JP2015188129A - Detection device, control method thereof, and detection system - Google Patents

Abstract

A technique for calculating a pixel value at high speed based on a signal value read out via an amplification transistor in the pixel is provided. A detection device includes a pixel including a conversion element that converts electromagnetic waves into electric charge and an amplification transistor that amplifies the electric charge, and a charge that is converted by the conversion element is amplified in a first path via the amplification transistor. And a read circuit that selectively reads out through any of the second paths that do not pass through the transistor. Based on the signal value obtained by reading the charge converted by the conversion element through the first path and the pixel value obtained by reading the charge converted by the conversion element through the second path, the signal value and the pixel value A function representing the correspondence relationship with is determined. The pixel value is calculated by applying a function to the signal value obtained by reading the charge converted by the conversion element through the first path. [Selection] Figure 3

Description

  The present invention relates to a detection apparatus, a control method thereof, and a detection system.

  The radiation reading apparatus of Patent Document 1 has an amplification transistor in a pixel, and charges obtained by the conversion element are amplified and read by the amplification transistor. With such a configuration, the S / N ratio of the obtained pixel value can be improved, and high-quality shooting can be performed. Patent Document 2 proposes a circuit configuration in which the electric charge obtained by the conversion element can be read out by both a route passing through the amplification transistor in the pixel and a route not passing through the amplification transistor. In these radiation reading apparatuses, a pixel value is calculated by taking a difference between a signal value read in a state where charges are accumulated in the conversion element and a signal value read in a state where the charges are reset.

JP-A-11-307756 JP 2005-176297 A

  If a signal value is read twice via an amplifying transistor in a pixel in order to calculate one pixel value, it takes much time. An object of the present invention is to provide a technique for calculating a pixel value at high speed based on a signal value read out via an amplification transistor in a pixel.

  In view of the above problem, in one embodiment, the detection device is a pixel including a conversion element that converts electromagnetic waves into electric charge, an amplification transistor that amplifies the electric charge, and the electric charge converted by the conversion element. A readout circuit that selectively reads out through either the first path that passes through the amplification transistor or the second path that does not pass through the amplification transistor, and the charge converted by the conversion element is read out through the first path. A decision to determine a function representing a correspondence relationship between the signal value and the pixel value based on the obtained signal value and a pixel value obtained by reading out the charge converted by the conversion element through the second path; And means for calculating a pixel value by applying the function to a signal value obtained by reading out the electric charge converted by the conversion element through the first path. Detection apparatus is provided, wherein.

  The above means provides a technique for calculating a pixel value at high speed based on a signal value read out via an amplification transistor in the pixel.

The block diagram explaining the structure of the radiation detection apparatus of some embodiment. FIG. 2 is a simplified equivalent circuit diagram of the pixel and signal processing IC in FIG. 1. The graph showing the correspondence of a signal value and a pixel value. The timing diagram explaining operation | movement of the radiation detection apparatus of FIG. FIG. 6 is a simplified equivalent circuit diagram of a pixel and a signal processing IC according to some embodiments. The timing diagram explaining operation | movement of the radiation detection apparatus of FIG. FIG. 6 is a simplified equivalent circuit diagram of a pixel according to some embodiments. The block diagram explaining the structure of the detection apparatus of some embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Throughout various embodiments, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, each embodiment can be appropriately changed and combined. Some embodiments of the present invention generally relate to a detection device that detects electromagnetic waves (visible light, infrared rays, radiation, etc.) in a specific wavelength band. Hereinafter, a radiation detection device that detects radiation will be described as an example. The radiation includes, for example, X-rays, α rays, β rays, γ rays and the like.

  With reference to the schematic block diagram of FIG. 1, the structure of the radiation detection apparatus 100 which concerns on some embodiment is demonstrated. The radiation detection apparatus 100 has the components shown in FIG. 1, for example. A plurality of pixels 111 are arranged in a two-dimensional array on the sensor substrate 110. Each pixel 111 generates a signal corresponding to the radiation incident on the radiation detection apparatus 100. The sensor substrate 110 includes, for example, pixels 111 in 3000 rows and 3000 columns.

  The pixels 111 arranged in the row direction (left-right direction in FIG. 1) are connected to the drive IC 121 through a common drive line. The driving IC 121 is connected to the scanning circuit 120. The scanning circuit 120 controls the driving IC 121 to sequentially output signals to the pixels 111. The pixels 111 arranged in the column direction (vertical direction in FIG. 1) are connected to the signal processing IC 131 through a common signal line. The signal processing IC 131 is connected to the output circuit 130. The output circuit 130 reads the signal from the pixel 111 by controlling the signal processing IC 131, calculates the pixel value from this signal, and outputs it to an external device. The scanning circuit 120 and the output circuit 130 are connected to the control circuit 140, and the control circuit 140 controls the overall operation of the radiation detection apparatus 100.

  Next, a configuration example of the pixel 111 and the signal processing IC 131 of the radiation detection apparatus 100 will be described with reference to the simplified equivalent circuit diagram of FIG. The pixel 111 and the signal processing IC 131 are connected by a signal line SL1 and a signal line SL2. The pixel 111 includes a conversion element CNV and three thin film transistors T1 to T3. These elements are formed using a semiconductor, for example. The conversion element CNV generates and accumulates charges corresponding to electromagnetic waves in a specific wavelength band. When the radiation detection apparatus 100 includes a scintillator (not shown), the conversion element CNV may convert visible light emitted from the scintillator into an electric charge. Instead of this, the conversion element CNV may directly convert radiation into electric charges.

  The gate electrode of the thin film transistor T1 is connected to the conversion element CNV, the first main electrode is connected to the signal line SL1, and the second main electrode is connected to the thin film transistor T2. The thin film transistor T1 operates as a source follower (amplification transistor) that amplifies the electric charge of the conversion element CNV. The gate electrode of the thin film transistor T2 is connected to the driving IC 121, the first main electrode is connected to the thin film transistor T1, and the second main electrode is connected to the voltage source. The thin film transistor T2 operates as a switch element that switches a connection state between the thin film transistor T1 and the voltage source. The thin film transistor T2 may be positioned between the thin film transistor T1 and the signal line SL1, and the thin film transistor T1 may be directly connected to the voltage source. The gate electrode of the thin film transistor T3 is connected to the drive IC 121, the first main electrode is connected to the conversion element CNV, and the second main electrode is connected to the signal line SL2. The thin film transistor T3 operates as a switch element that switches a connection state between the conversion element CNV and the signal line SL2.

  The signal processing IC 131 includes a signal processing circuit between the signal line SL1 and the output circuit 130, and a signal processing circuit between the signal line SL2 and the output circuit 130. The signal line SL1 and the output circuit 130 are connected by a thin film transistor T6, a buffer circuit BF, and a thin film transistor T8. The electric charge accumulated in the conversion element CNV is supplied to the signal processing IC 131 through the signal line SL1 as a voltage signal amplified by a gain (amplification factor) determined by a ratio between the capacitance of the conversion element CNV and the wiring capacitance of the signal line SL1. . The signal processing IC 131 outputs the voltage signal from the signal line SL1 to the output circuit 130 as it is.

  The signal line SL2 and the output circuit 130 are connected by a thin film transistor T5, an amplifier circuit AMP, and a thin film transistor T9. The charge accumulated in the conversion element CNV is supplied to the signal processing IC 131 through the signal line SL2 as a charge signal. The signal processing IC 131 amplifies the charge signal from the signal line SL2 and outputs it to the output circuit 130.

  The signal processing IC 131 includes a thin film transistor T7 that operates as a switch element that switches a connection state between the signal line SL1 and the voltage source, and a thin film transistor T5 that operates as a switch element that switches a connection state between the signal line SL2 and the voltage source. It has further. Each thin film transistor in the signal processing IC 131 is controlled to be turned on / off by a drive signal from the output circuit 130.

  The signal processing IC 131 selectively reads out the electric charge of the conversion element CNV through one of a path passing through the signal line SL1 (hereinafter referred to as a first path) and a path passing through the signal line SL2 (hereinafter referred to as a second path). Can do. The first path passes through the thin film transistor T1, but the second path does not pass through the thin film transistor T1.

  A signal value obtained by reading the charge of the conversion element CNV through the first path in a state where the charge is accumulated in the conversion element CNV is S, and the charge of the conversion element CNV is the first value in a state where the charge of the conversion element CNV is reset. Let S0 be a signal value obtained by reading through one path. At this time, the pixel value X can be calculated by X = S−S0. However, in order to calculate the pixel value by this method, it is necessary to read out the signal value S and the signal value S0 separately. Since the signal value S and the signal value S0 are amplified signals, reading takes time. Therefore, in some embodiments, the radiation detection apparatus 100 determines in advance a function that represents the correspondence between the signal value S and the pixel value X, and applies the signal value S to this function to thereby obtain the pixel value. Is calculated.

  The correspondence relationship between the signal value S and the pixel value X will be described with reference to the graph of FIG. In FIG. 3, the horizontal axis represents the signal value S and the vertical axis represents the pixel value X. It is assumed that a function representing the correspondence relationship between the signal value S and the pixel value X is given by the graph 301. When the signal value obtained by reading out the electric charge accumulated in the conversion element CNV at a certain time through the first path is S1, the pixel value X1 is obtained by applying this S1 to the function represented by the graph 301. .

  The threshold voltage of the thin film transistor T1 changes due to deterioration over time. When the threshold voltage of the thin film transistor T1 changes, the function representing the correspondence between the signal value S and the pixel value X also changes. When the input voltage of the thin film transistor T1 is Vin, the output voltage is Vout, the threshold voltage is Vth, and the gain by the thin film transistor T1 is 1, the relational expression Vin−Vout = Vth is established. For this reason, even if the amount of charge accumulated in the conversion element CNV is equal, the threshold voltage Vth changes, whereby the value of the output voltage Vout changes, and thereby the signal value S also changes. For example, it is assumed that a function representing the correspondence relationship between the signal value S and the pixel value X after the threshold voltage of the thin film transistor T1 is changed is represented by the graph 302. If the pixel value is calculated using the function represented by the graph 301 when the signal value S is S1, the original pixel value X is assumed to be X1 despite being X2. An error occurs. Therefore, in some embodiments, the radiation detection apparatus 100 appropriately re-determines a function representing the correspondence relationship between the signal value S and the pixel value X.

  Next, a method for determining a function representing the correspondence between the signal value S and the pixel value X will be described with reference to the timing chart of FIG. Each waveform in FIGS. 4A and 4B represents a drive signal supplied to the gate electrode of the thin film transistor to which the corresponding reference symbol is attached. Each thin film transistor is turned on when the driving signal is high, and is turned off when the driving signal is low.

  First, the control circuit 140 turns on the thin film transistors T2 and T6 and reads out the electric charge accumulated in the conversion element CNV through the first path. Thereafter, the control circuit 140 turns on the thin film transistor T8 and outputs the value (signal value S) read through the first path to the output circuit 130. The determination unit 132 of the output circuit 130 stores the signal value S in the storage unit 134. Since the reading of the signal value S is performed non-destructively, the charge remains accumulated in the conversion element CNV.

  Thereafter, the control circuit 140 turns on the thin film transistors T3, T4, and T7, and reads out the charges accumulated in the conversion element CNV through the second path. Thereafter, the control circuit 140 turns on the thin film transistor T9 and outputs a signal value (hereinafter referred to as a signal value Q) read through the second path to the output circuit 130. The signal value Q is a value read out without amplifying the charge accumulated in the conversion element CNV within the pixel. The determination unit 132 of the output circuit 130 stores the signal value Q in the storage unit 134. While reading the signal value Q, the control circuit 140 turns on the thin film transistor T7 to reset the potential of the signal line SL1.

  Thereafter, the control circuit 140 turns on the thin film transistor T5 to reset the charge accumulated in the conversion element CNV. Thereafter, the control circuit 140 turns on the thin film transistor T9 and outputs the signal value read through the second path (hereinafter referred to as the signal value Q0) to the output circuit 130. The signal value Q0 is a value read without amplifying the charge of the conversion element CNV in a state where the conversion element CNV is reset. The determination unit 132 of the output circuit 130 stores the signal value Q0 in the storage unit 134.

  Thereafter, the determination unit 132 calculates the pixel value X by X = Q−Q0. A pair of the signal value S and the pixel value X defines one point on the graph representing the correspondence relationship between the signal value S and the pixel value X. The determination unit 132 further performs the process of FIG. 4A at different times to obtain another point on the graph representing the correspondence relationship between the signal value S and the pixel value X. The determining unit 132 determines a linear function that passes through these two points, thereby determining a function that represents the correspondence between the signal value S and the pixel value X, and stores this function in the storage unit 134. These two points may be a point acquired with the charge accumulated in the conversion element CNV and a point acquired with the charge reset.

  Instead of this, the determining unit 132 may obtain three or more points on the graph and determine a linear function from these three points by, for example, the least square method. Further, instead of this, the determination unit 132 determines a linear function representing the correspondence between the signal value S and the pixel value X based on one point on the graph and the slope of the graph determined by the gain of the thin film transistor T1. Also good. The gain by the thin film transistor T1 may be measured in a prior test (for example, a test before product shipment) and stored in the storage unit 134.

  The determination of the function representing the correspondence relationship between the signal value S and the pixel value X may be automatically executed when the power of the radiation detection apparatus 100 is supplied. In addition or alternatively, the determination of this function may be performed in response to user input to the radiation detection apparatus 100. When the reference potential of the amplifier circuit AMP is equal to the reset potential of the conversion element CNV, the conversion element CNV can be reset by reading the charge accumulated in the conversion element CNV through the second path. In this case, the thin film transistor T5 may be omitted.

  Next, a method for calculating the pixel value X from the signal value S will be described with reference to the timing chart of FIG. First, the radiation detection apparatus 100 is irradiated with radiation, and charges are accumulated in the conversion element CNV. Thereafter, the control circuit 140 turns on the thin film transistors T2 and T6, and reads out the charges accumulated in the conversion element CNV through the first path. Thereafter, the control circuit 140 turns on the thin film transistor T8 and outputs the value (signal value S) read through the first path to the output circuit 130. The calculation unit 133 of the output circuit 130 reads out a function representing a correspondence relationship between the signal value S and the pixel value X from the storage unit 134, and applies the signal value S output from the signal processing IC 131 to the function to thereby obtain the pixel value. X is calculated and output to an external device. Thereafter, the control circuit 140 turns on the thin film transistors T3, T5, and T7 to reset the charge of the conversion element CNV and reset the potential of the signal line SL1. When the radiation detection apparatus 100 performs moving image shooting, the operation of FIG. 4B is repeatedly performed.

  Next, another configuration example of the pixel 111 and the signal processing IC 131 of the radiation detection apparatus 100 will be described with reference to the simplified equivalent circuit diagram of FIG. The pixel 111 and the signal processing IC 131 are connected by a single signal line SL. The pixel 111 has the same configuration as that shown in FIG. 3 except that the first main electrode of the thin film transistor T1 and the second main electrode of the thin film transistor T3 are both connected to the signal line SL.

  The signal processing IC 131 has a signal processing circuit between the signal line SL and the output circuit 130. The signal line SL and the output circuit 130 are connected by the thin film transistor T10 and the amplifier circuit AMP. The signal processing IC 131 further includes a thin film transistor T11 that operates as a switch element that switches a connection state between the signal line SL and the voltage source. Each thin film transistor in the signal processing IC 131 is controlled to be turned on / off by a drive signal from the output circuit 130.

  The signal processing IC 131 transfers the charge of the conversion element CNV in any of a path (hereinafter referred to as a first path) that passes through the thin film transistor T1 and a path that does not pass through the thin film transistor T1 (hereinafter referred to as a second path). Can be read selectively.

  Subsequently, a method for determining a function representing the correspondence between the signal value S and the pixel value X will be described with reference to the timing chart of FIG. Each waveform in FIGS. 6A and 6B represents a drive signal supplied to the gate electrode of the thin film transistor to which the corresponding reference symbol is attached. Each thin film transistor is turned on when the driving signal is high, and is turned off when the driving signal is low.

  First, the control circuit 140 turns on the thin film transistors T2 and T10, and outputs a signal value (hereinafter referred to as a signal value S) obtained by reading out the electric charge accumulated in the conversion element CNV through the first path to the output circuit 130. The determination unit 132 of the output circuit 130 stores the signal value S in the storage unit 134. Since the reading of the signal value S is performed non-destructively, the charge remains accumulated in the conversion element CNV.

  After that, the control circuit 140 turns on the thin film transistor T11 and resets the potential of the signal line SL. Thereafter, the control circuit 140 turns on the thin film transistors T3 and T10 and outputs a signal value (hereinafter referred to as a signal value Q) obtained by reading out the electric charge accumulated in the conversion element CNV through the second path to the output circuit 130. The signal value Q is a value read out without amplifying the charge accumulated in the conversion element CNV within the pixel. The determination unit 132 of the output circuit 130 stores the signal value Q in the storage unit 134.

  Thereafter, the control circuit 140 turns on the thin film transistors T3, T10, and T11 to reset the charge accumulated in the conversion element CNV, and a signal value read through the second path (hereinafter referred to as a signal value Q0). Output to the output circuit 130. The signal value Q0 is a value read without amplifying the charge of the conversion element CNV in a state where the conversion element CNV is reset. The determination unit 132 of the output circuit 130 stores the signal value Q0 in the storage unit 134. Thereafter, the determination unit 132 determines a function representing the correspondence relationship between the signal value S and the pixel value X in the same manner as described with reference to FIG. 4, and stores this function in the storage unit 134.

  Next, a method for calculating the pixel value X from the signal value S will be described with reference to the timing chart of FIG. First, the radiation detection apparatus 100 is irradiated with radiation, and charges are accumulated in the conversion element CNV. Thereafter, the control circuit 140 turns on the thin film transistors T2 and T10 and outputs a signal value (hereinafter referred to as a signal value S) obtained by reading out the electric charge accumulated in the conversion element CNV through the first path to the output circuit 130. The calculation unit 133 of the output circuit 130 reads out a function representing a correspondence relationship between the signal value S and the pixel value X from the storage unit 134, and applies the signal value S output from the signal processing IC 131 to the function to thereby obtain the pixel value. X is calculated and output to an external device. After that, the control circuit 140 turns on the thin film transistor T11 to reset the charge of the conversion element CNV and reset the potential of the signal line SL. When the radiation detection apparatus 100 performs moving image shooting, the operation in FIG. 6B is repeatedly performed.

  Next, another configuration example of the pixel 111 of the radiation detection apparatus 100 will be described with reference to the simplified equivalent circuit diagram of FIG. The pixel 111 and the signal processing IC 131 are connected by a single signal line SL. The signal processing IC 131 has the same configuration as that shown in FIG.

  The pixel 111 includes a conversion element CNV, a plurality of thin film transistors T1, T3, T12 to T14, and a capacitor C1. The electric charge accumulated in the conversion element CNV is once accumulated in the capacitor C1, and then transferred to the signal processing IC 131 via the thin film transistor T14. The thin film transistor T13 operates as a load resistor for the ground circuit of the source follower constituted by the thin film transistor T1, and improves the signal transfer speed to the capacitor C. Also in this pixel 111, the signal processing IC 131 selectively converts the charge of the conversion element CNV through one of the first path passing through the thin film transistor T1 and the second path passing through the thin film transistor T3 without passing through the thin film transistor T1. Can be read out.

  In each of the above-described radiation detection apparatuses, the determination unit 132 of the output circuit 130 may determine one function representing the correspondence between the signal value S and the pixel value X for each pixel 111, or for each of the plurality of pixels 111. One function may be determined.

  FIG. 8 is a diagram showing an application example of the radiation detection apparatus according to the present invention to an X-ray diagnosis system (radiation detection system). X-ray 6060 as radiation generated by the X-ray tube 6050 (radiation source) passes through the chest 6062 of the subject or patient 6061 and enters the detection device 6040 in which the scintillator is arranged above the detection device of the present invention. Here, the detection conversion device having the scintillator disposed thereon constitutes a radiation detection device. This incident X-ray includes information inside the body of the patient 6061. The scintillator emits light in response to the incidence of X-rays, and this is photoelectrically converted to obtain electrical information. This information is converted into a digital signal, image-processed by an image processor 6070 serving as a signal processing unit, and can be observed on a display 6080 serving as a display unit of a control room. The radiation detection system includes at least a detection device and a signal processing unit that processes a signal from the detection device.

  This information can be transferred to a remote location by a transmission processing unit such as a telephone line 6090, displayed on a display 6081 serving as a display unit such as a doctor room in another location, or stored in a recording unit such as an optical disc. It is also possible for a doctor to make a diagnosis. Moreover, it can also record on the film 6110 used as a recording medium by the film processor 6100 used as a recording part.

Claims (12)

A detection device,
A pixel including a conversion element that converts electromagnetic waves into electric charge, and an amplification transistor that amplifies the electric charge,
A readout circuit that selectively reads out the electric charge converted by the conversion element through one of a first path that passes through the amplification transistor and a second path that does not pass through the amplification transistor;
Based on the signal value obtained by reading the charge converted by the conversion element through the first path and the pixel value obtained by reading the charge converted by the conversion element through the second path, Determining means for determining a function representing a correspondence relationship between a signal value and the pixel value;
A detection apparatus comprising: a calculation unit that calculates a pixel value by applying the function to a signal value obtained by reading out the charge converted by the conversion element through the first path.   The determination means calculates the function based on the signal value and the pixel value when the conversion element is in the first state, and the signal value and the pixel value when the conversion element is in the second state. The detection device according to claim 1, wherein the detection device is determined.   The detection according to claim 2, wherein the first state is a state in which charges are accumulated in the conversion element, and the second state is a state in which charges accumulated in the conversion element are reset. apparatus.   The determination means determines the function based on the signal value and the pixel value when the conversion element is in a first state, and a gain of the amplification transistor measured in advance. Item 2. The detection device according to Item 1.   The detection device according to claim 4, wherein the first state is a state in which charges accumulated in the conversion element are reset. The detection device further comprises storage means,
The determination means determines the function when power is supplied to the detection device, stores the function in the storage means,
The detection device according to claim 1, wherein the calculation unit reads the function from the storage unit and uses the function for calculation of the pixel value. The detection apparatus further includes a first signal line and a second signal line that connect the pixel and the readout circuit, respectively.
The conversion element and the first signal line are connected via the amplification transistor,
The detection device according to claim 1, wherein the conversion element and the second signal line are connected without passing through the amplification transistor. The detection apparatus further includes a signal line connecting the pixel and the readout circuit,
The conversion element and the signal line are connected by a path through the amplification transistor and are connected by a path not through the amplification transistor. Detection device.   The detection apparatus according to claim 1, wherein the detection apparatus is a radiation detection apparatus.   The detection device according to claim 1, wherein the amplification transistor is formed of a thin film transistor. The detection device according to any one of claims 1 to 10,
A detection system comprising: signal processing means for processing a signal obtained by the detection device. A method for controlling a detection device, comprising:
The detection device includes:
A pixel including a conversion element that converts electromagnetic waves into electric charge, and an amplification transistor that amplifies the electric charge,
A read circuit that selectively reads out the charge converted by the conversion element through either the first path that passes through the amplification transistor or the second path that does not pass through the amplification transistor;
The control method is:
Based on the signal value obtained by reading the charge converted by the conversion element through the first path and the pixel value obtained by reading the charge converted by the conversion element through the second path, A determination step of determining a function representing a correspondence relationship between a signal value and the pixel value;
And a calculation step of calculating a pixel value by applying the function to a signal value obtained by reading out the electric charge converted by the conversion element through the first path.