Active pixel circuit for X-ray flat panel detector

Abstract

The utility model discloses an active pixel circuit for an X-ray flat panel detector. The active pixel circuit comprises a photoelectric device, a first transistor, a second transistor and a third transistor, the photoelectric device is connected with a first power supply; the photoelectric device is connected with the drain electrode of the first transistor; the source electrode of the first transistor is grounded; a drain electrode of the first transistor is connected with a top gate or a bottom gate of the first transistor through the third transistor; the photoelectric device is connected with the second transistor. According to the active pixel circuit, the third transistor works as a switching tube, and the active pixel circuit works in different working modes by regulating and controlling the switching tube, so that the control capability of the whole active pixel circuit is improved; by reducing the number of integrated transistors in the active pixel circuit, the pixel filling rate and resolution can be improved, the pixel sensitivity is further improved, and the manufacturing cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of circuits, and in particular to an active pixel circuit for an X-ray flat panel detector. Background Art

[0002] As one of the key components of the DR imaging system, the X-ray flat panel detector converts X-rays into electrical signals.

[0003] In the existing active pixel circuits for X-ray flat-panel detectors, a mixture of current-type active pixels and passive pixels is usually used; the active pixel circuit is usually composed of four transistors and a photodiode. The active pixel circuit can change different working modes according to the input signal to adapt to input signals of different sizes, solving the problem that the signal-to-noise ratio of passive pixels is low when the input signal is small, and the output of active pixels is easy to saturate when the input signal is large.

[0004] In a single pixel, the total pixel area is limited, and the fill rate = photodiode area / total area of ​​a single pixel. However, since multiple transistors are integrated in the active pixel circuit in the prior art, the area of ​​the photodiode is reduced, resulting in a lower pixel fill rate; the resolution is negatively correlated with the size of a single pixel area, that is, the smaller the pixel area, the higher the resolution, but due to the manufacturing process, the increase in the number of transistors will make it impossible to layout within a single pixel, and the pixel area can only be increased, resulting in a lower resolution; therefore, the active pixel circuit integrating multiple transistors will lead to low pixel fill rate, low resolution, and high production cost, and thus cannot effectively improve the sensitivity of the pixel. Utility Model Content

[0005] In order to overcome the above technical defects, the utility model provides an active pixel circuit for an X-ray flat panel detector, which can improve the sensitivity of the active pixel circuit and reduce the manufacturing cost.

[0006] In order to solve the above problems, the utility model is implemented according to the following technical solutions:

[0007] An active pixel circuit for an X-ray flat panel detector includes: a photoelectric device, a first transistor, a second transistor and a third transistor;

[0008] The photoelectric device is connected to a first power source; the photoelectric device is connected to a drain of the first transistor; the source of the first transistor is grounded; the drain of the first transistor is connected to a top gate or a bottom gate of the first transistor through the third transistor; and the photoelectric device is connected to the second transistor.

[0009] Compared with the prior art, the utility model provides an active pixel circuit for an X-ray flat-panel detector, and the beneficial effects are as follows: the active pixel circuit is composed of three transistors and one photoelectric device, wherein the third transistor works as a switch tube, and by regulating the switch tube, the active pixel circuit can work in different working modes, thereby improving the control ability of the entire active pixel circuit; by reducing the number of integrated transistors in the active pixel circuit, the pixel area occupied by the transistor can be reduced, thereby increasing the area of ​​the photodiode to improve the pixel fill rate and resolution, thereby improving the sensitivity of the pixel, and by reducing the number of integrated transistors in the active pixel circuit, the complexity of the manufacturing process can be reduced, thereby reducing the manufacturing cost.

[0010] Optionally, the first transistor is a dual-gate thin film transistor; the second transistor is a dual-gate thin film transistor; and the third transistor is a single-gate thin film transistor or a dual-gate thin film transistor.

[0011] Optionally, the photoelectric device is a photodiode; the first power supply is connected to the cathode of the photodiode; the anode of the photodiode is connected to the drain of the first transistor; and the anode of the photodiode is connected to the top gate or bottom gate of the second transistor.

[0012] Optionally, the optoelectronic device is composed of a photoconductive material.

[0013] Optionally, the drain of the second transistor is connected to a second power supply; and the source of the second transistor is a signal output terminal.

[0014] Optionally, the drain of the second transistor is connected to the source of the first transistor; the source of the second transistor is a signal output terminal.

[0015] Optionally, the photoelectric device is connected to the bottom gate or the top gate of the second transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The specific implementation of the utility model is further described in detail below with reference to the accompanying drawings, wherein:

[0017] Figure 1 This is a schematic diagram of Embodiment 1 of the present utility model;

[0018] Figure 2 This is a schematic diagram of the second embodiment of the present utility model;

[0019] Figure 3 This is a schematic diagram of the third embodiment of the present utility model;

[0020] Figure 4 This is a schematic diagram of the fourth embodiment of the present utility model;

[0021] Figure 5 This is a schematic diagram of Embodiment 5 of the present utility model. DETAILED DESCRIPTION

[0022] 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.

[0023] When the following description refers to the 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 the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0024] Embodiment 1

[0025] See also Figure 1 As shown, this embodiment discloses an active pixel circuit for an X-ray flat panel detector, including: a photoelectric device, a first double-gate thin film transistor TFT1, a second double-gate thin film transistor TFT2 and a third thin film transistor TFT3.

[0026] In the above embodiment, the photoelectric device is a photodiode PD, and the third thin film transistor TFT3 is a single-gate thin film transistor.

[0027] The first power supply VDD1 is connected to the cathode of the photodiode PD, and the first power supply VDD1 is used to provide a reverse bias voltage for the photodiode PD; the anode of the photodiode PD is connected to the drain of the first double-gate thin-film transistor TFT1; the drain of the first double-gate thin-film transistor TFT1 is connected to the bottom gate of the first double-gate thin-film transistor TFT1 through the 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 anode of the photodiode PD is connected to the bottom gate of the second double-gate thin-film transistor TFT2; the second power supply VDD2 is connected to the drain of the second double-gate thin-film transistor TFT2, and the second power supply VDD2 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 output as a signal output terminal.

[0028] The top gate of the first double-gate thin film transistor TFT1 is connected to the peripheral circuit, and the top gate voltage VTG1 of the first double-gate thin film transistor TFT1 is controlled by the peripheral circuit. The top gate voltage VTG1 is used to adjust the working area of ​​the first double-gate thin film transistor TFT1 to the subthreshold region.

[0029] The top gate of the second dual-gate thin film transistor TFT2 is connected to the peripheral circuit, and the top gate voltage VTG2 of the second dual-gate thin film transistor TFT2 is controlled by the peripheral circuit. The top gate voltage VTG2 is used to adjust the working area of ​​the second dual-gate thin film transistor TFT2 to the subthreshold area.

[0030] The top gate of the third thin-film transistor TFT3 is connected to the peripheral circuit, and the gate voltage VG3 of the third thin-film transistor TFT3 is controlled by the peripheral circuit. The gate voltage VG3 is used to adjust the working area of ​​the third thin-film transistor TFT3 to the saturation area, and is also used to control the switching state of the third thin-film transistor TFT3, specifically: regulating the gate voltage VG3, when the gate voltage VG3 minus the threshold voltage is greater than or equal to the drain voltage, the third thin-film transistor TFT3 is in the on state; when the gate voltage VG3 is less than or equal to the threshold voltage, the third thin-film transistor TFT3 is in the off state.

[0031] This embodiment can realize three working states by regulating the first dual-gate thin film transistor TFT1, the second dual-gate thin film transistor TFT2 and the third thin film transistor TFT3. Next, this embodiment is further explained in combination with the specific implementation process as follows:

[0032] The first working state:

[0033] When the first power supply VDD1 is a positive bias, the photodiode PD is in a reverse bias state. At this time, the photodiode PD can be sensitive to light. Therefore, the photogenerated carriers in the photodiode PD generate electron-hole pairs under the action of the external bias and move toward the cathode and the anode respectively, forming a photogenerated current Iphoto. At this time, the photodiode PD responds quickly to the light signal and can quickly capture changes in light intensity.

[0034] By regulating the gate voltage VG3 of the third thin-film transistor TFT3, the third thin-film transistor TFT3 is turned on. At this time, the first double-gate thin-film transistor TFT1 is also turned on. When the photocurrent Iphoto generated by the photodiode PD under light conditions flows to the drain of the first double-gate thin-film transistor TFT1, a sensing voltage VDS1 is generated. The sensing voltage VDS1 acts on the second double-gate thin-film transistor TFT2.

[0035] By adjusting the top gate voltage VTG2 of the second double-gate thin film transistor TFT2, the second double-gate thin film transistor TFT2 operates in the subthreshold region. At this time, the signal output by the source of the second double-gate thin film transistor TFT2 has a quasi-linear relationship with the instantaneous light intensity.

[0036] The first working state realizes that each pixel unit can be accessed and read at any time, that is, the active pixel circuit can be read randomly, which is suitable for fast imaging; and because the output signal has a quasi-linear relationship with the instantaneous light intensity, under weak light intensity, the output signal changes more obviously with the light intensity, so the active pixel circuit has higher sensitivity and a wider dynamic response range.

[0037] The second working state:

[0038] The first power source VDD1 is a forward bias voltage, and the photodiode PD can generate a photocurrent Iphoto under light conditions.

[0039] 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 photogenerated charge generated by the photodiode PD under illumination will not flow to the first double-gate thin film transistor TFT1, but only to the second double-gate thin film transistor TFT2, and the photogenerated charge will be stored in the parasitic capacitance of the second double-gate thin film transistor TFT2; the second power supply VDD2 is controlled to make the second double-gate thin film transistor TFT2 in the off state, at which time the photogenerated charge will continue to accumulate in the parasitic capacitance. The second working state realizes that the active pixel circuit has an integral working mode similar to the passive pixel circuit.

[0040] The third working state:

[0041] The difference from the second working state is that the second power supply VDD2 is controlled to turn on the second dual-gate thin film transistor TFT2, at which time the photogenerated charge is released from the parasitic capacitor, and the source of the second dual-gate thin film transistor TFT2 outputs a signal. The third working state realizes that the active pixel circuit has a reading working mode similar to that of the passive pixel circuit.

[0042] Embodiment 2

[0043] See also Figure 2 As shown, this embodiment discloses a second active pixel circuit for an X-ray flat panel detector, which is different from the first embodiment in that the third thin film transistor TFT3 is a dual-gate thin film transistor.

[0044] The working state of the third thin film transistor TFT3 is controlled by adjusting the gate voltages VBG3 and VTG3 of the third thin film transistor TFT3.

[0045] The active pixel circuit of this embodiment can realize the same function as the active pixel circuit of the first embodiment.

[0046] Embodiment 3

[0047] See also Figure 3 As shown, this embodiment discloses a third active pixel circuit for an X-ray flat panel detector, which differs from the first embodiment in that the top gate and the bottom gate of the first double-gate thin film transistor TFT1 are interchanged.

[0048] Specifically, the drain of the first double-gate thin film transistor TFT1 is connected to the top gate of the first double-gate thin film transistor TFT1 through a single-gate thin film transistor.

[0049] The active pixel circuit of this embodiment can realize the same function as the active pixel circuit of the first embodiment, but the control capability of the top gate voltage and the bottom gate voltage on the threshold voltage of the first dual-gate thin-film transistor TFT1 is different, which is specifically reflected in that the control coefficient γ of the gate voltage on the threshold voltage is related to different manufacturing processes. The larger γ is, the stronger the control capability is. Therefore, compared with the control capability of the active pixel circuit of the first embodiment, the control capability of the active pixel circuit of this embodiment will change.

[0050] Embodiment 4

[0051] See also Figure 4 As shown, this embodiment discloses a fourth active pixel circuit for an X-ray flat panel detector, which differs from the first embodiment in that the top gate and the bottom gate of the second double-gate thin film transistor TFT2 are interchanged.

[0052] Specifically, the anode of the photodiode PD is connected to the top gate of the second double-gate thin film transistor TFT2.

[0053] The active pixel circuit of this embodiment can achieve the same function as the active pixel circuit of the first embodiment, but the control capabilities of the top gate voltage and the bottom gate voltage on the threshold voltage of the second dual-gate thin-film transistor TFT2 are different, which is specifically reflected in that the control coefficient γ of the gate voltage on the threshold voltage is related to different manufacturing processes. The larger γ is, the stronger the control capability is. Therefore, compared with the control capability of the active pixel circuit of the first embodiment, the control capability of the active pixel circuit of this embodiment will change.

[0054] Embodiment 5

[0055] See also Figure 5 As shown, this embodiment discloses a fifth active pixel circuit for an X-ray flat panel detector, which differs from the first embodiment in that the second power supply VDD2 is connected to 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.

[0056] The active pixel circuit of this embodiment is an equivalent substitute for the active pixel circuit of the first embodiment.

[0057] Embodiment 6

[0058] This embodiment discloses a sixth active pixel circuit for an X-ray flat panel detector, which differs from the first embodiment in that the optoelectronic device is composed of a photoconductive material; the photoconductive material includes but is not limited to halides, calcium, titanium, and ore.

[0059] Specifically, a first power supply VDD1 is connected to the photoelectric device, and the first power supply VDD1 is used to provide a reverse bias voltage for the photoelectric device; the photoelectric device is connected to the drain of the first double-gate thin-film transistor TFT1; the drain of the first double-gate thin-film transistor TFT1 is connected to the bottom gate of the first double-gate thin-film transistor TFT1 through the 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 to the bottom gate of the second double-gate thin-film transistor TFT2; the second power supply VDD2 is connected to the drain of the second double-gate thin-film transistor TFT2, and the second power supply VDD2 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 output as a signal output terminal.

[0060] The active pixel circuit of this embodiment can realize the same function as the active pixel circuit of the first embodiment.

[0061] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, 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 active pixel circuit for an X-ray flat panel detector, characterized in that: include: A photoelectric device, a first transistor, a second transistor and a third transistor; The optoelectronic device is connected to a first power source; The photoelectric device is connected to the drain of the first transistor; The source of the first transistor is grounded; The drain of the first transistor is connected to the top gate or the bottom gate of the first transistor through the third transistor; The optoelectronic device is connected to the second transistor.

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

3. The active pixel circuit for an X-ray flat panel detector according to claim 2, characterized in that: The photoelectric device is a photodiode; The first power supply is connected to the cathode of the photodiode; The anode of the photodiode is connected to the drain of the first transistor; An anode of the photodiode is connected to a top gate or a bottom gate of the second transistor.

4. The active pixel circuit for an X-ray flat panel detector according to claim 2, characterized in that: The optoelectronic device is composed of a photoconductive material.

5. The active pixel circuit for an X-ray flat panel detector according to claim 2, characterized in that: The drain of the second transistor is connected to a second power supply; The source of the second transistor is a signal output terminal.

6. The active pixel circuit for an X-ray flat panel detector according to claim 2, characterized in that: The drain of the second transistor is connected to the source of the first transistor; The source of the second transistor is a signal output terminal.

7. The active pixel circuit for an X-ray flat panel detector according to claim 2, characterized in that: The photoelectric device is connected to the bottom gate or the top gate of the second transistor.

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