Abstract:
A physical quantity distribution sensor is disclosed. The sensor comprises: a plurality of sensor/storage sections each having a sensor element for sensing a received physical quantity and a storage element for storing the information of physical quantity sensed by the sensor element; a selector for selecting at least one of the sensor/storage sections; and a plurality of buffers each capable of detecting and supplying the information stored in at least one selected sensor/storage section. This sensor further comprises at least one selection signal transfer line for transferring an output of the selector. Power supply input portions of the buffers are connected to the selection signal transfer line, and the buffers are operated using, as a power voltage, an output of the selector entered into the buffers through the selection signal transfer line.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a physical quantity distribution sensor, a method of driving said sensor and a method of producing said sensor. 
     Recently, there is increased a demand for a semi-conductor device for sensing the spatial distribution of a physical quantity in a variety of fields. Particular attention is placed on a solid-state imaging device for sensing a light quantity as the physical quantity. More specifically, such a so-called amplifier-type solid-state imaging device is designed in the following manner. A plurality of storage sections are arranged to store a signal electric charge obtained through photo-electric conversion at the associated one of a plurality of photoelectric conversion sections. Each storage section is connected to the operation control portion of a transistor such as the gate of a field-effect transistor (FET) or the base of a bipolar transistor, or provision is made such that the storage section also serves as an operation control section. Accordingly, an electric current flowing in each transistor is controlled based on that potential of the associated storage section which varies with the amount of a signal electric charge. 
     With reference to FIG. 12, the following description will discuss the arrangement and operation of a physical quantity distribution sensor of prior art with an amplifier-type solid-state imaging device taken as an example. 
     As shown in FIG. 12, pixels  2  are arranged in a plurality of rows and a plurality of columns in an imaging region (generally, a region in which a physical quantity is to be sensed and stored)  1 . Each pixel  2  comprises a photoelectric conversion/storage section  3  and a driving transistor  5  having a gate  4 . 
     A selected-row-driving transistor  10  is disposed in each selected-row-driver  8 , and a voltage is to be supplied to each selected-row-driving transistor  10  from a selected-row-driving-voltage input portion  9 . Whether or not each selected-row-driving transistor  10  is electrically conductive, is controlled by a voltage of each output portion  7  of a shift register for row selection  6 . An output of a selected-row-driving transistor  10  is connected to a plurality of row-select-transistors  12  arranged in the row through one of row selection lines  11 , which allows a single pixel row to be selected out of the plurality of pixel rows. 
     The row-select-transistors  12  arranged in the same column are connected to a corresponding one of load transistors  14  through one of vertical signal lines  13 . The output potential of each photoelectric conversion/storage section  3  varies with the amount of signal electric charge stored therein. The output potential of each photoelectric conversion/storage section  3  is given to the gate  4  of a corresponding driving transistor  5  which is connected to one of power supply lines  17 . There is formed a source follower circuit in which the driving transistor  5  serves as a driving transistor and in which the load transistor  14  connected to a second power supply voltage (Vss) terminal  15  and to a gate input portion  16 , serves-as a load transistor. A power supply voltage.(Vdd) is supplied to each power supply line  17  from a first power supply voltage (Vdd) terminal  27 . 
     An output of the source follower circuit including the driving transistor  5  and the load transistor  14  is supplied to one of horizontal signal lines  24  through a signal column selection transistor  23  disposed in the associated one of column selection drivers  22 . Whether or not signal column selection transistors  23  are electrically conductive, is controlled by voltages generated at output portions  21  of a shift register  20  for column selection. According to this control, a single pixel column is selected out of the plurality of pixel columns. An output of the source follower circuit in a selected column, is selectively sent to an impedance conversion section  25  through the horizontal signal line  24 , and then supplied to an output portion  26  through the impedance conversion section  25 . 
     After the signals are read out from all the pixels  2  arranged in the selected row, a reset voltage input portion  28  sends a reset voltage to the selected-row-reset-driving transistor  29  in the selected-row-driver  8  for the selected row, thereby to drive the pixel reset transistors  30  in the selected row through a pixel-reset-voltage-supply line  19  associated with the selected row. This resets the signal electric charges stored in the photoelectric conversion/storage sections  3  in the selected row. Then, these photoelectric conversion/storage sections  3  again start storing signal electric charges. 
     According to the above-mentioned arrangement of prior art, each pixel has a photoelectric conversion section and an electric charge storage section, or a photoelectric conversion/storage section  3  having both conversion and storage functions as in the above example, a row-select-transistor  12 , a driving transistor  5  for amplifying an output of the photoelectric conversion/storage section  3 , and a reset transistor  30  for resetting the electric charge stored in the electric charge storage section or the photoelectric conversion/storage section  3 . Further, there are required a number of input/output lines such as the power supply lines  17  for driving transistors, the row-select-lines  11 , the pixel-reset-voltage-supply lines  19 , the vertical signal lines  13  and the like. 
     This complicates each pixel in arrangement and makes it difficult to enhance the performance thereof. It is also difficult to reduce each pixel in area to increase the number of pixels in the same area and to reduce the device in size. 
     In view of the foregoing, it is an object of the present invention to provide a physical quantity distribution sensor reduced in the number of input lines connected to pixels to simplify the pixels in arrangement, thus enabling to increase the number of pixels in the same area and to reduce the device in size. 
     SUMMARY OF THE INVENTION 
     The present invention provides a physical quantity distribution sensor comprising: a plurality of sensor/storage sections each having a sensor element for sensing a received physical quantity and a storage element for storing the information of physical quantity sensed by the sensor element; a selector for selecting at least one of the plurality of sensor/storage sections; and a plurality of buffers each capable of detecting and supplying the information stored in at least one selected sensor/storage section, and wherein there is disposed at least one selection signal transfer line for transferring an output of the selector, that power supply input portions of the buffers are connected to the selection signal transfer line, and that the buffers are operated using, as a power voltage, an output of the selector entered into the buffers through the selection signal transfer line. 
     The present invention provides another physical quantity distribution sensor having a plurality of unit cells arranged in N rows and M columns (each of N and M being a natural number not less than 2), each of the plurality of unit cells comprising (i) a sensor/storage section having (a) a sensor element for sensing a physical quantity and (b) a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) a reset element for resetting the storage element, and this physical quantity distribution sensor is characterized in that there are disposed: a row selector for selecting one row out of the N rows; buffers in the M columns each for detecting and supplying the information stored in the storage element of the sensor/storage section in a selected row; and N selection signal transfer lines each for transferring an output signal of the row selector to each of the N rows, and that power supply input portions of the buffers in the M columns are connected to the N selection signal transfer lines and arranged to receive a power voltage through the selection signal transfer line in a selected row. 
     The present invention provides a further physical quantity distribution sensor comprising: sensor/storage sections each of which is disposed in each of a plurality of unit cells in a region to be sensed and stored and each of which comprises a sensor element for sensing a received physical quantity and a storage element for storing the information of sensed physical quantity; a plurality of buffers each of which is assigned to at least one sensor/storage section and each of which is arranged to detect and supply the information stored in the sensor element of the sensor/storage section; and a selector for selecting at least one sensor/storage section, and this physical quantity distribution sensor is characterized in that each of the plurality of buffers comprises an electric current control element for controlling the electric current flowing in each buffer, that an control input portion of each of the electric current control elements is connected to each of output portions of the selector, and that only the buffer assigned to the sensor/storage section selected by the selector is operated. 
     The present invention provides still another physical quantity distribution sensor having a plurality of unit cells arranged in N rows and M columns (N being a natural number not less than 1 and M being a natural number not less than 2), each of the plurality of unit cells comprising (i) a sensor/storage section having (a) a sensor element for sensing a physical quantity and (b) a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) a reset element for resetting the storage element, and this physical quantity distribution sensor is characterized in that there are disposed: a column selector for selecting one column out of the M columns; and buffers in the M columns each for detecting and supplying the information stored in the storage element of at least one sensor/storage section in a selected column, and that output portions of the column selector are respectively connected to input portions of electric current control elements of the buffers. 
     The present invention provides a still further physical quantity distribution sensor having a plurality of unit cells arranged in N rows and M columns (N being a natural number not less than 1 and M being a natural number not less than 2), each of the plurality of unit cells comprising (i) a sensor/storage section having (a) a sensor element for sensing a physical quantity and (b) a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) a reset element for resetting the storage element, and this physical quantity distribution sensor is characterized by comprising: a column selector for selecting one column out of the M columns; buffers in the M columns each for detecting and supplying the information stored in the storage element of at least one sensor/storage section in a selected column; a sensor output portion for externally supplying a signal supplied from the output portion of each of the buffers; an output signal transfer line connected to the sensor output portion directly or through an impedance conversion section; and switching elements arranged such that an electric current flows in the buffer in a column selected by the column selector. 
     The present invention provides a method of driving a physical quantity distribution sensor which comprises (i) sensor/storage sections each of which is disposed in each of a plurality of unit cells and each of which includes a sensor element for sensing a received physical quantity and a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) buffers each for detecting and supplying the information stored in the storage element of at least one sensor/storage section, and in which at least one selection signal transfer line of a selector for selecting a portion of the plurality of unit cells, is electrically connected to power supply input portions of the buffers, and this driving method is characterized in that selection of a row to be read out is conducted by supplying a power voltage to the buffers of the row to be selected. 
     The present invention provides another method of driving a physical quantity distribution sensor which comprises (i) sensor/storage sections each of which is disposed in each of a plurality of unit cells and each of which includes a sensor element for sensing a received physical quantity and a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) buffers each for detecting and supplying the information stored in the storage element of at least one sensor/storage section, and in which at least one selection signal transfer line of a first selector for selecting a portion of the plurality of unit cells, is electrically connected to power supply input portions of the buffers, and this driving method is characterized in that selection in the nth row to be read out is conducted simultaneously with selection of the (n−1)th row to be reset. 
     The present invention provides a further method of driving a physical quantity distribution sensor which comprises (i) sensor/storage sections each of which is disposed in each of a plurality of unit cells and each of which includes a sensor element for sensing a received physical quantity and a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) buffers each for detecting and supplying the information stored in the storage element of at least one sensor/storage section, and in which output portions of a second selector for column selection are connected to input portions of electric current control means of the buffers, and this driving method is characterized in that column selection and control of an electric current flowing in the buffer in a selected column are conducted at the same timing. 
     The present invention provides still another method of driving a physical quantity distribution sensor which comprises (i) sensor/storage sections each of which is disposed in each of a plurality of unit cells and each of which includes a sensor element for sensing a received physical quantity and a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) buffers each for sensing and supplying the information stored in the storage element of at least one sensor/storage section, and in which a first input portion of an electric current control means of the buffer in the mth column is connected to a column selector at its output portion for the (m−a)th column (a≧1), and in which a second input portion of the electric current control means of the buffer in the mth column is connected to the column selector at its output portion for the (m−b)th column (b≧1), and this driving method is characterized in that an electric current in the buffer in the mth column rises at the time when the (m−a)th column is selected, and falls at the time when the (m−b)th column is selected. 
     The present invention provides a method of producing a physical quantity distribution sensor having a plurality of unit cells arranged in N rows and M columns (each of N and M being a natural number not less than 2), each of the plurality of unit cells comprising (i) a sensor/storage section having (a) a sensor element for sensing a physical quantity and (b) a storage element for storing the information of physical quantity sensed by the sensor element, and (ii) a reset element for resetting the storage element, the physical quantity distribution sensor comprising: a row selector for selecting one row out of the N rows; buffers in the M columns each for detecting and supplying the information stored in the storage element of the sensor/storage section in a selected row; and N selection signal transfer lines each for transferring an output signal of the row selector to each of the N rows, power supply input portions of the buffers in the M columns being connected to the N selection signal transfer lines and arranged to receive a power voltage through the selection signal transfer line in a selected row, each of the buffers in the M columns having a source follower circuit comprising a plurality of driving elements assigned to the unit cells of each column and at least one load element connected to the driving elements, and this producing method is characterized by comprising: a step of forming the selection signal transfer lines; and a step of forming a wiring for connecting the driving elements to the load elements, these two steps forming two wirings different in level from each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view illustrating the arrangement of a physical quantity distribution sensor according to a first embodiment of the present invention; 
     FIG. 2 is a timing chart illustrating a method of driving the physical quantity distribution sensor in FIG. 1; 
     FIG. 3 is a view illustrating the arrangement of a physical quantity distribution sensor according to a second embodiment of the present invention; 
     FIG. 4 is a view illustrating the arrangement of a physical quantity distribution sensor according to a third embodiment of the present invention; 
     FIG. 5 is a timing chart illustrating a method of driving the physical quantity distribution sensor in FIG. 4; 
     FIG. 6 is a view illustrating the arrangement of a physical quantity distribution sensor according to a fourth embodiment of the present invention; 
     FIG. 7 is a view illustrating the arrangement of a physical quantity distribution sensor according to a fifth embodiment of the present invention; 
     FIG. 8 is a view illustrating the arrangement of a physical quantity distribution sensor according to a sixth embodiment of the present invention; 
     FIG. 9 is a view illustrating the arrangement of a physical quantity distribution sensor according to a seventh embodiment of the present invention; 
     FIG. 10 is a view illustrating the arrangement of a physical quantity distribution sensor according to an eighth embodiment of the present invention; 
     FIG. 11 is a timing chart illustrating a method of driving the physical quantity distribution sensor in each of FIGS. 9 and 10; and 
     FIG. 12 is a view illustrating a physical quantity distribution sensor of prior art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the accompanying drawings, the following description will discuss a physical quantity distribution sensor according to the present invention and a sensor driving method according to the present invention. 
     (First Embodiment) 
     FIG. 1 illustrates the arrangement of a physical quantity distribution sensor according to the first embodiment of the present invention. This sensor is a solid-state imaging device in which unit cells are two-dimensionally arranged. 
     In an imaging area (a region in which physical quantities are to be sensed and stored)  31 , pixels  32  are arranged in a plurality of rows and a plurality of columns. FIG. 1 shows pixels  32  in the (n−1)th row, the nth row, the (n+1)th row, the (m−1)th column, the mth column and the (m+1)th column (in which each of n and m is a positive integer). Each pixel  32  has a photoelectric conversion/storage section  33 , a driving transistor  35  having a gate  34 , and a pixel reset transistor  60 . The photoelectric conversion/storage section  33  serves as a photoelectric conversion element and also as a storage element. 
     A shift register  36  for row selection successively selects one row out of the plurality of rows through selected-row-drivers  38  each including a selected-row-driving transistor  40 . An electrical potential at the output portion  37  assigned to a row to be selected is raised to allow the driving transistor  40  in the row to be selected. Thus, the shift register  36  controls the conductive/nonconductive state of each driving transistor  40 . A first power supply voltage (Vdd) is applied to each driving transistor  40  from a selected-row-driving voltage input portion  39 . Accordingly, when a selected one of the driving transistors  40  is made to be electrically conductive, the output of this selected driving transistor  40  is substantially equal to the power supply voltage (Vdd). The output of the selected transistor  40  is supplied to the driving transistors  35  arranged in the selected row through the associated one of a plurality of selected-row-power-supply lines  41 . In other words, the first embodiment is designed such that the power voltage is supplied only to a selected one of the rows with no power voltage supplied to the other rows which are not being selected. 
     Power input portions of the driving transistors  35  in each row are connected to the associated one of the plurality of selected-row-power-supply lines  41 . An output portion of each driving transistor  35 - is connected to a corresponding load transistor  44  through the associated one of a plurality of vertical signal lines  43 . Each load transistor  44  is connected to a second power supply voltage (Vss) terminal  45  and a gate input portion  46 . The electrical potential at each photoelectric conversion/storage section  33  which varies with the signal electric charges stored therein determined the electrical potential at the gate  34  of the associated driving transistor  35 . Each driving transistor  35  and the corresponding load transistor  44  form a source follower circuit. Each source follower circuit produces an output, in accordance with the signal electric charge of the associated photoelectric conversion/storage section  33 , on the associated vertical signal line  43 . 
     A shift register  50  for column selection is designed such that, the voltage of the output portion  51  assigned to a column to be selected is raised to allow the associated signal column selection transistor  53  in the column selection driver  52  to be electrically conductive. As a result, the electrical potential on the vertical signal line  43  in the selected column, i.e., the output from the source follower circuit in the selected column, is supplied to a horizontal signal line  54 . This output is then transferred to a device output portion  56  through an impedance conversion section (output buffer)  55 . 
     After the signals are read out from all the pixels in the selected row, the selected-row-reset-driving transistor  59  in the selected row becomes electrically conductive in response to a reset signal applied from a reset voltage input portion  58 , thereby to supply a voltage to a selected one of a plurality of pixel-reset-voltage-supply lines  49 . According to the voltage on the selected line  49 , the pixel reset transistors  60  in the selected row becomes electrically conductive to clear the signal electric charges stored in the photoelectric conversion/storage sections  33  in the selected row. The photoelectric conversion/storage sections  33  again start storing signal electric charges. 
     According to the arrangement above-mentioned, an electric power is supplied, through each selected-row-power-supply line  41 , to each source follower circuit formed of the driving transistors  35  and the corresponding load transistor  44 . This eliminates interconnection lines such as the power supply lines  17  (FIG. 12) in the prior art, thus simplifying the sensor in circuit arrangement. 
     According to the first embodiment, the power supply voltage Vdd applied to the input portion  39 , is used, without being lowered, as the power source of each source follower circuit. Accordingly, a so-called embedded transistor is preferably used as each selected-row-driving transistor  40 . Further, a bootstrap circuit may also be used as each selected-row-driving transistor  40  with similar effects produced. 
     With reference to FIGS. 1 and 2, the following description will discuss the operation of the sensor of the first embodiment. 
     FIG. 2 shows the waveforms of signals in a period  61  during which the nth row is being selected, and in a period  62  during which the (n+l)th row is being selected. 
     A row selection driving voltage  63  refers to the power supply voltage Vdd applied to the selected-row-driving-voltage input portion  39  in FIG.  1 . The voltage reference point (0 Volt) of the row selection driving voltage  63  is generally designated by  64 . In the period  61  during which the nth row is being selected, a row-select-voltage  65  supplied to the selected-row-power-supply line  41  in the nth row, becomes HIGH. In the period  62  during which the (n+1)th row is being selected, a row-select-voltage  66  supplied to the selected-row-power-supply line  41  in the (n+1)th row, becomes HIGH. 
     The following description will discuss in detail how the sensor is driven when the nth row is being selected. 
     In the shift register  36  for row selection, the output portion  37  assigned to the nth row supplies a row-select-signal to activate the selected-row-driving transistor  40  in the nth row. This electrically connects the selected-row-driving-voltage input portion  39  to the selected-row-power-supply line  41  in the nth row. Accordingly, in the period  61  during which the nth row is being selected, the row-select-voltage  65  supplied to the selected-row-power-supply line  41  in the nth row becomes HIGH. Therefore, the power supply voltage Vdd is supplied to the power supply input portions of the source follower circuits (serving as buffers) each formed of the driving transistor  35  in the nth row and the corresponding load transistor  44 , such that the pieces of information stored in the photoelectric conversion/storage sections  33  in the nth row are read out. According to the pieces of information thus read, the vertical signal lines  43  each connecting the driving transistor  35  to the corresponding load transistor  44  are changed in electrical potential. The changes in electrical potential of the vertical signal lines  43  occur for all the columns substantially at the same time. The load transistor  44  functions as a constant current source of the source follower circuit including the load transistor  44  and it determines an electric current flowing in that source follower circuit. 
     In the shift register  50  for column selection, the voltages of the output portions  51  are raised, in the form of a pulse, from LOW to HIGH respectively for the columns to be successively selected. As shown in FIG. 2, a column selection voltage  67  for the (m−1)th column, a column selection voltage  68  for the mth column and a column selection voltage  69  for the (m+1)th column have column selection pulses  72 ,  73 ,  74 , respectively. Accordingly, the outputs of the source follower circuits of the corresponding columns are transferred to the output buffer  55 . Such transfer is achieved when the signal column selection transistors  53  in the respective columns are successively conducted. As a result, the outputs of the source follower circuits assigned to the (m−1)th column, the mth column and the (m+1)th column, respectively, are supplied as an output voltage  70  through the output buffer  55 . The output from the nth-row/(m−1)th-column pixel is generally designated by a reference numeral of  75 . 
     After completion of the output from the pixels arranged in the nth row, a reset voltage  71  applied to the reset voltage input portion  58  is raised from LOW to HIGH in the form of a pulse to form a reset pulse  76 . This causes all the pixel reset transistors  60  in the nth row to be conducted. The power supply portions of the pixel reset transistors  60  in the nth row are connected to the selected-row-power-supply line  41  in the nth row. Accordingly, when the pixel reset transistors  60  in the nth row are made to be conductive, the potential levels of the photoelectric conversion/storage sections  33  in the nth row are reset to the level of the power supply voltage. Thereafter, the (n+1)th row is selected and similar operations are then conducted. 
     In the first embodiment, the description has been made of the arrangement in which each photoelectric conversion/storage section  33  serves as a photoelectric conversion element and also as a storage element for storing the output of the photoelectric conversion element. However, it is a matter of course that each photoelectric conversion/storage section  33  may comprise a photoelectric conversion element and a storage element for storing the output of the photoelectric conversion element. This is also applied to second to eighth embodiments discussed in the following. 
     (Second Embodiment) 
     FIG. 3 illustrates the circuit of a physical quantity distribution sensor according to the second embodiment of the present invention. In the following, there is omitted a description of those parts in the second embodiment which are similar in arrangement to parts in the first embodiment. 
     The sensor of the second embodiment differs from the sensor of the first embodiment in that each pixel further has a selected-row-transistor  42  disposed between the driving transistor  35  and the associated vertical signal line  43 . Since the gate input portion of each selected-row-transistor  42  is connected to the associated selected-row-power-supply line  41 , only the transistors  42  in a selected row are made electrically conductive. 
     According to the second embodiment, it is assured in a wide range of voltage that the selected one of the driving transistors  35  in a certain row is selectively connected to the associated vertical signal line  43 . Thus, a wide range of operational voltage can be used. 
     The timings in a method of driving the sensor of the second embodiment are the same as those in the first embodiment. 
     (Third Embodiment) 
     FIG. 4 is a view illustrating the circuit of a physical quantity distribution sensor according to the third embodiment of the present invention. In the following, there is omitted a description of those parts in the third embodiment which are similar in arrangement to parts in the first embodiment. 
     The third embodiment differs from the first embodiment in the following points. 
     In the third embodiment, the selected-row-reset-driving transistors  59  and the pixel-reset-voltage-supply lines  49  in the first embodiment are not disposed, and the selected-row-power-supply line  79  in the nth row (n=2, 3, . . . N) is connected to input control portions of the pixel reset transistors  80  in the (n−1)th row. In other words, the selected-row-power-supply line  79  in the nth row (n=2, 3, . . . N) also serves as a pixel-reset-voltage-supply source for the (n−1)th row. Accordingly, the third embodiment is further simplified in circuit arrangement. 
     With reference to FIG. 5, the following description will discuss the operation of the physical quantity distribution sensor of the third embodiment. 
     A row selection driving voltage  63  refers to the power supply voltage Vdd applied to the selected-row-driving-voltage input portion  39  in FIG.  4 . The voltage reference point (0 Volt) of the row selection driving voltage  63  is generally designated by  64 . In a period  61  during which the nth row is being selected, a row selection voltage  65  supplied to the selected-row-power-supply line  79  in the nth row, becomes HIGH. In a period  62  during which the (n+1)th row is being selected, a row-select-voltage  66  supplied to the selected-row-power-supply line  79  in the (n+1)th row, becomes HIGH. 
     In the shift register  36  for row selection, the output portion  37  in the nth row supplies a row-select-signal to activates the selected-row-driving transistor  40  in the nth row. This electrically connects the selected-row-driving voltage input portion  39  to the selected-row-power-supply line  79  in the nth row. Accordingly, in the period  61  during which the nth row is being selected, the row-select-voltage  65  on the selected-row-power-supply line  79  in the nth row becomes HIGH. Therefore, the power supply voltage Vdd is supplied to the power supply input portions of the source follower circuits. Further, there are conducted (i) the driving transistors  35  in the selected row and (ii) the selected-row-transistors  42  disposed between these driving transistors  35  and the corresponding vertical signal lines  43 . This operates the source follower circuits (buffers) formed of the driving transistors  35  in the nth row and the corresponding load transistors  44 , such that the pieces of information stored in the photoelectric conversion/storage sections  33  in the nth row are read out. According to the pieces of information thus read, the vertical signal lines  43  connecting the driving transistors  35  to the load transistors  44  are changed in potential. The changes in potential of the vertical signal lines  43  occur in all the columns substantially at the same time. The load transistor  44  of each column, functions as a constant electric current source for determining an electric current flowing in the source follower circuit of the column. 
     In the shift register  50  for column selection, the voltages of the output portions  51  are raised, in the form of a pulse, from LOW to HIGH respectively for the columns to be successively selected. As shown in FIG. 5, a column selection voltage  67  in the (m−1)th column, a column selection voltage  68  in the mth column and a column selection voltage  69  in the (m+1)th column have column selection pulses  72 ,  73 ,  74 , respectively. Accordingly, the outputs of the source follower circuits (buffers) of the corresponding columns are transferred to the output buffer  55 . Such transfer is achieved when the signal column selection transistors  53  in the respective columns are successively conducted. As a result, the outputs of the source follower circuits (buffers) assigned to the (m−1)th column, the mth column and the (m+1)th column, respectively, are supplied as an output voltage  70  through the output buffer  55 . The output from the nth-row/(m−1)th-column pixel is generally designated by a reference numeral of  75 . 
     After completion of the output from all the pixels in the nth row, the (n+1)th row is to be selected. When the (n+1)th row is selected, the pixel reset transistors  80  in the nth row are activated because the selected-row-power-supply line  79  in the (n+1)th row also serves as a pixel-reset-voltage-supply source in the nth row. This causes a reset operation for the nth row to be conducted in the period  62  during which the (n+1)th row is being selected. 
     The row-select-voltage  65  supplied to the selected-row-power-supply line  79  in the nth row, has a clock identical with a (n−1)th row reset clock  81  supplied to the input portions of the pixel reset transistors  80  in the (n−1)th row. The row-select-voltage  66  supplied to the selected-row-power-supply line  79  in the (n+1)th row has a clock identical with an nth row reset clock  82  supplied to the input portions of the pixel reset transistors  80  in the nth row. 
     (Fourth Embodiment) 
     FIG. 6 is a view illustrating the circuit of a physical quantity distribution sensor according to the fourth embodiment of the present invention. In the following, there is omitted a description of those parts in the fourth embodiment which are similar in arrangement to parts in the third embodiment. 
     The fourth embodiment differs from the third embodiment in that the column selection transistor  92  in each column selection driver  91  also serves as an electric current switch of the source follower circuit in a selected column. 
     Each of the first to third embodiments of the present invention and the prior art, is arranged such that, in a period during which a row is being selected, an electric current flows in the source follower circuits (buffers) of all the columns. A solid-state imaging device as an example generally has hundreds or thousands of columns. This results in enormous power consumption. However, the fourth embodiment is designed such that an electric current flows only in the source follower circuit in a selected column. This reduces the power consumption to the order of about one over hundreds to about one over thousands. Particularly, each of the first to third embodiments is arranged such that the electric currents in all the source follower circuits in the same row are supplied through the selected-row-power-supply line  41 ,  79 . Accordingly, when the current capacity of each power supply line  41 ,  79  is small, there is a possibility of each source follower circuit not operating normally due to voltage drop. According to the fourth embodiment, an electric current selectively flows only in the source follower circuit in a selected column. Thus, the problem above-mentioned can be solved. 
     (Fifth Embodiment) 
     FIG. 7 is a view illustrating the arrangement of a physical quantity distribution sensor according to the fifth embodiment of the present invention. In the following, there is omitted a description of those parts in the fifth embodiment which are similar in arrangement to parts in the fourth embodiment. 
     The fifth embodiment differs from the fourth embodiment in that the output of each source follower circuit is connected to a corresponding horizontal signal line  93  through a column selection transistor  92 . According to the fourth embodiment, all the vertical signal lines  43  are always connected to one another. It is therefore required that when a selected column is changed, the source follower circuit in the newly selected column electrically charges all of the vertical signal lines  43 . Accordingly, the time constant of each source follower circuit is required to be small to bring each source follower circuit into a steady state as early as possible. To this end, the driving transistor  35  in each pixel  32  must be increased in size. In view of the miniaturization of the sensor, however, restrictions are imposed to the sizes of each driving transistor  35 . 
     According to the fifth embodiment, the output portion of the source follower circuit in a selected column is not connected to the vertical signal lines  43  in other columns. Thus, the capacitance to be electrically charged by one source follower circuit is reduced to the order of one over hundreds to one over thousands as compared with the fourth embodiment. This hardly causes trouble of lengthening the electrically charging time. According to the fifth embodiment, the load transistors  44  respectively assigned to the columns may be replaced with a single common load transistor. 
     (Sixth Embodiment) 
     FIG. 8 illustrates the circuit arrangement of a physical quantity distribution sensor according to the sixth embodiment of the present invention. In the following, there is omitted a description of those parts in the sixth embodiment which are similar in arrangement to parts in the fourth embodiment. 
     The sixth embodiment differs from each of the fourth and fifth embodiments in the following points (a), (b) and (c). 
     (a) In each pixel, an electric current control column selection transistor  95  is disposed independently from the column selection transistor  92 . 
     (b) The gate of each electric current control column selection transistor  95  is connected to the corresponding output portion  51  of the shift register  50  for column selection. 
     (c) Each vertical signal line  43  is connected to the horizontal signal line  93  through the associated column selection transistor  92 . 
     With the arrangement above-mentioned, an electric current flows only in the source follower circuit in a selected column. Further, only the vertical signal line  43  for a selected column is connected to the horizontal signal line  93 , and only the load transistor  44  in the selected column functions as the load transistor of the source follower circuit. 
     (Seventh Embodiment) 
     FIG. 9 illustrates the circuit arrangement of a physical quantity distribution sensor according to the seventh embodiment of the present invention. In the following, there is omitted a description of those parts in the seventh embodiment which are similar in arrangement to parts in the sixth embodiment. 
     According to each of the fourth to sixth embodiments, each column selection period for signal reading is equal to each column selection period for letting flow an electric current in each source follower circuit. This causes no inconvenience when a time constant during which the output of each source follower circuit is brought into a steady state from the time an electric current starts flowing therein, is sufficiently small as compared with a period during which a signal in a selected column is supplied. However, there are instances where the electric current driving ability of each driving transistor  35  cannot sufficiently be increased in view of size or the like, or where capacitance of each vertical signal line  43  is not large due to a large number of pixels arranged in the vertical direction. In such instances, each period during which an electric current flows in each source follower circuit, is required to be longer than each signal output period. 
     The seventh embodiment is designed such that a time period during which an electric current flows in a certain source follower circuit can be determined independently from the signal output period. More specifically, a voltage generating circuit section  97  is disposed in each column. Each voltage generating circuit section  97  comprises a first input portion  98 , a second input portion  99  and an output portion  100 , and is arranged to supply a predetermined potential to the output portion  100  in a period between the time when the first input portion  98  receives a predetermined signal and the time when the second input portion  99  receives a predetermined signal. 
     The following description will discuss the voltage generating circuit section  97  for the source follower circuit in the mth column. The first input portion  98  of the voltage generating circuit section  97  is connected to an output portion for the (m−1)th column  51 - a  of the shift register for column selection  50 . The second input portion  99  of the voltage generating circuit section  97  is connected to an output portion for the (m+1)th column  51 - b  of the shift register for column selection  50 . The voltage output portion  100  in the mth column is connected to the gate of the electric current control column selection transistor  95  in the mth column. 
     When the (m−1)th column is selected by the shift register  50 , the voltage generating circuit section  97  in the mth column receives an output from the output portion for the (m−1)th column  51 - a  of the shift register  50  through the first input portion  98 . Then, the voltage generating circuit section  97  increases the potential of the output portion  100  in the mth column from LOW to HIGH, and maintains the potential thus increased. Accordingly, before the mth column a is actually selected, an electric current starts flowing in the source follower circuit in the mth column, thus starting a data reading operation. Thereafter, when the (m+1)th column is selected by the shift register for column selection  50 , the voltage generating circuit section  97  in the mth column receives, through the second input portion  99 , an output from the output portion for the (m+1)th column  51 - b  of the shift register for column selection  50 , and then stops operating. More specifically, the output portion  100  in the mth column is lowered in potential from HIGH to LOW to finish the reading operation using the source follower circuit in the mth column. 
     (Eighth Embodiment) 
     FIG. 10 is a view illustrating the arrangement of a main portion of a physical quantity distribution sensor according to the eighth embodiment of the present invention. Basically, the eighth embodiment has an arrangement similar to that of the seventh embodiment, but is different therefrom in the voltage generating circuit section. In the following, there is omitted a description of those parts in the eighth embodiment which are similar in arrangement to parts in the seventh embodiment. 
     A voltage generating circuit section  101  in FIG. 10 corresponds to an electric current control selection voltage generating circuit section  97  in FIG. 9, and is a circuit having a known arrangement which is called a static RS flip-flop circuit or a bistable unit. 
     The circuit section  101  has a first power supply input portion (Vdd)  102 , a second power supply input portion (Vss)  103 , a first input portion  104 , a second input portion  105  and an output portion  106 . Inside of the circuit section  101 , six transistors are mutually connected as shown in FIG.  10 . The first input portion  104 , the second input portion  105  and the output portion  106  respectively correspond to the first input portion  98 , the second input portion  99  and the electric current control selection voltage output portion  100  of each electric current control selection voltage generating circuit section  97  in FIG.  9 . 
     This circuit section  101  is a so-called bistable circuit and is operated such that the output portion  106  is brought into a first power voltage state by a positive pulse given to the first input portion  104  and that the output portion  106  is brought into a second power voltage state by a positive pulse given to the second input portion  105 . 
     With reference to FIG. 11, the following description will discuss a method of driving the sensor according to the eighth embodiment. 
     In FIG. 11, column selection voltages  110 ,  111 ,  112  for the (m−1)th column, the mth column, the (m+1)th column are voltages of the output portions  51  of the shift register for column selection  50 . Column selection pulses  113 ,  114 ,  115  respectively show the selection states of the (m−1)th column, the mth column, the (m+1)th column. Electric current control column selection voltages  116 ,  117 ,  118  for the (m−1)th column, the mth column, the (m+1)th column, are voltages of the output portions  106  of the electric current control selection voltage generating circuit sections  101  for the (m−1)th column, the mth column, the (m+1)th column. Electric current control column selection pulses  119 ,  120 ,  121  respectively show the electric current control selection states of the (m−1)th column, the mth column, the (m+1)th column. 
     In the following description, the electric current control column selection pulse  120  for the mth column is taken as an example. The pulse  120  is brought into the first power supply voltage state at the rising of the (m−1)th column selection pulse  113 , and is brought into the second power voltage state at the rising of the (m+1)th column selection pulse  115 . More specifically, an electric current starts flowing in the source follower circuit in the mth column before the mth column is selected as a column to be supplied, and the flow of an electric current in the source follower circuit in the mth column is stopped after the output in the mth column has been finished. 
     According to the eighth embodiment, the wirings are installed such that the pulse  120  for the mth column rises at the rising of the (m−1)th column selection pulse  113 , and falls at the rising of the (m+1)th column selection pulse  115 . However, it is a matter of course that provision may be made such that the pulse  120  rises at the rising of a further preceding column selection pulse. With such an arrangement, an electric current can flow in the source follower circuit earlier. As to the falling of the pulse  120 , too, it is possible to set, as necessary, such that the pulse  120  falls later than the rising of the pulse  115 . 
     A so-called bistable unit is shown in FIG. 10, as a specific example of the voltage generating circuit section for the electric current control section. However, the circuit section is not limited to such a circuit arrangement, but a CMOS circuit of such a bistable unit or other logic circuit may also be used. As an example, there is shown a circuit of which output rises or falls at the rising of a clock applied to an input portion thereof. However, there may also be used a circuit of which output rises or falls at the falling of a clock applied to an input portion thereof. 
     In the foregoing, the description has been made of each of the fourth to eighth embodiments having the arrangement of pixels and row selection portions identical with that of the third embodiment. However, each of the fourth to eighth embodiments may have an arrangement of pixels and row selection portions identical with that of each of the first to third embodiments, or identical with that of prior art. 
     In the arrangement of prior art in FIG. 12, it is only the vertical signal lines  13  and the power supply lines  17  that are required to be of low resistance (large electric current capacity). In the pixels  2  severely limited in view of designing, these lines  13 ,  17  can be disposed in parallel to each other and can be formed in the same wiring layer (for example, metallic layer) of low resistance. In each of the embodiments of the present invention shown in FIGS. 1 to  11 , however, it is the selected-row-power-supply lines  41  and the vertical signal lines  43  that are required to be of low resistance (large electric current capacitance). As shown in FIG. 1, these liens  41 ,  43  are not parallel to each other, but are at right angles to each other. To achieve each embodiment of the present invention, it is much easier to form these lines  41 ,  43  by wiring layers different in level from each other, than to form these lines  41 ,  43  by the same wiring layer. 
     In each of the embodiments above-mentioned, the description has been made, for simplification, of the arrangement having photoelectric conversion/storage sections serving as photoelectric conversion elements and also as signal electric charge storage elements. However, it is a matter of course that the present invention may be arranged such that photoelectric conversion elements and signal electric charge storage elements are independently disposed. 
     In the foregoing, the description has been made of the arrangement in which each output is supplied through the output buffer. However, it is apparent that the output buffer is not an indispensable element of the present invention. 
     Further, the foregoing description has been made with a solid-state imaging device taken as an example. However, when the sensor is equipped with sensor elements for sensing the physical quantity of x-rays, infrared rays, temperature, a magnetic field, an electric field, pressure or the like, and when provision is made such that the potential of each sensor elements changed due to received physical quantity, is transferred to the gate of each driving transistor, it is a matter of course that the present invention is also effective for a general physical quantity distribution sensor for other substance than light. 
     Further, the foregoing description has been made of the arrangement in which the unit cells are two-dimensionally arranged. However, the present invention is effective for the arrangement in which the unit cells are one-dimensionally arranged. 
     In each of the embodiments above-mentioned, a shift register is used for each of row and column selectors. However, a decoder may be used, instead of such a shift register, with similar effects produced. 
     According to the present invention, the lines each interconnecting a row of pixels have a row selection function, a power voltage supply function and a reset function, thus achieving a physical quantity distribution sensor simple in arrangement.