Abstract:
There is provided a solid-state image sensor including (a) a plurality of pixels arranged in a matrix in a photoelectric transfer region, (b) at least one movement-detector located in the photoelectric transfer region, (c) a first Y-scanner making successive access to the pixels in rows in a predetermined region in the photoelectric transfer region, and (d) a first X-scanner reading out signals running through signal output lines extending through the predetermined region. The first and second scanners both scan a predetermined region associated with a movement-detector which has transmitted a detection signal. The solid-state image sensor makes it possible to immediately detect movement when it has occurred, identify a region in which movement has occurred, and detect movement while carrying out scanning in a normal mode.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a solid-state image sensor and a method of driving the same, and more particularly to a MOS-type solid-state image sensor having a function of detecting movement, and method of driving the same. 
     2. Description of the Related Art 
     A MOS-type solid-state image sensor including a plurality of pixels each having a photoelectric converter and arranged in a two-dimensional array is sometimes designed to have a function of detecting movement. Such a MOS-type solid-state image sensor not only converts a scene detected by a sensor array, into an electric signal, but also detects movement of something in a scene detected by a sensor array, and transmits a signal accordingly. In the specification, such a MOS-type solid-state image sensor having a function of detecting movement is hereinafter called a movement-sensor. 
     A conventional solid-state image sensor not having a function of detecting movement is explained hereinbelow with reference to FIGS. 1 and 2. 
     FIG. 1 is a block diagram of a conventional MOS-type solid-state image sensor, and FIG. 2 is a circuit diagram of a pixel constituting a sensor array which is a part of the MOS-type solid-state image sensor illustrated in FIG.  1 . 
     As illustrated in FIG. 1, a conventional MOS-type solid-state image sensor is comprised of a sensor array  801  including a plurality of pixels arranged in an array, each pixel converting a light into an electric signal in accordance with brightness of an image, a scanning circuit  802  which scans electric signals converted by the pixels, a X-scanning circuit  803  which scans the electric signals converted by the pixels, and a plurality of line memories  804  each temporarily accumulating the electric signals. 
     The sensor array  801  is defined by a plurality of pixels arranged in a two-dimensional array. Each of the pixels is designed to include a photoelectric transfer diode. An image projected on the sensor array  801  is converted into an electric signal by the pixels. 
     The Y-scanning circuit  802  transmits Y-scanning signals  807  to thereby make access to the pixels row by row in the sensor array  801  from an uppermost row to a lowermost row. As a result, signals in each of rows in the sensor array  801  are concurrently read out as row signals  805 . 
     These row signals  805  are accumulated in the line memories  804 . Each of the line memories  804  is comprised of a switched capacitor, for instance. Since row signals are generally analog signals, they can be accumulated in switched capacitors by the number equal to the number of pixels existing in a row. 
     The X-scanning circuit  803  transmits X-scanning signals  808  to the line memories  804  to thereby make successive access to the row signals accumulated therein, and transmits an output signal  806 . 
     As illustrated in FIG. 2, a pixel which carries out photoelectric transfer is comprised of a photodiode  901 , a first n-MOSFET  902  including a gate electrically connected to a bias terminal  905 , a drain electrically connected to a source voltage VDD and a source electrically connected to the photodiode  901 , a second n-MOSFET  903  including a gate electrically connected to the photodiode  901 , a source electrically connected to the source voltage VDD and a drain, and a third n-MOSFET  904  including a gate electrically connected to a terminal  906  through which a signal is input, a source electrically connected to the drain of the second transistor  903  and a drain electrically connected to a output line  907 . 
     The photodiode  901  is kept biased by the first n-MOSFET  902 , and hence, keeps producing photoelectric current. A bias voltage is applied to the first n-MOSFET  902  through the bias terminal  905 . A voltage at the drain of the first n-MOSFET  902  is output at a low impedance through the second n-MOSFET  903 . 
     The third n-MOSFET  904  acts as a switch. When the third n-MOSFET  904  makes access to a pixel, the third n-MOSFET  904  is turned on by the Y-scanning circuit  802  through the terminal  906 . When the third n-MOSFET  902  is caused to be turned on, a pixel output signal is transmitted through the output line  907 . 
     The conventional solid-state image sensor has such a structure as mentioned above, and operates in the above-mentioned way. If a movement sensor is designed based on the above-mentioned conventional solid-state image sensor, the movement sensor would have such a structure as mentioned below. 
     FIG. 3 is a block diagram of a conventional movement sensor having a structure designed based on the structure of the solid-state image sensor illustrated in FIG.  1 . The movement sensor illustrated in FIG. 3 is comprised of a sensor array  1001  including a plurality of pixels arranged in a matrix array, each pixel converting a light into an electric signal in accordance with brightness of an image, a Y-scanning circuit  1002  which scans electric signals converted by the pixels, a X-scanning circuit  1003  which scans the electric signals converted by the pixels, a plurality of line memories  1004  each temporarily accumulating the electric signals, and a plurality of differential circuits  1007  electrically connected between the line memories  1004  and the X-scanning circuit  1003 . 
     In brief, the movement sensor additionally includes the differential circuit  1007  in comparison to the solid-state image sensor illustrated in FIG.  1 . 
     The Y-scanning circuit  1002  transmits Y-scanning signals  1009  to the sensor array  1001  to thereby make access to the pixels row by row in the sensor array  1001  from an uppermost row to a lowermost row. As a result, signals in each of rows in the sensor array  1001  are concurrently read out as first row signals  1005 . These first row signals  1005  are accumulated in the line memories  1004 . 
     Then, the Y-scanning circuit  1002  makes access again to the pixel row which has been previously accessed. As a result, signals in the row are read out as second row signals  1008 , which are accumulated in the line memories  1004 . The line memories  1004  separately transmits the first and second row signals a  1005  and  1008  to the differential circuits  1007 . The differential circuits  1007  calculates a difference between the first and second row signals  1005  and  1008 . The calculation is concurrently carried out for all the first and second row signals  1005  and  1008  transmitted from a pixel row. 
     The movement sensor illustrated in FIG. 3 includes the differential circuits  1007  by the number equal to the number of pixels in a row in the sensor array  1001 . 
     Output signals transmitted from the differential circuits  1007 , each indicating a difference between the first and second row signals  1005  and  1008 , are successively read out in accordance with X-scanning signals  1010  transmitted by the X-scanning circuit  1003 . The thus read-out output signals are transmitted from the X-scanning circuit  1003  as output signals  1006 . 
     In the above-mentioned movement sensor, since signals are read out twice from the same pixel row at a certain interval and a difference between the signals is calculated, the differential circuits  1007  transmit non-zero output signals for pixels in which a light intensity varies. When the differential circuits  1007  transmits such non-zero output signals, it is deemed that movement has occurred in the sensor array  1001 . 
     It should be noted that the movement sensor illustrated in FIG. 3 does never spoil functions of the conventional solid-state image sensor illustrated in FIG.  1 . Accordingly, the movement sensor can act as a solid-state image sensor. When the movement sensor acts as a solid-state image sensor, the Y-scanning circuit  1002  successively makes access to pixels row by row in the sensor array  1001 , and signals which were read out from each of rows are output through the differential circuits  1007 . 
     A movement sensor such as the above-mentioned one is detailed is described, for instance, in 1995 IEEE International Solid-State Circuits Conference Digest of Technical Papers, pp. 226-227, “A 256×256 CMOS Active Pixel Image Sensor with Motion Detection”, A. Dickinson et al. 
     Apart from the above-mentioned Technical Papers, Japanese Unexamined Patent Publication No. 8-292998 has suggested an image detector including a sensor cell array which can accomplish an operation between pixels when accumulated electric charges associated with a pixel signal are read out, an amplifier, an analog-digital convertor, a scanner and a multiplexer which operate with each other to scan a designated area, and a control circuit. An area in which a target pattern exists is detected by virtue of the operation between pixels carried out by the sensor cell array. The scanner and the multiplexer randomly scans the thus detected area to thereby read out image data therefrom. Thus, only an area in which a target pattern exists is read out among all of input images, ensuring high rate at which images are processed. 
     Japanese Unexamined Patent Publication No. 10-313426 has suggested a solid-state image sensor having a function of detecting movement, comprised of pixels each transmitting an electric signal in accordance with an intensity of incident light, vertical signal lines each associated with each of columns of the pixels, a vertical scanning circuit which transfers electric signals transmitted from a certain row of the pixels, to the associated vertical signal line at a predetermined timing, and a horizontal scanning circuit which transfers the electric signals to horizontal signal lines. Differential circuits are arranged in the vertical signal lines. The differential circuits accumulates electric signals transmitted at a timing from the pixels as signals of the previous frame and also accumulates electric signals transmitted at the next timing from the same pixels as electric signals of the present frame. The differential circuits compare those electric signals to each other to thereby transmit output signals indicative of comparison results. 
     Japanese Unexamined Patent Publication No. 11-8805 has suggested a solid-state image sensor having a function of detecting movement. A plurality of pixels are arranged in a matrix. Each of columns of the pixels is electrically connected to a vertical signal line. A vertical scanning circuit selects a row, reads out signals out of the selected row of pixels, and transfers the thus read out signals to the associated vertical signal line. A signal comparison circuit and a video-signal generating circuit are positioned in each of the vertical signal lines. The signal comparison circuit accumulates electric signals transmitted at a timing from the pixels as signals of the previous frame, and also accumulates electric signals transmitted at the next timing from the same pixels as electric signals of the present frame. The signal comparison circuit compares those electric signals to each other to thereby transmit an output signal indicative of comparison result, to a shift register. The video-signal generating circuit generates a video signal in accordance with electric signals of the present frame, and transmits the video signal to a horizontal scanning circuit. 
     However, the movement sensors as mentioned above are accompanied with the following problems. 
     The first problem is that it takes about one frame period of time to detect movement. Herein, the term “one frame period of time” means a time necessary for the Y-scanning circuit  1002  to scan pixels from a first row to a bottom row. In other words, the term “one frame period of time” means a time necessary for transmitting signals defining one scene. 
     For instance, it is now assumed that an image varies with the lapse of time at a lower end of the sensor array  1001 . This variation in an image can be first detected only when the Y-scanning circuit  1002  makes access to the pixels in a lowermost row of pixels. Since the Y-scanning circuit  1002  has made access to all rows of pixels until the Y-scanning circuit  1002  makes access to the pixels in a lowermost row of pixels, much time already passes after the variation in an image has actually occurred. 
     After detection of movement, an operator often desires to see a quite small area including an area in which the movement has been detected. However, it is impossible to do so by the conventional movement sensor. This is the second problem. 
     The third problem is that the conventional movement sensor cannot detect movement while it is operating as a solid-state image sensor, that is, not as a movement sensor, and in addition, the conventional movement sensor cannot act as a solid-state image sensor while it is in operation of detecting movement. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned problems, it is an object of the present invention to provide a solid-state image sensor which is capable of immediately detecting movement when it has occurred, identifying an area including an area in which movement has occurred, detecting movement even while it is operating as a solid-state image sensor, and independently carrying out reading out a signal from an area in which movement has occurred and reading out signals from entire pixels in a sensor array. 
     In one aspect of the present invention, there is provided a solid-state image sensor including (a) a plurality of pixels arranged in a matrix in a photoelectric transfer region, A) at least one movement-detector located in the photoelectric transfer region, (c) a first Y-scanner making successive access to the pixels in rows in a predetermined region in the photoelectric transfer region, and (d) a first X-scanner reading out signals running through signal output lines extending through the predetermined region, the first and second scanners both scanning a predetermined region associated with a movement-detector which has transmitted a detection signal. 
     It is preferable that the solid-state image sensor includes a plurality of ovement-detectors randomly positioned in the photoelectric transfer region. 
     For instance, the predetermined region may be a region extensive around the movement-detector. 
     It is preferable that the solid-state image sensor further includes (e) a second Y-scanner making successive access to all of the pixels in rows in the photoelectric transfer region, and (f) a second X-scanner reading out signals running through all of signal output lines extending through the photoelectric transfer region. 
     It is preferable that the solid-state image sensor further includes (g) a first switch to which the first Y-scanner makes access, and (h) a second switch to which the second Y-scanner makes access, a first signal being read through the first switch being output to a first signal output line, and a second signal being read through the second switch being output to a second signal output line. 
     It is preferable that the first NY- and X-scanners operate independently of the second Y- and X-scanners. 
     For instance, the predetermined region may be designed to have a size defined by M pixels×N pixel wherein M and N are integers not greater than the number of pixels defining the solid-state image sensor. 
     It is preferable that each of the pixels is comprised of (a1) a photodiode, (a2) a first transistor including a gate electrically connected to the photodiode, a source electrically connected to a voltage source, and a drain, and (a3) a second transistor including a gate electrically connected to a terminal through which a signal is input, a source electrically connected to the drain of the first transistor and, a drain electrically connected to a first output line. 
     It is also preferable that each of the pixels is comprised of (a1) a photodiode, (a2) a first transistor including a gate electrically connected to the photodiode, a source electrically connected to a voltage source, and a drain, (a3) a second transistor including a gate electrically connected to a terminal through which a signal is input, a source electrically connected to the drain of the first transistor and, a drain electrically connected to a first output line, and (a4) a third transistor including a gate electrically connected to a terminal through which a signal is input, a source electrically connected to both the drain of the first transistor and the source of the second transistor, and a drain electrically connected to a second output line, wherein when the second transistor is turned on, a pixel output is transmitted through the first output line, when the third transistor is turned on, a pixel output is transmitted through the second output line, and when both the second and third transistors are turned on, a pixel output is transmitted through both the first and second output lines. 
     There is further provided a solid-state image sensor including (a) a plurality of pixels arranged in a photoelectric transfer region defined by a plurality of sub-regions, (b) a plurality of movement-detectors randomly arranged in the photoelectric transfer region, each of the movement-detectors detecting movement which has occurred in the photoelectric transfer region, and transmitting a detection signal, and (c) a scanner identifying a pixel transmitting the detection signal to thereby identify a sub-region in which the movement has occurred. 
     For instance, the scanner may be comprised of a first Y-scanner making successive access to the pixels in rows in the photoelectric transfer region, and a first X-scanner reading out signals transmitted from the photoelectric transfer region, the first Y- and X-scanners identifying the sub-region associated with a movement-detector which has transmitted the detection signal. 
     It is preferable that the solid-state image sensor further includes (e) a second Y-scanner making successive access to all of the pixels in rows in the photoelectric transfer region, and (i) a second X-scanner reading out all signals transmitted from the photoelectric transfer region. 
     It is preferable that the solid-state image sensor further includes (g) a first switch to which the first Y-scanner makes access, and (h) a second switch to which the second Y-scanner makes access, a first signal being read through the first switch being output to a first signal output line, and a second signal being read through the second switch being output to a second signal output line. 
     In another aspect of the present invention, there is provided a method of driving a solid-state image sensor, including the steps of (a) transmitting a detection signal when movement has been detected in a photoelectric transfer region including a plurality of sub-regions, and (b) starting scanning a sub-region associated with a detecting circuit which has transmitted the detection signal. 
     It is preferable that the method further includes the step of stopping scanning the photoelectric transfer region when movement is detected while the photoelectric transfer region is being scanned in entirety, and starting scanning a sub-region associated with a detecting circuit which has detected the movement. 
     It is preferable that the method further includes the step of, when a second detecting circuit has transmitted a second detection signal indicating that movement had been detected in a second sub-region while a first sub-region is being scanned in response to a first detection signal transmitted by a first detecting circuit, indicating that movement had been detected in the first sub-region, starting scanning the second sub-region after the first sub-region has been completed to be scanned. 
     It is preferable that the method further includes the step of, when a second detecting circuit has transmitted a second detection signal indicating that movement had been detected in a second sub-region while a first sub-region is being scanned in response to a first detection signal transmitted by a first detecting circuit, indicating that movement had been detected in the first sub-region, immediately starting scanning the second sub-region, if the first and second sub-regions do not have common row and column. 
     It is preferable that when movements have been detected in a plurality of sub-regions, the sub-regions are scanned in accordance with a predetermined order. 
     The advantages obtained by the aforementioned present invention will be described hereinbelow. 
     In the solid-state image sensor in accordance with the present invention, a plurality of the movement-detectors are randomly arranged in a photoelectric transfer region independently of the pixels. The movement-detectors detect movement having occurred in a photoelectric transfer region regardless of whether the solid-state image sensor acts as an ordinary solid-state image sensor or a movement sensor. A detection signal transmitted by the movement-detectors when they detect movement in a photoelectric transfer region is immediately transmitted to the first X- and scanning circuits, which in response scan a pixel identified by the detection signal. Hence, the solid-state image sensor makes it possible to detect movement independently of a frame period, ensuring reduction in a time necessary for detecting movement in comparison with a conventional solid-state image sensor. 
     In addition, the solid-state image sensor in accordance with the present invention can detect movement while it operates as an ordinary solid-state image sensor, that is, it scans a photoelectric transfer region in entirety. 
     In accordance with the solid-state image sensor, it is possible to pick up images associated with a region in which movement has been detected, by means of the first X- and Y-scanning circuits. 
     Furthermore, by designing each one of the pixels to include two switches to each of which the first and second Y-scanning circuits make access. and designing the pixel to transmit output signals to separate output signal lines, the solid-state image sensor can scan a photoelectric transfer region in entirety and scan a sub-region in which movement has been detected, at the same time. 
     The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a conventional MOS-type solid-state image sensor. 
     FIG. 2 is a circuit diagram of a pixel which is a part of the conventional MOS-type solid-state image sensor illustrated in FIG.  1 . 
     FIG. 3 is a block diagram of a conventional MOS-type solid-state image sensor having a function of detecting movement. 
     FIG. 4 is a block diagram of a solid-state image sensor in accordance with the first embodiment of the present invention. 
     FIG. 5 illustrates a sub-region in which movement is to be detected. 
     FIG. 6 is a circuit diagram of a movement detecting circuit. 
     FIG. 7 is a graph showing a relation between an incident light and an output in the movement detecting circuit illustrated in FIG.  6 . 
     FIG. 8 is a block diagram of the solid-state image sensor in accordance with the first embodiment, showing connection between the movement detecting circuit and detecting signal lines. 
     FIG. 9 is a block diagram of a solid-state image sensor in accordance with the second embodiment of the present invention. 
     FIG. 10 is a circuit diagram of a pixel which is a part of the solid-state image sensor illustrated in FIG.  9 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 4 illustrates a solid-state image sensor in accordance with the first embodiment of the present invention. 
     The illustrated solid-state image sensor is comprised of sixteen rectangular sensor arrays  101  arranged in a matrix, nine movement detecting circuits  102 , a first X-scanning circuit  105 , a first Y-scanning circuit  106 , a second X-scanning circuit  103 , and a second Y-scanning circuit  104 . 
     The sixteen rectangular sensor arrays  101  define a photoelectric transfer region. Each of the sensor arrays  101  is comprised of a plurality of pixels arranged in a two-dimensional array. Each of the pixels has such a structure as illustrated in FIG.  2 . 
     Each of the movement detecting circuits  102  is positioned at a gap formed between the adjacent sensor arrays  101 . The movement detecting circuits  102  are arranged in a 3×3 matrix. Namely, the movement detecting circuits  102  are spaced away from one another in a photoelectric transfer region. In comparison with the solid-state image sensor illustrated in FIG. 1, the sensor array  801  is divided into the sixteen sensor arrays  101 , and the movement detecting circuits  102  are positioned between the adjacent sensor arrays  101  in the first embodiment. 
     In the solid-state image sensor illustrated in FIG. 4, the sensor arrays  101  are successively accessed by the second X-scanning circuit  103  and the second Y-scanning circuit  104 . That is, pixels in each of the sensor arrays  101  are successively accessed from a top row to a bottom row like the conventional solid-state image sensor having no movement detecting circuits, illustrated in FIG.  1 . 
     When movement has been detected in a photoelectric transfer region, the movement detecting circuit  102  transmits a detection signal indicative of detection of movement, to the first X-scanning circuit  105  as a first detection signal  107  through a first signal line  107   a , and to the first Y-scanning circuit  106  as a second detection signal  108  through a second signal line  108   a.    
     The first X-scanning circuit  105  and the first Y-scanning circuit  106  do not scan all pixels arranged in a photoelectric transfer region, but scan only a rectangular area located close to a movement detecting circuit which has transmitted a detection signal. For instance, with reference to FIG. 5, if a movement detecting circuit  102 .A transmits a detection signal, the first X-scanning circuit  105  and the first Y-scanning circuit  106  scan a rectangular area  211  extensive around the movement detecting circuit  102 A. 
     Specifically, when the movement detecting circuit  102 A transmits a detection signal, a first signal line  107 A and a second signal line  108 A are both activated. Then, the first X-scanning circuit  105  and the first Y-scanning circuit  106  start scanning the rectangular area  211 . As a result, the first X-scanning circuit  105  transmits an image signal as a local area signal  210 . 
     The local area  211  is designed in advance to have a size of M pixel×N pixel wherein M and N are integers not greater than the number of pixels constituting the solid-state image sensor. 
     A sensor array may be divided into the desired number of sensor arrays. Though the sensor array  801  illustrated in FIG. 1 is divided into the sixteen sensor arrays  101  in the first embodiment, the number by which the sensor array  801  is divided is not to be limited to sixteen. 
     The position and the number of the movement detecting circuits  102  are not to be limited to those illustrated in FIG.  4 . It is not always necessary to position the movement detecting circuits  102  in a matrix as illustrated in FIG.  4 . In addition, it is not always necessary for the solid-state image sensor to include a plurality of the movement detecting circuits  102 . The solid-state image sensor may be designed to include only one movement detecting circuit  102 . 
     FIG. 6 is a circuit diagram illustrating an example of a structure of the movement detecting circuit  102 . Strictly speaking, the circuit illustrated in FIG. 6 is a circuit for detecting how an intensity of an incident light varies with the lapse of time. This circuit is detailed in “Analog VLSI and Neural Systems”, Addison Wesley and C. Mead. 
     The movement detecting circuit  102  is comprised of a photodiode  301 , a first p-MOSFET  302  including a drain through which an output signal transmitted from the photodiode  301  is introduced, a gate electrically connected to the drain, and a source electrically connected to a source voltage VDD, an amplifier  303  having a positive input through which an output signal transmitted from the photodiode  301  is introduced and a negative input, a capacitor  305  electrically connected between the source voltage VDD and the negative input of the amplifier  303 , and a second p-MOSFET  304  including a source electrically connected to a node located intermediate between the capacitor  305  and the negative input of the amplifier  303 , a drain, and a gate electrically connected to the drain. 
     The illustrated movement detecting circuit  102  operates as follows. 
     It is now assumed that an intensity of a light radiated to the photodiode  301  varies with the lapse of time. Since a current flowing through the first p-MOSFET  302  varies in an intensity, a voltage at the drain of the first p-MOSFET  302 , which is equal to a voltage at the gate of the first p-MOSFET  302 , also varies. Accordingly an input to the positive input of the amplifier  303  also varies. 
     Since an output  306  transmitted from the amplifier  303  is negatively fed back to the amplifier  303  through the second p-MOSFET  304 , the output  306  follows a voltage input into the amplifier  303 . However, since the capacitor  305  is incorporated in the feed-back loop, it takes some time until a voltage input through the negative input becomes equal to a voltage input through the positive input. Hence, there is a big difference in those voltages in such transition period, and accordingly, the amplifier  303  transmits a signal having a quite great magnitude. After some time has passed, the voltage input through the positive input becomes equal to the voltage input through the negative input. 
     FIG. 7 is a graph showing how the output  306  varies with the lapse of time. Though FIG. 7 shows a curve of the output  306  found when an intensity of an incident light is decreased with the lapse of time, there is obtained a curve which is similar to the curve illustrated in FIG. 7, but is upwardly projecting, when an intensity of an incident light is increased with the lapse of time. 
     As is obvious in view of FIG. 7, the movement detecting circuit illustrated in FIG. 6 transmits an output having a great magnitude, when an intensity of an incident light varies. 
     Apart from the movement detecting circuit illustrated in FIG. 6, there re many examples of an analog circuit of detecting how an intensity of an incident light varies with the lapse of time. For instance, many examples of a ovement sensor are described in the above-mentioned reference “Analog VLSI and Neural Systems”. 
     FIG. 8 is a circuit diagram of the solid-state image sensor including the movement detecting circuits illustrated in FIG.  6 . 
     A movement detecting circuit  501  having the structure as illustrated in FIG. 6 is electrically connected to both the first and second signal lines  107   a  and  108   a  through a capacitor  502  and first to third p-MOSFETs  509 ,  510  and  503 . In FIG. 8, the second X-scanning circuit  103  and the second Y-scanning circuit  104  are omitted for simplification. 
     The movement detecting circuit  501  transmits an output thereof to a connection node at which the first to third p-MOSFETs  509 ,  510  and  503  are electrically connected, through the capacitor  502 . The capacitor  502  accomplishes AC-coupling among the movement detecting circuit  501  and the p-MOSFETs  509 ,  510  and  503 . The third p-MOSFET  503  enhances a voltage at the right side of the capacitor  502  to a source voltage VDD. 
     By designing the third p-MOSFET  503  to be driven by small power, AC components transmitted from the movement detecting circuit  501  can be transferred to the first and second p-MOSFETs  509  and  510 . On receipt of the AC components from the movement detecting circuit  501 , the first and second p-MOSFETs  509  and  510  activate the first and second signal lines  107   a  and  108   a , respectively 
     Each one of the first and second signal lines  107   a  and  108   a  is electrically connected to a n-MOSFET  504  for slowly reduce voltages of the first and second signal lines  107   a  and  108   a  to a ground level. Each of the n-MOSFETs  504  receives a biased input through a gate thereof. 
     The solid-state image sensor illustrated in FIG. 8 operates as follows. 
     When any one of the movement detecting circuits  501  detects variation in an intensity of an incident light, the first X- and Y-scanning circuits  105  and  506  judges which circuit has detected movement among the nine movement detecting circuits  501 . Then, the first X- and Y-scanning circuits  105  and  106  start scanning an area extensive around the movement detecting circuit  501  which has detected movement. 
     In the solid-state image sensor illustrated in FIG. 8, the first and second signal lines  107   a  and  108   a  are activated by a detection signal which is transmitted from a movement detecting circuit  501  when the movement detecting circuit  501  detects reduction in an intensity of an incident light. 
     If the first and second signal lines  107   a  and  108   a  are intended to be activated by a detection signal which is transmitted from a movement detecting circuit  501  when the movement detecting circuit  501  detects increase in an intensity of an incident light, it would be obvious for those skilled in the art to design the solid-state image sensor illustrated in FIG. 8 to include first and third p-MOSFETs having polarities opposite to the polarities of the first to third p-MOSFETs  509 ,  510  and  503 , in place of the first to third p-MOSFETs  509 .  510  and  503 . 
     Hereinbelow is explained an operation of the solid-state image sensor in accordance with the first embodiment. 
     The second X- and Y-scanning circuits  103  and  104  scan all the pixels arranged in the sensor arrays  101 . The first X- and Y-scanning circuits  105  and  106  scan a local area such as the area  211  illustrated in FIG. 5, when they receive a detection signal from any one of the movement detection circuits  102 . A detection signal transmitted from the movement detection signal  102  is transferred to the first X- and Y-scanning circuits  105  and  106  through the first and second signal lines  107   a  and  108   a  vertically and horizontally extending through the sensor arrays  101 , respectively. 
     Hereinbelow an operation of the solid-state image sensor in the case that a plurality of the movement detecting circuits  102  concurrently transmits detection signals and that areas associated with those movement detecting circuits  102  overlap each other. If a detection signal is newly transmitted while a first local area associated with a movement detecting circuit  102  having transmitted a detection signal is being scanned, a second local area associated with the movement detecting circuit  102  having newly transmitted a detection signal starts to be scanned after the first local area has been finished to be scanned. However, if the first and second local areas do not overlap each other, that is, if there is no X and Y scanning lines passing through both the first and second local areas, it is possible to concurrently scan both the first, and second local areas. 
     If a plurality of the movement detecting circuits  102  concurrently transmit detection signals, a local area to be scanned is determined in accordance with a predetermined order, for instance, an address assigned to each of the pixels. 
     FIG. 9 is a block diagram of a solid-state image sensor in accordance with the second embodiment. 
     The illustrated solid-state image sensor is comprised of sixteen rectangular sensor arrays  601  arranged in a matrix, nine movement detecting circuits  602  arranged in a 3×3 matrix and positioned at a gap formed between the adjacent sensor arrays  601 , a first X-scanning circuit  605 , a first Y-scanning circuit  606 , a second X-scanning circuit  603 , and a second Y-scanning circuit  604 . 
     The sixteen rectangular sensor arrays  601  define a photoelectric transfer region. Each of the sensor arrays  601  is comprised of a plurality of pixels arranged in a two-dimensional array. 
     The solid-state image sensor in accordance with the second embodiment is structurally different from the solid-state image sensor in accordance with the first embodiment in that each of the pixels in the second embodiment has such a structure as illustrated in FIG. 10, whereas each of the pixels in the first embodiment has such a structure as illustrated in FIG.  2 . 
     With reference to FIG. 10, the pixel in the second embodiment is comprised of a photodiode  701 , a first n-MOSFET  702  including a gate electrically connected to a bias terminal  706 , a drain electrically connected to a source voltage VDD and a source electrically connected to the photodiode  701 , a second n-MOSFET  703  including a gate electrically connected to the photodiode  701 , a source electrically connected to the source voltage VDD and a drain, a third n-MOSFET  704  including a gate electrically connected to a terminal  707  through which a signal is input, a source electrically connected to the drain of the second transistor  703 , and a drain electrically connected to a first output line  709 , and a fourth n-MOSFET  705  including a gate electrically connected to a terminal  708  through which a signal is input, a source electrically connected to a node at which the drain of the second transistor  703  and the source of the third n-MOSFET  704  are connected to each other, and a drain electrically connected to a second output line  710 . 
     In brief, the pixel illustrated in FIG. 10 is designed to additionally include the fourth n-MOSFET  705  in comparison with the pixel illustrated in FIG.  2 . 
     In operation, when the third n-MOSFET  704  is turned on, a pixel output is transmitted through the first output line  709 . When the fourth n-MOSFET  705  is turned on, a pixel output is transmitted through the second output line  710 . W hen both the third and fourth n-MOSFETs  704  and  705  are turned on, pixel outputs are transmitted through both the first and second output lines  709  and  710 . 
     The solid-state image sensor in accordance with the second embodiment is designed to include the first X- and Y-scanning circuits  605  and  606  for scanning a designated local area, and the second X- and Y-scanning circuits  603  and  604  for scanning all pixels. In accordance with the second embodiment, a signal for driving the first X- and Y-scanning circuits  605  and  606  and a signal for driving the second X- and Y-scanning circuits  603  and  604  can be transmitted independently of each other. 
     It is possible to design the solid-state image sensor as to stop driving he second X- and Y-scanning circuits  603  and  604  and start driving the first X- and Y-scanning circuits  605  and  606 , when a detection signal is newly transmitted while the second X- and Y-scanning circuits  603  and  604  are scanning all pixels. 
     While the present invention has been described in connection with a certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
     The entire disclosure of Japanese Patent Application No. 11-125518 filed on May 6, 13999 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.