(12) United States Patent
`Sugawara et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,724,855 B2
`Apr. 20, 2004
`
`US006724855B2
`
`(54) X-RAY FLAT PANEL DETECTOR
`
`(75) Inventors: Yasuhiro Sugawara, Nasu-gun (JP);
`Takayuki Tomisaki, OtaWara (JP);
`Manabu Tanaka, Nasu-gun (JP); Akira
`Tsukamoto, OtaWara (JP)
`
`(73) Assignee: Kabushiki Kaisha Toshiba, Tokyo (JP)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 150 days.
`
`(21) Appl. No.: 10/127,758
`(22) Filed:
`Apr. 23, 2002
`(65)
`Prior Publication Data
`
`US 2002/0153491 A1 Oct. 24, 2002
`Foreign Application Priority Data
`
`(30)
`
`Apr. 23, 2001
`Apr. 19, 2002
`
`(JP) ..................................... .. 2001-124682
`(JP) .... ..
`2002-117602
`
`(51) Int. Cl.7 .......................... .. G21K 4/00; H05G 1/60;
`G03B 42/02; G03C 5/16
`(52) US. Cl. ........................ .. 378/19; 378/98; 378/988;
`378/167; 378/189; 378/207; 250/206; 250/206.1;
`250/206.2; 250/206.3; 250/580; 250/591;
`257/546
`(58) Field of Search ............................ .. 250/206, 206.1,
`250/206.2, 206.3, 580, 591, 370.09, 370.14,
`361 R; 348/294; 378/19, 98, 98.8, 167,
`189; 438/56
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,818,898 A 10/1998 Tsukamoto et al.
`
`250/370.09
`5,852,296 A * 12/1998 Tsukamoto et a1.
`378/988
`6,044,128 A * 3/2000 Tanaka et al. .... ..
`6,185,274 B1 * 2/2001 Kinno et al. ............. .. 378/988
`6,225,632 B1
`5/2001 Kinno et 211.
`6,323,490 B1 * 11/2001 Ikeda et al. .......... .. 250/370.09
`6,353,229 B1 * 3/2002 Polischuk et al.
`250/370.14
`6,507,026 B2 * 1/2003 Ikeda et al. .......... .. 250/370.09
`6,607,935 B2 * 8/2003 KWOn
`........ .. 438/56
`2001/0008271 A1 * 7/2001 Ikeda et al. .......... .. 250/370.09
`2003/0146990 A1 * 8/2003 Tsukamoto et a1. ....... .. 348/294
`
`* cited by examiner
`
`Primary Examiner—John R. Lee
`Assistant Examiner—Mary El-Shammaa
`(74) Attorney, Agent, or Firm—Oblon, Spivak, McClelland,
`Maier & Neustadt, PC.
`
`(57)
`
`ABSTRACT
`
`An X-ray ?at panel detector includes sensor elements con
`stituted by a plurality of effective pixels that detect X-rays
`and a plurality of dummy pixels that are arranged adjacent
`to the effective pixel area and generate electrical signals
`irrelevant to X-rays, signal lines Which read out electrical
`signals from the respective pixels, scanning lines Which scan
`the respective pixels, a ?rst electrostatic Wiring line Which
`distributes static electricity accumulated in the signal lines,
`and a second electrostatic Wiring line Which distributes static
`electricity accumulated in the scanning lines. Aplurality of
`dummy pixels are classi?ed into a DA area Where noise
`superposed on the signal lines are removed and a DB area
`Where noise superposed on the scanning lines are removed.
`The ?rst and second electrostatic Wiring lines are laid out
`around the sensor elements, and physically disconnected
`betWeen the DA area and the DB area.
`
`20 Claims, 16 Drawing Sheets
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`Apr. 20, 2004
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`US 6,724,855 B2
`
`1
`X-RAY FLAT PANEL DETECTOR
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is based upon and claims the bene?t of
`priority from the prior Japanese Patent Applications No.
`2001-124682, ?led Apr. 23, 2001; and No. 2002-117602,
`?led Apr. 19, 2002, the entire contents of both of Which are
`incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to an X-ray ?at panel
`detector used in an X-ray diagnostic system.
`2. Description of the Related Art
`An X-ray ?at panel detector is an X-ray detector used in
`an X-ray diagnostic system Which displays as a halftone
`image the intensity of X-rays having passed through the
`body of an object to be examined. X-ray ?at panel detectors
`are recently being put into practical use in place of 1.1.
`(Image Intensi?er) and an imaging plate Which have con
`ventionally been used. X-ray ?at panel detectors can be
`classi?ed into a direct conversion type and indirect conver
`sion type depending on an incident X-ray conversion
`method. X-ray detection and read arrangements of the
`respective types are as folloWs.
`In the direct conversion method, incident X-rays are
`converted into electron-hole pairs by a photoelectric con
`version ?lm. The converted electron-hole pairs are supplied
`as charges by an externally applied high electric ?eld to
`pixel electrodes arrayed in a matrix. The electron-hole pairs
`are accumulated in the pixel electrodes. The accumulated
`charges are sequentially read out as electrical signals to an
`integrating ampli?er via a signal line under the control of
`sWitching elements (TFTs) (scanning lines are driven from
`an OFF potential to an ON potential). The readout signals
`are A/D-converted into image data, Which is output to a
`subsequent processing system.
`In the indirect conversion method, incident X-rays are
`temporarily converted into light by a phosphor, and the light
`is converted into electron-hole pairs by a photoelectric
`conversion ?lm. The generated charges are supplied by an
`externally applied high electric ?eld to pixel electrodes
`arrayed in a matrix. The charges supplied to the pixel
`electrodes are processed similarly to the direct conversion
`method, generating image data.
`In general, the X-ray ?at panel detector has effective
`pixels for acquiring diagnostic image data, and a pixel group
`for removing noise components from signals detected by the
`effective pixels. Pixels Which constitute the pixel group are
`called dummy pixels. The dummy pixels are used to remove
`noise components generated When the potential of a scan
`ning line Which forms a capacitance (parasitic capacitance)
`together With a signal line changes and charges Which
`depend on the potential change ?oW into the signal line.
`Each dummy pixel is covered With a protective electrode for
`preventing dielectric breakdoWn caused by application of a
`high electric ?eld.
`The protective electrode formed on the dummy pixel
`forms a capacitance together With the signal line or scanning
`line connected to the dummy pixel. When the dummy pixel
`is driven, the potential of the protective electrode is distrib
`uted on the surface and becomes unstable. The unstable
`potential of the protective electrode is transferred to the
`
`10
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`signal line of the dummy pixel and superposed as a noise
`component on the signal line. The effective pixel area is not
`in?uenced by the unstable potential of the protective elec
`trode. For this reason, the output values of the effective pixel
`and dummy pixel differ from each other in the absence of
`X-rays. This difference may act as an offset Within the output
`range of an A/D converter.
`The X-ray ?at panel detector has a Wiring line for static
`protection in a sWitching element array (TFT array) manu
`facturing process (antistatic Wiring line Will be called an
`“LC Wiring line” hereinafter). The LC Wiring line is not
`necessary in the use of the X-ray ?at panel detector, but is
`generally left Without removing it. HoWever, the LC Wiring
`line forms a conductive path: scanning line for driving the
`dummy pixel—>the dummy pixelQLC Wiring line—>the
`effective pixelQscanning line for driving the effective pixel.
`When the dummy pixel is driven in actual X-ray detection,
`the ?uctuation component of the scanning line potential of
`the dummy pixel is superposed on the potential of each
`scanning line of each effective pixel via this conductive path,
`increasing noise.
`
`BRIEF SUMMARY OF THE INVENTION
`
`It is an object of the present invention to provide an X-ray
`?at panel detector capable of acquiring a loW-noise, high
`quality X-ray diagnostic image.
`According to the ?rst aspect of the present invention,
`there is provided an X-ray ?at panel detector comprising an
`effective pixel array in Which a plurality of pixel electrodes
`are arrayed in a matrix and accumulate charges, a photo
`conductor Which covers the effective pixel array and gen
`erates charges on the basis of incident X-rays, a bias
`electrode Which is formed on a second surface of the
`photoconductor, covers an area of the pixel electrodes, and
`applies a bias voltage betWeen the photoconductor and the
`pixel electrodes, a plurality of signal lines to read out
`electronic signals from the effective pixel array, a plurality
`of scanning lines to scan the effective pixel array, ?rst
`dummy pixels Which are arranged adjacent to the effective
`pixel array and remove noise superposed on the plurality of
`signal lines, second dummy pixels Which are arranged
`adjacent to the effective pixel array and remove noise
`superposed on the plurality of scanning lines, a ?rst protec
`tive electrode Which is arranged in correspondence With the
`?rst dummy pixels and electrically shields the bias electrode
`and the plurality of signal lines or the plurality of scanning
`lines, and a second protective electrode Which is arranged in
`correspondence With the second dummy pixels, discon
`nected from the ?rst protective electrode and electrically
`shields the bias electrode and the plurality of signal lines or
`the plurality of scanning lines.
`According to the second aspect of the present invention,
`there is provided an X-ray ?at panel detector comprising an
`effective pixel array in Which a plurality of pixel electrodes
`are arrayed in a matrix and accumulate charges, a photo
`conductor Which covers the effective pixel array and gen
`erates charges on the basis of incident X-rays, a bias
`electrode Which is formed on a second surface of the
`photoconductor, covers an area of the pixel electrodes, and
`applies a bias voltage betWeen the photoconductor and the
`pixel electrodes, a plurality of signal lines to read out
`electronic signals from the effective pixel array, a plurality
`of scanning lines to scan the effective pixel array, ?rst
`dummy pixels Which are arranged adjacent to the effective
`pixel array and remove noise superposed on the plurality of
`signal lines, second dummy pixels Which are arranged
`
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`US 6,724,855 B2
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`3
`adjacent to the effective pixel array and remove noise
`superposed on the plurality of scanning lines, and a protec
`tive electrode Which is formed in such a Way to deviate from
`a position facing to at least either the ?rst dummy pixels or
`the second dummy pixels and electrically shields the bias
`electrode and the plurality of signal lines or the plurality of
`scanning lines.
`According to the third aspect of the present invention,
`there is provided an X-ray ?at panel detector comprising an
`effective pixel array in Which a plurality of pixel electrodes
`are arrayed in a matrix and accumulate charges, a photo
`conductor Which covers the effective pixel array and gen
`erates charges on the basis of incident X-rays, a plurality of
`?rst signal lines to read out electronic signals from the
`effective pixel array, a plurality of ?rst scanning lines to scan
`the effective pixel array, and an electrostatic dispersion
`Wiring line Which is connected directly or via a nonlinear
`element to at least one of the plurality of ?rst signal lines and
`at least one of the plurality of ?rst scanning lines, and
`distributes static electricity accumulated in at least one of the
`plurality of ?rst signal lines or the plurality of ?rst scanning
`lines, Wherein the electrostatic dispersion Wiring line has a
`?rst auxiliary Wiring line to disconnect the electrostatic
`dispersion Wiring line betWeen a connecting portion betWeen
`the electrostatic dispersion Wiring line and at least one of the
`plurality of ?rst signal lines and a connecting portion
`betWeen the electrostatic dispersion Wiring line and at least
`one of the ?rst scanning lines.
`According to the fourth aspect of the present invention,
`there is provided an X-ray ?at panel detector comprising an
`effective pixel array in Which a plurality of pixel electrodes
`are arrayed in a matrix and accumulate charges, a photo
`conductor Which covers the effective pixel array and gen
`erates charges on the basis of incident X-rays, a plurality of
`?rst signal lines to read out electronic signals from the
`effective pixel array, a plurality of ?rst scanning lines to scan
`the effective pixel array, an electrostatic dispersion Wiring
`line Which is connected directly or via a nonlinear element
`to at least one of the plurality of ?rst signal lines and at least
`one of the plurality of ?rst scanning lines, and distributes
`static electricity accumulated in at least one of the plurality
`of ?rst signal lines or the plurality of ?rst scanning lines, ?rst
`dummy pixels Which remove noise superposed on the plu
`rality of signal lines, second dummy pixels Which remove
`noise superposed on the plurality of scanning lines, a plu
`rality of second signal lines to read out electronic signals
`from the ?rst dummy pixels, and second scanning lines to
`scan the second dummy pixels, Wherein the electrostatic
`dispersion Wiring line has a ?rst Wiring line Which is
`connected to at least one of the plurality of ?rst signal lines
`and at least one of the plurality of second signal lines, a
`second Wiring line Which is connected to at least one of the
`plurality of ?rst scanning lines, and a third Wiring line Which
`is connected to at least one of the plurality of second
`scanning lines.
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING
`FIG. 1 is a diagram for explaining the schematic arrange
`ment of an X-ray ?at panel detector 12 according to an
`embodiment;
`FIG. 2 is a plan vieW shoWing pixel areas formed by
`respective pixels When X-ray sensor elements 16 are clas
`si?ed into effective pixels, dummy pixels A (DA), and
`dummy pixels B (DB);
`FIG. 3A is a plan vieW of the X-ray ?at panel detector 12
`for explaining a protective electrode 30;
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`FIG. 3B is a sectional vieW of the X-ray ?at panel detector
`12 for explaining the protective electrode 30;
`FIG. 4 is an enlarged vieW shoWing the inside of the circle
`in FIGS. 3A and 3B;
`FIG. 5 is a plan vieW for explaining an example of
`potential supply to the protective electrode 30;
`FIG. 6 is a plan vieW for explaining another example of
`potential supply to the protective electrode 30;
`FIG. 7 is a sectional vieW for explaining the example of
`potential supply to the protective electrode 30 in FIG. 6;
`FIG. 8 is a plan vieW for explaining still another example
`of potential supply to the protective electrode 30;
`FIG. 9 is a plan vieW for explaining still another example
`of potential supply to the protective electrode 30;
`FIG. 10 is a plan vieW for explaining the arrangement of
`an X-ray ?at panel detector 12 according to the second
`embodiment;
`FIG. 11 is a sectional vieW taken along the line P—P in
`FIG. 10;
`FIG. 12 is a plan vieW shoWing an X-ray ?at panel
`detector 12 having a C type protective electrode 30;
`FIG. 13 is a plan vieW for explaining a protective elec
`trode 30 Which is axially symmetrical about the central axis
`of the X-ray ?at panel detector 12;
`FIG. 14 is a plan vieW for explaining an example of an LC
`Wiring line 291 of the X-ray ?at panel detector 12;
`FIG. 15 is a plan vieW for explaining another example of
`the LC Wiring line 291 of the X-ray ?at panel detector 12;
`FIG. 16 is a circuit diagram for explaining an auxiliary
`Wiring line 295 of the LC Wiring line 291;
`FIG. 17 is a plan vieW for explaining an example of the
`LC Wiring structure of the X-ray ?at panel detector 12;
`FIG. 18 is a plan vieW for explaining another example of
`the LC Wiring structure of the X-ray ?at panel detector 12;
`and
`FIG. 19 is a plan vieW for explaining still another example
`of the LC Wiring structure of the X-ray ?at panel detector 12.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The ?rst to third embodiments of the present invention
`Will be described beloW With reference to the several vieWs
`of the accompanying draWing.
`First Embodiment
`The ?rst embodiment of the present invention Will be
`described beloW With reference to the several vieWs of the
`accompanying draWing. In the folloWing description, the
`same reference numerals denote the same functions and
`parts throughout the draWing, and a repetitive description
`thereof Will be omitted.
`The schematic arrangement of an X-ray ?at panel detector
`according to the ?rst embodiment of the present invention
`Will be described With reference to FIG. 1. FIG. 1 is a
`diagram for explaining the schematic arrangement of an
`X-ray ?at panel detector 12 according to the ?rst embodi
`ment.
`The X-ray ?at panel detector 12 comprises X-ray sensor
`elements 16 for detecting incident X-rays, a gate scanning
`line driving circuit 18, an integrating ampli?er circuit 20, a
`multiplexer 22, and an A/D converter 24.
`The X-ray sensor elements 16 have a plurality of photo
`electric conversion ?lms (not shoWn) Which are arrayed in a
`matrix and convert incident X-rays into charge information,
`pixel electrodes Which are arranged in respective pixels and
`
`Patent Owner’s Exhibit 2001
`IPR2015-00022
`Page 19 of 25
`
`

`

`US 6,724,855 B2
`
`5
`acquire charges from the photoelectric conversion ?lms, a
`plurality of capacitors in Which the charges acquired by the
`pixel electrodes are accumulated, and switching elements
`(e.g., TFTs: Thin Film Transistors) Which read out the
`charges accumulated in the capacitors as electrical signals
`on the basis of a control signal from the gate scanning line
`driving circuit 18. The plurality of X-ray sensor elements 16
`are arrayed in a tWo-dimensional matrix to form a sensor
`element array. As Will be described later, the X-ray sensor
`elements 16 are classi?ed into effective pixels, dummy
`pixelsA(to be referred to as “DAs” hereinafter), and dummy
`pixels B (to be referred to as “DBs” hereinafter) (see FIG.
`2).
`The gate scanning line driving circuit 18 is electrically
`connected to the gate terminal of the sWitching element of
`each X-ray sensor element 16 via a corresponding gate
`scanning line 27. The gate scanning line driving circuit 18
`supplies a control signal to the gate terminal of each sWitch
`ing element to ON/OFF-control sWitching elements on each
`gate scanning line 27. The gate scanning line driving circuit
`18 may have a scanning line driving IC Which is connected
`to each scanning line and has a function of supplying a
`potential to a protective electrode. In FIG. 1, the gate
`scanning line driving circuit 18 is formed on only one side.
`Alternatively, the gate scanning line driving circuits 18 may
`be arranged on tWo sides via the sensor element array to
`supply driving signals to the sWitching elements from the
`tWo sides.
`The integrating ampli?er circuit 20 ampli?es the electrical
`signals of pixels on the same column that are read out from
`the X-ray sensor elements 16 via a corresponding signal line
`26 every column at a predetermined timing.
`The multiplexer 22 sequentially selects signals ampli?ed
`by the integrating ampli?er 20, and sends them to the
`subsequent A/D converter 24.
`The A/D converter 24 converts an analog signal input
`from the multiplexer 22 into a digital signal.
`In FIG. 1, the integrating ampli?er circuit 20 and multi
`plexer 22 are arranged on only one side. Alternatively, the
`integrating ampli?er circuits 20 and multiplexers 22 may be
`arranged on tWo sides via the sensor element array to read
`out the detection signals of the sensor elements from the tWo
`sides.
`The effective pixel, dummy pixel A (DA), and dummy
`pixel B (DB) of the X-ray ?at panel detector 12 Will be
`explained With reference to FIG. 2.
`FIG. 2 is a plan vieW shoWing pixel areas formed by
`respective pixels When the X-ray sensor elements 16 are
`classi?ed into effective pixels, dummy pixels A (DA), and
`dummy pixels B (DB). Areas Where the respective pixels are
`distributed Will be called an effective pixel area, dummy
`pixel A area, and dummy pixel B area. As described above,
`pixels Which constitute each pixel area are formed from the
`sensor elements 16.
`The effective pixels are pixels for detecting incident
`X-rays. An X-ray diagnostic image is generated based on
`X-rays detected by these pixels.
`DAs are pixels arranged above and beloW the effective
`pixel area in the column direction (direction parallel to the
`signal line), as shoWn in FIG. 2, in order to cancel noise
`(NA) Which ?oWs into the signal line 26 and is superposed
`on the detection signals of the effective pixels When the gate
`scanning line driving circuit 18 changes the potential of the
`scanning line 27. A DA has a structure in Which no charge
`information based on X-rays is accumulated (e.g., a photo
`electric conversion ?lm and capacitor are not electrically
`connected, the surface (X-ray incident side) is covered With
`
`10
`
`25
`
`35
`
`45
`
`55
`
`65
`
`6
`a shield, or the like). Charges detected from the DA When
`TFT is changed from the OFF state to the ON state are only
`extracted noise (NA). Removal of noise (NA) from the
`effective pixel by using the DA is executed as folloWs. That
`is, in driving the scanning line of the effective pixel, the
`scanning line of the DA is driven With a phase opposite to
`that of the scanning line of the effective pixel. Then, noise
`(NA) With an opposite sign as that of the effective pixel is
`generated to cancel noise (NA) superposed on the detection
`signal.
`DBs are pixels arranged on the right and left sides of the
`effective pixel area in the roW direction (direction parallel to
`the scanning line), as shoWn in FIG. 2, in order to remove
`noise (NB) Which is generated by ?uctuations in the poten
`tial of the scanning line 27 in a steady state and is superposed
`on the detection signal of the effective pixel. A DB has a
`structure in Which no charge information based on X-rays is
`accumulated (e.g., a photoelectric conversion ?lm and
`capacitor are not electrically connected, the surface (X-ray
`incident side) is covered With a shield, or the like). Accord
`ing to a method of removing noise (NB) by the DB, the
`output value of the dummy pixel (DB) is subtracted from the
`output value of the effective pixel on the same gate line after
`irradiation of X-rays to remove the ?uctuation component of
`the scanning line potential. The dummy pixel (DB) is so
`designed as to to have the same output value as that in the
`absence of X-rays incident on the effective pixel.
`Function of Preventing Dielectric Breakdown Caused by
`Application of High Electric Field
`The function of the X-ray ?at panel detector 12 for
`preventing dielectric breakdoWn caused by application of a
`high electric ?eld Will be explained.
`Generally in X-ray diagnosis, a high electric ?eld is
`applied to the X-ray ?at panel detector in order to acquire
`charges generated in the photoelectric conversion ?lm to the
`pixel electrode. The applied high electric ?eld may cause
`dielectric breakdoWn in the effective pixel area and periph
`eral areas (dummy pixel A area, dummy pixel B area,
`scanning line area around the effective pixels, and signal line
`area around the effective pixels). A measure against dielec
`tric breakdoWn is adopted in each area.
`In the effective pixel area, a high electric ?eld is applied
`Within the photoelectric conversion ?lm. If a large number
`of X-rays are incident on the photoelectric conversion ?lm,
`a transient large current is generated to excessively increase
`the pixel potential. At this time, dielectric breakdoWn may
`occur betWeen the effective pixel and a common electrode
`(capacitance is formed betWeen them) or in the TFT. To
`prevent dielectric breakdoWn in the effective pixel area, the
`pixel is equipped With a function of externally removing
`charges When charges are excessively accumulated in the
`pixel. This function can be realiZed by, e.g., giving the TFT
`a diode function Within the pixel.
`Also in the peripheral area, a high electric ?eld is so
`applied as to suf?ciently enhance the characteristics of the
`photoelectric conversion ?lm. Application of the high elec
`tric ?eld may cause dielectric breakdoWn betWeen a high
`electric-?eld applying electrode, the dummy pixel, the scan
`ning line, and the signal line. To prevent dielectric
`breakdoWn in the peripheral area, a protective electrode
`(potential: GND) for shielding charging by an insulating
`?lm is formed betWeen the scanning line, the signal line, and
`the high-electric-?eld applying electrode in the X-ray ?at
`panel detector. The protective electrode is made of a material
`having an electrical resistance.
`FIGS. 3A and 3B are vieWs for explaining a protective
`electrode 30 of the X-ray ?at panel detector 12, and are
`
`Patent Owner’s Exhibit 2001
`IPR2015-00022
`Page 20 of 25
`
`

`

`US 6,724,855 B2
`
`7
`sectional views taken along the line D—D in FIG. 2. FIG.
`4 is an enlarged view showing the inside of the circle in FIG.
`3B. As shown in FIGS. 3A, 3B, and 4,
`the protective
`electrode 30 is formed between a high-voltage electrode 32
`and a signal line layer 33. The protective electrode 30 is
`formed in correspondence with the dummy pixel A or B, as
`described above. Thus, the protective electrode 30 exists
`around the effective pixel area.
`The protective electrode 30 is electrically divided
`between the effective pixel area and the dummy pixelA area,
`and between the effective pixel area and the dummy pixel B
`area (see FIGS. 3A, 3B, and 4). Further,
`the protective
`electrode 30 is also divided at G, H, I, and J between the
`dummy pixel A area and the dummy pixel B area. The
`purpose of this structure is not to transmit potential varia-
`tions generated upon driving DA to the signal
`line 26
`connected to the DB.
`
`the protective electrode 30 forms
`More specifically,
`capacitances together with all the signal lines 26 connected
`to DAs or DBs due to the structure of the X-ray flat panel
`detector. All the scanning lines 27 connected to DAs or DBs
`form capacitances together with the protective electrode 30.
`If a DA is driven by the gate scanning line driving circuit 18,
`the protective electrode 30 flows a transient current which
`depends on potential changes. Since the protective electrode
`30 is made of a material having a resistance component, the
`potential of the protective electrode 30 becomes unstable.
`Especially when the protective electrode 30 is not divided
`between the dummy pixel A area and the dummy pixel B
`area, the unstable potential of the protective electrode 30
`transfers to the signal line of the DB and is superposed as a
`noise component on the signal line. On the other hand, the
`effective pixel area is not influenced by driving of the DA
`because the protective electrode covers only the dummy
`pixels. As a result, the output values of the effective pixel
`and dummy pixel differ from each other in dark imaging.
`This difference acts as an offset within the output range of
`the A/D converter, and generates noise in an X-ray diag-
`nostic image.
`To the contrary, the protective electrode 30 of the X-ray
`flat panel detector is divided between the dummy pixel A
`area and the dummy pixel B area, and can prevent noise
`from flowing. This is because a transient current flowing
`through the protective electrode 30 which covers the DA
`upon driving the gate scanning line is not superposed on the
`signal line via the protective electrode 30 which covers the
`DB.
`
`Each divided protective electrode must receive a stable
`potential such as GND potential. As for supply of a potential
`to the protective electrode 30,
`four examples will be
`described below. Note that each example can also be applied
`to an X-ray flat panel detector according to any one of the
`following embodiments.
`
`Example 1-1
`
`An X-ray flat panel detector according to Example 1-1
`will be explained.
`FIG. 5 is a plan view for explaining an X-ray flat panel
`detector 121 according to Example 1-1. In the X-ray flat
`panel det