Abstract:
The present invention provides an image sensor comprising: pixels arranged along a plurality of row lines and column lines in a matrix form; a scan driving unit for selecting the row lines in the unit of n lines in a binning mode; and a read circuit unit for outputting n*m binning signals generated by sampling n*1 signals output in every column line according to the selection of the row lines and averaging the sampled n*1 signals in the unit of m neighboring column lines, wherein each of n and m is a natural number larger than or equal to 2.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an image sensor, and more particularly, to an image sensor and a method for driving the same capable of improving a readout speed in a binning mode. 
         [0003]    2. Description of the Related Art 
         [0004]    An image sensor is a device for detecting optical image signals from the outside and converting the optical image signals into electric signals and has been widely used by being installed in various electronic equipments. 
         [0005]    The image sensor has light detecting elements, i.e., pixels arranged along row lines and column lines in a matrix form, and each pixel includes a photodiode for converting incident lights into electrical signals. 
         [0006]    A pixel of the image sensor has a small size, and there is a limit to the amount of light which the photodiode can receive. To improve this, the image sensor driven in binning mode has been used. 
         [0007]    In a normal mode, an image is formed by using the electric signals generated in each pixel, but in the binning mode, an image is formed by summing electrical signals of neighboring pixels. 
         [0008]    According to the conventional art, even in the binning mode, the row lines and the column lines are selected one by one in reading out the signals similarly to the normal mode. Thus, the readout speed in the binning mode is reduced, and the quality of the binned images is degraded because the signal-to-noise ratio is reduced. 
         [0009]    Further, it is not easy to increase the frame rate with the conventional art because the signals of the odd-numbered row lines and the even-numbered row lines are read out in the opposite phase to each other so that the time delay is generated between the row lines. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to increase the signal-to-noise ratio and the frame rate by raising the readout speed in the binning mode. 
         [0011]    In order to achieve the above object, according to one aspect of the present invention, there is provided an image sensor, including: a plurality of pixels arranged in a matrix from along a plurality of row lines and column lines; a scan driver configured to select the row lines with n number line basis in a binning mode; and a readout circuit configured to read n×1 signals from each of the column lines in response to the selection of the row lines, to sample the n×1 signals, to average the n×1 signals with a m number of column line basis, and to output n×m binning signals, wherein n and m are natural numbers of 2 or more. 
         [0012]    The readout circuit may include first sampling circuits and second sampling circuits configured to sample, by turns, the n×1 signal output from each of the column lines, and to output, by turns, the n×m binning signals; and connecting switches configured to turn on/off respective connections of m number of the first sampling circuits and the second sampling circuits. 
         [0013]    Each of the first sampling circuits and the second sampling circuits may include a first switch configured to turn on/off input of the n×1 signal; a capacitor configured to store the n×1 signal and to store the n×m signal when the connecting switch is in a turns on state; and a second switch configured to turn on/ off output of n×m signals. 
         [0014]    The readout circuit is configured to sequentially output the n×m signals with the m number of column line basis. 
         [0015]    According to another aspect of the present invention, there is provided a method of driving an image sensor including a plurality of pixels arranged in a matrix from along a plurality of row lines and column lines, including: selecting the row lines with n number line basis in a binning mode; and sampling n×1 signals from each of the column lines in response to the selection of the row lines, and outputting n×m binning signals by averaging the n×1 signals with a m number of column line basis with a readout circuit wherein n and m are natural numbers of 2 or more. 
         [0016]    The method further includes: sampling, by turns, the n×1 signal output from each of the column lines, and outputting, by turns, the n×m binning signals with first sampling circuits and second sampling circuits configured of the readout circuit, wherein the n×m binning signals are formed by connecting m number of the first sampling circuits and the second sampling circuits. 
         [0017]    Each of the first sampling circuits and the second sampling circuits includes: a first switch configured to turn on/off input of the n×1 signal; a capacitor configured to store the n×1 signal and to store the n×m signal when the connecting switch is in a turn-on state; and a second switch configured to turn on/off output of n×m signals. 
         [0018]    The readout circuit is configured to sequentially output the n×m signals with the m number of column line basis. 
         [0019]    According to further another aspect of the present invention, there is provided an image sensor, including: a plurality of pixels arranged in a matrix from along a plurality of row lines and column lines; a plurality of scan lines extended from the row lines; a plurality of readout lines extended from the column lines; a scan driver connected to the scan lines and configured to select the row lines with n number line basis in a binning mode or to select the row lines with one line basis in a normal mode; and a readout circuit connected to the readout lines and configured to read n×1 signals from each of the readout lines, to sample the n×1 signals, to average the n×1 signals with a m number of column line basis, and to output n×m binning signals, in the binning mode or to sample and output signals from each of the readout lines sequentially in the normal mode, wherein the readout circuit includes: first sampling circuits and second sampling circuits coupled in parallel and configured to sample, by turns, the n×1 signal output from each of the column lines, and to output, by turns, the n×m binning signals in the binning mode; and connecting switches configured to turn on/off respective connections of m number of the first sampling circuits and the second sampling circuits in accordance with averaging control signals, wherein each of the first sampling circuits and the second sampling circuits includes a first switch configured to turn on/off input of the n×1 signal according to sampling control signals, a metal oxide semiconductor (MOS) capacitor configured to store the n×1 signal and to store the n×m signal when the connecting switch is in a turn-on state, and a second switch configured to turn on/off output of n×m signals, wherein while one of the first and second sampling circuits performs the sampling operation, the other performs the output operation of the 2×2 binning signal, and wherein n and m are natural numbers of 2 or more. 
         [0020]    According to still further another aspect of the present invention, there is provided a method of driving an image sensor including a plurality of pixels arranged in a matrix from along a plurality of row lines and column lines, a plurality of scan lines extended from the row lines, and a plurality of readout lines extended from the column lines, including: selecting the scan lines with n number line basis in a binning mode or selecting the scan lines with one line basis in a normal mode; and sampling the n×1 signal output from each of the column lines through the readout line, by turns, with first sampling circuits and second sampling circuits of the readout circuit in the binning mode or sampling signals from each of the column lines in the normal mode, outputting n×m binning signals by averaging the n×1 signals with a m number of column line basis in the binning mode or outputting signals from each of the column lines in the normal mode, wherein the n×m binning signals are formed by connecting m number of the first sampling circuits and the second sampling circuits, while one of the first and second sampling circuits samples the n×1 signals, the other of the first and second sampling circuits outputs the 2×2 binning signal, and wherein n and m are natural numbers of 2 or more. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
           [0022]      FIG. 1  is a perspective view schematically showing an imaging system in accordance with an embodiment of the present invention; 
           [0023]      FIG. 2  is a schematic block diagram illustrating an image sensor in accordance with an embodiment of the present invention; 
           [0024]      FIG. 3  is a circuit diagram schematically illustrating a readout circuit part of the image sensor in accordance with an embodiment of the present invention; and 
           [0025]      FIG. 4  is a view showing the waveform of the relevant signals at the binning mode of the image sensor in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Hereinafter, referring to the drawings, embodiments of the present invention will be described in detail. 
         [0027]      FIG. 1  is a perspective view schematically showing an imaging system including the image sensor in accordance with an embodiment of the present invention,  FIG. 2  is a schematic block diagram of the image sensor in accordance with an embodiment of the present invention, and  FIG. 3  is a schematic circuit diagram of a readout part of the image sensor in accordance with an embodiment of the present invention. 
         [0028]    As the imaging system  100  adopting an image sensor  200  in accordance with an embodiment of the present invention, various types or applications of imaging systems may be used. For example, an X-ray imaging system such as a mammography system, a computed tomography (CT) system or the like may be used as a medical imaging system. For convenience of description, a dental X-ray imaging system is to give an example of an X-ray imaging system. 
         [0029]    Referring to  FIG. 1 , the imaging system  100  according to an embodiment of the present invention includes a base  110 , a supporting column  120 , a lifting member  130 , a chin supporting member  140 , a rotary arm supporting member  150 , a rotary arm  160 , a rotary arm driving means  170 , an X-ray generator  180  and the image sensor  200 . 
         [0030]    The base  110  is placed on the floor to support the support column  120  where the above-described components are. The support column  120  is connected to the base  110  and extends vertically from the base  110  to have an established state. 
         [0031]    The lifting member  130  is installed on the support column  120 , thereby has a vertical movement up and down along the support column  120  with a driving means such as a motor. Through this operation, it is possible to adjust the height of the chin support member  140  according to the height of the patient to be examined. 
         [0032]    The chin support member  140  is provided on the lifting member  130  to support the chin of the patient. With this chin support member  140 , the head of the patient, i.e., a subject, is able to be positioned between the X-ray generator  180  and the image sensor  200 . The rotary arm supporting member  150  is connected to an upper portion of the lifting member  130  and extends along a direction parallel to the floor. 
         [0033]    The rotary arm  160  is connected to a lower portion of the rotary arm supporting member  150 . The rotary arm  160  connected in this way is able to make a horizontal movement along the direction parallel to the floor or a rotary motion relative to a rotation axis perpendicular to the floor by the rotary arm driving means  170 . The rotary arm  160  may include a horizontal part connected to the rotary arm supporting member  150  and vertical parts bent downward from both ends of the horizontal part. 
         [0034]    The X-ray generator  180  and the image sensor  200  may be respectively installed and disposed within the vertical parts at both sides of the rotary arm  160  so as to face each other. The X-ray generator  180  may be configured to generate and irradiate the X-rays to the subject, and the X-rays passing through the subject are incident on the image sensor  200 . 
         [0035]    The image sensor  200  is configured to detect the X-rays passing through the subject and to convert the X-rays to the corresponding electrical signals. The image sensor  200  may have a rectangular shape in plan, but the shape of the image sensor  200  is not limited to this. 
         [0036]    As the image sensor  200  in accordance with an embodiment, a direct type image sensor which converts the X-rays directly to the electrical signals or an indirect type image sensor which converts the visible rays into the electric signals after converting the X-rays into the visible rays may be adopted. 
         [0037]    In case of adopting the indirect type image sensor, the image sensor is configured to include a layer of scintillator (scintillating layer) that converts X-rays into the visible rays. In such a case, the scintillating layer may be formed of CsI (cesium iodide), but the scintillating layer is not limited to this. 
         [0038]    The image sensor  200  may be a contemporary metal oxide semiconductor (CMOS) type image sensor, but the type of the image sensor is not limited to this. 
         [0039]    Referring to  FIG. 2 , the image sensor  200  may include an array  210  where pixels, i.e., elements for converting the incident light into the electrical signals, are arranged in a matrix form along the row line and the column line and a driving circuit. 
         [0040]    The pixel P may include a photodiode, thereby converting the incident light into the electric signals.̂̂ 
         [0041]    The driving circuit may include a scan driver  220  and a read circuit  230 . 
         [0042]    The scan driver  220  may sequentially select the row lines through scan lines SL. If a row line is selected, the electric signals of the pixels P which are located on the selected row line are read out via readout line s LL that extend along the corresponding column line. 
         [0043]    The scan driver  220  may control the number of the row lines selected in accordance with driving modes. For example, in a normal mode, the row lines may be sequentially selected one by one, with a set of one row line. In the binning mode, the row lines may be sequentially selected at least two by two, with a set of at least two row lines. In the binning mode in accordance with the embodiment of the present invention, for convenience of explanation, the case of selecting the row lines with the set of the two row lines is explained as an example. 
         [0044]    Referring to  FIG. 3 , the readout circuit  230  may include a first sampling circuit and a second sampling circuit SC 1 , SC 2  connected in parallel with each other at the end of each readout line LL. 
         [0045]    The first and the second sampling circuits SC 1 , SC 2  may be formed to have the same circuit configuration. For example, each of first and second sampling circuits SC 1 , SC 2  may include a first switch and a second switch SW 1 , SW 2  and a capacitor between the first and second switches SW 1 , SW 2 . 
         [0046]    The first switch S 1  may be connected to the corresponding readout line LL and the operation of turn-on/turn-off is controlled by the corresponding sampling control signals SMP 1 , SMP 2 . When the first switch SW 1  is turned on, the electrical signals passed through the readout line LL is able to be sampled in the sampling circuit. 
         [0047]    The capacitor C may include a first electrode connected to the first switch SW 1  and may store electrical signals delivered by the turn-on operation of the first switch SW 1 . As the capacitor C, for example, a metal oxide (MOS transistor) capacitor may be used, but the type of the capacitor is not limited to this. 
         [0048]    The second switch SW 2  is connected to a second electrode of the capacitor C, and the turn-on/turn-off operation is controlled in accordance with the corresponding output control signals COLE, COLO. When the second switch SW 2  is turned on, the electrical signals stored in the capacitor C are able to be output. 
         [0049]    A connecting switch SW 3  may be provided between neighboring first sampling circuits SC 1  to control electrical connection of the first sampling circuits. For example, the connecting switch SW 3  may be configured to control turn-on/turn-off the connection between the capacitors C of a plurality of the first sampling circuits SC 1 . Similarly, the connecting switch SW 3  may also be provided between the neighboring second sampling circuits SC 2  to control the electrical connection of the neighboring second sampling circuits. According to an embodiment of the present invention, for convenience of explanation, the connecting switch SW 3  is configured to control on/off the electrical connection, for example, between the two sampling circuits in a set. 
         [0050]    The turn-on/ turn-off operation of the connecting switch SW 3  is controlled in accordance with corresponding control averaging signals SMPE_EQ, SMPO_EQ. When the connecting switch SW 3  is turned on, the sampling circuits connected to the switch  3  are electrically connected to each other and the electric signals sampled by the sampling circuits are averaged. 
         [0051]    The read out circuit  230  having the configuration as described above, drives the first and second sampling circuits SC 1 , SC 2  by turns to perform the signal sampling and the output. In particular, in the binning mode, the electric signals are averaged by electrically connecting the sampling circuits adjacent each other, and this will be described in more detail with reference  FIG. 4 . 
         [0052]      FIG. 4  shows waveforms of relevant signals in the binning mode of the image sensor in accordance an embodiment of the present invention. 
         [0053]    The scan driver  220  may select, for example, the first and the second row lines. The electrical signals, i.e., 2×1 signals of the pixels located at the first and the second row lines are output to the respective readout line s LL. Namely, the electric signals of the pixels located at the first and second row lines of each column line are output together to the readout line LL and averaged so that the 2×1 binning is performed. The 2×1 binning signals generated in this way are transmitted to the read out circuit  230  via the readout line LL. 
         [0054]    Next, the first sampling circuit SC 1  samples the 2×1 binning signals transmitted through the readout line LL for a first sampling period SP 1 . 
         [0055]    For this, a first sampling control signal SMP 1  having a high level as a turn-on level is generated and simultaneously applied to all of the first sampling circuits SC 1  for first the sampling period SP 1 . Accordingly, the first switch SW 1  of the first sampling circuit SC 1  is turned on, and the 2×1 binning signal is transmitted and stored in the corresponding capacitor C of the first sampling circuit SC 1 . 
         [0056]    Thereafter, if the first switch SW 1  is changed from the turn-on state to the turn-off state, the first averaging control signal SMPE EQ having a high level as a turn-on level is generated and applied to the connecting switch S 3  connected to the first sampling circuit SC 1 . Accordingly, the connecting switch S 3  is turned on, and the capacitors C of the two neighboring first sampling circuits SC 1  are electrically connected to each other. Thus, 2×1 binning signals stored in the first sampling circuit SC 1  are averaged and the 2×2 binning is performed. The 2×2 binning signal generated like this is stored in each capacitor C. 
         [0057]    Next, for a first output OP 1  after the first sampling period SP 1 , the first output control signals COLE are sequentially applied by the two column lines in a set. Thus, the second switches SW 2  are sequentially turned ON the two column lines in the set, the 2×2 binning signals stored in the first sampling circuit SC 1  are sequentially output. 
         [0058]    For example, the 2×2 binning signal of the first and second column lines-&gt;the 2×2 binning signal of the third and fourth column lines-&gt; . . . -&gt;the 2×2 binning signal of N−1 th  and n th  column lines are output in this order. 
         [0059]    After the sampling process is performed to the first and the second law lines for the first sampling period SP 1  as described above, another sampling process is performed to the third and the fourth raw lines for the second sampling period SP 2 . 
         [0060]    The sampling process performed for the second sampling period SP 2  with the use of the second sampling circuit SC 2  is substantially same with the above-mentioned sampling process performed for the first sampling period SP 1  with the use of the first sampling circuit SC 1 . 
         [0061]    In other words, in each column line, the 2×1 binning signal for the third and fourth row lines is sampled at the corresponding second sampling circuit SC 2 , and the 2×2 binning signal are stored after the signal averaging. 
         [0062]    The 2×2 binning signals stored in the second sampling circuit SC 2  as described above, are sequentially output to the two column lines, set by set, in a second output period OP 2  after the second sampling period SP 2 . 
         [0063]    The 2×1 binning signals, sequentially output by selecting two law lines as described above, are sampled, by turns, with the first and second sampling circuits SC 1 , SC 2 . While one of the first and second sampling circuits SC 1 , SC 2  performs the sampling operation, the other performs the output operation of the 2×2 binning signal. 
         [0064]    In the case of driving the image sensor  200  in the normal mode, electric signals of each pixel are output for the respective column line by selecting the row lines sequentially. 
         [0065]    In such a case, one of the first and second sampling circuits SC 1 , SC 2  is activated to perform the sampling and outputting, and the other sampling circuit may not be used by disabled. As another example, similar to the binning mode, the first and second sampling circuits SC 1 , SC 2  may be used alternately to perform sampling and output. 
         [0066]    And, in the normal mode, the connecting switch SW 3  is placed at the off state since the signal averaging is not required with the read out circuit  230 . 
         [0067]    As described above, according to the embodiment of the present invention, in the binning mode, the n×1 binning is performed by selecting n number of the law lines in a set, and then N×1 binning averaging is performed by m number of column lines in a set to carry out n×m binning. Furthermore, by using a plurality of the sampling circuits for each column line in side-by-side configurations, it is possible to perform the signal sampling, the averaging, and the outputting by turns. 
         [0068]    Accordingly, it is possible in the binning mode, the signal read speed may be increased, thereby the signal-to-noise ratio is improved and the frame rate can be increased.