JP4021090B2 - Photoelectric conversion device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes an optical sensor that receives light carrying image information and converts the light into an electrical signal, and an amplifier that amplifies the electrical signal input from the optical sensor via an input-side signal line. It relates to a photoelectric conversion device.
[0002]
[Prior art]
Conventionally, a photoelectric conversion device comprising a photomultiplier tube that receives light carrying image information and converts the light into an electric signal, and an amplifier that amplifies the electric signal input from the photomultiplier tube It has been known.
[0003]
Such a photoelectric conversion device records, for example, subject image information carried by the radiation on the stimulable phosphor sheet by causing the radiation that has passed through the subject such as a human body to enter the stimulable phosphor sheet. The stimulable phosphor sheet is scanned with excitation light such as laser light to produce stimulated emission light, and this stimulated emission light is photoelectrically converted by a photomultiplier tube to produce an electrical signal (image signal). A radiographic image information recording / reading / reproducing system for amplifying the electric signal with an amplifier and applying an appropriate signal processing to the electric signal, and then recording it on an appropriate recording medium or outputting and displaying it as a visible image by a display means such as a CRT. Is conventionally used.
[0004]
[Problems to be solved by the invention]
The photomultiplier tube is affected by the surrounding electromagnetic field, causing a change in the multiplication factor during photoelectric conversion, generating noise at the output, and the output current of the photomultiplier tube is very small. It is easy to receive. And since the photomultiplier tube has such characteristics, in the photoelectric conversion device using the photomultiplier tube for the light carrying the image information as described above, the electromagnetic wave noise in the photomultiplier tube It is necessary to take measures to improve and improve immunity (electromagnetic noise resistance).
[0005]
As a countermeasure against such electromagnetic wave noise, for example, a conventional method of strengthening the magnetic shield of a photomultiplier tube and electromagnetic shielding can be considered, but the photomultiplier tube has a photocathode (a surface on which light is incident). Since it cannot be shielded to the light incident optical path, sufficient shielding is difficult, or the entire device including the photomultiplier tube can be shielded, but in that case, the cost is increased. For this reason, there are many problems in avoiding and reducing the influence of electromagnetic noise by the electromagnetic shield of the photomultiplier tube.
[0006]
The above problem is not limited to the one using a photomultiplier tube, and similarly exists in a photoelectric conversion device using a photosensor that receives light carrying image information and converts the light into an electric signal.
[0007]
In view of the above circumstances, an object of the present invention is to provide a photoelectric conversion device that can easily and inexpensively solve the problem of electromagnetic noise in an optical sensor without electromagnetically shielding the optical sensor such as a photomultiplier tube. There is.
[0008]
[Means for Solving the Problems]
The photoelectric conversion device according to the present invention achieves the above object,
Photoelectric conversion device comprising: an optical sensor that receives light carrying image information and converts the light into an electrical signal; and an amplifier that amplifies the electrical signal input from the optical sensor via an input-side signal line An impedance member whose impedance increases with an increase in frequency of a signal transmitted through the signal line is provided on the input side signal line between the optical sensor and the amplifier.
[0009]
In the photoelectric conversion device, an electromagnetic shield can be applied to at least a portion of the amplifier that converts a minute current into a voltage.
[0010]
In the photoelectric conversion device, the impedance member can be disposed at a boundary of the electromagnetic shield.
[0011]
Further, a log amplifier can be used as the amplifier, and a photomultiplier tube can be used as the photosensor.
[0012]
【The invention's effect】
The present invention is intended for photoelectric conversion of light carrying an image signal, and the electromagnetic wave noise component usually has a higher frequency than the image signal, and therefore even after the noise component is superimposed on the image signal. It is possible to reduce noise components satisfactorily by the impedance member.
[0013]
The photoelectric conversion device according to the present invention has been made by paying attention to the above points, and with the increase in the frequency of the signal transmitted through the signal line to the input side signal line between the optical sensor and the amplifier. Therefore, even if noise is generated due to fluctuations in the electromagnetic field in the optical sensor and superimposed on the image signal, the noise component can be effectively reduced by the impedance member. An image signal with less noise can be output from the amplifier.
[0014]
In particular, noise generated in the optical sensor due to electromagnetic noise is reduced by causing the impedance member to act on the image signal output from the photomultiplier instead of electromagnetically shielding the optical sensor. Noise can be reduced at low cost. In order to finally obtain an image signal with reduced noise caused by electromagnetic noise, an impedance member can be applied to the output from the amplifier, but the amplifier is a non-linear circuit such as a log amplifier. In this case, it is difficult to remove only the noise component after the amplifier. In the present invention, since the impedance member is made to act before input to the amplifier in particular, it is more effective than the case where the impedance member is made to act on the output from the amplifier, that is, the noise component is also amplified. In particular, the noise component can be reduced.
[0015]
In the photoelectric conversion device of the present invention, when an electromagnetic shield is applied to at least a portion of the amplifier that converts a minute current into a voltage, the noise caused by the electromagnetic wave noise in the optical sensor is reduced and the electromagnetic wave noise in the amplifier portion is reduced. The influence can be suppressed, and an image signal with less influence of electromagnetic noise can be output from the amplifier.
[0016]
In the photoelectric conversion device of the present invention, when the impedance member is further disposed at the boundary of the electromagnetic shield, the impedance member is disposed at a predetermined distance from the electromagnetic shield at a predetermined interval. Thus, electromagnetic noise generated between the impedance member and the electromagnetic shield can be prevented from being input to the amplifier together with the image signal, and as a result, the noise component of the image signal output from the amplifier is reduced. be able to.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a schematic view showing a radiological image information reading apparatus provided with a first embodiment of the photoelectric conversion apparatus of the present invention. This radiation image information reading apparatus is used in a radiation image information recording / reading / reproducing system using the above-described stimulable phosphor sheet.
[0019]
In this radiographic image information reading apparatus, as shown in the figure, the stimulable phosphor sheet 5 on which the X-ray image information of the subject is recorded is set at the reading position shown in the figure and is driven by a driving means (not shown). Is conveyed (sub-scanned) in the arrow Y direction by the sheet conveying means 15. On the other hand, the light beam 17 emitted from the laser light source 16 is reflected and deflected by a rotating polygon mirror 19 driven by a motor 18 and rotated at a high speed in the direction of arrow Z, and after passing through a focusing lens 20 such as an fθ lens, the light path 17 Is incident on the stimulable phosphor sheet 5 and is subjected to main scanning in an arrow X direction substantially perpendicular to the sub-scanning direction (arrow Y direction).
[0020]
From the portion of the stimulable phosphor sheet 5 irradiated with the light beam 17, the amount of stimulated emission light 22 corresponding to the stored and recorded X-ray image information is emitted. The photomultiplier tube (photomultiplier) 24, which is an example of an optical sensor, is photoelectrically detected. The light guide 23 is made by molding a light guide material such as an acrylic plate, and is arranged such that a linear incident end face 23a extends along the main scanning line on the stimulable phosphor sheet 5. The light receiving surface of the photomultiplier tube 24 is coupled to the emission end surface 23b formed in an annular shape. The stimulated emission light 22 that has entered the light guide 23 from the incident end face 23a repeatedly undergoes total internal reflection in the light guide 23, is emitted from the emission end face 23b, and is received by the photomultiplier tube 24. Is converted into an electric signal (image signal) by the photomultiplier tube 24.
[0021]
The analog signal S output from the photomultiplier tube 24 is logarithmically amplified by a log amplifier 25 which is an example of an amplifier, and then input to an A / D converter (not shown) and sampled to obtain a digital image signal. The obtained digital image signal is appropriately subjected to image processing and then recorded on a recording medium or output and displayed as a visible image by a display means such as a CRT.
[0022]
The photoelectric conversion apparatus according to the first embodiment including the photomultiplier tube 24 and the log amplifier 25 has a photomultiplier tube 24 and a log for inputting the image signal output from the photomultiplier tube 24 to the log amplifier 25. The input side signal line 26 connected to the amplifier 25 is provided with an impedance member 31 whose impedance increases as the frequency of the signal transmitted through the signal line 26 increases.
[0023]
In the first embodiment, since the impedance member 31 is disposed between the photomultiplier tube 24 and the log amplifier 25 as described above, noise due to electromagnetic wave noise is generated in the photomultiplier tube 24, which is imaged. Even if superimposed on the signal, the noise component can be effectively reduced by the impedance member 31, and an image signal with less noise can be output from the log amplifier 25.
[0024]
In particular, noise generated in the photomultiplier tube 24 is reduced by causing the impedance member 31 to act on the image signal output from the photomultiplier tube 24, instead of electromagnetically shielding the photomultiplier tube 24. Therefore, noise can be reduced more easily and inexpensively. Further, in order to finally obtain an image signal in which noise caused by electromagnetic wave noise is reduced, the impedance member 31 can be made to act on the output from the log amplifier 25. Since the impedance member 31 is made to act before input, even a non-linear circuit such as the log amplifier 25 can easily remove only noise components.
[0025]
Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown in the figure, in addition to the arrangement of the impedance member 31 in the first embodiment, the log amplifier 25 is further electromagnetically shielded by covering the log amplifier 25 with an electromagnetic shield member 35, and the impedance The member 31 is disposed at the boundary of the electromagnetic shield.
[0026]
In the second embodiment, since the log amplifier 25 is further provided with an electromagnetic shield, the influence of the electromagnetic wave noise in the log amplifier 25 can be suppressed as well as the influence of the electromagnetic wave noise in the photomultiplier tube 24 can be reduced. 25 can output an image signal with less noise. Further, since the impedance member 31 is disposed at the boundary of the electromagnetic shield, the impedance member 31 and the electromagnetic shield are compared with a case where the impedance member 31 is disposed at a predetermined interval on the photomultiplier tube 24 side than the electromagnetic shield. It is possible to prevent electromagnetic noise generated between them from being input to the log amplifier 25 together with the image signal, and as a result, the noise component of the image signal output from the log amplifier 25 can be reduced.
[0027]
Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown in the drawing, in addition to the arrangement of the impedance member 31 and the electromagnetic shield of the log amplifier 25 in the second embodiment, an image signal output from the log amplifier 25 connected to the log amplifier 25 is also transmitted. Also on the output side signal line 27 to be transmitted, an impedance member 32 similar to the impedance member 31 is disposed at the boundary of the electromagnetic shield in the same manner as the impedance member 31.
[0028]
In the third embodiment, since the impedance member 32 is also provided on the output signal line 27 of the log amplifier 25, the influence of electromagnetic wave noise on the image signal output from the log amplifier 25 can be further reduced. At the same time, electromagnetic noise that tends to flow into the log amplifier 25 via the output-side signal line 27 can be blocked.
[0029]
Next, a fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown in the figure, in addition to the arrangement of the impedance members 31 and 33 and the electromagnetic shield of the log amplifier 25 in the third embodiment, the log amplifier 25 is further connected to the positive (+) power source. The negative power supply line 29 that connects the power supply line 28 and the log amplifier 25 to the negative (−) power supply also has impedance members 33 and 34 that are the same as the impedance member 31 in the same manner as the impedance member 31 in the boundary of the electromagnetic shield. It is arrange | positioned.
[0030]
In the fourth embodiment, since the impedance members 33 and 34 are also provided on the positive power supply line 28 and the negative power supply line 29 of the log amplifier 25, the influence of electromagnetic wave noise on the image signal output from the log amplifier 25 is achieved. Can be further reduced.
[0031]
For example, a cylindrical ferrite core is used as the impedance members 31, 32, 33, and 34 in each of the above-described embodiments, and the signal lines 26 and 27 or the power supply lines 28 and 29 are inserted into the center hole of the ferrite core. Can be arranged. Of course, if the same effect as the case is produced, other appropriate impedance members such as feedthrough capacitors can be arranged by other appropriate methods.
[0032]
In each of the above-described embodiments, a conventionally known magnetic shield can be applied to the photomultiplier tube 24 as necessary.
[0033]
Further, the electromagnetic shield in each of the above-described embodiments is performed by using a metal plate having an electromagnetic shielding action such as copper or permalloy as the electromagnetic shielding member 35, thereby covering the log amplifier 25 as a whole. Electromagnetic shielding may be performed by any other method. Further, the entire log amplifier 25 does not necessarily need to be electromagnetically shielded. It is sufficient if electromagnetic shielding can be applied to at least a portion of the log amplifier 25 that converts a minute current into a voltage.
[0034]
In each of the above-described embodiments, the impedance members 31, 32, 33, and 34 are all disposed at the boundary of the electromagnetic shield. However, the impedance members 31, 32, 33, and 34 are not necessarily disposed at the boundary of the electromagnetic shield. However, it may be disposed at a position away from the boundary of the electromagnetic shield by a predetermined distance in the inner or outer direction of the electromagnetic shield. For example, the impedance member 31 can be disposed at a position a predetermined distance away from the boundary of the electromagnetic shield on the photomultiplier tube 24 side.
[0035]
Furthermore, in each of the above embodiments, a photomultiplier tube was used as an example of a photosensor, and a log amp was used as an example of an amplifier. However, the photosensor and the amplifier of the present invention are not limited thereto, Other types of optical sensors and amplifiers may be used.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram illustrating a first embodiment according to the present invention. FIG. 2 is a conceptual diagram illustrating a second embodiment according to the present invention. FIG. 3 is a conceptual diagram illustrating a third embodiment according to the present invention. FIG. 4 is a conceptual diagram showing a fourth embodiment according to the present invention.
24 Light sensor
25 Amplifier
26 Input signal line
27 Output signal line
28 Positive power line
29 Negative power line
31, 32, 33, 34 Impedance members
35 Electromagnetic shielding material

Claims (2)

It comprises a photomultiplier tube which converts the light into an electric signal by receiving the light carrying the image information, and an amplifier for amplifying the electric signal inputted via the input-side signal line from the photomultiplier tube A photoelectric conversion device comprising:
An input side signal line between the photomultiplier tube and the amplifier is provided with an impedance member whose impedance increases as the frequency of a signal transmitted through the signal line increases,
An electromagnetic shield is applied to at least a portion of the amplifier that converts a minute current into a voltage,
A photoelectric conversion device, wherein the impedance member is disposed at a boundary of the electromagnetic shield.   The photoelectric conversion device according to claim 1, wherein the amplifier is a log amplifier.

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