X-ray detector and method for driving the same

Described embodiments provide an X-ray detector and a method for driving the same. The X-ray detector includes: a sensor panel in which a plurality of pixels are defined, the plurality of pixels each including a photodiode for converting light corresponding to incident X-ray into an electric signal, and a switching element connected to one terminal of the photodiode to control the output of the electric signal; a light emitting unit for providing light to the photodiode; and a voltage supply unit connected to the other terminal of the photodiode to selectively supply first and second voltages different from each other.

The present application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2012-0069094 (filed on Jun. 27, 2012).

TECHNICAL FIELD

The present invention relates to an X-ray detector and a method for driving the same, and more particularly, to an X-ray detector capable of residual image removal and offset stabilization and a method for driving the same.

BACKGROUND ART

X-ray detectors, such as flat panel X-ray detectors (FPXDs), have been introduced and widely used in medical industries and the like.

An X-ray detector includes a scintillator and a sensor panel. The scintillator is configured to convert incident X-ray into light. The sensor panel is provided, with a plurality of pixels and a switching element. Each pixel includes a photodiode that receives light from the scintillator and converts the light into an electric signal. The switching element is connected to an output terminal of the photodiode to output the electric signal. The sensor panel may further include a signal detector and a gate driver. The signal detector detects the electric signal output from the pixel. The gate driver turns on the switching element to enable the signal detector to detect the electric signal. The electric signal detected by the signal detector is converted into an image signal through a predetermined process performed by a controller or the like provided in a main board. The image signal is transmitted to a display device for displaying an X-ray image.

Between an X-ray incidence and the next X-ray incidence, the X-ray detector performs a reset process to equalize electric charges stored in the photodiodes of the plurality of pixels. This process is required for removing a residual image caused by previous X-ray incidence.

Generally, as the reset process occurs, the photodiode is saturated by charging the electric charges to the photodiode using light incident from a light emitting sheet disposed on the backside of the sensor panel. However, in this case, the offset level of the photodiode increases excessively.

In addition, the input terminal of the photodiode is generally connected to a negative bias voltage. In this case, the offset level of the photodiode becomes unstable. For example, electric charges may be unnecessarily charged to the photodiode by leakage current through the switching element for a waiting time.

DISCLOSURE

Problem(s) to be Solved by the Invention

The present invention has been made in an effort to solve the above-mentioned problems occurring in the prior art. Therefore, it is an object of the present invention to provide an X-ray detector may be capable of removing a residual image and maintain an offset level of a photodiode appropriately and stably.

Means for Solving the Problems

In accordance with an embodiment of the present invention, an X-ray detector may include a sensor panel, a light emitting unit, and a voltage supply unit. The sensor panel may include a plurality of pixels each including a photodiode and a switching element. The photodiode may convert light corresponding to incident X-ray into an electric signal. The switching element is connected to one terminal of the photodiode and controls the output of the electric signal. The light emitting unit may provide light to the photodiode. The voltage supply unit is connected to the other terminal of the photodiode and selectively supply first and second voltages different from each other.

In accordance with another embodiment of the present invention, a method may be provided for driving an X-ray detector. The X-ray detector may be provided with a plurality of pixels each including a photodiode for converting light corresponding to incident X-ray into an electric signal and a switching element connected to one terminal of the photodiode to control the output of the electric signal. In this case, the method may include performing an offset stabilization process to provide a first voltage to the other terminal of the photodiode; performing an X-ray detection process to provide a second voltage which is different from the first voltage, to the other terminal of the photodiode, convert light corresponding to incident X-ray into an electric signal, and output the electric signal; and performing a reset process to provide the second voltage to the other terminal of the photodiode, and supply light to the photodiode, so that the photodiode is charged with electric charges.

Effects of the Invention

In accordance with embodiments of the present invention, the X-ray detector and the driving method thereof may remove the residual image and maintain the offset level of the photodiode appropriately and stably.

DETAILED DESCRIPTION FOR CARRYING OUT THE INVENTION

FIG. 1is a schematic diagram illustrating a configuration of an X-ray detector in accordance with an embodiment of the present invention.

Referring toFIG. 1, the X-ray detector100according to the embodiment of the present invention includes a scintillator unit130, a sensor panel unit120, and a light emitting unit110. The scintillator unit130may be configured to convert incident X-ray into light. The sensor panel unit120includes a plurality of pixels for receiving light converted by the scintillator unit130and converting the received light into an electric signal. The light emitting unit110is disposed on the backside of the sensor panel unit120and provides light so as to reset the pixels.

The scintillator unit130may include a substrate, and a scintillator material formed on the substrate, such as NaI(Tl), ZnS(Ag), CsI(Tl), and LiI(Tl).

The light emitting unit110may be, for example, an electro luminescence sheet, but the present invention is not limited thereto. Any device may be used as the light emitting unit110as long as the device can provide light to the pixels of the sensor panel unit120.

The sensor panel unit120includes the plurality of pixels as described above, and may further include a variety of circuits for controlling the plurality of pixels. The sensor panel unit120will be described below in more detail with reference toFIG. 2.

FIG. 2is a detailed diagram illustrating the sensor panel unit120of the X-ray detector ofFIG. 1.

Referring toFIG. 2, the sensor panel unit120includes a pixel unit122, in which a plurality of pixels PX are arranged, a gate driver124disposed outside the pixel unit122so as to control the pixels PX, a signal detector126, and a voltage supply unit128.

Specifically, the pixel unit122includes a plurality of gate lines GL1, GL2, GL3, . . . , extending in parallel in a first direction (for example, row direction), and a plurality of data lines DL1, DL2, DL3. . . extending in parallel in a second direction (for example, column direction) intersecting with the first direction. The pixels PX are arranged at respective regions defined by the gate lines GL1, GL2, GL3, . . . and the data lines DL1, DL2, DL3. . . .

Each of the pixels PX includes a photodiode PD and a switching element such as a transistor Tr. The photodiode PD converts incident light into an electric signal. The switching element is connected to the output terminal of the photodiode PD and controls the output of the electric signal. As described above, the output terminal of the photodiode PD is connected to the input terminal of the transistor Tr, and the input terminal of the photodiode PD is connected to the voltage supply unit128that applies a bias voltage Bias or a ground voltage through a bias line BL. Also, the output terminal of the transistor Tr is connected to the signal detector126through the corresponding data line DL. A gate of the transistor Tr serving as a control terminal is connected to the gate driver124through the gate line GL.

The voltage supply unit128may include a first switch and a second switch. The first switch controls the connection between the bias line BL and a first voltage terminal such as a ground voltage terminal. The second switch controls the connection between the bias line BL and a second voltage terminal such as a bias voltage terminal. The voltage supply unit128selectively applies the ground voltage or the bias voltage Bias to the bias line BL. For this purpose, when the first switch is in on-state, the second switch is in off-state. Furthermore, when the first switch is in off-state, the second switch is in on-state. In this embodiment, the voltage supply unit128has been described as including the two switches such as the first and second switches, but the present invention is not limited thereto. The voltage supply unit128may have any configuration as long as the ground voltage or the bias voltage Vbias can be selectively applied to the bias line BL. The bias voltage Vbias may be a negative voltage.

The gate driver124generates gate signals and applies the gate signals to the gate lines GL1, GL2, GL3. . . . The gate signals may be sequentially applied in units of the gate lines GL1, GL2, GL3, . . . , that is, in units of rows. The gate signal may swing between a signal for turning on the transistor Tr and a signal for turning off the transistor Tr. When the transistor Tr connected to the corresponding gate line GL is turned on according to the application of the gate signal, the electric signal output from the photodiode PD is transferred to the corresponding data line DL, through the turned-on transistor Tr.

The signal detector126reads the electric signal transferred from the data line DL. For this purpose, the signal detector126may include amplifiers and a multiplexer. The amplifiers are connected to the plurality of data lines DL1, DL2, DL3, . . . in 1:1 correspondence. The multiplexer is connected to output terminals of the amplifiers. The present invention, however, is not limited thereto. A detailed configuration of the signal detector126may be modified in various forms. The electric signal detected by the signal detector126is transferred to a controller or the like provided in a main board (not illustrated), is converted into an image signal, and is transmitted to a display device for displaying an X-ray image. Since the signal detecting process of the signal detector126and subsequent processes have no relation to the features of the present invention, a detailed description thereof will be omitted.

Hereinafter, a method for driving an X-ray detector according to an embodiment of the present invention will be described with reference toFIGS. 1,2and3.

FIG. 3is a diagram for describing a method for driving an X-ray detector in accordance with an embodiment of the present invention. Specifically, a waveform (a) ofFIG. 3represents X-ray incident on the X-ray detector100. A waveform (b) ofFIG. 3denotes the gate signal of the gate driver140, a waveform (c) ofFIG. 3shows light provided from the light emitting unit110, and a waveform (d) ofFIG. 3shows the voltage applied by the voltage supply unit110.

Referring toFIG. 3, a driving cycle of the X-ray detector100may include an offset stabilization period P1, an X-ray detection period P2, and a reset period P3. The driving cycle may repeat for every X-ray photographing.

For convenience and ease of understanding, the X-ray detection period P2is described first. During the X-ray detection period P2, X-ray is incident on the X-ray detector100, light corresponding to the incident X-ray is converted into an electric signal in the pd unit122, and the electric signal is transferred to the signal detector126.

Particularly, the X-ray detection period P2begins at a fifth time point t5. At the fifth time point t5, the X-ray incidence starts. From the fifth time point t5to a sixth time point t6(see EX), light converted by the scintillator unit130is converted into an electric signal in the photodiode PD of the pixel PX and the photodiode PD is charged with electric charges. Such charging of the electric charges continues until the sixth time point t6.

At sixth time point t6, the gate signal of the gate driver124is converted from a turn-off signal of the transistor Tr to a turn-on signal thereof. Therefore, the electric charges charged in the photodiode PD are transferred to the turned-on transistor Tr and the corresponding signal detector126through the data line DL.FIG. 3illustrates that the X-ray incidence EX is stopped and the gate signal is simultaneously converted into the turned-on signal at sixth time point t6However, it is apparent, that a predetermined delay may exist between the stop time point of the X-ray incidence EX and the conversion time point of the gate signal.

At a seventh time point t7, the electric charges are completely transferred from the photodiode PD to the signal detector126and the gate signal is converted into the turn-off signal again. In this manner, the X-ray incidence EX and detection RD are completed.

In accordance with an embodiment, the reset period P3comes after the X-ray photographing period, such as illustrated inFIG. 3as the X-ray detection period P2. The reset period P3is a period that prevents subsequent X-ray photographing result from being affected. Substantially all the electric signals remaining in the photodiodes PDs of the plurality of pixels PX are controlled so as to be uniform after the X-ray detection period P2.

Particularly the reset period P3begins at a seventh time point t7. At the seventh time point t7, the X-ray detection RD is completed. At the seventh time point t7, the light emitting unit110starts to provide light (see EL) for charging electric charges to the photodiode PD. The light provision EL may continue until an eighth time point t8. In this manner, the photodiode PD is saturated and a residual image caused in the X-ray detection period P2may be completely removed.

In accordance with embodiments of the present invention, the light provision (EL) is performed during a part of the reset period P3. The present invention, however, is not limited thereto. The light provision (EL) may be performed during the entire reset period P3. That is the reset period P3may include the light provision (EL) period and the remaining period. The light provision (EL) period is from the seventh time point t7to the eighth time point t8and the remaining period is from the eighth time point t8to a ninth time point t9. The transistor Tr may be in a turned-on state SC in at least a part of the period between the eight time point t8and the ninth time point t9. That is, the transistor Tr may be in a turned-on state SC in a period except the light provision (EL) period in the reset period P3. In this case, since the electric charges of the photodiode are discharged through the transistor Tr, the offset level of the photodiode PD may be lowered. In accordance with an embodiment, the transistor Tr is in the turned-on state (SC) during the entire period from the eighth time point t8to the ninth time point t9, but the present invention is not limited thereto. The turned-on state SC of the transistor Tr may be appropriately shown between the eighth time point t8and the ninth time point t9.

Consequently, the residual image caused by the X-ray photographing may be substantially or completely removed by saturating the photodiode PD through the light provision EL in the reset period P3. In addition, the offset level of the photodiode PD may be stably maintained in a lower state by controlling the turn-on/turn-off of the transistor Tr while appropriately changing the gate signal of the gate driver124after the light provision EL.

FIG. 3illustrates that the gate signal is converted into the turn-off signal and the light provision EL is started at the same time in the seventh time point t7. The present invention, however, is not limited thereto. It is apparent that a predetermined delay may exist between the conversion time point of the gate signal and the time point of the light provision EL.

In accordance with embodiments of the present invention, the offset stabilization period P1comes before the X-ray photographing such as the X-ray detection period P2. The offset stabilization period P1is a period for preventing the unnecessary increase in electric charges of the photodiode PD due to leakage current during the waiting time after the reset period P3. Furthermore, the offset stabilization period P1is a period for preventing the change in the offset level of the photodiode.

Particularly, in the offset stabilization period P1begins at the first time point t1. At the first time period t1, the voltage supply unit128turns off the second switch connected to the bias voltage terminal and turns on the first switch connected to the ground voltage terminal. Accordingly, the ground voltage GND is applied to the input terminal of the photodiode PD through the bias line BL. The transistor Tr may be in the turned-on state SC in a part of the period from first time point t1to fourth time point t4. During the turned-on state SC, the ground voltage is applied to an input terminal of the photodiode (PD) through a bias line (BL). For example, the transistor Tr may be in the turned-on state SC during a period between a second time point t2and a third time point t3. Therefore, the photodiode PD is saturated. The ground voltage application GND starts at the first time point t1. Such first time point t1may be determined by a predetermined ready signal indicating the X-ray incidence EX of the X-ray detection period P2.

In accordance with embodiments of the present invention, the ground voltage GND may be applied during a part of the offset stabilization period P1. The present invention, however, is not limited thereto. The ground voltage GND may be applied during the entire offset stabilization period P1. That is, the offset stabilization period P1may include the ground voltage (GND) application period and the remaining period. The GND application period may be from the first time point t1to the fourth time point t4and the remaining period may be from the fourth time point t4to fifth time point t5. The transistor Tr may be in a turned-on state SC in at least of a part other than the ground voltage (GND) application period in the offset stabilization period P1. For example, the transistor Tr may be in a turned-on state SC in at least a part of the period from the fourth time point t4to the fifth time point t5. In this case, since the electric charges of the photodiode are discharged through the transistor Tr, the offset level of the photodiode PD may be lowered, in accordance with embodiments of the present invention, the transistor Tr is in the turned-on state SC during the entire period from fourth time point t4to fifth time point t5, but the present invention is not limited thereto. The turned on state SC of the transistor Tr may be appropriately shown between fourth time point t4and fifth time point t5.

Consequently, in the offset stabilization period P1, the increase in the electric charge of the photodiode PD, which is generally caused by leakage current, and the resultant change in the offset level may be prevented by applying the ground voltage, instead of the bias voltage, to the input terminal of the photodiode PD. In addition, the offset level of the photodiode PD may be stably maintained in a lower state by controlling the turn-on/turn-off of the transistor Tr while appropriately changing the gate signal of the gate driver124after the ground voltage GND application.

In accordance with embodiments of the present invention, the X-ray detector and the driving method thereof may stabilize the offset level of the photodiode PD during the offset stabilization period P1just before the X-ray detection period P2and remove the residual image by saturating the photodiode PD during the reset period P3after the X-ray detection period P2.