JP4724311B2 - Radiation detection apparatus and imaging system using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation detection apparatus used for a digital camera, an X-ray imaging apparatus, and the like, and more particularly, to a radiation detection apparatus having an area sensor that performs matrix driving and a DC / DC converter for supplying power to the area sensor.
[0002]
[Prior art]
FIG. 8 shows a schematic circuit example of a conventional radiation detection apparatus having an area sensor that detects radiation and converts it into an electrical signal, and FIG. 9 shows its drive timing. Further, FIG. 10 shows a schematic circuit example of a DC / DC converter of a conventional radiation detection apparatus.
[0003]
As shown in FIG. 8, the area sensor performs matrix driving by two-dimensionally arranging pixels composed of photodiodes and TFTs. The gate electrode of the TFT of each pixel is connected to common gate lines Vg1 to Vg3, and the common gate line is connected to a gate drive circuit 2 constituted by a shift register (not shown). On the other hand, the source electrode of each TFT is connected to common data lines Sig1 to Sig3, and is connected to a pixel readout device 1 composed of an amplifier, a sample hold, an analog multiplexer, and the like.
[0004]
The area sensor has a DC / DC converter 3 as a power source. From the output of the DC / DC converter 3, the regulator circuit 4 uses each reference potential of the area sensor, that is, sensor bias potential (Vs), sample hold reference potential (VREF1). ), An amplifier reset potential (VREF2), a TFT on potential (Von), and a TFT off potential (Voff).
[0005]
Further, the operation of each unit will be described using the drive timing shown in FIG. In the figure, RES is the reset of the amplifier of the readout device, Vg1 to 3 are the timing of the gate pulse to each common gate line, SMPL is the sampling timing of the sample hold of the readout device, and CLK is the analog synchronization signal from the analog multiplexer Each is shown. First, the amplifier is reset, and then the TFT is turned on (Vg1), whereby the signal charges of the photodiodes D1 to D3 are transferred to the amplifier of the reading device 1, sampled by the sample hold, and output from the analog multiplexer as an analog output. , Output in synchronization with CLK.
[0006]
FIG. 10 is a circuit example of a DC / DC converter of a conventional radiation detection apparatus. A conventional DC / DC converter 3 of the radiation detection apparatus includes a triangular wave oscillation circuit 31, a comparator 32, a MOS transistor 33, a diode 34, a coil 35, resistors 36 and 37, and the like. The oscillation waveform in A of FIG. 10 is shown in DC / DC of FIG. As shown, the oscillation of the DC / DC converter 3 is a high-frequency pulse.
[0007]
[Problems to be solved by the invention]
However, in the conventional radiation detection apparatus, since the oscillation operation waveform of the DC / DC converter is a high-frequency pulse, this high-frequency pulse may cause electric field noise or magnetic field noise. For example, line noise (electric field noise) is generated if a high-frequency pulse fluctuates the amplifier reset potential VREF2 and the sample hold reference potential VREF1 in FIG. 8 due to capacitive coupling on the printed circuit board. Also, if the high frequency pulse fluctuates the amplifier reset potential VREF2 or the sample hold reference potential VREF1 by the action of electromagnetic induction, line noise (magnetic field noise) is generated. That is, the difference between “ideal analog output” and “actual analog output” in FIG. 9 is line noise. Such line noise appears as a streak when the signal read out by the area sensor is reproduced as an image, and degrades the quality of the image.
[0008]
In particular, when image data acquisition with high accuracy is required, such as application to an X-ray imaging apparatus, these line noises may be a big problem. That is, the conventional radiation detection apparatus has a problem that image quality may be deteriorated due to electric field noise and magnetic field noise caused by the oscillation operation of the DC / DC converter.
[0009]
Furthermore, the conventional radiation detection apparatus has a problem that it is difficult to construct a high-quality imaging system due to these noises.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation detection apparatus having a DC / DC converter that reduces the influence on the image quality caused by electric field noise and magnetic field noise generated by the DC / DC converter.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, a radiation detection apparatus according to the present invention includes an element for detecting radiation and converting it into an electrical signal, and a TFT connected to the element, and a plurality of two-dimensionally arranged elements. and the pixel, a plurality of gate lines gate lines are respectively arranged in the column direction, which is connected to the gate electrode of the TFT, a drive circuit connected to the gate line, in common with a plurality of the pixels in the column direction a plurality of data lines connected data lines are respectively arranged in the row direction, it has a plurality of amplifiers that can be reset, among the plurality of amplifiers to one data line of the plurality of data lines an area sensor for performing matrix driving possess a reading device in which one amplifier is connected, the switching power supply for supplying the amplifier reset potential in common to said plurality of amplifiers In the radiation detecting apparatus having, a control device for controlling switching between oscillation and non-oscillation of the switching power supply, the switching power supply to at least a portion of the period of time in which the plurality of amplifiers are reset non It is characterized by oscillation.
[0012]
Further, as another aspect of the radiation detection apparatus of the present invention, a plurality of pixels that have an element for detecting radiation and converting it into an electrical signal and a TFT connected to the element are arranged two-dimensionally. When a plurality of gate lines connected to the gate line and the gate electrode of the TFT are respectively arranged in the column direction, and a drive circuit connected to the gate line, are commonly connected to the plurality of the pixels in the column direction A plurality of data lines each arranged in a row direction, and a plurality of sample holds, and one sample hold of the plurality of sample holds in one data line of the plurality of data lines common but an area sensor for performing matrix driving have a, a device out read is connected, the sample and hold reference potential to said plurality of sample-and-hold A radiation detecting apparatus having a switching power supply for feeding, a control device for controlling the oscillation and non-oscillation of the switching power supply, at least a portion of the period of time in which the plurality of sample and hold performs sampling The switching power supply is made non-oscillating.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is a schematic circuit diagram of the radiation detection apparatus of the present invention. FIG. 2 is a drive timing chart for explaining the operation. 3 and 4 are schematic circuit diagrams of a DC / DC converter used in the radiation detection apparatus of the present invention.
[0015]
In the following description, since the basic operation is the same as that of the above-described conventional example, the overlapping portion is omitted. As shown in FIGS. 1 to 4, the present invention is characterized by having a DC / DC control device 5 connected to a DC / DC converter (switching power supply) 3. Further, the DC / DC control device 5 is characterized in that it supplies an ENB signal that controls switching between “oscillation” and “non-oscillation” of the DC / DC converter.
[0016]
As described in the “Problem” section above, when the amplifier of the reading device 1 is reset (RES) and sampled (SMPL), the electric field noise or magnetic field noise caused by the oscillation operation of the DC / DC converter has a reference potential. If it fluctuates, it will cause line noise. As shown in the timing chart of FIG. 2, the present invention is characterized in that the DC / DC converter is set to “non-oscillation” at the time of amplifier reset (RES) and sampling (SMPL).
[0017]
In this embodiment, the DC / DC converter is set to “non-oscillation” in both periods of amplifier reset and sampling, but either one may be used. In this embodiment, the DC / DC converter is set to “non-oscillation” throughout the amplifier reset and sampling periods, but only a part of the periods may be used.
[0018]
3 and 4 are specific configuration examples of a DC / DC converter for realizing the present embodiment. The DC / DC control device 5 in FIG. 3 can switch between “oscillation” and “non-oscillation” of the triangular wave oscillation circuit 31 of the DC / DC converter by the ENB signal. It is desirable to make the oscillation circuit fundamentally “non-oscillation” as shown in this explanatory diagram.
[0019]
Further, in the DC / DC control device 5 of FIG. 4, the “operation” and “non-operation” of the comparator 32 can be switched by the ENB signal. In the case where the oscillation circuit cannot be fundamentally made “non-oscillation”, the oscillation waveform may be prohibited in the subsequent circuit as described above.
[0020]
The points to be particularly noted in the present invention are as follows. That is, first, it has a DC / DC control device connected to a DC / DC converter. Secondly, the DC / DC controller must switch between “oscillation” and “non-oscillation” of the DC / DC converter. Thirdly, the DC / DC converter is set to “non-oscillation” at the time of amplifier reset and sample hold of the reading device.
[0021]
With the above configuration, line noise caused by the oscillation operation of the DC / DC converter can be prevented. As a result, a high-quality imaging system can be realized.
[0022]
FIG. 5 is a cross-sectional view of an example of a pixel of an indirect area sensor that converts radiation into light and photoelectrically converts the light. The pixel is composed of a photodiode 12 and a TFT 13 on a glass substrate 11. In addition, a phosphor (wavelength converter) 15 for converting incident X-rays into visible light is provided on the pixel. Photodiode 12 and TFT 13 are preferably made of amorphous silicon or polysilicon, and phosphor 15 is preferably made of cesium iodide or gadolinium-based material.
[0023]
FIG. 6 is a cross-sectional view of an example of a pixel of a direct area sensor that directly converts radiation into an electrical signal. In this example, the pixel includes an X-ray-electron conversion layer 26 made of a semiconductor material that directly converts X-rays into electric charge, and a storage capacitor 22 and a TFT 23 connected thereto. As in the example of FIG. 5, the TFT 23 is preferably made of amorphous silicon or polysilicon. Further, the material of the X-ray-electron conversion layer 26 may be gallium arsenide, gallium phosphide, lead iodide, mercury iodide, amorphous selenium, CdZn, CdZnTe, or the like.
[0024]
FIG. 7 shows an application example to an X-ray imaging system using the radiation detection apparatus of the present invention. X-rays 6060 generated by an X-ray tube 6050 as an X-ray generation source pass through an observation portion 6062 such as a chest of a patient or a subject 6061 and enter a radiation detection apparatus 6040 according to the present invention. This incident X-ray includes information inside the subject 6061. The radiation detection device 6040 converts it into an electrical signal containing the information in response to the incidence of X-rays. The electrical signal is digitally converted, image-processed by an image processor 6070, and can be observed on a display 6080 in a control room.
[0025]
This information can be transferred to a remote place by a transmission means such as a telephone line or wireless 6090, and can be displayed on a display 6081 in a doctor room in another place or stored on an optical disk, a magneto-optical disk, a magnetic disk, etc. A remote doctor can make a diagnosis. Further, it can be recorded on a recording medium 6110 such as a film or paper by a film processor or a laser printer 6100.
[0026]
A radiation detection apparatus used in an X-ray imaging system used for non-destructive inspection such as for medical diagnosis and internal inspection needs to read an image with high accuracy. Since the radiation detection apparatus of the present invention reduces the influence of line noise, it is suitable for such an application example.
[0027]
In the above embodiment, the X-ray imaging system has been described as an example, but the same applies to an apparatus configuration that converts radiation into light and photoelectrically converts the light. The radiation includes α, β, γ rays other than X-rays.
[0028]
【The invention's effect】
As described above, the radiation detection apparatus of the present invention can prevent image quality deterioration due to electric field noise and magnetic field noise caused by the oscillation operation of the DC / DC converter. When applied to an X-ray imaging apparatus or the like, it is possible to realize a high-quality imaging system that is less affected by electric field noise and magnetic field noise.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit example of the radiation detection apparatus of the present invention. FIG. 2 is a diagram showing a driving timing of the radiation detection apparatus of the present invention. FIG. 3 is a circuit example of a DC / DC converter of the radiation detection apparatus of the present invention. Fig. 4 is a diagram showing a circuit example 2 of the DC / DC converter of the radiation detection apparatus of the present invention. Fig. 5 is a cross-sectional view of an indirect pixel. Fig. 6 is a cross-sectional view of a direct pixel. 7 is a diagram showing an X-ray imaging system to which the radiation detection apparatus of the present invention is applied. FIG. 8 is a diagram showing a circuit example of a conventional radiation detection apparatus. FIG. 9 is a diagram showing drive timing of the conventional radiation detection apparatus. 10] Diagram showing a circuit example of a conventional DC / DC converter of a radiation detector [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reading apparatus 2 Gate drive circuit 3 DC / DC converter 4 Regulator circuit 5 DC / DC control apparatus

Claims (7)

A plurality of pixels arranged in two dimensions and a gate line connected to the gate electrode of the TFT have an element for detecting radiation and converting it into an electric signal and a TFT connected to the element. A plurality of data lines in which a plurality of gate lines arranged in the direction, a driving circuit connected to the gate lines, and a data line commonly connected to the plurality of pixels in the column direction are arranged in the row direction, respectively. And a plurality of amplifiers that can be reset, and a readout device in which one of the plurality of amplifiers is connected to one data line of the plurality of data lines, and matrix driving is performed. An area sensor to perform,
A switching power supply for commonly supplying an amplifier reset potential to the plurality of amplifiers;
In a radiation detection apparatus having
A control device for switching and controlling oscillation and non-oscillation of the switching power supply is provided, wherein the switching power supply is made non-oscillate during at least a part of a period during which the plurality of amplifiers are reset. Radiation detection device. A plurality of pixels arranged in two dimensions and a gate line connected to the gate electrode of the TFT have an element for detecting radiation and converting it into an electric signal and a TFT connected to the element. A plurality of data lines in which a plurality of gate lines arranged in the direction, a driving circuit connected to the gate lines, and a data line commonly connected to the plurality of pixels in the column direction are arranged in the row direction, respectively. A plurality of sample holds, and a readout device in which one sample hold of the plurality of sample holds is connected to one data line of the plurality of data lines. An area sensor to perform,
A switching power supply for commonly supplying a sample hold reference potential to the plurality of sample holds;
In a radiation detection apparatus having
A control device for controlling oscillation and non-oscillation of the switching power supply is provided, wherein the switching power supply is non-oscillated during at least a part of a period during which the plurality of sample and hold samples. Radiation detection device. Wherein the data line radiation detecting apparatus according to claim 1 or 2, characterized in that it is connected to the source electrode of the TFT.   The radiation detection apparatus according to claim 1, wherein the element includes a wavelength converter that converts radiation into light and an element that converts the light into the electrical signal.   The element has a conversion layer for directly converting radiation into electric charge, and the conversion layer is made of gallium arsenide, gallium phosphide, lead iodide, mercury iodide, amorphous selenium, CdZn, or CdZnTe. The radiation detection apparatus according to any one of claims 1 to 3.   The radiation detection apparatus according to claim 1, wherein the TFT is made of amorphous silicon or polysilicon. The radiation detection apparatus according to any one of claims 1 to 6,
An image processor that performs image processing on a signal detected by the radiation detection device;
An imaging system comprising: a display that displays an image processed by the image processor.

Images