pixel circuit further includes step 102b:

[0055] Step 102b: stop exposure, input a charge release signal, and the release circuit 13 clears the charge in the photoelectric conversion element 11 according to the charge release signal output; wherein the input charge release signal is maintained during the process of outputting the integrated charge signal. The potential of the charge release signal can be the potential of a weak shutdown signal or the channel potential when the anti-charge crosstalk transistor is in the on state.

[0056] By clearing the charge in the photoelectric conversion element 11 before exposure and after stopping exposure, the accuracy of acquiring the image signal is improved.

[0057] In a specific implementation, a reset control signal, an anti-charge crosstalk control signal, a charge modulation signal, a control selection signal, and a charge release signal can be output by the control logic.

[0058] In one embodiment, during the generation of the integrated charge signal:

[0059] The gate voltage of the transmission transistor is <0<the gate voltage of the anti-charge crosstalk transistor corresponding to the weak shutdown signal of the release circuit<the positive power supply voltage; or, the gate voltage of the transmission transistor is <the gate voltage of the anti-charge crosstalk transistor corresponding to the weak shutdown signal of the release circuit<0<the positive power supply voltage; or, 0<the gate voltage of the transmission transistor<the gate voltage of the anti-charge crosstalk transistor corresponding to the weak shutdown signal of the release circuit<the positive power supply voltage.

[0060] In a further example, during the generation of the integrated charge signal:

[0061] The channel potential of the charge transfer transistor < the channel potential of the anti-charge crosstalk transistor in the release circuit when it is in a weak off state < the potential when the photoelectric conversion element is fully depleted < the channel potential of the capacitance modulation transistor < the reset potential of the floating diffusion region < the positive power supply potential.

[0062] Figure 2 An exemplary circuit structure of a high dynamic range image sensor pixel circuit provided by an embodiment of the present invention is shown. For ease of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0063] The electric signal readout circuit 14 includes a reset transistor 103 , a source follower transistor 104 , and a pixel selection transistor 105 .

[0064] The source of the reset transistor 103 and the gate of the source follower transistor 104 are commonly connected to the input terminal of the electric signal readout circuit 14, and the input terminal of the electric signal readout circuit 14 serves as the integrated charge signal input terminal;

[0065] The gate of the reset transistor 103 is connected to the reset signal control line to serve as the input terminal of the reset control signal of the electrical signal readout circuit 14; the drain of the reset transistor 103 is connected to the first power supply VDD, and the drain of the source follower transistor 104 is connected to the 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 104 is connected to the drain of the pixel selection transistor 105, and the source of the pixel selection transistor 105 is connected to the output terminal of the electrical signal readout circuit 14, and the output terminal of the electrical signal readout circuit 14 serves as the output terminal of the electrical signal; the gate of the pixel selection transistor is connected to the pixel selection signal control line to serve as the input terminal of the pixel selection control signal of the electrical signal readout circuit.

[0066] The charge storage transfer circuit 12 includes a charge transfer transistor 102 and a charge storage control device 107 .

[0067] The source of the charge transfer transistor 102 and the first end of the charge storage control device 107 are connected to the charge input end of the charge storage transfer circuit 12, the charge input end is connected to the output end of the photoelectric conversion element 11, and the drain of the charge transfer transistor 102 is connected to the integrated charge signal output end of the charge storage transfer circuit 12; the gate of the charge transfer transistor 102 is connected to the control selection signal control line as the control selection signal input end. The second end of the charge storage device 108 is connected to the charge input signal control line as the charge modulation signal input end.

[0068] The release circuit 13 includes an anti-charge crosstalk transistor 106. The source of the anti-charge crosstalk transistor is connected to the output end of the photoelectric conversion element 11, the drain of the anti-charge crosstalk transistor is connected to the control power supply, and the gate of the anti-charge crosstalk transistor is connected to the anti-charge crosstalk transistor control line. In one example, a weak shutdown signal is input to the anti-charge crosstalk transistor 106 through the control line during the exposure phase, an anti-crosstalk control signal is input before exposure, and a charge release signal is output during the readout phase. Among them, the control voltage corresponding to the anti-crosstalk control signal is equal to the control voltage corresponding to the weak shutdown signal and is less than the control voltage corresponding to the charge release signal.

[0069] The photoelectric conversion element 11 includes but is not limited to a pinned photodiode, a polysilicon gate photodiode, and a current-assisted photoelectric device; the charge storage device includes but is not limited to a MOS transistor capacitor, a polysilicon gate-insulator-polysilicon gate capacitor, and a metal-insulator-metal capacitor. The channel potential of the anti-charge crosstalk transistor is controlled based on the anti-charge crosstalk transistor control line to be less than the full depletion potential of the photodiode and greater than the channel potential of the charge transfer transistor to release part of the charge.

[0070] The charge storage control device comprises a capacitance modulation transistor; the gate of the capacitance modulation transistor is the second end of the charge storage control device, and the source of the capacitance modulation transistor and the drain of the capacitance modulation transistor are the first end of the charge storage control device;

[0071] There is a logarithmic relationship between the potential of the gate of the capacitance modulation transistor and the exposure time, with a base greater than 1.

[0072] like Figure 3 As shown, 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.

[0073] The following is a combination of working principles Figure 2 and Figure 3 As shown for further explanation:

[0074] The operation process of collecting a frame of photoelectric signals by the pixel circuit of a high dynamic range image sensor includes three stages: pixel reset stage, photoelectric charge collection stage and photoelectric signal output stage.

[0075] The pixel reset stage is the first stage in the operation of collecting photoelectric signals in a frame by the pixel circuit of the high dynamic range image sensor. The specific operation is to give a high-potential pulse operation to the reset transistor 103 and the charge transfer transistor 102 to clear the charge in the photodiode 101, and then set the gate of the charge release transistor 106 to a low potential Vanti (i.e., input a weak shutdown signal and set it to a weak shutdown state) to start exposure.

[0076] In the second stage of photoelectric charge collection, the gate potential configuration of the charge transfer transistor 102, the charge release transistor 106 and the capacitance modulation transistor 107 is as follows: Figure 4 As shown, the vertical axis is the potential value, the horizontal axis is the exposure time t, and the exposure period is T. Figure 4In it, during the exposure period T, the charge transfer transistor 102 remains in the off state, and its gate potential is configured as Vtx, as shown in Figure 4 shown in 203 in; the charge release transistor 106 remains in the weakly off state, and its gate potential is configured as Vanti, as shown in Figure 2 shown in 202 in; during the exposure period T, the gate terminal potential VSG of the capacitance modulation transistor 107 gradually increases from 0V to the positive power supply voltage Vdd, as shown in the curve of 201 in Figure 2 ; there is a logarithmic relationship with a base greater than 1 between the gate terminal potential VSG of the capacitance modulation transistor 107 and the exposure time t. The relationship between the gate terminal potential Vtx of the charge transfer transistor 102, the gate terminal potential Vanti of the charge release transistor 106, the power supply ground 0V, and the positive power supply voltage Vdd is shown by the following formula:

[0077] Vtx < 0 < Vanti < Vdd (1) or

[0078] Vtx < Vanti < 0 < Vdd (2) or

[0079] 0 < Vtx < Vanti < Vdd (3)

[0080] The photodiode 101 receives an optical signal and converts it into charge during the exposure period, and the charge is collected in the photodiode 101 and the capacitance modulation transistor 107.

[0081] In the third stage, the photoelectric signal output stage, after the photoelectric charge collection stage is completed, the pixel selection transistor 105 is turned on, and the charge transfer transistor 102 is given a high potential pulse operation (input control selection signal), and the charge in the photodiode 101 and the capacitance modulation transistor 107 is transferred to the floating diffusion active region FD. Subsequently, the source follower transistor 104 reads the photoelectric signal in the floating diffusion active region FD and outputs the photoelectric signal through the signal output line output. Among them, the floating diffusion active region FD is connected to the source of the charge transfer transistor 102, the source of the reset transistor 103, and the gate of the source follower transistor 104.

[0082] During the photoelectric charge collection stage, the schematic diagram of the potential well of the pixel under strong light irradiation is as shown in Figure 5 shown, and as shown in 5 is Figure 3The device potential well state is marked with the dotted line AB position. The charge release transistor 106 is kept in a weak off state, with a gate potential of Vanti and a channel potential of Vanti_off; the fully depleted potential in the photodiode 101 is Vpin; the gate terminal potential of the capacitance modulation transistor 107 is VSG, and its channel potential is VSG_channal, the capacitance value contributed by the charge storage control device 107 is CSG, and the capacitance value contributed by the photodiode 101 is CPD; the gate terminal potential of the charge transfer transistor 102 is Vtx, and its channel potential is Vtx_off; the reset potential of the floating diffusion active area FD is Vrst, and the positive potential of the power supply is Vdd. The magnitude relationship of the above potentials is shown in the following formula:

[0083] Vtx_off <Vanti_off<Vpin<VSG_channal<Vrst<Vdd (4)

[0084] Because Vanti_off is greater than Vtx_off, the photodiode 101 generates excessive charges under strong light and overflows to the positive power supply terminal Vdd through the channel of the charge release transistor 106. During the pixel exposure period T, the gate terminal VSG potential of the capacitance modulation transistor 107 gradually increases from 0V to the positive power supply voltage Vdd, and the gate terminal VSG potential change of the capacitance modulation transistor 107 is in a logarithmic relationship with the exposure time t, with a base greater than 1.

[0085] In the photoelectric charge collection stage, under strong light irradiation, within the exposure period T, Figure 5 The relationship between the potential and the photoelectric charge and the exposure time t is shown in FIG. Figure 6 shown. Figure 6 In the figure, the left vertical axis is the charge amount, the horizontal axis is the exposure time t, the right vertical axis is the electric potential, 401 is the relationship curve between the total photoelectric charge Qpd collected by the photodiode 101 and the capacitor modulation transistor 107 and the exposure time t, 402 is the relationship curve between VSG_channel and the exposure time t, and 403 is the photoelectric charge Qleak that overflows from the photodiode 101 to the positive power supply Vdd through the channel of the charge release transistor 106.

[0086] Qpd_max is the sum of the maximum photoelectric charges that can be collected by the photodiode 101 and the capacitor modulation transistor 107, Qleak_max is the maximum photoelectric charge that overflows from the photodiode 101 to the positive power supply Vdd through the channel of the charge release transistor 106, VSG_channal_max is the highest potential of the channel of the capacitor modulation transistor 107, and Vpin is the fully depleted potential of the photodiode 101.

[0087] The number of photons received by the photodiode 101 per unit time is n, and the photoelectric conversion efficiency of the photodiode 101 is k. Then the expression of the photoelectric charge Q generated by the photodiode 101 is:

[0088] Q=knt (t<=T) (5)

[0089] The amount of charge Qpd that can be collected by the photodiode 101 and the capacitance modulation transistor 107 is expressed as:

[0090] Qpd=CPD*(Vpin-Vanti_off)+CSG*(VSG_channal-Vpin) (6)

[0091] The photoelectric charge Qleak that overflows from the photodiode 101 to the positive power supply Vdd through the channel of the charge release transistor 106 is expressed as:

[0092] Qleak=Q-Qpd (7)

[0093] Because VSG and exposure time t have a logarithmic relationship with a base greater than 1, and VSG_channel is proportional to VSG, VSG_channel and exposure time t have a logarithmic relationship with a base greater than 1, such as Figure 6 As shown in 402; From equations 6 and 7, we can know that Figure 6 The 401 curve and the 403 curve are nonlinear curves, and the 401 curve is a logarithmic relationship curve with a base greater than 1.

[0094] It can be seen that the photodiode 101 and the capacitive modulation transistor 107 collect photoelectric charges together, and the total effective photoelectric charge Qpd is the sum of the two; under strong light irradiation, the total effective photoelectric charge Qpd and the exposure time t have a logarithmic relationship similar to a base greater than 1. It can be seen that under strong light irradiation, the photosensitivity of the photodiode 101 is suppressed and the photosensitivity is reduced. Therefore, the photoelectric response of the photodiode 101 is a nonlinear mode, and this type of sensor is called a nonlinear image sensor.

[0095] Therefore, the high dynamic range image sensor pixel circuit with nonlinear photosensitivity characteristics of the present invention can effectively expand the signal acquisition within the strong light intensity range, and effectively improves the pixel photosensitivity dynamic range relative to related technologies.

[0096] The embodiment of the present invention receives a light signal during an exposure period through a photoelectric conversion element to generate a charge; a charge storage transfer circuit stores the charge according to a charge modulation signal to generate an integrated charge signal, and outputs the integrated charge signal according to a control selection signal; the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1; the release circuit releases part of the charge generated by the photoelectric conversion element according to a weak shutdown signal at least in the process of generating the integrated charge signal; the electrical signal readout circuit converts the integrated charge signal into an electrical signal according to a pixel selection control signal to obtain an image signal; the charge in the photoelectric conversion element irradiated with strong light is partially released through the release circuit, and the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1, the photosensitivity of the pixel irradiated with strong light is suppressed, and the photosensitivity sensitivity is reduced, while the photosensitivity and sensitivity of the pixel irradiated with weak light remain unchanged, thereby increasing the photosensitivity dynamic range of the pixel circuit of the high dynamic range image sensor, and increasing the flexibility of adjusting the photosensitivity dynamic range of the pixel circuit of the high dynamic range image sensor.

[0097] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0098] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A high dynamic range image sensor pixel circuit, characterized in that: include: A photoelectric conversion element configured to receive a light signal during an exposure period to generate electric charge; 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 according to the charge modulation signal to generate the integrated charge signal, and the charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1; a release circuit connected to the photoelectric conversion element and an input end of the charge storage transfer circuit, and configured to release part of the charge generated by the photoelectric conversion element according to a weak shutdown signal at least during the process of generating the integrated charge signal; an electrical signal readout circuit connected to the output end of the charge storage transfer circuit and configured to convert the integrated charge signal into an electrical signal according to a pixel selection control signal to obtain an image signal; The electrical signal readout circuit is further configured to clear at least the charge in the photoelectric conversion element according to a clear signal; The release circuit includes an anti-charge crosstalk transistor; The photoelectric conversion element and the charge storage transfer circuit jointly collect photoelectric charges, and the total effective photoelectric charge is the sum of the two; under strong light irradiation, the total effective photoelectric charge and the exposure time are in a logarithmic relationship with a base greater than 1; under strong light irradiation, the photosensitivity of the photoelectric conversion element is suppressed and the photosensitivity is reduced.

2. The high dynamic range image sensor pixel circuit according to claim 1, wherein: When the electric 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 according to the anti-charge crosstalk control signal; The control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to releasing part of the charges generated by the photoelectric conversion element according to the weak shutdown signal.

3. The high dynamic range image sensor pixel circuit according to claim 1, wherein: The electrical signal readout circuit includes a reset transistor, a source follower transistor and a pixel selection transistor; The source of the reset transistor and the gate of the source follower transistor are commonly connected to the input terminal of the electric signal readout circuit, and the input terminal of the electric signal readout circuit serves as the integrated charge signal input terminal; The gate of the reset transistor is connected to a reset signal control line to serve as an input terminal of a reset control signal of the electrical signal readout circuit; The drain of the reset transistor is connected to a first power supply, the drain 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 of the source follower transistor is connected to the drain of the pixel selection transistor, the source of the pixel selection transistor is connected to the output end of the electrical signal readout circuit, and the output end of the electrical signal readout circuit serves as the output end of the electrical signal; The gate of the pixel selection transistor is connected to a pixel selection signal control line to serve as an input terminal of the pixel selection control signal of the electrical signal readout circuit.

4. The high dynamic range image sensor pixel circuit according to any one of claims 1 to 3, characterized in that: The charge storage transfer circuit includes a charge transfer transistor and a charge storage control device; The source of the charge transfer transistor and the first end of the charge storage control device are connected to the charge input terminal of the charge storage transfer circuit, and the drain of the charge transfer transistor is connected to the integrated charge signal output terminal of the charge storage transfer circuit; The gate of the charge transfer transistor is connected to a control selection signal control line to serve as an input terminal of the control selection signal; The second end of the charge storage control device is connected to the charge modulation signal control line to serve as an input end of the charge modulation signal.

5. The high dynamic range image sensor pixel circuit according to claim 4, characterized in that: The charge storage control device comprises a capacitance modulation transistor; the gate of the capacitance modulation transistor is the second end of the charge storage device, and the source of the capacitance modulation transistor and the drain of the capacitance modulation transistor are the first end of the charge storage device; There is a logarithmic relationship between the potential of the gate of the capacitance modulation transistor and the exposure time, with a base greater than 1.

6. The high dynamic range image sensor pixel circuit according to claim 5, characterized in that: In the layout of the high dynamic range image sensor pixel circuit, the gate of the capacitance modulation transistor is located above the photoelectric conversion element and between the charge transfer transistor and the release circuit.

7. The high dynamic range image sensor pixel circuit according to claim 6, wherein: The photoelectric conversion element includes a photodiode; wherein, based on the anti-charge crosstalk transistor control line, the channel potential of the anti-charge crosstalk transistor is controlled to be less than the full depletion potential of the photodiode and greater than the channel potential of the charge transfer transistor to release the partial charge.

8. A method for operating a high dynamic range image sensor pixel circuit according to any one of claims 1 to 7, characterized in that: include: During the exposure process, the charge modulation signal is input, and the charge storage conversion circuit stores the charge according to the charge modulation signal to generate an integrated charge signal; The charge modulation signal and the exposure time form a logarithmic relationship with a base greater than 1; In the process of inputting the charge modulation signal, inputting the weak shutdown signal, so that the release circuit releases part of the charge generated by the photoelectric conversion element according to the weak shutdown signal at least in the process of generating the integrated charge signal; A control selection signal is input to enable the charge storage transfer circuit to output the integrated charge signal according to the control selection signal to obtain an image signal.

9. The method for operating a high dynamic range image sensor pixel circuit as claimed in claim 8, characterized in that: In the process of generating the integrated charge signal: The gate voltage of the charge transfer transistor is <0<the gate voltage of the anti-charge crosstalk transistor corresponding to the weak shutdown signal of the release circuit<the positive power supply voltage; or, the gate voltage of the charge transfer transistor is <the gate voltage of the anti-charge crosstalk transistor corresponding to the weak shutdown signal of the release circuit<0<the positive power supply voltage; or, 0<the gate voltage of the charge transfer transistor<the gate voltage of the anti-charge crosstalk transistor corresponding to the weak shutdown signal of the release circuit<the positive power supply voltage.

10. The method for operating a high dynamic range image sensor pixel circuit as claimed in claim 8, characterized in that: Before generating the integrated charge signal, it also includes: Before starting exposure, a clear signal is input, and the electric signal readout circuit clears the charge in the photoelectric conversion element according to the clear signal; when the clear signal is stopped, exposure starts.

11. The method for operating a high dynamic range image sensor pixel circuit as claimed in claim 10, characterized in that: During the input of the clear signal, an anti-charge crosstalk control signal is input, and the release circuit clears the charge in the photoelectric conversion element according to the anti-charge crosstalk control signal; The control voltage corresponding to the anti-charge crosstalk control signal is equal to the control voltage corresponding to releasing part of the charges generated by the photoelectric conversion element according to the weak shutdown signal.

12. The method for operating a high dynamic range image sensor pixel circuit as claimed in claim 8, characterized in that: The control selection signal is input to enable the charge storage transfer circuit to output the integrated charge signal, and before the integrated charge signal is output and after the exposure is completed, the method further includes: Exposure is stopped, a charge release signal is input, and the release circuit clears the charge in the photoelectric conversion element according to the charge release signal; wherein the charge release signal is kept input during the process of outputting the integrated charge signal.

13. The method for operating a high dynamic range image sensor pixel circuit according to any one of claims 8 to 12, characterized in that: Before the charge storage transfer circuit outputs the integrated charge signal and after generating the integrated charge signal, the method further includes: A reset control signal is input, and the electric signal readout circuit outputs a reset signal according to the reset control signal.

14. The method for operating a high dynamic range image sensor pixel circuit according to any one of claims 8 to 12, characterized in that: In the process of generating the integrated charge signal: The channel potential of the charge transfer transistor < the channel potential of the anti-charge crosstalk transistor in the release circuit when it is in a weak off state < the potential when the photoelectric conversion element is fully depleted < the channel potential of the capacitance modulation transistor < the reset potential of the floating diffusion region < the positive power supply potential.

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