Abstract:
This invention is to provide a solid-state image pickup element including a sensor unit including a plurality of lines of photoelectric conversion units for generating charges from received light by photoelectric conversion, a memory unit including a plurality of lines of storage units for storing signals from the plurality of lines of photoelectric conversion units, a transfer unit for transferring a signal from the sensor unit to the memory unit, a control unit for causing storage units of an arbitrary block in the memory unit to output an image signal from the photoelectric conversion units and causing the photoelectric conversion units corresponding to the storage units of the arbitrary block to output a noise signal, and a subtracting unit for calculating a difference between the image signal and the noise signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solid-state image pickup element for outputting a signal of incident video light and an image pickup apparatus using the same. 
     2. Related Background Art 
     A solid-state image pickup element according to a first example of prior art will be described. 
     FIG. 1 is a circuit diagram of the solid-state image pickup element of the first example of prior art. Referring to FIG. 1, the solid-state image pickup element comprises a photodiode  101  as a photodetecting element for generating charges corresponding to incident light, a floating diffusion region  102 , a transfer transistor  103  for transferring charges generated by the photodiode  101  to the floating diffusion region  102 , a reset transistor  104  for removing charges stored in the floating diffusion region  102 , amplification transistors  105 ,  106 , and  107 , a capacitor  108  for storing a voltage generated in the floating diffusion region upon resetting, a capacitor  109  for storing a voltage generated in the floating diffusion region in an operative state, a switching transistor  110  for connecting an amplifier to the capacitor  108 , a switching transistor  111  for connecting an amplifier to the capacitor  109 , a capacitor discharging transistor  112  for discharging the capacitors  108  and  109 , buffers  113  and  114 , switching transistors  115  and  116  for switching the capacitors  108  and  109  to capacitors of another line and supplying the voltages of the capacitors  108  and  109  to the buffers  113  and  114 , respectively, reset transistors  117  and  118  for resetting input voltages to the buffers  113  and  114 , respectively, horizontal output lines  119  and  120 , a vertical scanning circuit  121 , and a horizontal scanning circuit  122 . The amplifier formed from the transistors  105 ,  106 , and  107  serves as a source-follower-type amplifier only when the transistors  106  and  107  are ON. The photodiode  101 , floating diffusion region  102 , and transistors  103 ,  104 ,  105 , and  106  form one pixel. 
     FIG. 2 is a timing chart showing the operation timing of the solid-state image pickup element shown in FIG.  1 . The operation of the solid-state image pickup element shown in FIG. 1 will be described with reference to FIGS. 1 and 2. 
     At time T801, a vertical scanning start pulse is input to a terminal  2 ,: a vertical scanning pulse is input to a terminal  3  to select the first line, and a signal  20   a  goes high (not shown). A pulse of high level is input to a terminal  8  to reset the floating diffusion region  102 . Terminals  11 ,  12 , and  13  are simultaneously set at high level, and the capacitors  108  and  109  are reset. At time T802, the reset pulse at the terminal  8  goes low to set the floating diffusion region  102  in an electrically floating state. At time T803, a pulse of high level is applied to a terminal  10 , and simultaneously, a pulse of high level is applied to the terminal  12 , so the voltage (reset voltage) immediately after resetting the floating diffusion region  102  is read out to the capacitor  108 . At time T804, a pulse of high level is applied to a terminal  9  to transfer charges generated by the photodiode  101  to the floating diffusion region  102 . At time T805, pulses of high level are applied to the terminals  10  and  13  to read out the voltage (signal voltage+reset voltage) of the floating diffusion region  102  to the capacitor  109 . At time T806, the voltage at a terminal  14  changes from high level to low level to reset the horizontal output lines  119  and  120 . At the same time, a horizontal scanning start pulse is input to a terminal  5 , and a horizontal scanning pulse is input to a terminal  6  to start the signal read from line memories formed from capacitors of the respective columns. The input signal to the terminal  14  is in an opposite phase to that of the horizontal scanning pulse to prevent interference between the capacitors of the respective columns. Reset voltages of the respective columns are sequentially output from a terminal  16 . Sums of signal voltages and reset voltages of the respective columns are sequentially output from a terminal  17 . When the difference between two outputs is calculated by a subtracting means connected to the output side, a signal voltage containing no reset voltage that varies between pixels can be obtained. Hence, an output with a high S/N ratio, which contains no noise component due to a variation in reset voltage, can be obtained. 
     The photodiode  101  is reset at time T804 when charges are transferred from the photodiode  101  to the floating diffusion region  102 . Resetting is completed when the signal at the terminal  9  goes low to end transfer. After this, storage of charges corresponding to incident light is restarted. This storage operation continues until T804 of the next frame cycle. 
     From time T801B, the signals input to the terminals  3 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  5 ,  6 , and  14  repeat their patterns from time T801 to time T801B. Referring to FIG. 3, by operation of the vertical scanning circuit  121 , the signal  20   a  goes high during only the first line period. Sequentially, a signal  20   b  goes high during only the second line period, and then, a signal  20   c  goes high during only the third line period. Because of the presence of a gate group  123 , signals supplied to the terminals  8 ,  9 , and  10  become valid for only the first line during the first line period, for only the second line during the second line period, and for only the third line during the third line period, and this also applies to the following lines. 
     Hence, signals output from the terminals  16  and  17  are signals stored in the photodiodes at timings that sequentially shift in units of lines. This scheme is called a rolling shutter scheme. 
     The floating diffusion region  102  holds the transferred charges after charge transfer from the photodiode  101  until resetting and therefore functions as a memory. 
     A second example of prior art will be described next. 
     FIG. 4 is a circuit diagram of a solid-state image pickup element of the second example of prior art. The same reference numerals as in the first example of prior art shown in FIG. 1 denote the same parts in FIG. 4, and a detailed description thereof will be omitted. A gate group  123  has the same arrangement as in the first example of prior art although it is represented by different symbols. In the second example of prior art, an OR gate  124  is inserted between the output terminal of the elements of the gate group  123  for receiving a signal from a terminal  9  and the gate of a transfer transistor  103 . 
     FIG. 5 is a timing chart showing the operation timings of the solid-state image pickup element shown in FIG.  4 . The operation of the solid-state image pickup element shown in FIG. 4 will be described with reference to FIGS. 4 and 5. 
     At time T901, pulses of high level are applied to terminals  8  and  19  to reset floating diffusion regions  102  of all pixels and reset photodiodes  101  of all pixels. When resetting is ended, storage of charges corresponding to incident light by the photodiodes  101  of all pixels is started. At time T902, a pulse of high level is applied to the terminal  19  again to transfer charges stored in the photodiodes  101  of all pixels to the floating diffusion regions  102 . After this pulse of high level goes low, the charges transferred to the floating diffusion regions  102  are held. At time T903, a vertical scanning start pulse is input to a terminal  2 , and a vertical scanning pulse is input to a terminal  3  to select the first line, and a signal  20   a  goes high (not shown). At time T903, pulses of high level are applied to terminals  11 ,  12 , and  13  to reset capacitors  108  and  109 . At time T904, pulses of high level are applied to terminals  10  and  12  to read out (signal voltage+reset voltage) from the photodiode of the floating diffusion region  102  to a capacitor  110 . At time T905, a pulse of high level is applied to the terminal  8  to reset the floating diffusion region  102 . At time T906, pulses of high level are applied to the terminals  10  and  13  to read out the reset voltage of the floating diffusion region  102  to the capacitor  109 . At time T906, the voltage at a terminal  14  changes from high level to low level to reset horizontal output lines  119  and  120 . At time same time, a horizontal scanning start pulse is input to a terminal  5 , and a horizontal scanning pulse is input to a terminal  6  to start the signal read from line memories formed from capacitors of the respective columns. The input signal to the terminal  14  is in an opposite phase to that of the horizontal scanning pulse to prevent interference between the capacitors of the respective columns. Reset voltages of the respective columns are sequentially output from a terminal  16 . Sums of signal voltages and reset voltages of the respective columns are sequentially output from a terminal  17 . When the difference between two outputs is calculated by a subtracting means connected to the output side, a signal voltage containing no reset voltage that varies between pixels can be obtained. Hence, an output with a high S/N ratio, which contains no noise component due to a variation in reset voltage, can be obtained. 
     As in the first example of prior art, the operation for the first line in the period from time T903 to time T903B is sequentially performed for lines from the second lines even after time T903B, and signals of the respective lines are sequentially output from the terminals  16  and  17 . 
     The scheme of the second example of prior art is called a high-speed shutter scheme. 
     In the first example of prior art, when an object moves at a high speed, the contents at the upper portion of an image shift from those at the lower portion of the screen, resulting in a distortion in image. If an object is to be photographed by irradiating the object with electronic flash light, the brightness of the object changes between the upper portion of the screen and the lower portion of the screen. 
     The second example of prior art solves the two problems of the first example of prior art by using charges stored in the photodiodes  101  from time 901 to time 902 as signals of all pixels. However, the second example of prior art has the following problem. 
     FIG. 6 is a sectional view of each pixel. Referring to FIG. 6, the pixel is formed from the photodiode  101  shown in FIG. 4, floating diffusion region  102  shown in FIG. 4, transfer transistor  103  shown in FIG. 4, a well  130 , and a shielding plate  131 . Light hν is incident on the pixel. The light incident on the pixel contains obliquely incoming components that reach portions near the floating diffusion region  102  of the photodiode  101  or floating diffusion region  102 . Some of charges generated by the light incident on portions near the floating diffusion region  102  of the photodiode  101  make a detour through the transfer transistor  103  and moves to the floating diffusion region  102 . Charges are also generated by light incident on the floating diffusion region  102 . Even after the charges are transferred from the photodiode  101  to the floating diffusion region  102  at time  903 , the number of charges in the floating diffusion region  102  increases as the time elapses. Hence, in the second example of prior art in which charges stored in the floating diffusion region  102  are read out in one frame period sequentially from pixels of the upper line to pixels of the lower line, a noise signal due to the above reason becomes large toward the lower line, and smearing occurs in the output image signal. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a solid-state image pickup element which can prevent any shift between contents at the upper portion of an image and those at the lower portion of the screen even when the object moves at a high speed. 
     It is another object of the present invention to provide a solid-state image pickup element which can prevent brightness at the upper portion of a screen from changing from that at the lower portion of the screen even in photographing using an electronic flash. 
     It is still another object of the present invention to provide a solid-state image pickup element which outputs a signal without any smearing due to a variation in charges in a floating diffusion region after transfer of charges from a photoelectric conversion means such as a photodiode. 
     It is still another object of the present invention to provide a solid-state image pickup element capable of obtaining the image signal of an object by only receiving electronic flash light. 
     It is still another object of the present invention to obtain an image signal almost free from noise. 
     In order to achieve the above objects, according to the first aspect of the present invention, there is provided a solid-state image pickup element comprising a plurality of pixel cells each including photoelectric conversion means for photoelectrically converting received light to generate charges, first transfer means for transferring the charges generated by the photoelectric conversion means, first storage means for storing the transferred charges, first output means for time-divisionally outputting a potential generated in the first storage means, and initialization means for initializing the voltage in the first storage means to a predetermined value, means for simultaneously operating the first transfer means of the plurality of pixel cells; means for simultaneously operating the initialization means of the plurality of pixel cells, a plurality of first output lines for receiving outputs from the pixel cells in units of columns, a plurality of second storage means arranged in a one-to-one correspondence with significant pixel cells of the plurality of pixel cells, a plurality of second transfer means for selectively transferring signals of the plurality of first output lines to the plurality of second storage means in units of columns, and control means for controlling the first transfer means, the output means, and the plurality of second transfer means. 
     According to another aspect of the present invention, there is provided a solid-state image pickup element comprising a sensor unit including a plurality of lines of photoelectric conversion means for generating charges from received light by photoelectric conversion, a memory unit including a plurality of lines of storage means for storing signals from the plurality of lines of photoelectric conversion means, transfer means for transferring a signal from the sensor unit to the memory unit, control means for causing storage means of an arbitrary block in the memory unit to output an image signal from the photoelectric conversion means and causing the photoelectric conversion means corresponding to the storage means of the arbitrary block to output a noise signal, and removal means for removing the noise signal from the image signal. 
     According to still another aspect of the present invention, there is provided a solid-state image pickup element comprising photoelectric conversion means for generating charges from received light, storage means for storing a signal from the photoelectric conversion means, read means for reading out a first signal output from the photoelectric conversion means and a second signal output from the same photoelectric conversion means through the same storage means, and subtracting means for calculating a difference between the first signal and the second signal, which are read out by the read means. 
     According to still another aspect of the present invention, there is provided an image pickup apparatus comprising a sensor unit including a plurality of lines of photoelectric conversion means for generating charges from received light by photoelectric conversion, a memory unit including a plurality of lines of storage means for storing signals from the plurality of lines of photoelectric conversion means, transfer means for transferring a signal from the sensor unit to the memory unit, control means for causing storage means of an arbitrary block in the memory unit to output an image signal from the photoelectric conversion means and causing the photoelectric conversion means corresponding to the storage means of the arbitrary block to output a noise signal, subtracting means for calculating a difference between the image signal and the noise signal, and adjustment means for performing at least one of exposure adjustment, focusing adjustment, and zoom adjustment on the basis of a signal output from the subtracting means. 
     According to still another aspect of the present invention, there is provided an image pickup apparatus comprising photoelectric conversion means for generating charges from received light, storage means for storing a signal from the photoelectric conversion means, read means for reading out a first signal output from the photoelectric conversion means and a second signal output from the same photoelectric conversion means through the same storage means, subtracting means for calculating a difference between the first signal and the second signal, which are read out by the read means, and adjustment means for performing at least one of exposure adjustment, focusing adjustment, and zoom adjustment on the basis of a signal output from the subtracting means. 
     Other objects, features, and advantages of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the arrangement of a solid-state image pickup element according to prior art 1; 
     FIG. 2 is a first timing chart showing the operation timings of the solid-state image pickup element according to prior art 1; 
     FIG. 3 is a second timing chart showing the operation timings of the solid-state image pickup element according to prior art 1; 
     FIG. 4 is a block diagram showing the arrangement of a solid-state image pickup element according to prior art 2; 
     FIG. 5 is a timing chart showing the operation timings of the solid-state image pickup element according to prior art 2; 
     FIG. 6 is a sectional view of part of a pixel of the present invention and prior arts; 
     FIG. 7 is a block diagram showing the arrangement of a solid-state image pickup element according to the first embodiment of the present invention; 
     FIG. 8 is a block diagram showing the arrangement of the solid-state image pickup element according to the first embodiment of the present invention; 
     FIG. 9 is a timing chart showing the operation timings of the solid-state image pickup element according to the first embodiment of the present invention; 
     FIG. 10 is a timing chart showing the operation timings of a solid-state image pickup element according to the second embodiment of the present invention; 
     FIGS. 11A,  11 B,  11 C,  11 D and  11 E are equivalent circuit diagrams of a pixel of a solid-state image pickup element according to the third embodiment of the present invention; 
     FIG. 12 is a block diagram of a video camera using the solid-state image pickup element of the present invention; and 
     FIG. 13 is a block diagram of a still camera using the solid-state image pickup element of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 7 is a circuit diagram of a solid-state image pickup element according to the first embodiment. 
     Referring to FIG. 7, the solid-state image pickup element comprises a photodiode  101  as a photodetecting element for generating charges corresponding to incident light, a floating diffusion region  102 , a transfer transistor  103  for transferring charges generated by the photodiode  101  to the floating diffusion region  102 , a reset transistor  104  for removing charges stored in the floating diffusion region  102 , amplification transistors  105 ,  106 , and  107 , a first capacitor  108 B for storing a voltage generated in the floating diffusion region, a second capacitor  109 B for storing a voltage generated in the floating diffusion region, a switching transistor  110  for connecting an amplifier to the capacitor  108 B, a switching transistor  111  for connecting an amplifier to the capacitor  109 B, a capacitor discharging transistor  112  for discharging the capacitors  108 B and  109 B, buffers  113  and  114 , switching transistors  115  and  116  for switching the capacitors  108 B and  109 B to capacitors of another line and supplying the voltages of the capacitors  108 B and  109 B to the buffers  113  and  114 , respectively, reset transistors  117  and  118  for resetting input voltages to the buffers  113  and  114 , respectively, horizontal output lines  119  and  120 , a vertical scanning circuit  121 , and a first horizontal scanning circuit  122 . The amplifier formed from the transistors  105 ,  106 , and  107  serves as a source-follower-type amplifier only when the transistors  106  and  107  are ON. The photodiode  101 , floating diffusion region  102 , and transistors  103 ,  104 ,  105 , and  106  form one pixel. 
     In this embodiment, an OR gate  124  is inserted between the output terminal of the elements of a gate group  123  for receiving a signal from a terminal  9  and the gate of a transfer transistor  103 , as in the second example of prior art. 
     In this embodiment, an OR gate  125  is inserted between the output terminal of the elements of the gate group  123  for receiving a signal from a terminal  8  and the gate of the reset transistor  104 . 
     Additionally, in this embodiment, a transfer transistor  140 , a buffer  141  with output enable control, a second vertical scanning circuit  142 , and a second gate group  143  are added. A diffusion floating region  144  for storing signals from all pixels is formed between the transfer transistor  140  and buffer  141 . The transfer transistor  140 , buffer  141 , and diffusion floating region  144  construct a memory. 
     FIG. 9 is a block diagram showing the arrangement of the solid-state image pickup element according to the first embodiment. Unlike the block diagram of FIG. 7 that shows the arrangement of the solid-state image pickup element, FIG. 9 shows details of the arrangement of the buffer  141 . Referring to FIG. 9, the buffer  141  is constructed by a transistor  141   a  and a transistor  141   b.    
     FIG. 8 is a timing chart showing the operation timings of the solid-state image pickup element shown in FIG.  7 . The operation of the solid-state image pickup element shown in FIG. 7 will be described with reference to FIGS. 7 and 8. 
     At time T101, pulses of high level are applied to terminals  19  and  26  to reset the floating diffusion regions  102  of all pixels and reset the photodiodes  101  of all pixels. When resetting is ended, storage of charges corresponding to incident light by the photodiodes  101  of all pixels is started. At time T102, a pulse of high level is applied to the terminal  19  again to transfer charges stored in the photodiodes  101  of all pixels to the floating diffusion regions  102 . At time T103, a vertical scanning start pulse is input to terminals  2  and  25 , and a vertical scanning pulse is input to terminals  3  and  21  to select the first line, and signals  20   a  and  26   a  go high (not shown). At time T104, pulses of high level are applied to terminals  10  and  24  to transfer the voltage held in the floating diffusion region  102  to the diffusion floating capacitance  144  in the first line. From time T105, signals  20   b  and  26   b  go high, and the voltage is transferred from the floating diffusion region  102  to the diffusion region  144  in the second line. From time T106, signals  20   c  and  26   c  go high, and the voltage is transferred from the floating diffusion region  102  to the diffusion region  144  in the third line. 
     When this transfer is ended, voltage transfer from the floating diffusion regions  102  to the diffusion floating capacitances  144  in all pixels. This transfer does not require transfer in the horizontal direction, that is performed to output signals from terminals  16  and  17 , and therefore is executed in a short time. 
     At time T107, a vertical scanning start pulse is input to the terminals  2  and  25 , and a vertical scanning pulse is input to the terminals  3  and  21  to select the first line, and the signals  20   a  and  26   a  go high (not shown). Simultaneously, a pulse of high level is applied to the terminal  8  to reset the floating diffusion regions  102  of the first line. At time T108, pulses of high level are applied to terminals  11 ,  12 , and  13  to reset the first capacitor  108 B and second capacitor  109 B. At time T109, pulses of high level are applied to the terminals  12  and  23  to read out the voltage in the floating diffusion region  144 , i.e., a sum voltage of the signal voltage and reset voltage, to the first capacitor  108 B. At time T110, pulses of high level are applied to the terminals  10  and  24  to transfer the voltage of the floating diffusion region  102  to the floating diffusion region  144 . The voltage in the floating diffusion region  102  at this time corresponds to the reset voltage rarely containing smearing because not so long time has elapsed from resetting. At time T111, pulses of high level are applied to the terminals  13  and  23  to read out the voltage in the floating diffusion region  144 , i.e., the reset voltage to the second capacitor  109 B. At time T112, the voltage at the terminal  14  changes from high level to low level to reset the horizontal output lines  119  and  120 . At the same time, a horizontal scanning start pulse is input to a terminal  5 , and a horizontal scanning pulse is input to a terminal  6  to start the signal read from line memories formed from the capacitors of the respective columns. The input signal to a terminal  14  is in an opposite phase to that of the horizontal scanning pulse to prevent interference between the capacitors of the respective columns. Sums of signal voltages and reset voltages of the respective columns are sequentially output from the terminal  16 . The reset voltages of the respective columns are sequentially output from the terminal  17 . When the difference between two outputs is calculated by a subtracting means  126  connected to the output side, a signal voltage containing no reset voltage that varies between pixels can be obtained. Hence, an output with a high S/N ratio, which contains no noise component due to a variation in reset voltage, can be obtained. 
     From time T107B, the signals  20   b  and  26   b  and signals  20   c  and  26   c  sequentially go high. By the operation of the gate groups  123  and  143 , the operation from time T107 to time T107B, which is performed for the first line, is continuously performed for the second and third lines. 
     The same time as that for the normal frame read is required from the start of output of signals of the first line from the terminals  16  and  17  to the end of output of signals of the third lines from the terminals  16  and  17 . However, since no light leaks to the floating diffusion region  144 , and the floating diffusion region  144  is formed in a well different from that of the photodiode  101 , the voltage in the floating diffusion region  144  is held without any variation. Hence, a signal containing no smearing is output from the terminal  16 . 
     The reset voltages of pixels of each line are also transferred to the floating diffusion region  144  and read out in the horizontal direction immediately after the floating diffusion regions  102  are reset in units of lines. Hence, a signal containing no smearing is output from the terminal  17 . 
     The output signal from the terminal  16  and the output signal from the terminal  17  are input to a differential circuit (not shown). Hence, an image output signal that has no reset voltage varying between pixels and contains no smearing can be obtained from the output terminal of the differential circuit. 
     The signal in the floating diffusion region  144  can be read out not only in units of lines using the line memories of this embodiment but also in units of two-dimensional blocks of, e.g., 2×2 pixels. 
     The arrangement of the solid-state image pickup element according to the second embodiment is the same as that of the solid-state image pickup element of the first embodiment shown in FIG.  7 . The second embodiment is different from the first embodiment in the application purpose and operation timings. 
     FIG. 10 is a timing chart showing the operation timings of the solid-state image pickup element of the second embodiment. The operation from time T201 to time T206 in this embodiment is the same as the operation from time T101 to time T106 in the first embodiment, and a detailed description thereof will be omitted. An object to be picked up during the period between time T201 and time T202 will be referred to as a first object. 
     The image pickup element picks up the second object during the period between time T207 and time T208. More specifically, at time T207, pulses of high level are applied to terminals  19  and  26  to reset a floating diffusion region  102  and a photodiode  101 . At time T208, a pulse of high level is applied to the terminal  19  to transfer a signal corresponding to an image picked up during the period from time T207 to time T208 to the floating diffusion region  102 . 
     Next, at time T209, a vertical scanning start pulse is input to terminals  2  and  25 , and a vertical scanning pulse is input to terminals  3  and  21  to select the first line. Signals  20   a  and  26   a  go high (not shown). At time T210, pulses of high level are applied to terminals  11 ,  12 , and  13  to reset a first capacitor  108 B and a second capacitor  109 B. At time T211, pulses of high level are applied to the terminals  12  and  23  to read out the voltage in a floating diffusion region  144 , i.e., the sum voltage of the signal voltage corresponding to the first object and the reset voltage to the first capacitor  108 B. At time T212, pulses of high level are applied to terminals  10  and  24  to transfer the voltage in the floating diffusion region  102  to the floating diffusion region  144 . The voltage in the floating diffusion region  102  at this time corresponds to the sum voltage of the signal voltage corresponding to the second object and the reset voltage, which rarely contains smearing because not so long time has elapsed from resetting. At time T213, pulses of high level are applied to the terminals  13  and  23  to read out the voltage in the floating diffusion region  144 , i.e., the sum voltage of the signal voltage corresponding to the second object, which rarely contains smearing, and the reset voltage to the second capacitor  109 B. At time T214, the voltage at a terminal  14  changes from high level to low level to reset horizontal output lines  119  and  120 . Simultaneously, a horizontal scanning start pulse is input to a terminal  5 , and a horizontal scanning pulse is input to a terminal  6  to start the signal read from line memories formed from the capacitors of the respective columns. The input signal to the terminal  14  is in an opposite phase to that of the horizontal scanning pulse to prevent interference between the capacitors of the respective columns. Sums of signal voltages corresponding to the first object and reset voltages of the respective columns are sequentially output from a terminal  16 . Sums of signal voltages corresponding to the second object and reset voltages of the respective columns are sequentially output from a terminal  17 . When the difference between two outputs is calculated by a subtracting means  126  connected to the output side, a signal voltage obtained by subtracting the signal voltage corresponding to the second object from the signal voltage corresponding to the first object can be obtained. When the polarity of the subtracting means  126  is inverted, a signal voltage obtained by subtracting the signal voltage corresponding to the first object from the signal voltage corresponding to the second object can be obtained. Hence, an output with a high S/N ratio, which contains no noise component due to a variation in reset voltage, can be obtained. From time T209B, signals  20   b  and  26   b  and signals  20   c  and  26   c  sequentially go high. By the operation of the gate groups  123  and  143 , the operation from time T209 to time T209B, which is performed for the first line, is continuously performed for the second and third lines. 
     When an image pickup apparatus with the solid-state image pickup element of this embodiment, which has an electronic flash, photographs the first object using electronic flash light, and the signal of the second object is subtracted from the signal of the first object by the subtracting means  126 , an image signal corresponding to a signal obtained by subtracting the brightness of an object photographed using the external light from the brightness of an object photographed using electronic flash light can be obtained. In this image signal, the variation in reset voltage is canceled, so no noise due to the variation in reset voltage is contained. 
     When an image pickup apparatus with the solid-state image pickup element of this embodiment, which has an electronic flash, photographs the second object using electronic flash light, and the signal of the first object is subtracted from the signal of the second object by the subtracting means  126 , an image signal corresponding to a signal obtained by subtracting the brightness of an object photographed using the external light from the brightness of an object photographed using electronic flash light can be obtained. In this image signal, the variation in reset voltage is canceled, so no noise due to the variation in reset voltage is contained. 
     The third embodiment is associated with various arrangements of pixels of a solid-state image pickup element. FIGS. 11A to  11 E are equivalent circuit diagrams showing the arrangements of a pixel according to the third embodiment. 
     The pixel shown in FIG. 11A is the same as in the first and second embodiments. The photodiode and all transistors of this pixel are formed from NMOS transistors. 
     In the pixel shown in FIG. 11B, a transistor  106  is replaced with a transistor  105   b . This pixel operates like the pixel shown in FIG.  11 A. 
     In the pixel shown in FIG. 11C, a transistor  103  is omitted. In this pixel, the floating diffusion region as a memory is not formed. 
     The photodiode and all transistors of the pixel shown in FIG. 11D are formed from PMOS transistor. This pixel can be regarded as the pixel shown in FIG. 11A with the inverted polarity. 
     In the pixel shown in FIG. 11E, the photodiode of the pixel shown in FIG. 11A is replaced with a photogate. The storage/read of photocarriers (charges) in/from the photogate is controlled by a gate voltage. 
     As described above, according to the above embodiments, an image signal corresponding to light received by all pixels in the same time period is formed. For this reason, even when the object moves at a high speed, the contents at the upper portion of the image do not shift from the contents at the lower portion of the screen. 
     According to the above embodiments, an image signal corresponding to light received by all pixels in the same time period is formed. For this reason, even in photographing using electronic flash light, the brightness at the upper portion of the screen can be prevented from being different from that at the lower portion of the screen. 
     According to the above embodiments, charges transferred from the photodiode to the floating diffusion region adjacent to the photodiode are transferred to the memory at high speed before an image signal is output. For this reason, a signal without any smearing due to a variation in charges in the floating diffusion region after reception of charges transferred from the photodiode can be output. 
     According to the above embodiments, an image signal corresponding to a signal obtained by subtracting the image signal of an image illuminated with only external light from the image signal of the object illuminated with not only the external light but also electronic flash light can be obtained. Hence, the image signal of the object receiving only the electronic flash light can be obtained. 
     According to the above embodiments, both the signal containing the signal voltage and reset voltage obtained upon receiving light and the signal corresponding to only the reset voltage are read out through the memory constructed by the transfer transistor  140 , buffer  141 , and floating diffusion region  144 . Eventually, not only noise in the pixel but also noise generated by, e.g., a variation between the memories can be corrected. 
     In the above-described first and second embodiments, the output signal of the pixel is supplied to the buffer in the memory cell through the transistor  140 . However, a clamp circuit or a level shift circuit may be disposed between the pixel and the buffer to adjust an output voltage range of the pixel to an input dynamic range of the buffer  141 . 
     The fourth embodiment in which the solid-state image pickup element of the present invention is applied to a video camera will be described with reference to FIG.  12 . 
     FIG. 12 is a block diagram showing a case wherein the solid-state image pickup element of the present invention is applied to a video camera. A photographing lens  201  comprises a focus lens  201 A for adjusting focusing, a zoom lens  201 B for zooming, and an imaging lens  201 C. 
     The video camera has an iris  202 , a solid-state image pickup element  203  for photoelectrically converting an object image formed on the image pickup surface into an electrical image pickup signal, and a sample/hold circuit (S/H circuit)  204  for sampling/holding the image pickup signal output from the solid-state image pickup element  203  and amplifying the level of the signal. The sample/hold circuit  204  outputs a video signal. 
     A process circuit  205  performs predetermined processing such as gamma correction, color separation, and blanking processing for the video signal output from the sample/hold circuit  204  and outputs a luminance signal Y and chrominance signals C. 
     The chrominance signals C output from the process circuit  205  are subjected to white balance and color balance correction by a chrominance signal correction circuit  221  and output as color difference signals R-Y and B-Y. 
     The luminance signal Y output from the process circuit  205  and the color difference signals R-Y and B-Y output from the chrominance signal correction circuit  221  are modulated by an encoder circuit (ENC circuit)  224  and output as a standard television signal. The signal is supplied to a video recorder or monitor EVF such as an electronic viewfinder (none are shown). 
     An iris control circuit  206  controls an iris drive circuit  207  on the basis of the video signal supplied from the sample/hold circuit  204  and automatically controls an ig meter  208  to control the aperture amount of the iris  202  such that the video signal has a predetermined level. 
     Bandpass filters (BPF)  213  and  214  with different band limits extract high-frequency components necessary for in-focus detection from the video signal output from the sample/hold circuit  204 . Signals output from the first bandpass filter (BPF 1 )  213  and second bandpass filter (BPF 2 )  214  are gated through a gate circuit  215  in accordance with a focus gate frame signal. The peak values of the signals are held and detected by a peak detection circuit  216 , and then, the signals are input to a logic control circuit  217 . These signals are called focus voltages, and focusing is done in accordance with the focus voltages. 
     A focus encoder  218  detects the moving position of the focus lens  201 A. A zoom encoder  219  detects the focal length of the zoom lens  201 B. An iris encoder  220  detects the aperture amount of the iris  202 . The detection values of these encoders are supplied to the logic control circuit  217  for performing system control. 
     The logic control circuit  217  detects the in-focus state of an object and adjusts focusing on the basis of a video signal corresponding to a set in-focus detection region. More specifically, the logic control circuit  217  receives the peak value information of high-frequency components supplied from the bandpass filters  213  and  214 , supplies control signals for controlling the rotational direction, rotational speed, and rotation/stop of a focus motor  210  to a focus drive circuit  209 , and controls the focus motor  210  to drive the focus lens  201 A to a position where the peak values of the high-frequency components are maximized. 
     The fifth embodiment in which the solid-state image pickup element of the present invention is applied to a still camera will be described with reference to FIG.  13 . 
     FIG. 13 is a block diagram showing a case wherein the solid-state image pickup element of the present invention is applied to a “still video camera”. 
     Referring to FIG. 13, a barrier  301  serves as a lens protector and a main switch. A lens  302  forms an optical image of an object on a solid-state image pickup element  304 . An iris  303  changes the amount of light passing through the lens  302 . The solid-state image pickup element  304  receives the object image formed by the lens  302  as an image signal. An A/D converter  306  analog/digital-converts the image signal output from the solid-state image pickup element  304 . A signal processing unit  307  performs various correction operations for the image data output from the A/D converter  306  and compresses the data. A timing generation unit  308  outputs various timing signals to the solid-state image pickup element  304 , an image pickup signal processing circuit  305 , the A/D converter  306 , and the signal processing unit  307 . A system control and operation unit  309  performs various calculations and controls the entire still video camera. A memory unit  310  temporarily stores image data. An interface unit  311  is used to record/read data in/from a recording medium. A detachable recording medium  312  such as a semiconductor memory is used to record or read image data. An interface unit  313  is used to communicate with an external computer or the like. 
     The operation of the still video camera with the above-described arrangement in photographing will be described next. 
     When the barrier  301  is opened, the main power supply is turned on. Next, the power supply of the control system is turned on. In addition, the power supply of the image pickup system circuit including the A/D converter  306  is turned on. 
     To control the exposure amount, the system control and operation unit  309  opens the iris  303 . A signal output from the solid-state image pickup element  304  is converted by the A/D converter  306  and input to the signal processing unit  307 . On the basis of the data, exposure calculation is performed by the system control and operation unit  309 . 
     The brightness is determined on the basis of the photometry result. In accordance with the determination result, the system control and operation unit  309  controls the iris. 
     A high-frequency component is extracted from the signal output from the solid-state image pickup element  304 . The system control and operation unit  309  calculates the distance from the object. After this, the lens is driven to determine the in-focus state. If it is determined that no in-focus state is set, the lens is driven again to measure the distance. 
     After the in-focus state is confirmed, exposure is started. When exposure is ended, the image signal output from the solid-state image pickup element  304  is A/D-converted by the A/D converter  306 , passes through the signal processing unit  307 , and is written in the memory unit by the system control and operation unit  309 . The data stored in the memory unit  310  is recorded in the detachable recording medium  312  such as a semiconductor memory through the recording medium control I/F unit under the control by the system control and operation unit  309 . The image data may be directly input to a computer through the external interface unit  313  and processed. 
     May widely different embodiments of the present invention may be constructed without departing form the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.