A random readable active pixel circuit and driving method thereof

Abstract

The present invention discloses an active pixel circuit that can be randomly read and a driving method thereof, the active pixel circuit comprising: a photodiode, a first transistor, a second transistor, a first power supply and a second power supply; the first power supply is connected to the drain of the second transistor and is connected to the drain of the first transistor through the diode, the drain of the first transistor is connected to the gate of the first transistor and the top gate of the second transistor, the source of the first transistor is grounded, the bottom gate of the second transistor is connected to the second power supply, and the source of the second transistor is a signal output terminal. The present invention makes the output current of the randomly readable active pixel sensor circuit have a power function relationship with the photocurrent of the diode, and achieves a quasi-linear relationship between the output signal of the circuit and the light intensity, so that the sensitivity and dynamic response range of the sensor can be optimized at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of circuit technology, and in particular relates to an active pixel circuit capable of random reading and a driving method thereof. Background Art

[0002] A conventional active pixel circuit generally includes three transistors (a reset switch transistor Trst, a source follower Tsf, and a selection switch transistor Tsel) and a photodiode. If the gate and drain of the reset switch transistor Trst are short-circuited, a circuit such as Figure 1 Logarithmic Active Pixel Sensor (Log.APS). Compared with ordinary active pixel circuits, the output signal of Log.APS changes logarithmically with the change of light intensity, so it has a wider dynamic response range, generally at least 100dB or more. In addition, Log.APS does not need to reset the sensor, the circuit is simple, the pixel fill factor is larger, and the operation is faster and simpler. At the same time, each pixel in Log.APS works independently and the photogenerated charge does not need to be time-integrated during the photoelectric conversion process, so it can be read randomly in space and time. The random readability in space allows important signals to be read and processed independently, making the sensor more intelligent, while the random readability in time allows the signal to be read and processed more quickly. Therefore, the random readability in space and time makes the reading speed of effective signals faster.

[0003] However, the way the devices are connected inside the Log.APS pixel causes the output signal to decrease as the light intensity increases, requiring the back-end signal readout and processing circuits to be redesigned. Moreover, because the Log.APS output is logarithmically related to the input, the sensor has a low sensitivity in low light. Finally, the design of the active pixel with three transistors also makes it difficult to further reduce the pixel size, which in turn affects the sensitivity of the pixel. Summary of the invention

[0004] In order to overcome the above technical defects, the present invention provides a randomly readable active pixel sensor circuit, which can improve the sensitivity and dynamic range of the randomly readable active pixel sensor circuit.

[0005] In order to solve the above problems, the present invention is implemented according to the following technical solutions:

[0006] A randomly readable active pixel circuit comprises: a photodiode, a first transistor, a second transistor, a first power supply and a second power supply;

[0007] The first power supply is connected to the drain of the second transistor and is connected to the drain of the first transistor through the diode, the drain of the first transistor is connected to the gate of the first transistor and the top gate of the second transistor, the source of the first transistor is grounded, the bottom gate of the second transistor is connected to the second power supply, and the source of the second transistor is a signal output terminal.

[0008] Compared with the prior art, the beneficial effect of this circuit is as follows: on the basis of Log.APS, the two transistors of the source follower and the selection switch tube are replaced by one transistor, so that the sensor circuit retains the random reading performance of Log.APS while making the output and input present a quasi-linear relationship, thereby improving the sensitivity and dynamic range of the sensor under weak light, and reducing the number of active devices in the pixel, which also improves the aperture ratio and fill factor of the pixel.

[0009] As a further improvement of the present invention, the first transistor is a single-gate transistor, and the second transistor is a double-gate transistor.

[0010] As a further improvement of the present invention, the photodiode is a diode with a nip structure, the first transistor and the second transistor are both n-type semiconductor devices, the first power supply is connected to the cathode of the photodiode, and the anode of the photodiode is connected to the drain of the first transistor.

[0011] As a further improvement of the present invention, the photodiode is a diode with a pin structure, the first transistor and the second transistor are p-type semiconductor devices, the first power supply is connected to the anode of the photodiode, and the cathode of the photodiode is connected to the drain of the first transistor.

[0012] Meanwhile, the present invention also provides another randomly readable active pixel circuit, comprising: a photodiode, a first transistor, a second transistor, a first power supply and a second power supply;

[0013] The first power supply is connected to the drain of the first transistor and the drain of the second transistor, the drain of the first transistor is connected to the gate of the first transistor, the source of the first transistor is connected to the top gate of the second transistor and is grounded through the photodiode, the bottom gate of the second transistor is connected to the second power supply, and the source of the second transistor is a signal output terminal.

[0014] As a further improvement of the present invention, the first transistor is a single-gate thin film transistor, and the second transistor is a double-gate thin film transistor.

[0015] As a further improvement of the present invention, the photodiode is a diode with a nip structure, the first transistor and the second transistor are both n-type semiconductor devices, the cathode of the diode is connected to the source of the first transistor and the top gate of the second transistor, and the anode of the diode is grounded.

[0016] As a further improvement of the present invention, the photodiode is a photodiode with a pin structure, the first transistor and the second transistor are both p-type semiconductor devices, the anode of the photodiode is connected to the source of the first transistor and the top gate of the second transistor, and the cathode of the photodiode is grounded.

[0017] The present invention also provides a driving method for the above-mentioned randomly readable active pixel circuit, comprising the following steps:

[0018] When the randomly readable active pixel circuit is in an operating state, a voltage is applied to the photodiode, so that the photodiode is in a reverse biased state and generates a photocurrent under light, so that the first transistor and the second transistor operate in a subthreshold region, so that the output current of the randomly readable active pixel circuit is in a power function relationship with the photocurrent of the photodiode.

[0019] Compared with the prior art, the beneficial effect of this method is that the output current of the randomly readable active pixel circuit is in a power function relationship with the photocurrent of the diode, and the output signal of the sensor circuit and the light intensity are in a quasi-linear relationship, forming a logarithmic-exponential pixel circuit, so that the sensitivity and dynamic response range of the sensor can be optimized at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings, wherein:

[0021] Figure 1 is a schematic diagram of a conventional logarithmic active pixel circuit;

[0022] Figure 2 is a schematic diagram of the active pixel circuit described in Example 1;

[0023] Figure 3 is a schematic diagram of an active pixel circuit according to Embodiment 2;

[0024] Figure 4 is a schematic diagram of an active pixel circuit according to Embodiment 3;

[0025] Figure 5 Schematic diagram of the active pixel circuit described in Example 4. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0027] Embodiment 1

[0028] This embodiment discloses a randomly readable active pixel circuit, such as Figure 2 As shown, it includes: a photodiode D, a single-gate thin film transistor TFT1, a double-gate thin film transistor TFT2, a first power supply V DD The anode of the photodiode D is connected to the drain of the double-gate thin film transistor TFT2, and the cathode of the photodiode D is connected to the drain of the single-gate thin film transistor TFT1. DD The drain of the single-gate thin film transistor TFT1 is connected to the gate of the single-gate thin film transistor TFT1 and the top gate of the double-gate thin film transistor TFT2, the source of the single-gate thin film transistor TFT1 is grounded, and the bottom gate of the double-gate thin film transistor TFT2 is connected to the second power supply V BG The source of the dual-gate thin film transistor TFT2 is the signal output terminal, and the first power supply V DD Used to provide reverse bias voltage for photodiode D, second power supply V BG Used to control dual-gate thin-film transistors.

[0029] In the above embodiment, the photodiode D is a photodiode with a nip structure, which may be a variety of diodes such as an amorphous silicon diode or an organic diode or a similar photodetector.

[0030] In the above embodiment, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are both one of n-type materials such as amorphous silicon, indium gallium zinc oxide, n-type organic semiconductor and n-type low-temperature polycrystalline silicon. The double-gate thin film transistor TFT2 replaces the source follower and the selection switch tube in the Log APS, reducing the number of devices inside the pixel and improving the aperture ratio and fill factor of the pixel.

[0031] This embodiment improves the circuit so that the pixel output and input have a quasi-linear positive correlation while maintaining random readability in space and time, which facilitates the design of the back-end signal readout and signal processing circuit.

[0032] Next, this embodiment is further explained in conjunction with the specific implementation process, as follows:

[0033] When the sensor pixel circuit is in working state, the photodiode D needs to be reverse biased to enable it to sense light, so the first power supply V DD , the second power supply V BGAll of them are external bias ports; and since a-Si, IGZO, n-type organic semiconductors and n-type low-temperature polysilicon used to make thin-film transistors are all n-type materials, they generally require a positive voltage to drive, so a nip-structured photodiode D is used, that is, the cathode is used as the external bias port, and the anode is connected to the gate of TFT1. When the sensor pixel circuit is working, V DD The photodiode D is in a reverse bias state. At this time, the photogenerated carriers in the photodiode D generate electron-hole pairs due to the external bias and move toward the cathode and anode respectively, forming a photogenerated current I photo :

[0034]

[0035] Among them, q is the elementary charge, η0 is the quantum efficiency of diode D, P is the light intensity, A PD is the photosensitive area of ​​diode D, λ is the wavelength, R is the reflection coefficient, α and t are the absorption coefficient and thickness of the active layer of diode D, h is Planck's constant, and c is the speed of light in vacuum. Therefore, the total current flowing through diode D is:

[0036] I PD =I DS1 =I dark +I photo (2)

[0037] I dark is the leakage current when the diode D is reverse biased in the dark state.

[0038] In the single-gate thin-film transistor TFT1, the gate and drain are short-circuited, so the gate voltage V GS The source-drain voltage V DS1 equal:

[0039] V GS =V DS1 (3)

[0040] When the single-gate thin film transistor TFT1 is operated in the subthreshold region, the source-drain current I of TFT1 can be obtained according to the subthreshold region current formula of the thin film transistor: DS1 for:

[0041]

[0042] Among them, I D01 V GS =V T1 And V DS1 >>kT / q, the output current of the single-gate thin-film transistor TFT1, V T1 is the threshold voltage of the single-gate thin film transistor TFT1 S1 is the subthreshold swing of the single-gate thin-film transistor TFT1, k is the Boltzmann constant, and T is the temperature. That is V DS1 >>0.0258V (at room temperature), equation (4) can be simplified to:

[0043]

[0044] By transforming the above formula (5), we can get the source-drain voltage V of the single-gate thin-film transistor TFT1: DS1 for:

[0045]

[0046] Because the anode of the photodiode D, the gate and drain of the single-gate thin-film transistor TFT1, and the top gate of the double-gate thin-film transistor TFT2 are connected together, we have:

[0047] V TG =V DS1 (7)

[0048] For the dual-gate thin film transistor TFT2, its threshold voltage V T2 It can be expressed as:

[0049] V T2 =V TH0 +γV TG (8)

[0050] Among them, V TH0 V TG =0 is the threshold voltage of TFT2, and γ is the control coefficient of the second gate voltage on the threshold voltage.

[0051] Adjust V DG The size of makes the dual-gate thin film transistor TFT2 work in the subthreshold region, then the subthreshold region output current I of the dual-gate thin film transistor TFT2 can be obtained. DS2 for:

[0052]

[0053] Among them, I D02 V BG =V T2 And V DS2 >>kT / q, the output current of the dual-gate thin film transistor TFT2, S2 is the subthreshold swing of the dual-gate thin film transistor TFT2. That is V DS2 >>0.0258V (at room temperature), equation (9) can be simplified to:

[0054]

[0055] Therefore, the final output current I of the random read active pixel sensor circuit is DS2 The photocurrent I of diode D photo It is a power function relationship, that is:

[0056]

[0057] For thin film transistors with the same active material and the same process technology, the subthreshold swing is basically unchanged, that is, S1≈S2, so the output current I DS2 It has a power function relationship with the light intensity P, that is:

[0058] I DS2 ∝P -γ

[0059] If the control coefficient γ of the top gate voltage of the n-type dual-gate thin film transistor on the threshold voltage is -0.9 to -2, the output current of the active pixel circuit is quasi-linear with the light intensity. Therefore, for a general logarithmic active pixel sensor, the active pixel circuit based on the n-type semiconductor device designed in this embodiment retains the characteristic of being randomly readable, and because the output of the pixel circuit is quasi-linear with the light intensity, the output current changes more obviously with the light intensity under weak light intensity, so it has higher sensitivity and wider dynamic response range.

[0060] Embodiment 2

[0061] This embodiment discloses another active pixel circuit capable of random reading, such as Figure 3 As shown, the difference between the embodiment 1 and the embodiment 1 is that the photodiode D is a pin structure photodiode, and the first power supply V DD The anode of the photodiode D is connected to the cathode of the photodiode D and the drain of the single-gate thin film transistor TFT1. The first power supply V DD Used to provide reverse bias voltage for photodiode D, second power supply V BG is the operating voltage of the dual-gate thin film transistor TFT2.

[0062] In the above embodiment, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are both p-type materials such as p-type low-temperature polycrystalline silicon or p-type organic semiconductor. The double-gate thin film transistor TFT2 replaces the source follower and the selection switch tube in the Log APS, thereby reducing the use of internal devices in the pixel, improving the aperture ratio of the pixel and simplifying the production process.

[0063] Next, this embodiment is further explained in conjunction with the specific implementation process, as follows:

[0064] When the sensor pixel circuit is in working state, because it is composed of a pin-type diode and a p-type thin film device, the first power supply VDD must apply a negative bias voltage to make the photodiode D in a reverse bias state and the thin film transistor in a working state. The total current flowing through the photodiode D is:

[0065] I PD =I SD1 =I dark +I photo (11)

[0066] The gate voltage and source-drain voltage of the single-gate thin-film transistor TFT1 are also the same as formula (3), that is, the gate voltage is equal to the source-drain voltage. The subthreshold current I of TFT1 can be obtained from the current formula of the subthreshold region of the p-type thin-film transistor: SD1 for:

[0067]

[0068] in, β1 is the ideal parameter of the single-gate thin-film transistor TFT1. DS1 <<-V sth1 When , formula (12) can be simplified as:

[0069]

[0070] By transforming equation (13), we can get the source-drain voltage V of the single-gate thin-film transistor TFT1: DS1 for:

[0071]

[0072] From formula (7) and (8), we can get the top gate voltage V of the dual-gate thin film transistor TFT2: TG and threshold voltage V T2 Similarly, adjust V DG The size of makes the dual-gate thin film transistor TFT2 work in the subthreshold region, then the subthreshold region output current I of the dual-gate thin film transistor TFT2 can be obtained. SD2 for:

[0073]

[0074] When V DS2 <<-V sth2 , formula (14) can be simplified as:

[0075]

[0076] Therefore, the final output current I of the randomly readable active pixel sensor circuit is SD2 The photocurrent I of diode Dphoto It is a power function relationship, that is:

[0077]

[0078] For thin film transistors with the same active material and the same process technology, the ideal factor remains basically unchanged, that is, β1≈β2, so the output current ISD2 and the light intensity P are in a power function relationship, that is:

[0079] I SD2 ∝P -γ

[0080] If the control coefficient γ of the top gate voltage of the double-gate thin film transistor with the active layer material being p-type material on the threshold voltage is -0.9 to -2, the output current of the pixel circuit is in a quasi-linear relationship with the light intensity. Therefore, the active pixel circuit has the characteristics of random readability, high sensitivity, and wide dynamic range.

[0081] Embodiment 3

[0082] This embodiment discloses another active pixel circuit that can be randomly read, such as Figure 4 As shown, it includes: a photodiode D, a single-gate thin film transistor TFT1, a double-gate thin film transistor TFT2, a first power supply V DD , the second power supply V BG , the first power supply V DD The drain of the single-gate thin film transistor TFT1 and the drain of the double-gate thin film transistor TFT2 are connected, the drain of the single-gate thin film transistor TFT1 is connected to the gate of the single-gate thin film transistor TFT1, the source of the single-gate thin film transistor TFT1 is connected to the cathode of the diode D, the anode of the photodiode D is grounded, the source of the single-gate thin film transistor TFT1 is connected to the gate of the double-gate thin film transistor TFT2, and the double-gate thin film transistor TFT2 is connected to the second power supply V BG The source of the dual-gate thin film transistor TFT2 is the signal output terminal, and the first power supply V DD It is used to provide the single-gate thin film transistor TFT1 with an operating voltage and a second power supply V BG Used to control the dual-gate thin film transistor TFT2.

[0083] In the above embodiment, the photodiode D is a photodiode with a nip structure.

[0084] In the above embodiment, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are both one of n-type materials such as amorphous silicon, indium gallium zinc oxide, n-type organic semiconductor and n-type low-temperature polycrystalline silicon. The double-gate thin film transistor TFT2 replaces the source follower and the selection switch tube in the Log APS, reduces the use of internal devices in the pixel, improves the aperture ratio of the pixel and simplifies the production process.

[0085] Next, this embodiment is further explained in conjunction with the specific implementation process, as follows:

[0086] When the sensor pixel circuit is in working state, the photodiode D needs to be reverse biased to make it sensitive to light, so the first power supply V DD , the second power supply V BG All of them are external bias ports; and since a-Si, IGZO, n-type organic semiconductors and n-type low-temperature polysilicon used to make thin-film transistors are all n-type materials, they generally require a positive voltage to drive, so a nip-structured photodiode D is used, that is, the cathode is used as the external bias port and the anode is grounded. When the sensor pixel circuit is working, V DD The photodiode D is in a reverse bias state when the positive bias voltage is applied. At this time, the photogenerated carriers in the photodiode D generate electron-hole pairs due to the external bias voltage and move toward the cathode and anode respectively. The photocurrent and total current flowing through the photodiode D are the same as equations (1) and (2). The gate-drain voltage, subthreshold current and source-drain voltage of the single-gate thin-film transistor TFT1 are the same as equations (3), (4) and (6) respectively.

[0087] Because the cathode of the photodiode D, the source of the single-gate thin-film transistor TFT1, and the top gate of the double-gate thin-film transistor TFT2 are connected together, we have:

[0088] V TG =V DD -V DS1 (17)

[0089] From formula (8), we can get the threshold voltage V of the dual-gate thin film transistor TFT2: T2 . Adjust V DG The size of makes the dual-gate thin film transistor TFT2 work in the subthreshold region, then the subthreshold region output current I of the dual-gate thin film transistor TFT2 can be obtained. DS2 for:

[0090]

[0091] Among them, I D02 V BG =V T2 And V DS2 >>kT / q, the output current of the dual-gate thin film transistor TFT2, S2 is the subthreshold swing of the dual-gate thin film transistor TFT2. That is V DS2 >>0.0258V (at room temperature), equation (18) can be simplified to:

[0092]

[0093] Therefore, the final output current I of the random read active pixel sensor circuit is DS2 The photocurrent I of diode D photo It is a power function relationship, that is:

[0094]

[0095] For thin film transistors with the same active material and the same process technology, the subthreshold swing is basically unchanged, that is, S1≈S2, so the output current I DS2 It has a power function relationship with the light intensity P, that is:

[0096] I DS2 ∝P γ

[0097] If the control coefficient γ of the top gate voltage of the double-gate thin-film transistor with an active layer material of n-type on the threshold voltage is -0.9 to -2, the output current of the pixel circuit is quasi-linearly related to the light intensity. For a general logarithmic active pixel sensor, the active pixel image sensor designed in this embodiment retains the characteristic of being randomly readable, and because the output of the sensor is quasi-linearly related to the light intensity, under weak light intensity, the output current changes more obviously with the light intensity, and therefore has higher sensitivity and a wider dynamic response range.

[0098] Embodiment 4

[0099] This embodiment discloses another active pixel circuit capable of random reading, such as Figure 5 As shown, the difference between the embodiment 3 and the embodiment 3 is that the photodiode D is a pin structure diode, the anode of the photodiode D is connected to the source of the single-gate thin film transistor TFT1, the cathode of the photodiode D is grounded, and the first power supply V DD The second power source V is used to provide an operating voltage for the single-gate thin film transistor TFT1. BG Provides an operating voltage for the dual-gate thin film transistor TFT2.

[0100] In the above embodiment, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are both p-type materials such as p-type low-temperature polycrystalline silicon or p-type organic semiconductor. The double-gate thin film transistor TFT2 replaces the source follower and the selection switch tube in the Log APS, thereby reducing the use of internal devices in the pixel, improving the aperture ratio of the pixel and simplifying the production process.

[0101] Next, this embodiment is further explained in conjunction with the specific implementation process, as follows:

[0102] When the sensor pixel circuit is in working state, because it is composed of a pin-type photodiode and a p-type thin film device, the first power supply VDD must apply a negative bias voltage to make the thin film transistor in working state and the photodiode D in reverse bias state. The total current flowing through the photodiode D is the same as formula (11). The gate voltage and source-drain voltage of the single-gate thin film transistor TFT1 are also the same as formula (3), that is, the gate voltage is equal to the source-drain voltage. The gate-drain voltage, subthreshold current and source-drain voltage of the single-gate thin film transistor TFT1 are the same as formula (3), formula (4) and formula (14) respectively.

[0103] Because the three ports of the anode of the photodiode D, the source of the single-gate thin-film transistor TFT1, and the top gate of the double-gate thin-film transistor TFT2 are connected together, we have:

[0104] V TG =V DD -V DS1 (20)

[0105] From formula (8), we can get the threshold voltage V of the dual-gate thin film transistor TFT2: T2 . Adjust V DG The size of makes the dual-gate thin film transistor TFT2 work in the subthreshold region, then the subthreshold region output current I of the dual-gate thin film transistor TFT2 can be obtained. SD2 for:

[0106]

[0107] When V DS2 <<-V sth2 , formula (21) can be simplified as:

[0108]

[0109] Therefore, the final output current I of the randomly readable active pixel sensor circuit is SD2 The photocurrent I of diode D photo It is a power function relationship, that is:

[0110]

[0111] For thin film transistors with the same active material and the same process technology, the ideal factor remains basically unchanged, that is, β1≈β2, so the output current ISD2 and the light intensity P are in a power function relationship, that is:

[0112] I SD2 ∝P γ

[0113] If the control coefficient γ of the top gate voltage of the double-gate thin film transistor with the active layer material being p-type material on the threshold voltage is -0.9 to -2, the output current of the pixel circuit is in a quasi-linear relationship with the light intensity. Therefore, the active pixel circuit has the characteristics of random readability, high sensitivity, and wide dynamic range.

[0114] Embodiment 5

[0115] This embodiment discloses a driving method for a randomly readable active pixel circuit, which is applicable to Embodiment 1 to Embodiment 4 and includes the following steps:

[0116] When the randomly readable active pixel circuit is in an operating state, a voltage is applied to the photodiode to put the photodiode in a reverse biased state and generate a photocurrent under light, so that the first transistor and the second transistor operate in a subthreshold region, so that the output current of the randomly readable active pixel circuit is in a power function relationship with the photocurrent of the photodiode, so that the output signal of the randomly readable active pixel sensor circuit is in a quasi-linear relationship with the light intensity, so that the sensitivity and the dynamic response range can be optimized at the same time.

[0117] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A randomly readable active pixel circuit, characterized in that: include: A photodiode, a first transistor, a second transistor, a first power supply, and a second power supply; The first power supply is connected to the drain of the second transistor and is connected to the drain of the first transistor through the diode, the drain of the first transistor is connected to the gate of the first transistor and the top gate of the second transistor, the source of the first transistor is grounded, the bottom gate of the second transistor is connected to the second power supply, and the source of the second transistor is a signal output terminal; The first transistor is a single-gate transistor, and the second transistor is a double-gate transistor.

2. The active pixel circuit according to claim 1, characterized in that: The photodiode is a photodiode with a nip structure, the first transistor and the second transistor are both n-type semiconductor devices, the first power supply is connected to the cathode of the photodiode, and the anode of the photodiode is connected to the drain of the first transistor.

3. The active pixel circuit according to claim 2, characterized in that: The photodiode is a photodiode with a pin structure, the first transistor and the second transistor are both p-type semiconductor devices, the first power supply is connected to the anode of the photodiode, and the cathode of the photodiode is connected to the drain of the first transistor.

4. A randomly readable active pixel circuit, characterized in that: include: A photodiode, a first transistor, a second transistor, a first power supply, and a second power supply; The first power supply is connected to the drain of the first transistor and the drain of the second transistor, the drain of the first transistor is connected to the gate of the first transistor, the source of the first transistor is connected to the top gate of the second transistor and is grounded through the photodiode, the bottom gate of the second transistor is connected to the second power supply, and the source of the second transistor is a signal output terminal; The first transistor is a single-gate thin film transistor, and the second transistor is a double-gate thin film transistor.

5. The active pixel circuit according to claim 4, characterized in that: The photodiode is a photodiode with a nip structure, the first transistor and the second transistor are both n-type semiconductor devices, the cathode of the photodiode is connected to the source of the first transistor and the top gate of the second transistor, and the anode of the diode is grounded.

6. The active pixel circuit according to claim 4, characterized in that: The photodiode is a photodiode of a pin structure, the first transistor and the second transistor are both p-type semiconductor devices, the anode of the photodiode is connected to the source of the first transistor and the top gate of the second transistor, and the cathode of the diode is grounded.

7. A driving method for a randomly readable active pixel circuit according to any one of claims 1 to 6, characterized in that: The steps include: When the randomly readable active pixel circuit is in an operating state, a voltage is applied to the photodiode, so that the photodiode is in a reverse biased state and generates a photocurrent under light, so that the first transistor and the second transistor operate in a subthreshold region, so that the output current of the randomly readable active pixel circuit is in a power function relationship with the photocurrent of the photodiode.

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