CA2521145A1 - Pixel circuit for radiation detection - Google Patents
Pixel circuit for radiation detection Download PDFInfo
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- CA2521145A1 CA2521145A1 CA002521145A CA2521145A CA2521145A1 CA 2521145 A1 CA2521145 A1 CA 2521145A1 CA 002521145 A CA002521145 A CA 002521145A CA 2521145 A CA2521145 A CA 2521145A CA 2521145 A1 CA2521145 A1 CA 2521145A1
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- circuit
- tft
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- 230000005855 radiation Effects 0.000 title abstract description 10
- 238000001514 detection method Methods 0.000 title abstract description 9
- 238000005516 engineering process Methods 0.000 abstract description 7
- 230000003321 amplification Effects 0.000 abstract description 6
- 238000003199 nucleic acid amplification method Methods 0.000 abstract description 6
- 238000003491 array Methods 0.000 abstract description 4
- 230000015556 catabolic process Effects 0.000 abstract description 3
- 238000006731 degradation reaction Methods 0.000 abstract description 3
- 230000007613 environmental effect Effects 0.000 abstract description 3
- 229910021417 amorphous silicon Inorganic materials 0.000 description 8
- 230000010354 integration Effects 0.000 description 6
- 101100191136 Arabidopsis thaliana PCMP-A2 gene Proteins 0.000 description 4
- 101100422768 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) SUL2 gene Proteins 0.000 description 4
- 101100048260 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) UBX2 gene Proteins 0.000 description 4
- 238000013459 approach Methods 0.000 description 4
- 238000003384 imaging method Methods 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 4
- 239000011669 selenium Substances 0.000 description 4
- 239000003990 capacitor Substances 0.000 description 3
- 239000010409 thin film Substances 0.000 description 3
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 229920005591 polysilicon Polymers 0.000 description 2
- 238000002601 radiography Methods 0.000 description 2
- 229910052711 selenium Inorganic materials 0.000 description 2
- 208000004434 Calcinosis Diseases 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000004195 computer-aided diagnosis Methods 0.000 description 1
- 230000007850 degeneration Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 238000009607 mammography Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 229910021424 microcrystalline silicon Inorganic materials 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 229910021423 nanocrystalline silicon Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- -1 organic Polymers 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
Classifications
-
- 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
- G01J1/46—Electric circuits using a capacitor
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
- G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Electromagnetism (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Measurement Of Radiation (AREA)
Abstract
The present invention relates to an on-pixel readout circuit for detectors, and more particularly to an active pixel sensor (APS) circuit for radiation detection, capable of providing stable and predictable on-pixel amplification in the presence of device degradation and/or mismatch, and variation in environmental factors like temperature and mechanical strain. This invention is applicable to various detector technologies such as flat panel imagers, sensor arrays, x-ray detectors, CMOS cameras, etc.
Description
FIELD OF THE INVENTION
The present invention relates to an on-pixel readout circuit for detectors, and more particularly to an active pixel sensor (APS) circuit for radiation detection, capable of providing stable and predictable on-pixel amplification in the presence of device degradation and/or mismatch, and variation in environmental factors like temperature and mechanical strain. This invention is applicable to various detector technologies such as flat panel imagers, sensor arrays, x-ray detectors, CMOS cameras, etc.
BACKGROUND OF THE INVENTION
The following description will be based on an example of a flat panel x-ray imaging system, although the present disclosure is not restricted to this invention.
Flat-panel detectors have gained significant interest recently in view of their ability to provide an immediate, high quality radiographs after the exposure.
They require less handling, more convenient management, immediate image viewing, computer aided analysis and more convenient storage on computer disks rather than archive film stacks [1].
Flat-panel detectors convert incident radiation images to charge images. In the case of x-rays, for instance, the radiated x-rays may be converted to charge directly [2] by using an x-ray sensitive photoconductor such as amorphous selenium, a-Se, or indirectly [3] by using a phosphor screen to convert an incident x-ray image to light, which is then converted to a charge distribution. In both approaches the final charge image is stored on the pixel capacitors. This stored image is then read out using a large area integrated circuit backplane usually referred to as active matrix. Active matrix addressing involves a layer of backplane electronics, based on thin-film transistors (TFTs) fabricated using amorphous silicon (a-Si:H), polycrystalline silicon (poly-Si), CMOS, organic, polymer, or other transistor technologies, to provide on-pixel amplification and read out capability in each imaging pixel. In order to utilize the flat panel for reliable radiation detection, it is necessary to decrease the electronic noise or increase the radiation signal. One basic approach to increase the signal to noise ratio would be on-pixel amplification of the input signal. In this approach, the TFTs will act as both analog amplifiers and switches compared to the conventional case where the transistors were used just as switches [3].
However, transistor threshold voltage and mobility instability, and mismatch issues are a major hurdle in flat panel active matrix applications with on-pixel amplification. This is because the amplifying circuits are far more sensitive to TFT instability. As an example of instability, Fig. 1 shows the threshold voltage shift in amorphous silicon TFTs. In a flat panel, the instability would mean that the amplifier gain and the output DC current would vary across the array and/or decrease over time, which is unacceptable.
One solution to this stability problem is to use voltage programmed pixel circuits.
The circuit shown in Fig. 2 is a voltage programmed pixel circuit, which automatically compensates for any shift or mismatch in the threshold voltage of the drive TFT to ensure that the output DC current and circuit gain do not decrease over time.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide pixel circuits for radiation detectors, capable of providing stable and predictable on-pixel amplification, despite device degradation and/or mismatch, and change in environmental factors such as temperature and mechanical strain.
In order to achieve these goals, a pixel circuit for radiation detection is presented.
The present invention comprises a plurality of transistors in CMOS or thin film technology for amplifying the x-ray generated signal in each pixel of the flat panel. The pixel circuit is automatically capable of compensating shifts and mismatches in the characteristics properties of the transistors in a pixel.
The basic architecture comprises of a plurality of switching transistors, an amplifying transistor, and a sensor for detection of radiation (such as optical signal, x-ray signal, etc.). Each pixel has a driving TFT whose overdrive voltage is generated by applying a waveform independent of its threshold voltage.
In the presented method, the threshold voltage of the driving TFT can be retrieved and saved during the programming time. It is known that the time constant change of the TFT threshold voltage is much longer than the frame time in a normal size array detector. Therefore, it is rational to expect the driving TFT
threshold voltage to be relatively constant for several subsequent programming of each pixel in the active matrix array. As a result, at the beginning of a time interval consisting of several frames, the threshold voltage can be extracted.
This extracted value can be used as the threshold voltage of the driving TFT for the whole time interval.
ADVANTAGES
The driving schemes provide stable current independent of the threshold voltage shift of the drive TFT under prolonged detector operation, to efficiently improve the detector operating lifetime. This approach will significantly decrease the programming time and provide for large detector arrays. Since the threshold voltage compensation is not performed for each frame, the power consumption is expected to be significantly low.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and features of the present invention will become more apparent by the following description of the preferred embodiments with reference to the attached drawings. Although they directly apply to TFT
circuits in amorphous silicon (a-Si) flat panel technology, they can be readily extended to other technologies like polysilicon, organic, polymer, CMOS, etc. for visible and x-ray detection.
Fig.1 Threshold voltage shift as a function of stress voltage of a discrete a-Si TFT.
Fig.2 Schematic of voltage mode active pixel sensor circuit with TFT parameter compensation capability along with the driving waveforms.
Fig.3 Output current for different threshold voltage values of TAMP presented here.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2(a) and FIG. 2(b) show the presented pixel circuit along with its control signals. It comprises three transistors T1, T2 and TAMP, a storage capacitor CSTORE and a radiation sensor (SENSOR). The pixel circuit is connected to a common power supply line (VDD), two select lines (SEL1 and SEL2), an input signal line (VIN), an output signal line (IOUT). The three transistors T1, T2 and TAMP can be amorphous silicon, nano/micro crystalline silicon, poly silicon, organic thin-film transistors (TFT), or transistors in standard CMOS
technology.
The source and drain terminals of the driving transistor TAMP are connected to the common terminal of the storage capacitance and sensor and VDD, respectively. The gate terminal of TAMP is connected to the input signal line (VIN) through T1 and the source terminal of TAMP is connected to the output signal line through T2. In the circuit, transistors T1 and T2 act as switches.
The gate terminals of T1 and T2 are connected to the select lines SEL1 and SEL2, respectively. The source terminal of T1 is connected to the gate of TAMP and its drain terminal is connected to the input signal line (VIN). The drain terminal of T2 is connected to the source terminal of TAMP and its source terminal is connected to the output signal line (IOUT).
The operation of this pixel consists of three major operating cycles:
programming cycle, integration cycle and readout cycle. During the programming cycle, node A
is charged to the voltage value equal to the sum of the bias voltage (VBIAS), the voltage of node B (VB) and the threshold voltage of TAMP (VT). Therefore the gate-source voltage of TAMP becomes:
VGS = (VBIAS + VT + VB) - (VB) = VBIAS + VT .
With reference to the waveform shown on FIG. 2(b) the operating cycles are described as follows:
The first operating cycle (Programming): SEL1 and SEL2 signals go to a high positive voltage. Therefore both switches T1 and T2 turn ON. T1 provides access path from VIN to the gate of TAMP while T2 connects the source of TAMP to IOUT. First VIN and IOUT are set to OV. After that, a linearly increasing voltage starting from OV will be applied to VIN. Subsequently, this ramp voltage is applied to the gate terminal of TAMP through the ON resistance of T1. As long as this linearly increasing voltage has not reached VT, the driving and amplifying TFT
TAMP will not turn ON and there would be no current flow from drain to the source terminal of this TFT. When the gate voltage reaches VT, TAMP turns ON
abruptly and flows considerable amount of current to the output signal line IOUT
through T2. This increase in the output current will be detected by the off pixel circuitry through monitoring IOUT. Upon detection, the output circuitry prevents the input ramp voltage from further increase. Therefore the applied voltage to the gate of TAMP will remain at VT. Next, the bias voltage VBIAS will be added to the previously retrieved value. Consequently, the total applied voltage to VIN
at the end of the first operating cycle will become:
VBIAS + VT
The second operating cycle (Integration): SEL1 and SEL2 go to zero. Therefore, the transistors T1 and T2 turn OFF. The storage capacitor CSTORE retains its previously gained value (VBIAS+VT). As a result, the overdrive voltage of TAMP
becomes independent of the threshold voltage of TAMP. The voltage stored in CSTORE remains constant, except for the initial drop due to charge feed-through stemming from the gate-source capacitance of T1 when it turns off.
Subsequently, the integration starts, during which the incident x-ray photons will generate electron-hole pairs in the x-ray sensitive a-Se layer. These electron-hole pairs are separated and driven by an applied electric field to the surfaces of the photoconductor where they will form a latent charge image. In the integration period T,NT, the input signal, h v , generates carriers that charge CSTORE by OQP and increase its potential by a small-signal voltage of dV~ .
The third operating cycle (Read Out): After integration, the T2 is turned ON.
As a result, a common source topology with source degeneration in which TAMP is the amplifying transistor and T2 acts as a passive resistor, will be constructed.
The output current of the circuit at this point would be I aiAS + G m x d V~
(1) Here Gn, is the transconductance of the total readout circuit IS Gm = gm 1 + gmRoN
The present invention relates to an on-pixel readout circuit for detectors, and more particularly to an active pixel sensor (APS) circuit for radiation detection, capable of providing stable and predictable on-pixel amplification in the presence of device degradation and/or mismatch, and variation in environmental factors like temperature and mechanical strain. This invention is applicable to various detector technologies such as flat panel imagers, sensor arrays, x-ray detectors, CMOS cameras, etc.
BACKGROUND OF THE INVENTION
The following description will be based on an example of a flat panel x-ray imaging system, although the present disclosure is not restricted to this invention.
Flat-panel detectors have gained significant interest recently in view of their ability to provide an immediate, high quality radiographs after the exposure.
They require less handling, more convenient management, immediate image viewing, computer aided analysis and more convenient storage on computer disks rather than archive film stacks [1].
Flat-panel detectors convert incident radiation images to charge images. In the case of x-rays, for instance, the radiated x-rays may be converted to charge directly [2] by using an x-ray sensitive photoconductor such as amorphous selenium, a-Se, or indirectly [3] by using a phosphor screen to convert an incident x-ray image to light, which is then converted to a charge distribution. In both approaches the final charge image is stored on the pixel capacitors. This stored image is then read out using a large area integrated circuit backplane usually referred to as active matrix. Active matrix addressing involves a layer of backplane electronics, based on thin-film transistors (TFTs) fabricated using amorphous silicon (a-Si:H), polycrystalline silicon (poly-Si), CMOS, organic, polymer, or other transistor technologies, to provide on-pixel amplification and read out capability in each imaging pixel. In order to utilize the flat panel for reliable radiation detection, it is necessary to decrease the electronic noise or increase the radiation signal. One basic approach to increase the signal to noise ratio would be on-pixel amplification of the input signal. In this approach, the TFTs will act as both analog amplifiers and switches compared to the conventional case where the transistors were used just as switches [3].
However, transistor threshold voltage and mobility instability, and mismatch issues are a major hurdle in flat panel active matrix applications with on-pixel amplification. This is because the amplifying circuits are far more sensitive to TFT instability. As an example of instability, Fig. 1 shows the threshold voltage shift in amorphous silicon TFTs. In a flat panel, the instability would mean that the amplifier gain and the output DC current would vary across the array and/or decrease over time, which is unacceptable.
One solution to this stability problem is to use voltage programmed pixel circuits.
The circuit shown in Fig. 2 is a voltage programmed pixel circuit, which automatically compensates for any shift or mismatch in the threshold voltage of the drive TFT to ensure that the output DC current and circuit gain do not decrease over time.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide pixel circuits for radiation detectors, capable of providing stable and predictable on-pixel amplification, despite device degradation and/or mismatch, and change in environmental factors such as temperature and mechanical strain.
In order to achieve these goals, a pixel circuit for radiation detection is presented.
The present invention comprises a plurality of transistors in CMOS or thin film technology for amplifying the x-ray generated signal in each pixel of the flat panel. The pixel circuit is automatically capable of compensating shifts and mismatches in the characteristics properties of the transistors in a pixel.
The basic architecture comprises of a plurality of switching transistors, an amplifying transistor, and a sensor for detection of radiation (such as optical signal, x-ray signal, etc.). Each pixel has a driving TFT whose overdrive voltage is generated by applying a waveform independent of its threshold voltage.
In the presented method, the threshold voltage of the driving TFT can be retrieved and saved during the programming time. It is known that the time constant change of the TFT threshold voltage is much longer than the frame time in a normal size array detector. Therefore, it is rational to expect the driving TFT
threshold voltage to be relatively constant for several subsequent programming of each pixel in the active matrix array. As a result, at the beginning of a time interval consisting of several frames, the threshold voltage can be extracted.
This extracted value can be used as the threshold voltage of the driving TFT for the whole time interval.
ADVANTAGES
The driving schemes provide stable current independent of the threshold voltage shift of the drive TFT under prolonged detector operation, to efficiently improve the detector operating lifetime. This approach will significantly decrease the programming time and provide for large detector arrays. Since the threshold voltage compensation is not performed for each frame, the power consumption is expected to be significantly low.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and features of the present invention will become more apparent by the following description of the preferred embodiments with reference to the attached drawings. Although they directly apply to TFT
circuits in amorphous silicon (a-Si) flat panel technology, they can be readily extended to other technologies like polysilicon, organic, polymer, CMOS, etc. for visible and x-ray detection.
Fig.1 Threshold voltage shift as a function of stress voltage of a discrete a-Si TFT.
Fig.2 Schematic of voltage mode active pixel sensor circuit with TFT parameter compensation capability along with the driving waveforms.
Fig.3 Output current for different threshold voltage values of TAMP presented here.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2(a) and FIG. 2(b) show the presented pixel circuit along with its control signals. It comprises three transistors T1, T2 and TAMP, a storage capacitor CSTORE and a radiation sensor (SENSOR). The pixel circuit is connected to a common power supply line (VDD), two select lines (SEL1 and SEL2), an input signal line (VIN), an output signal line (IOUT). The three transistors T1, T2 and TAMP can be amorphous silicon, nano/micro crystalline silicon, poly silicon, organic thin-film transistors (TFT), or transistors in standard CMOS
technology.
The source and drain terminals of the driving transistor TAMP are connected to the common terminal of the storage capacitance and sensor and VDD, respectively. The gate terminal of TAMP is connected to the input signal line (VIN) through T1 and the source terminal of TAMP is connected to the output signal line through T2. In the circuit, transistors T1 and T2 act as switches.
The gate terminals of T1 and T2 are connected to the select lines SEL1 and SEL2, respectively. The source terminal of T1 is connected to the gate of TAMP and its drain terminal is connected to the input signal line (VIN). The drain terminal of T2 is connected to the source terminal of TAMP and its source terminal is connected to the output signal line (IOUT).
The operation of this pixel consists of three major operating cycles:
programming cycle, integration cycle and readout cycle. During the programming cycle, node A
is charged to the voltage value equal to the sum of the bias voltage (VBIAS), the voltage of node B (VB) and the threshold voltage of TAMP (VT). Therefore the gate-source voltage of TAMP becomes:
VGS = (VBIAS + VT + VB) - (VB) = VBIAS + VT .
With reference to the waveform shown on FIG. 2(b) the operating cycles are described as follows:
The first operating cycle (Programming): SEL1 and SEL2 signals go to a high positive voltage. Therefore both switches T1 and T2 turn ON. T1 provides access path from VIN to the gate of TAMP while T2 connects the source of TAMP to IOUT. First VIN and IOUT are set to OV. After that, a linearly increasing voltage starting from OV will be applied to VIN. Subsequently, this ramp voltage is applied to the gate terminal of TAMP through the ON resistance of T1. As long as this linearly increasing voltage has not reached VT, the driving and amplifying TFT
TAMP will not turn ON and there would be no current flow from drain to the source terminal of this TFT. When the gate voltage reaches VT, TAMP turns ON
abruptly and flows considerable amount of current to the output signal line IOUT
through T2. This increase in the output current will be detected by the off pixel circuitry through monitoring IOUT. Upon detection, the output circuitry prevents the input ramp voltage from further increase. Therefore the applied voltage to the gate of TAMP will remain at VT. Next, the bias voltage VBIAS will be added to the previously retrieved value. Consequently, the total applied voltage to VIN
at the end of the first operating cycle will become:
VBIAS + VT
The second operating cycle (Integration): SEL1 and SEL2 go to zero. Therefore, the transistors T1 and T2 turn OFF. The storage capacitor CSTORE retains its previously gained value (VBIAS+VT). As a result, the overdrive voltage of TAMP
becomes independent of the threshold voltage of TAMP. The voltage stored in CSTORE remains constant, except for the initial drop due to charge feed-through stemming from the gate-source capacitance of T1 when it turns off.
Subsequently, the integration starts, during which the incident x-ray photons will generate electron-hole pairs in the x-ray sensitive a-Se layer. These electron-hole pairs are separated and driven by an applied electric field to the surfaces of the photoconductor where they will form a latent charge image. In the integration period T,NT, the input signal, h v , generates carriers that charge CSTORE by OQP and increase its potential by a small-signal voltage of dV~ .
The third operating cycle (Read Out): After integration, the T2 is turned ON.
As a result, a common source topology with source degeneration in which TAMP is the amplifying transistor and T2 acts as a passive resistor, will be constructed.
The output current of the circuit at this point would be I aiAS + G m x d V~
(1) Here Gn, is the transconductance of the total readout circuit IS Gm = gm 1 + gmRoN
(2) and dV~ is the small signal voltage generated during the integration period.
The on-pixel gain of the pixel is the change in the output currentdloUT , with respect to the incident x-ray illumination h v g = d ~~OUT ~ - d ~OQP ~ . d ~0 V~ ~ d ~41 our J
d~hv~ d~hv~ d~OQP~~ d~4V~~
(4) Here, dQP is the input charge signal due to pixel irradiation and dV~ is the corresponding change in the gate voltage of the AMP TFT. The value of the first term is identified by the characteristics of the x-ray detector and the amount of change in the charge of CSTORE it gives with changing h v . The second term depends upon the voltage change across CSTORE due to change in its charge dQP = dV~ .CSTORE
(5) For the last term to be constant, the linear small signal condition on the AMP
TFT
should be imposed during operation dV~ « 2~V~ - Tar (6) Here V~ and Yr are the gate bias voltage of TAMP and its threshold voltage, respectively.
REFERENCES
1. Chan HP, Doi K, Galhotra S, Vborny CJ, MacMahon H, Jokich PM, " Image feature analysis and computer-aided diagnosis in digital radiography:
automated detection of microcalcifications in mammography," Med Phys 14, 538-548, 1987.
2. W. Zhao and J. A. Rowlands, "X-ray imaging using amorphous selenium:
Feasibility of a flat panel self-scanned detector for digital radiography,"
Med.
Phys. 22, 1595-1604, 1995.
The on-pixel gain of the pixel is the change in the output currentdloUT , with respect to the incident x-ray illumination h v g = d ~~OUT ~ - d ~OQP ~ . d ~0 V~ ~ d ~41 our J
d~hv~ d~hv~ d~OQP~~ d~4V~~
(4) Here, dQP is the input charge signal due to pixel irradiation and dV~ is the corresponding change in the gate voltage of the AMP TFT. The value of the first term is identified by the characteristics of the x-ray detector and the amount of change in the charge of CSTORE it gives with changing h v . The second term depends upon the voltage change across CSTORE due to change in its charge dQP = dV~ .CSTORE
(5) For the last term to be constant, the linear small signal condition on the AMP
TFT
should be imposed during operation dV~ « 2~V~ - Tar (6) Here V~ and Yr are the gate bias voltage of TAMP and its threshold voltage, respectively.
REFERENCES
1. Chan HP, Doi K, Galhotra S, Vborny CJ, MacMahon H, Jokich PM, " Image feature analysis and computer-aided diagnosis in digital radiography:
automated detection of microcalcifications in mammography," Med Phys 14, 538-548, 1987.
2. W. Zhao and J. A. Rowlands, "X-ray imaging using amorphous selenium:
Feasibility of a flat panel self-scanned detector for digital radiography,"
Med.
Phys. 22, 1595-1604, 1995.
3. L. E. Antonuk, J. Boudry, W. Huang, J. L. McShan, E. J. Morton, J.
Yorkston, M. J. Longo, and R. A. Street, "Demonstration of megavoltage and diagnostic x-ray imaging with hydrogenated amorphous silicon arrays," Med. Phys. 19, 1455-1466, 1992.
Yorkston, M. J. Longo, and R. A. Street, "Demonstration of megavoltage and diagnostic x-ray imaging with hydrogenated amorphous silicon arrays," Med. Phys. 19, 1455-1466, 1992.
Claims
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002521145A CA2521145A1 (en) | 2005-10-11 | 2005-10-11 | Pixel circuit for radiation detection |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002521145A CA2521145A1 (en) | 2005-10-11 | 2005-10-11 | Pixel circuit for radiation detection |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2521145A1 true CA2521145A1 (en) | 2007-04-11 |
Family
ID=37913440
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002521145A Abandoned CA2521145A1 (en) | 2005-10-11 | 2005-10-11 | Pixel circuit for radiation detection |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2521145A1 (en) |
-
2005
- 2005-10-11 CA CA002521145A patent/CA2521145A1/en not_active Abandoned
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