JP2004134711A - Radiation solid state detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve S/N ratio of the signal outputted from a linear reading electrode in a radiation solid detector provided with the linear reading electrode and a linear auxiliary electrode. <P>SOLUTION: A charge amplifier 71 is connected with the linear reading electrode 26a of an electrostatic recording medium 20a, and the charge outputted from the linear reading electrode 26a is converted into voltage therein and outputted. A buffer amplifier 72 is provided to convert the potential of a non-inversion input terminal 73b in a processing amplifier 73 into low impedance and supply it to the linear auxiliary electrode 27a. The potential of an inversion input terminal 73a in the processing amplifier 73 becomes almost the same as that of an output terminal 77c of the buffer amplifier 72, so that the linear reading electrode 26a and the linear auxiliary electrode 27a are made almost the same in potential, and an electrostatic capacity between them is apparently made small. Therefore, an AC amplification rate in the charge amplifier 71 is reduced and that of noises superimposed upon the outputted charge from the linear reading electrode 26a is reduced. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation solid-state detector having a power storage unit that accumulates, as a latent image charge, an amount of charge corresponding to the dose of irradiated radiation or the amount of light emitted by excitation of the radiation.
[0002]
[Prior art]
Today, in radiography for medical diagnosis and the like, charges obtained by detecting radiation are temporarily stored as latent image charges in a power storage unit, and the stored latent image charges are converted into electrical signals representing radiation image information. Various types of radiation image information reading devices using a radiation solid-state detector (hereinafter also simply referred to as a detector) for outputting the same have been proposed. Various types of solid-state radiation detectors used in this apparatus have been proposed. From the viewpoint of a charge reading process for reading out the accumulated charges to the outside, reading light (electromagnetic waves for reading) is applied to the detector. ) And a TFT readout system that reads and reads out TFTs (thin film transistors).
[0003]
As a radiation solid-state detector of an optical readout system capable of achieving both high-speed readout response and efficient signal charge extraction, the applicant of the present application is a recording radiation or light emitted by excitation of the radiation (hereinafter referred to as the radiation solid-state detector). A first electrode that is transparent to the recording light), a photoconductive layer for recording that exhibits conductivity by receiving the recording light, and substantially insulated against charges having the same polarity as the charges charged in the first electrode A charge transport layer that acts as a body and acts as a conductor for charges of the same polarity and opposite polarity, and reading that exhibits conductivity by irradiation with reading light (reading electromagnetic waves). A photoconductive layer for recording and a second electrode that is transparent to reading light are stacked in this order, and image information is carried on a power storage unit formed at the interface between the photoconductive layer for recording and the charge transport layer. Signal charge (latent image charge) It proposes that a radiation solid-state detector (see Patent Document 1, Patent Document 2 and Patent Document 3).
[0004]
And in the said patent document 2 and patent document 3, while making the 2nd electrode transparent with respect to reading light into many linear reading electrodes, it is to the quantity of the latent image charge accumulate | stored in the electrical storage part. There has been proposed an electrostatic recording body in which a large number of linear auxiliary electrodes for outputting electrical signals of corresponding levels are provided alternately with the linear readout electrodes and in parallel with each other. Note that when the second electrode is configured as a linear readout electrode, the reading light can be transmitted between the linear readout electrodes, and thus the second electrode does not necessarily have transparency to the reading light.
[0005]
In this way, by providing a large number of linear auxiliary electrodes on the second electrode, a new capacitor is formed between the power storage unit and the linear auxiliary electrode, and the latent image charge accumulated in the power storage unit by the recording light and It is possible to charge the linear auxiliary electrode with the transport charge having the reverse polarity by charge rearrangement at the time of reading. Accordingly, the amount of the transport charge distributed to the capacitor formed between the linear readout electrode and the power storage unit via the readout photoconductive layer is set to be relatively larger than that in the case where the linear auxiliary electrode is not provided. As a result, the amount of signal charge that can be extracted from the detector to the outside is increased to improve the reading efficiency, and at the same time, both high-speed reading response and efficient signal charge extraction are achieved. Can be done. Usually, the charges read from the linear readout electrodes are converted into voltage signals by a charge-voltage conversion circuit such as a charge amplifier, then A / D converted, and stored as digital image data.
[0006]
[Patent Document 1]
JP 2000-105297 A
[0007]
[Patent Document 2]
JP 2000-284056 A
[0008]
[Patent Document 3]
JP 2000-284057 A
[0009]
[Problems to be solved by the invention]
By the way, the radiation solid detector is often a detector having the same size as the subject, and the linear readout electrode is a very long electrode, and its resistance value often exceeds several tens of kΩ. For this reason, the linear readout electrode easily generates thermal noise and easily picks up external noise.
[0010]
On the other hand, when the linear auxiliary electrode is arranged in parallel with the linear readout electrode, there may be a large capacitance Ci between the linear readout electrode and the linear auxiliary electrode. In general, at the time of signal readout, the linear readout electrode is grounded via an operational amplifier or the like, and the linear auxiliary electrode is also often grounded. However, from a microscopic viewpoint, the linear readout electrode and the linear readout electrode are often grounded. Since the potential between the auxiliary electrodes is not the same, the value of the capacitance Ci becomes a large value. The value varies somewhat depending on the structure of the electrode, but the capacitance Ci may be 100 pF or more. If the capacitance Ci is larger than the capacitance Cf of a capacitor used in a charge-voltage conversion circuit such as a charge amplifier connected to the linear readout electrode, the charge amplifier operates as an AC amplifier.
[0011]
That is, for a signal of frequency f, input impedance Zi, feedback loop impedance Zf, and gain G as an AC amplifier are obtained by the following equations.
[0012]
Zi = (2πf · Ci)^-1
Zf = (2πf · Cf)^-1
G = Zf / Zi = Ci / Cf
As can be seen from the above equation, when the capacitance Ci is larger than the capacitance Cf of the capacitor used for charge-voltage conversion of the charge amplifier, the charge amplifier operates as an AC amplifier having a constant gain regardless of the frequency. To do.
[0013]
The capacitance Cf of the capacitor used for charge-voltage conversion of the charge amplifier is determined based on the amount of charge generated per pixel and the full-scale voltage of the A / D converter connected to the charge amplifier, and is usually a few It is often set to pF or less. On the other hand, as described above, the capacitance Ci between the linear readout electrode and the linear auxiliary electrode may be 100 pF or more, and at the present time, as the definition of the linear electrode increases, it increases more and more. It's getting on.
[0014]
For this reason, if thermal noise or external noise is included in the signal read from the linear readout electrode, the thermal amplifier or external noise is amplified by the charge amplifier, and the signal output from the charge amplifier is output. There is a problem that the S / N ratio of the lowering.
[0015]
The present invention has been made in view of the above circumstances, and an object of the present invention is to improve S / N in a radiation solid state detector including a linear readout electrode and a linear auxiliary electrode.
[0016]
[Means for Solving the Problems]
A radiation solid state detector according to the present invention includes a power storage unit that records image information as an electrostatic latent image, and
A number of linear readout electrodes that output a charge corresponding to the electrostatic latent image;
A plurality of linear auxiliary electrodes arranged substantially parallel to the plurality of linear readout electrodes;
An operational amplifier in which the linear readout electrode is connected to the inverting input side; an integration capacitor connected between the inverting input side and the output of the operational amplifier; and a short-circuit means connected in parallel to the integration capacitor; A radiation solid-state detector comprising charge-voltage conversion means for converting charge output from the linear readout electrode into voltage by short-circuiting the integration capacitor at a desired cycle.
The plurality of linear auxiliary electrodes are individually arranged in pairs with respect to the plurality of linear readout electrodes;
A potential difference reducing circuit for reducing a potential difference between the potential on the non-inverting input side of the operational amplifier and the potential of the linear auxiliary electrode paired with the linear readout electrode connected to the operational amplifier; It is characterized by.
[0017]
Note that the phrase “arranged substantially in parallel” includes a state in which they are arranged substantially in parallel in an adjacent state, a state in which they are arranged substantially in parallel in an opposed state, and the like. Further, “shorting the integration capacitor at a desired cycle” is not limited to short-circuiting the integration capacitor at the same cycle when reading image information of one image. When reading the image information from a part of the region, the integration capacitor is short-circuited at a certain desired cycle, and when reading the image information from another region, the other desired cycle different from the above desired cycle The integration capacitor may be short-circuited.
[0018]
Further, the “potential difference reducing circuit for reducing the potential difference” means that, when this potential difference reducing circuit is provided, the “potential on the non-inverting input side of the operational amplifier and the linear readout electrode connected to the operational amplifier; This means a circuit in which the “potential difference between the paired linear auxiliary electrodes” can be made smaller than the potential difference generated when this circuit is not provided.
[0019]
The potential difference reduction circuit may be an impedance conversion circuit that impedance-converts the potential on the non-inverting input side of the operational amplifier and supplies it to the linear auxiliary electrode with a low impedance. An example of such an impedance conversion circuit is a voltage follower circuit.
[0020]
The radiation solid detector may output charges corresponding to the electrostatic latent image from the plurality of linear readout electrodes by receiving irradiation of readout light. As such a radiation solid state detector, for example, as described in Patent Document 2 or Patent Document 3, a first electrode having transparency to recording light and photoconductivity by being irradiated with recording light are used. A photoconductive layer for recording that exhibits the property, a power storage unit that accumulates an amount of charge corresponding to the amount of recording light as a latent image charge, and a photoconductive layer for reading that exhibits photoconductivity when irradiated with reading light A second electrode having a plurality of linear readout electrodes transparent to the reading light and a plurality of linear auxiliary electrodes, wherein the linear readout electrodes and the linear auxiliary electrodes are arranged alternately. There are radiation solid state detectors laminated in this order. The radiation solid detector has a first electrode, a recording photoconductive layer, a reading photoconductive layer, and a second electrode in this order, and between the recording photoconductive layer and the reading photoconductive layer. In addition, the power storage unit may be formed, and another layer, a micro conductive member (micro plate), or the like may be stacked.
[0021]
Further, as a method of forming the power storage unit, a method of forming a power storage unit at the interface between the charge transport layer and the recording photoconductive layer by providing a charge transport layer (Japanese Patent Laid-Open No. 2000-105297 by the present applicant). , Japanese Patent Laid-Open No. 2000-284056), and a method in which a trap layer is provided and a power storage unit is formed in the trap layer or at the interface between the trap layer and the recording photoconductive layer (see, for example, US Pat. No. 4,535,468) Alternatively, a method of providing a minute conductive member or the like for concentrating latent image charges and storing electricity (see Japanese Patent Application Laid-Open No. 2000-284057 by the applicant) may be used.
[0022]
The “linear readout electrode having transparency to the reading light” is an electrode that transmits the reading light and generates a charge pair in the reading photoconductive layer. In the case where the reading light can be transmitted between the linear readout electrodes, the linear readout electrode does not necessarily need to be transmissive to the reading light. Further, the “linear auxiliary electrode” is an electrode for outputting an electric signal at a level corresponding to the amount of latent image charge accumulated in the power storage unit, and desirably has a light shielding property against the reading light. However, when a light shielding film having a light shielding property is provided between the linear auxiliary electrode and the reading light irradiation means, the linear auxiliary electrode does not necessarily have a light shielding property. Here, the “light-shielding property” is not limited to the one in which the reading light is completely blocked and no charge pair is generated. Including those that do not cause any substantial problems. Therefore, the charge pairs generated in the reading photoconductive layer are not necessarily all due to the reading light that has passed through the linear readout electrode, and even in the reading photoconductive layer by reading light that has passed through the linear auxiliary electrode slightly. It is assumed that charge pairs can be generated.
[0023]
Further, the “reading light” is not limited as long as it can move the electric charge in the electrostatic recording body and can electrically read the electrostatic latent image. Specifically, it is light, radiation, or the like. .
[0024]
【The invention's effect】
According to the radiation solid-state detector of the present invention, the linear auxiliary electrodes are individually arranged in pairs with respect to the readout electrodes, and the potential on the non-inverting input side of the operational amplifier and the line connected to the operational amplifier By providing a potential difference reduction circuit for reducing the potential difference between the potential of the linear auxiliary electrode paired with the linear readout electrode, the linear readout electrode and the linear auxiliary electrode paired with the linear readout electrode are provided. Since the value of the capacitance Ci generated during the period is apparently reduced, the AC amplification factor in the charge-voltage conversion means is also reduced, and the thermal noise or noise amplification factor superimposed on the charge output from the linear readout electrode is reduced. And the S / N ratio of the signal output from the charge-voltage conversion means is improved.
[0025]
If the potential difference reduction circuit is an impedance conversion circuit that converts the potential on the non-inverting input side of the operational amplifier to a low impedance and supplies it to the linear auxiliary electrode, the potential of the linear auxiliary electrode can be easily obtained from the operational amplifier. It is possible to follow the vicinity of the potential on the non-inverting input side.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an electrostatic recording body provided in a radiation solid state detector according to a first embodiment of the present invention. FIG. 1A is a perspective view of an electrostatic recording body 20a. 1 (B) is an XZ cross-sectional view of the Q arrow portion of the electrostatic recording body 20a, and FIG. 1 (C) is an XY cross-sectional view of the P arrow portion of the electrostatic recording body 20a. FIG. 2 is a schematic view of a recording / reading system using a radiation solid state detector. In FIG. 2, the support 18, the insulating layer 30, and the light shielding film 31 are omitted.
[0027]
The radiation solid state detector according to the first embodiment of the present invention includes an electrostatic recording body 20 a and a signal detection means 70.
[0028]
The electrostatic recording body 20a includes a first electrode 21 having transparency to recording light (radiation or light generated by excitation of radiation) carrying image information of radiation such as X-rays transmitted through the subject. The recording photoconductive layer 22 made of a photoconductive material mainly composed of a-Se (amorphous selenium) or the like, which generates a charge pair and exhibits conductivity when irradiated with the recording light transmitted through the electrode 21, the charge For a latent image polar charge (for example, a negative charge) in a pair, it acts as an insulator, and for a transport polar charge (a positive charge in the above example) of the opposite polarity to the latent image polar charge. A charge transport layer 23 made of an organic compound or the like that substantially acts as a conductor, and a photoconductive material mainly composed of a-Se (amorphous selenium) or the like that exhibits conductivity by generating charge pairs upon irradiation with reading light. From sex substances The reading photoconductive layer 24, the second electrode 25 including the stripe electrode 26 and the auxiliary stripe electrode 27, the insulating layer 30 that is transmissive to the reading light, and the glass substrate that is transmissive to the reading light. The support 18 is arranged in this order. At the interface between the recording photoconductive layer 22 and the charge transport layer 23, a two-dimensionally distributed power storage unit 29 for accumulating latent image polar charges carrying image information generated in the recording photoconductive layer 22 is formed. The The thickness of the recording photoconductive layer 22 is preferably 50 μm or more and 1000 μm or less so that the recording light can be sufficiently absorbed.
[0029]
Further, the total thickness of the charge transport layer 23 and the reading photoconductive layer 24 is preferably less than or equal to ½ of the thickness of the recording photoconductive layer 22. Therefore, for example, it is preferably 1/10 or less, more preferably 1/100 or less.
[0030]
The material of each of the above layers is a power storage unit 29 formed at the interface between the recording photoconductive layer 22 and the charge transport layer 23 by charging the first electrode 21 with a negative charge and the second electrode 25 with a positive charge. The negative charge as the latent image polar charge is accumulated in the charge transport layer 23, and the mobility of the positive charge as the transport polar charge having the opposite polarity to that of the negative charge as the latent image polar charge is increased. These are examples of those that are larger and are suitable as a so-called hole transport layer, but these may be charges of opposite polarity, and in this way, when reversing the polarity, It is only necessary to make a slight change such as changing the charge transport layer functioning as the transport layer to a charge transport layer functioning as the electron transport layer.
[0031]
The first electrode 21 may be any material as long as it is transmissive to recording light. For example, when it is transmissive to visible light, a well-known Nesa film (SnO2) as a light-transmissive metal thin film. , ITO (Indium Tin Oxide), or IDIXO (Idemitu Indium X-metal Oxide; Idemitsu Kosan Co., Ltd.), which is an amorphous light-transmitting oxide that is easy to etch, is about 50 to 200 nm thick, preferably It can be used with a thickness of 100 nm or more. Further, by making a pure metal such as aluminum Al, gold Au, molybdenum Mo, and chromium Cr to have a thickness of, for example, 20 nm or less (preferably about 10 nm), transparency to visible light can be given. Note that, when X-rays are used as recording light and an image is recorded by irradiating the X-rays from the first electrode 21 side, the first electrode 21 does not need transparency to visible light. For the first electrode 21, for example, a pure metal such as Al or Au having a thickness of 100 nm can be used.
[0032]
The second electrode 25 is formed by arranging a stripe electrode 26 in which a large number of read light transmitting linear read electrodes 26a are arranged in a stripe shape and a number of read light shielding linear auxiliary electrodes 27a in a stripe shape. And an auxiliary stripe electrode 27. The linear readout electrodes 26a and 27a are arranged so that the linear readout electrodes 26a and the linear auxiliary electrodes 27a are alternately arranged in parallel with each other. A part of the reading photoconductive layer 24 is interposed between the two linear electrodes, and the stripe electrode 26 and the auxiliary stripe electrode 27 are electrically insulated. The auxiliary stripe electrode 27 is a conductive material for outputting an electric signal of a level corresponding to the amount of latent image charge accumulated in the power storage unit 29 formed at a substantially interface between the recording photoconductive layer 22 and the charge transport layer 23. It is a member.
[0033]
Here, as the material of the electrode material for forming each linear readout electrode 26a of the stripe electrode 26, ITO (Indium Tin Oxide), IDIXO (Idemit Indium X-metal Oxide; Idemitsu Kosan Co., Ltd.), aluminum, molybdenum or the like is used. Can be used. Further, as a material of an electrode material for forming each linear auxiliary electrode 27a of the auxiliary stripe electrode 27, aluminum, molybdenum, chromium, or the like can be used.
[0034]
Further, the irradiation intensity of the read light on the linear auxiliary electrode 27a is linear in the read light at portions corresponding to each linear auxiliary electrode 27a on the support 18 and between the linear read electrode 26a and the linear auxiliary electrode 27a. A light shielding film 31 made of a member having inferior light transmittance is provided so as to be smaller than the irradiation intensity to the readout electrode 26a.
[0035]
The signal detection means 70 includes a charge amplifier 71 that is a charge-voltage conversion means connected to each linear readout electrode 26a, and a buffer amplifier 72 that is an impedance conversion circuit connected to each linear auxiliary electrode 27a.
[0036]
The charge amplifier 71 includes an operational amplifier 73 in which the linear readout electrode 26a is connected to the inverting input terminal 73a, an integration capacitor 74 connected between the inverting input terminal 73a and the output 73c of the operational amplifier 73, and the integration capacitor 74 in parallel. And a reset switch 75 connected thereto. The operational amplifier 73 and the integrating capacitor 74 constitute an integrating circuit. In the charge amplifier 71, the reset switch 75 is short-circuited and the integration capacitor 74 is short-circuited in the readout cycle of one pixel, whereby the charge output from the linear readout electrode 26a is converted into a voltage, and a signal is output from the output terminal 73c. The voltage is output to a signal processing circuit (not shown). The non-inverting input terminal 73 b is connected to the buffer amplifier 72 and grounded via the resistor 76.
[0037]
The buffer amplifier 72 includes an operational amplifier 77 connected as a voltage follower, and the non-inverting input terminal 77 b is connected to the non-inverting input terminal 73 b of the operational amplifier 73 and is grounded via a resistor 76. The output terminal 77c is connected to the linear auxiliary electrode 27a and the inverting input terminal 77a. In such a voltage follower-connected operational amplifier, the input impedance is high and the output impedance is low, and the potential of the output terminal is substantially the same as the potential of the non-inverting input terminal.
[0038]
In the charge amplifier 71, since negative feedback is applied by the integrating capacitor 74, the inverting input terminal 73a and the non-inverting input terminal 73b are in a virtual short circuit state, and their potentials are substantially equal. Become. Therefore, if the non-inverting input terminal 73b is grounded via the resistor 76, and the potential of the non-inverting input terminal 73b is impedance-converted to a low impedance and supplied to the linear auxiliary electrode 27a, the on-line auxiliary electrode 27a Is substantially the same as the potential of the on-line readout electrode 26a.
[0039]
Next, a basic method for recording image information as an electrostatic latent image on the above-described electrostatic recording body 20a and further reading out the recorded electrostatic latent image will be briefly described. FIG. 2 is a schematic view of a recording / reading system using the electrostatic recording body 20a.
[0040]
This recording / reading system includes an electrostatic recording body 20a, a recording light irradiation means (not shown), a signal detection means 70 as an image signal acquisition means, and a reading light scanning means (not shown).
[0041]
Next, a method of recording image information as an electrostatic latent image on the electrostatic recording body 20a and reading out the recorded electrostatic latent image in the recording / reading system having the above configuration will be described. First, the electrostatic latent image recording process will be described with reference to the charge model shown in FIG. Note that the negative charge (−) and the positive charge (+) generated in the recording photoconductive layer 22 by the recording light L1 are represented by enclosing − or + in circles in the drawing.
[0042]
When an electrostatic latent image is recorded on the electrostatic recording body 20a, a DC voltage is applied between the first electrode 21, the stripe electrode 26, and the auxiliary stripe electrode 27 to charge them. At this time, if a control voltage is applied so that the stripe electrode 26 and the auxiliary stripe electrode 27 have the same potential, the electric field distribution formed between the first electrode 21 and the second electrode 25 can be made uniform.
[0043]
Next, radiation is blown onto the subject 9, and the recording light L1 carrying the radiation image information of the subject 9 that has passed through the transmission part 9a of the subject 9 is irradiated onto the electrostatic recording body 20a. Then, positive and negative charge pairs are generated in the recording photoconductive layer 22 of the electrostatic recording body 20a, and the negative charges in the pair move to the power storage unit 29 along the electric field distribution in the electrostatic recording body 20a.
[0044]
On the other hand, the positive charge generated in the recording photoconductive layer 22 moves at high speed toward the first electrode 21, and the negative charge injected from the power source 74 at the interface between the first electrode 21 and the recording photoconductive layer 22. The charge recombines and disappears. Further, since the recording light L1 does not pass through the light shielding portion 9b of the subject 9, the portion corresponding to the lower portion of the light shielding portion 9b of the electrostatic recording body 20a does not change at all.
[0045]
In this way, by bombarding the subject 9 with the recording light L 1, charges corresponding to the subject image can be accumulated in the power storage unit 29, which is an interface between the photoconductive layer 22 and the charge transfer layer 23. Become. Since the amount of accumulated latent image charge (negative charge) is substantially proportional to the dose of radiation that has passed through the subject 9 and entered the electrostatic recording body 20a, this latent image charge carries an electrostatic latent image. The electrostatic latent image is recorded on the electrostatic recording body 20a.
[0046]
Next, when reading the electrostatic latent image from the electrostatic recording body 20a, the first electrode 21 is set to the ground potential, and the reading light irradiation means is moved in the longitudinal direction of the linear readout electrode 26a, that is, sub-scanning is performed. Thus, the entire surface of the electrostatic recording body 20a is scanned and exposed with the line-shaped reading light L2. The scanning exposure of the reading light L2 generates positive and negative charge pairs in the reading photoconductive layer 24 on which the reading light L2 corresponding to the sub-scanning position is incident.
[0047]
Then, the latent image charge of the portion corresponding to the linear auxiliary electrode 27a, that is, the sky portion of the linear auxiliary electrode 27a is sequentially read out via the linear auxiliary electrode 27a. That is, as shown in FIG. 2B, a discharge is generated from the linear readout electrode 26a toward the latent image charge (in the sky) corresponding to the adjacent linear auxiliary electrode 27a, thereby reading out. proceed. At this time, positive charges flow into the linear readout electrode 26a.
[0048]
Due to the flow of positive charges into the linear readout electrode 26a, charges are accumulated in the integrating capacitor 74 of the charge amplifier 71. When the integration capacitor 74 is short-circuited by the reset switch 75 in the readout cycle of one pixel, the electric charge output from the linear readout electrode 26a is converted into a voltage, which is converted into a signal voltage from the output terminal 73c, and a signal processing circuit (not shown). Is output.
[0049]
In the present embodiment, since the non-inverting input terminal 77b of the operational amplifier 77 is connected to the non-inverting input terminal 73b of the operational amplifier 73 via the buffer amplifier 72, the potential of the inverting input terminal 73a of the operational amplifier 73 is determined. Is substantially the same as the potential of the output terminal 77 c of the operational amplifier 77. Accordingly, the potential of the on-line auxiliary electrode 27a is substantially the same as the potential of the on-line readout electrode 26a. Therefore, when viewed from the charge amplifier 71 side, the capacitance Ci existing between the line readout electrode 26a and the line auxiliary electrode 27a has a very small value. If the capacitance Ci is small, the amplification factor of the charge amplifier 71 as an AC amplifier is also small. Therefore, thermal noise and noise superimposed on the charge output from the linear readout electrode 26a are not amplified, and the charge amplifier 71 is charged. The S / N of the voltage signal output from the amplifier 71 is improved. Further, since the line auxiliary electrode 27a is driven with a low impedance by the buffer amplifier 72, noise superimposed on the line auxiliary electrode 27a is difficult to be guided to the line read electrode 26a, and the signal S / N is further improved.
[0050]
In the above embodiment, when the S / N improvement is not essential, the capacitance Cf of the integration capacitor 74 of the charge amplifier 71 can be reduced. If the capacitance Cf is reduced, the signal detection means 70 can be downsized, that is, the radiation solid state detector can be downsized. In addition, since the charge-voltage conversion coefficient of the charge amplifier is increased, a sufficient amplification degree can be obtained with only the charge amplifier, and an amplifier connected to the subsequent stage is not necessary.
[0051]
In general, a semiconductor control element such as an analog switch is often used as the reset switch 75. However, in these switches, a phenomenon called charge injection in which an indeterminate component appears in both poles of the switch occurs at the moment of opening. This indeterminate component becomes reset noise, and the level of the output signal from the charge amplifier immediately after the end of reset may be different for each reset. When such a reset noise has a magnitude that cannot be ignored compared to the amount of charge detected by the charge amplifier, the influence of the reset noise can be reduced by providing a correlated double sampling circuit after the charge amplifier. it can.
[0052]
In the present embodiment, as shown in FIG. 3A, the charge amplifier 71 and the buffer amplifier 72 are connected to the opposite end portions of the paired line readout electrode 26a and line auxiliary electrode 27a. However, as shown in FIG. 3 (2), it may be connected to the end on the same side. Further, the shape of the line readout electrode 26a and the line auxiliary electrode 27a may be a combination of a plurality of line electrodes as shown in FIG.
[0053]
The preferred embodiments of the radiation solid state detector according to the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without changing the gist of the invention. is there.
[0054]
For example, in any of the detectors according to the above-described embodiments, the recording photoconductive layer exhibits conductivity when irradiated with recording radiation, but the recording photoconductive layer of the detector according to the present invention is not necessarily provided. However, the present invention is not limited to this, and the recording photoconductive layer may exhibit conductivity when irradiated with light emitted by excitation of recording radiation (see JP-A-2000-105297). In this case, a wavelength conversion layer called a so-called X-ray scintillator that converts the wavelength of recording radiation into light of another wavelength region such as blue light may be laminated on the surface of the first electrode. As this wavelength conversion layer, for example, cesium iodide (CsI) is preferably used. The first electrode is transmissive to light emitted from the wavelength conversion layer by excitation of recording radiation.
[0055]
In the electrostatic recording body according to the above embodiment, a charge transport layer is provided between the recording photoconductive layer and the reading photoconductive layer, and a power storage unit is provided at the interface between the recording photoconductive layer and the charge transport layer. However, the charge transport layer may be replaced with a trap layer. In the case of the trap layer, the latent image charge is trapped in the trap layer, and the latent image charge is accumulated in the trap layer or at the interface between the trap layer and the recording photoconductive layer. In addition, a microplate may be provided for each pixel at the interface between the trap layer and the recording photoconductive layer.
[0056]
Even when the TFT readout method is used as a readout method, a large number of linear readout electrodes that output charges corresponding to the electrostatic latent image and a substantially parallel to the numerous linear readout electrodes. The present invention can be applied to any radiation individual detector including a large number of linear auxiliary electrodes arranged in a line.
[Brief description of the drawings]
FIG. 1 is a perspective view (A) of an electrostatic recording body provided in a radiation solid detector according to an embodiment of the present invention, an XZ sectional view (B) of a Q arrow portion, and an XY sectional view (C) of a P arrow portion. )
FIG. 2 shows a charge model (A) showing an electrostatic latent image recording process and a charge model (B) showing an electrostatic latent image reading process in the case of using the radiation solid state detector according to the first embodiment of the present invention. )
FIG. 3 is a schematic diagram of a second electrode and signal detection means of a radiation solid state detector according to an embodiment of the present invention.
[Explanation of symbols]
20a Radiation solid state detector
21 1st electrode
22 Photoconductive layer for recording
23 Charge transport layer
24 Photoconductive layer for reading
25 Second electrode
26 Striped electrode
26a Linear readout electrode
27 Auxiliary stripe electrode
27a linear auxiliary electrode
29 Power storage unit
70 Signal detection means
71 Charge amplifier
72 Buffer amplifier
73 Operational amplifier
74 Integration capacitor
75 Reset switch

Claims (3)

A power storage unit for recording image information as an electrostatic latent image;
A number of linear readout electrodes that output a charge corresponding to the electrostatic latent image;
A plurality of linear auxiliary electrodes arranged substantially parallel to the plurality of linear readout electrodes;
An operational amplifier in which the linear readout electrode is connected to the inverting input side; an integration capacitor connected between the inverting input side and the output of the operational amplifier; and a short-circuit means connected in parallel to the integration capacitor; A radiation solid-state detector comprising charge-voltage conversion means for converting charge output from the linear readout electrode into voltage by short-circuiting the integration capacitor at a desired cycle.
The plurality of linear auxiliary electrodes are individually arranged in pairs with respect to the plurality of linear readout electrodes;
A potential difference reducing circuit for reducing a potential difference between the potential on the non-inverting input side of the operational amplifier and the potential of the linear auxiliary electrode paired with the linear readout electrode connected to the operational amplifier; A radiation solid state detector. 2. The radiation according to claim 1, wherein the potential difference reduction circuit is an impedance conversion circuit that converts the potential of the non-inverting input side of the operational amplifier to impedance and supplies the same to the linear auxiliary electrode. Solid state detector. The radiation solid state detector is
3. The radiation solid state detector according to claim 1, wherein a charge corresponding to the electrostatic latent image is output from the plurality of linear readout electrodes when irradiated with reading light.

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