JP2007005938A - Photoelectric converter and drive method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric converter that has a high sensitivity by avoiding a limit placed on the dynamic range and to provide a drive method thereof. <P>SOLUTION: An amount Q0 of electric charges is precharged to pixels connected to a common gate line Vg1 for periods t<SB>2</SB>, t<SB>3</SB>and photoelectric conversion and discharging are applied to the pixels for a period t<SB>4</SB>to decrease the amount of electric charges by a ΔQ. Then the precharged electric charges (amount of electric charges: Q0) are subtracted from the charges of the pixels for periods t<SB>5</SB>, t<SB>6</SB>to bring the remaining electric charges in storage capacitors of the pixels to ΔQ. Then the electric charges ΔQ corresponding to an incident luminous quantity are read for periods t<SB>7</SB>, t<SB>8</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device using a thin film transistor (TFT) having photoresponsiveness as a photodetecting element, and a driving method thereof.

  In recent years, a photoelectric conversion device using a photoresponsive TFT such as amorphous silicon as a photodetecting element has been reported. FIG. 5 is a circuit diagram illustrating a configuration of the photoelectric conversion apparatus.

  This photoelectric conversion device is provided with a two-dimensional area sensor array 2 in which pixels each having a storage capacitor CS and a thin film transistor Tr are arranged in an array. Here, for convenience, it is assumed that pixels in 4 rows and 4 columns are arranged. The gate electrode of the thin film transistor Tr of each pixel is connected to the common gate lines Vg1 to Vg4 for each row. The source electrode of the thin film transistor Tr is connected to the common signal lines Sig1 to Sig4 for each column. One electrode of the storage capacitor CS is connected to the drain electrode of the thin film transistor Tr, and the other electrode is connected to the common Cs drive line (bias line) Vcs. The common gate lines Vg1 to Vg4 are connected to a gate driver (gate driving device) 4 including a shift register (not shown). The common signal lines Sig1 to Sig4 are connected to the readout circuit 5.

  The readout circuit 5 is provided with a reset switch, an integration amplifier Amp having an integration capacitor, and a sample hold circuit for each common signal line. The integrating amplifier Amp is configured to be reset by a reset switch. The other input of the integrating amplifier Amp is connected to a reference potential (here, ground potential GND). Further, the read circuit 5 is provided with an analog multiplexer 6 and a buffer amplifier BA connected to the subsequent stage of each sample and hold circuit SH. An A / D conversion circuit 7 is provided at the subsequent stage of the read circuit 5, and the analog signal output from the read circuit 5 is converted into a digital signal and output from the digital output bus.

  The common Cs drive line Vcs is connected to a power source 3 that can switch and output two kinds of voltages VA (low potential) and VB (high voltage). Further, a control circuit 1 for controlling operations of the power supply 3, the gate driver 4 and the readout circuit 5 is provided. For example, the Cs_DRV signal is output from the control circuit 1 to the power supply 3, the RC signal is output to the reset switch in the readout circuit 5, and the SH signal is output to the sample hold circuit in the readout circuit 5. The RC switch and the SH signal turn on / off the reset switch and the sample hold circuit, respectively. FIG. 12 is a diagram showing details of the power supply 3.

  Next, details of each pixel and its driving method will be described. FIG. 6 is a circuit diagram showing one pixel and its peripheral circuit. As described above, the pixels of the two-dimensional area sensor array are provided with the storage capacitor CS and the thin film transistor Tr, and one electrode of the storage capacitor CS and the drain electrode of the thin film transistor Tr are connected to each other. The gate electrode of the thin film transistor Tr is connected to the gate driver 4, and the source electrode is connected to one input of the integration amplifier Amp of the readout circuit 5. The output of the integrating amplifier Amp is connected to a sample and hold circuit. The other electrode of the storage capacitor CS is connected to the power source 3.

FIG. 7 is a cross-sectional view schematically showing the structure of the pixel shown in FIG. The pixel is provided with a thin film transistor Tr having a switching function and a photoelectric conversion function, and a storage capacitor CS connected to the thin film transistor Tr. The thin film transistor Tr is, for example, a bottom gate TFT using amorphous silicon. That is, the gate electrode 102 is provided on the glass substrate 101, and the insulating film 104 made of an amorphous silicon nitride film or the like is formed on the gate electrode 102. The insulating film 104 extends into the storage capacitor CS, but the portion on the gate electrode 102 functions as a gate insulating film. Further, an amorphous silicon semiconductor layer 105 is formed as a channel portion on the insulating film 104 (gate insulating film), and n ⁺ layers 106 are formed at two locations on the semiconductor layer 105. Conductive layers 106 and 107 are formed on the two n ⁺ layers 106. The conductive layer 106 extends into the storage capacitor CS, but the portion on the n ⁺ layer 106 functions as a drain electrode, and the conductive layer 107 functions as a source electrode. On the other hand, the lower electrode 103 is formed on the glass substrate 101 for the storage capacitor CS. An insulating film 104 and a conductive layer 108 extending from the thin film transistor Tr are formed on the lower electrode 103. The portions of the insulating film 104 and the conductive layer 108 on the lower electrode 103 function as a capacitive insulating film and an upper electrode, respectively. These are covered with a protective layer 109. The gate electrode of the thin film transistor Tr and the lower electrode of the storage capacitor are formed from the same layer, and the gate insulating film of the thin film transistor Tr and the insulating layer of the storage capacitor CS are formed from the same layer. The drain electrode and the upper electrode of the storage capacitor CS are formed in the same layer.

  Here, characteristics of a thin film transistor (TFT) having photoresponsiveness will be described. FIG. 8 is a graph showing characteristics of a TFT having photoresponsiveness (dependence of TFT source-drain current Ids on gate voltage). That is, FIG. 8 shows a change in the current Ids when the gate voltage Vg is changed in a state where the voltage Vds is applied between the source and the drain. As shown in FIG. 8, when light is incident with a negative potential applied to the gate electrode so that the TFT is turned off, the current Ids changes from Idark to Iphoto. That is, the off-resistance value of the TFT changes with light incidence. A conventional photoelectric conversion device uses such a change in resistance value.

  FIG. 9 is a timing chart showing a driving method of one pixel in a conventional photoelectric conversion device. In FIG. 9, Light is light irradiation to the thin film transistor Tr, RC is an RC signal to the reset switch of the integrating amplifier Amp, Vg is a gate pulse of the thin film transistor Tr, Cs_DRV is a pulse applied from the power source 3 to the storage capacitor CS, and Vd is The potential of the drain electrode of the thin film transistor Tr, Vout indicates the output of the integrating amplifier Amp, and SH indicates the change of the SH signal to the switch of the sample hold circuit. The following control is mainly performed by the control circuit 1.

In driving the pixel as described above, in the period u ₁ , the thin film transistor Tr is turned on and RC is set high. Therefore, Vd is reset to GND.

In the period u ₂ , the potential of Cs_DRV is set to VB by controlling the power supply 3. As a result, the potential on the power supply 3 side of the storage capacitor CS becomes VB, but since the thin film transistor Tr is kept on and the reset switch is kept on, Vd remains GND.

In the period u ₃ , the thin film transistor Tr is turned off. However, the drain electrode potential Vd remains GND.

In the period u ₄ , the potential of Cs_DRV is changed from VB to VA. As a result, the potential supplied from the power source 3 changes by ΔV. At this time, since the thin film transistor Tr is in an off state, Vd becomes −ΔV. On the other hand, the potential of the source electrode of the thin film transistor Tr is held at the GND potential because the reset switch remains on. That is, in the period u ₄ , a potential difference of ΔV is generated between the source and drain of the thin film transistor Tr. In other words, assuming that the capacitance of the storage capacitor CS is Cs, the charge Q0 represented by ΔV × Cs is precharged to the storage capacitor CS.

In the period u ₅ , light is incident on the thin film transistor Tr. Due to the incidence of light, the current Iphoto flows between the source and the drain, and at least a part of the charge precharged in the storage capacitor CS in the period u ₄ is discharged. That is, if the light incident time is Tphoto, the charge ΔQ represented by Iphoto × Tphoto is discharged. However, since the integration amplifier Amp is continuously reset in the period u ₅ , the discharged charge ΔQ is not read as a signal.

In the period u ₆ , light incidence is turned off. The off-current Idark flows even when no light is incident, but since this value is extremely small, the charge accumulated in the storage capacitor CS is kept as it is.

In the period u ₇ , the reset switch is turned off, and the reset operation of the integrating amplifier Amp is finished. At this time, since the thin film transistor Tr is in an off state, the charge of the storage capacitor CS is held.

In a period u ₈ , a pulse is applied from the gate driver 4 to the gate electrode of the thin film transistor Tr to turn on the thin film transistor Tr. As a result, the electric charge (Q0−ΔQ) held in the storage capacitor CS is transferred to the integration capacitor of the integration amplifier Amp, and the output Vout changes. The drain potential Vd basically converges to GND as the charge moves.

Thereafter, in the period u ₉ , the output of the integrating amplifier Amp is sampled and held in the readout circuit 5, and in the period u ₁₀ , the sample and hold ends.

Then, returning to the period u ₁ , Vd and Vout are converged to GND, and the processes in the periods u _{1 to} u ₁₀ are repeated.

Such control can be paraphrased as follows. That is, in the period u _{1 to} u ₄ , the initial charge Q0 is precharged to the storage capacitor CS (precharge period). In the period u ₅ , the charge ΔQ is discharged according to the intensity and time of incident light, and the charge amount is set to “Q0−ΔQ” (photoelectric conversion period). In the period u ₈ ~u _9, reads the remaining charge "Q0-Delta] Q '(reading period). That is, it can be said that the conventional photoelectric conversion device performs the light detection operation by repeating the precharge period, the photoelectric conversion period, and the readout period.

  The timing chart shown in FIG. 9 relates to one pixel as shown in FIG. 6, but the timing chart showing the operation of the photoelectric conversion apparatus provided with the two-dimensional area sensor array 2 as shown in FIG. It will be as shown in In FIG. 10, Vg1 to Vg3 are gate pulses applied to the common gate lines Vg1 to Vg3, Vd1 to Vd3 are potentials of the drain electrodes of the thin film transistors Tr connected to the common gate lines Vg1 to Vg3, and Vout1 is applied to the common signal line Sig1. Changes in the output of the connected integrating amplifier Amp are shown. Other signals are the same as those shown in FIG.

  The basic operation of the photoelectric conversion device shown in FIG. 5 is the same as that shown in FIG. 9 except that a precharge period for each common gate line is provided and common to all pixels after the precharge period. A photoelectric conversion period is provided, a readout period for each common gate line is provided after the photoelectric conversion period, and the light detection operation is performed by repeating these periods.

That is, for the pixel connected to the common gate line Vg1, performs photoelectric conversion and a discharge in the period u _5, reads the period u ₈ ~u _9, performs precharge at time u ₁₁ ~u _14, these repeat.

As for the pixel connected to the common gate line Vg2, performs photoelectric conversion and a discharge in the period u _5, reads the period u ₁₆ ~u _17, performs a pre-charge in the period u ₁₉ ~u _22, these repeat.

Also, the pixels connected to the common gate line Vg3, performs photoelectric conversion and a discharge in the period u _5, reads the period u ₂₄ ~u _25, performs a pre-charge in the period u ₂₇ ~u _30, these repeat.

Furthermore, although not shown, for the pixels which are connected to a common gate line Vg4, performs photoelectric conversion and a discharge in the period u _5, reads the period u ₃₂ ~u ₃₃ (not shown), the period u ₃₅ Precharge is performed at ˜u ₃₈ (not shown), and these are repeated.

  In such a conventional photoelectric conversion device, the charge Q0 (= ΔV × Cs) is precharged in the storage capacitor CS, and then ΔQ (= Ids × ΔT) corresponding to light incidence for a predetermined period ΔT (= Tphoto). The electric charge is discharged, the residual charge “Q0−ΔQ” is read, and the output of the integrating amplifier Amp is obtained. When the capacitance of the integration capacitor is Cf, the output voltage of the integration amplifier Amp is (Q0−ΔQ) / Cf. Note that FIG. 10 shows only the change in the output of the integrating amplifier Amp connected to the common signal line Sig1, but the integrating amplifier Amp connected to the other common signal lines Sig2 to Sig 4 also shows the amount of incident light. The output changes accordingly.

  Such a photoelectric conversion device and a driving method thereof are disclosed in, for example, Patent Document (Japanese Patent Laid-Open No. 2004-147102) and Non-Patent Document 1 (IDW '03 p.363-366).

JP 2004-147102 A IDW '03 p.363-366

  In the conventional photoelectric conversion device, when the amount of incident light is zero, ΔQ is 0, so that the output voltage of the integrating amplifier Amp is “Q0 / Cf”. That is, as shown in FIG. 11, the output voltage of the integrating amplifier Amp has an offset with respect to the amount of incident light. As shown in FIG. 11, the amount of this offset is proportional to the potential difference ΔV at the time of precharging.

  However, in the conventional photoelectric conversion device, the offset is limited to the finite dynamic range of the integration amplifier Amp of the readout circuit 5, and therefore the potential difference ΔV at the time of precharging cannot be increased.

  The current Ids that flows along with the incidence of light is proportional to the voltage difference ΔV during precharging. If this characteristic is used, the change in the current Ids with respect to the amount of incident light can be increased by setting ΔV to be large. However, as shown in FIG. 11, when the potential difference ΔV is increased, the offset is also increased, which causes output saturation beyond the dynamic range of the integrating amplifier Amp.

  That is, the conventional photoelectric conversion device has a problem that the potential difference (precharge amount) of ΔV is limited to the dynamic range of the integrating amplifier Amp. In addition, due to this limitation, there is a problem that it is difficult to increase sensitivity.

  An object of the present invention is to provide a photoelectric conversion device that can obtain a high sensitivity by avoiding the limitation of the dynamic range and a control method thereof.

  As a result of intensive studies to solve the above problems, the present inventor has come up with various aspects of the invention described below.

  The photoelectric conversion device according to the present invention includes a thin film transistor having a light detection function and a switching function, a storage capacitor connected to the thin film transistor, a reading unit for reading the amount of charge stored in the storage capacitor, the thin film transistor, Control means for controlling the operation of the reading means, wherein the control means precharges the storage capacitor with a predetermined amount of charge in a first interval, and a second interval following the first interval. In the third interval, the light is incident on the thin film transistor while the thin film transistor is turned off to discharge at least a part of the charge precharged in the storage capacitor, and in a third interval following the second interval. From the amount of charge remaining in the storage capacitor, Subtracted recharge, predetermined amount of charge, in the fourth interval following the third interval, characterized in that to read the amount of charge remaining in the storage capacitor to the read means.

  A driving method of a photoelectric conversion device according to the present invention is a driving method of a photoelectric conversion device including a thin film transistor having a light detection function and a switching function and a pixel including a storage capacitor connected to the thin film transistor, and the storage capacitor includes A first interval for precharging a predetermined amount of charge and a first interval for discharging at least a part of the charge precharged in the storage capacitor by making light incident on the thin film transistor while the thin film transistor is turned off. 2, a third interval in which the predetermined amount of precharged charge is subtracted from the amount of charge remaining in the storage capacitor, and the amount of charge remaining in the storage capacitor. And a fourth interval to be read out.

  According to the present invention, the voltage applied to the photoresponsive thin film transistor can be increased without being restricted by the dynamic range of the integrating amplifier constituting the reading device. For this reason, a sensitivity can be improved further.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

(First embodiment)
First, a first embodiment of the present invention will be described. In the first embodiment, the function and operation of the control circuit 1 are different from those of the conventional photoelectric conversion device shown in FIGS. FIG. 1 is a timing chart showing a driving method of one pixel in the first embodiment of the present invention. Similarly to FIG. 9, Light is light irradiation to the thin film transistor Tr, RC is an RC signal to the reset switch of the integrating amplifier Amp, Vg is a gate pulse of the thin film transistor Tr, Cs_DRV is a pulse applied from the power source 3 to the storage capacitor CS, Vd represents the potential of the drain electrode of the thin film transistor Tr, Vout represents the output of the integrating amplifier Amp, and SH represents the change of the SH signal to the switch of the sample hold circuit. The following control is mainly performed by the control circuit 1.

In the present embodiment, in the period t ₁ , the thin film transistor Tr is turned on and RC is set high. Therefore, Vd is reset to GND. Further, the potential of Cs_DRV is set to VB.

In the period t ₂ , the thin film transistor Tr is turned off. However, the drain electrode potential Vd remains GND.

In the period t ₃ , the potential of Cs_DRV is changed from VB to VA. As a result, the potential supplied from the power source 3 changes by ΔV. At this time, since the thin film transistor Tr is turned off, Vd becomes −ΔV. On the other hand, the potential of the source electrode of the thin film transistor Tr is held at the GND potential because the reset switch remains on. That is, in the period t ₃ , a potential difference of ΔV is generated between the source and drain of the thin film transistor Tr. In other words, assuming that the capacitance of the storage capacitor CS is Cs, the charge Q0 represented by ΔV × Cs is precharged to the storage capacitor CS.

In the period t ₄ , light is incident on the thin film transistor Tr. Due to the incidence of light, the current Iphoto flows between the source and the drain, and at least a part of the charge precharged in the storage capacitor CS in the period t ₃ is discharged. That is, if the light incident time is Tphoto, a charge of an amount ΔQ expressed by Iphoto × Tphoto is discharged. However, since the integration amplifier Amp is continuously reset during the period t ₄ , the discharged charge ΔQ is not read as a signal.

In the period t ₅ , the light incidence is turned off. The off-current Idark flows even when no light is incident, but since this value is extremely small, the charge accumulated in the storage capacitor CS is kept as it is.

In the period t ₆ , the potential of Cs_DRV is changed from VA to VB. At this time, since the thin film transistor Tr is in an off state, Vd increases by ΔV. That is, a potential corresponding to the amount of charge ΔQ discharged in the period t ₄ appears in Vd.

In a period t ₇ , the reset switch is turned off, and the reset operation of the integrating amplifier Amp is finished. At this time, since the thin film transistor Tr is in an off state, the charge of the storage capacitor CS is held.

In a period t ₈ , a pulse is applied from the gate driver 4 to the gate electrode of the thin film transistor Tr to turn on the thin film transistor Tr. As a result, the potential Vd of the drain electrode, that is, the charge amount ΔQ (= Iphoto × Tphoto) is transferred to the integration capacitor of the integration amplifier Amp, and the output voltage Vout changes. That is, when the capacitance of the integration capacitor is Cf, the output voltage Vout of the integration amplifier Amp is “ΔQ / Cf”.

Thereafter, in the period t _9, the output of the integrating amplifier Amp is sampled and held in the read circuit 5, in the period t _10, and ends the sample-and-hold.

Then, returning to the period t ₁ , Vout is converged to GND, and the processes in the periods t _{1 to} t ₁₀ are repeated.

Such control can be paraphrased as follows. That is, in the period t _{1 to} t ₃ , the initial charge Q0 is precharged to the storage capacitor CS (precharge period). In period u ₄ , the charge of ΔQ is discharged according to the intensity and time of incident light, and the charge amount is set to “Q0−ΔQ” (photoelectric conversion period). In the period t ₅ ~t _6, performs subtraction of the pre-charge charge Q0, the same ΔQ and the discharge amounts of the SOC (subtraction period). In the period t _{7 to} t ₈ , the remaining charge amount ΔQ is read (reading period). That is, the photoelectric conversion device according to the present embodiment performs the light detection operation by repeating the precharge period, the photoelectric conversion period, the subtraction period, and the readout period.

  The timing chart shown in FIG. 1 relates to one pixel as shown in FIG. 6, but the timing chart showing the operation of the photoelectric conversion apparatus provided with the two-dimensional area sensor array 2 as shown in FIG. It will be as shown in Similarly to FIG. 10, Vg1 to Vg3 are gate pulses applied to the common gate lines Vg1 to Vg3, Vd1 to Vd3 are potentials of the drain electrodes of the thin film transistors Tr connected to the common gate lines Vg1 to Vg3, and Vout1 is a common signal line. Changes in the output of the integrating amplifier Amp connected to Sig1 are shown. Other signals are the same as those shown in FIG.

  The basic operation of the photoelectric conversion device provided with the two-dimensional sensor array 2 is the same as that shown in FIG. 1, but a precharge period, a photoelectric conversion period, and a subtraction period common to all the pixels are provided. After these periods, a readout period is provided for each common gate line, and the light detection operation is performed by repeating these periods.

That is, for the pixels connected to the common gate line Vg1, precharges at time t ₂ ~t _3, performs photoelectric conversion and a discharge in the period t _4, in the period t ₅ ~t ₆ charges precharged Subtraction is performed, and the amount of charge ΔQ corresponding to the amount of incident light is read in the period t _{7 to} t ₈ , and these are repeated.

Also, the pixels connected to the common gate line Vg2, to pre-charge in the period t ₂ ~t _3, performs photoelectric conversion and a discharge in the period t _4, in the period t ₅ ~t ₆ charges precharged Subtraction is performed, and the amount of charge ΔQ corresponding to the amount of incident light is read during the period t _{13 to} t ₁₄ , and these are repeated.

Also, the pixels connected to the common gate line Vg3, precharges at time t ₂ ~t _3, performs photoelectric conversion and a discharge in the period t _4, in the period t ₅ ~t ₆ charges precharged Subtraction is performed, and the amount of charge ΔQ corresponding to the amount of incident light is read during the period t _{19 to} t ₂₀ , and these are repeated.

Furthermore, although not shown, for the pixels which are connected to a common gate line Vg4, precharges at time t ₂ ~t _3, performs photoelectric conversion and a discharge in the period t _4, in the period t ₅ ~t ₆ The precharged charge is subtracted, the charge amount ΔQ corresponding to the amount of incident light is read in the period t _{25 to} t ₂₆ , and these are repeated.

  FIG. 2 shows only the change Vout1 of the output of the integrating amplifier Amp connected to the common signal line Sig1, but the incident light quantity is also applied to the integrating amplifier Amp connected to the other common signal lines Sig2 to Sig4. The output changes in response to.

  In such a first embodiment, the control circuit 1 controls the power supply 3, the gate driver 4, and the readout circuit 5 so that the precharge period, the photoelectric conversion period, the subtraction period, and the readout period are repeated in each pixel. ing. That is, in the present embodiment, unlike the conventional technique, the precharged charge amount Q0 is subtracted during the subtraction period. For this reason, it is possible to read only the discharged charge amount ΔQ as a signal without the precharged charge amount Q0 being an offset.

  FIG. 3 is a graph showing the relationship between the amount of incident light and the output of the integrating amplifier Amp in the photoelectric conversion apparatus according to the first embodiment. In the present embodiment, as described above, it is possible to read only the discharged charge amount ΔQ, and therefore it is possible to prevent the occurrence of offset as shown in FIG. Therefore, it is easy to increase the sensitivity by increasing the potential difference ΔV of Cs_DRV.

  In the first embodiment, Cs_DRV has two types of potentials VA and VB, and a potential difference of ΔV = VA−VB is applied between the source and drain of the photoresponsive thin film transistor Tr during the photoelectric conversion period. However, it is more preferable to switch the bias depending on the incident light amount, the light irradiation time, and / or the required S / N ratio so that another controllable potential VC can be applied.

Moreover, the incident ray in this invention can be not only visible light but various radiations, such as X-rays. In the apparatus for detecting X-rays, the cross-sectional structure is as shown in FIG. That is, the phosphor layer 112 is pasted by the adhesive layer 111 on the protective layer 109 in FIG. In such a photoelectric conversion device, the X-ray is wavelength-converted into visible light by the phosphor layer 111, and this visible light is incident on the thin film transistor Tr. The content of the control is the same as when visible light is incident. Accordingly, when a timing chart is drawn, “Light” in FIGS. 1 and 2 is replaced with “X-rays”. The phosphor layer 111 (wavelength converter) is configured using, for example, one type selected from Gd ₂ O ₃ , Gd ₂ O ₂ S, and CsI as a base material.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 4 is a schematic diagram illustrating an application example (second embodiment) of the photoelectric conversion apparatus according to the first embodiment to an X-ray imaging system.

  The X-ray 6060 generated by the X-ray tube 6050 passes through the chest 6062 of the patient or subject 6061 and enters the image sensor 6040 provided with the photoelectric conversion device according to the first embodiment. The incident X-ray includes information inside the body of the patient 6061. The scintillator (phosphor) emits light in response to the incidence of X-rays, and this is photoelectrically converted by the photoelectric conversion element of the sensor panel to obtain electrical information. The image sensor 6040 outputs this information to the image processor 6070 as A / D converted digital output. An image processor 6070 as image processing means performs image processing on the received signal and outputs the processed signal to a display 6080 as display means in the control room. The user can observe the image displayed on the display 6080 and obtain information on the inside of the patient 6061 body. Note that the image processor 6070 also has a function of a control unit, and controls the power source 3, the readout circuit 4, and the gate driver 5 in the photoelectric conversion device, the image sensor 6040, an X-ray tube (X-ray generator) It is also possible to control 6050, displays 6080 and 6081, film processor 6100, and the like.

  Further, the image processor 6070 transfers the electric signal output from the image sensor 6040 to a remote place via a transmission processing unit such as a telephone line 6090, and displays it on a display unit (display) 6081 in another place such as a doctor room. It can also be displayed. It is also possible to store the electrical signal output from the image sensor 6040 in a recording means such as an optical disk and make a diagnosis by a remote doctor using this recording means. Moreover, it can also record on the film 6110 by the film processor 6100 used as a recording means.

  The embodiment of the present invention can be realized by, for example, a computer executing a program. Also, means for supplying a program to a computer, for example, a computer-readable recording medium such as a CD-ROM recording such a program, or a transmission medium such as the Internet for transmitting such a program is also applied as an embodiment of the present invention. Can do. The above program can also be applied as an embodiment of the present invention. The above program, recording medium, transmission medium, and program product are included in the scope of the present invention.

  The present invention can be applied to, for example, an image capturing apparatus and an X-ray image capturing apparatus.

3 is a timing chart illustrating a driving method of one pixel in the first embodiment of the present invention. It is a timing chart which shows the drive method of the photoelectric conversion apparatus which concerns on 1st Embodiment. It is a graph which shows the relationship between the incident light quantity in the photoelectric conversion apparatus which concerns on 1st Embodiment, and the output of integral amplifier. It is a schematic diagram which shows the application example (2nd Embodiment) to the X-ray imaging system of the photoelectric conversion apparatus which concerns on 1st Embodiment. It is a circuit diagram which shows the structure of a photoelectric conversion apparatus. It is a circuit diagram which shows 1 pixel and its peripheral circuit. It is sectional drawing which shows typically the structure of the pixel shown in FIG. It is a graph which shows the characteristic of TFT which has photoresponsiveness. It is a timing chart which shows the drive method of 1 pixel in the conventional photoelectric conversion apparatus. It is a timing chart which shows the drive method of the conventional photoelectric conversion apparatus. It is a graph which shows the relationship between the incident light quantity in the conventional photoelectric conversion apparatus, and the output of integral amplifier. 3 is a diagram showing details of a power supply 3. FIG. It is sectional drawing which shows typically the structure of 1 pixel in a radiation imaging device.

Explanation of symbols

1: control circuit 2: two-dimensional area sensor array 3: power supply 4: gate driver 5: readout circuit 6: analog multiplexer 7: A / D conversion circuit CS: storage capacitor Tr: thin film transistor (TFT)

Claims (9)

A thin film transistor having a light detection function and a switching function;
A storage capacitor connected to the thin film transistor;
Reading means for reading out the amount of charge accumulated in the storage capacitor;
Control means for controlling the operation of the thin film transistor and readout means;
Have
The control means includes
In the first interval, the storage capacitor is precharged with a predetermined amount of charge,
In a second interval following the first interval, light is incident on the thin film transistor while turning off the thin film transistor, thereby discharging at least a part of the charge precharged in the storage capacitor,
In a third interval following the second interval, the predetermined amount of precharged charge is subtracted from the amount of charge remaining in the storage capacitor,
In the fourth interval subsequent to the third interval, the amount of electric charge remaining in the storage capacitor is caused to be read by the reading unit. A gate driving means to which a gate electrode of the thin film transistor is connected;
Power supply means connected to the storage capacitor and capable of switching between at least a first voltage and a second voltage to be applied to the storage capacitor;
Have
The photoelectric conversion device according to claim 1, wherein the control device also controls the gate driving unit and a power source.   3. The photoelectric conversion device according to claim 1, wherein the reading unit includes an integrating amplifier capable of resetting one input terminal connected to a source electrode of the thin film transistor. The control means includes
In the first interval, with the integration amplifier reset and the thin film transistor turned off, the power supply means is changed from the first voltage to the second voltage,
In the second interval, the integrating amplifier is reset, the thin film transistor is turned off, and light is incident on the thin film transistor with the power supply means at the second voltage,
In the third interval, with the integration amplifier reset and the thin film transistor turned off, the power supply means is changed from the second voltage to the first voltage,
In the fourth interval, in a state where the power supply means is maintained at the first voltage, by resetting the integration amplifier and turning on the thin film transistor, the charge accumulated in the storage capacitor is reduced. The photoelectric conversion apparatus according to claim 3, wherein the readout unit causes the readout unit to read out. The power supply means can set a plurality of voltage values,
5. The photoelectric conversion device according to claim 2, wherein the control unit is capable of precharging the storage capacitor with a plurality of types of charges.   6. The photoelectric conversion device according to claim 1, wherein the thin film transistor includes at least one of amorphous silicon and polysilicon as a raw material.   The photoelectric conversion device according to claim 1, further comprising a wavelength converter that converts a wavelength of the irradiated radiation into a wavelength of a light beam. The photoelectric conversion device according to any one of claims 1 to 7,
X-ray generation means for irradiating the photoelectric conversion device with X-rays;
Have
The X-ray imaging system, wherein the control unit controls the operations of the thin film transistor, the reading unit, and the X-ray generation unit to cause the reading unit to read an X-ray image transmitted through a subject. A method of driving a photoelectric conversion device including a thin film transistor having a light detection function and a switching function and a pixel including a storage capacitor connected to the thin film transistor,
A first interval for precharging the storage capacitor with a predetermined amount of charge;
A second interval for discharging at least part of the charge precharged in the storage capacitor by causing light to enter the thin film transistor while the thin film transistor is in an off state;
A third interval for subtracting the predetermined amount of precharged charge from the amount of charge remaining in the storage capacitor;
A fourth interval for reading out the amount of charge remaining in the storage capacitor to the readout means;
A method for driving a photoelectric conversion device comprising:

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