US20010012070A1 - Photoelectric conversion apparatus and photoelectric conversion system having the apparatus - Google Patents

Photoelectric conversion apparatus and photoelectric conversion system having the apparatus Download PDF

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Publication number
US20010012070A1
US20010012070A1 US08/815,532 US81553297A US2001012070A1 US 20010012070 A1 US20010012070 A1 US 20010012070A1 US 81553297 A US81553297 A US 81553297A US 2001012070 A1 US2001012070 A1 US 2001012070A1
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Prior art keywords
photoelectric conversion
circuit section
reading
signal
operational amplifier
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English (en)
Inventor
Tadao Enod
Noriyuki Kaifu
Toshiaki Sato
Masakazu Morishita
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Canon Inc
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Assigned to CANON KABUSHIKI KAISHA reassignment CANON KABUSHIKI KAISHA ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ENDO, TADAO, KAIFU, NORIYUKI, SATO, TOSHIAKI, MORISHITA, MASAKAZU
Publication of US20010012070A1 publication Critical patent/US20010012070A1/en
Priority to US10/606,418 priority Critical patent/US7440017B2/en
Priority to US11/620,997 priority patent/US7643077B2/en
Priority to US12/615,345 priority patent/US8179469B2/en
Priority to US13/452,755 priority patent/US8488037B2/en
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/30—Circuitry of solid-state image sensors [SSIS]; Control thereof for transforming X-rays into image signals
    • 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
    • H01L27/14665—Imagers using a photoconductor layer
    • H01L27/14676—X-ray, gamma-ray or corpuscular radiation imagers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/65—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
    • H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
    • H04N25/673—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction by using reference sources
    • 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
    • H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
    • H04N25/75—Circuitry for providing, modifying or processing image signals from the pixel array
    • 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
    • H04N25/767—Horizontal readout lines, multiplexers or registers
    • 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
    • H04N25/78—Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/30—Transforming light or analogous information into electric information
    • H04N5/32—Transforming X-rays
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements

Definitions

  • the present invention relates to a photoelectric conversion apparatus and a photoelectric conversion system having the apparatus. More particularly, the invention relates to a photoelectric conversion apparatus applicable to X-ray detectors for nondestructive examination such as medical care or internal examination, to image input units for business machines such as digital copiers, electronic blackboards, and facsimile machines, and so on, and also relates to a system having the apparatus.
  • X-ray image pickup apparatus used for medical diagnosis employs a so-called film method in which X-rays are radiated to a human body, then the X-rays transmitted by the human body irradiate a fluorescent member for converting X-rays to visible light, and a film is exposed to fluorescence therefrom.
  • FIG. 1 is an equivalent circuit diagram of an example of the two-dimensional photoelectric conversion apparatus applicable to such X-ray image pickup apparatus.
  • FIG. 1 illustrates the two-dimensional photoelectric conversion apparatus of 3 ⁇ 3 for simplifying the description, but practical photoelectric conversion apparatus are constructed of much more bits, though depending upon the purpose of apparatus.
  • each of T 1 - 1 , T 1 - 2 , T 1 - 3 , T 2 - 1 , . . . , T 3 - 3 designates a switching element, each of S 1 - 1 , S 1 - 2 , S 1 - 3 , S 2 - 1 , . . . , S 3 - 3 a photoelectric conversion element, SR 1 a shift register, SR 2 a shift register, each of G 1 , G 2 , G 3 a gate drive wire, each of M 1 , M 2 , M 3 a signal wire, each of C 1 , C 2 , C 3 an accumulating capacitors (e.g.
  • photoelectric conversion elements S 1 - 1 to S 3 - 3 are photoelectrically converted by the photoelectric conversion elements S 1 - 1 to S 3 - 3 to charges of photoelectric conversion signals, which are accumulated in interelectrode capacitances of the respective photoelectric conversion elements S 1 - 1 to S 3 - 3 .
  • These photoelectric conversion signals pass through transfer switch T 1 - 1 to T 3 - 3 and signal wire M 1 to M 3 to become parallel voltage outputs. Further, they are converted to serial signals by the reading switch circuit section to be taken out to the outside.
  • the photoelectric conversion elements of 9-bit pixels in total are separated in three rows, each including three bits.
  • the above-stated operation is carried out in row units in order.
  • FIG. 2 is a timing chart to show an example of the operation of the photoelectric conversion apparatus shown in FIG. 1.
  • Optical information (hv) input to the photoelectric conversion elements S 1 - 1 to S 1 - 3 in the first row is photoelectrically converted to signal charges, which are accumulated in interelectrode capacitors in the respective photoelectric conversion elements of S 1 - 1 to S 1 - 3 .
  • the shift register SR 1 gives a first voltage pulse for transfer to the gate driving wire G 1 during a period of time T 1 to switch the transfer switch elements T 1 - 1 to T 1 - 3 on.
  • the shift register SR 2 successively gives voltage pulses to gate driving wires N 1 to N 3 to switch reading switches U 1 to U 3 on in order, thereby converting the signals of the first row having been transferred to the load capacitances C 1 to C 3 to serial signals, and after impedance transformation by the voltage follower type operational amplifier OP, the signal of three pixels (Vout) is output to the outside of the photoelectric conversion apparatus during a period of time T 3 (reading operation).
  • a voltage pulse CRES for reset is applied to reset switches RES 1 to RES 3 during a period of time T 2 to reset the load capacitances C 1 to C 3 , thereby getting ready for the reading operation of the next row (reset operation).
  • the shift register SR 1 successively drives the gate driving wires G 2 , G 3 , thereby outputting data of the all pixels of the photoelectric conversion elements S 2 - 1 to S 3 - 3 in time series.
  • the photoelectric conversion apparatus of an area type in which photosensors are arrayed two-dimensionally is generally arranged to successively perform the operations of transfer, reading, and reset in row units as described above, the image signals from the photoelectric conversion apparatus are intermittently output as shown by Vout in FIG. 2.
  • the time necessary for reading one row is T 1 +T 3 +T 2
  • the time of three times thereof is necessary for reading the all bits.
  • the size of the photoelectric conversion apparatus portion of the medical X-ray image pickup apparatus is said to be approximately 40 cm ⁇ 40 cm necessary for the example of the X-ray image pickup apparatus for photographing the lung part.
  • the time of 4000 ⁇ (T 1 +T 2 +T 3 ) is necessary.
  • the time necessary for T 3 becomes longer, and therefore, a normal arrangement is provided with a plurality of (N) reading circuit sections to permit parallel reading scanning of N bits, thereby reading the all pixels in the time of 4000 ⁇ (T 1 +T 2 +T 3 /N).
  • transfer switching elements T 1 - 1 to T 3 - 3
  • a-Si amorphous silicon
  • TFTs Thin Film Transistors
  • the load capacitors are illustrated as capacitance elements of reading capacitors C 1 to C 3 in FIG. 1, but practically, without a need for provision of separate elements, they are normally comprised of the interelectrode capacitances (Cgs) formed by the gate electrodes of the switching elements T 1 - 1 to T 3 - 3 and the electrodes on the side of signal wires M 1 to M 3 .
  • Cgs interelectrode capacitances
  • the capacitance of the load capacitor (reading capacitor) C 1 is the sum of Cgs of the switching elements T 1 - 1 , T 2 - 1 , and T 3 - 1 parasitic on the signal wire M 1 .
  • the capacitance of C 2 is the sum of Cgs of the switching elements T 1 - 2 , T 2 - 2 , and T 3 - 2 parasitic on the signal wire M 2 .
  • the load capacitor (C 1 to C 3 ) is given by addition of three capacitances of Cgs of the switching elements.
  • the load capacitance of each signal line in the matrix will have the capacitance of Cgs ⁇ 4000.
  • Vj (4 KTRB ) 1 ⁇ 2 ( Vrms ).
  • K is the Boltzmann constant, 1.38 ⁇ 10 ⁇ 23 (J/K)
  • T is an absolute temperature (K)
  • B is the frequency bandwidth (Hz) of system.
  • R is a resistance ( ⁇ ) in the case of the thermal noise occurring in a resistor. In the case of this system, it may be considered as ON resistance ( ⁇ ) of the switching elements.
  • CL ⁇ Ca is series combined capacitance of CL and Ca.
  • the KTC noise also occurs upon resetting the load capacitances to the reset potential by the reset switches RES 1 to RES 3 , which raises the problem of reduction in S/N of the photoelectric conversion apparatus.
  • This KTC noise upon reset is given by (KT/CL) 1 ⁇ 2 (V).
  • the KTC noise occurring upon transfer and the KTC noise occurring upon reset appears as random noise of photoelectric conversion apparatus.
  • the apparatus will necessitate the photoelectric conversion apparatus with higher S/N ratios than the business machines such as copiers or electronic blackboards, and, the KTC noise could be a big problem.
  • the N reading circuit sections are not preferred to be located with long extension of the signal wires also in respect of an anti-noise property, but the necessary circuits are desired to be mounted near the photoelectric conversion circuit section.
  • N many ICs are provided, heat generation thereof will increase the temperature of the photoelectric conversion circuit section in some cases.
  • the switching elements are amorphous silicon TFTs, it is said that the dark current during OFF will increase, and there is a possibility of raising another problem that the heat generation of ICs could increase fixed pattern noise of photoelectric conversion apparatus.
  • the noise quantity required for the whole apparatus including the photoelectric conversion elements is said to be ⁇ fraction (1/10000) ⁇ or less against the dynamic range of signal if the image quality higher than that of the film method is desired to achieve.
  • the resolution of 14 or more bits is required as performance of the A/D converter necessary for achieving the “digitization of X-ray image information.”
  • A/D converters of 16 bits are commercially available presently, but it is a present status that the conversion speed decreases with increase of bit number, and to date there has been and is no high-speed A/D converter of 14 or more bits that can be used practically and actually in the X-ray image pickup apparatus having the photoelectric conversion apparatus of 4000 ⁇ 4000 pixels as described above.
  • An object of the present invention is to provide a photoelectric conversion apparatus that can reduce the read scanning time so as to enable high-speed reading and also to provide a system having the apparatus.
  • Another object of the present invention is to provide a photoelectric conversion apparatus that can perform signal reading at high S/N with little generation of thermal noise (KTC noise) and also to provide a system having the apparatus.
  • KTC noise thermal noise
  • An additional object of the present invention is to provide a photoelectric conversion apparatus that can obtain good image information without density unevenness or unnecessary stripes, reduced in fixed pattern noise, and also to provide a system having the apparatus.
  • a further object of the present invention is to provide a photoelectric conversion apparatus that can obtain image information excellent in tone level and also to provide a system having the apparatus.
  • Still another object of the present invention is to provide a photoelectric conversion apparatus that can be corrected readily for nonuniformity of characteristic such as one caused by manufacturing dispersion of photoelectric conversion element or the like, thereby enabling further promotion of cost reduction and also to provide a system having the apparatus.
  • An object of the present invention is to provide a photoelectric conversion apparatus having a photoelectric conversion circuit section comprising a plurality of photoelectric conversion elements, switching elements, matrix signal wires, and gate drive wires arranged on a same substrate in order to output parallel signals, a driving circuit section for applying a driving signal to said gate drive wire, and a reading circuit section for converting the parallel signals transferred through said matrix signal wires to serial signals to output the serial signals,
  • said reading circuit section comprises at least one analog operational amplifier connected with each of said matrix signal wires, transfer switches for transferring output signals from said respective matrix signal wires, output through each said analog operational amplifier, reading capacitors for accumulating said output signals transferred, and reading switches for successively reading signals out of said reading capacitors in the form of serial signals.
  • a further object of the present invention is to provide a photoelectric conversion system having at least: a photoelectric conversion apparatus having a photoelectric conversion circuit section comprising a plurality of photoelectric conversion elements, switching elements, matrix signal wires, and gate drive wires arranged on a same substrate in order to output parallel signals, a driving circuit section for applying a driving signal to said gate drive wire, and a reading circuit section for converting the parallel signals transferred through said matrix signal wires to serial signals to output the serial signals; and a light source;
  • said reading circuit section of said photoelectric conversion apparatus comprises at least one analog operational amplifier connected with each of said matrix signal wires, transfer switches for transferring output signals from said respective matrix signal wires, output through each said analog operational amplifier, reading capacitors for accumulating said output signals transferred, and reading switches for successively reading signals out of said reading capacitors in the form of serial signals.
  • FIG. 1 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 2 is a timing chart for explaining an example of the driving method of the photoelectric conversion apparatus
  • FIG. 3 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 4 is a timing chart for explaining an example of the driving method of the photoelectric conversion apparatus
  • FIG. 5A is a schematic top plan view for explaining an example of the photoelectric conversion element
  • FIG. 5B is a schematic cross-sectional view for explaining an example of the photoelectric conversion element
  • FIG. 6 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 7 is a schematic structural drawing for explaining an example of a device having the photoelectric conversion apparatus
  • FIG. 8 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 9 is a timing chart for explaining an example of drive of the photoelectric conversion apparatus.
  • FIG. 10 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 11 is a schematic circuit diagram for explaining an example of the operational amplifier
  • FIG. 12 is a schematic circuit diagram for explaining an example of the operational amplifier
  • FIG. 13 is a schematic circuit diagram for explaining an example of the A/D conversion circuit
  • FIG. 14 is a schematic circuit diagram for explaining an example of a selector circuit section
  • FIG. 15 is a schematic circuit diagram for explaining an example of a bit conversion circuit section
  • FIG. 16 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 17 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 18 is a timing chart for explaining an example of input/output to and from a delay circuit shown in FIG. 17;
  • FIG. 19 is a schematic circuit diagram for explaining an example of a sample hold circuit
  • FIG. 20 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus
  • FIG. 21 is a timing chart for explaining an example of drive of the photoelectric conversion apparatus
  • FIGS. 22A, 22B and 22 C are schematic energy band diagrams for explaining an example of drive of photoelectric conversion element
  • FIG. 23 is a schematic circuit diagram for explaining an example of the photoelectric conversion apparatus.
  • FIG. 24 is a timing chart for explaining an example of drive of the photoelectric conversion apparatus.
  • a photoelectric conversion apparatus of the present invention has a photoelectric conversion circuit section comprising a plurality of photoelectric conversion elements, switching elements, matrix signal wires, and gate drive wires arranged on a same substrate in order to output parallel signals, a driving circuit section for applying a driving signal to said gate drive wire, and a reading circuit section for converting the parallel signals transferred through said matrix signal wires to serial signals to output them, wherein said reading circuit section comprises at least one analog operational amplifier connected in cascade connection with each of said matrix signal wires, transfer switches for transferring output signals from said respective matrix signal wires, output through the analog operational amplifiers, reading capacitors for accumulating said output signals transferred, and reading switches for successively reading signals out of said reading capacitors in the form of serial signals.
  • said analog operational amplifier of first stage connected to each of the matrix signal wires have a noise voltage density Vn (V/ ⁇ square root ⁇ square root over (Hz) ⁇ ) converted at an input terminal portion thereof and a frequency band B (Hz) enough to amplify a signal from said photoelectric conversion circuit section and satisfy the relation of: Vn ⁇ square root ⁇ square root over (B) ⁇ Tn against thermal noise effective voltage Tn (Vrms) of said switching element at the input terminal portion of said analog operational amplifier, occurring when the switching element in said photoelectric conversion circuit section is turned on.
  • a capacitor element for letting only alternating-current components pass be connected to midway of an output wire from an output terminal of said analog operational amplifier connected with each of said matrix signal wires and that a reset switch for DC restoration of said capacitor element be provided.
  • the at least one analog operational amplifier connected with each of the matrix signal wires be provided with a function to change an amplification factor thereof by a signal from the outside.
  • the analog operational amplifier connected with each of the matrix signal wires be provided with a function to reduce a consumption electric current thereof by a signal from the outside.
  • the foregoing reading circuit section is configured preferably in such an arrangement that near the first analog operational amplifier (amp 1 ) connected to each of the matrix signal wires there is provided another analog operational amplifier (amp 2 ), the amp 1 is constructed as a non-inverting amplifier having an amplification factor of not less than 1 ⁇ , the amp 2 is constructed as a buffer amplifier having an amplification factor of 1 ⁇ , and a reference potential to be a reference of operation of the amp 1 is supplied from an output terminal of the amp 2 .
  • the reading circuit section is configured preferably in such an arrangement that a capacitor element for passing only ac components is connected to midway of an output wire from an output terminal of the analog operational amplifier connected to each of the matrix signal wires, a reset switch for dc restoration of the capacitor element is provided, and a resistance element is interposed between the capacitor element and the reset switch.
  • the reading circuit section is configured preferably in such an arrangement that a capacitor element for passing only ac components is connected to midway of an output wire from an output terminal of the analog operational amplifier connected to each of the matrix signal wires, a reset switch for dc restoration of the capacitor element is provided, a resistance element is interposed between the capacitor element and the reset switch, and there is provided a function for varying an on/off time of the reset switch by a signal from the outside.
  • the reading circuit section is configured preferably in such an arrangement that a capacitor element for passing only ac components is connected to midway of an output wire from an output terminal of the analog operational amplifier connected to each of the matrix signal wires, a reset switch for dc restoration of the capacitor element is provided, and a low-pass filter circuit is connected to a terminal out of those of the capacitor element, opposite to a terminal connected to the output of the analog operational amplifier.
  • the reading circuit section is configured preferably in such an arrangement that the at least one analog operational amplifier connected with each of the matrix signal wires has a function to vary a slew rate thereof by a signal from the outside.
  • the photoelectric conversion elements and switching elements in said photoelectric conversion circuit section be made using an amorphous silicon semiconductor as a semiconductor material.
  • each of the photoelectric conversion elements is comprised of, from the insulating substrate side, a first metal thin-film layer (first electroconductive layer) as a lower electrode, an amorphous silicon nitride insulating layer (a-SiNx) for preventing passage of electron carriers and hole carriers, a hydrogenated amorphous silicon photoelectric conversion layer (a-Si:H) as a semiconductor layer, an n-type injection preventing layer for preventing injection of hole carriers, and a transparent electroconductive layer or a second metal thin-film layer located in a part on the injection preventing layer, as an upper electrode (second electroconductive layer), that each of the switching elements (thin-film transistors) is comprised of, from the insulating substrate side, a first metal thin-film layer as a lower gate electrode, a gate insulating layer (a-SiNx) of amorphous silicon nitride, a hydrogenated amorphous silicon semiconductor layer (aS
  • the apparatus may be configured in such an arrangement that the photoelectric conversion elements are divided into a plurality of groups, the photoelectric conversion elements in each group can be set in the refresh mode independently of the other groups, and the photoelectric conversion elements in each group can be set in the photoelectric conversion mode independently of the other groups.
  • the apparatus may have a wavelength converting member such as a fluorescent member.
  • row scanning can be performed almost within only the reading time in reading scanning of each row, as compared with the operation time in the case of one set including the sequence of from transfer through reading to reset, thus enabling great increase in the reading speed of the photoelectric conversion apparatus.
  • the firststage analog operational amplifier connected to each of the matrix signal wires has a noise voltage density Vn (V/ ⁇ square root ⁇ square root over (Hz) ⁇ ) converted at an input terminal portion thereof and a frequency band B (Hz) enough to amplify a signal from said photoelectric conversion circuit section and satisfies the relation of: Vn ⁇ square root ⁇ square root over (B) ⁇ Tn against thermal noise effective voltage Tn (Vrms) of said switching element at the input terminal portion of said analog operational amplifier, occurring when the switching element in said photoelectric conversion circuit section is turned on, which can reduce the drop of S/N due to the KTC noise upon transfer.
  • a capacitor element for letting only alternating-current components pass is connected to midway of an output wire from an output terminal of the analog operational amplifier connected in cascade connection with each of the matrix signal wires and a reset switch for DC restoration of the capacitor element is provided, which can reduce the drop of S/N due to the KTC noise upon reset. Further, the reduction in the drop of S/N due to those KTC noise will result in the operational effect of achieving high-quality image information with less random noise.
  • the analog operational amplifier connected with each of the matrix signal wires is provided with a function to reduce a consumption electric current thereof by a signal from the outside, which can reduce the dark current upon OFF of the transfer switching elements due to heat generation of IC, which can reduce the fixed pattern noise, and which can achieve images without density unevenness and without stripes in the image plane.
  • an output of one A/D converter is selected out of the N A/D converters in accordance with an output level of an analog signal from the reading circuit section and is output as a digital value of (N+M ⁇ 1) bits, which enables high-resolution and high-speed A/D conversion of photoelectric conversion signals, which achieves a high-tone-level photoelectric conversion apparatus, and which can provide a high-performance X-ray image pickup apparatus using it.
  • the photoelectric conversion elements and switching elements in said photoelectric conversion circuit section are made of the amorphous silicon semiconductor material, which permits a large-area photoelectric conversion apparatus to be provided cheaply.
  • the at least one analog operational amplifier connected with each of the matrix signal wires is provided with the function capable of controlling the amplification factor by a signal from the outside, it can compensate for the gain dispersion caused by the film thickness dispersion on fabrication of amorphous silicon semiconductor thin film easily and cheaply.
  • the reference potential of amp 1 can be stabilized so as to obtain accurate photoelectric conversion signals and also enhance S/N by configuring the reading circuit section in such an arrangement that near the first analog operational amplifier (amp 1 ) connected to each of the matrix signal wires there is provided another analog operational amplifier (amp 2 ), the amp 1 is constructed as a non-inverting amplifier having an amplification factor of not less than 1 ⁇ , the amp 2 is constructed as a buffer amplifier having an amplification factor of 1 ⁇ , and a reference potential to be a reference of operation of the amp 1 is supplied from an output terminal of the amp 2 .
  • the low-pass filter can be configured upon dc restoration so as to decrease the random noise of the analog operational amplifiers and also enhance S/N by configuring the reading circuit section in such an arrangement that a capacitor element for passing only ac components is connected to midway of an output wire from an output terminal of the analog operational amplifier connected to each of the matrix signal wires, a reset switch for dc restoration of the capacitor element is provided, and a resistance element is interposed between the capacitor element and the reset switch.
  • S/N can be enhanced in a still image mode and the frame rate can be increased in a moving-picture mode so as to improve operability furthermore by configuring the reading circuit section in such an arrangement that a capacitor element for passing only ac components is connected to midway of an output wire from an output terminal of the analog operational amplifier connected to each of the matrix signal wires, a reset switch for dc restoration of the capacitor element is provided, a resistance element is interposed between the capacitor element and the reset switch, and there is provided a function for varying an on/off time of the reset switch by a signal from the outside.
  • the random noise of the analog operational amplifiers can be decreased so as to enhance S/N by configuring the reading circuit section in such an arrangement that a capacitor element for passing only ac components is connected to midway of an output wire from an output terminal of the analog operational amplifier connected to each of the matrix signal wires, a reset switch for dc restoration of the capacitor element is provided, and a low-pass filter circuit is connected to a terminal out of those of the capacitor element, opposite to a terminal connected to the output of the analog operational amplifier.
  • the apparatus becomes advantageous in reading weak photoelectric conversion signals necessitating noise reduction by configuring the reading circuit section in such an arrangement that the at least one analog operational amplifier connected with each of the matrix signal wires has a function to vary a slew rate thereof by a signal from the outside.
  • each of the photoelectric conversion elements is comprised of, from the insulating substrate side, a first metal thin-film layer (first electroconductive layer) as a lower electrode, an amorphous silicon nitride insulating layer (a-SiNx) for preventing passage of electron carriers and hole carriers, a hydrogenated amorphous silicon photoelectric conversion layer (a-Si:H) as a semiconductor layer, an n-type injection preventing layer for preventing injection of hole carriers, and a transparent electroconductive layer or a second metal thin-film layer located in a part on the injection preventing layer, as an upper electrode (second electroconductive layer), that each of the switching elements (thin-film transistors) is comprised of, from the insulating substrate side, a first metal thin-film layer as a lower gate electrode, a gate insulating layer (a-SiNx) of amorphous silicon nitride, a hydrogenated amorph
  • the frame rate can be increased substantially in the moving-picture mode so as to obtain a lot of sequential images by such an arrangement that the photoelectric conversion elements are divided into a plurality of groups, the photoelectric conversion elements in each group can be set in the refresh mode independently of the other groups, and the photoelectric conversion elements in each group can be set in the photoelectric conversion mode independently of the other groups.
  • FIG. 3 is a circuit diagram of a photoelectric conversion apparatus to show the first embodiment of the present invention.
  • the figure illustrates the structure of 3 ⁇ 3, nine pixels in total. Further, the same members as those in FIG. 1 will be denoted by the same symbols.
  • S 1 - 1 to S 3 - 3 are photoelectric conversion elements for receiving the visible light and converting it to electric signals
  • T 1 - 1 to T 3 - 3 are switch elements for transferring signal charges obtained by photoelectric conversion in the photoelectric conversion elements S 1 - 1 to S 3 - 3 to the matrix signal wires M 1 to M 3 .
  • G 1 to G 3 represent wires for driving the gates of switches, connected to the shift register (SR 1 ) and connected to the switch elements T 1 - 1 to T 33 .
  • the capacitance comprised of three interelectrode capacitances (Cgs) of switch elements is applied to the matrix signal wire M 1 upon transfer, as described above, and it is not illustrated as a capacitor element in FIG. 3. The same is also applied to the other matrix signal wires M 2 , M 3 .
  • photoelectric conversion elements S 1 - 1 to S 3 - 3 There are photoelectric conversion elements S 1 - 1 to S 3 - 3 , switching elements T 1 - 1 to T 3 - 3 , gate drive wires G 1 to G 3 , and matrix signal wires M 1 to M 3 illustrated in the photoelectric conversion circuit section 101 in the drawing, and they are placed on one insulating substrate, though not shown.
  • Numeral 102 denotes a driving circuit section comprised of a shift register (SR 1 ) for switching the switch elements T 1 - 1 to T 3 - 3 .
  • a 1 to A 3 are OP amps for amplifying signal charges of the matrix signal wires M 1 to M 3 and performing impedance transformation thereof, each being described only as a buffer amplifier constituting a voltage follower circuit in the drawing.
  • Sn 1 to Sn 3 are transfer switches, each reading an output from the OP amp A 1 to A 3 , i.e., an output on each matrix signal wire M 1 to M 3 and transferring it to a capacitor CL 1 to CL 3 .
  • the reading capacitors CL 1 to CL 3 are read out by reading switchs Sr 1 to Sr 3 through buffer amplifiers B 1 to B 3 constituting a voltage follower circuit.
  • Numeral 103 designates a shift register (SR 2 ) for switching the reading switches Sr 1 to Sr 3 .
  • the parallel signals of CL 1 to CL 3 are converted to serial signals by Sr 1 to Sr 3 and shift register (SR 2 ) 103 and they are input into an OP amp 104 constituting a final-stage voltage follower circuit and further are digitized by an A/D conversion circuit section 105 .
  • RES 1 to RES 3 are reset switches for resetting the signal components accumulated in the capacitances (three Cgs's) applied to the matrix signal wires M 1 to M 3 , which are reset to the reset potential (or reset to the GND potential in the drawing) by a pulse from CRES terminal.
  • 106 designates a power supply for applying a bias to the photoelectric conversion elements S 1 - 1 to S 3 - 3 .
  • the reading circuit section 107 is composed of the buffer amplifiers Al to A 3 , transfer switches Sn 1 to Sn 3 , reading capacitors CL 1 to CL 3 , buffer amplifiers B 1 to B 3 , reading switches Sr 1 to Sr 3 , shift register SR 2 , final-stage OP amp 104 , and reset switches RES 1 to RES 3 .
  • FIG. 4 is a timing chart to illustrate the operation of the photoelectric conversion apparatus shown in FIG. 3. Using FIG. 4, the details of the operation will be explained.
  • the signal charges obtained by photoelectric conversion in the photoelectric conversion elements S 1 - 1 to S 3 - 3 are accumulated in the capacitance components formed in the photoelectric conversion elements only during a selected period.
  • the signal charges having been accumulated in the photoelectric conversion elements S 1 - 1 to S 1 - 3 in the first row are transferred to the capacitance components (the capacitances of three Cgs's of the switching elements T 1 - 1 to T 3 - 3 ) formed in the respective matrix signal wires M 1 to M 3 while the gate pulse signal G 1 of the shift register (SR 1 ) 102 keeps the switching elements T 1 - 1 to T 1 - 3 “ON” only during a period of time t 1 .
  • M 1 to M 3 indicate states of the transfer and show a case of different signal quantities stored in the respective photoelectric conversion elements.
  • the output levels thereof indicate S 1 - 2 >S 1 - 1 >S 1 - 3 .
  • the signal outputs on the matrix signal wires M 1 to M 3 are subjected to impedance transformation by the respective OP amps A 1 to A 3 .
  • the switching elements Sn 1 to Sn 3 in the reading circuit section are turned “ON” only during a period of time t 2 by the SMPL pulse shown in FIG. 4 to transfer the signals to the reading capacitors CL 1 to CL 3 .
  • the signals in the reading capacitors CL 1 to CL 3 are subjected to impedance transformation by the respective buffer amplifiers B 1 to B 3 .
  • the reading switches Sr 1 to Sr 3 are successively turned “ON” by shift pulses Sp 1 to Sp 3 from the shift register (SR 2 ) 103 , whereby the parallel signal charges having been transferred to the reading capacitors CL 1 to CL 3 are converted to serial signals to be read out.
  • the serially converted signals are output from the final-stage OP amp 104 to be further digitized by the A/D conversion circuit section 105 .
  • Vout shown in FIG. 4 indicates an analog signal before input to the A/D conversion circuit section.
  • the parallel signals of S 1 - 1 to S 1 - 3 in the first row that is, the parallel signals of signal potentials on the matrix signal wires M 1 to M 3 are serially converted on the Vout signal in proportion to magnitudes of those signals.
  • the signal potentials of the matrix signal wires M 1 to M 3 are reset to the predetermined reset potential (the GND potential) through the reset switch elements RES 1 to RES 3 by turning the CRES pulse “ON” only during a period of time t 4 , thereby getting ready for next transfer of signal charges in the second row of the photoelectric conversion elements S 2 - 1 to S 2 - 3 .
  • photoelectrically converted signals of the second row and the third row are repetitively read out in the same manner.
  • the two operations, the reset operation of capacitances of the matrix signal wires M 1 to M 3 in the first row and the transfer operation by the gate pulse G 2 for the second-row photoelectric conversion elements S 2 - 1 to S 2 - 3 can be performed within the time range of t 3 ⁇ 3 necessary for the reading operation of signal charges of CL 1 to CL 3 in the first row.
  • the time necessary for reading of one row is t 4 +t 1 +t 2 , and this time can be set to be nearly equal to (t 3 ⁇ 3)+t 2 .
  • the capacitance formed in one of the matrix signal wires M 1 to M 3 is, in the case of FIG.
  • each row includes several hundred to several thousand bits in the case of construction of actual photoelectric conversion elements, and therefore, the capacitance value becomes very large as compared with the reading capacitor CL.
  • the time t 2 necessary for transfer by the SMPL pulse is sufficiently determined to be about the time of several times the time constant determined by the product of the capacitance value of reading capacitor CL and the ON resistance value of the switch element Snx (x:1 to 3).
  • FIG. 5A is a schematic top plan view of the photoelectric conversion circuit section where the photoelectric conversion elements and switching elements are made using the amorphous silicon semiconductor thin film
  • FIG. 5B is a schematic cross-sectional structural view along 5 A- 5 B in FIG. 5A.
  • the photoelectric conversion elements 301 and switching elements 302 are formed on a same substrate 303 , a same first metal thin film layer 304 is used in common to the lower electrodes of the photoelectric conversion elements 301 and the lower electrodes (gate electrodes) of TFTs 302 , and a same second metal thin film layer 305 is used in common to the upper electrodes of photoelectric conversion elements 301 and the upper electrodes (source electrodes and drain electrodes) of TFTs 302 .
  • the first and second metal thin film layers are also used in common to the gate driving wires 306 and matrix signal wires 307 in the photoelectric conversion circuit section.
  • the pixel number of 2 ⁇ 2, four pixels in total, are drawn.
  • the hatching portions represent light receiving surfaces of the photoelectric conversion elements.
  • Numeral 309 designates power-supply lines for giving a bias to the photoelectric conversion elements.
  • 310 denotes contact holes for connecting the photoelectric conversion elements 301 with TFTs 302 .
  • chromium (Cr) is evaporated over the insulating substrate 303 by sputtering or by resistance heating to form the first metal thin film layer 304 approximately 500 ⁇ thick, it is patterned by photolithography, and unnecessary areas are etched.
  • This first metal thin film layer 304 becomes the lower electrodes of photoelectric conversion elements 301 and the gate electrodes of switching elements 302 .
  • a-SiNx ( 311 ), a-Si:H ( 312 ), and N + layer ( 313 ) are successively deposited in the thicknesses of 3000, 5000, and 1000 ⁇ , respectively, in a same vacuum.
  • These layers are insulating layer/photoelectric conversion semiconductor layer/hole injection preventing layer of the photoelectric conversion elements 301 and also become gate insulating film/semiconductor layer/ohmic contact layer of the switching elements 302 (TFTs). Further, they are also utilized as insulating layers at cross portions ( 314 in FIG. 5A) between the first metal thin film layer 304 and the second metal thin film layer 305 .
  • the film thicknesses of the respective layers are optimally designed depending upon the voltage in use as a photoelectric conversion apparatus, charge, quantity of incident light to the light receiving surfaces of photoelectric conversion elements, or the like.
  • a-SiNx is desirably 500 or more ⁇ so as not to permit electrons and holes to pass and so as to well function as a gate insulating film of TFT 302 .
  • the areas to become contact holes are subjected to dry etching by RIE or CDE or the like, and thereafter aluminum (Al) is deposited in the thickness of about 10000 ⁇ as a second metal thin film layer 305 by sputtering or by resistance heating. Further, patterning is carried out by photolithography and unnecessary areas are etched.
  • the second metal thin film layer becomes the upper electrodes of photoelectric conversion elements 301 , the source and drain electrodes of switching TFTs 302 , the other wires, and so on.
  • the upper and lower metal thin film layers are connected to each other at the contact hole portions 310 at the same time as film formation of the second metal thin film layer 305 .
  • parts between the source electrode and drain electrode are etched by RIE, and thereafter unnecessary a-SiNx layer, a-Si:H layer, and N+layer are etched by RIE, thereby separating the elements from each other.
  • FIG. 5B illustrates only two pixels, it is needless to mention that a number of pixels are formed on the insulating substrate 303 at the same time.
  • the elements and wires are coated with a passivation film (protection film) 315 of SiNx.
  • the photoelectric conversion elements, switching TFTs, and wires are formed by the common first metal thin film layer, a-SiNx, a-Si:H, N + layer, and second metal thin film layer each deposited at the same time and only etching of each layer.
  • the photoelectric conversion elements, switching elements, gate driving wires, and matrix signal wires can be fabricated at the same time on the same substrate, thereby providing the large-area photoelectric conversion circuit section easily and cheaply.
  • the amorphous silicon TFTs have lower mobility of electron as a material thereof than the switch elements of crystal silicon, and thus have extremely large ON resistance.
  • the ON resistance of TFT in the channel size (W/L): 50 ⁇ m/10 ⁇ m fabricated by the above process will be very large as 8 M ⁇ with application of the bias (Vgs) of 12 V.
  • the photoelectric conversion circuit section as shown in FIG. 5A and FIG. 5B is constructed at the pixel pitch 100 ⁇ m using this TFT, the capacitance components formed in the photoelectric conversion elements will be 2 to 3 (pF) and the time necessary for transfer from the photoelectric conversion elements to the matrix signal wires will be approximately 20 ( ⁇ sec) as a time constant ⁇ . For sufficient transfer, the time of several times the time constant is necessary. Supposing the time of 4 ⁇ is set, the pulse width of the driving gate pulse of TFT will be 80 ( ⁇ sec).
  • Cgs of one above TFT is about 0.05 (pF) and if the number of pixels in one row is 4000, the capacitance component formed in a single matrix signal wire is
  • the ON resistance of the reset switch elements (RES 1 to RES 3 ) in the reading circuit section shown in FIG. 3 can be readily made in the range of about several hundred ⁇ and several k ⁇ if the reading circuit section is of IC (crystal silicon); and the time constant ⁇ R necessary for reset thereof is below 1 ( ⁇ sec) as long as the resistance components of wires can be ignored.
  • the passing line of the reset current in the reset operation flows via Cgs of TFT through the gate drive wire (G 1 , G 2 , or G 3 in FIG. 1, for example). If the material for the gate drive wires is chromium and if the photoelectric conversion circuit section is constructed in the structure as shown in FIG. 5A and FIG.
  • the resistance value of the wires is expected to be high. If the wire width is made wider in order to decrease the resistance value, the area occupied by the light receiving surface of the photoelectric conversion element against the pixel region of 100 ( ⁇ m) ⁇ 100 ( ⁇ m) will decrease, which will result in failing to ensure sufficient signal quantities; if the film thickness of wire is made thicker, the coverage property of the protection film 315 will be lowered, which will degrade the reliability. Accordingly, the appropriate size on design is approximately the wire width 10 ( ⁇ m) and the film thickness of wire 1000 ( ⁇ ) or so.
  • the sheet resistance thereof is approximately 2 ⁇ / ⁇
  • the wire length is 4000 (pixels) ⁇ 100 ( ⁇ m) in the above example, which is approximately 40 or more (cm), so that the resistance of wire can be even 80 (k ⁇ ).
  • ⁇ R 1 ( ⁇ sec) is not sufficient for the time necessary for resetting the capacitance of about 200 (pF) formed in the matrix signal wire.
  • the present invention enables reading scanning of each row to be performed substantially in the time of only reading, thereby greatly increasing the speed of reading of the photoelectric conversion apparatus.
  • the same constituent members as those in FIG. 3 showing Embodiment 1 are denoted by the same reference symbols and description thereof is omitted herein.
  • FIG. 6 is different from FIG. 3 in that the buffer amplifiers L 1 to L 3 connected to the respective matrix signal wires in the reading circuit section are replaced by non-inverting amplifiers with an amplification factor G determined by resistors R 1 , R 2 . Further, though not shown in FIG. 6, the OP amps of the buffer amplifiers L 1 to L 3 are excellent in very low noise performance as compared with the other amplifiers.
  • the amplification factor is 1+(R 2 /R 1 ).
  • the OP amps generate random voltage-nature noise, it is dominated by noise occurring in transistors incorporated, especially in first-stage transistors.
  • the first-stage section is composed of a bipolar transistor, it is said that the thermal noise occurring in the base resistance determines the noise quantity of OP amp.
  • the noise quantity is normally expressed against unit bandwidth, and the unit thereof is (Volt/ ⁇ square root ⁇ square root over (Hz) ⁇ ).
  • the noise quantity is also multiplied by 1+(R 2 /R 1 ) in accordance with the frequency band to operate.
  • the noise occurring in the OP amps will be considered to be a noise value before multiplied by the amplification factor, i.e., equivalent input noise voltage, which will be represented by Vn (V/ ⁇ square root ⁇ square root over (Hz) ⁇ ).
  • Vn of OP amps (L 1 to L 3 ) shown in FIG. 6 is set below a certain selected value.
  • the certain selected value is the noise value due to the so-called KTC noise occurring upon the transfer operation through the switching elements T 1 - 1 to T 3 - 3 in the photoelectric conversion circuit section 101 .
  • noise quantities occurring in the first-stage OP amp portions (L 1 to L 3 ) in the reading circuit section are set to be not more than the KTC noise quantity occurring in the photoelectric conversion circuit section 101 .
  • Either noise is intrinsic noise potentially occurring on principle, which cannot be made to be “zero” on design.
  • each noise will be roughly estimated.
  • the KTC noise (Tn) occurring upon performing the transfer operation by the switching elements (TFTs) T 1 - 1 to T 3 - 3 is as follows when obtained as voltage noise on the capacitance C 2 of the matrix signal wire M 1 to M 3 .
  • Tn ( K ⁇ T ⁇ (C 1 ⁇ C 2 )) 1 ⁇ 2 /(C 1 +C 2 )
  • K the Boltzmann constant (1.38 ⁇ 10 ⁇ 23 (J/K)
  • T is an absolute temperature
  • C 1 ⁇ C 2 is a series combined capacitance of C 1 and C 2 .
  • This noise Tn statistic-probabilistically shows a Gaussian distribution and is expressed by an effective noise voltage value (Vrms).
  • Vrms effective noise voltage value
  • Tn 0.55 ( ⁇ Vrms).
  • the noise occurring in the OP amps L 1 to L 3 varies depending upon the handling frequency band B.
  • the OP amps are operated in the frequency band B of four times that value, i.e., 25 (kHz), the photoelectric conversion signals transferred and the KTC noise occurring in the photoelectric conversion circuit section are amplified sufficiently (G times).
  • FIG. 7 is a schematic cross-sectional view of a medical X-ray detecting apparatus constructed using the two-dimensional photoelectric conversion apparatus.
  • X-rays emitted from an X-ray source 1501 are radiated to a subject 1502 such as a human body (the affected part of patient or an examined part of an object), and X-rays associated with intracorporeal information about lung part, bone, focus, or the like or associated with internal information about a structure or an inner space travel toward a grid plate 1503 .
  • the grid plate 1503 is provided for the purpose to prevent the X-rays scattered in the subject from irradiating the fluorescent member 1504 and photoelectric conversion apparatus 1506 , and is constructed of a substance 1507 for absorbing X-rays, such as lead, and a substance 1508 for transmitting X-rays, such as aluminum.
  • the X-rays passing through the grid irradiate the X-ray-to-visible conversion fluorescent member 1504 , being a wavelength conversion member, to be converted to wavelengths in the range including the sensitivity of photoelectric conversion element, for example, to visible light therein. Fluorescence from the X-ray-to-visible conversion fluorescent member is photoelectrically converted by the photoelectric conversion apparatus 1506 .
  • 1509 denotes the photoelectric conversion elements, 1510 the switching elements, and 1511 a protection film for protecting the photoelectric conversion elements 1509 and switching elements 1510 .
  • Numeral 1512 designates an insulating substrate on which the photoelectric conversion elements 1509 and switching elements 1510 are placed.
  • the illuminance obtained on the light receiving surfaces of photoelectric conversion elements becomes maximum, and the illuminance at that time can be that of several (Lx) or so, though depending upon the fluorescent member used or a dose of the X-ray source.
  • the apparatus can fully function as a photoelectric conversion section of the X-ray image pickup apparatus.
  • the noise in the OP amp portion includes not only Vn, but also the thermal noise occurring in the resistance of R 1 , R 2 , for example. It can be easily reduced far smaller than the noise due to Vn by decreasing their resistance values. Also, there exists a current-nature noise component (In) in the input portion in the OP amps. This can be decreased to be far smaller than the noise due to Vn by using field-effect transistors for the first-stage transistors of the OP amps. Namely, since the equivalent input noise voltage Vn owned by the OP amps greatly affects S/N of the photoelectric conversion apparatus, Vn of OP amps is specified in the present invention.
  • the same constituent members as those in FIG. 6 shown in the second embodiment are denoted by the same reference symbols and description thereof is omitted.
  • FIG. 8 is different from FIG. 6 in that in the reading circuit section capacitor elements CC 1 to CC 3 for letting only AC components pass are connected to midway of output wires from the output terminals of OP amps L 1 to L 3 and in that reset switches D 1 to D 3 for DC restoration of the capacitor elements are provided. Further, a buffer amplifier A 1 to A 3 for impedance transformation is connected to each capacitor element CC 1 to CC 3 .
  • FIG. 9 is a timing chart to show the operation in FIG. 8, which especially illustrates the operation related to the capacitor elements CC 1 to CC 3 and reset switches D 1 to D 3 , and the other operation is the same as in FIG. 4.
  • the operation of the present embodiment will be explained using FIG. 8 and FIG. 9.
  • CRES is a control signal of the switches RESI to RES 3 for resetting the capacitor CL (three Cgs of TFTs T 1 - 1 to T. 3 - 3 which are not shown in FIG. 8) formed in the matrix signal wire M 1 to M 3 to the reset potential (GND).
  • P 1 shows states of change of potential at a node (for example, represented by P 1 on FIG. 8) of matrix signal wire. Essentially, the node P 1 should be reset to GND being the reset potential by the CRES signal “Hi.” However, when the capacitor C 2 of matrix signal wire is reset, the thermal noise probabilistically occurs as KTC noise because of the ON resistance of switch RES 2 .
  • C 2 200 pF
  • the reset switch D 2 is connected to the node P 2 and is controlled by control signal DRES.
  • DRES becomes “ON” nearly at the same time as CRES and DRES becomes “OFF” a little after “OFF” of CRES.
  • the reset potential GND is given at the node P 2 .
  • the node P 2 is held at the GND potential. In that state, for example, when the gate (G 2 ) of transfer TFT is turned “ON,” the signal charge accumulated in the capacitance of photoelectric conversion element S 22 is transferred to the capacitor C 2 of matrix signal wire. Its state is shown in the waveform P 1 of FIG.
  • the present invention involves such an arrangement that in the reading circuit section 107 the capacitor elements CC 1 to CC 3 for letting only the AC components pass are connected to midway of the output wires from the output terminals of OP amps L 1 to L 3 and that the reset switches D 1 to D 3 for DC restoration of the capacitor elements are provided, whereby the KTC noise occurring upon reset of capacitance formed in each matrix signal wire can be removed, thus permitting enhancement of S/N of photoelectric conversion apparatus and permitting high-quality images to be obtained.
  • the same constituent members as those in FIG. 8 shown in the third embodiment are denoted by the same reference symbols, and description thereof is omitted.
  • FIG. 10 is different from FIG. 8 in that in the reading circuit section 107 OP amps K 1 to K 3 having a function capable of variably controlling the amplification factor thereof by a signal from the outside are added.
  • FIG. 10 there are four signal lines A 1 to A 4 for controlling the amplification factor from the outside, thereby permitting selection of four amplification factors.
  • FIG. 11 shows schematic circuitry inside of the amplification-factor-variable OP amp K 1 to K 3 in FIG. 10. The function will be explained briefly.
  • Terminals A 1 , A 2 , A 3 , A 4 are those for inputting a signal for selecting an amplification factor from the outside, and only one of the four terminals is assumed to be “Hi.”
  • the switch element S 1 , S 2 , S 3 , S 4 connected to either terminal A 1 , A 2 , A 3 , A 4 is turned on.
  • the OP amp K 1 to K 3 operates as a non-inverting amplifier.
  • the present embodiment showed an example of switching the four amplification factors by the four control signals, but without having to be limited to four, a desired number of control signals may be arranged to switch associated amplification factors. If a multiplexer circuit is connected to the control terminals, N external control signals permits switch of 2 N ways.
  • the photoelectric conversion apparatus of the present invention can compensate for the output dispersion easily because of the function capable of controlling the amplification factor by a signal from the outside in the reading circuit section, and therefore, it has a merit of decrease in the cost of apparatus as a result.
  • FIG. 12 is an example of a circuit diagram of one of OP amps incorporated in the reading circuit section of a photoelectric conversion apparatus according to the fifth embodiment of the present invention.
  • the feature of the present invention resides in provision of a switch element SWp controlled by a signal from a terminal PS. Explanation of the operation concerning the function of this switch element SWp will be given.
  • Terminals Vdd, Vss are power terminals of the OP amp, and the power of Vdd>Vss is input. Normally, assuming that the GND of the system of photoelectric conversion apparatus is the zero potential, positive voltage is applied to Vdd while negative voltage to Vss, respectively.
  • a control signal from PS terminal is not input to the switch element SWp, that is, when SWp is “OFF,” current flows through resistor R 9 , diode D 1 , and diode D 2 to bias the base potential of transistor Q 7 to the potential given by forward threshold voltage of D 1 , D 2 .
  • the transistor Q 7 turns into the “ON” state, the collector current I of transistors Q 6 , Q 7 flows from Vdd terminal to resistor R 8 . Since Q 6 and Q 5 , and, Q 6 and Q 8 are in the relation of current mirror structure, when the transistors of Q 5 , Q 6 , Q 8 have the same performance, current equal to the collector current I of Q 6 flows to the collectors of Q 5 , Q 8 . Q 5 becomes a constant current supply for implementing the function as an OP amp.
  • Bipolar transistors Q 1 , Q 2 are input-stage transistors, current according to input difference voltage between input terminals VIN(+), VIN( ⁇ ) flows into (or flows out of) the base of transistor Q 9 , and it is amplified in the output stage comprised of transistors Q 8 , Q 9 , Q 10 to be output from the terminal Vout.
  • Transistors Q 3 , Q 4 compose current mirror structure to function as an active load on the input-stage transistors Q 1 , Q 2 . In practical use, it is used as a negative feedback circuit for effecting negative feedback from the output terminal Vout to the VIN( ⁇ ) terminal of input terminal, a non-inverting amplifier circuit, or an impedance converting circuit, a voltage follower circuit, or the like. Also, it is often used as an inverting amplifier circuit.
  • the power-supply current often exceeds 100 ⁇ A in common sense, though depending upon resistance values used.
  • Vss Supposing the power-supply voltage of Vdd, Vss is +5 (V), ⁇ 5 (V), respectively, the consumption power of 40 (W) is necessary in the reading circuit section.
  • This power is always consumed as long as the power is input to each OP amp, even in the state where SR 1 , SR 2 , or the other switches, etc. do not operate in FIG. 3, FIG. 6, FIG. 8, or FIG. 10, that is, even in the non-reading state.
  • This is converted to heat in the reading circuit section (IC), and the heat is radiated to the surroundings.
  • the switch element SWp shown in FIG. 12 is purposed to decrease the above consumption power during the periods except for reading. The operation will be described below.
  • a control signal from the terminal PS turns the switch element SWp “ON,” thereby keeping no current flowing in the diodes of D 1 , D 2 .
  • the transistors Q 6 , Q 7 become “OFF,” so that no current flows.
  • the collector current of transistors Q 5 , Q 8 is also shut off.
  • the control signal from the terminal PS causes the constant current supply in the OP amp to be shut off, which enables the consumption current to be reduced greatly.
  • the switching element SWp may be, for example, an MOS transistor where it is switched by the voltage signal of 0 (V)/5 (V).
  • the temperature of the photoelectric conversion circuit section disposed around it can be prevented from increasing because of heat generation of the reading circuit section (IC), increase in the dark current “upon OFF” of TFTs of the switching elements can be decreased, and the fixed pattern noise of the photoelectric conversion apparatus can be decreased. Also, the decrease in the consumption power of the reading circuit section (IC) during the periods except for reading is of course economically advantageous.
  • FIG. 13 is a schematic circuit diagram of the A/D conversion circuit section of the photoelectric conversion apparatus, for explaining the sixth embodiment of the present invention.
  • the A/D conversion circuit section of the present embodiment is composed mainly of three OP amps, three A/D converters, two selector circuits, and a bit converting circuit. The operation thereof will be explained.
  • the analog signal Va as serially converted in the reading circuit section is input into the three OP amps in the A/D conversion circuit section.
  • the three OP amps will be referred to as amp 1 , amp 2 , and amp 3 , and amplification factors G 1 , G 2 , G 3 thereof are set in the ratio of 1:2:4.
  • Each amplification factor is determined by a resistance value connected to the OP amp.
  • the amplification factors G 1 , G 2 , G 3 of amp 1 , amp 2 , and amp 3 are set to be x 1 , x 2 , and x 4 , respectively.
  • the signal Va from the reading circuit section is assumed to be output in the range of 0 (V) to 1 (V). Namely, a signal over 1 (V) or a signal of minus voltage will never be input to the A/D conversion circuit section.
  • the signal Va from the reading circuit section is amplified by amp 1 , amp 2 , and amp 3 , and an output from each amp is input to the A/D converter AD 1 , AD 2 , AD 3 .
  • Two reference voltages are supplied to terminal REF+and to terminal REF ⁇ in the A/D converter AD 1 , AD 2 , AD 3 , and the analog input signal is digitized with respect to difference voltage between the reference terminals.
  • AD 3 Since AD 3 is connected to the OP amp having the fourfold gain, A/D conversion is effected when Va is between 0 (V) inclusive and 0.25 (V) inclusive. When the signal Va is over 0.25 (V), overflow terminal OF outputs the logic signal of “Hi.” Since AD 2 is connected to the OP amp having the twofold gain, A/D conversion is effected when Va is between 0 (V) inclusive and 0.5 (V) inclusive. When Va is over 0.5 (V), the overflow terminal OF outputs the logic signal of “Hi.” Since AD 1 is connected to the OP amp having the onefold gain, A/D conversion is effected when Va is between 0 (V) inclusive and 1 (V) inclusive. When the signal Va is over 1 (V), the OF terminal of overflow terminal outputs the logic signal of “Hi.”
  • selector 1 has such a function that when the digital signals from AD 3 and AD 2 are input thereto and if the OF terminal of AD 3 is “Lo” then it outputs the digital signal from AD 3 as it is but if the OF terminal of AD 3 is “Hi” then it outputs the digital signal from AD 2 as it is.
  • selector 2 has such a function that when the digital signals from selector 1 and AD 1 are input thereto and if the OF terminal of AD 2 is “Lo” then it outputs the digital signal from selector 1 as it is but if the OF terminal of AD 2 is “Hi” then it outputs the digital signal from AD 3 as it is.
  • AD 3 is output when Va: 0 (V) to 0.25 (V);
  • AD 2 is output when Va: 0.25 (V) to 0.5 (V);
  • AD 1 is output when Va: 0.5 (V) to 1 (V).
  • the selector 1 and selector 2 are identical on a circuit basis, and FIG. 14 shows an example of schematic circuitry of selector 1 in FIG. 13.
  • FIG. 15 is an example of schematic circuitry of the bit conversion circuit in FIG. 13.
  • the 12-bit digital signal of selector 2 input thereto i.e., the digital signal of the selected A/D converter
  • the bit conversion circuit is converted to 14 bits.
  • the shift operation of bits corresponding to the selected A/D converter is carried out.
  • AD 2 if AD 2 is selected and if the output thereof is as follows from the MSB side:
  • AD 3 if AD 3 is selected and if the output thereof is as follows from the MSB side:
  • the desired bit shift operation is carried out according to the digital signal of selected A/D converter by an input signal of terminal SEL 1 , terminal SEL 2 , or terminal SEL 3 of the bit conversion circuit section. That signal can be made by a simple logic circuit, using the signal from the OF terminal of each A/D converter.
  • terminal SELL is “Hi”
  • bit conversion is carried out for the digital output from ADl
  • terminal SEL 2 is “Hi”
  • bit conversion is carried out for the digital output from AD 2
  • terminal SEL 3 is “Hi”
  • bit conversion is carried out for the digital output from AD 3 .
  • signals with Va not more than 0.25 (V) are quantized in 1 ⁇ 2 14 for the dynamic range: 1 (V). Namely, signals in low levels of 1 ⁇ 4 or less are expressed in high resolution, and it is suitable, especially, for applications such as medical X-ray image pickup apparatus. Since offset components such as the fixed pattern noise (FPN) in the dark state caused in the photoelectric conversion circuit section and FPN caused in the reading circuit are digitized in high resolution, the accuracy of correction is improved in execution of offset correction.
  • FPN fixed pattern noise
  • the A/D conversion circuit section included three OP amps and three A/D converters, but it may be provided with a plurality of respective elements (N elements).
  • the reference voltage of the A/D converters may be 8 (V) according to the amplification factors.
  • the ratio of gains of the respective OP amps may be set to 2 0 :2 1 :2 2 : . . . :2 N-1 , and N A/D converters are to be used. Further, the present embodiment employed the 12-bit A/D converters, but any-bit A/D converters may be used.
  • N OP amps and N M-bit A/D converters in the A/D conversion circuit section permits us to obtain digital outputs of (M+N ⁇ 1) bits, and the data can be processed as digital values of (M+N ⁇ 1) bits in a succeeding data processing apparatus using a computer and a memory circuit.
  • analog signals of 1 ⁇ 2 N-1 or less to the dynamic range can be converted to digital signals substantially in the same accuracy as in the case of using the A/D converters of (M+N ⁇ 1) bits. This means that if the A/D converters of (M+N ⁇ 1) bits do not exist or if they exist but cannot be used because of their conversion speed, (M+N ⁇ 1) bit-equivalent digital conversion can be achieved by using N M-bit A/D converters.
  • FIG. 16 is a circuit diagram of a photoelectric conversion apparatus showing the seventh embodiment of the present invention.
  • the number of pixels of the photoelectric conversion circuit section 101 is not 3 ⁇ 3, but FIG. 16 illustrates an arrangement assuming a lot of pixels.
  • the capacitor elements CL 1 to CL 3 , switches Sn 1 to Sn 3 , amplifiers BI to B 3 , and switches Sr 1 to Sr 3 shown in the reading circuit section of FIG. 6 are not illustrated in FIG. 16, there actually exist 128 elements for each of them.
  • the shift register 103 , amplifier 104 , and A/D conversion circuit section in FIG. 6 are not illustrated in FIG. 16, either.
  • the number of inputs to the reading circuit section 107 is 128 as illustrated. If the number of columns in the two-dimensional photoelectric conversion element circuit section 101 is, for example, 2560, twenty reading circuit sections 107 (ICs) will be used.
  • BND 1 to BND 128 indicate interconnections between the matrix signal wires (M 1 to M 128 ) in the photoelectric conversion circuit section and the reading circuit section, which are connected by the wire bonding method or the anisotropic connection method.
  • FIG. 16 is different from FIG. 6 in that the potential (GND) to be a reference of the first-stage operational amplifier L 1 to L 128 for amplifying a signal from the matrix signal wire is supplied from buffer amplifier E 1 to E 128 , respectively.
  • the operational amplifiers L 1 to L 128 are purposed to amplify signals from the photoelectric conversion circuit section and are those having characteristics excellent in noise performance.
  • the thermal noise at a resistor in the configuration as a non-inverting amplifier in addition to the random noise occurring in the operational amplifiers of L 1 to L 128 .
  • the thermal noise (4KTRB) occurring at input resistor RA 1 to RA 128 interposed between the inverting terminal and GND of operational amplifier will result in being amplified by an amplification factor of non-inverting amplifier by the operational amplifiers of L 1 to L 128 . Therefore, the input resistors of L 1 to L 128 need to be set small in order to keep the thermal noise occurring in the resistors smaller.
  • the impedance of GND is large, the electric current flowing through the input resistor will cause a voltage drop.
  • GND wiring is routed from that point to supply GND to the operational amplifiers of L 1 to L 128 .
  • the number of inputs is 128 as shown in FIG. 16
  • electric currents flowing in the 128 input resistors all flow into the GND wire, which would change the reference potentials (GND) of operational amplifiers existing away from the supply point of GND.
  • GND reference potentials
  • amounts of the change will be dependent on input signals of the other signal wires, which could cause failure in obtaining correct photoelectric conversion signals.
  • the voltage drop amount of reference potential can be decreased by increasing the line width of the GND wire thus routed, but it will also increase the chip area, which is not a desirable solution. Also, the impedance can be lowered by supplying GND from the outside to each operational amplifier of from L 1 to L 128 , but it is not practical to provide lead-out pads in the same number as the number of inputs.
  • the operational amplifiers of L 1 to L 128 are provided each with the individual buffer amplifiers E 1 to E 128 to supply the reference potential (GND) for the low-noise amplifiers of L 1 to L 128 from the respective outputs of the buffer amplifiers of E 1 to E 128 .
  • GND reference potential
  • the thermal noise occurring at the input resistors is low because of the small input resistances RA 1 to RA 128 , so that S/N can be enhanced. Resistance values of the input resistors do not have to be too small and may be set in consideration of the thermal noise occurring at the resistors and the noise occurring at the buffer amplifiers E 1 to E 128 .
  • FIG. 17 is a circuit diagram of a photoelectric conversion apparatus for explaining, the eighth embodiment of the present invention.
  • the same members as those in FIG. 8 are denoted by the same reference symbols and description thereof will be omitted.
  • the capacitor elements CC 1 to CC 3 are connected through resistance elements RB 1 to RB 3 to the switch elements D 1 to D 3 .
  • a signal for opening/closing the switch element D 1 to D 3 i.e., a DRES signal is made by CRES signal and delay circuit DL 1 (or DL 2 ) and, in addition, it can be selected by control signal DSEL from the outside.
  • a low-pass filter comprised of buffer amplifier F 1 to F 3 , resistance element RF 1 to RF 3 , and capacitor element CF 1 to CF 3 is provided between the capacitor element CC 1 to CC 3 and the buffer amplifier A 1 to A 3 .
  • the slew rate of buffer amplifier A 1 to A 3 functioning in sampling a signal into the capacitor element CL 1 to CL 3 for sample and hold is arranged as capable of being varied by a control signal SR from the outside.
  • the photoelectric conversion apparatus of the present embodiment is illustrated with nine pixels of 3 ⁇ 3, the apparatus may be constructed with much more pixels without departing from the spirit of the invention. Since no inconvenience will occur with description about only one line of matrix signal wire, the present embodiment will be described with the drawing as to only the line of matrix signal wire of
  • the operational amplifier L 1 of first stage in the reading circuit section 107 for amplifying the signal from the photoelectric conversion circuit section 101 , is excellent in low-noise performance, as also described in Embodiment 2.
  • the frequency band thereof may be a band in which the photoelectric conversion signal transmitted by the transfer operation at TFT in the photoelectric conversion circuit section can be amplified enough.
  • the operational amplifier L 1 has a frequency band broader than necessary, the photoelectric conversion signal can be amplified, while the high-frequency components of random noise occurring at L 1 will be also amplified.
  • the noise of high-frequency components appears in the output of the photoelectric conversion circuit section upon resetting it and results in being terminated at the capacitor element CC 1 . This will be a cause to degrade S/N.
  • the high-frequency components of noise of L 1 are also amplified in transfer of photoelectric conversion signal at TFT, which also degrades S/N.
  • the performance required for the operational amplifier of L 1 is the frequency band in which the amplifier can amplify the photoelectric conversion signal transmitted by the transfer operation at TFT in the photoelectric conversion circuit section enough and which is not broader than necessary.
  • the operational amplifier L 1 is designed in a little broader frequency band, taking account of the dispersion, rather than the frequency band in which the photoelectric conversion signal transmitted by the transfer operation at TFT in the photoelectric conversion circuit section can be amplified.
  • FIG. 18 shows a timing chart of the CRES signal and DL 1 output and DL 2 output of delay circuit.
  • the delay circuit DL 1 , DL 2 is a circuit for effecting a delay only at a trailing edge of CRES signal and a delay amount of DL 2 is greater than that of DL 1 .
  • DRES signals of different delay amounts by a control signal from the outside.
  • LPF primary low-pass filter
  • the buffer amplifier F 1 During transfer of photoelectric conversion signal through TFT after end of reset, the buffer amplifier F 1 , capacitor element CF 1 , and resistance element RF 1 function as a primary LPF. In other words, the highfrequency-side noise of L 1 can be cut thereby.
  • the band of buffer amplifier F 1 can be set slightly high and the constants of CF 1 and RF 1 can be selected to be those achieving the frequency band in which the photoelectric conversion signal transmitted by the transfer operation at TFT in the photoelectric conversion circuit section can be amplified enough and which is not broader than necessary.
  • the delay time of trailing edge of DRES signal by the delay circuit DL 1 , DL 2 is controlled by the DSEL signal.
  • Td be a delay time of trailing edge of DRES signal.
  • the KTC noise occurring in resetting the reading capacitance (C 2 ) of matrix signal wire by CRES, can be canceled by coupling the capacitor element CC 1 on an AC basis and effecting the timing operation shown in FIG. 6.
  • the KTC noise can be accumulated sufficiently in CC 1 by setting Td sufficiently longer than the time constant CC 1 ⁇ RB 1 and the KTC noise can be canceled upon transfer of TFT.
  • setting of longer Td will increase the time necessary for reading of one row, which in turn means that the reading time of photoelectric conversion signal for one frame becomes longer.
  • Td may be set longer for obtaining a high-quality still image of one shot, but in the case of obtaining a plurality of continuous moving pictures, the increase of reading time will decrease the acquisition rate (frame rate: the number of frames/sec) of moving picture.
  • the present embodiment enables Td to be switched by the DSEL signal.
  • the shift register 103 in the reading circuit section is of a circuit system for performing synchronous output with basic clock, though not illustrated in FIG. 17, photoelectric conversion signals (analog signals) after serial conversion by 103 are output in synchronism with the basic clock.
  • the basic clock is 10 MHz
  • the output rate of analog signal can also be designed at 10 MHz.
  • the operation may be performed at the basic clock, for example, of 5 MHz.
  • DL 1 may be arranged to effect a delay of 16 clock pulses while DL 2 a delay of 32 clock pulses.
  • Td can also be kept constant by switching of DSEL.
  • the capacitance of CC 1 and the resistance of RB 1 can be properly set in consideration of the KTC noise, the band of operational amplifier L 1 , and the reading speed and the DRES signals can be switched by the DSEL signal, depending upon the purpose.
  • FIG. 19 shows an example of a specific circuit configuration of the portion forming the sample hold section in FIG. 17, i.e., the region of buffer amplifier A 1 , switching element Sn 1 , capacitor element CL 1 , and buffer amplifier B 1 .
  • Electric currents flowing in transistors Q 6 , Q 5 can be varied between in an on state and in an off state of the external control signal SR. This changes an amount of charge that can be charged in CL in a unit time when the SMPL signal is on, that is, when the photoelectric conversion signal from the photoelectric conversion circuit section is sampled in the capacitor element CL. Namely, SR changes the slew rate (V/ ⁇ sec) of amplifier A 1 .
  • the noise occurring in the amplifier A 1 is given by the reciprocal of gain of amplifier L 1 : 1/G (G:1+R 2 /Rl) when converted at the input portion of the reading circuit section. Similarly as with L 1 and the other amplifiers, it is dependent on the noise density (V/ ⁇ square root ⁇ square root over (Hz) ⁇ ) and frequency band of A 1 .
  • the SR signal is turned to “Lo” at the amplifier of A 1 , the slew rate decreases. This means that the frequency band of amplifier A 1 is decreased.
  • FIG. 20 is a schematic circuit diagram of a photoelectric conversion apparatus to show the ninth embodiment of the present invention. For simplicity of description only nine pixels of 3 ⁇ 3 are illustrated.
  • FIG. 20 is different in the way of representing the photoelectric conversion elements S 1 - 1 to S 3 - 3 from FIG. 3. It is also different in the power-supply circuit section for supplying a bias to the photoelectric conversion elements.
  • the reading circuit section is the same as in FIG. 3 and the same constituent members are denoted by the same reference symbols.
  • the method for fabricating the photoelectric conversion circuit section is described in Embodiment 1. Accordingly, the schematic top plan view and the schematic cross-sectional view of photoelectric conversion element, switching element (TFT), etc. are the same as FIG. 5A and FIG. 5B, respectively.
  • the photoelectric conversion elements have the same layer structure as the switching elements and are constructed as MIS capacitors.
  • the N + layer is utilized as an upper electrode of photoelectric conversion element, different from the normal MIS capacitors, because of the necessity of incidence of light.
  • Each photoelectric conversion element is also a capacitor element and a charge of photoelectrically converted signal will be accumulated in a capacitance of itself. Described in the present embodiment is a method of operation to perform accumulation of photoelectric conversion charge, transfer by TFT, and reading of signal after resetting of the photoelectric conversion elements also being capacitors with a bias circuit provided outside.
  • the reset operation of photoelectric conversion element will be called “refresh.”
  • the photoelectric conversion elements S 1 - 1 to S 3 - 3 are illustrated in the different representation from FIG. 3, and the first metal thin-film layer in FIG. 5A and FIG. 5B will be called as “G” electrode of photoelectric conversion element, while the second metal thin-film layer thereof as “D” electrode.
  • the D electrode functions as an electrode including the N + layer, as described above, for the photoelectric conversion elements S 1 - 1 to S 3 - 3 .
  • FIG. 22A to FIG. 22C are energy band diagrams for explaining the device operation.
  • FIG. 22A and FIG. 22B show the operation in a refresh mode and the operation in a photoelectric conversion mode, respectively, of the present embodiment and show states in the thickwise direction of the respective layers of the photoelectric conversion element of FIG. 5A or FIG. 5B.
  • M 1 denotes the lower electrode (G electrode) made of the first metal thin-film layer (Cr).
  • the a-SiNx layer is the insulating layer for preventing the both electrons and holes from passing therethrough and needs to have the thickness enough to prevent occurrence of tunnel effect, specifically set in 500 or more ⁇ .
  • A-Si is the photoelectric conversion semiconductor layer made of an intrinsic semiconductor i-layer.
  • the N + layer is the injection preventing layer of N-type a-Si layer formed for preventing holes from being injected into the a-Si layer.
  • M 2 is the upper electrode (D electrode) made of the second metal thin-film layer (A 1 ).
  • the D electrode does not cover the N + layer completely, but movement of electron is free between the D electrode and the N + layer.
  • the D electrode and the N + layer are always at the same potential, which the following description assumes as a premise.
  • the present photoelectric conversion elements operate in two types of operation modes, which are the refresh mode and photoelectric conversion mode, depending upon how to apply the voltage to the D electrode and to the G electrode.
  • FIG. 22A of the refresh mode a negative potential is given to the D electrode with respect to the G electrode and the holes indicated by dots in the i-layer are guided to the D electrode by the electric field. At the same time, the electrons indicated by circles are injected into the i-layer. At this time, some holes and electrons are recombined in the N + layer and i-layer to annihilate. If this state continues for a sufficiently long time, the holes in the i-layer will be swept away from the i-layer.
  • the photoelectric conversion elements in the present embodiment can output the quantity of incident light in real time and can also detect the total quantity of incident light in a certain period.
  • the electric field in the i-layer will be applied in the direction to guide the holes to the D electrode.
  • the characteristics of the injection preventing layer of the N + layer capability of injecting the electrons into the i-layer is not a necessary condition, either.
  • the control signal VSC is for giving two types of bias to the bias line REF of photoelectric conversion element, i.e., to the D electrode of photoelectric conversion element.
  • the D electrode becomes VREF (V) when VSC is “Hi,” but VS (V) when “Lo.”
  • 106 A, 106 B are DC power supplies, which are reading power supply VS (V) and refresh power supply VREF (V), respectively.
  • VSC is switched to the state of “Lo” to turn the D electrodes of the all photoelectric conversion elements into a biased state (positive potential) to the reading power supply VS. Then the photoelectric conversion elements go into the photoelectric conversion mode. In this state all signals from the shift register 102 are made “Lo” and the CRES signal in the reading circuit section is turned into the state of “Lo.” Then all TFTs (T 1 - 1 to T 3 - 3 ) for switching become off and the switch elements RES 1 to RES 3 in the reading circuit also become off.
  • the G electrodes of the all photoelectric conversion elements become open on a DC basis, but potentials are maintained because the photoelectric conversion elements are also capacitors.
  • the light source is not illustrated specifically in FIG. 20, it is, for example, a fluorescent tube, an LED, a halogen lamp, or the like in the case of the copiers.
  • the light source is nothing but the X-ray source and in this case, a scintillator is used for conversion between X-rays and visible light. The photocurrent flowing due to this light is accumulated as a charge in each photoelectric conversion element and is retained after off of the light source.
  • An image is obtained through the refresh period, photoelectric conversion period, and reading period, and the above operation is repeated for obtaining a plurality of images such as moving pictures. Since the present embodiment is constructed in such an arrangement that the D electrodes of the photoelectric conversion elements are connected to the common wire and that this common wire is controlled by the VSC signal between the potentials of the refresh power supply VREF and reading power supply VS, the all photoelectric conversion elements can be switched simultaneously between the refresh mode and the photoelectric conversion mode. Because of this arrangement, a photooutput can be obtained by one TFT per pixel without performing complex control.
  • FIG. 23 is a schematic circuit diagram of a photoelectric conversion apparatus for explaining the tenth embodiment of the present invention.
  • each set of photoelectric conversion element and switching TFT is illustrated simply by a square for simplicity of drawing.
  • the present embodiment is characterized in that there are four groups of power-supply circuits for switching the refresh power supply to the reading power supply and vice versa and, in addition thereto, four groups of reset circuits for resetting the matrix signal wires. Switching of power supply is effected by VSC 1 to VSC 4 and switching of reset by CRES 1 to CRES 4 . Portions corresponding to the operational amplifiers A 1 to A 3 in the reading circuit 107 in FIG. 20 are also the operational amplifiers of A 1 to A 3 in FIG. 23.
  • the photoelectric conversion elements in the other columns i.e., the photoelectric conversion elements in the second column, the sixth column, the tenth column, . . . , and the third column, the seventh column, the eleventh column, . . . , and the fourth column, the eighth column, the twelfth column, . . .
  • VSC 2 , VSC 3 , VSC 4 corresponding to the respective columns are in the “Lo” state (where the D electrodes are biased to VS) and the signals of CRES 2 , CRES 3 , CRES 4 repeat the normal reset operation (in the same manner as the CRES signal of FIG. 4).
  • VSC 1 is transitioned from the “Hi” state to the “Lo” state and the CRES 1 signal is maintained in the “Hi” state.
  • the shift register SR 1 is operated normally from G 1 to GN.
  • the D electrodes of the all photoelectric conversion elements corresponding to the first column, the fifth column, the ninth column, . . . , that is, the (4 ⁇ 1+1) columns (1: integers not less than 0) are biased to the reading power supply VS, while the G electrodes thereof are kept in the state of the GND potential. Namely, the operation mode is shifted into the photoelectric conversion mode.
  • the photoelectric conversion elements in the other columns i.e., the photoelectric conversion elements in the second column, the sixth column, the tenth column, . . . , and the third column, the seventh column, the eleventh column, . . . , and the fourth column, the eighth column, the twelfth column, . . . , are in the state of the reading operation performed by the reading circuit section, because VSC 2 , VSC 3 , VSC 4 corresponding to the respective columns are in the “Lo” state (the D electrodes are biased to VS) and the signals of CRES 2 , CRES 3 , CRES 4 repeat the normal reset operation (in the same manner as the CRES signal of FIG. 4).
  • the photoelectric conversion elements in the three groups under the two consecutive reading operations output information of the dark state in the first frame and output information of the state of exposure to the light in the next frame.
  • correction can be made for the information of the dark state (the fixed pattern noise: FPN) by subtraction thereof in the digital process circuit after the A/D conversion circuit section of later stage. If data of photoelectric conversion elements in the columns under refresh is interpolated with data of photoelectric conversion elements under the reading operation in the adjacent columns, image data continuous in time series can be attained in the moving-picture mode.
  • the present invention can provide the photoelectric conversion apparatus that can reduce the reading scanning time and can enable high-speed reading and the system having the apparatus.
  • the present invention can provide the photoelectric conversion apparatus that can perform reading of signal of high S/N with little occurrence of thermal noise (KTC noise) and the system having the apparatus.
  • KTC noise thermal noise
  • the present invention can provide the photoelectric conversion apparatus that can obtain good image information without density unevenness and without unnecessary stripes, decreased in the fixed pattern noise, and the system having the apparatus.
  • the present invention can provide the photoelectric conversion apparatus that can obtain the image information excellent in tone level and the system having the apparatus.
  • the present invention can provide the photoelectric conversion apparatus that can easily compensate for unevenness of characteristics caused by the manufacturing dispersion of photoelectric conversion element or the like and that can promote further reduction of cost and the system having the apparatus.
  • the amplified output signals from the matrix signal lines of each photoelectric conversion circuit section are transferred once to the reading capacitors by the transfer switches and thereafter are successively switched by the reading switches, whereby the reading scanning time for one row can be decreased greatly as compared with that in the conventional apparatus.
  • the present invention can provide the photoelectric conversion apparatus and system permitting high-speed reading.
  • the first-stage analog operational amplifiers in the reading circuit section have low-noise performance, whereby the obtained outputs become unlikely to be affected by the KTC noise occurring in the photoelectric conversion circuit section.
  • the present invention can provide the photoelectric conversion apparatus and system with high S/N. Also, by connecting the capacitor elements for letting only the AC components pass in series with the output terminals of the foregoing analog operational amplifiers and locating the reset switches for DC restoration of the capacitor elements, a drop of S/N due to the KTC noise occurring upon reset of the photoelectric conversion circuit section can be suppressed, the photoelectric conversion apparatus and system with high S/N can be provided, and high-quality images without roughness can be obtained.
  • the present invention by having the function to reduce the consumption current of the OP amps used in the reading circuit section in the so-called standby state where the reading operation is not carried out, heat generation of IC can be restricted and the dark current of the switching elements in the photoelectric conversion circuit section upon operation can be decreased. Namely, the present invention decreases the fixed pattern noise of the photoelectric conversion apparatus, thereby obtaining excellent images without density unevenness in the plane and without stripes.
  • N (N:2 or more) operational amplifiers for amplifying the signal from the reading circuit section are provided, N A/D converters of M bits are provided, the ratio of amplification factors G 1 , G 2 , . . . , GN of the N operational amplifiers is set to G 1 :G 2 : . . . :GN 2 0 :2 1 : . . .
  • outputs from the N operational amplifiers are input to the N A/D converters, respectively, an output from one A/D converter out of the N A/D converters is selected in accordance with the output level of the analog signal from the reading circuit section, and it is output as a digital value of (N+M ⁇ 1) bits, whereby the photoelectric conversion signal can be A/D-converted in high resolution and at high speed.
  • the present invention can obtain image data of high tone level.
  • the photoelectric conversion apparatus of the present invention may also be suitably applied to a system such as the high-performance medical X-ray image pickup apparatus.
  • the photoelectric conversion elements and switching elements in the photoelectric conversion circuit section are made of the amorphous silicon semiconductor material, whereby the large-area photoelectric conversion apparatus can be provided cheaply by the easy processes.
  • the function capable of controlling the amplification factors of the analog operational amplifiers in the matrix signal wires in the reading circuit section by the signal from the outside it is easy to compensate for the gain dispersion due to the film thickness dispersion on fabrication of amorphous silicon semiconductor thin film, which can promote reduction of cost of apparatus.
  • the photoelectric conversion apparatus of the present invention is very excellent in respect of the speed, S/N, tone level, and cost, can meet the demand for “digitization of X-ray image information” strongly desired in the medical and industrial fields these years, and can improve the diagnostic efficiency in the hospitals not only in Japan going into the aging society, but also in the whole world, and the examination efficiency of buildings and the other various members and dealing efficiency after examination.

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US20120206608A1 (en) 2012-08-16
US20100054407A1 (en) 2010-03-04
DE69723136D1 (de) 2003-08-07
US7643077B2 (en) 2010-01-05
EP0796000B1 (en) 2003-07-02
US7440017B2 (en) 2008-10-21
KR970067953A (ko) 1997-10-13
DE69723136T2 (de) 2004-04-22
US20070115379A1 (en) 2007-05-24
US8179469B2 (en) 2012-05-15
US20040027472A1 (en) 2004-02-12
US8488037B2 (en) 2013-07-16
JP4035194B2 (ja) 2008-01-16
HK1002577A1 (en) 1998-09-04
EP0796000A3 (en) 1998-03-18
KR100266534B1 (ko) 2000-09-15
EP0796000A2 (en) 1997-09-17
JPH09307698A (ja) 1997-11-28

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