JP2003329777A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the degradation of image quality due to the effect of radiation. <P>SOLUTION: An imaging device generates radiation pulse with a specific intervals in turn. It comprises an imaging region having a plurality of pixels for imaging a subject, a scanning means for scanning the imaging region, and a control means for controlling a scanning circuit so as to scan the imaging region while the radiation pulse is not generated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus used for radiation medical equipment and the like.

[0002]

2. Description of the Related Art Digitization is progressing in various fields of medicine. Also in the field of X-ray diagnosis, a two-dimensional X-ray imaging apparatus that converts incident X-rays into visible light with a scintillator (phosphor) and further captures the visible light image with an image sensor is used for digitizing images. Has been developed. The advantages of digitized X-ray equipment over analog photography are: It is filmless, expanding acquired information by image processing, and creating a database.
In addition, the ability to instantly display a photographed image on the spot is useful in an urgent medical field. Radiation means X-rays, α, β, γ-rays, or high-energy rays that can detect the internal structure of a subject, and light is an electromagnetic wave in a wavelength region that can be easily detected by photoelectric conversion means such as a photodiode. Includes visible light and infrared light. Hereinafter, the case of X-rays as radiation will be described.

In the field of X-ray still images, as a two-dimensional X-ray imaging apparatus, for example, for mammography and chest imaging, a maximum of four can be used.
A large-sized still image pickup device (flat panel detector) using 3 cm square amorphous silicon (a-Si) is manufactured. As an example of this type of technology, US Pat.
There is one described in No. 15101. This conventional technique is shown in FIG. It is easy to obtain a large image pickup device using an amorphous silicon semiconductor on a glass substrate, and there is one that realizes a large-plate X-ray image pickup device by laminating four panels. There is also a proposal to configure a large X-ray image pickup device using a plurality of single crystal image pickup devices (silicon image pickup device, etc.). An example of this type of technology is US Pat. No. 4,323,925, 5,159,455 shown in FIG.
As the single crystal image pickup device, there are a CCD type image pickup device using silicon, a MOS type image pickup device, a CMOS type image pickup device and the like. As an X-ray converter, a fiber optic plate (FOP) with a phosphor is used. As the material of the fiber optic plate, a material containing lead glass or the like that does not easily transmit X-rays is used. In general, a single crystal silicon device such as a CCD is easily damaged by radiation such as X-rays and deteriorates such as an increase in dark current and a decrease in photoelectric conversion efficiency. As a result, the X-ray resistance is enhanced and the reliability is improved. Conventional CC
In the D-type image pickup element, the MOS-type image pickup element, and the CMOS type image pickup element, a circuit for driving the element (shift register, decoder,
The multiplexer and the like) and the memory circuit are arranged on the outer peripheral portion of the pixel area of the device. FIG. 13 shows a case where four CMOS image pickup elements are bonded together. Similar to the pixel part, these circuits cause malfunction and deterioration when X-rays directly enter, so
In general, lead is used to shield X-rays.

In the field of X-ray moving images, incident X-rays are transmitted through a scintillator (phosphor) and an I.D. I. A two-dimensional digital X-ray fluoroscopic apparatus has been developed which converts visible light by an (image intensifier) and captures the visible light image with a TV camera using a CCD type image sensor. However, this is not a flat panel detector.

In the field of medical X-ray diagnosis, which is becoming more digital, there are expectations for a next-generation moving image pickup device (such as fluoroscopy) that is miniaturized, has a high sensitivity, and has a high speed due to a flat panel.

[0006]

A radiation image pickup device (flat panel detector) using amorphous silicon (a-Si) can be easily made into a large plate, but due to the characteristics of the material of amorphous silicon, high sensitivity and high speed cannot be achieved. Have difficulty. Therefore, it is limited to still images. A radiation imaging device that combines single-crystal silicon and FOP is easy to achieve high speed and high sensitivity, but it is a very expensive taper-shaped FOP for making a large plate.
Since we cannot help but use it, we cannot reduce the cost. Therefore, there has been no X-ray imaging device that is fully equipped with a large plate, high speed, high definition, high sensitivity, and low cost. Further, in order to reduce the influence of X-rays on single crystal silicon, there has been no driving that considers the relationship between the driving of X-ray pulses and the X-ray noise due to direct incidence.

[0007]

In order to solve the above-mentioned problems, an imaging device in which radiation pulses are sequentially generated at predetermined intervals, the imaging region having a plurality of pixels for picking up a subject image, and the imaging device. Scanning means for scanning the area,
An imaging apparatus comprising: a driving unit that drives the scanning circuit to scan the imaging region during a period in which the radiation pulse is not generated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a diagram showing the configuration of an image pickup device in which peripheral circuits such as horizontal and vertical shift registers as scanning means are incorporated in an effective pixel region. FIG. 2 is a diagram showing a layout of pixels in an effective pixel area, a shift register, a protection circuit, external terminals, and the like. 3, 4 and 5 are views for explaining an image pickup module in which nine image pickup elements are stuck together. FIG. 11 is a block diagram showing the configuration of the image pickup apparatus according to this embodiment.

As shown in FIG. 11, when a moving image of a subject is obtained, an X-ray pulse is generated from a pulse X-ray generator 100, which is a radiation source, and the image pickup panel 1 which has transmitted the subject.
X-rays inside 01 are converted into visible light by the scintillator. This light is converted into an electric signal by the image pickup element in the image pickup panel 101. A / D converter 10 converts analog electric signals
After being converted into a digital signal by 2, the image processing circuit 103 performs image processing and stores the moving image in the storage unit 106 that stores a plurality of frames. Then, the display unit 105
The image is displayed on. The image sensor is driven by the sensor drive unit 107, and the pulsed X-ray device 100 is driven by the X-ray drive unit 108. The control of the pulse X-ray generator, each image pickup device of the image pickup module, and the image processing device is performed by the controller 109 which is a control means. An operation device and an operation monitor are used for the input operation to this controller.

FIG. 4 shows an image pickup element portion of a large area image pickup module of 414 mm square formed by laminating nine 138 mm square image pickup elements in a tile shape.

FIG. 5 shows a cross section taken along the line AA 'of FIG. Gd ₂ O using europium, terbium, etc. as active substances
_{2 A} scintillator plate made of scintillator such as S or CsI is installed on the FOP. The X-rays hit the scintillator and are converted into visible light. This visible light is detected by the image sensor. The scintillator is preferably selected so that its emission wavelength matches the sensitivity of the image sensor. The external processing board supplies a power supply, a clock, and the like for the image pickup device, and has a circuit for extracting a signal from the image pickup device and processing it. TAB
(Tape Automated Bonding)
Electrically connects each image sensor to the external processing substrate.

The nine image pickup devices are attached so that there is substantially no gap between the image pickup devices. The fact that there is substantially no gap here means that there is no gap between the image pickup elements in the image formed by the nine image pickup elements. Input of a clock or the like of the image pickup device, power supply, and output of a signal from the pixel are performed through an TAB connected to an electrode pad provided at an end portion of the image pickup device with an external processing substrate arranged on the back side of the image pickup device. The thickness of the TAB is sufficiently thin with respect to the pixel size, and even if it passes through the gap between the image pickup elements, no defect on the image occurs.

FIG. 3 shows a case where one image pickup element is taken out from the currently mainstream 8-inch wafer. 8-inch wafer is N
This is a mold wafer, and using this, a CMOS type 138 mm square CMOS image sensor is prepared in one sheet.

FIG. 6 shows a block diagram of a pixel portion constituting each pixel of the CMOS type image pickup device. A photodiode PD for photoelectric conversion, a floating diffusion C _FD for accumulating charges, a transfer MOS transistor (transfer switch) for transferring the charges generated by the photodiode to the floating diffusion, and a reset for discharging the charges accumulated in the floating diffusion. MO
It has an S transistor (reset switch), a row selection MOS transistor (row selection switch) for selecting a row, and an amplification MOS transistor (pixel amplifier) that functions as a source follower.

FIG. 7 shows a schematic diagram of the whole circuit of 3 × 3 pixels.

The gate of the transfer switch is connected to φTX from a vertical shift register which is a kind of vertical scanning circuit,
The gate of the reset switch is φRE from the vertical scanning circuit.
It is connected to S and the gate of the row selection switch is connected to φSEL from the vertical scanning circuit.

Photoelectric conversion is carried out by the photodiode, and the transfer switch is in the OFF state during the accumulation period of the light quantity charge, and the charge photoelectrically converted by the photodiode is transferred to the gate of the source follower constituting the pixel amplifier. Not done. The gate of the source follower that constitutes the pixel amplifier is initialized to an appropriate voltage by turning on the reset switch before the start of accumulation. That is, this is the dark level. Next or at the same time, when the row selection switch is turned on, the source follower circuit composed of the load current source and the pixel amplifier is activated, and by turning on the transfer switch here, the charge accumulated in the photodiode is changed. , To the gate of the source follower that constitutes the pixel amplifier.

Here, the output of the selected row is generated on the vertical output line (signal output line). This output is sequentially read out to the output section amplifier by driving the column selection switch (multiplexer) by a horizontal shift register which is a kind of horizontal scanning circuit.

FIG. 2 shows a unit block (unit for selecting and driving one row) of the vertical shift register as one pixel area (1
A cell is shown together with one pixel circuit. The one-pixel circuit is shown in FIG. The vertical shift register has a transfer signal φTX, a reset signal φRES, and a row selection signal φS.
A simple circuit composed of a static shift register and a transfer gate for producing EL is shown. These are driven by a signal from a clock signal line (not shown). The circuit configuration of the shift register is not limited to this, and an arbitrary circuit configuration can be taken according to various driving methods such as pixel addition and thinning-out reading. However, as in the present embodiment, the functional block is arranged in one cell together with the pixel circuit, and the shift register is provided in the effective pixel area to realize an image sensor in the entire effective pixel area.

[0020] In this embodiment, the vertical shift register and n pairs 2 ⁿ vertical scanning circuit such as a decoder, the horizontal shift register and n pairs 2 ⁿ each pixel region (cell inside the effective pixel area horizontal scanning circuit such as the decoder ) Is placed inside.

Similarly, the present embodiment is characterized in that the common processing circuit is arranged in each pixel area (cell) in the effective pixel area. Here, the common processing circuit means a circuit for collectively processing a plurality of pixels in common such as a final signal output amplifier, a serial / parallel conversion multiplexer, a buffer, and various gate circuits.

On the other hand, the individual circuit means a circuit that processes only one pixel, such as a photodiode, a transfer switch, a pixel selection switch, and a pixel output amplifier circuit.

FIG. 1 shows the configuration (plan view) of the image pickup device of this embodiment. In this embodiment, the vertical shift register and the horizontal shift register are arranged in the effective pixel area of the image sensor.
One block of the shift register that commonly processes one line is arranged so as to fit within one pixel pitch. These blocks are arranged side by side to form a series of vertical shift register blocks and horizontal shift register blocks. These blocks extend linearly in the vertical and horizontal directions. The area of the light-receiving portion of one pixel of these shift register blocks and the area of the light-receiving portion of another pixel are made equal to eliminate variations in sensitivity. Furthermore, the center of gravity of all light-receiving parts (center of gravity of pixels)
Are the same. A static shift register is used as the shift register. Various circuit configurations of the shift register can be applied by design. In this embodiment, a general circuit example is taken up.

According to this embodiment, since no dead space is generated around the image sensor, the entire surface of the image sensor becomes the effective pixel area.

By arranging these image pickup devices in a tile shape so that there is substantially no gap, a large-plate image pickup device (flat panel detector) can be formed. It is possible to obtain an image of a large plate that is substantially seamless.

In the medical X-ray image pickup device, the size of the pixel may be as large as 100 μm □ to 200 μm □, so that a sufficiently large aperture ratio can be realized even if a static shift register having a large number of constituent elements is arranged. it can.

Further, as the scanning means, an n to 2 ⁿ decoder can be used instead of the shift register. By connecting the output of the counter that increments sequentially to the input of the decoder, it is possible to perform sequential scanning in the same way as a shift register, while by inputting the address of the area where the image is to be obtained to the input of the decoder, random scanning It is possible to obtain an image of an arbitrary region by.

In this embodiment, a CMOS is used as an image pickup device.
Since the image pickup device is used, it consumes less power and is suitable for forming a large image pickup device.

The reason why the multiplexer is built in the image pickup device is to accelerate the operation of the image pickup device.

A signal is taken out from the image pickup device to the outside via the electrode pad, but there is a large stray capacitance around this electrode pad. Therefore, by providing an amplifier in the preceding stage of the electrode pad, the signal transmission characteristics can be compensated.

In this embodiment, since the vertical and horizontal shift registers are arranged in the effective pixel area, the X-rays passing through the scintillator plate directly hit the shift register. X-rays are a problem because they damage the elements in these circuits and cause errors and noise in the circuits.

An example of the error is a phenomenon in which electric charges are accumulated at the interface between the insulating oxide film SiO ₂ and silicon, and the threshold value varies and the leak current increases. Another example of damage is a defect that occurs in the pn junction surface, and this defect causes an increase in leak current. Another example of the error is similar to the error (soft error) due to the action of hot electrons known as a malfunction in the MOS dynamic RAM. For example, in the driving circuit, noise is generated in the reset circuit, the scanning is temporarily stopped, and the shift pulse is displaced. In other peripheral circuits, it often becomes noise. Hot electrons generated by an electric field are likely to occur in a short channel structure in which the electric field is high, but hot electrons generated by X-rays are generated regardless of size, and therefore, when an X-ray hits regardless of a planar size, an imaging device Is prone to instability. As noise, electron-hole pairs are generated in silicon by X-rays that have penetrated into single crystal silicon. There is noise generated when these carriers enter the circuit, and is added to the inherent system noise of the circuit. Such a phenomenon occurs not only in the case of using the shift register but also in the case of using a circuit such as a decoder or a common amplifier that may be directly irradiated with X-rays.

By using the FOP, it is possible to reduce the amount of X-rays (X-ray photons) directly entering the image pickup device to several tenths or less. Since the X-ray damage is proportional to the total amount of absorbed X-rays, the FOP can considerably reduce the X-ray damage. On the other hand, errors and noise due to X-rays depend not only on the total amount of X-rays but also on the energy of X-rays. The energy of X-rays generated at a tube voltage of 80 kVp is 80 keV at maximum and about 60 keV on average, which is very large. If even one high-energy X-ray photon is absorbed, tens of thousands of electron-hole pairs are generated.
When these enter the light receiving portion, a spike-like signal is generated, and at the same time, fluctuations of this signal are added as noise. If it enters the capacitance, signal line, or transistor other than the light receiving part, it becomes a noise component and is added. Further, if it enters a logic circuit such as a shift register, it may cause an operation error. In other words, FOP alone can reduce damage, but it is difficult to reduce errors and noise.

In the present invention, an X-ray image pickup device which is resistant to noise due to direct X-rays can be realized by considering the following driving. FIG. 8 is a timing chart showing the operation of the image pickup apparatus of this embodiment. The operation of 3 × 3 pixels will be described.

At T1, the reset signal φRES becomes high level and the reset MOS transistors of all pixels are turned on, whereby the floating diffusion C _FD is reset. An X-ray pulse for imaging a subject is emitted to expose the photodiode. By setting the transfer signal φTX to a high level and turning on the transfer switch for all pixels at once, the charges accumulated in the photodiode are completely transferred to the floating diffusion C _FD formed in the gate part of the source follower forming the pixel amplifier. . When the row selection signal SEL1 becomes high level, the row selection MOS transistor of the corresponding row is turned on, and the amplification MO
The image pickup signal is read out to the signal output line via S. The image pickup signal for one row thus read is read out to the outside of the image pickup device via the common amplifier when the column selection signals φSH1, φSH2, and φSH3 are sequentially turned on by the horizontal shift register. Similarly, the signal of each row is read.
In this embodiment, the X-ray pulse is emitted between the reset signal φRES and the transfer signal φTX. While the X-rays are irradiated on the entire surface of the FOS pixel area, the horizontal shift register and the vertical shift register provided in the pixel area do not generate driving signals, so that they do not malfunction.
Also, noise due to X-rays is not added to these circuits.

It is the vertical and horizontal shift registers installed in the pixel area that perform these operations. X-rays are not emitted while these circuits are being driven, and they do not malfunction. . Further, during this period, carriers are not generated by X-rays that have entered the silicon bulk, and noise is not added during the circuit operation. In addition, an addition switch for adding and outputting pixel signals may be provided in order to perform pixel addition or the like for each pixel. In such a case, a common processing circuit is provided in the pixel region in order to commonly process the pixels. When performing operations such as addition with this common processing circuit,
Perform when X-ray is off. During addition, noise due to X-rays is not added directly to the signal after addition, and the common processing circuit does not malfunction.

In the embodiment described above, the phosphor is used to convert the X-ray into visible light, but a general scintillator, that is, a wavelength converter may be used. Alternatively, the photoelectric conversion element itself may directly detect radiation and generate an electric charge without a phosphor.

Although the case of using X-rays has been described as an example, radiation such as α, β and γ rays can be used.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The image sensor used in the second embodiment has the same basic configuration as that of the first embodiment, but the circuit configuration of one pixel is different from that of the first embodiment. FIG. 9 shows a one-pixel circuit according to the second embodiment of the present invention. In the present embodiment, the kTC correction in the photoelectric conversion unit is performed in the pixel, and the sensitivity switching unit is further provided in the pixel, whereby still image shooting and high-speed moving image shooting are realized by mode switching.

Now, the specific conditions required for the photoelectric conversion unit in the image pickup device for both still image shooting and moving image shooting will be described. The irradiation X-ray dose during movie shooting is 1/1 as compared with still image shooting
The number of X-ray photons per pixel is at most about 00 (actually incident visible light obtained by converting the X-rays into the pixel), and the maximum sensitivity is required for the image sensor. However, there is no problem with the dynamic range. Further, a reading speed of 60 to 90 frames / second is required.
The pixel resolution may be as coarse as 200 μm □ to 400 μm □. On the other hand, when capturing a still image, a dynamic range close to 80 dB is required. Pixel resolution is 100 μm
□ to 200 μm □ is required. Until now, there has been no image sensor that simultaneously satisfies these specifications.

Therefore, in this embodiment, the CMOS type image pickup device has a pixel circuit configuration as shown in FIG. 9 to realize an image pickup device satisfying these specifications. In FIG. 9, PD is an embedded photodiode that is the same as that used in a CCD or the like as a photoelectric conversion unit. The buried photodiode suppresses a dark current generated on the SiO ₂ surface by providing a p ⁺ layer having a high impurity concentration on the surface. In addition, the photodiode P
The capacity C _PD of D is designed to be minimum in order to obtain maximum sensitivity when shooting a moving image. As will be described later, when the capacitance of the photodiode _PD is reduced, the dynamic range is reduced. Since the dynamic range is insufficient when capturing a still image in which the irradiation X-ray dose is 100 times or more that of a moving image, the capacitance C1 for expanding the dynamic range is provided in parallel with the photodiode FD.

M1 is a switch for switching between the still image mode (high dynamic range) and the moving image mode (high sensitivity mode). The floating diffusion (floating diffusion region) capacitance C _FD (not shown) for accumulating electric charges is also designed to have the minimum capacitance so as to have the maximum sensitivity during a moving image. Floating diffusion (floating diffusion area) is amplified M
It is formed so as to be connected to the gate portion of the OS transistor M4. M2 is a reset MOS transistor (reset switch) for discharging the charges accumulated in the floating diffusion, M3 is a selection MOS transistor (selection switch) for selecting the pixel amplifier 1, and M
Reference numeral 4 is an amplification MOS transistor (pixel amplifier 1) that functions as a source follower.

A clamp circuit, which is a feature of this embodiment, is provided at the subsequent stage of the pixel amplifier 1. This clamp circuit removes kTC noise generated in the photoelectric conversion unit. C _CL is a clamp capacitance, and M5 is a clamp switch. A sample hold circuit is provided after the clamp circuit as in the first embodiment. M6 is a selection MOS transistor (selection switch) for selecting the pixel amplifier 2, and M7 is an amplification MO functioning as a source follower.
It is an S transistor (pixel amplifier 2). M8 is a sample MO that constitutes a sample hold circuit for accumulating an optical signal.
The S-transistor switch and CH1 are hold capacitors.

Further, M9 is a selection MOS transistor (selection switch) for selecting the pixel amplifier 3, and M10 is an amplification MOS transistor (pixel amplifier 3) functioning as a source follower. M11 is a sample MOS transistor switch that constitutes a sample hold circuit for accumulating noise signals, and CH2 is a hold capacitor.
M12 is a selection MOS transistor (selection switch) for selecting the pixel amplifier 3, and M13 is an amplification MOS transistor (pixel amplifier 3) that functions as a source follower.

In the present embodiment, in-pixel sample and hold circuits for these optical signals and noise are used to remove FPN due to thermal noise, 1 / f noise, temperature difference and process variation in the pixel amplifier.

Next, the structure of the pixel portion will be described. In this embodiment, since the pixel is as large as 160 μm □, there is a limit in reducing the capacitance C _PD with an appropriate aperture ratio (photodiode area). By taking the method of reducing the electrode area while keeping the area of the photodiode unchanged, the capacitance C _PD
However, this method lowers the efficiency of collecting charges to the electrodes, and makes it difficult to completely transfer the signal charges to the floating diffusion by the transfer switch.
In this embodiment, the design is such that complete transfer is not performed, no transfer switch is provided, and the photodiode and the floating diffusion are directly connected to each other to form a photoelectric conversion unit. Further, the capacitance C _{PD of the} photodiode and the capacitance C _{FD of the} floating diffusion are set so that the maximum sensitivity is obtained when shooting a moving image.
Is designed to be minimal.

In this embodiment, since kTC noise is generated when the photoelectric conversion unit is reset because it is not a complete transfer, it is necessary to remove this kTC noise (reset noise) in a circuit in order to improve the S / S ratio of the photoelectric conversion device. This is an important point for N conversion. Therefore, in the present embodiment, the clamp circuit is provided for each pixel. It is known to use a clamp circuit for removing kTC noise. This is not the case because the kTC noise does not occur in the photoelectric conversion unit when the pixel size is relatively small, from 50 to 100 μm □, and complete transfer is possible.

However, in order to provide an image pickup device for both the still image mode and the moving image mode, it is necessary to remove kTC noise even in the still image mode, and it is essential to provide a clamp circuit in each pixel. In this embodiment, a clamp circuit is provided in front of the sample hold circuit for collective exposure so that the kTC noise can be removed even in the collective exposure moving image mode.

Further, in order to increase the dynamic range of the photodiode for still image shooting, it is preferable that the capacitance C _PD be large, but if this is done, the signal voltage will drop and the S / N will drop. A sensitivity (dynamic range) switching circuit is provided to increase the dynamic range during still image shooting while maintaining the maximum sensitivity during moving image shooting, and a capacity and a changeover switch are provided in each pixel in this embodiment. When shooting still images, S /
N becomes worse, but in order to improve S / N,
In particular, a clamp circuit that removes kTC noise is required.

FIG. 10 is a timing chart showing the operation of the pixel portion when the present embodiment is driven in the moving image mode. The drive timing of this image sensor will be described with reference to FIG. First, all the pixels are grouped together in the vertical shift register VS.
The signals φEN and φCHG from R are set to a high level and the selection switches M3 and M6 are turned on to turn on the constant current source to the amplification transistor, and the signal φRES is set to a high level to reset the electric charge of the photodiode to the reset potential. Next, the signal φCL is set to the high level to turn on the MOS transistor M5, so that one end of the clamp capacitor is biased to the clamp potential. In this way, kTC noise (reset noise) generated by resetting the charge of the photodiode is accumulated in the clamp capacitor. When the signal φTN is set to the high level, the clamp potential of the clamp capacitor is stored in the noise sample hold capacitor CH2. The above is the noise signal accumulation operation.

Next, exposure is performed by pulse irradiation of X-rays, and photocharges are accumulated in the photodiode (this is the exposure operation). After that, when the signal φEN is set to the high level, the potential at the one end of the clamp capacitor fluctuates by the signal component corresponding to the photocharge. That is, kT is
Since the C noise component is accumulated, the potential at one end of the clamp capacitor fluctuates by the potential obtained by subtracting the kTC noise component from the image pickup signal including the kTC noise component.
In order to read the image pickup signal in which this kTC noise is canceled, the signal CHG and the signal φTS are set to the high level. By doing so, the image pickup signal (optical signal) in which kTC noise has been canceled is accumulated in the signal sample and hold capacitor. The above is the optical signal accumulation operation.

The above series of operations are repeated. Here, the exposure possible time of the image pickup device is the signal φR after the clamp potential is transferred to the capacitor, that is, after the signal EN becomes low level.
Until ES becomes high level and the reset MOS transistor is turned on. In the present embodiment, attention is particularly paid to the relationship between the timing of the X-ray pulse and the drive timing of the shift register installed in the pixel area. In this embodiment, X-rays are not emitted during signal reading. As shown in FIG. 10, X-ray irradiation is performed after the signal reading is completed and before the next φEN is turned on. That is, while the X-ray pulse is not being emitted, the signal φSEL is set to the high level for each row, and the signal φSELH is set to the high level for each column, whereby the noise signal and the optical signal are output. It is the vertical and horizontal shift registers that produce these drive signals, and no X-rays are emitted while these shift registers produce the signals. That is, the elements in the pixel are not driven by the shift register while the photodiode is exposed by being irradiated with the X-ray pulse. Therefore, when the X-ray pulse directly enters the image sensor, an error (malfunction) occurs in the shift register,
No noise is generated during signal transfer.

The signal transferred to the noise signal output line and the optical signal output line is (signal-noise) by a subtraction output amplifier (not shown) connected to the noise signal output line and the optical signal output line.
Is subtracted. At this time, the optical signal and the noise signal are captured by the sample hold circuit from the pixel amplifier 2 with a very fast time difference, so that the 1 / f noise having a large value at low frequency can be removed, and the high frequency component can be ignored. Further, with this time difference, there is no variation in the threshold Vth due to the temperature difference of the output stage source follower. The output charge stored in the hold capacitor is the output of one pixel amplifier at the time of both reset and signal charge input, which is obtained continuously in terms of time. By taking the difference, it is possible to remove FPN due to thermal noise, 1 / f noise, temperature difference, and process variation in the pixel amplifier.

On the other hand, in the still image mode, the same operation as described above is performed when the signal φSC is set to the high level and the capacitor C1 is connected in parallel to the photodiode PD. in this case,
Since the capacitance C1 has a capacitance close to 10 times the capacitance C _FD , a wide dynamic range can be realized. Further, kTC noise of the photoelectric conversion unit can be removed for each pixel by the clamp circuit. Further, by providing a sample hold circuit for optical signal storage and noise signal storage in the pixel, it is possible to remove thermal noise, 1 / f noise, temperature difference in the pixel amplifier, FPN due to process variation. As a result, in the moving image mode, it is possible to realize high-speed and high-sensitivity moving image shooting that is temporally and spatially seamless with nine image sensors.
On the other hand, in the still image mode, high sensitivity and high dynamic range still image shooting can be realized.

It is the vertical and horizontal shift registers installed in the pixel area that perform these operations. X-rays are not emitted while these circuits are being driven, and they do not malfunction. . Further, during this period, carriers are not generated by X-rays that have entered the silicon bulk, and noise is not added during the circuit operation. In addition, an addition switch for adding and outputting pixel signals may be provided in order to perform pixel addition or the like for each pixel. In such a case, a common processing circuit is provided in the pixel region in order to commonly process the pixels. When performing operations such as addition with this common processing circuit,
Perform when X-ray is off. During addition, noise due to X-rays is not added directly to the signal after addition, and the common processing circuit does not malfunction.

The present embodiment has sample and hold circuits for signals and noise. When X-rays are emitted when signals are accumulated in these circuits, noise may occur in these circuits and the image quality may be degraded. Therefore, preferably, the X-ray pulse is not emitted while the signals are accumulated in these sample hold circuits.

In each of the embodiments described above, a phosphor is used to convert X-rays into visible light, but a general scintillator, that is, a wavelength converter may be used. In addition, the photoelectric conversion element itself directly detects radiation without a phosphor,
It may be one that generates an electric charge. In each embodiment, X
Although the case of using rays has been described as an example, radiation rays such as α, β, and γ rays can be used.

As described above, in the first and second embodiments, the vertical and horizontal shift registers are scanned during the period in which the radiation pulse generated from the pulse X-ray generator 100 is not generated at the predetermined intervals. As the means scans the imaging area,
By having the controller 119 that controls the sensor driving unit 107 and the X-ray driving unit 108, it is possible to obtain a good image.

(Third Embodiment) FIG. 12 shows an application example of the image pickup apparatus described in the first and second embodiments to an X-ray diagnostic system.

X-ray 60 generated by X-ray tube 6050
Reference numeral 60 passes through the chest 6062 of the patient or subject 6061 and enters a radiation imaging apparatus 6040 including a scintillator, FOP, an image sensor, and an external processing substrate. The incident X-ray contains information on the inside of the body of the patient 6061. The scintillator emits light in response to the incidence of X-rays, and the image sensor photoelectrically converts the light to obtain electrical information. This information is converted to digital image processor 6070.
The image is processed by and can be observed on the display 6080 in the control room.

Further, this information can be transferred to a remote place by a transmission means such as a telephone line 6090, can be displayed on a display 6081 such as a doctor room at another place, or can be stored in a storage means such as an optical disk, so that a doctor at a remote place can use it. It is also possible to diagnose. Also, the film processor 61
00 to record on the film 6110.

[0062]

As described above, according to the image pickup apparatus of the present invention, it is possible to obtain a high quality moving image.

[Brief description of drawings]

FIG. 1 is a plan view showing a layout of an image sensor.

FIG. 2 is a diagram showing a relationship between one pixel circuit in an image sensor and a unit block of a shift register.

FIG. 3 is a plan view showing an image pickup element and a wafer which is a source thereof.

FIG. 4 is a plan view showing an arrangement of image pickup devices and an arrangement of scanning circuits in the image pickup module.

5 is a cross-sectional view showing a configuration of an imaging module, showing a cross section AA ′ of FIG.

FIG. 6 is a one-pixel circuit diagram of the image sensor according to the first embodiment of the present invention.

FIG. 7 is an equivalent circuit of the image sensor according to the first embodiment of the present invention.

FIG. 8 is an operation timing in the first embodiment of the present invention.

FIG. 9 is a one-pixel circuit diagram of the image sensor according to the second embodiment of the present invention.

FIG. 10 is an operation timing in the second embodiment of the present invention.

FIG. 11 is a block diagram of an imaging device.

FIG. 12 is a conceptual diagram showing a configuration of a radiation imaging system.

FIG. 13 is a diagram showing a first conventional technique.

FIG. 14 is a diagram showing a second conventional technique.

FIG. 15 is a diagram showing a third conventional technique.

[Explanation of symbols]

100 pulse X-ray equipment 101 imaging module 107 sensor drive unit 108 X-ray drive unit 109 controller

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G088 EE01 FF02 FF04 FF05 FF06                       GG19 JJ05                 4C093 AA01 EA02 EB12 EB13 EB17                       EB20 FA19 FA32 FA43                 5C024 AX12 AX16 AX17 GX01 GY31                       HX01 JX41

Claims (6)

[Claims] 1. An image pickup apparatus in which radiation pulses are sequentially generated at predetermined intervals, the image pickup area having a plurality of pixels for picking up a subject image, a scanning unit for scanning the image pickup area, and the radiation. An image pickup apparatus comprising: a control unit that controls the scanning circuit to scan the image pickup area during a period in which no pulse is generated. 2. The control unit according to claim 1, wherein the control unit generates the radiation pulse after resetting the pixel, and the scanning unit scans the imaging region after the generation of the radiation pulse ends. An image pickup apparatus, which is controlled to 3. The photoelectric conversion unit according to claim 1 or 2, wherein each of the plurality of pixels resets an amplification unit that amplifies and outputs a signal from the photoelectric conversion unit and an input unit of the amplification unit. A reset means, the control means,
The input unit of the amplifying unit is reset, the signal after the reset is read from the amplifying unit, and the signal generated in the photoelectric conversion unit is read from the amplifying unit during the period when the radiation pulse is not generated. An imaging device characterized by the above. 4. The pixel according to claim 1, wherein each of the plurality of pixels has a photoelectric conversion unit, and the control unit controls the plurality of pixels during a period in which the radiation pulse is not generated. An image pickup apparatus characterized in that the scanning means is controlled so as to add signals from the photoelectric conversion section. 5. The image pickup apparatus according to claim 1, wherein the scanning unit is arranged between pixels in the image pickup area. 6. The signal processing unit according to claim 1, wherein the signal processing unit processes a signal from the imaging region, a recording unit records a signal from the signal processing unit, and the signal processing unit. And a display unit for displaying a signal from the unit.