CA2670180A1 - System, device and method for high dynamic range digital imaging - Google Patents
System, device and method for high dynamic range digital imaging Download PDFInfo
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- 239000002800 charge carrier Substances 0.000 claims description 5
- 239000011159 matrix material Substances 0.000 claims description 5
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- 239000012212 insulator Substances 0.000 claims description 3
- 230000005855 radiation Effects 0.000 abstract description 11
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- 230000003321 amplification Effects 0.000 description 28
- 238000003199 nucleic acid amplification method Methods 0.000 description 28
- 229910021417 amorphous silicon Inorganic materials 0.000 description 20
- XQPRBTXUXXVTKB-UHFFFAOYSA-M caesium iodide Chemical compound [I-].[Cs+] XQPRBTXUXXVTKB-UHFFFAOYSA-M 0.000 description 14
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- 238000002059 diagnostic imaging Methods 0.000 description 2
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/24—Measuring radiation intensity with semiconductor detectors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/24—Measuring radiation intensity with semiconductor detectors
- G01T1/247—Detector read-out circuitry
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
- H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
- H04N25/771—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components comprising storage means other than floating diffusion
-
- 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
- H01L27/14643—Photodiode arrays; MOS imagers
- H01L27/14658—X-ray, gamma-ray or corpuscular radiation imagers
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- Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- High Energy & Nuclear Physics (AREA)
- Molecular Biology (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Engineering & Computer Science (AREA)
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- Solid State Image Pick-Up Elements (AREA)
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Abstract
The invention provides a detecting system which is configured to selectively adjustment the capacitance associated therewith. The detecting system comprises a detector for converting electromagnetic radiation into an electrical charge, wherein the detector is operatively coupled to a capacitive system configured to selectively switch between a first detecting system capacitance and a second detecting system capacitance. This selective adjustment of the capacitance of the detecting system is based at least in part on the radiation intensity impinging on the detector.
Further provided is an imaging device which comprises a detecting system and readout circuitry operatively coupled to the detecting system, wherein the readout circuitry provides a means for sampling a signal indicative of the radiation impinging on the detector.
Further provided is an imaging device which comprises a detecting system and readout circuitry operatively coupled to the detecting system, wherein the readout circuitry provides a means for sampling a signal indicative of the radiation impinging on the detector.
Description
MBM File No. 1308-110 SYSTEM, DEVICE AND METHOD FOR HIGH DYNAMIC
RANGE DIGITAL IMAGING
FIELD OF THE INVENTION
[0001) The present invention pertains to the field of digital imaging, and in particular, to pixels for digital imaging systems capable of providing large amplification, high dynamic range and fast pixel readout time.
BACKGROUND
100021 Active matrix flat-panel imagers (AMFPIs) have gained considerable significance in digital imaging, and specifically in diagnostic medical imaging applications, in view of their large area readout capability. An AMPFI comprises a matrix of pixels, each forming a fundamental unit of the active matrix. Each pixel comprises a detector and readout circuitry for transfer of collected electrons to external electronics for data acquisition.
The pixel most commonly used for large area X-ray imaging is the passive pixel sensor (PPS) 100 shown in Figure IA. The PPS comprises a detector 101, for example, an amorphous selenium (a-Se) based photoconductor or a Caesium Iodide (CsI) phosphor coupled to an amorphous silicon (a-Si:H) PIN photodiode, or an adequate metal insulator diode that is integrated with a readout circuit comprising an a-Si:H thin-film transistor (TFT) switch. Charges generated by photons are accumulated on the pixel capacitance during an integration cycle and is transferred to an external charge amplifier via the TFT switch during a readout/reset cycle. The capacitance may arise from the PIN photodiode capacitance or an integrated storage capacitor for the a-Se photoconductor arrangement, for example. Figure 1 B illustrates a timing diagram for a sequence of operations of a PPS. Cycle 110 and 120 represent the integration cycle and readout/reset cycle, respectively. Other sequences are possible, for example, where double sampling mechanisms are introduced, wherein double sampling mechanisms are typically used to correct for the effect of non-uniformities within the circuitry. These non-uniformities may comprise process non-uniformities in the form of offsets, and, in the case of a-Si:H
technology, non-uniformities in pixel circuit performance due to transistor instability. For example, International MBMFile No. 1308-110 Patent Application Publication Nos. WO 96/34416 and WO 97/05659 disclose flat-panel detectors for radiation imaging using a PPS.
[00031 While the PPS has the advantage of being compact and thus amenable to high-resolution imaging, reading a small output signal of the PPS for low input, real-time, large area applications, such as low dose fluoroscopy, requires high performance off-panel column charge amplifiers. These charge amplifiers can add noise and degrade the signal-to-noise ratio (SNR) at low signal levels and reduce the useful dynamic range of the pixel. In particular, fluoroscopy can be one of the most demanding applications for flat-panel imaging systems due to the requirement of real-time readout. Real-time X-ray imaging or fluoroscopy is used in many medical interventional procedures where a catheter is moved through the arterial system under X-ray guidance. The technical challenge to be addressed for these types of fluoroscopy is the need for extremely low noise, or alternatively, an increase in signal size before readout. Studies on a-Si:H
PPS suggest that an improvement in SNR of an order of magnitude is desirable in order to apply these systems to more advanced imaging applications.
[0004] One approach for improved SNR is disclosed in International Patent Application Publication No. WO 02/067337 which discloses that the SNR can be increased by employing in-situ, per-pixel amplification via an a-Si:H current-mediated active pixel sensor (C-APS) 200 as illustrated in Figure 2A. The gain, linearity and noise results reported show an improvement and indicate that the a-Si:H C-APS, coupled together with an established X-ray detection technology such as a-Se or CsI/PIN photodiodes, can meet the stringent noise requirements for digital X-ray fluoroscopy. Noise may be required to be less than 103 electrons.
[0005] To perform amplification of input signals of small magnitude that are vulnerable to noise, such as in fluoroscopy, the C-APS pixel can be used in three operating cycles; a reset cycle, an integration cycle and a readout cycle. Figure 2B illustrates a timing diagram for a method of operating the C-APS readout circuit employing a double sampling mechanism. During an integration cycle 210, READ transistor 24 and RESET transistor 21 are kept OFF while AMP_RESET transistor 27 is kept ON. Photons incident upon detector 22 result in the generation of electron-hole pairs that can discharge or charge the capacitance CDETECTOR at node 201 and thus can reduce or increase the voltage at node 201, VG, by an amount AVG.
RANGE DIGITAL IMAGING
FIELD OF THE INVENTION
[0001) The present invention pertains to the field of digital imaging, and in particular, to pixels for digital imaging systems capable of providing large amplification, high dynamic range and fast pixel readout time.
BACKGROUND
100021 Active matrix flat-panel imagers (AMFPIs) have gained considerable significance in digital imaging, and specifically in diagnostic medical imaging applications, in view of their large area readout capability. An AMPFI comprises a matrix of pixels, each forming a fundamental unit of the active matrix. Each pixel comprises a detector and readout circuitry for transfer of collected electrons to external electronics for data acquisition.
The pixel most commonly used for large area X-ray imaging is the passive pixel sensor (PPS) 100 shown in Figure IA. The PPS comprises a detector 101, for example, an amorphous selenium (a-Se) based photoconductor or a Caesium Iodide (CsI) phosphor coupled to an amorphous silicon (a-Si:H) PIN photodiode, or an adequate metal insulator diode that is integrated with a readout circuit comprising an a-Si:H thin-film transistor (TFT) switch. Charges generated by photons are accumulated on the pixel capacitance during an integration cycle and is transferred to an external charge amplifier via the TFT switch during a readout/reset cycle. The capacitance may arise from the PIN photodiode capacitance or an integrated storage capacitor for the a-Se photoconductor arrangement, for example. Figure 1 B illustrates a timing diagram for a sequence of operations of a PPS. Cycle 110 and 120 represent the integration cycle and readout/reset cycle, respectively. Other sequences are possible, for example, where double sampling mechanisms are introduced, wherein double sampling mechanisms are typically used to correct for the effect of non-uniformities within the circuitry. These non-uniformities may comprise process non-uniformities in the form of offsets, and, in the case of a-Si:H
technology, non-uniformities in pixel circuit performance due to transistor instability. For example, International MBMFile No. 1308-110 Patent Application Publication Nos. WO 96/34416 and WO 97/05659 disclose flat-panel detectors for radiation imaging using a PPS.
[00031 While the PPS has the advantage of being compact and thus amenable to high-resolution imaging, reading a small output signal of the PPS for low input, real-time, large area applications, such as low dose fluoroscopy, requires high performance off-panel column charge amplifiers. These charge amplifiers can add noise and degrade the signal-to-noise ratio (SNR) at low signal levels and reduce the useful dynamic range of the pixel. In particular, fluoroscopy can be one of the most demanding applications for flat-panel imaging systems due to the requirement of real-time readout. Real-time X-ray imaging or fluoroscopy is used in many medical interventional procedures where a catheter is moved through the arterial system under X-ray guidance. The technical challenge to be addressed for these types of fluoroscopy is the need for extremely low noise, or alternatively, an increase in signal size before readout. Studies on a-Si:H
PPS suggest that an improvement in SNR of an order of magnitude is desirable in order to apply these systems to more advanced imaging applications.
[0004] One approach for improved SNR is disclosed in International Patent Application Publication No. WO 02/067337 which discloses that the SNR can be increased by employing in-situ, per-pixel amplification via an a-Si:H current-mediated active pixel sensor (C-APS) 200 as illustrated in Figure 2A. The gain, linearity and noise results reported show an improvement and indicate that the a-Si:H C-APS, coupled together with an established X-ray detection technology such as a-Se or CsI/PIN photodiodes, can meet the stringent noise requirements for digital X-ray fluoroscopy. Noise may be required to be less than 103 electrons.
[0005] To perform amplification of input signals of small magnitude that are vulnerable to noise, such as in fluoroscopy, the C-APS pixel can be used in three operating cycles; a reset cycle, an integration cycle and a readout cycle. Figure 2B illustrates a timing diagram for a method of operating the C-APS readout circuit employing a double sampling mechanism. During an integration cycle 210, READ transistor 24 and RESET transistor 21 are kept OFF while AMP_RESET transistor 27 is kept ON. Photons incident upon detector 22 result in the generation of electron-hole pairs that can discharge or charge the capacitance CDETECTOR at node 201 and thus can reduce or increase the voltage at node 201, VG, by an amount AVG.
MBMFile No. 1308-110 [0006] The readout cycle 220 follows the integration cycle 210 and during this cycle, READ
transistor 24 is turned ON, RESET transistor 21 is kept OFF and the AMP_RESET
transistor 27 is turned OFF, resulting in a current, Ibias Dlbias, that is proportional to VG AVG flowing in the AMP transistor 23 and READ transistor 24 branch. The current, Ibias Dlbias is then integrated by charge amplifier 25 to obtain and store an output voltage, VovTi, on the amplifier feedback capacitor 26.
[0007] The reset cycle 230 occurs subsequent to the readout cycle 220 where RESET transistor 21 is pulsed ON and CDETECTOR is charged, or discharged, to reset the voltage at node 201 to VG
while RESET transistor 21 is ON. During this reset cycle, READ transistor 24 is turned OFF and AMP RESET transistor 27 is turned ON.
[0008] To perform the double sampling operation, an additional read cycle 240 follows the reset cycle 230 where again READ transistor 24 is turned ON, RESET transistor 21 is turned OFF and AMP_RESET transistor 27 is turned OFF. Ibias is integrated by charge amplifier 25 to obtain and store an output voltage, VoUu, on feedback capacitor 26.
Subtracting VOUTI from VoUT2 yields a OVoUT that can be free from non-uniformities and is proportional to AVG. AIbias is proportional to AVG and is given as:
Dlbias = gmAVG, [0009] where gm is the transconductance of the AMP transistor 23 and READ
transistor 24 readout circuit branch.
[0010] The C-APS produces a charge gain, Gi, to amplify the noise vulnerable input signal.
The Gi for the C-APS is given as:
Gi = (gmTSYCDETECTOR, [0011] where Ts is the amount of time Ibias and AIbias are integrated on the feedback capacitor 26. As indicated by the equation above, Gi is programmable via g,,,, Ts and the choice of an appropriate CDETECTOR.
transistor 24 is turned ON, RESET transistor 21 is kept OFF and the AMP_RESET
transistor 27 is turned OFF, resulting in a current, Ibias Dlbias, that is proportional to VG AVG flowing in the AMP transistor 23 and READ transistor 24 branch. The current, Ibias Dlbias is then integrated by charge amplifier 25 to obtain and store an output voltage, VovTi, on the amplifier feedback capacitor 26.
[0007] The reset cycle 230 occurs subsequent to the readout cycle 220 where RESET transistor 21 is pulsed ON and CDETECTOR is charged, or discharged, to reset the voltage at node 201 to VG
while RESET transistor 21 is ON. During this reset cycle, READ transistor 24 is turned OFF and AMP RESET transistor 27 is turned ON.
[0008] To perform the double sampling operation, an additional read cycle 240 follows the reset cycle 230 where again READ transistor 24 is turned ON, RESET transistor 21 is turned OFF and AMP_RESET transistor 27 is turned OFF. Ibias is integrated by charge amplifier 25 to obtain and store an output voltage, VoUu, on feedback capacitor 26.
Subtracting VOUTI from VoUT2 yields a OVoUT that can be free from non-uniformities and is proportional to AVG. AIbias is proportional to AVG and is given as:
Dlbias = gmAVG, [0009] where gm is the transconductance of the AMP transistor 23 and READ
transistor 24 readout circuit branch.
[0010] The C-APS produces a charge gain, Gi, to amplify the noise vulnerable input signal.
The Gi for the C-APS is given as:
Gi = (gmTSYCDETECTOR, [0011] where Ts is the amount of time Ibias and AIbias are integrated on the feedback capacitor 26. As indicated by the equation above, Gi is programmable via g,,,, Ts and the choice of an appropriate CDETECTOR.
MBMFile No. 1308-110 [0012] A concern with the C-APS circuit is the small-signal linearity on the X-ray input signal.
Using such a pixel sensor, for example in real-time fluoroscopy applications, where the radiation intensity levels are small, is feasible since the voltage change at the amplifier input is also small and in the order of mV. In applications that require higher radiation intensity, however, for example in digital chest radiography, mammography or higher dose fluoroscopy, the voltage change at the amplifier input can be much larger due to the larger X-ray exposure levels, which can cause the C-APS pixel sensor output to be non-linear thus reducing the dynamic range of the pixel sensor. Another consequence of a non-linear transfer function of the amplifier is that, for example a double sampling mechanism, can not effectively be implemented in hardware due to this non-linearity.
[0013] One solution to the problem of low dynamic range is to employ a multi-mode pixel sensor (MMPS) as disclosed in International Patent Application Publication No. WO 2005/015639. In the MMPS the readout circuitry functions in different modes which may be selected depending on the characteristics of the input signal transferred to the readout circuitry from the detector. For example, when the input signal has a particular magnitude or range of magnitudes the readout circuitry can function in a first mode wherein the input signal can be amplified, and when the input signal has a different magnitude or range of magnitudes the readout circuitry can function in an alternate mode wherein the signal can be read out with a different or no amplification.
[0014] Another shortcoming of the C-APS pixel is that the presence of a large output current can cause saturation of the external or off-panel charge amplifier. Large pixel output currents can also occur when a large charge gain is required since g,, is proportional to Ib;as. International Patent Application Publication No. WO 2005/015639 discloses the use of a current subtraction circuit to deal with saturation of the amplifier. Current subtraction may require additional circuitry for dealing with offsets between pixels and can add cost to the system and introduce undesired noise to the output signal.
[0015] Another approach disclosed in International Patent Application Publication No. WO 02/067337 teaches a near-unity gain pixel amplifier, for example, an a-Si:H voltage-mediated active pixel sensor (V-APS). A general V-APS schematic is illustrated in Figure 3.
MBMFile No. 1308-110 CA 02670180 2009-06-22 Detector 32, READ transistor 34, AMP transistor 33 and RESET transistor 31 are components of the V-APS pixel and function in a similar manner as in the C-APS pixel.
Resistive load 35 is connected to the pixel output node to convert the current in the AMP
transistor 33 and READ
transistor 34 branch into an output voltage. Resistive load 35 can comprise a resistor load device or a transistor load device. The input signal voltage VG is translated to a pixel output voltage VOUT with a near unity gain. The V-APS, like the C-APS, can be used in three operating cycles; a reset cycle, an integration cycle and a readout cycle. Like the C-APS, double sampling mechanisms can be applied to the V-APS to correct for the effect of non-uniformities within the circuitry. A problem with the V-APS is that essentially no gain is provided to the input signal. In addition, with current state of the art amorphous silicon technology, it is difficult to achieve real time readout using this pixel when large column bus capacitances are charged and discharged.
[0016] U.S. Patent Application Publication Nos. 2007/0187609 and 2008/0259182 describes pixels for multi-mode readout to extend the prior art described above. Here, the pixel readout is separated into multiple modes: unity gain (PPS mode and V-APS) and high gain (C-APS mode).
In the unity gain mode the readout speed of the pixel, however, is limited by either the RC time constant of the pixel capacitance and readout transistor for the PPS or the RC
time constant of the column line capacitance and the readout transistor for the V-APS. The readout for the PPS
and V-APS imposes a limit on the overall readout speed of the pixel in multi-mode operation.
[0017] Therefore, there is a need for pixels that may overcome at least one of the deficiencies known in the art.
[0018] This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
SUMMARY OF THE INVENTION
[0019] An object of the invention is to provide a system, device and method for high dynamic range digital imaging. In accordance with an aspect of the invention, there is provided a detecting system for an imaging device, the detecting system comprising: a detector for MBMFile No. 1308-110 CA 02670180 2009-06-22 converting electromagnetic radiation to electrical charge; and a capacitor system operatively connected to the detector, the capacitor system configured to be switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge.
[0020] In accordance with another aspect of the invention, there is provided an imaging device comprising: a detecting system including: a detector for converting electromagnetic radiation to electrical charge; and a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge.
[0021] In accordance with another aspect of the invention, there is provided an imaging system comprising: a plurality of imaging devices, each imaging device comprising: a detecting system including a detector for converting electromagnetic radiation to electrical charge and a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge; and a control system operatively coupled to the plurality of imaging devices for collecting the plurality of output signals received from the plurality of imaging devices.
[0022] In accordance with another aspect of the invention, there is provided a method for operating a detecting system for an imaging device, the detecting system comprising a detector operatively coupled to a capacitor system switchable between a first capacitance and a second capacitance, the method comprising: determining a desired capacitance of the capacitor system;
configuring the capacitor system with the desired capacitance; converting electromagnetic radiation into electrical charge carriers by the detector; storing at least a portion of the charge carriers as charge in the capacitor system; and determining the charge.
MBMFile No. 1308-110 BRIEF DESCRIPTION OF THE FIGURES
[0023] Figure lA illustrates a schematic of a passive pixel sensor.
[0024] Figure 1 B illustrates a timing diagram for a method of operation of the pixel sensor of Figure 1 A.
[0025] Figure 2A illustrates a schematic of a current-mediated active pixel sensor.
100261 Figure 2B illustrates a timing diagram for a method of operation of the pixel sensor of Figure 2A.
100271 Figure 3 illustrates a schematic of a voltage-mediated active pixel sensor.
[0028] Figure 4 illustrates a schematic of a pixel sensor according to embodiments of the invention.
[0029] Figure 5 illustrates a schematic of another pixel sensor according to embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions [00301 The term "detector" is used to 'refer to a device that can convert electromagnetic radiation within a predetermined wavelength range into electrical charge. The predetermined wavelength range may include one or more portions of the electromagnetic spectrum, for example, X-ray, ultraviolet, infrared, or other electromagnetic radiation range or combination of ranges or portions thereof, as would be readily understood. The term "electromagnetic radiation"
may be used herein synonymously with the term "photon" as the case may be.
[0031] The term "sensor" is used to define the combination of one or more detectors and circuitry that may be used for determining all or a portion of the electrical charge of a detector.
[0032] The term "unity gain" is used to define a signal amplification, for example a current or voltage gain, wherein the order of magnitude of the output signal obtained as a result of the gain MBMFile No. 1308-110 being applied to an input signal substantially corresponds with the order of magnitude of the input signal.
[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
[0034] The invention provides a detecting system which is configured to selectively adjustment the capacitance associated therewith. The detecting system comprises a detector for converting electromagnetic radiation into an electrical charge, wherein the detector is operatively coupled to a capacitive system configured to selectively switch between a first detecting system capacitance and a second detecting system capacitance. This selective adjustment of the capacitance of the detecting system is based at least in part on the radiation intensity impinging on the detector. Further provided is an imaging device which comprises a detecting system and readout circuitry operatively coupled to the detecting system, wherein the readout circuitry provides a means for sampling a signal indicative of the radiation impinging on the detector. As used herein, an imaging device may also be referred to as a "pixel". Further provided is an imaging system according to embodiments of the invention, which comprises a plurality of imaging devices, each of which includes a detecting system and readout circuitry.
[0035] Each detector generates charge carriers, for example electrons and/or holes, in response to photons that are adequately absorbed by the detector. Absorbed photons can result in a voltage change across the detector. This voltage change produces the input signal to the readout circuitry.
According to embodiments of the invention, the readout circuit is configured to provide electrical current or charge representative of the input signal.
[0036] According to some embodiments of the invention, the readout circuitry achieves high dynamic range and high gain while operating in one of one or more readout modes, for example in C-APS or V-APS. According to embodiments of the invention, this may be achieved by varying the capacitance of the pixel used to hold the charge generated by absorbed photons. A
pixel according to embodiments of the invention may optionally be configured to provide more than one readout mode.
MBMFile No. 1308-110 Detecting System [0037] The detecting system comprises a detector for converting electromagnetic radiation into an electrical charge. The detector is operatively coupled to a capacitive system configured to selectively switch between a first detecting system capacitance and a second detecting system capacitance. This selective adjustment of the capacitance of the detecting system is based at least in part on the radiation intensity impinging on the detector. According to embodiments of the invention, one or more of a third detecting system capacitance, fourth detecting system capacitance etc. may also be provided by the detecting system.
[0038] Figure 4 illustrates a schematic of a detecting system according to embodiments of the invention. The detecting system comprises a readout circuit 401, a detector 402, a pixel capacitor 403, a pixel switch 404 and an additional pixel capacitor 405. The combination of pixel switch 404 and additional pixel capacitor 405 allows for selection of the pixel capacitance from a plurality of predetermined capacities in correspondence with radiation intensity requirements of the application.
[0039] According to some embodiments of the invention a detecting system may comprise one or more switches and capacitors operatively interconnected to form one of one or more predetermined network configurations by selectively opening and/or closing predetermined switches. According to embodiments of the invention a detecting system may be configured to operate linearly within one or more ranges of predetermined operating conditions. For example, for low signal (i.e. small input charge), pixel capacitor 403 may be dimensioned to yield a first predetermined voltage to get a linear response from readout circuit 401; and for high signal (i.e.
large input charge), pixel capacitor 405 can be connected in parallel to pixel capacitor 403 via switch 404 to increase the pixel capacitance in order to provide a predetermined voltage for a linear response from 401.
[0040] A detecting system according to embodiments of the invention may comprise a serially connected, non-biased detector and a pixel capacitor, and one switch for selectively shorting the pixel capacitor. The one switch may be used to operatively activate the one pixel capacitor in parallel to the intrinsic capacitance of the detector in order to add the capacitance of the pixel capacitor to the intrinsic capacitance when the switch is closed. It is noted that one detector, one MBMFile No. 1308-110 pixel capacitor and one switch may be interconnected in other ways to provide and controllable capacitance.
[0041] The detector may comprise an amorphous selenium (a-Se) based photoconductor or a Caesium Iodide (CsI) phosphor coupled to an amorphous silicon (a-Si:H) PIN
photodiode, or an adequate metal insulator diode that is integrated with a readout circuit comprising an a-Si:H thin-film transistor (TFT) switch, for example. The detector may be any type of detector, for example, solid-state photodetectors such as a-Si:H, amorphous selenium, lead iodide, mercuric iodide, lead oxide or cadmium zinc telluride based detectors or other appropriate detector.
In addition, direct detection based detectors such as molybdenum Schottky diodes, as well as detectors based on indirect detection such as those comprising phosphors, for example gadolinium oxysulfide detectors or caesium iodide detectors, may also be used. A photodiodes may be configured and employed in a detecting system to provide a combination of detector and pixel capacitor.
[0042] The one or more pixel capacitors may comprise metallic layers separated by one or more layers of one or more adequate dielectric materials. A switch may comprise an adequately configured transistor, for example, a field effect transistor. Components of the detecting system including detectors, capacitors and/or switches, may be disposed using thin-film technology, epitaxially or in another manner as would be readily understood. For example, a switch may be a transistor configured as a n-type, p-type or ambi-polar transistor. Components of the detecting system may be at least partially integrally formed, for example, the detector and one or more of the capacitors may share a one or more common layers of one or more materials.
Interconnections between components of the detecting may be formed from/by common elements of components and/or traces of adequately conductive material. Like aspects may apply to readout circuitry and imaging systems.
[0043] A capacitor system according to embodiments of the invention may comprise two or more capacitors and one or more switches for operatively interconnecting the capacitors in a number of predetermined configurations, for example, in a purely parallel or serial, or in a mixed parallel-serial configuration. The capacitor system may be configured to permit reconfiguration of the interconnection of the capacitors during operation.
MBMFile No. 1308-110 [0044] According to embodiments, the detecting system comprises a reset switch, for example a transistor, for operatively connecting the capacitor system to a predetermined potential for disposing a predetermined charge in the capacitor system when closing the reset switch.
Readout Circuitry [0045] A readout circuitry according to some embodiments of the invention may be configured to provide large amplification to small, noise sensitive input signals, improved noise immunity, and/or fast pixel readout time, for example. A pixel according to some embodiments of the invention may be able to provide high speed readout irrespective of whether the pixel operates in unity or high gain mode and/or be able to achieve real-time readout as well as achieve high gain to detect small noise-vulnerable signals with a large signal-to-noise ratio while being capable of sensing a wide range of input signals.
[0046] According to some embodiments of the invention, a readout circuit may be preconfigured to operate in one predetermined mode, for example in a voltage-or current-mediated active pixel sensor mode, or in one out of two or more predetermined modes which can be selected during operation. For example, in a multi-mode imaging device or multi-mode imaging devices of an imaging system, the readout circuitry may be configured to operate in one of a plurality of modes which may be selected depending on the characteristics of the input signal provided to the readout circuitry from the detector. For example, when the input signal has a particular magnitude or range of magnitudes the readout circuitry can function in a first mode wherein the input signal can be amplified, and when the input signal has a different magnitude or range of magnitudes the readout circuitry can function in an alternate mode wherein the signal can be read out with a different or no amplification, for example, as is described in International Patent Application Publication No. W02005/015639.
[0047] A readout circuitry according to embodiments of the invention comprises an on-pixel amplifier, for example a transistor, and additional transistors for reading out the amplified signal and/or to reset the amplified output signal stored by a portion of the circuit prior to reading a subsequent signal. Transistors for reading and resetting may be disposed in various parts of the readout circuitry. One of more transistors and/or additional components, for example resistors, inductors or capacitors, may also be used in addition to the amplification transistor for MBM File No. 1308-110 amplification. Power sources and components such as resistors, inductors and capacitors, in addition to the amplification, read and reset transistors may also be implemented in the readout circuitry.
[0048] The readout circuitry is configured to provide a signal representative of the voltage or charge generated by the one or more detectors in response to adequately absorbed photons.
According to embodiments of the invention, the readout circuitry may be configured to provide large amplification of small, noise sensitive input signals to improve their noise immunity, as well as capable of providing a fast pixel readout time. The readout circuitry may comprise an on-pixel amplification transistor as well as additional transistors used to read out the amplified signal and/or to reset the amplified output signal stored by a portion of the circuit prior to reading a subsequent signal, wherein the read transistors and reset transistors are able to occupy various positions within the readout circuitry. More than one transistor as well as additional components, such as resistors, inductors and capacitors, may also be used in addition to the amplification transistor for amplification. Power sources and components such as resistors, inductors and capacitors, in addition to the amplification, read and reset transistors may also be implemented in the readout circuitry. For example, the readout circuitry may comprise an independently programmable current source to reduce electrical current in elements of a number of components of the readout circuitry when a large charge gain is used. This can help prevent saturation of the components and mitigate the need for additional off-panel correction circuitry for offsets between pixels. Such circuitry may be used to provide a digital imaging system with a large dynamic range of detection.
[0049] In some embodiments of the invention, the readout circuitry is capable of providing large amplification and thus additional noise immunity to the input signal from the detector by implementing another amplification stage within the readout circuitry. In some embodiments the voltage change produced across the detector produces the input signal to the first amplification stage, or pre-amplification stage. The output signal from the pre-amplification stage forms the input signal to the second amplification stage, or the amplification transistor, which then provides an output signal with a larger gain than would have been obtained with solely the amplification transistor. Additional amplification stages may be employed in the readout circuitry.
MBMFile No. 1308-110 [0050] A readout circuitry according to some embodiments of the invention may be configured to operate in one or more modes and configured to be operated in one mode depending on characteristics of the input signals transferred to the readout circuitry from the detectors, or can depend on the characteristics of the output signal required from the readout circuitry. For example, when the input signal has a particular magnitude or range of magnitudes, the readout circuitry can function in a first mode in which the input signal can be amplified to a specific level, and when the input signal has a magnitude or range of magnitudes, the readout circuitry can function in an alternate mode in which the input signal can be read out with a different or no amplification.
[0051] For applications such as low dose fluoroscopy, high dose fluoroscopy, chest radiography and mammography, readout circuitry may be configured to provide two or more modes to provide a sufficient dynamic range for these X-ray detection techniques, or other detection techniques as would be readily understood. A readout circuitry according to embodiments of the invention may be configured to provide additional modes to accommodate various levels of amplification to the input signal, for example, three or more modes of operation of the readout circuitry can be implemented.
[0052] According to embodiments of the invention, more than one mode may be used to read out the same input signal. In addition, some embodiments may function in both a single mode and a dual mode without modifications to the readout circuitry. In some embodiments, selection of the mode of operation of the readout circuitry may be actuated manually or automatically. For example, an automated switching system can comprise a feedback circuit enabling automatic selection of an appropriate mode of operation of the readout circuitry, or a pre-programmed sequence to enable automatic selection of an appropriate mode of operation of the readout circuitry, or other means of enabling automatic selection of an appropriate mode of operation of the readout circuitry as would be readily understood.
[0053] According to embodiments of the invention further increasing the dynamic range of detection may be achieved by implementing a current subtraction circuit in the readout circuitry.
The current subtraction circuit may be used to reduce the total amount of current flowing through parts of the readout circuitry which can saturate, for example, when a large charge gain is used.
MBMFile No. 1308-110 Reducing the total output current can result in an increase in the dynamic range of the sensor by allowing smaller input signals to be detected by enabling greater amplification of the input signals.
[0054] A readout circuit according to embodiments of the invention may comprise a plurality of amorphous silicon based thin-film transistors of which one may be formed in a source follower circuit for producing an output current, the readout circuit is embedded under the detector to provide a high fill factor. The readout circuit may comprise a current-mediated a-Si thin-film transistor or a voltage-mediated a-Si thin-film transistor. The readout circuit may be configured to produce an output current through a reset, integration and readout mode operation sequence. The readout circuit may be configured as an a-Si TFT on-pixel V-APS
readout circuit that can provide in-situ voltage amplification and eliminate the need for an external amplifier. A
readout circuit according to an embodiment of the present invention may be configured to provide a desired linearity, dynamic range, and/or near unity gain.
[0055] A readout circuitry according to some embodiments of the present invention may be configured and operated in a number of ways including pixel amplifier designs and operating methods as disclosed in U.S. Patent Application Publication Nos. 2008/0259182 or 2007/0187609 or International Patent Application Publication No. WO 02/067337, for example.
[0056] The invention will now be described with reference to specific examples. It will be understood that the following examples are intended to describe embodiments of the invention and are not intended to limit the invention in any way.
EXAMPLE
[0057] Figure 5 illustrates a pixel 500 according to embodiments of the invention in combination with an example C-APS readout circuit 501. The pixel may be used in low-dose fluoroscopy applications where the input signal from the detector 502 is very small or in high-dose applications where the input signal is large. According to embodiments of the invention capacitor 503 may be configured to provide an appropriate capacitance and predetermined signal gain via the readout circuit 501. In higher dose applications, for example in chest radiography, the pixel switch 504 can be turned ON to increase the pixel capacitance connecting 503 and 505 MBMFile No. 1308-110 in parallel (thus increasing pixel capacitance to the sum of 503 and 505) to achieve predetermined gain as desired for the application.
[0058] The example pixel illustrated in Figure 5 may be configured to operate linearly at substantially all times. For example, for low signal (i.e. small input charge), pixel capacitor 503 may be designed to yield a first predetermined voltage to get a linear response from readout circuit 501; and for high signal (i.e. large input charge), pixel capacitor 505 can be added to pixel capacitor 503 via switch 504 to increase the pixel capacitance in order to provide a predetermined linear voltage charge response from readout circuit 501. Figure 5 further illustrates column circuitry 510 comprising an amplifier 250, feedback capacitor 260 and a transistor 270 for resetting the column circuitry 510.
[0059] A pixel according to some embodiments of the present invention can be configured to provide fast readout speed at a predetermined gain over a large signal range, for example from low to high levels without the need to select among signal readout methods based on signal strength. This can help reduce X-ray dose to patients during imaging and/or increase contrast resulting in clearer images in large area digital X-ray imaging applications, for example.
[0060] According to embodiments of the invention a pixel may comprise one or more detectors. According to embodiments of the invention, the readout circuitry may be partially present within the on-panel pixels and partially present off the imaging panel, or substantially present on the imaging panel. The imaging panel may be rigid, for example comprising a rigid glass or rigid metal substrate, or flexible, for example comprising a flexible plastic or flexible metal substrate. In addition, a pixel may be operatively separated onto more than one imaging panel. For example, one panel may comprise some parts of the pixel and another panel may comprise other parts of the pixel. Furthermore, the pixel electronics may be fabricated on a single chip or on multiple chips. Furthermore, the readout circuitry present within a pixel may be physically located in the same plane as the detector or this readout circuitry may be embedded under, or fabricated above, the detector to provide a high fill factor.
[0061] According to embodiments, portions of the readout circuitry common to a column, row or other group of pixels may be used in a multiplex manner to perform readout of an array or matrix of pixels included in a digital imaging apparatus according to some embodiments of the MBMFile No. 1308-110 present invention. It is noted that common column, row or group readout circuitry and the multiplexed readout of pixels may require additional circuitry, for example switching circuits or multiplexing circuits. Employ of multiplexing circuitry, however, may also reduce complexity of the readout circuit by reducing the total number of amplifiers required for a column, row, or group of pixels, for example. Furthermore, conunon column or row readout circuitry may also be implemented such that the common readout circuitry is individual to each pixel, for example, one readout circuit may be disposed per pixel.
[0062] According to embodiments of the invention, the pixels may be disposed and operatively arranged in arrays of predetermined sizes. According to some embodiments, portions of readout circuitry that have been identified as operatively being shared among one or more columns of pixels, may also be shared by one or more rows of pixels or one or more other groups of pixels.
[0063] Embodiments of the invention can be operated with various switching and timing sequences. For example, where a double sampling technique is used, the transistor switching and timing may vary from a sequence in which no double sampling technique is used.
While a number of transistor switching, timing cycles and sequences are described herein, numerous other cycles and sequences are possible. Some sequences may have advantages over others.
[0064] The detector may be any type of detector, for example, solid-state photodetectors such as a-Si:H, amorphous selenium, lead iodide, mercuric iodide, lead oxide or cadmium zinc telluride based detectors or other appropriate detector. In addition, direct detection based detectors such as molybdenum Schottky diodes, as well as detectors based on indirect detection such as those comprising phosphors for example gadolinium oxysulfide detectors or caesium iodide detectors, may also be used. In the case of photodiode based detectors, the pixel capacitor is provided by the photodiode. Pixel capacitors 503 and/or 505 may be provided by a photodiode, portions of a photodiode, or by sharing of photodiode area as would be readily understood by a worker skilled in the art.
[0065] Other types of detectors for radiation detection may further be used as would be readily understood by a worker skilled in the art. The transistors used in various embodiments of the invention may be amorphous silicon (a-Si:H) thin-film transistors (TFTs), poly-crystalline silicon TFTs, micro-crystalline silicon TFTs, nano-crystalline silicon TFTs, crystalline silicon MBM FileNo. 1308-110 CA 02670180 2009-06-22 transistors, or other similar device as would be readily understood by a worker skilled in the art.
In addition, the transistors may be n-type, p-type or ambi-polar. In further embodiments, radiation in any region of the electromagnetic spectrum may be detected using the present invention with the selection of detectors, and devices for the readout circuitry being made in order that an appropriate portion of the electromagnetic spectrum can be detected as would be readily understood by a worker skilled in the art.
[0066] As would be readily understood by a worker skilled in the art, the present invention may be applied to any digital imaging application. For example, the present invention may be applied to medical imaging, X-ray inspection systems such as in the inspection of aircraft wings, security systems such as screening of luggage at airports, non-destructive material tests, radiography, tomosynthesis or optical imaging, as well as other forms of digital imaging applications as would be readily understood.
[0067] The embodiments of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Using such a pixel sensor, for example in real-time fluoroscopy applications, where the radiation intensity levels are small, is feasible since the voltage change at the amplifier input is also small and in the order of mV. In applications that require higher radiation intensity, however, for example in digital chest radiography, mammography or higher dose fluoroscopy, the voltage change at the amplifier input can be much larger due to the larger X-ray exposure levels, which can cause the C-APS pixel sensor output to be non-linear thus reducing the dynamic range of the pixel sensor. Another consequence of a non-linear transfer function of the amplifier is that, for example a double sampling mechanism, can not effectively be implemented in hardware due to this non-linearity.
[0013] One solution to the problem of low dynamic range is to employ a multi-mode pixel sensor (MMPS) as disclosed in International Patent Application Publication No. WO 2005/015639. In the MMPS the readout circuitry functions in different modes which may be selected depending on the characteristics of the input signal transferred to the readout circuitry from the detector. For example, when the input signal has a particular magnitude or range of magnitudes the readout circuitry can function in a first mode wherein the input signal can be amplified, and when the input signal has a different magnitude or range of magnitudes the readout circuitry can function in an alternate mode wherein the signal can be read out with a different or no amplification.
[0014] Another shortcoming of the C-APS pixel is that the presence of a large output current can cause saturation of the external or off-panel charge amplifier. Large pixel output currents can also occur when a large charge gain is required since g,, is proportional to Ib;as. International Patent Application Publication No. WO 2005/015639 discloses the use of a current subtraction circuit to deal with saturation of the amplifier. Current subtraction may require additional circuitry for dealing with offsets between pixels and can add cost to the system and introduce undesired noise to the output signal.
[0015] Another approach disclosed in International Patent Application Publication No. WO 02/067337 teaches a near-unity gain pixel amplifier, for example, an a-Si:H voltage-mediated active pixel sensor (V-APS). A general V-APS schematic is illustrated in Figure 3.
MBMFile No. 1308-110 CA 02670180 2009-06-22 Detector 32, READ transistor 34, AMP transistor 33 and RESET transistor 31 are components of the V-APS pixel and function in a similar manner as in the C-APS pixel.
Resistive load 35 is connected to the pixel output node to convert the current in the AMP
transistor 33 and READ
transistor 34 branch into an output voltage. Resistive load 35 can comprise a resistor load device or a transistor load device. The input signal voltage VG is translated to a pixel output voltage VOUT with a near unity gain. The V-APS, like the C-APS, can be used in three operating cycles; a reset cycle, an integration cycle and a readout cycle. Like the C-APS, double sampling mechanisms can be applied to the V-APS to correct for the effect of non-uniformities within the circuitry. A problem with the V-APS is that essentially no gain is provided to the input signal. In addition, with current state of the art amorphous silicon technology, it is difficult to achieve real time readout using this pixel when large column bus capacitances are charged and discharged.
[0016] U.S. Patent Application Publication Nos. 2007/0187609 and 2008/0259182 describes pixels for multi-mode readout to extend the prior art described above. Here, the pixel readout is separated into multiple modes: unity gain (PPS mode and V-APS) and high gain (C-APS mode).
In the unity gain mode the readout speed of the pixel, however, is limited by either the RC time constant of the pixel capacitance and readout transistor for the PPS or the RC
time constant of the column line capacitance and the readout transistor for the V-APS. The readout for the PPS
and V-APS imposes a limit on the overall readout speed of the pixel in multi-mode operation.
[0017] Therefore, there is a need for pixels that may overcome at least one of the deficiencies known in the art.
[0018] This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
SUMMARY OF THE INVENTION
[0019] An object of the invention is to provide a system, device and method for high dynamic range digital imaging. In accordance with an aspect of the invention, there is provided a detecting system for an imaging device, the detecting system comprising: a detector for MBMFile No. 1308-110 CA 02670180 2009-06-22 converting electromagnetic radiation to electrical charge; and a capacitor system operatively connected to the detector, the capacitor system configured to be switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge.
[0020] In accordance with another aspect of the invention, there is provided an imaging device comprising: a detecting system including: a detector for converting electromagnetic radiation to electrical charge; and a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge.
[0021] In accordance with another aspect of the invention, there is provided an imaging system comprising: a plurality of imaging devices, each imaging device comprising: a detecting system including a detector for converting electromagnetic radiation to electrical charge and a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge; and a control system operatively coupled to the plurality of imaging devices for collecting the plurality of output signals received from the plurality of imaging devices.
[0022] In accordance with another aspect of the invention, there is provided a method for operating a detecting system for an imaging device, the detecting system comprising a detector operatively coupled to a capacitor system switchable between a first capacitance and a second capacitance, the method comprising: determining a desired capacitance of the capacitor system;
configuring the capacitor system with the desired capacitance; converting electromagnetic radiation into electrical charge carriers by the detector; storing at least a portion of the charge carriers as charge in the capacitor system; and determining the charge.
MBMFile No. 1308-110 BRIEF DESCRIPTION OF THE FIGURES
[0023] Figure lA illustrates a schematic of a passive pixel sensor.
[0024] Figure 1 B illustrates a timing diagram for a method of operation of the pixel sensor of Figure 1 A.
[0025] Figure 2A illustrates a schematic of a current-mediated active pixel sensor.
100261 Figure 2B illustrates a timing diagram for a method of operation of the pixel sensor of Figure 2A.
100271 Figure 3 illustrates a schematic of a voltage-mediated active pixel sensor.
[0028] Figure 4 illustrates a schematic of a pixel sensor according to embodiments of the invention.
[0029] Figure 5 illustrates a schematic of another pixel sensor according to embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions [00301 The term "detector" is used to 'refer to a device that can convert electromagnetic radiation within a predetermined wavelength range into electrical charge. The predetermined wavelength range may include one or more portions of the electromagnetic spectrum, for example, X-ray, ultraviolet, infrared, or other electromagnetic radiation range or combination of ranges or portions thereof, as would be readily understood. The term "electromagnetic radiation"
may be used herein synonymously with the term "photon" as the case may be.
[0031] The term "sensor" is used to define the combination of one or more detectors and circuitry that may be used for determining all or a portion of the electrical charge of a detector.
[0032] The term "unity gain" is used to define a signal amplification, for example a current or voltage gain, wherein the order of magnitude of the output signal obtained as a result of the gain MBMFile No. 1308-110 being applied to an input signal substantially corresponds with the order of magnitude of the input signal.
[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
[0034] The invention provides a detecting system which is configured to selectively adjustment the capacitance associated therewith. The detecting system comprises a detector for converting electromagnetic radiation into an electrical charge, wherein the detector is operatively coupled to a capacitive system configured to selectively switch between a first detecting system capacitance and a second detecting system capacitance. This selective adjustment of the capacitance of the detecting system is based at least in part on the radiation intensity impinging on the detector. Further provided is an imaging device which comprises a detecting system and readout circuitry operatively coupled to the detecting system, wherein the readout circuitry provides a means for sampling a signal indicative of the radiation impinging on the detector. As used herein, an imaging device may also be referred to as a "pixel". Further provided is an imaging system according to embodiments of the invention, which comprises a plurality of imaging devices, each of which includes a detecting system and readout circuitry.
[0035] Each detector generates charge carriers, for example electrons and/or holes, in response to photons that are adequately absorbed by the detector. Absorbed photons can result in a voltage change across the detector. This voltage change produces the input signal to the readout circuitry.
According to embodiments of the invention, the readout circuit is configured to provide electrical current or charge representative of the input signal.
[0036] According to some embodiments of the invention, the readout circuitry achieves high dynamic range and high gain while operating in one of one or more readout modes, for example in C-APS or V-APS. According to embodiments of the invention, this may be achieved by varying the capacitance of the pixel used to hold the charge generated by absorbed photons. A
pixel according to embodiments of the invention may optionally be configured to provide more than one readout mode.
MBMFile No. 1308-110 Detecting System [0037] The detecting system comprises a detector for converting electromagnetic radiation into an electrical charge. The detector is operatively coupled to a capacitive system configured to selectively switch between a first detecting system capacitance and a second detecting system capacitance. This selective adjustment of the capacitance of the detecting system is based at least in part on the radiation intensity impinging on the detector. According to embodiments of the invention, one or more of a third detecting system capacitance, fourth detecting system capacitance etc. may also be provided by the detecting system.
[0038] Figure 4 illustrates a schematic of a detecting system according to embodiments of the invention. The detecting system comprises a readout circuit 401, a detector 402, a pixel capacitor 403, a pixel switch 404 and an additional pixel capacitor 405. The combination of pixel switch 404 and additional pixel capacitor 405 allows for selection of the pixel capacitance from a plurality of predetermined capacities in correspondence with radiation intensity requirements of the application.
[0039] According to some embodiments of the invention a detecting system may comprise one or more switches and capacitors operatively interconnected to form one of one or more predetermined network configurations by selectively opening and/or closing predetermined switches. According to embodiments of the invention a detecting system may be configured to operate linearly within one or more ranges of predetermined operating conditions. For example, for low signal (i.e. small input charge), pixel capacitor 403 may be dimensioned to yield a first predetermined voltage to get a linear response from readout circuit 401; and for high signal (i.e.
large input charge), pixel capacitor 405 can be connected in parallel to pixel capacitor 403 via switch 404 to increase the pixel capacitance in order to provide a predetermined voltage for a linear response from 401.
[0040] A detecting system according to embodiments of the invention may comprise a serially connected, non-biased detector and a pixel capacitor, and one switch for selectively shorting the pixel capacitor. The one switch may be used to operatively activate the one pixel capacitor in parallel to the intrinsic capacitance of the detector in order to add the capacitance of the pixel capacitor to the intrinsic capacitance when the switch is closed. It is noted that one detector, one MBMFile No. 1308-110 pixel capacitor and one switch may be interconnected in other ways to provide and controllable capacitance.
[0041] The detector may comprise an amorphous selenium (a-Se) based photoconductor or a Caesium Iodide (CsI) phosphor coupled to an amorphous silicon (a-Si:H) PIN
photodiode, or an adequate metal insulator diode that is integrated with a readout circuit comprising an a-Si:H thin-film transistor (TFT) switch, for example. The detector may be any type of detector, for example, solid-state photodetectors such as a-Si:H, amorphous selenium, lead iodide, mercuric iodide, lead oxide or cadmium zinc telluride based detectors or other appropriate detector.
In addition, direct detection based detectors such as molybdenum Schottky diodes, as well as detectors based on indirect detection such as those comprising phosphors, for example gadolinium oxysulfide detectors or caesium iodide detectors, may also be used. A photodiodes may be configured and employed in a detecting system to provide a combination of detector and pixel capacitor.
[0042] The one or more pixel capacitors may comprise metallic layers separated by one or more layers of one or more adequate dielectric materials. A switch may comprise an adequately configured transistor, for example, a field effect transistor. Components of the detecting system including detectors, capacitors and/or switches, may be disposed using thin-film technology, epitaxially or in another manner as would be readily understood. For example, a switch may be a transistor configured as a n-type, p-type or ambi-polar transistor. Components of the detecting system may be at least partially integrally formed, for example, the detector and one or more of the capacitors may share a one or more common layers of one or more materials.
Interconnections between components of the detecting may be formed from/by common elements of components and/or traces of adequately conductive material. Like aspects may apply to readout circuitry and imaging systems.
[0043] A capacitor system according to embodiments of the invention may comprise two or more capacitors and one or more switches for operatively interconnecting the capacitors in a number of predetermined configurations, for example, in a purely parallel or serial, or in a mixed parallel-serial configuration. The capacitor system may be configured to permit reconfiguration of the interconnection of the capacitors during operation.
MBMFile No. 1308-110 [0044] According to embodiments, the detecting system comprises a reset switch, for example a transistor, for operatively connecting the capacitor system to a predetermined potential for disposing a predetermined charge in the capacitor system when closing the reset switch.
Readout Circuitry [0045] A readout circuitry according to some embodiments of the invention may be configured to provide large amplification to small, noise sensitive input signals, improved noise immunity, and/or fast pixel readout time, for example. A pixel according to some embodiments of the invention may be able to provide high speed readout irrespective of whether the pixel operates in unity or high gain mode and/or be able to achieve real-time readout as well as achieve high gain to detect small noise-vulnerable signals with a large signal-to-noise ratio while being capable of sensing a wide range of input signals.
[0046] According to some embodiments of the invention, a readout circuit may be preconfigured to operate in one predetermined mode, for example in a voltage-or current-mediated active pixel sensor mode, or in one out of two or more predetermined modes which can be selected during operation. For example, in a multi-mode imaging device or multi-mode imaging devices of an imaging system, the readout circuitry may be configured to operate in one of a plurality of modes which may be selected depending on the characteristics of the input signal provided to the readout circuitry from the detector. For example, when the input signal has a particular magnitude or range of magnitudes the readout circuitry can function in a first mode wherein the input signal can be amplified, and when the input signal has a different magnitude or range of magnitudes the readout circuitry can function in an alternate mode wherein the signal can be read out with a different or no amplification, for example, as is described in International Patent Application Publication No. W02005/015639.
[0047] A readout circuitry according to embodiments of the invention comprises an on-pixel amplifier, for example a transistor, and additional transistors for reading out the amplified signal and/or to reset the amplified output signal stored by a portion of the circuit prior to reading a subsequent signal. Transistors for reading and resetting may be disposed in various parts of the readout circuitry. One of more transistors and/or additional components, for example resistors, inductors or capacitors, may also be used in addition to the amplification transistor for MBM File No. 1308-110 amplification. Power sources and components such as resistors, inductors and capacitors, in addition to the amplification, read and reset transistors may also be implemented in the readout circuitry.
[0048] The readout circuitry is configured to provide a signal representative of the voltage or charge generated by the one or more detectors in response to adequately absorbed photons.
According to embodiments of the invention, the readout circuitry may be configured to provide large amplification of small, noise sensitive input signals to improve their noise immunity, as well as capable of providing a fast pixel readout time. The readout circuitry may comprise an on-pixel amplification transistor as well as additional transistors used to read out the amplified signal and/or to reset the amplified output signal stored by a portion of the circuit prior to reading a subsequent signal, wherein the read transistors and reset transistors are able to occupy various positions within the readout circuitry. More than one transistor as well as additional components, such as resistors, inductors and capacitors, may also be used in addition to the amplification transistor for amplification. Power sources and components such as resistors, inductors and capacitors, in addition to the amplification, read and reset transistors may also be implemented in the readout circuitry. For example, the readout circuitry may comprise an independently programmable current source to reduce electrical current in elements of a number of components of the readout circuitry when a large charge gain is used. This can help prevent saturation of the components and mitigate the need for additional off-panel correction circuitry for offsets between pixels. Such circuitry may be used to provide a digital imaging system with a large dynamic range of detection.
[0049] In some embodiments of the invention, the readout circuitry is capable of providing large amplification and thus additional noise immunity to the input signal from the detector by implementing another amplification stage within the readout circuitry. In some embodiments the voltage change produced across the detector produces the input signal to the first amplification stage, or pre-amplification stage. The output signal from the pre-amplification stage forms the input signal to the second amplification stage, or the amplification transistor, which then provides an output signal with a larger gain than would have been obtained with solely the amplification transistor. Additional amplification stages may be employed in the readout circuitry.
MBMFile No. 1308-110 [0050] A readout circuitry according to some embodiments of the invention may be configured to operate in one or more modes and configured to be operated in one mode depending on characteristics of the input signals transferred to the readout circuitry from the detectors, or can depend on the characteristics of the output signal required from the readout circuitry. For example, when the input signal has a particular magnitude or range of magnitudes, the readout circuitry can function in a first mode in which the input signal can be amplified to a specific level, and when the input signal has a magnitude or range of magnitudes, the readout circuitry can function in an alternate mode in which the input signal can be read out with a different or no amplification.
[0051] For applications such as low dose fluoroscopy, high dose fluoroscopy, chest radiography and mammography, readout circuitry may be configured to provide two or more modes to provide a sufficient dynamic range for these X-ray detection techniques, or other detection techniques as would be readily understood. A readout circuitry according to embodiments of the invention may be configured to provide additional modes to accommodate various levels of amplification to the input signal, for example, three or more modes of operation of the readout circuitry can be implemented.
[0052] According to embodiments of the invention, more than one mode may be used to read out the same input signal. In addition, some embodiments may function in both a single mode and a dual mode without modifications to the readout circuitry. In some embodiments, selection of the mode of operation of the readout circuitry may be actuated manually or automatically. For example, an automated switching system can comprise a feedback circuit enabling automatic selection of an appropriate mode of operation of the readout circuitry, or a pre-programmed sequence to enable automatic selection of an appropriate mode of operation of the readout circuitry, or other means of enabling automatic selection of an appropriate mode of operation of the readout circuitry as would be readily understood.
[0053] According to embodiments of the invention further increasing the dynamic range of detection may be achieved by implementing a current subtraction circuit in the readout circuitry.
The current subtraction circuit may be used to reduce the total amount of current flowing through parts of the readout circuitry which can saturate, for example, when a large charge gain is used.
MBMFile No. 1308-110 Reducing the total output current can result in an increase in the dynamic range of the sensor by allowing smaller input signals to be detected by enabling greater amplification of the input signals.
[0054] A readout circuit according to embodiments of the invention may comprise a plurality of amorphous silicon based thin-film transistors of which one may be formed in a source follower circuit for producing an output current, the readout circuit is embedded under the detector to provide a high fill factor. The readout circuit may comprise a current-mediated a-Si thin-film transistor or a voltage-mediated a-Si thin-film transistor. The readout circuit may be configured to produce an output current through a reset, integration and readout mode operation sequence. The readout circuit may be configured as an a-Si TFT on-pixel V-APS
readout circuit that can provide in-situ voltage amplification and eliminate the need for an external amplifier. A
readout circuit according to an embodiment of the present invention may be configured to provide a desired linearity, dynamic range, and/or near unity gain.
[0055] A readout circuitry according to some embodiments of the present invention may be configured and operated in a number of ways including pixel amplifier designs and operating methods as disclosed in U.S. Patent Application Publication Nos. 2008/0259182 or 2007/0187609 or International Patent Application Publication No. WO 02/067337, for example.
[0056] The invention will now be described with reference to specific examples. It will be understood that the following examples are intended to describe embodiments of the invention and are not intended to limit the invention in any way.
EXAMPLE
[0057] Figure 5 illustrates a pixel 500 according to embodiments of the invention in combination with an example C-APS readout circuit 501. The pixel may be used in low-dose fluoroscopy applications where the input signal from the detector 502 is very small or in high-dose applications where the input signal is large. According to embodiments of the invention capacitor 503 may be configured to provide an appropriate capacitance and predetermined signal gain via the readout circuit 501. In higher dose applications, for example in chest radiography, the pixel switch 504 can be turned ON to increase the pixel capacitance connecting 503 and 505 MBMFile No. 1308-110 in parallel (thus increasing pixel capacitance to the sum of 503 and 505) to achieve predetermined gain as desired for the application.
[0058] The example pixel illustrated in Figure 5 may be configured to operate linearly at substantially all times. For example, for low signal (i.e. small input charge), pixel capacitor 503 may be designed to yield a first predetermined voltage to get a linear response from readout circuit 501; and for high signal (i.e. large input charge), pixel capacitor 505 can be added to pixel capacitor 503 via switch 504 to increase the pixel capacitance in order to provide a predetermined linear voltage charge response from readout circuit 501. Figure 5 further illustrates column circuitry 510 comprising an amplifier 250, feedback capacitor 260 and a transistor 270 for resetting the column circuitry 510.
[0059] A pixel according to some embodiments of the present invention can be configured to provide fast readout speed at a predetermined gain over a large signal range, for example from low to high levels without the need to select among signal readout methods based on signal strength. This can help reduce X-ray dose to patients during imaging and/or increase contrast resulting in clearer images in large area digital X-ray imaging applications, for example.
[0060] According to embodiments of the invention a pixel may comprise one or more detectors. According to embodiments of the invention, the readout circuitry may be partially present within the on-panel pixels and partially present off the imaging panel, or substantially present on the imaging panel. The imaging panel may be rigid, for example comprising a rigid glass or rigid metal substrate, or flexible, for example comprising a flexible plastic or flexible metal substrate. In addition, a pixel may be operatively separated onto more than one imaging panel. For example, one panel may comprise some parts of the pixel and another panel may comprise other parts of the pixel. Furthermore, the pixel electronics may be fabricated on a single chip or on multiple chips. Furthermore, the readout circuitry present within a pixel may be physically located in the same plane as the detector or this readout circuitry may be embedded under, or fabricated above, the detector to provide a high fill factor.
[0061] According to embodiments, portions of the readout circuitry common to a column, row or other group of pixels may be used in a multiplex manner to perform readout of an array or matrix of pixels included in a digital imaging apparatus according to some embodiments of the MBMFile No. 1308-110 present invention. It is noted that common column, row or group readout circuitry and the multiplexed readout of pixels may require additional circuitry, for example switching circuits or multiplexing circuits. Employ of multiplexing circuitry, however, may also reduce complexity of the readout circuit by reducing the total number of amplifiers required for a column, row, or group of pixels, for example. Furthermore, conunon column or row readout circuitry may also be implemented such that the common readout circuitry is individual to each pixel, for example, one readout circuit may be disposed per pixel.
[0062] According to embodiments of the invention, the pixels may be disposed and operatively arranged in arrays of predetermined sizes. According to some embodiments, portions of readout circuitry that have been identified as operatively being shared among one or more columns of pixels, may also be shared by one or more rows of pixels or one or more other groups of pixels.
[0063] Embodiments of the invention can be operated with various switching and timing sequences. For example, where a double sampling technique is used, the transistor switching and timing may vary from a sequence in which no double sampling technique is used.
While a number of transistor switching, timing cycles and sequences are described herein, numerous other cycles and sequences are possible. Some sequences may have advantages over others.
[0064] The detector may be any type of detector, for example, solid-state photodetectors such as a-Si:H, amorphous selenium, lead iodide, mercuric iodide, lead oxide or cadmium zinc telluride based detectors or other appropriate detector. In addition, direct detection based detectors such as molybdenum Schottky diodes, as well as detectors based on indirect detection such as those comprising phosphors for example gadolinium oxysulfide detectors or caesium iodide detectors, may also be used. In the case of photodiode based detectors, the pixel capacitor is provided by the photodiode. Pixel capacitors 503 and/or 505 may be provided by a photodiode, portions of a photodiode, or by sharing of photodiode area as would be readily understood by a worker skilled in the art.
[0065] Other types of detectors for radiation detection may further be used as would be readily understood by a worker skilled in the art. The transistors used in various embodiments of the invention may be amorphous silicon (a-Si:H) thin-film transistors (TFTs), poly-crystalline silicon TFTs, micro-crystalline silicon TFTs, nano-crystalline silicon TFTs, crystalline silicon MBM FileNo. 1308-110 CA 02670180 2009-06-22 transistors, or other similar device as would be readily understood by a worker skilled in the art.
In addition, the transistors may be n-type, p-type or ambi-polar. In further embodiments, radiation in any region of the electromagnetic spectrum may be detected using the present invention with the selection of detectors, and devices for the readout circuitry being made in order that an appropriate portion of the electromagnetic spectrum can be detected as would be readily understood by a worker skilled in the art.
[0066] As would be readily understood by a worker skilled in the art, the present invention may be applied to any digital imaging application. For example, the present invention may be applied to medical imaging, X-ray inspection systems such as in the inspection of aircraft wings, security systems such as screening of luggage at airports, non-destructive material tests, radiography, tomosynthesis or optical imaging, as well as other forms of digital imaging applications as would be readily understood.
[0067] The embodiments of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Claims (23)
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A detecting system for an imaging device, the detecting system comprising:
a. a detector for converting electromagnetic radiation to electrical charge;
and b. a capacitor system operatively connected to the detector, the capacitor system configured to be switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge.
a. a detector for converting electromagnetic radiation to electrical charge;
and b. a capacitor system operatively connected to the detector, the capacitor system configured to be switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge.
2. The detecting system according to claim 1, wherein the capacitor system comprises one or more capacitors and one or more switches for operatively interconnecting the capacitors and the detector.
3. The detecting system according to claim 2, wherein the one or more switches include one or more transistors.
4. The detecting system according to claim 3, wherein one or more of the transistors are thin-film transistors.
5. The detecting system according to any one of claims 2 to 4, wherein one or more of the switches connect one or more of the capacitors in parallel.
6. The detecting system according to any one of claims 2 to 4, wherein one or more of the switches connect one or more of the capacitors in series.
7. The detecting system according to claim 5, wherein one or more of the switches connect one or more of the capacitors in series.
8. The detecting system according to any one of claims 1 to 7, wherein the detector comprises a PIN diode.
9. The imaging device according to any one of claims 1 to 8, wherein the detector comprises a metal-insulator diode.
10. The detecting system according to any one of claims 1 to 9 further comprising a reset switch for operatively connecting the capacitor system to a predetermined potential for disposing a predetermined charge in the capacitor system when closing the reset switch.
11. The detecting system according to claim 10, wherein the reset switch is configured as a transistor.
12. An imaging device comprising:
a. a detecting system including:
i. a detector for converting electromagnetic radiation to electrical charge;
and ii. a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and b. readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge.
a. a detecting system including:
i. a detector for converting electromagnetic radiation to electrical charge;
and ii. a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and b. readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge.
13. The imaging device according to claim 12, wherein the readout circuitry is configured as a current-mediated active pixel sensor.
14. The imaging device according to claim 12, wherein the readout circuitry is configured as a voltage-mediated active pixel sensor.
15. The imaging device according to claim 12, wherein the readout circuitry is configured as a multimode active pixel sensor.
16. An imaging system comprising:
a. a plurality of imaging devices, each imaging device comprising:
i. a detecting system including a detector for converting electromagnetic radiation to electrical charge and a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and ii. readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge; and b. a control system operatively coupled to the plurality of imaging devices for collecting the plurality of output signals received from the plurality of imaging devices.
a. a plurality of imaging devices, each imaging device comprising:
i. a detecting system including a detector for converting electromagnetic radiation to electrical charge and a capacitor system operatively connected to the detector, the capacitor system switchable between a first capacitance and a second capacitance, thereby providing the detecting system with a controllable capacitance for storing the electrical charge; and ii. readout circuitry operatively coupled to the detecting system, the readout circuitry configured to determine the stored electrical charge and provide an output signal indicative of the stored electrical charge; and b. a control system operatively coupled to the plurality of imaging devices for collecting the plurality of output signals received from the plurality of imaging devices.
17. The imaging system according to claim 16, wherein the imaging devices are operatively disposed on a substrate in a predetermined manner.
18. The imaging system according to claim 17, wherein the substrate is planar.
19. The imaging system according to claim 17, wherein the imaging devices are disposed in a rectangular matrix defining one or more rows and one or more columns, each row comprising one or more of the imaging devices and each column comprising one or more of the imaging devices.
20. The imaging system according to claim 19 further comprising one or more row circuitries operatively connected to the control system and the imaging devices of the one or more rows for reading the charge thereof.
21. The imaging system according to claim 19 further comprising one or more column circuitries operatively connected to the control system and the imaging devices of the one or more columns for reading the charge thereof.
22. A method for operating a detecting system for an imaging device, the detecting system comprising a detector operatively coupled to a capacitor system switchable between a first capacitance and a second capacitance, the method comprising:
a. determining a desired capacitance of the capacitor system;
b. configuring the capacitor system with the desired capacitance;
c. converting electromagnetic radiation into electrical charge carriers by the detector;
d. storing at least a portion of the charge carriers as charge in the capacitor system;
and e. determining the charge.
a. determining a desired capacitance of the capacitor system;
b. configuring the capacitor system with the desired capacitance;
c. converting electromagnetic radiation into electrical charge carriers by the detector;
d. storing at least a portion of the charge carriers as charge in the capacitor system;
and e. determining the charge.
23. The method according to claim 22, wherein the determined capacitance is based at least in part on a predetermined application of the imaging device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002670180A CA2670180A1 (en) | 2008-06-23 | 2009-06-22 | System, device and method for high dynamic range digital imaging |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2636926 | 2008-06-23 | ||
| CA2,636,926 | 2008-06-23 | ||
| CA002670180A CA2670180A1 (en) | 2008-06-23 | 2009-06-22 | System, device and method for high dynamic range digital imaging |
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| Publication Number | Publication Date |
|---|---|
| CA2670180A1 true CA2670180A1 (en) | 2009-12-23 |
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ID=41449634
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002670180A Abandoned CA2670180A1 (en) | 2008-06-23 | 2009-06-22 | System, device and method for high dynamic range digital imaging |
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| Country | Link |
|---|---|
| CA (1) | CA2670180A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109521455A (en) * | 2018-12-13 | 2019-03-26 | 北京纳米维景科技有限公司 | A kind of X ray image detector and its method for realizing automatic gain switching |
-
2009
- 2009-06-22 CA CA002670180A patent/CA2670180A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109521455A (en) * | 2018-12-13 | 2019-03-26 | 北京纳米维景科技有限公司 | A kind of X ray image detector and its method for realizing automatic gain switching |
| CN109521455B (en) * | 2018-12-13 | 2024-02-27 | 北京纳米维景科技有限公司 | X-ray image detector for realizing automatic gain switching and method thereof |
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