JP2017201750A - Radiation imaging device, method for driving the same, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique to suppress the occurrence of a delay in signal output due to the frequency of a frame rate.SOLUTION: A radiation imaging device comprises a plurality of sensors and a control part. The sensors include detection elements and sampling parts, and the control part periodically resets the detection elements, causes the sampling parts to sample signals generated by the detection elements after the resetting for every unit period from the start of resetting the detection elements to the start of the subsequent resetting, when the time required for a reading operation is equal to or more than the time from the end of sampling in a unit time of attention to the start of resetting in the subsequent unit period, starts the reading operation after resetting in the unit period subsequent to the unit period of attention and before sampling, and when the time required for the reading operation is less than the time from the end of sampling in the unit time of attention to the start of resetting in the subsequent unit period, starts the reading operation before resetting in the unit period subsequent to the unit period of attention.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a radiation imaging apparatus, a driving method thereof, and a program.

  The radiation imaging apparatus includes a plurality of sensors each including a detection element that generates a signal corresponding to incident radiation in order to acquire a radiation image, and a drive unit for driving the plurality of sensors. Since the signal output from each sensor includes a signal component generated by the detection element and a noise component caused by dark current or the like, the drive unit initializes the detection element before starting irradiation of radiation. Perform a reset operation. In an operation mode in which radiation imaging is repeatedly performed, such as continuous imaging or moving image imaging, the driving unit repeatedly performs a reset operation and a reading operation for outputting a signal from the sensor. One piece of image data formed on the basis of signals obtained by these series of operations is also called a frame, and the quantity of image data obtained in a unit time is also called a frame rate.

  Patent Documents 1 and 2 show a configuration including a sampling unit that samples a signal in addition to a plurality of sensors and a driving unit. The sampled signal is held in the sampling unit until the sampling unit samples the signal in the next frame, and is output from the sampling unit by the driving unit at an arbitrary timing. Japanese Patent Application Laid-Open No. 2004-228561 shows that since the reset operation for the next frame is started during the readout operation for a certain frame, the interval between repeated radiography can be shortened and the frame rate can be increased. Japanese Patent Application Laid-Open No. H10-228561 discloses that a signal sampled in a certain frame is read out after a reset operation for the next frame is performed and sampling of a signal in the next frame is started.

JP 2012-85124 A Japanese Unexamined Patent Publication No. 2016-10064

  The noise component of the signal output from the sensor depends on the time from when the reset operation is completed until the signal is sampled. In the driving method of Patent Document 1, since the read operation is temporarily interrupted during the reset operation, the noise component differs between the signal output in the read operation before the interrupt and the signal output in the read operation after the interrupt. . Different noise components before and after the interruption of the reading operation can cause a light and dark step in the radiographic image formed based on this signal. In the driving method of Patent Document 2, as the frame rate decreases, the interval from the end of sampling to the start of the reset operation of the next frame becomes longer, and the time until the signal reading operation becomes longer. When radiation imaging is performed continuously while switching the imaging conditions, it may be a factor that increases the imaging time.

  It is an object of the present invention to provide a technique for suppressing the occurrence of signal output delay due to the size of a frame rate.

  In view of the above problems, a radiation imaging apparatus according to an embodiment of the present invention includes a plurality of sensors and a control unit that controls the plurality of sensors, and each of the plurality of sensors includes radiation. And a sampling unit that samples a signal output from the detection element. The control unit periodically resets the detection element, starts resetting the detection element, and then detects the detection element. For each unit period until the resetting of the signal is started, the sampling unit samples the signal generated by the detection element after the reset, and the time required for the read operation for reading the signal sampled in the unit time period of interest in the unit period is as follows: If it is longer than the time from the end of sampling of the unit of interest to the start of reset of the next unit period of the unit of interest After the reset of the next unit period and before the sampling of the next unit period of the target unit period, the time required for the read operation to read the signal sampled in the target unit period of the unit period is In the case where it is less than the time from the end of sampling to the start of resetting of the next unit period of the target unit period, the read operation is started before resetting of the next unit period of the target unit period.

  The above means provides a technique for suppressing the occurrence of signal output delay due to the size of the frame rate.

The figure which shows the system configuration example of the radiation imaging device which concerns on embodiment of this invention. The figure which shows the structural example of the sensor unit of the radiation imaging device of FIG. The figure which shows the structural example of the reading part of the radiation imaging device of FIG. The timing chart which shows the example of the drive method of the radiation detection apparatus of FIG. The figure which shows the structural example of one sensor of the radiation imaging device of FIG. 2 is a timing chart showing an example of driving a sensor of the radiation imaging apparatus of FIG. 1. 2 is a timing chart showing an example of sensor driving in the first drive mode of the radiation imaging apparatus of FIG. 1. The timing chart which shows the example of a drive of the sensor in the 2nd drive mode of the radiation imaging device of FIG.

  Hereinafter, specific embodiments and examples of a radiation imaging apparatus according to the present invention will be described with reference to the accompanying drawings. Note that, in the following description and drawings, common reference numerals are given to common configurations over a plurality of drawings. Therefore, a common configuration is described with reference to a plurality of drawings, and a description of a configuration with a common reference numeral is omitted as appropriate. The radiation in the present invention includes a beam having energy of the same degree or more, such as X-rays, β-rays, γ-rays, etc., which are beams formed by particles (including photons) emitted by radiation decay, such as X It can also include rays, particle rays, and cosmic rays.

  With reference to FIGS. 1-8, the structure of the radiation imaging device by embodiment of this invention and the drive method are demonstrated. FIG. 1 is a system block diagram showing an overall configuration example of a radiation imaging apparatus IA (or may be referred to as a “radiation imaging system”) in an embodiment of the present invention. The radiation imaging apparatus IA includes an imaging unit 100, a control unit 101, a display unit 102, an irradiation control unit 103, and a radiation source 104.

  The imaging unit 100 acquires image data indicating internal information of the subject by radiography, and outputs the image data to the control unit 101. The control unit 101 functions as a processing unit that performs image processing and data processing on the image data output from the imaging unit 100. The control unit 101 also functions as a control unit that exchanges control signals between the units and performs system control and synchronization control of the entire radiation imaging apparatus IA including the imaging unit 100 and the irradiation control unit 103. The display unit 102 includes, for example, a display, and displays a radiation image based on image data output from the imaging unit 100 via the control unit 101.

  The irradiation control unit 103 is controlled by the control unit 101 so as to be synchronized with the imaging unit 100 during radiography. The irradiation control unit 103 outputs a signal for performing radiation irradiation to the radiation source 104 in accordance with a control signal output from the control unit 101. The radiation source 104 generates radiation for performing radiography in accordance with a signal output from the irradiation control unit 103.

  The image capturing unit 100 transmits each unit in the image capturing unit 100 while exchanging signals such as a control signal between the sensor unit 120, a reading unit 121 that reads a signal output from the sensor unit 120, and the control unit 101. And a sensor control unit 109 for controlling.

  The sensor unit 120 may be, for example, a sensor panel 105 formed by arranging a plurality of sensor units 106. Each sensor unit 106 is a sensor chip manufactured by a known semiconductor manufacturing process using a semiconductor substrate such as a silicon wafer. In each sensor unit 106, a plurality of sensors are arranged in an array so as to form a plurality of rows and a plurality of columns. The sensor units 106 adjacent to each other may be physically separated by dicing, or may not be separated. For example, the sensor panel 106 may be formed by inspecting each sensor unit 106 formed on the semiconductor substrate before dicing and arranging the sensor units 106 whose inspection results satisfy a predetermined standard. The configuration shown in FIG. 1 shows a configuration in which the sensor units 106 are arranged in 2 rows × 14 columns for ease of explanation, but the configuration of the sensor unit 120 is not limited to this quantity.

  On the sensor unit 120, for example, a scintillator (not shown) that converts radiation into light is disposed, and the sensor unit 120 obtains an electrical signal corresponding to the light converted from the radiation. In the present embodiment, a configuration example of a radiation imaging apparatus using an indirect type conversion element that converts radiation into light by a scintillator and photoelectrically converts the converted light has been described. However, radiation is directly converted into an electrical signal. A radiation imaging apparatus using a direct type conversion element may be used.

  The reading unit 121 includes, for example, a multiplexer 131, a signal amplification unit 141, and an AD conversion unit 151. The multiplexer 131 functions as a selection unit that selects a sensor from which a signal is read out in a predetermined unit. For example, the multiplexer 131 can select a sensor from which a signal is read out for each sensor unit 106 or each column. The signal amplification unit 141 and the AD conversion unit 151 function as an output unit that outputs a signal (sensor signal) of each sensor to be selected. For example, the signal amplification unit 141 amplifies the signal using a differential amplifier or the like, and the AD conversion unit 151 performs analog-digital (A / D) conversion on the signal amplified by the signal amplification unit 141.

  Electrodes for transmitting / receiving signals or supplying power are arranged on the upper side and the lower side of the sensor unit 120. The electrodes are connected to an external circuit by a flying lead type printed wiring board (not shown) or the like. For example, a signal from the sensor unit 120 is read by the reading unit 121 via the electrode, and a control signal from the sensor control unit 109 is supplied to the sensor unit 120 via the electrode.

  The sensor control unit 109 exchanges signals such as control signals with the control unit 101 via various interfaces. Further, the sensor control unit 109 forms image data based on the sensor signal read from the sensor unit 120 and outputs the image data to the control unit 101. The control interface 110 is an interface for exchanging shooting information and setting information such as a drive mode and various parameters. Further, the control interface 110 may exchange device information such as an operation state of the imaging unit 100. The image data interface 111 is an interface for outputting image data output from the imaging unit 100 to the control unit 101.

  In addition, the sensor control unit 109 notifies the control unit 101 by the READY signal 112 that the imaging unit 100 is ready to take a picture. In response to the READY signal 112 output from the sensor control unit 109, the control unit 101 notifies the sensor control unit 109 of the timing of radiation irradiation start (exposure) using the synchronization signal 113. The control unit 101 outputs a control signal to the irradiation control unit 103 to start radiation irradiation while the exposure permission signal 114 output from the sensor control unit 109 is enabled.

  With the configuration described above, control of each unit in the radiation imaging apparatus IA, for example, drive control, synchronization control, drive mode control, and the like are performed. For example, the control unit 101 may be connected to an input unit (not shown) such as an information input unit or an information input terminal for the user to input setting information such as an operation mode and various parameters. The control is performed based on shooting conditions input by the user. For example, the control unit 101 functions as a drive mode setting unit, and controls the entire radiation imaging apparatus IA so that the radiation imaging apparatus IA operates by selecting a drive mode based on imaging conditions. Then, the imaging unit 100 synthesizes the sensor signal read from the sensor unit 120 into frame data for each unit period, and outputs the frame data to the control unit 101 as image data. The control unit 101 performs predetermined image processing and data processing on the image data, and causes the display unit 102 to display a radiation image based on the image data.

  Each unit in the radiation imaging apparatus IA is not limited to the above configuration, and the configuration of each unit may be changed as appropriate according to the purpose and the like. For example, the functions of two or more units such as the control unit 101 and the irradiation control unit 103 may be achieved by one unit, and some functions of a unit may be achieved by another unit. May be.

  FIG. 2 shows a configuration example of the sensor unit 106 that is one sensor chip. Each sensor unit 106 includes a plurality of sensors s, a vertical scanning circuit 201 for driving the plurality of sensors s, and a horizontal scanning circuit 202 for reading signals from the plurality of sensors s.

  The plurality of sensors s are arranged to form, for example, m rows × n columns. In the configuration shown in FIG. 2, for example, the sensor s in the first row and the second column is indicated as “s (1, 2)”. Although details will be described later, each sensor s holds an S signal corresponding to a signal component and an N signal corresponding to a noise component, and the S signal and the N signal are respectively stored in the respective sensors s. Are output individually.

  The vertical scanning circuit 201 and the horizontal scanning circuit 202 are constituted by shift registers, for example, and operate based on a control signal output from the sensor control unit 109. The vertical scanning circuit 201 functions as a driving unit that drives the sensor s to be read out for each row based on a control signal output from the sensor control unit 109. Specifically, the vertical scanning circuit 201 supplies drive signals to the plurality of sensors s via the control line 203. Based on the drive signal output from the vertical scanning circuit 201, the plurality of sensors s are driven in units of rows. In addition, the horizontal scanning circuit 202 sequentially outputs the signals of the sensors s in each column based on the control signal output from the sensor control unit 109 (also referred to as “horizontal transfer”). Specifically, the horizontal scanning circuit 202 outputs signals (S signal and N signal) of the sensor s driven by the vertical scanning circuit 201 to column signal lines 204 and 205 and analog output lines 206 and 207. Through the sensor unit 106 in order.

The sensor unit 106 includes a terminal E _S for reading the S signal held by the sensor s, a terminal E _N for reading the N signal held by the sensor s. The sensor unit 106 further includes a select terminal _{E CS,} select by terminal _E signal received at the _CS is activated, the signal of each sensor s of the sensor unit 106, terminal _{E S,} and terminal E _Read through _N.

More specifically, each sensor s includes a terminal ts for outputting an S signal and a terminal tn for outputting an N signal. The terminal ts is connected to the column signal line 204, and the terminal tn is Connected to the column signal line 205. Column signal lines 204 and 205, through the switch SW _H which becomes conductive in response to a control signal from the horizontal scanning circuit 202 are connected to the analog output line 206 and 207. The signals on the analog output lines 206 and 207 are output from the terminal E _S and the terminal E _N via the switch SW _CS that becomes conductive in response to a signal received by the select terminal E _CS .

  The sensor unit 106 further includes a terminal VST that receives a control signal for controlling the vertical scanning circuit 201 and the horizontal scanning circuit 202. Terminal VST receives a start pulse input to vertical scanning circuit 201. The terminal CLKV receives a clock signal input to the vertical scanning circuit 201. Terminal HST receives a start pulse input to horizontal scanning circuit 202. Terminal CLKH receives a clock signal input to horizontal scanning circuit 202. These nuclear control signals are supplied from the sensor control unit 109.

  With the above configuration, in the sensor unit 106, each sensor s is controlled in units of rows, and the signals (S signal and N signal) of the sensors s in each column are sequentially output, and signal reading is performed.

FIG. 3 shows a part of the circuit configuration of the reading unit 121. Signal output from the terminal E _S is the inverted input terminal of the signal amplifier 141 (-) are inputted, the signal output from the terminal E _N is input to the non-inverting input terminal of the signal amplifier 141 (+) The The signal amplifier 141, the signal output from the terminal E _S, the difference between the signal output from the terminal E _N (the difference between the signal value) is amplified, the signal corresponding to the difference is output to the AD conversion unit 151 The The AD conversion unit 151 receives a clock signal at the terminal CLKAD, and A / D converts the signal output from the signal amplification unit 141 based on the clock signal. The A / D converted signal is output as a sensor signal to the sensor control unit 109 via the terminal ADOUT. Here, for ease of explanation, the signal amplification unit 141 and the AD conversion unit 151 have been described as examples, but the same applies to the case where the multiplexer 131 is further included.

FIG. 4 illustrates a timing chart of the reading operation RO which is a reading process for reading a signal for reading a signal from the imaging unit 100. The horizontal axis represents the time axis, and the vertical axis represents the control signal. Here, for ease of explanation, a case where signal reading is performed from four sensor units 106 (referred to as sensor units 106 _{0 to} 106 ₃ ) will be described.

The selection signals Sel0 to Sel3 are control signals for selecting the sensor unit 106 that is a signal reading target. Selection signal Sel0~3 respectively correspond to the sensor unit ₁₀₆ 0-106 _3, are input to the select terminal _{E CS} of the corresponding sensor unit 106. For example, when the sensor unit 106 ₁ and the target signal readout, the selection signal Sel1 to a high level (H), the other selection signals Sel0,2,3 to the low level (L).

  The other control signals VST and the like indicate control signals input to the respective terminals. For example, a control signal input to the terminal VST is indicated as a signal VST. The same applies to other control signals.

  The signal VST is a row selection start pulse signal. Based on this signal, the vertical scanning circuit 201 selects each sensor s in the first row in the sensor unit 106 selected by the selection signals Sel0 to Sel0-3. The The signal CLKV is a clock signal, and each time the clock signal is received at the terminal CLKV, the selected row is sequentially shifted from the first row to the m-th row. That is, each sensor s is sequentially selected for each row from the first row to the m-th row.

  The signal HST is a start pulse signal for column selection. Based on this signal, the horizontal scanning circuit 202 selects each sensor s in the first column in the sensor unit 106 selected by the selection signals Sel0 to Sel0-3. The The signal CLKH is a clock signal, and each time the clock signal is received at the terminal CLKH, the selected column is sequentially shifted from the first column to the nth column. That is, each sensor s is sequentially selected for each row from the first column to the n-th column.

  The signal KLCAD is a clock signal, and as described above, based on this signal, a signal corresponding to the difference between the S signal and the N signal of each sensor s is A / D converted by the AD converter 151.

First, the signal VST, and, after the signal CLKH becomes H, the selection signal Sel0~3 becomes H in the order, the sensor unit ₁₀₆ 0-106 ₃ are sequentially selected. At a timing when a certain selection signal Sel becomes H (or after it becomes H), the clock signals CLKH and CLKAD are inputted until the signal HST becomes H and then the next selection signal Sel becomes H. The

With such a driving method, for example, in the period T1, signal reading from each sensor s in the first row is performed from each of the sensor units 106 _{0 to} 106 ₃ . Specifically, first, for each sensor s in the first row of the sensor units 106 _0, the first column to the n-th column, in turn, is A / D conversion of the sensor signals of the sensor s is made. Then, A / D conversion of the sensor signal of each sensor s in the first row of the sensor unit 106 ₁ is made in the same manner. Then, A / D conversion of the sensor signal of each sensor s in the first row of the sensor unit 106 ₂ is performed similarly, Thereafter, the sensor signal of each sensor s in the first row of the sensor unit 106 ₃ A / D conversion is similarly performed. The period after the period T2 (the period for reading signals from each sensor s in the second row of each sensor unit 106) is the same as the period T1.

  The read operation RO is performed as described above. From the viewpoint of the vertical scanning circuit 201 that functions as a driving unit, the sensor control unit 109 that controls the operation, or the control unit 101 that controls the radiation imaging apparatus IA, the reading operation RO is performed by using signals from the sensors s. It may be referred to as an output operation for outputting.

FIG. 5 shows a circuit configuration example of one sensor s arranged in the sensor unit 106. The sensor s includes, for example, a part ps1, a part ps2, and a part ps3. Portion ps1 includes a photodiode PD, and transistors M1, M2, and a floating diffusion (FD) capacitance _{C FD,} and a capacitance _{C FD} 'for sensitivity switching. The photodiode PD is a photoelectric conversion element that converts light generated by the above-described scintillator into an electric signal in accordance with the irradiated radiation. Specifically, an amount of charge corresponding to the amount of light generated in the scintillator is generated in the photodiode PD, and the voltage of the FD capacitor C _FD corresponding to the amount of generated charge is output to the part ps2.

  In the present embodiment, the sensor unit 120 using the indirect type conversion element is considered as described above, and the configuration using the photodiode PD as the detection element for detecting radiation is shown. May be used. For example, a direct conversion element that directly converts radiation into an electrical signal may be used as a detection element for detecting radiation.

The sensitivity switching capacitance C _FD ′ is used to switch the sensitivity of the sensor s to the radiation, and is connected to the photodiode PD via the transistor M1 (switch element). When the signal WIDE is activated, the transistor M1 is turned on, and the voltage of the combined capacitance of the FD capacitor _CFD and the capacitor _CFD ′ is output to the part ps2.

With such a configuration, the sensor s enters the low sensitivity mode when the signal WIDE is H, and enters the high sensitivity mode when the signal WIDE is L. Thus, the sensor s can change the sensitivity to radiation depending on whether or not the capacitor C _FD ′ is used.

  When the signal PRES is activated, the transistor M2 resets (initializes) the charge of the photodiode PD, and resets the voltage output to the portion ps2.

Portion ps2 includes transistors M3～M7, and the clamp capacitor _{C CL,} and a constant current source (e.g., transistors of the current mirror configuration). The transistor M3, the transistor M4, and the constant current source are connected in series so as to form a current path. When the enable signal EN input to the gate of the transistor M3 is activated, the transistor M4 receiving the voltage from the portion ps1 performs a source follower operation, and a voltage corresponding to the voltage input from the portion ps1 is output.

Downstream of the transistors M3, M4, the clamping circuit formed by transistors M5~M7 and the clamp capacitor _{C CL} is provided. Specifically, one terminal n1 of the clamp capacitor C _CL is connected to a node between the transistors M3 and M4, the other terminal n2 is connected to the clamp voltage VCL via a transistor M5. The transistor M6, the transistor M7, and the constant current source are connected in series so as to form a current path, and the terminal n2 is connected to the gate of the transistor M7.

With such a configuration, kTC noise (so-called reset noise) generated in the photodiode PD of the partial ps1 is removed. Specifically, a voltage corresponding to the voltage from the portion ps1 during the aforementioned reset is input to the terminal n1 of the clamp capacitor C _CL. Further, by clamp signal PCL is activated, the transistor M5 is in a conductive state, the clamp voltage VCL is supplied to the terminal n2 of the clamp capacitor _{C CL.} Thus, the potential difference between the terminal n1 and the terminal n2 of the clamp capacitor C _CL is clamped as a noise component. In other words, the part ps2 can hold a voltage corresponding to the electric charge generated in the photodiode PD, and functions as a holding unit that holds a voltage corresponding to kTC noise by the clamp capacitor _CCL . In the configuration shown in FIG. 5, the voltage obtained by removing the clamped noise component from the voltage output according to the charge generated in the photodiode PD from the transistor M4 that performs the source follower operation in the part ps2 is held.

  The enable signal EN is supplied to the gate of the transistor M6, and when the enable signal EN is activated, the transistor M7 performs a source follower operation, and a voltage corresponding to the gate voltage of the transistor M7 is output to the part ps3. . For example, when charge is generated in the photodiode PD, the gate voltage of the transistor M7 changes, and a voltage corresponding to the changed voltage is output to the portion ps3.

The part ps3 includes transistors M8, M10, M11, and M13, analog switches SW9 and SW12, and capacitors CS and CN. Here, the transistors M8 and M10, the analog switch SW9, and the capacitor CS constitute a unit U _SHS that outputs a signal from the terminal ts. Similarly to the unit U _SHS , the transistors M11 and M13, the analog switch SW12, and the capacitor CN constitute a unit U _SHN that outputs a signal from the terminal tn.

In the unit _USSH , the transistor M8 and the capacitor CS form a sample and hold circuit. Specifically, by switching the state (conductive state or nonconductive state) of the transistor M8 using the control signal TS, the signal input from the part ps2 is held in the capacitor CS as the S signal. In other words, the unit U _SHS functions as a sampling unit that samples the S signal. The transistor M10 performs a source follower operation, whereby the S signal is amplified. The amplified S signal is output from the terminal ts by making the analog switch SW9 conductive using the control signal VSR.

In the unit _USHN , the N signal is held by the capacitor CN. In other words, the unit _USHN functions as a sampling unit that samples N signals. As described above, the reading unit 121 reads the difference between the S signal and the N signal through the terminal ts and the terminal tn. Thereby, fixed pattern noise (FPN: Fixed Pattern Noise) caused by the part ps2 is removed.

  As described above, in the sensor s, the S signal and the N signal are held in the capacitors CS and CN, respectively, and the held S signal and N signal make the analog switches SW9 and SW12 conductive. Thus, reading is performed by so-called nondestructive reading. That is, while the transistors M8 and M11 are in the non-conductive state, the held S signal and N signal can be read at an arbitrary timing.

  FIG. 6 is a timing chart showing an example of driving the sensor s when performing one radiography. This driving method can be applied to an operation mode such as still image shooting, for example. Here, for ease of explanation, the case of the high sensitivity mode (that is, the control signal WIDE is L) will be described.

As shown in FIG. 6A, first, at time t50, the user sets shooting conditions, which are information necessary for shooting, such as setting the drive mode. Next, at time t51, in accordance with the synchronization signal SYNC output from the control unit 101, a reset operation RD for resetting each sensor s and the clamp capacitor C _CL is performed. At time t60, a sampling operation SD for reading the sensor signal is performed. Thereafter, the read operation RO described with reference to FIG. 4 is performed.

FIG. 6B shows a specific timing chart of the reset operation RD. At time t51, the enable signal EN is set to H, and the transistors M3 and M6 are turned on. As a result, the transistors M4 and M7 perform a source follower operation. Next, at time t52, the signal PRES is set to H, so that the transistor M2 is turned on. As a result, the photodiode PD is connected to the reference voltage VRES, the photodiode PD is reset, and the voltage of the FD capacitor C _FD is also reset. Further, a voltage corresponding to the gate voltage of the transistor M4 at a reset is supplied to one terminal n1 of the clamp capacitor C _CL. At time t53, the signal PCL is set to H, and the transistor M5 is turned on. Thus, the clamp voltage VCL is supplied to the terminal n2 of the clamp capacitor _{C CL.} At time t54, the signal PRES is set to L to turn off the transistor M2. Thus, terminal n1 of the clamp capacitor C _CL is set to a voltage corresponding to the gate voltage of the transistor M4 during above reset. At time t55, the signal PCL is set to L to turn off the transistor M5. Thus, kTC noise charge corresponding to the potential difference (potential difference between the voltage and the clamp voltage VCL according to the reference voltage VRES) between the terminal n1 and the terminal n2 is held by the clamp capacitance C _CL, due like the heat of the photodiode PD Is clamped. At time t56, the enable signal EN is set to L, and the transistors M3 and M6 are turned off. This puts the transistors M4 and M7 into a non-operating state. Thereafter, the above-described exposure permission signal 114 is set to H (permission state).

As described above, a series of operations of the reset operation RD is completed. That is, in the reset operation RD, resets the photodiode PD, and resets the clamp capacitor C _CL, the clamp capacitor C _CL which is reset voltage corresponding to a kTC noise is maintained. Thereafter, according to the irradiation of radiation, the photodiode PD generates a charge corresponding to the amount of irradiated radiation. The reset operation RD is performed collectively for all the sensors s, and by preventing the control timing from being shifted, the continuity of data between the adjacent sensor units 106 and between the adjacent sensors s can be maintained.

  FIG. 6C shows a specific timing chart of the sampling operation SD. In the sampling operation SD, the signal level corresponding to the amount of charge generated in the photodiode PD is sampled as an S signal and held in the capacitor CS. In the sampling operation SD, the noise level corresponding to the fixed pattern noise caused by the configuration of the sensor s and the manufacturing variation of each element is sampled as an N signal and held in the capacitor CN.

First, at time t60, the enable signal EN is set to H, the transistors M3 and M6 are turned on, and the transistors M4 and M7 are set to perform the source follower operation. The gate voltage of the transistor M4 is changed in accordance with the generated in the photodiode PD accumulated charge amount, a voltage corresponding to the changed gate voltage is input to the terminal n1 of the clamp capacitor C _CL, the potential of the terminal n1 Changes. Then, in accordance with the potential change in the terminal n1, the potential of the terminal n2 of the clamp capacitor _{C CL} is changed.

Next, at time t61, the signal TS is set to H, and the transistor M8 is turned on. As a result, a voltage corresponding to the potential of the terminal n2 (the above-described changed potential of the terminal n2) is charged in the capacitor CS. At time t62, the signal TS is set to L, and the transistor M8 is turned off. As a result, a voltage corresponding to the potential of the terminal n2 at time t62 is fixed to the capacitor CS (S signal sampling). At time t62, the exposure permission signal 114 is set to L (prohibited state). At time t63, the signal PCL is set to H, and the transistor M5 is turned on. Thus, the clamp voltage VCL is supplied to the terminal n2 (transistors M7 side terminal) of the clamp capacitor _{C CL.} At time t64, the signal TN is set to H to turn on the transistor M11. As a result, a voltage corresponding to the potential of the terminal n2 (the above-mentioned supplied voltage VCL) is charged in the capacitor CN. At time t65, the signal TN is set to L, and the transistor M11 is turned off. As a result, the voltage corresponding to the potential of the terminal n2 at time t65 is fixed to the capacitor CN (N signal sampling). At time t66, the signal PRES is set to H, the transistor M2 is turned on, the voltage of the FD capacitor C _FD (and the capacitor C _FD ') is reset to the reference voltage VRES, and the voltage of the terminal n1 is also reset. At time t67, the signal PRES is set to L, and the transistor M2 is turned off. As a result, the terminal n1 of the clamp capacitor CCL is set to a voltage corresponding to the gate voltage of the transistor M4 at the time of reset at time t66. Next, at time t68, the signal PCL is set to L, and the transistor M5 is turned off. Thereafter, at time t69, the enable signal EN is set to L, the transistors M3 and M6 are turned off, and the transistors M4 and M7 are turned off.

In summary, in the sampling operation SD, the S signal is sampled from time t61 to time t62. Then, reset the potential of the terminal n2 of the clamp capacitor _{C CL} at time t63~ time t68, during which, after the sampling of the N signals at time t64~ time t65, the reset of the photodiode PD at time t66~ time t67 .

  As described above, a series of operations of the sampling operation SD is completed. In other words, in the sampling operation SD, the signal level corresponding to the amount of charge generated in the photodiode PD is sampled as an S signal and held in the capacitor CS, and the noise level corresponding to the fixed pattern noise is sampled as an N signal and the capacitor is sampled. Hold on CN.

  Note that the sampling operation SD can be performed collectively for all the sensors in order to prevent a shift in the control timing of each sensor unit 106, similarly to the above-described reset operation RD. As described above, in the read operation RO after the sampling operation SD, signals corresponding to the difference between the S signal and the N signal are sequentially A / D converted and output as one image data.

  7 and 8 are timing charts showing an example of driving the sensor s in an operation mode in which radiation imaging is repeatedly performed. This driving method can be applied to an operation mode such as continuous shooting or moving image shooting. In this driving method, each time the synchronization signal SYNC is received, a series of operations of a reset operation RD, radiation irradiation, a sampling operation SD, and a read operation RO are periodically performed. 7 and 8, a period from the start of the reset operation RD upon receipt of a certain synchronization signal SYNC to the start of the reset operation RD upon receipt of the next synchronization signal SYNC is defined as a period FT. It can be said that the period FT is one frame period (unit period) for generating image data constituting one radiation image. Also, the time or period required for one read operation RO is the period ST, the period when the exposure permission signal is at the high level (H) is the period XT, and after the end of the sampling operation SD until the start of the next reset operation RD. Each period is indicated by a period ET. In the present embodiment, the control unit 101 performs a plurality of drivings including the driving mode illustrated in FIG. 7 and the driving mode illustrated in FIG. 8 based on the lengths of the period ST and the period ET that are determined according to the imaging conditions. Radiation imaging is performed by selecting one drive mode from the modes. Specifically, when the time required for the read operation RO is equal to or longer than the time from the end of the sampling operation SD in the unit time period of interest to the start of the reset operation RD in the next unit period of the unit time period of interest (period ST ≧ period ET) The control unit 101 performs shooting by selecting the drive mode shown in FIG. Further, when the time required for the read operation RO is less than the time from the end of the sampling operation SD of the unit time period of interest to the start of the reset operation RD of the next unit period of the unit time period of interest (period ST <period ET) In 101, the drive mode shown in FIG.

  FIG. 7 illustrates a timing chart in the drive mode when the period ST ≧ the period ET. First, at time t701, for example, the k-th (k-th) synchronization signal SYNC is received, and from time t701 to time t703, the k-th reset operation RD (referred to as “RD (k)” for distinction) is performed. . Further, at least at time t702, which is the time after the signal PCL is set to L, the exposure permission signal is set to H, and the k-th irradiation of radiation (“EX (k)”) is started. Then, at least at time t704, which is the time after the reset operation RD (k) is completed, the (k−1) th read operation RO (referred to as “RO (k−1)”) is started. Image data based on the signal sampled in the (k−1) th sampling operation SD (k−1) (not shown) is obtained by the read operation RO (k−1). At time t705 to time t707, for example, the k-th sampling operation SD (referred to as “SD (k)”) is performed. Further, the irradiation EX (k) is ended at least at a time t706 that is a time before the signal PCL is set to H. By the sampling operation SD (k), a signal corresponding to the irradiation EX (k) is sampled in each sensor s. From time t712 to time t714, for example, the (k + 1) th sampling operation SD (k + 1) is performed. Further, the irradiation EX (k + 1) ends at least at time t713, which is the time before the signal PCL is set to H. By the sampling operation SD (k + 1), a signal corresponding to the irradiation EX (k + 1) is sampled in each sensor s. Next, the (k + 2) th synchronization signal SYNC is received at time t715, and the (k + 2) th reset operation RD (k + 2) is performed at time t715 to time t717. Further, at least at time t716, which is the time after the signal PCL is set to L, the exposure permission signal is set to H, and the (k + 2) th irradiation EX (k + 2) of radiation is started. Thereafter, at least time t718, which is the time after the reset operation RD (k + 2) is completed, the (k + 1) th read operation RO (k + 1) is performed. Image data based on the signal sampled in the sampling operation SD (k + 1) is obtained by the read operation RO (k + 1). The k-th read operation RO (k) ends before the (k + 1) -th sampling operation SD (k + 1) performed in the next unit period. According to the procedure exemplified above, the series of operations of the reset operation RD, radiation irradiation, sampling operation SD, and read operation RO can be similarly repeated after time t717. Here, according to the main drive mode, the reset operation RD (k) from time t701 to time t707, the radiation irradiation EX (k), the sampling operation SD (k), and the read operation RO (k) at time t711. Image data obtained by the k-th radiography can be obtained. Then, the (k + 1) th radiography is performed by the reset operation RD (k + 1), the radiation irradiation EX (k + 1), the sampling operation SD (k + 1), and the readout operation RO (k + 1) at time t718 from time t708 to time t714. Is obtained.

  FIG. 8 illustrates a timing chart in the driving mode in the case where the period ST <the period ET. First, at time t801, for example, the k-th (k-th) synchronization signal SYNC is received, and the k-th reset operation RD (k) is performed from time t801 to time t803. In addition, at time t802, which is at least after the signal PCL is set to L, the exposure permission signal is set to H, and the k-th irradiation EX (k) of radiation is started. From time t804 to time t807, for example, the k-th sampling operation SD (k) is performed. Further, the irradiation EX (k) is ended at least at time t805, which is a time before the signal PCL is set to H. A signal corresponding to the irradiation EX (k) is sampled in each sensor s by the sampling operation SD (k). Thereafter, at least time t807, which is the time after the completion of the sampling operation SD (k), the kth read operation RO (k) is started. Image data based on the signal sampled by the sampling operation SD (k) is obtained by the read operation RO (k). Next, the (k + 1) th synchronization signal SYNC is received at time t808, and the (k + 1) th reset operation RD (k + 1) is performed from time t808 to time t810. Further, at least at time t809, which is the time after the signal PCL is set to L, the exposure permission signal is set to H, and the k-th irradiation EX (k) of radiation is started. From time t811 to time t813, for example, the (k + 1) th sampling operation SD (k + 1) is performed. Further, the radiation irradiation EX (k + 1) is terminated at least at time t812, which is the time before the signal PCL is set to H. By the sampling operation SD (k + 1), a signal corresponding to the irradiation EX (k + 1) is sampled in each sensor s. Thereafter, at least time t814, which is the time after the completion of the sampling operation SD (k + 1), the (k + 1) th read operation RO (k + 1) is performed. Image data based on the signal sampled in the sampling operation SD (k + 1) is obtained by the read operation RO (k + 1). The k-th read operation RO (K) may end before the (k + 1) -th reset operation RD (k + 1) performed in the next unit period. In accordance with the procedure exemplified above, a series of operations of the reset operation RD, radiation irradiation, sampling operation SD, and read operation RO can be similarly repeated after time t815. Here, according to this drive mode, the reset operation RD (k) from time t801 to time t807, the radiation irradiation EX (k), the sampling operation SD (k), and the readout operation RO (k) Image data obtained by radiography can be obtained. Then, the (k + 1) th radiography is performed by the reset operation RD (k + 1), the radiation irradiation EX (k + 1), the sampling operation SD (k + 1), and the readout operation RO (k + 1) at time t814 from time t808 to time t814. Is obtained. In the case of this drive mode, the time taken from the reset operation RD to the read operation RO for reading an image is constant even if the shooting interval is increased.

  As shown in the present embodiment, when the control unit 101 selects an efficient drive mode according to the frame rate, for example, in the case of continuously shooting while switching shooting conditions one after another, the time required for shooting is reduced. Can be shortened.

  The present invention can also be performed by executing a program or software by a computer. Specifically, for example, a program that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media. The computer of the system or apparatus (or CPU, MPU, etc.) then reads and executes the program.

  As mentioned above, although embodiment which concerns on this invention was shown, it cannot be overemphasized that this invention is not limited to these embodiment, In the range which does not deviate from the summary of this invention, embodiment mentioned above and an Example are changed suitably. Combinations are possible.

101: Control unit, FT: Unit period, IA: Radiation imaging device, RO: Reading operation, s: Sensor

Claims (7)

A radiation imaging apparatus including a plurality of sensors and a control unit that controls the plurality of sensors,
Each of the plurality of sensors includes a detection element that detects radiation, and a sampling unit that samples a signal output from the detection element,
The controller is
Periodically reset the sensing element;
For each unit period from the start of reset of the detection element to the start of reset of the detection element next, the signal generated by the detection element after reset is sampled by the sampling unit,
The time required for the read operation for reading the signal sampled in the unit time period of interest in the unit period is equal to or longer than the time from the end of the sampling of the unit time period of interest to the start of reset of the unit period next to the unit period of interest , Starting the read operation after reset of the next unit period of the target unit period and before sampling of the next unit period of the target unit period,
When the time required for the reading operation for reading the signal sampled in the unit time period of interest in the unit period is less than the time from the end of the sampling of the unit time period of interest to the start of reset of the unit period next to the unit time period of interest The radiation imaging apparatus is characterized in that the readout operation is started before reset of a unit period next to the unit period of interest.   When the time required for the read operation is equal to or longer than the time from the end of sampling of the unit period of interest to the start of reset of the unit period next to the unit period of interest, the control unit The radiation imaging apparatus according to claim 1, wherein the reading operation is terminated before sampling.   When the time required for the reading operation is less than the time from the end of sampling of the unit period of interest to the start of reset of the unit period next to the unit period of interest, the control unit The radiation imaging apparatus according to claim 1, wherein the readout operation is terminated before resetting. The radiation imaging apparatus further includes a radiation source controlled by the control unit,
The radiation control apparatus according to claim 1, wherein the control unit controls the radiation source to emit radiation after reset.   The radiation imaging apparatus provides an imaging condition for determining a time from the end of sampling of the unit time period of interest to a start of reset of a unit period next to the unit time period of interest and a time required for the reading operation. 5. The radiation imaging apparatus according to claim 1, further comprising an input unit that inputs. A method for driving a radiation imaging apparatus including a plurality of sensors,
Each of the plurality of sensors includes a detection element that detects radiation, and a sampling unit that samples a signal output from the detection element,
Periodically resetting the detection element;
For each unit period from the start of resetting the detection element to the start of resetting the detection element, sampling a signal generated by the detection element after reset;
Reading a signal sampled in the unit period, and
The time required for the reading step of reading the signal sampled in the target unit period in the unit period is equal to or longer than the time from the end of sampling in the target unit period to the start of reset in the next unit period of the target unit period. The reading step is started after the reset of the next unit period of the target unit period and before the sampling of the next unit period of the target unit period;
The time required for the reading step of reading the signal sampled in the unit time period of interest in the unit period is less than the time from the end of the sampling of the unit time period of interest to the start of resetting of the unit period next to the unit period of interest. In this case, the driving method is characterized in that the reading step is started before the reset of the unit period next to the unit period of interest.   The program for making a computer perform each process of the drive method of Claim 6.

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