Amplifier circuit for x-ray flat panel detector

Abstract

The present utility model provides an amplifier circuit for an X-ray flat panel detector. The amplifier circuit comprises a first transistor, a second transistor, and a third transistor; a drain of the first transistor is connected to the second transistor; a source of the first transistor is grounded; the first transistor is connected to the third transistor; the drain of the first transistor is connected to an active pixel unit or a passive pixel unit; the third transistor in the amplifier circuit works as a switch transistor; when the amplifier circuit is connected to the active pixel unit, the switch transistor is regulated, so that an active pixel circuit works in different working modes, and thus when one row works, information exposed in other rows is stored and read, thereby improving the utilization rate of rays; and when the amplifier circuit is connected to the passive pixel unit, a 3T passive pixel amplifier circuit is formed, and an amplifier having a signal amplifying function is realized inside pixels, so that the sensitivity and signal-to-noise ratio are improved, thereby meeting the requirements of detection under low light and low-dose X-ray conditions.

Description

Amplification circuit for X-ray flat panel detector TECHNICAL FIELD

[0001] The utility model relates to the circuit technical field of amplification circuit, especially relates to a kind of amplification circuit for X-ray flat panel detector. BACKGROUND

[0002] Mainstream commercial flat panel detector is mainly based on TFT process passive pixel (PPS) and based on CMOS process active pixel (APS) sensing circuit.

[0003] Active pixel APS improves signal-to-noise ratio by integrating common source or common drain amplifier inside the pixel, but in a single pixel, the total area of the pixel is limited, fill rate=photoelectric device area / total area of single pixel, the more transistors, the less area left for photoelectric device, and fill rate will decrease, and resolution is negatively related to the size of single pixel area, the smaller the pixel area, the higher the resolution, but limited by manufacturing process, the increase of transistor number will lead to that single pixel cannot be laid out, only the pixel area can be increased, which leads to the decrease of resolution, so the spatial resolution and fill rate are greatly limited, active pixel APS has active transistor inside which can amplify signal, so it has high gain compared with passive pixel PPS, but active pixel PPS starts exposure by row scanning, and all rows complete the work mode, so when a row works, other rows do not work but are still exposed, so that the utilization rate of X-ray is low, most of the X-ray working time is in empty exposure state.

[0004] Passive pixel PPS has the advantages of simple structure and high spatial resolution, but because passive pixel PPS has no amplifier inside, it needs to amplify signal through external charge amplifier, which leads to low sensitivity and signal-to-noise ratio, and cannot meet the detection requirements under weak light and low dose X-ray conditions.

[0005] Therefore, in the prior art, when using active pixel circuit, there is a problem of unable to improve the utilization rate of rays, and when using passive pixel circuit, there is a problem of unable to improve signal-to-noise ratio and sensitivity.

[0006] Utility model content

[0007] In order to overcome the shortcomings of the prior art, the utility model aims at providing an amplification circuit for X-ray flat panel detector, which can solve the problem of unable to improve the utilization rate of rays when using active pixel circuit or unable to improve signal-to-noise ratio and sensitivity when using passive pixel circuit in the prior art.

[0008] In order to solve the above problems, the utility model is implemented according to the following technical scheme:

[0009] An amplification circuit for an X-ray flat panel detector, comprising:

[0010] A first transistor, a second transistor and a third transistor;

[0011] The drain of the first transistor is connected to the second transistor;

[0012] The source of the first transistor is grounded;

[0013] The first transistor is connected to the third transistor;

[0014] The drain of the first transistor is connected to an active pixel unit or a passive pixel unit.

[0015] Compared with the prior art, the amplification circuit for the X-ray flat panel detector has the following beneficial effects: the third transistor in the amplification circuit works as a switch tube, when the amplification circuit is connected to an active pixel unit, it is a 3T1D active pixel circuit, by controlling the switch tube, the active pixel circuit works in different working modes, and information exposed by other rows is stored and read when working in a row, thereby improving the utilization rate of rays; when the amplification circuit is connected to a passive pixel unit, it is a 3T passive pixel amplification circuit, an amplifier with an amplification signal function in the pixel is realized, the sensitivity and signal-to-noise ratio can be improved, and the demand for detection under weak light and low-dose X-ray conditions can be met.

[0016] Optionally, the first transistor is a double-gate thin film transistor; the second transistor is a double-gate thin film transistor; and the third transistor is a single-gate thin film transistor or a double-gate thin film transistor.

[0017] Optionally, the drain of the second transistor is connected to a second power supply.

[0018] The source of the second transistor is a signal output end.

[0019] Optionally, the drain of the second transistor is connected to the source of the first transistor.

[0020] The source of the second transistor is a signal output end.

[0021] Optionally, the drain of the first transistor is connected to the top gate or the bottom gate of the first transistor through the third transistor.

[0022] Optionally, the drain of the first transistor is connected to the top gate or the bottom gate of the second transistor.

[0023] Optionally, the active pixel unit comprises a photoelectric device, and the photoelectric device is connected to the drain of the first transistor and a first power supply.

[0024] Optionally, the optoelectronic device is a photodiode.

[0025] The first power source is connected to the cathode of the photodiode.

[0026] The anode of the photodiode is connected to the drain of the first transistor.

[0027] The anode of the photodiode is connected to the top gate or bottom gate of the second transistor.

[0028] Optionally, the optoelectronic device is a photoconductive material optoelectronic device.

[0029] Optionally, the passive pixel cell comprises a photodiode and a fourth transistor.

[0030] The cathode of the photodiode is connected to the drain of the first transistor through the fourth transistor. BRIEF DESCRIPTION OF DRAWINGS

[0031] Fig. 1 is a schematic diagram of an embodiment of the present application;

[0032] Fig. 2 is a schematic diagram of another embodiment of the present application;

[0033] Fig. 3 is a schematic diagram of a third embodiment of the present application;

[0034] Fig. 4 is a schematic diagram of a fourth embodiment of the present application;

[0035] Fig. 5 is a schematic diagram of a fifth embodiment of the present application;

[0036] Fig. 6 is a schematic diagram of a sixth embodiment of the present application;

[0037] Fig. 7 is a timing diagram of random read of a 3T1D active pixel circuit;

[0038] Fig. 8 is a timing diagram of integration read of a 3T1D active pixel circuit;

[0039] Fig. 9 is a timing diagram of random read and integration read of a 3T1D active pixel circuit;

[0040] Fig. 10 is a schematic diagram of an eighth embodiment of the present application;

[0041] Fig. 11 is a schematic diagram of a passive pixel cell in the eighth embodiment of the present application.

[0042] Reference signs, 1, amplification circuit. DETAILED DESCRIPTION

[0043] The preferred embodiments of the present application will be described below in conjunction with the accompanying drawings, and it should be understood that the preferred embodiments described herein are only used to explain and illustrate the present application, and are not used to limit the present application.

[0044] In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0045] Example 1

[0046] Referring to Figure 1, this embodiment discloses an amplification circuit for an X-ray flat panel detector, including: a first dual-gate thin-film transistor TFT1, a second dual-gate thin-film transistor TFT2, and a third thin-film transistor TFT3. In this embodiment, the third thin-film transistor TFT3 is a single-gate thin-film transistor.

[0047] The drain of the first dual-gate thin-film transistor TFT1 and the signal line Signal in Connection, the bottom gate of the second dual-gate thin-film transistor TFT2 and the signal line Signal in Connection, signal line in The other end is connected to either the active pixel unit (PPS) or the passive pixel unit (APS); the drain of the first dual-gate thin-film transistor (TFT1) is connected to the bottom gate of the first dual-gate thin-film transistor (TFT1) through the third thin-film transistor (TFT3), which is a switching transistor; the source of the first dual-gate thin-film transistor (TFT1) is grounded; the second power supply V... DD2 The second power supply V is connected to the drain of the second dual-gate thin-film transistor TFT2. DD2 Used to control the switching state of the second dual-gate thin-film transistor TFT2; the source of the second dual-gate thin-film transistor TFT2 is used as the signal output terminal.

[0048] The top gate of the first dual-gate thin-film transistor TFT1 is connected to the peripheral circuit, and the top gate voltage V of the first dual-gate thin-film transistor TFT1 is controlled by the peripheral circuit. TG1 Top gate voltage V TG1 Used to regulate the operating region of the first dual-gate thin-film transistor TFT1 to the subthreshold region.

[0049] The top gate of the second dual-gate thin-film transistor TFT2 is connected to the peripheral circuit, and the top gate voltage V of the second dual-gate thin-film transistor TFT2 is controlled by the peripheral circuit. TG2 Top gate voltage V TG2The third thin film transistor TFT3 is controlled to be in the saturation region and the switching state.

[0050] The gate of the third thin film transistor TFT3 is connected with the peripheral circuit, and the gate voltage V G3 of the third thin film transistor TFT3 is controlled by the peripheral circuit. G3 The third thin film transistor TFT3 is controlled to be in the saturation region and the switching state. G3 When the gate voltage V G3 is greater than the threshold voltage and is equal to the drain voltage, the third thin film transistor TFT3 is in the open state; and when the gate voltage V G3 is less than or equal to the threshold voltage, the third thin film transistor TFT3 is in the closed state.

[0051] Embodiment Two

[0052] Referring to FIG. 2, the second amplification circuit for the X-ray flat panel detector is disclosed in the embodiment, which is different from the amplification circuit in the first embodiment in that the third thin film transistor TFT3 is a double-gate thin film transistor.

[0053] The top gate and the bottom gate of the third thin film transistor TFT3 are connected with the peripheral circuit, and the top gate voltage V TG3 and the bottom gate voltage V BG3 of the third thin film transistor TFT3 are controlled by the peripheral circuit.

[0054] The amplification circuit in the embodiment can achieve the same function as the amplification circuit in the first embodiment.

[0055] Embodiment Three

[0056] Referring to FIG. 3, the third amplification circuit for the X-ray flat panel detector is disclosed in the embodiment, which is different from the amplification circuit in the first embodiment in that the top gate and the bottom gate of the first double-gate thin film transistor TFT1 are interchanged.

[0057] Specifically, the drain of the first double-gate thin film transistor TFT1 is connected with the top gate of the first double-gate thin film transistor TFT1 through the third thin film transistor TFT3.

[0058] The bottom gate of the first double-gate thin film transistor TFT1 is connected with the peripheral circuit, and the bottom gate voltage V BG1 of the first double-gate thin film transistor TFT1 is controlled by the peripheral circuit. BG1 The first double-gate thin film transistor TFT1 is controlled to be in the sub-threshold region.

[0059] The amplification circuit of the embodiment can achieve the same function as the amplification circuit of the first embodiment, but the top gate voltage V TG1 is different from the bottom gate voltage V BG1 The control ability of the threshold voltage of the first double-gate thin film transistor TFT1 is different, which is embodied in that the control coefficient γ of the gate voltage on the threshold voltage is related to different manufacturing processes. The greater γ is, the stronger the control ability is. Therefore, compared with the control ability of the amplification circuit of the first embodiment, the control ability of the amplification circuit of the embodiment will change.

[0060] Embodiment Four

[0061] Referring to FIG. 4, the fourth amplification circuit for an X-ray flat panel detector is disclosed in the embodiment, which is different from the first embodiment in that the top gate and the bottom gate of the second double-gate thin film transistor TFT2 are interchanged.

[0062] Specifically, the drain of the first double-gate thin film transistor TFT1 is connected with the top gate of the second double-gate thin film transistor TFT2.

[0063] The bottom gate of the second double-gate thin film transistor TFT2 is connected with a peripheral circuit, and the bottom gate voltage V BG2 of the second double-gate thin film transistor TFT2 is controlled by the peripheral circuit. BG2 The bottom gate voltage V TG2 is used to control the working region of the second double-gate thin film transistor TFT2 to the sub-threshold region.

[0064] The amplification circuit of the embodiment can achieve the same function as the amplification circuit of the first embodiment, but the top gate voltage V TG2 is different from the bottom gate voltage V BG2 The control ability of the threshold voltage of the second double-gate thin film transistor TFT2 is different, which is embodied in that the control coefficient γ of the gate voltage on the threshold voltage is related to different manufacturing processes. The greater γ is, the stronger the control ability is. Therefore, compared with the control ability of the amplification circuit of the first embodiment, the control ability of the amplification circuit of the embodiment will change.

[0065] Embodiment Five

[0066] Referring to FIG. 5, the fifth amplification circuit for an X-ray flat panel detector is disclosed in the embodiment, which is different from the first embodiment in that the second power supply V DD2 is connected with the source of the first double-gate thin film transistor TFT1, that is, the drain of the second double-gate thin film transistor TFT2 is grounded.

[0067] The amplification circuit of the embodiment is equivalent to the amplification circuit of the first embodiment.

[0068] Embodiment Six

[0069] The embodiment one is connected with an active pixel unit to form a 3T1D active pixel circuit shown in Fig. 6, wherein the active pixel unit comprises a photoelectric device, in this embodiment, the photoelectric device is a photodiode PD, the anode of the photodiode PD is connected with the drain of a first double-gate thin film transistor TFT1 through a signal line, and the cathode of the photodiode PD is connected with a first power supply V DD1 .

[0070] Embodiment seven

[0071] This embodiment discloses a second 3T1D active pixel circuit, which is different from the embodiment six in that: the photoelectric device of the active pixel unit is a photoconductive material photoelectric device; the photoconductive material photoelectric device includes but is not limited to halide, calcium, titanium, and minerals.

[0072] Specifically, the first power supply V DD1 is connected with the photoelectric device, the first power supply V DD1 is used to provide a reverse bias voltage for the photoelectric device; the photoelectric device is connected with the drain of a first double-gate thin film transistor TFT1; the drain of the first double-gate thin film transistor TFT1 is connected with the bottom gate of the first double-gate thin film transistor TFT1 through a third thin film transistor TFT3, and the third thin film transistor TFT3 is a switch tube; the source of the first double-gate thin film transistor TFT1 is grounded; the photoelectric device is connected with the bottom gate of a second double-gate thin film transistor TFT2; a second power supply V DD2 is connected with the drain of the second double-gate thin film transistor TFT2, and the second power supply V DD2 is used to control the switching state of the second double-gate thin film transistor TFT2; the source of the second double-gate thin film transistor TFT2 is used as a signal output end.

[0073] The 3T1D active pixel circuit of this embodiment can achieve the same function as the 3T1D active pixel circuit of the embodiment six.

[0074] When forming the 3T1D active pixel circuit, three working states can be realized by controlling the first double-gate thin film transistor TFT1, the second double-gate thin film transistor TFT2 and the third thin film transistor TFT3. Next, the 3T1D active pixel circuit is further explained in combination with a specific implementation process as follows:

[0075] The first working state is random reading.

[0076] Referring to Fig. 7, when the first power supply V DD1 is a positive bias voltage, the photodiode PD is in a reverse bias state, at this time, the photodiode PD can perform photosensing, therefore, the photo-generated carriers in the photodiode PD will separate to form photo-generated electron-hole pairs under the action of an electric field, and the photo-generated electron-hole pairs will move to the cathode and the anode of the photodiode PD respectively under the action of an external bias voltage to form a photo-generated current Iphoto , realizes photoelectric conversion process; at this time, the photoelectric diode PD has fast response speed to optical signal and can quickly capture light intensity change; the photo-generated current I photo The expression is as follows:

[0077] Wherein, η0 is the quantum efficiency of the photoelectric diode PD; P is the optical power; A is the light receiving area of the photoelectric diode PD; λ is the wavelength of light; R is the reflection coefficient; α and t are the absorption coefficient and thickness of the active light sensing layer of the photoelectric diode PD respectively; h is the Planck constant; c is the speed of light in vacuum.

[0078] By adjusting the gate voltage V G3 of the third thin film transistor TFT3, the third thin film transistor TFT3 is in an open state, at this time, the first double-gate thin film transistor TFT1 is also in an open state, the first double-gate thin film transistor TFT1 and the photoelectric diode PD are in the same branch, therefore, the current flowing through the two is equal, and the current expressions of the two are as follows: I DS1 =I PD =I dark +I photo

[0079] Wherein, I dark is the dark state current of the photoelectric diode PD; the photo-generated current I photo of the photoelectric diode PD under light conditions flows to the drain of the first double-gate thin film transistor TFT1, and a sensing voltage V DS1 is generated, the sensing voltage V DS1 acts on the second double-gate thin film transistor TFT2. For the first double-gate thin film transistor TFT1 in diode connection mode, the drain voltage (sensing voltage V DS1 ) and the bottom gate voltage V BG1 are equal, and the expressions are as follows: V DS1 =V BG1

[0080] When the first double-gate thin film transistor TFT1 works in the sub-threshold region, according to the current expression of the sub-threshold region of the transistor, the source-drain current I DS1 of the first double-gate thin film transistor TFT1 is as follows:

[0081] Wherein, I D01 is the source-drain current of the first double-gate thin film transistor TFT1 when V BG1 =V TH1 and V DS1 >>kTq; V TH1 is the threshold voltage of the first double-gate thin film transistor TFT1.

[0082] By simplifying the above two equations, we can get:

[0083] The drain voltage of the first double-gate thin film transistor TFT1, i.e. the sensing voltage V DS1 , is expressed as follows:

[0084] From the above derivation, it can be seen that the drain voltage of the first double-gate thin film transistor TFT1 (sensing voltage V DS1 ) is logarithmically related to the light intensity.

[0085] By adjusting the size of the top gate voltage V TG2 of the second double-gate thin film transistor TFT2, the second double-gate thin film transistor TFT2 is made to work in the sub-threshold region, at which time the signal output from the source of the second double-gate thin film transistor TFT2 is in a quasi-linear relationship with the instantaneous light intensity.

[0086] The first working state realizes that each pixel unit can be accessed and read at any time, i.e. the active pixel circuit can be randomly read, which is suitable for fast imaging; and because the output signal is in a quasi-linear relationship with the instantaneous light intensity, the change of the output signal with the light intensity is more obvious under weak light intensity, so the active pixel circuit has higher sensitivity and wider dynamic response range.

[0087] The second working state is integral reading:

[0088] Referring to FIG. 8, the first power supply V DD1 is a forward bias, and the photodiode PD can generate a photo-generated current I photo under light conditions.

[0089] When the third thin film transistor TFT3 is in the off state, the first double-gate thin film transistor TFT1 is also in the off state, so the photo-generated charge generated by the photodiode PD under light conditions does not flow to the first double-gate thin film transistor TFT1, but only flows to the second double-gate thin film transistor TFT2, and the photo-generated charge is stored in the parasitic capacitance of the second double-gate thin film transistor TFT2; the second power supply V DD2 is controlled to make the second double-gate thin film transistor TFT2 in the off state, at which time the photo-generated charge continuously accumulates in the parasitic capacitance; the second power supply V DD2 is controlled to make the second double-gate thin film transistor TFT2 in the on state, at which time the photo-generated charge flows out of the parasitic capacitance to release and thus generate a signal. The second working state realizes that the active pixel circuit has an integral-reading working mode similar to the passive pixel circuit.

[0090] The third working state is random reading and integral reading:

[0091] Referring to Fig. 9, for each row in the array, the second double-gate thin film transistor TFT2 and the third thin film transistor TFT3 are controlled to be in the off state; when performing the first working state (random reading), the second double-gate thin film transistor TFT2 and the third thin film transistor TFT3 are controlled to be in the on state; after the random reading is performed, the second double-gate thin film transistor TFT2 and the third thin film transistor TFT3 are controlled to be in the off state again to perform the integration mode, at this time, other rows in the array are still performing random reading, and the rays are still exposed, and the row performing the random reading can perform the integration mode to store the ray information in the parasitic capacitor; when all rows in the array perform the random reading, the rays are turned off, and the second double-gate thin film transistor TFT2 of each row in the array is controlled row by row to be in the on state, so that the ray information stored in the parasitic capacitor is released for reading.

[0092] When the amplification circuit is connected with the active pixel unit, the third thin film transistor TFT3 works as a switch tube, by controlling the third thin film transistor TFT3, the on or off state of the first double-gate thin film transistor TFT1 is controlled, and the on or off state of the second double-gate thin film transistor TFT2 is controlled by the peripheral circuit, so that the 3T1D active pixel circuit can work in different working modes, thereby improving the utilization rate of the rays; and the drain voltage (sensing voltage V DS1 ) of the first double-gate thin film transistor TFT1 is logarithmically related to the incident light intensity, which can effectively widen the dynamic response range of the pixel circuit; and the second double-gate thin film transistor TFT2 works as an amplifier, which improves the sensitivity of the 3T1D active pixel circuit under weak light conditions; therefore, in Embodiment Six and Embodiment Seven, after the amplification circuit is connected with the active pixel unit, the lower limit of detection can be reduced, thereby expanding the dynamic response range.

[0093] Embodiment Eight

[0094] The active pixel unit in Embodiment One is connected with the multi-column passive pixel unit to form a 3T passive pixel amplification circuit shown in Fig. 10, and each passive pixel unit includes a photodiode PD and a transistor TFT, and the transistor TFT is connected with the amplification circuit 1.

[0095] The passive pixel units (Pixel 1.1, Pixel 2.1, Pixel m.1, Pixel 1.2, Pixel 2.2, Pixel m.2,...) in each column are connected in series, so that the plurality of passive pixel units can be connected with only one amplification circuit, that is, the plurality of passive pixel units share one amplification circuit, so that only one switch thin film transistor (transistor TFT in FIG. 11) needs to be reserved in the passive pixel unit, which greatly improves the pixel fill factor, and at the same time, the amplification circuit 1 is applied outside the passive pixel unit, that is, when the first row is turned on and the other rows are turned off, the amplification circuit 1 and the passive pixel units in the first row constitute an active pixel, and when the second row is turned on and the other rows are turned off, the amplification circuit 1 and the passive pixel units in the second row constitute an active pixel. Through this mode of sharing the same amplification circuit, both the fill factor and the high sensitivity and wide dynamic characteristics of the active pixel can be improved, that is, the high sensitivity and wide dynamic range characteristics of the 3T amplification circuit are retained.

[0096] Therefore, the amplification circuit disclosed in the present application can be applied to both active pixels and passive pixels, that is, the amplification circuit can be connected with active pixel units or passive pixel units.

[0097] When the amplification circuit is used for active pixel units, high gain, high radiation utilization rate, and multiple working modes can be obtained, so that it not only has the signal amplification advantage of traditional active pixel circuits, but also solves the problem of low radiation utilization rate of traditional active pixel circuits.

[0098] When the amplification circuit is used for passive pixels, high gain and high resolution can be obtained, so that it not only has the signal amplification advantage of traditional active pixel circuits, but also solves the problem of low signal-to-noise ratio of traditional passive pixel circuits and the inability to detect weak signals.

[0099] The above is only a preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An amplification circuit for an X-ray flat panel detector, characterized by, The application relates to a pixel unit, comprising: a first transistor, a second transistor and a third transistor; a drain of the first transistor is connected with the second transistor; a source of the first transistor is grounded; the first transistor is connected with the third transistor; a drain of the first transistor is connected with an active pixel unit or a passive pixel unit.

2. An amplification circuit for an X-ray flat panel detector according to claim 1, characterized in that, The first transistor is a double-gate thin film transistor; the second transistor is a double-gate thin film transistor; and the third transistor is a single-gate thin film transistor or a double-gate thin film transistor.

3. An amplification circuit for an X-ray flat panel detector according to claim 2, characterized in that, a drain of the second transistor is connected with a second power supply; a source of the second transistor is a signal output end.

4. The amplification circuit for an X-ray flat panel detector according to claim 2, wherein a drain of the second transistor is connected with a source of the first transistor; a source of the second transistor is a signal output end.

5. The amplification circuit for an X-ray flat panel detector according to claim 2, wherein a drain of the first transistor is connected with a top gate or a bottom gate of the first transistor through the third transistor.

6. The amplification circuit for an X-ray flat panel detector according to claim 2, wherein a drain of the first transistor is connected with a top gate or a bottom gate of the second transistor.

7. The amplification circuit for an X-ray flat panel detector according to claim 2, wherein The active pixel unit comprises a photoelectric device, and the photoelectric device is connected with a drain of the first transistor and a first power supply.

8. An amplification circuit for an X-ray flat panel detector according to claim 7, characterized in that, The photoelectric device is a photodiode. The first power supply is connected with a cathode of the photodiode. An anode of the photodiode is connected with a drain of the first transistor. An anode of the photodiode is connected with a top gate or a bottom gate of the second transistor.

9. The amplification circuit for an X-ray flat panel detector according to claim 7, wherein The photoelectric device is a photoconductive material photoelectric device.

10. The amplification circuit for an X-ray flat panel detector according to claim 2, wherein The passive pixel unit comprises a photodiode and a fourth transistor. A cathode of the photodiode is connected with a drain of the first transistor through the fourth transistor.

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