JP4872017B2 - Imaging apparatus, driving method thereof, radiation imaging apparatus, and radiation imaging system using the same - Google Patents

Description

  The present invention relates to an imaging apparatus, a driving method thereof, a radiation imaging apparatus, and a radiation imaging system using the imaging apparatus. It relates to the system used.

  In recent years, digitization has progressed in various fields of medicine. Also in the field of X-ray diagnosis, in order to digitize an image, a two-dimensional X-ray imaging apparatus that converts incident X-rays into visible light by a scintillator (phosphor) and further captures the visible light image with an imaging device. Has been developed.

  As a two-dimensional X-ray imaging device, for example, a small CCD type imaging device has been put into practical use for dentistry, and a large size using amorphous silicon (a-Si) having a maximum of 43 cm □ for mammography and chest imaging. An area still image capturing apparatus has been put into practical use. An image pickup device using an amorphous silicon semiconductor on a glass substrate can be easily manufactured with a large area, and there are some which realize a large area X-ray image pickup device by tiling four panels. An example of this type of technique is described in US Pat. No. 5,315,101.

  In addition, proposals have been made to configure a large-area X-ray imaging apparatus using a plurality of single crystal imaging elements (silicon imaging elements or the like). Examples of this type of technology include those described in Patent Document 1 and Patent Document 2. Examples of the single crystal imaging device include a CCD type imaging device using silicon, a MOS type, a CMOS type imaging device, and the like. In the medical X-ray diagnostic field where digitization is progressing in this way, next-generation moving image imaging devices (such as fluoroscopy) of still image imaging devices are expected.

  Technical issues here include (1) high sensitivity, high-speed reading technology, (2) enlargement, and (3) cost reduction. With respect to the problems of (1) high sensitivity and (2) high-speed reading, in order to capture a moving image, a sensitivity and a reading speed that are 10 times higher than that of an imaging device using amorphous silicon are required. To capture a moving image, humans are continuously irradiated with X-rays. However, considering the effects of X-ray irradiation, the irradiation amount of X-rays is reduced from several tens to one hundredth, and the reading speed is set from 60. 90 frames / second is required, and several tens of times higher sensitivity and several tens of times higher speed are required to perform this reading.

  Amorphous silicon does not have sufficient semiconductor characteristics for high-speed operation, and it is difficult to finely process a semiconductor on a glass substrate compared to a single-crystal silicon semiconductor substrate with a large-area imaging device using this. The capacity of the signal line is increased. This capacity causes the largest noise (kTC noise). The manufacturing process of the amorphous silicon type large-plate imaging device is advantageous in that a large-area imaging device is obtained as compared with a CCD type imaging device or a CMOS type imaging device. However, the photoelectric conversion unit is not completely depleted, and a drive circuit and an amplifier for the image sensor are required outside (see FIG. 52 of Patent Document 3), and it is necessary to determine whether the image sensor is good after incorporating peripheral components. For this reason, the image pickup device itself is relatively inexpensive, but the cost is finally high. As described above, it is difficult to realize the above-described requirements.

  The CCD image sensor is completely depleted and highly sensitive, but is not suitable as a large-area image pickup device. Since the CCD type image pickup device is a charge transfer type, transfer becomes more problematic as the area becomes larger and the number of transfer stages increases (the number of pixels becomes higher). That is, the driving voltage is different between the driving end and near the center, and complete transfer becomes difficult. The power consumption is represented by CVf2 (C is the capacitance between the substrate and the well, V is the pulse amplitude, and f is the pulse frequency). The larger the area, the larger C and V, and the power consumption is CMOS type. It is 10 times larger than the image sensor. As a result, the peripheral drive circuit becomes a heat source and a noise source and does not have a high S / N ratio. As described above, the CCD type image pickup device has a surface that is not suitable for a large image pickup device.

  Furthermore, in the configuration of a simple large-area image pickup device using a large number of single crystal image pickup devices, there is always a dead space in the joint portion of each image pickup device (peripheral circuits such as shift registers and amplifiers, and exchange of signals and power with external devices). Therefore, an area for providing an external terminal and a protection circuit is always necessary separately from the area), and this part becomes a line defect, and the image quality deteriorates. For this reason, a configuration is adopted in which a tapered FOP (fiber optic plate) is used to guide light from the scintillator to the image sensor while avoiding dead space. However, an extra FOP is required and manufacturing costs are increased. In particular, the tapered FOP is very expensive. Further, in the tapered FOP, there is a problem that light from the scintillator becomes difficult to enter the FOP according to the taper angle, the output light amount is reduced, and the sensitivity of the image pickup device is offset to deteriorate the sensitivity of the entire apparatus.

  In order to compensate for the drawbacks of the amorphous silicon imaging device and the CCD imaging device as described above, a configuration in which a large-area CMOS imaging device is tiled has been proposed (Patent Document 4).

US Pat. No. 4,323,925 US Pat. No. 6,0059,911 Japanese Patent Laid-Open No. 8-111004 JP 2000-184282 A

However, the conventional amplification type imaging device such as a CMOS type imaging device has the following disadvantages.
(A) In a general amplifying type image pickup device driving method, accumulated charges for each horizontal scanning line are sequentially read out in units of horizontal scanning lines in the same row. While the accumulated charges are read from a certain horizontal scanning line, the remaining horizontal scanning lines accumulate charges. In this case, the charge accumulation time differs for each horizontal scanning line. If this charge is read out and reproduced as an image, an image with a different timing is obtained for each scanning period. In still image shooting, this difference in accumulation time is rarely a problem, but in moving image shooting, an image flows and becomes a problem. In particular, in an image pickup apparatus in which a plurality of image pickup elements (an image pickup element panel in which a plurality of pixels are formed) is tiled, discontinuity occurs in images between the image pickup elements as described later, which is a serious problem. Also, in X-ray video shooting, during the reading time of one horizontal scanning line, it is the exposure time of another horizontal scanning line, and it is necessary to perform partially unnecessary X-ray irradiation, so that the exposure dose should be reduced as much as possible. This method is difficult to apply in the field.
(B) In order to prevent the charge accumulation period from being different between the horizontal scanning line to be read first and the horizontal scanning to be read later, a mechanical shutter is provided to accumulate charges on each horizontal scanning line. There is a method of making the period constant, but this method has a drawback that the apparatus becomes large.

  The following is a description of the problem relating to (a) above, particularly when high-speed moving image shooting is performed using an image pickup device in which four large-area CMOS image pickup elements are tiled. FIG. 14 is a plan view of an image pickup apparatus in which four image pickup elements are tiled. The imaging regions (imaging device panels) A1, A2, B1, and B2 are configured by arranging a plurality of pixel portions in the horizontal and vertical directions. In the imaging region, Hn represents a column scanned by the column scanning circuit, and Vn represents a row scanned by the row scanning circuit. Further, a column scanning circuit, a row scanning circuit, a memory circuit, and an output amplifier are provided for each imaging region.

  FIG. 15 shows a schematic configuration of one pixel portion of each image sensor and a signal readout circuit. In FIG. 15, a method of scanning and reading for each row is adopted. In the conventional circuit of FIG. 15, the signal readout circuit is a double sampling circuit as will be described in detail later. In FIG. 15, VSR is a row scanning circuit, and HSR is a column scanning circuit. PD is a photodiode, TR1 is a transfer switch, TR2 is a reset switch, TR3 is a row selection switch, TR4 is an amplification transistor, TR5 is a switch for resetting a signal line, TR6 and 7 are sample switches, and TR8 and TR9 are readout switches. It is. TR1 to TR9 are MOS transistors. CTS is an optical signal holding capacitor, and CTN is a reset signal holding capacitor.

  As will be described later in detail in the conventional circuit of FIG. 15, the reset signal (noise component, dark current component) is held in the reset signal holding capacitor CTN, and the optical signal (light signal component, noise component, dark current component) is held in the optical signal. Hold in capacity CTS. Thereafter, the signals held in the holding capacitors CTN and CTS are read out and differentially detected by a differential circuit (not shown), thereby outputting an optical signal from which noise components have been removed. In such an image pickup apparatus in which a plurality of image pickup elements are bonded together, when a moving subject is picked up, “connection” of moving images between the image pickup elements becomes important.

  FIG. 16 shows image composition when four image sensors are bonded. When the four image sensors are separately driven independently in the scanning direction as indicated by the arrows in FIG. 16, the four screen connecting portions (the connection portions of the imaging regions A1 and B2, the connection portions of the imaging regions B1 and A2). The correlation between the images is lost at the connection between the imaging areas A1 and B1 and the connection between the imaging areas B2 and A2. For example, the scanning period in the row direction is adjacent to the row of the imaging region A1 (the row where scanning ends) and the row of the imaging region B2 (the row where scanning starts) near the connection portion between the imaging regions A1 and B2. Since there is a time shift of minutes, the correlation of images is lost. At that time, the “connection” of the moving images is basically concerned with the imaging regions A1 and B1, the imaging regions A1 and B2, the imaging regions B2 and A2, and the imaging regions B1 and A2 to which the images are connected. It is. As described above, in the configuration in which an image pickup device using an amplification type image pickup device such as a CMOS type image pickup device is bonded, there is a problem in that image correlation is lost at the joint between the image pickup devices and image quality is deteriorated.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an imaging apparatus and an imaging apparatus capable of obtaining a seamless image with high speed and high sensitivity even when a plurality of imaging elements are bonded together. And a radiation imaging apparatus and a radiation imaging system using the same.

  The imaging device of the present invention includes an imaging device having a plurality of pixels arranged two-dimensionally, and the pixels hold a photoelectric conversion unit and a first holding for holding a photoelectric conversion signal generated by the photoelectric conversion unit. A second holding unit for holding a noise signal generated in the pixel, an amplifying element for amplifying and outputting a signal from the photoelectric conversion unit, the amplifying element, the first and first A clamp circuit having a capacitor, a switch for applying a predetermined potential to a terminal on the output side of the capacitor, and an amplification MOS transistor provided on the output side of the capacitor, between the two holding units; The first and second holding units are provided in parallel to each other on the output side of the amplification MOS transistor, and the imaging element has a drive circuit for supplying a drive signal to a plurality of the pixels, and the drive The circuit is the photoelectric conversion signal Of the first drive signal, the second drive signal for resetting the photoelectric conversion unit after the first drive signal, and the second drive signal. A plurality of a third drive signal for clamping a signal generated in the photoelectric conversion unit later by the clamp circuit and a fourth drive signal for holding the noise signal in the second holding unit. It is characterized in that it is given to all pixels at once.

  A radiation imaging apparatus according to the present invention includes the imaging apparatus and a scintillator.

  Further, the radiation imaging system of the present invention includes the radiation imaging apparatus, processing means for processing signals from the radiation imaging apparatus, recording means for recording signals from the processing means, and processing means from the processing means. It is characterized by comprising display means for displaying a signal and transmission means for transmitting a signal from the processing means.

  In addition, the driving method of the imaging apparatus of the present invention includes an imaging element having a plurality of pixels arranged in two dimensions, and the pixels hold a photoelectric conversion unit and a photoelectric conversion signal generated by the photoelectric conversion unit. A first holding unit, a second holding unit for holding a noise signal generated in the pixel, an amplification element for amplifying and outputting a signal from the photoelectric conversion unit, and the amplification element, A clamp circuit having a capacitor, a switch for applying a predetermined potential to a terminal on the output side of the capacitor, and an amplification MOS transistor provided on the output side of the capacitor, between the first and second holding units; In the method of driving an imaging device, wherein the first and second holding units are provided in parallel to each other on the output side of the amplification MOS transistor, the photoelectric conversion signals are collectively output in the plurality of pixels. 1 holding part A first step of holding, a second step of collectively resetting the photoelectric conversion unit in the plurality of pixels after the first step, and a batch of the pixel in the plurality of pixels after the second step. A third step of clamping the signal generated in the photoelectric conversion unit in the second step by the clamp circuit; and a fourth step of holding the noise signal in the second holding unit in a batch in the plurality of pixels. It is characterized by having.

  In the present invention, since the sample and hold circuits for optical signals and noise signals are provided in the pixels, the exposure dose can be made appropriate by performing collective exposure and irradiating radiation exposure at this timing. In addition, even when high-speed shooting is performed with a plurality of image sensors, there is no joint or flow of images. Further, FPN correction due to variations in each transistor and the like can be performed for each pixel.

As described above, the present invention can obtain the following effects.
(1) Since a sample and hold circuit for optical signal and noise signal is provided in the pixel, the imaging exposure time of the imaging area of each image sensor bonded together can be made at the same time by performing batch exposure, and noise correction A circuit can be provided for each pixel, and high-speed moving image shooting with high image quality can be performed.
(2) Since a plurality of image sensors can be configured with the same type of image sensor, the process up to the manufacture of the image sensor unit can be simplified, and the manufacture is facilitated, so that the cost can be reduced.
(3) Since a plurality of image sensors can be driven with a common drive pulse, the number of peripheral drive circuits is reduced, mounting is simple, and further low power consumption, low noise, and low cost can be achieved.
(4) A radiation imaging device can be configured with a high-sensitivity imaging device, and the exposure dose can be made appropriate by irradiating the radiation exposure pulsed at the timing of batch exposure. it can.

1 is a circuit diagram illustrating a pixel circuit of a first embodiment of an imaging apparatus according to the present invention. It is a figure which shows the whole circuit of the image pick-up element of embodiment of FIG. 2 is a timing chart for explaining the operation of the pixel circuit according to the embodiment of FIG. 1. It is a figure which shows the layout of the image pick-up element of embodiment of FIG. It is sectional drawing in the AA of FIG. It is a figure which shows the example in the case of producing one image sensor from one piece of wear. It is a figure which shows a mode that the unit block of the vertical shift register of embodiment of FIG. 1 was arrange | positioned with 1 pixel circuit in 1 area | region (cell). It is a figure which shows the layout of 1 area | region (cell) containing the shift register of embodiment of FIG. It is a figure which shows the state in which the pixel of embodiment of FIG. 1 was arranged. It is a circuit diagram which shows the pixel circuit of 2nd Embodiment by this invention. It is a timing chart which shows the operation timing of embodiment of FIG. It is a block diagram showing one embodiment of a radiation imaging device of the present invention. It is a figure which shows one Embodiment of the radiation imaging system of this invention. It is a top view which shows the imaging device of a prior art example. It is a circuit diagram which shows the pixel circuit of the imaging device of a prior art example. It is a figure for demonstrating the image composition of the imaging device of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit diagram showing a first embodiment of an imaging apparatus according to the present invention. FIG. 1 is a circuit diagram of one pixel. In the present embodiment, high-speed and high-sensitivity moving images that are temporally and spatially seamless are realized by pasting image sensors. In addition, charges accumulated in a common time from all the elements can be read out with a high signal-to-noise ratio (S / N) using a CMOS type image pickup element. In addition, the image sensor referred to in the present specification refers to an image sensor panel in which a plurality of pixels are two-dimensionally arranged. The entire surface of the image pickup device panel is a pixel region, and a large-area image pickup device is realized by bonding a plurality of image pickup device panels on a base (see FIG. 4).

  In FIG. 1, PD is a photodiode that performs photoelectric conversion, CPD is a junction capacitance of the photodiode (shown by a broken line), CFD is a capacitance of a floating diffusion (floating diffusion region) that accumulates charges (shown by a broken line), and M1 is a photo diode. Transfer MOS transistor (transfer switch) that transfers the charge generated by the diode PD to the floating diffusion, M2 is a reset MOS transistor (reset switch) for discharging the charge accumulated in the floating diffusion, and M3 selects the photoelectric conversion unit A selection MOS transistor (selection switch) M4 is an amplification MOS transistor (pixel amplifier 1) that functions as a source follower.

  Further, M8 is a MOS transistor as a sample switch that constitutes a sample and hold circuit for storing optical signals, which is a feature of the present embodiment, and CH1 is a hold capacitor for optical signals. M11 is a MOS transistor as a sample switch constituting a sample and hold circuit for accumulating noise signals, and CH2 is a noise signal hold capacitor. M10 is an amplification transistor (pixel amplifier 2) as a source follower for amplifying the output from the optical signal sample hold and outputting it to the signal line. M13 is an amplifying transistor (pixel amplifier 3) as a source follower for amplifying the output from the noise signal sample hold and outputting it to the signal line. Further, M9 and M12 are MOS transistors as selection switches for the pixel amplifiers 2 and 3, respectively.

  In the present embodiment, these optical signal and noise signal sample and hold circuits are used in order to perform batch reset and batch exposure at the same timing for each image sensor. Further, since the image signal can be stored in the sample and hold circuit portion independently of the exposure, the optical signal and the noise signal can be read out any number of times during the exposure period without being destroyed. It is also possible to read out a signal for automatic exposure while performing exposure using this function.

  Next, noise will be described. In general, in an amplification type imaging device such as a CMOS type imaging device, in order to improve a signal-to-noise ratio (S / N) at the time of reading, an amplification means (in-pixel amplifier) is provided inside to increase a signal gain. Yes. In the source follower of a MOS transistor generally used as this amplifying means, the threshold value Vth of the MOS transistor tends to vary. This variation is inherent in the design and manufacture of the device and is malicious in that it varies from pixel to pixel and from device to device. In particular, an imaging element for an X-ray imaging apparatus is large and tends to have large variations in the element. In addition, when a plurality of image sensors are used, the variation between the elements is large. This variation appears as a fixed output variation, so-called fixed pattern noise (FPN), or a non-uniform background image.

  In addition, 1 / f noise (flicker noise) and thermal noise are likely to occur in the MOS transistor, and this is random noise, so that a random background image is generated. In terms of device design, if the channel length of the MOS transistor is L and the channel width is W, the thermal noise is proportional to (L / W) · 1/2 and the 1 / f noise is inversely proportional to L · W. In order to reduce the noise of the transistor, the channel length L should be minimized and the channel width W should be set large. However, when the channel width W of the source follower as an amplifier which becomes a large noise source is particularly set large, the gate-drain gap is reduced. This increases the parasitic capacitance of the device, lowers the gain, and lowers the sensitivity, which is difficult to implement.

  In this embodiment, a PMOS transistor with essentially low 1 / f noise is used as at least a source follower. As a result, the size can be reduced to about 1/10 that of an NMOS transistor. Further, even if the X-rays that have passed through the scintillator directly hit the transistor, the PMOS transistor is more preferable because the X-ray durability is higher than that of the NMOS transistor (leakage current increases and threshold Vth fluctuation is small).

  In general, it is known to use a double sampling circuit in order to reduce low frequency noise components such as fixed pattern noise (FPN) due to variations in 1 / f noise and threshold values, and noise from a power source. FIG. 15 shows a conventional double sampling circuit in a single pixel circuit and a signal readout circuit as described above.

  In this circuit, first, the reset switch Tr2 is closed by the reset signal ΦRES, and then the photodiode PD is reset. Next, the row selection MOS transistor Tr3 is closed, and the dark signal appears on the output signal line through the amplification MOS transistor Tr4. At this time, by closing the sample switch Tr6, the reset signal (noise component, dark current component) is held in the reset signal holding capacitor CTN, and then the sample switch Tr6 is opened. Next, the reset switch Tr2 is opened, and the optical signal charge accumulated in the photodiode PD is transferred to the amplification MOS transistor Tr4 by opening the transfer MOS transistor Tr1. At the same time, the row selection MOS transistor Tr3 is closed, and the optical signal appears on the output signal line through the amplification MOS transistor Tr4. At this time, by closing the sample switch Tr7, the optical signal (optical signal component, noise component, dark current component) is held in the optical signal holding capacitor CTS, and then the sample switch Tr7 is opened.

  Next, the readout switches Tr8 and Tr9 are opened at the same time, and the reset signal held in the reset signal holding capacitor CTN and the optical signal held in the optical signal holding capacitor CTS are read out to a differential circuit (not shown). By subtracting the signal, an optical signal from which noise has been removed is output. Next, in order to read out all rows, each column line is selectively sampled, and then the next row is selected, and the same operation is repeated again.

  Here, thermal noise (kTC noise) in the photoelectric conversion unit does not occur if complete depletion transfer is performed by the pixel switch. The reset noise (kTC noise) in the floating diffusion is removed by this correlated double sampling circuit together with the 1 / f noise and the FPN due to the threshold Vth variation. However, although the two source followers and capacities for the correlated double sampling circuit for each column are roughly the same, they are not completely the same. A line-like fixed pattern is generated (for each column).

  In addition, since the threshold value Vth changes exponentially depending on the temperature, even if each source follower has a temperature difference of 1 ° C. or less, it appears as a fluctuation in output, and imaging is performed at a low irradiation dose like X-ray fluoroscopy. Even this slight fluctuation affects the image quality. Therefore, the two source followers of the sample and hold circuit must have an arrangement structure that minimizes variations in the threshold value Vth in terms of layout as will be described later, and a mechanism that does not generate a temperature difference during operation. If the readout timing from the sample and hold of the optical signal and the noise signal is different as in the prior art, a temperature change occurs due to this time difference.

  Therefore, in the present embodiment, as described above, the sample signal hold circuit for the optical signal and the noise signal is provided in the pixel, and the optical signal and the noise signal are stored independently of the exposure, and simultaneously from the sample hold circuit. A structure for outputting (each column 2-line output) is adopted. For batch exposure, it is necessary to provide a memory in the pixel, and this sample and hold circuit first functions as an in-pixel memory. Furthermore, it has a noise removal function. Since the optical signal and the noise signal are taken into the sample hold circuit from the pixel amplifier 1 with a very fast time difference, a large 1 / f noise can be ignored at a low frequency.

  Further, this circuit is used to remove thermal noise, 1 / f noise, and FPN in the pixel amplifier. The variation of the two sample-and-hold circuit elements is to arrange the capacitor as close as possible in the pixel, and the output source follower is a cross arrangement that is used in the normal MOS circuit layout to reduce the variation of the threshold Vth as much as possible. It is reduced as much as possible. In this way, this sample and hold circuit functions as a storage means for each pixel for batch exposure and also functions as a means for noise removal.

  FIG. 2 shows a schematic diagram of the entire circuit in the case of 3 × 3 pixels for simplicity. The details of one pixel circuit portion are as shown in FIG. The gate of the transfer switch M1 is connected to ΦTX from a vertical shift register VSR which is a kind of vertical scanning circuit, and the gate of the reset switch M2 is connected to ΦRES from the vertical scanning circuit. The gate of the selection switch M3 is connected to ΦSEL from the vertical scanning circuit. For simplicity, only these three control lines are shown. An optical signal and a noise signal from each pixel are output to the differential amplifier A1 via the column scanning circuit (horizontal shift register, multiplexer) via two signal output lines. The column selection MOS transistor M20 is operated by a signal from the horizontal shift register HSR, and is a switch for selecting a signal line in the column direction.

  FIG. 3 is a timing chart showing the operation timing of the pixel portion in this embodiment. The circuit operation will be described below with reference to FIG. First, photoelectric conversion is performed by the photodiode PD. The exposure is a batch exposure and is performed at the same timing and period for all the pixels of each image sensor. Therefore, there is no time shift of the image between the image pickup devices and between the scanning lines. During the photocharge accumulation period, the transfer switch M1 is in an off state, and the generated photocharge is accumulated in the junction capacitor CPD. During this time, no photocharge is transferred to the floating diffusion CFD formed in the gate portion of the source follower constituting the pixel amplifier 1 (M4).

  When the accumulation of the photodiode PD is finished, as shown in FIG. 3C, the signal ΦTX from the vertical shift register VSR is set to the high level for all the pixels and the transfer switch M1 is turned on to accumulate the photodiode PD. The transferred charges are completely transferred to the floating diffusion CFD formed in the gate portion of the source follower M4 constituting the pixel amplifier 1. Thereafter, the signal ΦTX is set to the low level for all the pixels, the transfer switch M1 is turned off, and the signal ΦSEL1 from the vertical shift register VSR is set to the high level for all the pixels as shown in FIG. 3 (d). As a result, the selection switch M3 is turned on, and the source follower circuit composed of the load current source I and the pixel amplifier 1 is set in an operating state.

  At the same time, as shown in FIG. 3 (f), the signal ΦSH1 from the vertical shift register VSR is set to the high level, and the sample switch M8 is turned on so that the signal from the photodiode PD is collectively applied to the capacitor CH1 through the pixel amplifier 1 (M4). Forward. At the same time, as shown in FIG. 3C, by setting the signal ΦTX to the low level for all the pixels at once, the photodiode PD can be exposed to the next frame. At the same time, as shown in FIG. 3D, the signal ΦSH1 is set to the low level for all the pixels at the same time, and the sample switch M8 is turned off, thereby completing the operation of holding the optical signal charge in the sample hold circuit.

  Next, as shown in FIG. 3B, the floating diffusion CFD is reset by setting the signal ΦRES from the vertical shift register VSR to the high level for all the pixels and turning on the reset switch M2. As shown in FIG. 3G, the signal ΦSH2 from the vertical shift register VSR is set to the high level for all the pixels at once, and the reset signal is transferred to the capacitor CH2 by turning on the sample switch M11. Next, the transfer of the optical signal and the noise signal to the sample hold circuit is completed by setting the signal ΦSH2 to the low level and turning off the sample switch M11 for all the pixels at once.

  Further, as shown in FIG. 3 (e), the signal ΦSEL2 is set to the high level for each row by the signal input to the vertical shift register VSR, and the selection switches M9, M12 are turned on to turn on the load current source and the pixel amplifiers 2, 3 The source follower circuit configured by (M10, M13) is set in an operating state. As a result, the optical signal and the noise signal held in the hold capacitors CH1 and CH2 are simultaneously transferred to the noise signal output line and the optical signal output line through the pixel amplifiers 2 and 3. The signal transferred to the noise signal output line and the optical signal output line is subjected to subtraction processing of (signal-noise) by a subtraction output amplifier (not shown) connected to the noise signal output line and the optical signal output line. A signal from which thermal noise, 1 / f noise, and FPN are removed is output. The subtraction output amplifier corresponds to the differential amplifier of FIG.

  In the above operation, the charge from the photodiode PD is completely transferred to the floating diffusion CFD, so that no kTC noise is generated. However, when the pixel size is as large as 160 μm □, complete transfer becomes difficult. In this case, kTC noise is generated, and the reset noise (kTC noise) in the floating diffusion included in the optical signal and the noise signal is output as random noise because there is no correlation. However, during moving image shooting, the fixed pattern noise has a greater influence on the image quality than the random noise. Therefore, in this embodiment, sufficient image quality can be obtained even when complete transfer is difficult. An example of further removing the reset noise will be described later.

  In this way, after performing a batch reset of the photodiode PD, a batch exposure is performed, and an optical signal and a noise signal are accumulated in the sample and hold circuit in the pixel, so that the exposure of the next frame and the reading of these signals are independent. Can be done. As a result, exposure can be performed while performing high-speed readout, so that the accumulation time can be made as long as possible even in high-speed operation with multiple pixels driven under a low irradiation dose as in a large area X-ray imaging device, and the optical signal intensity is increased. In addition, noise can be further reduced and the signal-to-noise ratio (S / N) can be improved.

  Furthermore, since a plurality of image sensors can be driven with a common drive pulse, the peripheral drive pulse generation circuit can be simplified. In addition, it can be seen that the image pickup element driving circuit can be shared by common driving, which is excellent in mounting.

  FIG. 4 shows an example in which a 408 mm □ large-area radiation moving image pickup apparatus is configured by bonding nine 136 mm □ image pickup elements having the pixels of FIG. 1 together. Nine image sensors 100 are bonded on the base, and a large-screen image pickup apparatus is configured as a whole.

  FIG. 5 is a sectional view taken along line AA in FIG. The scintillator 101 is composed of Gd2 O2 S, CsI, or the like using europium, terbium, or the like as an activator, and is installed on a FOP (Fiber Optical Plate) 102. The FOP 102 is a unity optical transmission means for guiding the light generated by the scintillator 101 to the image sensor at a unity magnification. The FOP 102 absorbs X-rays that are not absorbed by the scintillator 101 and protects the image sensor from X-ray damage.

  The X-ray hits the scintillator 101 and is converted into visible light, which is transmitted by the FOP 102 and 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 substrate 103 is a substrate having a circuit for supplying power to the image sensor, a clock, and the like, and extracting and processing signals from the image sensor. The flexible substrate 104 is a wiring substrate that performs electrical connection by TAB (Tape Automated Bonding) between each image sensor and an external processing substrate. Although X-rays are used as radiation, α rays, β rays, γ rays, and the like can be used.

  The nine image pickup devices 100 are bonded on the base 105 so that there is substantially no gap between the image pickup devices. The fact that there is no gap substantially means that an image formed by the nine image pickup devices is not formed. This means that there is no gap between the image sensors. The imaging device clock and the like, the input of the power supply and the output of the signal from the imaging device are transmitted to the external processing substrate 103 disposed on the back side of the imaging device through the flexible substrate 104 connected to the electrode pad at the end of the imaging device. Between. The thickness of the TAB flexible substrate 104 is sufficiently small with respect to the size, and even if it passes through the gap between the image pickup elements, no defect on the image occurs.

  FIG. 6 shows an example in which one image sensor is taken out from the currently mainstream 8-inch wafer 301. A 136 mm square CMOS type image pickup device substrate is produced by a single CMOS process. In a medical X-ray imaging apparatus, the pixel size may be as large as about 100 μm □ to 200 μm □. In this embodiment, the pixel size is 160 μm □. As shown in FIG. 6, a vertical shift register and a horizontal shift register are formed in the image sensor, and an external terminal (electrode pad) is provided at the end of the element near the horizontal shift register. This electrode pad is used for connection with a flexible substrate as described above.

  FIG. 7 shows a state in which unit blocks (units for selecting and driving one row) of vertical shift registers are arranged in one area (one cell) together with one pixel circuit. One pixel circuit is shown in FIG. The area of the unit block and the pixel circuit does not reflect the actual element layout because it is a schematic diagram. The vertical shift register is a simple circuit composed of a static shift register and a transfer gate for generating a transfer signal ΦTX, a reset signal ΦRES, and a selection signal ΦSEL. These are driven by signals 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 adopted by various driving methods such as addition and thinning readout. However, as in the present embodiment, functional blocks are arranged together with pixel circuits in one cell, a shift register is provided in the effective area, and an imaging device in the entire effective area is realized.

  Further, instead of a shift register, an n-to-2n decoder can be used as the scanning circuit. In this case, by connecting the output of the counter that sequentially increments to the input of the decoder, it becomes possible to scan sequentially in the same way as the shift register. On the other hand, by inputting the address of the area to obtain an image to the input of the decoder, An image of an arbitrary region can be obtained by scanning. The common processing circuit arranged in each area (cell) in the effective area means a circuit that collectively processes a plurality of signals such as a final signal output amplifier, a serial / parallel conversion multiplexer, a buffer, and various gate circuits. .

  FIG. 8 shows a layout of one region (cell) in which the shift register is arranged. A light receiving area is arranged at the center, and a scanning circuit (shift register, etc.) area, pixel amplifier, wiring area, signal and noise S / H circuit areas are provided around the light receiving area.

Cell size: 160 μm
S / H circuit area: 15 μm × 320 μm
Pixel light receiving area: 130 μm
Pixel amplifier, wiring area: 15 μm × 320 μm
Shift register block: 15 μm × 160 μm
It is said. Therefore, the aperture ratio is 66%. The layout of one area where no shift register is arranged is obtained by deleting the shift register block from the one shown in FIG. 8, and at least one of the areas where no shift register is arranged is provided with a shift register. It is the same as the light receiving area of the area (cell).

  FIG. 9 shows the configuration (plan view) of the image sensor of this embodiment. In this embodiment, a vertical shift register and a horizontal shift register are arranged in the effective area of the image sensor, and a plurality of pixels are arranged two-dimensionally in the vertical and horizontal directions in the image sensor. Further, one block of the shift register that processes one line is arranged so as to be within one pitch, and these blocks are arranged to form a series of vertical shift register blocks and a horizontal shift register block. These blocks extend linearly in the vertical and horizontal directions.

  Furthermore, at least the light receiving region has the same area for all pixels. In FIG. 9, the area of one pixel circuit and the area of a light receiving region in one pixel circuit are equal between cells. In addition, although it is preferable that the area of the light receiving region is the same among all the cells, the area of the light receiving region in the cell within one line at the end of the image sensor has a margin for slicing. It may be different from the area of the light receiving region. In FIG. 9, a bump is provided on the external terminal, and a protective resistor and a protective diode for protecting the internal circuit from static electricity are connected to the bump.

  In the present embodiment, the light receiving areas are uniformly sized between the image sensors and between the image sensors, and the centers of gravity are arranged at an equal pitch. Since variations in sensitivity within the imaging device and variations in the center of gravity of the light receiving area do not occur, a substantially seamless image can be obtained even with a tiled configuration. In addition, since no dead space is generated around the image sensor, the entire surface of the image sensor is an effective area.

  By arranging these image pickup elements in a tile shape so that there is substantially no gap, an image pickup device having a large area can be formed. Furthermore, with the circuit configuration as described above, it is possible to obtain a large-area image that is substantially seamless in terms of time and space. Here, in the medical X-ray imaging apparatus, since the size of the pixel may be as large as about 100 μm □ to 200 μm □, a circuit such as a sample hold is provided in the pixel even if a shift register is arranged in the effective pixel region. Since a sufficiently large aperture ratio can be realized even if it is arranged, there is no problem.

  In this embodiment, since the shift register is arranged in the effective region, the X-rays that have passed through the scintillator directly hit the shift register. However, by using a static shift register as the shift register, it is not affected by the X-rays. ing. The shift register circuit is used for sequentially transferring pulse signals. That is, in principle, the static type is relatively less susceptible to the influence of X-rays, so that it can be used in a place where X-rays directly hit as in this embodiment. Therefore, if a static shift register is used, an imaging apparatus with reduced X-ray damage and errors and improved reliability can be realized.

  Furthermore, in the present embodiment, since a CMOS type image sensor is used as the image sensor, the power consumption is low, which is suitable for the case of configuring a large area image pickup apparatus. The reason why the multiplexer is built in the image sensor is to speed up the operation of the image sensor. Further, a signal is taken out from the image pickup device via the electrode pad, and there is a large stray capacitance around the electrode pad. Therefore, signal transmission characteristics can be compensated by providing an amplifier in front of the electrode pad.

  In the present embodiment, FOP is used as the equal-magnification optical transmission means, but an equal-magnification lens optical system such as a Selfoc lens may be used. Compared with FOP, the lens optical system has lower light utilization efficiency, but has the advantage of significantly reducing the manufacturing cost of the imaging device.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The basic configuration of the imaging apparatus of the second embodiment is the same as that of the first embodiment, but the circuit configuration of one pixel is different from that of the first embodiment. FIG. 10 shows a one-pixel circuit according to the second embodiment of the present invention. In the present embodiment, kTC correction in the photoelectric conversion unit is performed in the pixel, and sensitivity switching means is provided in the pixel, so that still image shooting and high-speed moving image shooting are realized by mode switching.

  Here, the specific conditions required for the photoelectric conversion unit in the X-ray image sensor for both still image shooting and moving image shooting will be described. The irradiation X-ray dose at the time of moving image shooting is about 1/100 of that at the time of still image shooting, and the amount of X-ray photons at most per pixel (actually incident on this pixel is the visible light converted from this X-ray). There is a need for maximum sensitivity as an 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, a dynamic range close to 80 dB is required during still image shooting. The pixel resolution needs to be 100 μm □ to 200 μm □. There has been no image sensor that satisfies these specifications at the same time.

  Therefore, in this embodiment, an image sensor satisfying these specifications is realized by adopting a pixel circuit configuration as shown in FIG. 10 in a CMOS image sensor. In FIG. 10, PD is the same embedded photodiode used in a CCD or the like as a photoelectric conversion unit. The buried type photodiode is provided with a p + layer having a high impurity concentration on the surface to suppress dark current generated on the SiO2 surface. Further, the capacitance CPD of the photodiode PD is designed to be the minimum in order to obtain the maximum sensitivity during moving image shooting. As will be described later, when the capacitance of the photodiode PD is reduced, the dynamic range is reduced. Since a dynamic range is insufficient at the time of still image shooting in which the irradiation X-ray dose is 100 times or more compared with that at the time of moving images, a capacitor C1 for expanding the dynamic range is provided in parallel with the photodiode PD.

  M14 is a changeover switch for switching between a still image mode (high dynamic range) and a moving image mode (high sensitivity mode). A floating diffusion (floating diffusion region) capacitor CFD (not shown) for accumulating charges is also designed to have a minimum capacity so as to have the maximum sensitivity during moving images. The floating diffusion (floating diffusion region) is formed connected to the gate portion of the amplification MOS transistor M4. M2 is a reset MOS transistor (reset switch) for discharging charges accumulated in the floating diffusion, M3 is a selection MOS transistor (selection switch) for selecting the pixel amplifier 1, and M4 is an amplification MOS functioning as a source follower. This is a transistor (pixel amplifier 1).

  A clamp circuit, which is a feature of the present embodiment, is provided at the subsequent stage of the pixel amplifier 1. This clamp circuit removes kTC noise generated in the photoelectric conversion unit. CCL is a clamp capacitor, and M5 is a clamp switch. A sample and 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 MOS transistor (pixel amplifier 2) that functions as a source follower. M8 is a sample MOS transistor switch constituting a sample hold circuit for storing optical signals, and CH1 is a hold capacitor.

  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 constituting a sample and 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) functioning as a source follower.

  In the present embodiment, similar to the first embodiment, these optical signals and the in-pixel sample and hold circuit for noise are used in order to perform batch reset and batch exposure for each image sensor at the same timing. Further, since the image signal can be stored in this portion independently of the exposure, the optical signal and the noise signal can be read out any number of times during the exposure period without being destroyed. Using this function, signal readout for automatic exposure can be performed while performing exposure.

  Next, the configuration of the pixel portion will be described. In a conventional pixel portion, signal charges generated in a photodiode are transferred to a floating diffusion by a transfer switch, and the charges accumulated in the floating diffusion are converted into charges / voltages, and are amplified by an amplification MOS transistor (pixel amplifier) that functions as a source follower. Output as voltage. In the case of a photodiode with a small area, signal charges can be completely transferred to the floating diffusion by applying a sufficiently large voltage to the gate of the transfer transistor, and the photodiode can be completely depleted. In this case, kTC noise does not occur because of complete transfer. However, as described above, there are specific conditions required for the photoelectric conversion unit in the X-ray imaging element for both still image shooting and moving image shooting. In order to satisfy this condition, the present embodiment is configured as described below.

First, in a photodiode having a pn junction, when the photogenerated carrier QP is accumulated in the capacitance CPD of the photodiode section and converted into a voltage, the optical signal voltage VP by the photogenerated carrier is
VP = QP / CPD (1)
It becomes. There is reset noise that occurs every time the photodiode is reset. This appears as random noise. Reset noise VN is
VN = √ (kTCPD) (2)
It becomes. k: Boltzmann constant, T: temperature (K).

The S / N ratio is
VP / VN = QP · √ (1 / (kTCPD)) (3)
It becomes. In order to increase the light utilization rate, it is preferable that the area of the photodiode is large. However, if the area of the photodiode is increased, the capacitance CPD also increases. In order to obtain the highest sensitivity (S / N ratio) during moving image shooting, it is desirable to make the capacitance CPD of the photodiode as small as possible.
Further, the magnitude ΔV of the pixel amplifier output having the floating diffusion amplifier structure is expressed as follows.

ΔV = G · QP / CFD (4)
G is the gain of the source follower, CFD is the capacity of the floating diffusion, and QP is the signal charge stored in the capacity CFD.

  As is clear from the equation (4), the larger the ΔV with respect to the same signal charge QP, the larger the charge / voltage conversion gain, which is advantageous from the viewpoint of the S / N plane and the like. In order to increase ΔV with respect to the same signal charge Q, the gain G of the source follower is usually hardly changed to about 0.7 to 0.9, and therefore it is necessary to make the capacitance CFD as small as possible like the photodiode. .

  In this embodiment, since the pixel is as large as 160 μm □, there is a limit to reducing the capacitance CPD with an appropriate aperture ratio (photodiode area). Capacitance CPD can be reduced by taking a method of reducing the electrode area while keeping the area of the photodiode intact. However, in this method, the charge collection efficiency to the electrode is reduced, and the signal charge is completely transferred to the floating diffusion by the transfer switch. Becomes difficult. In this embodiment, the design is such that complete transfer is not performed, no transfer switch is provided, and a photodiode and a floating diffusion are directly connected to form a photoelectric conversion unit. In addition, the photodiode capacitance CPD and the floating diffusion capacitance CFD are designed to be minimum so as to obtain the highest sensitivity during moving image shooting.

  In the present embodiment, since the transfer is not complete, kTC noise is generated when the photoelectric conversion unit is reset. However, removing this kTC noise (reset noise) in terms of the circuit can increase the S / N ratio of the photoelectric conversion device. It becomes an important point. Therefore, in this embodiment, a clamp circuit is provided for each pixel. It is known to use a clamp circuit to remove kTC noise. If the pixel size is relatively small, such as 50 to 100 μm □, and complete transfer is possible, kTC noise does not occur in the photoelectric conversion unit, so this is not the case.

  This is not the case when FPN is more important than kTC noise during moving image shooting as in the first embodiment. However, in order to obtain an image sensor that uses 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 the pixel. In the present embodiment, a clamp circuit is provided before the sample-and-hold circuit for batch exposure so that kTC noise can be removed even in the batch 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 CPD is large. However, if this is done, the signal voltage decreases, so the S / N decreases. In order to expand the dynamic range at the time of still image shooting while maintaining the highest sensitivity at the time of moving image shooting, a sensitivity (dynamic range) switching circuit is provided, and a capacitor and a changeover switch are provided in each pixel in this embodiment. Since the capacity increases during still image shooting, the S / N deteriorates, but in order to improve the S / N, a clamp circuit that specifically removes kTC noise is necessary.

  FIG. 11 is a timing chart showing the operation timing of the pixel portion in the present embodiment. The circuit operation will be described below with reference to FIG. First, photoelectric conversion is performed by the photodiode PD. The exposure is a batch exposure and is performed at the same timing and period for all the pixels of each image sensor. Therefore, there is no time shift of the image between the image pickup devices and between the scanning lines. In this embodiment, the charge of the photodiode PD is not completely transferred to the floating diffusion, and no transfer switch is provided. Photoelectric charges generated in the photodiode PD are accumulated in the capacitors CPD and CFD. This photoelectric charge includes reset noise (kTC noise) at the end of the previous frame. The operation from this state will be described. In the moving image mode, the signal ΦSC is set to a low level.

  First, as shown in FIG. 11C, the signal ΦSEL1 from the vertical shift register VSR is set to the high level for all the pixels and the selection switches M3 and M6 are turned on so that the charges accumulated in the capacitors CPD and CFD are changed to the pixels. The voltage is converted into a voltage by the source follower constituting the amplifier 1 (M4) and held in the clamp capacitor CCL. The clamp capacitor CCL is clamped to a reset level including reset noise of the photoelectric conversion unit at the time of resetting the previous frame. By holding the photoelectric charge including reset noise here, the reset noise is removed from the clamp capacitor CCL. The optical signal is output.

  Further, as shown in FIG. 11 (f), simultaneously with the signal ΦSEL1 from the vertical shift register VSR, the signal ΦSH1 is set to the high level, and the sample switch M8 is turned on so that this optical signal is passed through the pixel amplifier 2 (M7) to the capacitor CH1. Batch transfer. Next, the signal ΦSH1 is set to the low level for all the images and the sample switch M8 is turned off to complete the holding of the optical signal charge in the sample hold circuit. As shown in FIG. 11B, the floating diffusion CFD is reset by setting the signal ΦRES from the vertical shift register VSR to the high level and turning on the reset switch M2 for all the pixels at once.

  At the same time, as shown in FIG. 11E, the signal ΦCL from the vertical shift register VSR is set to the high level, and the clamp switch M5 is turned on to set the clamp capacitor CCL to the reference voltage. At the same time, as shown in FIG. 11 (g), the signal .PHI.SH2 from the vertical shift register VSR is set to the high level for all the pixels at the same time, and the noise signal when set to the reference voltage by turning on the sample switch M11 is converted into the capacitance CH2. Forward to. Next, the signal ΦSH2 is set to the low level for all the pixels at the same time, and the transfer holding of the optical signal and the noise signal to the sample hold circuit is finished.

  Next, as shown in FIG. 11 (d), the signal ΦSEL2 is set to the high level for each row by the signal input to the shift register VSR, and the selection switches M9 and M12 are turned on to turn on the load current source and the pixel amplifiers 3 and 4 ( The source follower circuit configured by M10 and M13) is set in an operating state. Thus, the optical signal and the noise signal held in the hold capacitors CH1 and CH2 are simultaneously transferred to the noise signal output line and the optical signal output line through the pixel amplifiers 3 and 4.

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

  In this way, after performing a batch reset of the photodiode PD, a batch exposure is performed, and an optical signal and a noise signal are accumulated in the sample and hold circuit in the pixel, so that the exposure of the next frame and the reading of these signals are independent. Can be done. As a result, since exposure can be performed while performing high-speed readout, multi-pixel driving under a low irradiation dose as in a large area X-ray imaging apparatus, storage time can be as long as possible even at high speed operation, and the optical signal intensity can be increased. Furthermore, noise reduction can be performed to improve the signal-to-noise ratio (S / N).

  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, the capacitor C1 has a capacity close to 10 times the capacity CFD, so that a wide dynamic range can be realized. Further, the 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 storing optical signals and noise signals in the pixel, it is possible to remove FPN caused by thermal noise, 1 / f noise, temperature difference, and process variation in the pixel amplifier. Thereby, 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, the still image mode can realize still image shooting with high sensitivity and high dynamic range.

(Third embodiment)
FIG. 12 is a block diagram showing an overall configuration when an imaging apparatus is configured using an imaging device including the pixels of FIG. 1 or FIG. In FIG. 12, a subject (for example, a human chest) 110 is irradiated with radiation from an X-ray source 111, and the radiation transmitted through the subject 110 is incident on an image sensor unit 112. The image sensor unit is configured by tiling the nine image sensors of the first or second embodiment, and further includes a scintillator that converts X-rays into visible light, an X-ray shielding member, a peripheral drive circuit, and the like. The pixels of the image sensor have the configuration of the first or second embodiment. A radiation imaging apparatus can be configured by combining scintillators.

  4 × 8 system signals (signals output from 9 image sensors through 9 × 2 output lines) from the image sensor unit 112 are analogized by the signal A / D converter 113 and the FPN A / D converter 114. The signal is converted to a digital signal. The image sensor driving unit 115 is mounted adjacent to the image sensor unit 112. The A / D converted signal is sent to the image processing circuit 116, and the image processing circuit 116 and the memory 117 synthesize image signals of nine image sensors and correct defect noise. The processed signal is recorded in the recording unit 118 or displayed on the display unit (monitor) 119 and printed as necessary. These circuits and devices are controlled by the controller 120, and the controller 120 controls the timing of the X-ray source 111 and the image sensor.

  The memory signal stored in the temporary storage memory 117 is subjected to image processing (γ processing, interpolation processing, etc.) for synthesizing each image sensor signal as a single image (image processing circuit 116), and its output is a large image. The data is stored in the memory, and the memory output is displayed on the display unit 119 or the like. Image processing ends when shooting is completed. Data captured by the imaging apparatus is transferred to a personal computer or the like, where software processing for analyzing the subject is performed.

  Such an image processing method can be performed based on a program stored in a computer such as a personal computer. The present invention also includes an information recording medium such as a CDROM in which such a program is recorded. The image processing method according to the present invention can be executed by reading a program recorded in a CD ROM or the like.

(Fourth embodiment)
FIG. 13 is a diagram showing an example when an X-ray imaging system is configured using the radiation imaging apparatus of the present invention. In FIG. 13, X-rays 6060 generated by the X-ray tube 6050 pass through a chest 6062 of a patient or subject 6061 and enter a radiation imaging apparatus 6040 including a scintillator, an FOP, an imaging device, an external processing substrate, and the like. The incident X-ray includes information inside the body of the patient 6061. The scintillator emits light in response to the incidence of the X-ray, and the image sensor performs photoelectric conversion to obtain electrical information. This information is converted into a digital signal, image processed by an image processor 6070, and can be viewed on a control room display 6080.

  This information can be transferred to a remote location by transmission means such as a telephone line 6090, displayed on a display 6081 such as a doctor's room in another location, or stored in a storage means such as an optical disk, and diagnosed by a remote doctor. It is also possible to do. It can also be recorded on the film 6110 by the film processor 6100.

M1 transfer switch M2 reset switch M3 selection switch M4 amplification MOS transistor M5 clamp switch M6 selection switch M7 amplification MOS transistor M8, M11 sample switch M9, M12 selection switch M10, M13 amplification transistor M14 mode changeover switch PD photodiode CH1 optical signal hold Capacitance CH2 Noise signal hold capacitance CPD Photodiode junction capacitance CFD Floating diffusion capacitance 100 Image sensor 101 Scintillator 102 FOP
DESCRIPTION OF SYMBOLS 103 External processing board 104 Flexible board 105 Base 110 Subject 111 X-ray source 112 Image sensor unit 113, 114 A / D converter 115 Image sensor drive circuit 116 Image processing circuit 117 Memory 118 Recording part 119 Display part 120 Controller 6040 Radiation imaging Equipment 6050 X-ray tube 6060 X-ray 6070 Image processor 6081 Display 6090 Telephone line 6100 Film processor 6110 Film

Claims (9)

An image sensor having a plurality of pixels arranged in two dimensions, wherein the pixels are generated by the photoelectric conversion unit, a first holding unit for holding a photoelectric conversion signal generated by the photoelectric conversion unit, and the pixel; A second holding unit for holding the noise signal, an amplification element for amplifying and outputting the signal from the photoelectric conversion unit, and between the amplification element and the first and second holding units A clamp circuit having a capacitor, a switch for applying a predetermined potential to a terminal on the output side of the capacitor, and an amplification MOS transistor provided on the output side of the capacitor, and the first and second The holding unit is provided in parallel to each other on the output side of the amplification MOS transistor,
The image sensor has a drive circuit for supplying a drive signal to the plurality of pixels,
The drive circuit includes a first drive signal for holding the photoelectric conversion signal by the first holding unit, and a second drive signal for resetting the photoelectric conversion unit after the first drive signal. A third drive signal for clamping the signal generated in the photoelectric conversion unit after the second drive signal by the clamp circuit, and a second for holding the noise signal in the second holding unit. 4. The imaging device according to claim 4, wherein four drive signals are collectively supplied to the plurality of pixels.   The imaging apparatus according to claim 1, comprising a plurality of the imaging elements.   The imaging apparatus according to claim 1, wherein the pixel further includes a reset element that resets between the photoelectric conversion unit and the amplification element. 4. The imaging device according to claim 1, wherein the photoelectric conversion unit directly connects a photodiode and a floating diffusion formed of a gate portion of a MOS transistor that is the amplification element. 5. Is,
The first holding unit is a first sample-and-hold circuit having a first hold capacitor and a first sample switch provided between the amplification MOS transistor and the first hold capacitor. ,
The second holding unit is a second sample hold circuit having a second hold capacitor and a second sample switch provided between the amplification MOS transistor and the second hold capacitor. An imaging apparatus characterized by that. 5. The imaging device according to claim 4, wherein the pixel further includes sensitivity switching means connected to the photodiode,
The image pickup apparatus, wherein the sensitivity switching means includes a capacitor connected in parallel to the photodiode, and a sensitivity switching switch disposed between the photodiode and the capacitor.   6. The imaging device according to claim 1, wherein the pixel amplifies a signal from the first holding unit and outputs the amplified signal to a first output line. An image pickup apparatus comprising: a second amplifying unit that amplifies a signal from the second holding unit and outputs the amplified signal to a second output line different from the first output line.   A radiation imaging apparatus comprising: the imaging apparatus according to any one of claims 1 to 6; and a scintillator. The radiation imaging apparatus according to claim 7;
Processing means for processing signals from the radiation imaging apparatus;
Recording means for recording a signal from the processing means;
Display means for displaying a signal from the processing means;
Transmission means for transmitting a signal from the processing means;
A radiation imaging system comprising: An image sensor having a plurality of pixels arranged in two dimensions, wherein the pixels are generated by the photoelectric conversion unit, a first holding unit for holding a photoelectric conversion signal generated by the photoelectric conversion unit, and the pixel; A second holding unit for holding the noise signal, an amplification element for amplifying and outputting the signal from the photoelectric conversion unit, and between the amplification element and the first and second holding units A clamp circuit having a capacitor, a switch for applying a predetermined potential to a terminal on the output side of the capacitor, and an amplification MOS transistor provided on the output side of the capacitor, and the first and second In the driving method of the imaging device provided on the output side of the amplification MOS transistor in parallel with each other, the holding unit,
A first step of holding the photoelectric conversion signals in the plurality of pixels at a time by the first holding unit;
A second step of collectively resetting the photoelectric conversion unit in the plurality of pixels after the first step;
A third step of clamping the signals generated in the photoelectric conversion unit in the second step by the clamp circuit in a batch in the plurality of pixels after the second step;
A fourth step of holding the noise signal in the plurality of pixels at once by the second holding unit;
A method for driving an imaging apparatus, comprising:

Images