CN110672202A - Flat panel detector pixel circuit, flat panel detection system and flat panel detection method - Google Patents
Flat panel detector pixel circuit, flat panel detection system and flat panel detection method Download PDFInfo
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- 238000001514 detection method Methods 0.000 title claims abstract description 50
- 230000005669 field effect Effects 0.000 claims abstract description 9
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 18
- 229910052738 indium Inorganic materials 0.000 claims description 12
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 12
- 239000010409 thin film Substances 0.000 claims description 12
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 claims description 9
- 229910052733 gallium Inorganic materials 0.000 claims description 9
- 239000011787 zinc oxide Substances 0.000 claims description 9
- JAONJTDQXUSBGG-UHFFFAOYSA-N dialuminum;dizinc;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Al+3].[Al+3].[Zn+2].[Zn+2] JAONJTDQXUSBGG-UHFFFAOYSA-N 0.000 claims description 3
- AJNVQOSZGJRYEI-UHFFFAOYSA-N digallium;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Ga+3].[Ga+3] AJNVQOSZGJRYEI-UHFFFAOYSA-N 0.000 claims description 3
- 229910001195 gallium oxide Inorganic materials 0.000 claims description 3
- ATFCOADKYSRZES-UHFFFAOYSA-N indium;oxotungsten Chemical compound [In].[W]=O ATFCOADKYSRZES-UHFFFAOYSA-N 0.000 claims description 3
- TYHJXGDMRRJCRY-UHFFFAOYSA-N zinc indium(3+) oxygen(2-) tin(4+) Chemical compound [O-2].[Zn+2].[Sn+4].[In+3] TYHJXGDMRRJCRY-UHFFFAOYSA-N 0.000 claims description 3
- 238000003384 imaging method Methods 0.000 abstract description 6
- 230000010354 integration Effects 0.000 abstract description 4
- 238000000034 method Methods 0.000 abstract description 4
- 229910021417 amorphous silicon Inorganic materials 0.000 description 7
- 238000010586 diagram Methods 0.000 description 5
- 239000003990 capacitor Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000013256 coordination polymer Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000007689 inspection Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 230000003321 amplification Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 239000002210 silicon-based material Substances 0.000 description 1
- YVTHLONGBIQYBO-UHFFFAOYSA-N zinc indium(3+) oxygen(2-) Chemical compound [O--].[Zn++].[In+3] YVTHLONGBIQYBO-UHFFFAOYSA-N 0.000 description 1
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- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/44—Electric circuits
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/44—Electric circuits
- G01J2001/4446—Type of detector
- G01J2001/448—Array [CCD]
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Abstract
The invention provides a pixel circuit of a flat panel detector, a flat panel detection system and a flat panel detection method, which comprise the following steps: the reset switch is connected between the reset signal and the cathode of the photosensitive diode, and the control end of the reset switch is connected with the reset control signal; the anode of the photosensitive diode is connected with a bias voltage; the source electrode follower is connected between the working voltage and the selection switch, and the control end is connected with the cathode of the photosensitive diode; the compensation switch of the source electrode follower is connected to output compensation current, and the control end is connected with a reset control signal; the first end is connected with a selection switch of the source electrode follower and outputs current change values before and after exposure, and the control end is connected with a selection signal. According to the invention, the influence of threshold voltage drift on the change value of the output current is deducted through data processing, so that the imaging quality of the flat panel detector is improved; the method has the advantages of high field effect mobility, low off-state current and high uniformity, and can realize the integration of 4T APS and obtain high signal-to-noise ratio and large size.
Description
Technical Field
The invention relates to the field of flat panel detection, in particular to a flat panel detector pixel circuit, a flat panel detection system and a flat panel detection method.
Background
The size of the flat panel detector can reach dozens of centimeters, the pixel unit array can reach millions or even tens of millions of pixel units, and each pixel unit circuit is composed of devices such as a switch, a photosensitive diode and the like. The flat panel detector can be applied to a plurality of fields such as medical radiation imaging, industrial flaw detection, security inspection and the like. In X-ray radiation imaging, the area of a flat panel detector can reach 43cm multiplied by 43cm, and currently, the field mainly adopts the technology of amorphous silicon (a-Si) Thin Film Transistors (TFT).
The flat panel detector consists of millions and even tens of millions of pixel points. Generally, each pixel of the indirect flat panel detector comprises a photodiode and at least one thin film transistor. Generally, a Pixel circuit may be divided into a Passive Pixel Sensor (PPS) and an Active Pixel Sensor (APS) structure. PPS pixel structures generally consist of a photodiode and a switch; APS pixel structures typically include more than 3 switches, which is more complex than PPS pixel structures that include only 1 switch. And the APS pixel structure has a higher signal-to-noise ratio than the PPS pixel structure. In addition, the source follower is arranged in the APS pixel structure, the source follower works in a saturation region, and the source follower has the effect of amplifying the change value of the output current signal, so that the required exposure dose is low.
However, due to the presence of the source follower, the output signal of the APS pixel structure is affected by the drift of the threshold voltage of the source follower, causing interference, resulting in poor quality of the output image.
Therefore, how to reduce the interference of the output signal of the APS pixel structure and improve the image quality has become one of the problems to be solved by those skilled in the art.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a flat panel detector pixel circuit, a flat panel detection system and a flat panel detection method, which are used to solve the problem of poor image quality caused by the interference of the output signal of the APS pixel structure in the prior art.
To achieve the above and other related objects, the present invention provides a flat panel detector pixel circuit, including at least:
the device comprises a reset switch, a photosensitive diode, a source electrode follower, a compensation switch and a selection switch;
the first end of the reset switch is connected with a reset signal, the control end of the reset switch is connected with a reset control signal, the second end of the reset switch is connected with the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage;
the first end of the source electrode follower is connected with working voltage, and the control end of the source electrode follower is connected with the cathode of the photosensitive diode;
the first end of the compensation switch is connected with the second end of the source electrode follower, the control end of the compensation switch is connected with the reset control signal, and the second end of the compensation switch outputs compensation current;
the first end of the selection switch is connected with the second end of the source electrode follower, the control end of the selection switch is connected with the selection signal, and the second end of the selection switch outputs current change values before and after exposure.
Optionally, the reset switch, the source follower, the compensation switch and the selection switch are amorphous oxide thin film transistors.
More optionally, the amorphous oxide comprises amorphous indium gallium zinc oxide, amorphous indium gallium oxide, amorphous indium tungsten oxide, amorphous indium tin zinc oxide, or amorphous aluminum zinc oxide.
The flat panel detector pixel circuit, the reset switch, the source follower, the compensation switch and the selection switch adopt N-type transistors or P-type transistors.
To achieve the above and other related objects, the present invention further provides a flat panel detection system, comprising:
the flat panel detector comprises the flat panel detector pixel circuit;
the driving circuit is connected with the flat panel detector;
the compensation current reading circuit is connected with the output end of the flat panel detector and is used for reading the compensation current;
the current change value reading circuit before and after exposure is connected with the output end of the flat panel detector and is used for reading the current change value before and after exposure;
and the data processing circuit is connected with the compensation current reading circuit and the output end of the current change value reading circuit before and after exposure, calculates the actual value of the threshold voltage of the source follower based on the compensation current, compares the actual value of the threshold voltage with the initial value, and compensates the current change value before and after exposure based on the comparison result.
Optionally, the flat panel detection system further includes an image display connected to the output end of the data processing circuit, and displaying the acquired image based on the output signal of the data processing circuit.
To achieve the above and other related objects, the present invention further provides a flat panel detection method using the pixel circuit of the flat panel detector as claimed in any one of claims 1 to 4, the flat panel detection method at least comprising:
a reset stage: turning off the selection switch, turning on the reset switch and the compensation switch, receiving a reset signal by a cathode of a photosensitive diode, enabling the photosensitive diode to be in a reverse bias state, amplifying the reset signal by a source follower, and outputting the amplified reset signal to obtain a compensation current;
and (3) an exposure stage: turning off the selection switch, the reset switch and the compensation switch, enabling the source electrode follower to work in a saturation area to finish exposure, and enabling the cathode voltage of the photosensitive diode to change;
a reading stage: and opening a selection switch, closing a reset switch and a compensation switch, amplifying the cathode voltage change value of the photosensitive diode by the source electrode follower, and outputting the amplified cathode voltage change value to obtain the current change value before and after exposure.
Optionally, the flat panel detection method further includes: and (3) a data processing stage: and calculating an actual value of the threshold voltage of the source follower based on the compensation current, comparing the actual value of the threshold voltage with an initial value, and compensating the current change value before and after exposure based on a comparison result.
More optionally, the compensation current satisfies the following relation:
ICP＝1/2·μN·Cox·W/L·(VGS-VTH)2＝1/2·μN·Cox·W/L·(VRST-VTH)2，
wherein, ICPTo compensate for the current, muNIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, VGSIs the gate-source voltage, V, of the source followerTHIs the source follower threshold voltage, VRSTIs the voltage value of the reset signal.
More optionally, the current change values before and after the exposure satisfy the following relation:
ΔIOUT＝μN·Cox·W/L·((VGS-VTH)ΔVGS+ΔVGS 2/2)≈μN·Cox·W/L·(VRST-VTH)ΔVGS，
wherein, V should be adjustedGS-VTH>>△VGS/2，ΔIOUTThe current change before and after exposure, μNIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, Δ VGSA gate-source voltage variation value, V, of the source follower before and after exposureGSIs the gate-source voltage, V, of the source followerTHIs the source follower threshold voltage, VRSTIs the voltage value of the reset signal.
As described above, the flat panel detector pixel circuit, the flat panel detection system and the flat panel detection method of the present invention have the following advantages:
1. the flat panel detector pixel circuit, the flat panel detection system and the flat panel detection method adopt the 4T APS pixel circuit, and can simultaneously read the output current of the source follower when the photodiode is reset based on the compensation switch, so that the threshold voltage value and the drift condition of the source follower can be obtained through data processing.
2. The flat panel detector pixel circuit, the flat panel detection system and the flat panel detection method can read the threshold voltage value of the source follower and judge the drift condition thereof in the reset stage, and store the relevant data of the threshold voltage drift; in the reading stage, the influence of threshold voltage drift on the change value of the output current is deducted through data processing, and the imaging quality of the flat panel detector is improved.
3. The invention adopts the amorphous oxide thin film transistor to prepare the APS pixel circuit, has higher field effect mobility, lower off-state current and better uniformity, can realize the integration of 4T APS, and obtains higher signal-to-noise ratio and large size.
Drawings
Fig. 1 is a schematic structural diagram of a pixel circuit of a flat panel detector according to the present invention.
Fig. 2 is a schematic diagram illustrating the reset phase of the flat panel detection method according to the present invention.
FIG. 3 is a schematic diagram of the exposure phase of the flat panel inspection method of the present invention.
FIG. 4 is a schematic diagram of the reading stage of the flat panel detection method of the present invention.
FIG. 5 is a schematic diagram of the flat panel detection system according to the present invention.
Description of the element reference numerals
1 Flat panel detector
11 flat panel detector pixel circuit
2 drive circuit
3 compensating current sensing circuit
Current change value reading circuit before and after 4 exposure
5 data processing circuit
6 image display
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 5. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and although the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation, the type, quantity and proportion of the components in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.
Example one
As shown in fig. 1, the present embodiment provides a flat panel detector pixel circuit 11, where the flat panel detector pixel circuit 11 includes: reset switch TRSTPhotodiode PD, source follower TSFCompensating switch TCPAnd a selection switch TSEL。
Wherein the reset switch TRSTFirst terminal of (2) is connected with a reset signal VRSTThe control end is connected with a reset control signal VGRSTThe second end is connected with the cathode of the photosensitive diode PD, and the anode of the photosensitive diode PD is connected with a bias voltage VCOM；
The source electrode follower TSFIs connected with the working voltage VDDThe control end is connected with the cathode of the photosensitive diode PD;
the compensation switch TCPIs connected to the source follower TSFA second terminal of the reset control signal V, the control terminal being connected to the reset control signal VGRSTThe second end outputs a compensation current ICP；
The selection switch TSELIs connected to the source follower TSFA control terminal connected to the selection signal VSELBefore and after the second end outputs exposureCurrent change value Δ I ofOUT。
It should be noted that the photodiode PD includes a junction capacitor CPDSaid junction capacitance CPDThe junction capacitor C is illustrated in fig. 1 for convenience of illustration, and is a capacitor inside the photodiode PD and is not independent from the outside of the photodiode PD in practical usePD。
Specifically, in the present embodiment, the reset switch TRSTThe source follower TSFThe compensation switch TCPAnd the selection switch TSELAn amorphous oxide thin film transistor is used. Further, the amorphous oxide includes amorphous indium gallium zinc oxide (a-IGZO). The amorphous indium gallium zinc oxide is an amorphous oxide semiconductor material proposed by the thin-field xixixixixiong research group of tokyo industrial university in 2004, and compared with an amorphous silicon thin film transistor, the amorphous indium gallium zinc oxide thin film transistor has higher field effect mobility which can reach dozens or even dozens of times of that of the amorphous silicon thin film transistor. In addition, the amorphous indium gallium zinc oxide material has a wider forbidden band width which is about 3.4eV, while the forbidden band width of the amorphous silicon material is only 1.7-1.8 eV; therefore, the amorphous indium gallium zinc oxide thin film transistor has a lower off-state current, which can reach the fA level, and is lower than the off-state current of the amorphous silicon thin film transistor (tens to hundreds of fA levels), so that the amorphous indium gallium zinc oxide detector has a higher frame rate and lower noise compared with the amorphous silicon detector.
It should be noted that the reset switch TRSTThe source follower TSFThe compensation switch TCPAnd the selection switch TSELThe material of the second electrode can be set according to the requirement, including but not limited to amorphous indium zinc oxide, amorphous indium gallium oxide, amorphous indium tungsten oxide, amorphous indium tin zinc oxide, or amorphous aluminum zinc oxide, and is not limited to this embodiment.
Specifically, in the present embodiment, the reset switch TRSTThe source follower TSFThe compensation switch TCPAnd the selection switch TSELAre all made ofAn N-type transistor; when the control end receives a high level, each switch is switched on, and when the control end receives a low level, each switch is switched off.
It should be noted that each switch may employ a P-type transistor; each switch can be partially set as an N-type transistor and partially set as a P-type transistor according to requirements; the semiconductor material is not limited to one, and is not limited to the embodiment.
Example two
As shown in fig. 2 to 4, the present embodiment provides a flat panel detection method, and in the present embodiment, the flat panel detection method is implemented based on the pixel circuit 11 of the flat panel detector of the first embodiment, and in practical use, the flat panel detection method may be based on any circuit structure capable of implementing the method, and is not limited to the present embodiment. The flat panel detection method comprises the following steps:
1) a reset stage: the cathode of the photodiode PD receives a reset signal VRSTThe photodiode PD is in reverse bias state and sends the reset signal VRSTAmplified by a source follower and then output to obtain a compensation current ICP. According to the compensation current ICPAnd source follower TSFThreshold voltage V ofTHSatisfy the relationship between T and TSFAt this time VTHThe value is obtained.
Specifically, as shown in fig. 2, in the present embodiment, the reset control signal VGRSTSet to high level, the reset switch TRSTAnd the compensation switch TCPOn (operating in the linear region), the reset signal VRSTAt a high level, the cathode of the photodiode PD is charged to the reset signal VRSTOf (c) is detected. The bias voltage VCOMSet to a negative voltage, in this embodiment in the range of-4 to-10V, the photodiode PD is in a reverse biased state. The selection signal VSELSet to low level, the selection switch TSELAnd (6) turning off. The source electrode follower TSFWorking in the saturation region, the cathode voltage of the photodiode PD (the reset signal V)RSTCan pass through the source follower TSFAnd the compensation switch TCPReading to obtain corresponding compensation currentICPThe compensation current ICPSatisfies the following relation:
ICP＝1/2·μN·Cox·W/L·(VGS-VTH)2＝1/2·μN·Cox·W/L·(VRST-VTH)2(1)，
wherein, ICPTo compensate for the current, muNIs the source follower TSFField effect mobility of (2), CoxIs the source follower TSFA capacitance value of the gate insulating layer per unit area, W/L being the source follower TSFWidth to length ratio of VGSIs the source follower TSFGate-source voltage of VTHIs the source follower TSFThreshold voltage of VRSTIs the voltage value of the reset signal.
According to the above formula, can be obtainedCPAnd VTHThe relationship between them, so that the source follower T can be calculatedSFAt this time VTHThe value is obtained.
2) And (3) an exposure stage: the source electrode follower TSFAnd then is in an open state and works in a saturation region. After the exposure is completed, the voltage of the cathode (gate of the source follower) of the photodiode PD changes.
Specifically, as shown in fig. 3, in the present embodiment, the reset control signal VGRSTSet to low level, the reset switch TRSTAnd the compensation switch TCPAnd (6) turning off. The selection signal VSELSet to low level, the selection switch TSELAnd (6) turning off. Before exposure, the cathode voltage of the photosensitive diode is the reset signal VRSTAfter exposure, the X-ray is converted into visible light, at which time the photodiode PD is in a reverse bias state, and exposure results in the junction capacitor CPDChange value of the amount of charge on is △ QPixelThereby causing the voltage of the cathode (gate of source follower) of the photodiode PD to vary by △ VG。
3) A reading stage: the voltage change value of the cathode (the gate of the source follower) of the photodiode PD is transmitted throughThe source follower TSFThe current change value delta I before and after exposure can be obtained by amplifying and outputtingOUT。
Specifically, as shown in fig. 4, in the present embodiment, the reset control signal VGRSTSet to low level, the reset switch TRSTAnd the compensation switch TCPAnd (6) turning off. The selection signal VSELSet to high level, the selection switch TSELThe voltage change value of the cathode (gate of source follower) of the photodiode PD before and after X-ray exposure is △ V when the photodiode PD is turned on (operated in the linear region)GBy the source follower TSF(working in the saturation region) amplification and then passing through the selection switch TSELReading to obtain corresponding current change value delta I before and after exposureOUTCurrent change value Δ I before and after the exposureOUTSatisfies the following relation:
ΔIOUT＝μN·Cox·W/L·((VGS-VTH)ΔVGS+ΔVGS 2/2)≈μN·Cox·W/L·(VRST-VTH)ΔVGS(2)，
wherein, in order to ensure the current change value delta I before and after the exposureOUTAnd the cathode voltage change value △ V of the photosensitive diode PDGShould make V beGS-VTH>>△VGS/2。ΔIOUTThe current change before and after exposure, μNIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, Δ VGSA gate-source voltage variation value, V, of the source follower before and after exposureGSIs the gate-source voltage, V, of the source followerTHIs the source follower threshold voltage, VRSTIs the voltage value at the high level of the reset signal.
It should be noted that the level of each signal can be set based on the specific device type, and is not limited to this embodiment.
As an implementation of the present embodiment, the followingThe flat panel detection method further comprises 4) a data processing stage: based on the compensation current ICPCalculating to obtain a source follower TSFThreshold voltage VTHWill be said threshold voltage VTHIs compared with the initial value, and the current change value delta I before and after the exposure is compared based on the comparison resultOUTCompensation is performed.
Specifically, the source follower T is calculated based on the above formula (1)SFThreshold voltage VTHBased on said threshold voltage VTHThe actual value of (2) is compared with the initial value to determine the threshold voltage drift condition and the influence of the threshold voltage drift on the output current change, which influences the current change value delta I before and after the exposureOUTAnd interference is reduced, and more accurate change values of output current generated before and after X-ray exposure are obtained.
EXAMPLE III
As shown in fig. 5, the present embodiment provides a flat panel detection system, which includes:
the device comprises a flat panel detector 1, a driving circuit 2, a compensation current reading circuit 3, a current change value reading circuit 4 before and after exposure and a data processing circuit 5.
As shown in fig. 5, the flat panel detector 1 includes the flat panel detector pixel circuits 11 according to the first embodiment, and the flat panel detector pixel circuits 11 are arranged in an array to form a detection panel.
As shown in fig. 5, the driving circuit 2 is connected to the flat panel detector 1.
In particular, the driving circuit 2 is used for providing driving signals, including but not limited to the reset signal VRSTSaid bias voltage VCOMSaid selection signal VSELAnd the reset control signal VGRST。
As shown in fig. 5, the compensation current readout circuit 3 is connected to the output terminal of the flat panel detector 1 for reading out the compensation current ICP。
Specifically, the compensation current sensing circuit 3 includes a plurality of compensation current sensing units respectively connected toThe compensation switches T are arranged in the pixel circuits 11 of the flat panel detector in the same column (or the same row)CPTo sense each compensation current ICP。
As shown in fig. 5, the current variation value reading circuit 4 before and after exposure is connected to the output terminal of the flat panel detector 1 for reading the current variation value Δ I before and after exposureOUT。
Specifically, the circuit 4 for reading out the current variation before and after exposure includes a plurality of units for reading out the current variation before and after exposure, which are respectively connected to the source followers T in the pixel circuits 11 of the flat panel detector in the same column (or the same row)SFTo read out the current change value delta I before and after each exposureOUT。
As shown in fig. 5, the data processing circuit 5 is connected to the output terminals of the compensation current sensing circuit 3 and the current change value sensing circuit 4 before and after exposure, and is based on the compensation current ICPCalculating to obtain a source follower TSFThreshold voltage VTHWill be said threshold voltage VTHIs compared with the initial value, and the current change value delta I before and after the exposure is compared based on the comparison resultOUTCompensation is performed.
In particular, the data processing circuit 5 receives the compensation current ICPCalculating the source follower TSFThreshold voltage VTHAnd storing the actual value of (1); and the current change value delta I before and after the exposureOUTCompensation is performed.
As an implementation manner of this embodiment, the flat panel detection system further includes an image display 6, where the image display 6 is connected to the output end of the data processing circuit 5, and displays the acquired image based on the output signal of the data processing circuit 5.
The flat panel detection system of the present embodiment first passes the compensation current ICPCalculating to obtain a source follower TSFThreshold voltage V ofTHAnd saves the value. Then, the current change value Δ I before and after exposure generated by exposure is read by the current change value reading circuit 4 before and after exposureOUT. Passing through data processingThe threshold voltage drift is used to measure the current change value delta I before and after exposureOUTAnd (4) deducting the influence of the image, and finally finishing the display of the image.
The flat panel detector pixel circuit, the flat panel detection system and the flat panel detection method form a novel 4TAPS pixel circuit, influence of threshold voltage drift of the source follower on the change value of an output current signal is deducted, and the anti-interference performance of the flat panel detector is improved; the threshold voltage drift of the source electrode follower can be compensated in a large range, real-time online compensation can be realized, interference is reduced, and imaging quality is guaranteed; in addition, the amorphous indium gallium zinc oxide thin film transistor can realize higher integration level, higher frame rate, higher signal-to-noise ratio and large size.
In summary, the present invention provides a pixel circuit of a flat panel detector, a flat panel detection system and a flat panel detection method, including: the device comprises a reset switch, a photosensitive diode, a source electrode follower, a compensation switch and a selection switch; the first end of the reset switch is connected with a reset signal, the control end of the reset switch is connected with a reset control signal, the second end of the reset switch is connected with the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage; the first end of the source electrode follower is connected with working voltage, and the control end of the source electrode follower is connected with the cathode of the photosensitive diode; the first end of the compensation switch is connected with the second end of the source electrode follower, the control end of the compensation switch is connected with the reset control signal, and the second end of the compensation switch outputs compensation current; the first end of the selection switch is connected with the second end of the source electrode follower, the control end of the selection switch is connected with the selection signal, and the second end of the selection switch outputs current change values before and after exposure. The flat panel detector pixel circuit, the flat panel detection system and the flat panel detection method adopt the 4T APS pixel circuit, and simultaneously read the output current of the source follower through the compensation switch when the photodiode is reset on the basis of the reset switch, so that the threshold voltage value of the source follower can be obtained through data processing, the drift condition of the threshold voltage value can be judged, and relevant threshold voltage drift data can be stored; in the reading stage, the influence of threshold voltage drift on the change value of the output current is deducted through data processing, and the imaging quality of the flat panel detector is improved; in addition, the method has the advantages of higher field effect mobility, lower off-state current and better uniformity, and can realize the integration of 4T APS and obtain higher signal-to-noise ratio, frame rate and larger size. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A flat panel detector pixel circuit, characterized in that the flat panel detector pixel circuit comprises at least:
the device comprises a reset switch, a photosensitive diode, a source electrode follower, a compensation switch and a selection switch;
the first end of the reset switch is connected with a reset signal, the control end of the reset switch is connected with a reset control signal, the second end of the reset switch is connected with the cathode of the photosensitive diode, and the anode of the photosensitive diode is connected with a bias voltage;
the first end of the source electrode follower is connected with working voltage, and the control end of the source electrode follower is connected with the cathode of the photosensitive diode;
the first end of the compensation switch is connected with the second end of the source electrode follower, the control end of the compensation switch is connected with the reset control signal, and the second end of the compensation switch outputs compensation current;
the first end of the selection switch is connected with the second end of the source electrode follower, the control end of the selection switch is connected with the selection signal, and the second end of the selection switch outputs current change values before and after exposure.
2. The flat panel detector pixel circuit according to claim 1, wherein: the reset switch, the source electrode follower, the compensation switch and the selection switch adopt amorphous oxide thin film transistors.
3. The flat panel detector pixel circuit according to claim 2, wherein: the amorphous oxide includes amorphous indium gallium zinc oxide, amorphous indium gallium oxide, amorphous indium tungsten oxide, amorphous indium tin zinc oxide, or amorphous aluminum zinc oxide.
4. The flat panel detector pixel circuit according to claim 1, wherein: the flat panel detector pixel circuit, the reset switch, the source follower, the compensation switch and the selection switch adopt N-type transistors or P-type transistors.
5. A flat panel detection system, comprising at least:
a flat panel detector comprising a flat panel detector pixel circuit according to any of claims 1 to 4;
the driving circuit is connected with the flat panel detector;
the compensation current reading circuit is connected with the output end of the flat panel detector and is used for reading the compensation current;
the current change value reading circuit before and after exposure is connected with the output end of the flat panel detector and is used for reading the current change value before and after exposure;
and the data processing circuit is connected with the compensation current reading circuit and the output end of the current change value reading circuit before and after exposure, calculates the actual value of the threshold voltage of the source follower based on the compensation current, compares the actual value of the threshold voltage with the initial value, and compensates the current change value before and after exposure based on the comparison result.
6. The flat panel detection system according to claim 5, wherein: the panel detection system further comprises an image display connected to the output end of the data processing circuit and used for displaying the acquired image based on the output signal of the data processing circuit.
7. A flat panel detection method using the pixel circuit of the flat panel detector according to any one of claims 1 to 4, wherein the flat panel detection method at least comprises:
a reset stage: turning off the selection switch, turning on the reset switch and the compensation switch, receiving a reset signal by a cathode of a photosensitive diode, enabling the photosensitive diode to be in a reverse bias state, amplifying the reset signal by a source follower, and outputting the amplified reset signal to obtain a compensation current;
and (3) an exposure stage: turning off the selection switch, the reset switch and the compensation switch, enabling the source electrode follower to work in a saturation area to finish exposure, and enabling the cathode voltage of the photosensitive diode to change;
a reading stage: and opening a selection switch, closing a reset switch and a compensation switch, amplifying the cathode voltage change value of the photosensitive diode by the source electrode follower, and outputting the amplified cathode voltage change value to obtain the current change value before and after exposure.
8. The flat panel detection method according to claim 7, characterized in that: the flat panel detection method further includes: and (3) a data processing stage: and calculating an actual value of the threshold voltage of the source follower based on the compensation current, comparing the actual value of the threshold voltage with an initial value, and compensating the current change value before and after exposure based on a comparison result.
9. The flat panel detection method according to claim 7 or 8, characterized in that: the compensation current satisfies the following relation:
ICP＝1/2·μN·Cox·W/L·(VGS-VTH)2＝1/2·μN·Cox·W/L·(VRST-VTH)2，
wherein, ICPTo compensate for the current, muNIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, VGSFor the source to followGate-source voltage, V, of the deviceTHIs the source follower threshold voltage, VRSTIs the voltage value of the reset signal.
10. The flat panel detection method according to claim 7 or 8, characterized in that: the current change values before and after exposure satisfy the following relational expression:
ΔIOUT＝μN·Cox·W/L·((VGS-VTH)ΔVGS+ΔVGS 2/2)≈μN·Cox·W/L·(VRST-VTH)ΔVGS，
wherein, V should be adjustedGS-VTH>>△VGS/2，ΔIOUTThe current change before and after exposure, μNIs the field effect mobility of the source follower, CoxIs the capacitance value of the gate insulating layer per unit area of the source follower, W/L is the width-to-length ratio of the source follower, Δ VGSA gate-source voltage variation value, V, of the source follower before and after exposureGSIs the gate-source voltage, V, of the source followerTHIs the source follower threshold voltage, VRSTIs the voltage value of the reset signal.
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