Abstract:
There is disclosed a radiation image taking apparatus including a radiation detecting unit which includes a plurality of photo-electric conversion elements and converts radiation into an electrical signal, a plate-like support member which supports the radiation detecting unit, an analog circuit unit having at least one of functions of controlling the radiation detecting unit, receiving an analog signal from the radiation detecting unit, processing the analog signal, and converting the analog signal into a digital signal, a digital circuit unit having at least one of functions of controlling at least one of other units and communicating with a unit outside the apparatus, and a power circuit unit for supplying power to at least one of other units, wherein the analog circuit unit, the digital circuit unit, and the power circuit unit are formed on separate circuit boards, respectively, and the analog circuit unit and the digital circuit unit are arranged in the opposite side of the radiation detecting unit in respect to the support member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a radiation image taking apparatus using photo-electric conversion elements.  
           [0003]    2. Related Background Art  
           [0004]    Conventionally, a read apparatus in a facsimile apparatus, copying machine, scanner, radiographic apparatus, or the like uses a system constituted by a combination of a reduction optical system and a CCD sensor.  
           [0005]    Recently, with the development of photoelectric conversion semiconductor materials typified by hydrogenated amorphous silicon (a-Si), a contact sensor has been developed, which is obtained by forming a photo-electric conversion element and a signal processing unit on a large-area board and designed to perform read operation by using an optical system obtaining an image equal in size to an information source.  
           [0006]    Since a-Si, in particular, can be used not only as a photo-electric conversion element material but also as a semiconductor material for TFTs (Thin-Film Transistors), a photo-electric conversion semiconductor layer and a semiconductor layer of a TFT can be simultaneously formed.  
           [0007]    [0007]FIG. 5 is a sectional view of a conventional electronic cassette. An electronic cassette  1  used for radiography has a support member  3  placed in an outer cover  2 . A radiation detecting unit  4  formed by sequentially stacking pixels  4   b  arranged in a matrix pattern, each constituted by a photo-electric conversion element and signal transfer element (the above TFT or the like) for converting visible light into an electrical signal and transferring the signal to an external circuit, and a scintillator  4   c  for converting radiation or the like into visible light is supported on a board  4   a  on the support member  3 . An electric circuit board  5  on which an electronic component for processing an electrical signal obtained by photo-electric conversion by the radiation detecting unit  4  and the like are mounted is placed on the lower surface of the support member  3 . This electric circuit board  5  is connected to each pixel  4   b  through an interconnection  6 . In addition, a power supply circuit board  8  is connected to the electric circuit board  5  through a power supply interconnection  7 .  
           [0008]    The circuits mounted on the electric circuit board  5  include a photo-electric conversion element driving and reading circuit for generating a potential to be applied into the radiation detecting unit  4  and performing signal processing of receiving a signal from a photo-electric conversion element and converting it into serial data, a signal transfer element driving circuit for driving the signal transfer element, an A/D conversion circuit for converting the analog signal detected by the radiation detecting unit  4  and processed by the photo-electric conversion element driving and reading circuit into a digital signal, and an I/F (interface) circuit for generating a control signal for controlling each circuit and transmitting/receiving a signal for controlling the driving operation of the photo-electric conversion unit and aforesaid digital signal to/from an external unit.  
           [0009]    With these circuits, this apparatus performs control on the radiation detecting unit  4 , a read of a detection signal, conversion to a digital signal, and data transfer to an external digital processor.  
           [0010]    The power supply circuit board  8  is constituted by a battery and DC/DC power supply circuit. Alternatively, a predetermined voltage may be externally applied to the radiation image taking apparatus through a power cable (not shown), and different voltages may be generated by the DC/DC power supply.  
           [0011]    In the above prior art, however, the pixel  4   b  handles an electrical signal with a very low level, and hence is susceptible to electromagnetic noise. If the pixel  4   b  is affected by this electromagnetic noise, noise is superimposed on a taken image, resulting in a deterioration in image quality.  
           [0012]    Switching noise produced from the power supply circuit board  8  incorporated in the outer cover  2  is a big factor that causes electromagnetic noise. Another factor is noise produced from an electric circuit, especially a digital circuit or the like.  
           [0013]    In addition, the power supply interconnection  7  that connects the power supply circuit board  8  to the respective circuits and the interconnection  6  for distributing control signals for controlling the respective circuits to them also become similar noise sources.  
           [0014]    Assume that circuits are integrally formed on one board due to limitations on mount spaces for the circuits and the like. In this case, an analog circuit (e.g., a photo-electric conversion element driving and reading circuit) that handles weak analog signals detected by the radiation detecting unit  4  and a digital circuit such as an I/F circuit serving to generate signals for controlling the respective circuits are mounted on the same board. In addition, a circuit for reading/scanning the pixels  4   b  and a circuit for transmitting/receiving signals which are asynchronous with the scanning (frame period) are formed on the same board.  
           [0015]    Stray capacitances, in particular, between circuits through an insulating layer of the electric circuit board  5 , which is made of epoxy resin or the like and has a large dielectric constant, becomes a load to cause noise interference between the circuits. As a consequence, noise originated from a digital signal is superimposed on an analog signal, resulting in a deterioration in image quality.  
           [0016]    In addition, although a digital circuit is more resistant to noise than an analog circuit, an increase in the number of digital circuits around a digital circuit is not preferred because of an increase of the number of noise sources.  
         SUMMARY OF THE INVENTION  
         [0017]    It is an object of the present invention to solve the above problem and provide a radiation image taking apparatus which can obtain a high-quality image with reduced influence of noise.  
           [0018]    According to the present invention, there foregoing object is attained by providing a radiation image taking apparatus comprises a radiation detecting unit which includes a plurality of photoelectric conversion elements and converts radiation into an electrical signal;  
           [0019]    a plate-like support member which supports the radiation detecting unit,  
           [0020]    an analog circuit unit having at least one of functions of controlling the radiation detecting unit, receiving an analog signal from the radiation detecting unit, processing the analog signal, and converting the analog signal into a digital signal,  
           [0021]    a digital circuit unit having at least one of functions of controlling at least one of other units and communicating with a unit outside the apparatus, and  
           [0022]    a power circuit unit for supplying electric power to at least one of other units,  
           [0023]    wherein the analog circuit unit, the digital circuit unit, and the power circuit unit are formed on separate circuit boards, respectively, and the analog circuit unit and the digital circuit unit are arranged in the opposite side of the radiation detecting unit in respect to the support member.  
           [0024]    According to another aspect of the present invention, there foregoing object is attained by providing the power circuit unit is placed outside a region formed from all normals of a supporting surface of the support member.  
           [0025]    According to another aspect of the present invention, there foregoing object is attained by providing a shield wall having a noise shield function is provided for between at least two of the radiation detecting unit, the analog circuit unit, the digital circuit unit, and the power circuit unit.  
           [0026]    According to another aspect of the present invention, there foregoing object is attained by providing the shield wall is provided for by the support member.  
           [0027]    According to another aspect of the present invention, there foregoing object is attained by providing the shield wall is provided for by an outer cover of the apparatus.  
           [0028]    According to another aspect of the present invention, there foregoing object is attained by providing the digital circuit unit is placed adjacent to the power circuit unit.  
           [0029]    According to another aspect of the present invention, there foregoing object is attained by providing the digital circuit unit includes a first digital circuit unit for controlling a read of an analog signal from the radiation detecting unit and a second digital circuit unit different from the first digital circuit unit, and the power supply circuit unit, the first digital circuit unit, and the second digital circuit unit are formed on separate circuit boards, respectively, and arranged in the order named along a predetermined direction along the supporting surface of the support member.  
           [0030]    According to another aspect of the present invention, the analog circuit unit includes a first analog circuit unit for performing at least one of processing of the analog signal and conversion from the analog signal into a digital signal, and the power circuit unit, the first digital circuit unit, the second digital circuit unit, and the first analog circuit unit are formed on separate circuit boards, respectively, and arranged in the order named along a predetermined direction along the supporting surface of the support member.  
           [0031]    According to another aspect of the present invention, there foregoing object is attained by providing a detection surface of the radiation detecting unit is substantially rectangular, the analog circuit unit includes a second analog circuit which receives an analog signal from the radiation detecting unit and is formed on a circuit board different from other circuit units, the first digital circuit unit is placed along a first side of the detection surface, and the second analog circuit unit is placed along a second side of the detection surface which is perpendicular to the first side.  
           [0032]    According to another aspect of the present invention, there foregoing object is attained by providing the first digital circuit unit is divided into units, the first digital circuit units are respectively arranged along the first side of the detection surface and a third side opposing the first side, the second analog circuit unit is divided into units, and the second analog circuit units are respectively arranged along the second side of the detection surface and a fourth side opposing the second side.  
           [0033]    Other objects, features and advantages of the present invention will be apparent from the following descriptions taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the descriptions, serve to explain the principle of the invention.  
         [0035]    [0035]FIG. 1 is a sectional view of the first embodiment;  
         [0036]    [0036]FIG. 2 is a plan view of the first embodiment;  
         [0037]    [0037]FIG. 3 is a sectional view of the second embodiment;  
         [0038]    [0038]FIG. 4 is a plan view of the second embodiment; and  
         [0039]    [0039]FIG. 5 is a sectional view of the prior art.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    A preferred embodiments of the present invention will be described in detail in accordance with the accompanying drawings of FIGS.  1  to  4 . In the following embodiments, a medical X-ray image taking apparatus for radiographing the human body by using X-rays will be described as an example of the radiation image taking apparatus according to the present invention. However, the present invention can also be applied to an X-ray image taking apparatus for taking an image of another kind of object or an image taking apparatus using another kind of radiation.  
         [0041]    The present invention will be described in detail with reference to the embodiments shown in FIGS.  1  to  4 .  
         [0042]    (First Embodiment)  
         [0043]    [0043]FIG. 1 is a sectional view of a radiation image taking apparatus according to the first embodiment. FIG. 2 is a plan view of the radiation image taking apparatus seen through the outer cover from the lower surface side. A radiation image taking apparatus  11  has a plate-like support member  13  in an outer cover  12 . These components are made of a metal such as aluminum or magnesium. The outer cover  12  and support member  13  are electrically connected to each other by fitting, with screws, or the like in an assembly process, and grounded at proper portions.  
         [0044]    A board  14   a , an image detection element  14   b  (forming a detection surface for a visible light image, i.e., a radiation image) formed by arranging photo-electric conversion elements and signal transfer elements in a matrix pattern which convert visible light into electrical signals and transfer the signals to an external circuit, and a scintillator  14   c  for converting X-rays into visible light are sequentially stacked on the support member  13 , thus forming a radiation detecting unit  14 . Note that the radiation detecting unit is not limited to such an arrangement. For example, a direct conversion type radiation detecting unit may be used, which directly converts radiation into an electrical signal by using a photo-electric conversion element without the mediacy of a scintillator.  
         [0045]    On the lower surface of the support member  13 , the following boards are separately mounted: photoelectric conversion element driving and reading circuit boards  15   a  and  15   b  on which photo-electric conversion element driving and reading circuits for generating potentials to be applied into the photoelectric conversion elements and performing signal processing of receiving signals from the photoelectric conversion elements and converting them into serial data are formed and electric components, connectors, and the like (not shown) are mounted; signal transfer element driving circuit boards  16   a  and  16   b  on which signal transfer element driving circuits for driving the signal transfer elements of the radiation detecting unit  14  are formed; and an A/D conversion (analog-digital conversion) circuit board  17  for converting the analog signals detected by the photo-electric conversion elements and processed by the photo-electric conversion element driving and reading circuits into digital signals. Since the photo-electric conversion element driving and reading circuit boards  15   a  and  15   b  and signal transfer element driving circuit boards  16   a  and  16   b , in particular, are directly connected to the radiation detecting unit  14  for transmitting/receiving weak signals, noise must be minimized. Therefore, these circuit boards are preferably positioned as near to an interconnection portion (not shown) formed on the outer periphery of the board  14   a  as possible. As shown in FIG. 1, these boards are arranged near the outer periphery of the board  14   a  (the outer periphery of the lower surface of the support member  13 ).  
         [0046]    An I/F circuit board  18  is also mounted on the lower surface of the support member  13 . An I/F circuit for generating control signals for controlling the respective circuits on the photoelectric conversion element driving and reading circuit boards  15   a  and  15   b , signal transfer element driving circuit boards  16   a  and  16   b  and A/D conversion circuit board  17 , and transmitting/receiving control signals for controlling the driving operation of the radiation detecting unit  14  and digital image signals detected by the photo-electric conversion elements to/from an external unit is formed on the I/F circuit board  18 . External control signals are input to the I/F circuit board  18  through a cable or the like. The I/F circuit board  18  performs control on the operation and detection timing of the radiation detecting unit  14 , data transfer to an external digital processor, and the like in accordance with the inputs.  
         [0047]    The respective circuit boards and the radiation detecting unit  14  are connected to each other through connectors, solder lands, and the like mounted on a circuit by an interconnection means (not shown) such as a flexible board made of polyimide resin or the like.  
         [0048]    Electric components, connectors, and the like are mounted on a power supply circuit board  19 . The power supply circuit board  19  is placed outside the support member  13  so as not to overlap the radiation detecting unit  14  when viewed from the direction of the normal to the radiation detecting unit  14 . Power required for operation is supplied to the power supply circuit board  19  from outside the radiation image taking apparatus  11  through a cable, connectors, and the like. A DC/DC converter in the power supply circuit board  19  generates a desired potential used inside the radiation image taking apparatus  11 .  
         [0049]    In addition, the radiation detecting unit  14  and driving and reading circuit boards  15   a  and  15   b  which transmit weak signals must be separated from the power supply circuit board  19  which is the largest noise source as far as possible or the area thereof adjacent to the power supply circuit board  19  must be minimized. For this reason, the power supply circuit board  19  is placed on a side of the radiation detecting unit  14  to minimize the influence of noise from the power supply circuit board  19 .  
         [0050]    Note that the I/F circuit board  18  is formed from a pure digital circuit and has a data transfer circuit for transferring digitized detection signal. Since this data transfer circuit is connected to an external unit, the I/F circuit board  18  is placed on the lower surface of the support member  13  so as to be adjacent to the power supply circuit board  19  which receives external power, thereby minimizing external interconnections (wiring, not shown).  
         [0051]    The power supplies generated by the power supply circuit board  19  are connected to the A/D conversion circuit board  17 . Necessary power is distributed to the I/F circuit board  18 , driving and reading circuit boards  15   a  and  15   b , and the like through the A/D conversion circuit board  17 . Note that the interconnections from the power supply circuit board  19  are routed to the A/D conversion circuit board  17  over the driving circuit board  16   a  and I/F circuit board  18  which handle only digital signals and have relatively high noise resistance.  
         [0052]    On the other hand, control signals for controlling the respective circuit boards are all generated by a memory or timing generator on the I/F circuit board  18  on the basis of the supply of power and external control signals, and are sent to the A/D conversion circuit board  17  through connection means arranged on adjacent portions of the two boards. In addition, control signals required for the operation of the radiation detecting unit  14  and reading of detection signals are supplied from the A/D conversion circuit board  17  to the driving and reading circuit boards  15   a  and  15   b  through connection means arranged on adjacent portions of the two boards.  
         [0053]    Note that detection signals from the photoelectric conversion elements of the image detection element  14   b  of the radiation detecting unit  14  are distributed to the driving and reading circuit boards  15   a  and  15   b  arranged vertically in FIG. 2, and lines for controlling the signal transfer elements are distributed to the driving circuit boards  16   a  and  16   b  arranged laterally in FIG. 2. This makes it possible to decrease the number of connection terminals per side of the board  14   a  and hence to prevent an increase in the size of the board  14   a . In addition, the number of shared pixels per line can be decreased, and the driving and processing speeds can be increased.  
         [0054]    In addition, since the A/D conversion circuit board  17  needs to receive detected analog signals from the driving and reading circuit boards  15   a  and  15   b , the A/D conversion circuit board  17  and I/F circuit board  18  are separately arranged in the lateral direction, and the A/D conversion circuit board  17  is located near the two driving and reading circuit boards  15   a  and  15   b . This minimizes the routing of interconnections that connect the two circuit boards to each other.  
         [0055]    As described above, since the driving and reading circuit boards  15   a  and  15   b , driving circuit boards  16   a  and  16   b , A/D conversion circuit board  17 , I/F circuit board  18 , and power supply circuit board  19  are separately formed on the respective circuit boards, only necessary power and control signals can be distributed to the respective circuit boards, thereby minimizing noise sources for the respective circuits. In addition, since the respective circuit boards are separated from each other, the stray capacitances between the respective circuit interconnections become small loads through air. This makes it possible to effectively suppress noise interference between the respective circuits. In addition, since the number of intermediate conducive layers required for each circuit board can be determined, even if many intermediate conductive layers are required for some of circuit boards, there is no need to match the numbers of layers on the remaining circuit boards with the above number of layers. Therefore, the total cost required for the circuit boards can be reduced.  
         [0056]    In addition, as in this embodiment, for example, interconnections for power from the power supply circuit board  19  and control signals from the I/F circuit board  18  are arranged so as not to be routed over the driving and reading circuit boards  15   a  and  15   b  and A/D conversion circuit board  17 , which handle analog signals, depending on the arrangement of the respective circuit boards, the interconnections between the respective circuit boards, and the interconnections between the respective circuit boards and radiation detecting unit  14 . This also makes it possible to minimize the influences of noise from noise sources through the interconnections.  
         [0057]    (Second Embodiment)  
         [0058]    [0058]FIG. 3 is a sectional view of a radiation image taking apparatus according to the second embodiment. FIG. 4 is a plan view of the radiation image taking apparatus seen through the outer cover from the lower surface side. Note that the same reference numerals as in the first embodiment denote the same parts in the second embodiment.  
         [0059]    As in the first embodiment, photo-electric conversion element driving and reading circuit boards  15   a  and  15   b , signal transfer element driving circuit boards  16   a  and  16   b , A/D conversion circuit board  17 , and I/F circuit board  18  are arranged on the lower surface of a support member  13  of a radiation image taking apparatus  21 . In addition, a power supply circuit board  19  is placed outside a radiation detecting unit  14  so as not to overlap. Furthermore, the arrangement of the respective circuit boards, the interconnections between the respective circuit boards, and the interconnections between the respective circuit boards and the radiation detecting unit  14  are the same as those in the first embodiment.  
         [0060]    In the radiation image taking apparatus  21  of this embodiment, shield walls  22   a  to  22   f  are arranged between the respective circuit boards to spatially shield (isolate) the respective circuit boards from each other. In addition, the radiation detecting unit  14  and the respective circuit boards are spatially shielded from each other by a shield wall  23  formed between an outer cover  12  and the support member  13 . The shield wall  22   a  that isolates the power supply circuit board  19  from the remaining circuit boards is made of the same material as that for the outer cover  12 . The shield walls  22   b  to  22   f  and  23  are made of the same material as that for the support member  13 . The shield wall  22   a , and the shield walls  22   b  to  22   f  and  23  are integrally formed with the outer cover  12  and support member  13 , respectively.  
         [0061]    In the second embodiment, the same effects as those of the first embodiment can be obtained. In addition, since the shield walls  22   a  to  22   f  and  23  made of the same material as that for the outer cover  12  and support member  13  are provided, the respective circuit boards are spatially shielded from each other by the outer cover  12 , support member  13 , and shield walls  22   a  to  22   f  and  23 , thereby reducing the influence of noise on the respective board circuits and radiation detecting unit  14 .  
         [0062]    In this embodiment, the outer cover  12  and support member  13  are made of a metal such as aluminum or magnesium. However, the present invention is not limited to this. For example, a member formed by plating a base made of a resin such as PC (polycarbonate) with a metal such as copper or the like can be used because it has a noise shield (mainly an electric field shield) effect. Alternatively, a member whose noise shield (mainly magnetic field shield) effect is improved by coating a resin base or the like with a magnetic powder can be used. Obviously, a member made of a material having high X-ray transmission and light shielding characteristics is used for a portion of the outer cover on which X-rays are incident.  
         [0063]    As has been described above, even if the respective members are arranged close to each other because of high-density packing for a reduction in size, the noise interferences between circuits can be reduced by forming the respective circuits on separate circuit boards. This makes it possible to obtain a low-noise, high-quality image. This arrangement is therefore effective in reducing the size and weight of an electronic cassette whose size and weight tend to increase as compared with a conventional film cassette housing a film.  
         [0064]    In addition, since the shield walls are integrally formed with the support member or outer cover between the respective circuit boards to spatially shield the respective circuit boards by at least one of the support member or outer cover, the noise interferences between the respective circuits can be further reduced. This makes it possible to obtain a low-noise, high-quality image.  
         [0065]    The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore to apprise the public of the scope of the present invention, the following claims are made.