Imaging apparatus, imaging system, and driving method of imaging apparatus
During a period in which an electric potential of one node of a holding capacitance shifts from a first electric potential to a second electric potential, the other node of the holding capacitance is in an electrically-floating state.
1. An imaging apparatus, comprising:
a plurality of pixels arrayed in a matrix, the plurality of pixels each including a photoelectric conversion unit, a charge-voltage converter configured to convert charges into a voltage, a transfer unit configured to transfer the charges from the photoelectric conversion unit to the charge-voltage converter, and an output unit configured to output a signal that is based on an electric potential of the charge-voltage converter;
a signal line;
a holding unit;
a clipping unit;
a holding capacitance; and
a supply unit connected to a power supply line, wherein
the clipping unit includes a clipping transistor for clipping an electric potential of the signal line, one of a source and a drain of the clipping transistor is connected to the signal line, and a reference electric potential is supplied to the other one of the source and the drain of the clipping transistor,
the holding capacitance includes a first node connected to a control node of the clipping transistor, and a second node to which a plurality of electric potentials being different in electric potential from one another is supplied from the supply unit,
the output unit outputs, to the signal line, a first signal that is based on a reset electric potential of the charge-voltage converter,
the holding unit holds the first signal that is output to the signal line,
the output unit subsequently outputs, to the signal line, a second signal that is based on the electric potential of the charge-voltage converter to which the charges are transferred from the photoelectric conversion unit,
the holding unit holds the second signal that is output to the signal line,
an electric potential of the first node is a first electric potential during a period in which the charge-voltage converter is reset,
the electric potential of the first node shifts from the first electric potential to a second electric potential during a period from when the holding unit holds the first signal to when the holding unit holds the second signal, and
by maintaining causing a path between the second node and the supply unit to be in a non-conductive state during a period from when the electric potential of the first node starts to shift from the first electric potential to the second electric potential to when the holding unit holds the second signal, the second node is maintained being in an electrically-floating state during a period from when the electric potential of the first node starts to shift from the first electric potential to the second electric potential to when the holding unit holds the second signal.
2. The imaging apparatus according to claim 1 , wherein
the output unit is a transistor of a same conductivity type as that of the clipping transistor,
one of a source and a drain of the transistor is connected to the signal line,
the other one of the source and the drain of the transistor is connected to the power supply line,
the charge-voltage converter is connected to a gate of the transistor, and
the first signal and the second signal are signals output by the transistor to the signal line based on an electric potential of the gate.
3. The imaging apparatus according to claim 2 , wherein
the source and the drain of the transistor and the source and the drain of the clipping transistor are provided in a common well region.
4. The imaging apparatus according to claim 3 , wherein
the supply unit is provided in a well region separated from the well region in which the source and the drain of the transistor and the source and the drain of the clipping transistor are provided.
5. The imaging apparatus according to claim 1 , wherein
the power supply line and the second node are connected to the supply unit via a buffer,
another power supply line is connected to the second node via a switch, and
the switch and the buffer are in a parallel relation with respect to the second node.
6. The imaging apparatus according to claim 5 , wherein
the imaging apparatus includes a plurality of signal lines, a plurality of clipping units, a plurality of holding capacitances, and a plurality of switches, and
the plurality of signal lines, the plurality of clipping units, the plurality of holding capacitances, and the plurality of switches are arranged so as to respectively correspond to columns of a plurality of output units that are arrayed in a matrix.
7. An imaging system, comprising:
the imaging apparatus according to claim 1 ; and
a processing unit configured to output image data that is based on a signal output from the imaging apparatus.
8. A driving method of an imaging apparatus including:
a plurality of pixels arrayed in a matrix, the plurality of pixels each including a photoelectric conversion unit, a charge-voltage converter for converting charges into a voltage, and an output unit for outputting a signal that is based on an electric potential of the charge-voltage converter;
a signal line;
a holding unit;
a clipping unit;
a holding capacitance; and
a supply unit connected to a power supply line,
the clipping unit including a clipping transistor for clipping an electric potential of the signal line, one of a source and a drain of the clipping transistor being connected to the signal line, and a reference electric potential being supplied to the other one of the source and the drain of the clipping transistor,
the holding capacitance including a first node connected to a control node of the clipping transistor, and a second node to which a plurality of electric potentials being different in electric potential from one another is supplied from the supply unit, the driving method comprising:
outputting to the signal line a first signal that is based on a reset electric potential of the charge-voltage converter;
holding the first signal output to the signal line;
subsequently outputting to the signal line a second signal that is based on an electric potential of the charge-voltage converter to which the charges are transferred from the photoelectric conversion unit;
holding the second signal output to the signal line;
setting an electric potential of the first node to a first electric potential during a period in which the charge-voltage converter is reset;
shifting the electric potential of the first node from the first electric potential to a second electric potential during a period from when the holding unit holds the first signal to when the holding unit holds the second signal; and
by maintaining causing a path between the second node and the supply unit to be in a non-conductive state during a period from when the electric potential of the first node starts to shift from the first electric potential to the second electric potential to when the holding unit holds the second signal, maintaining causing the second node to be in an electrically-floating state during a period from when the electric potential of the first node starts to shift from the first electric potential to the second electric potential to when the holding unit holds the second signal.
9. The driving method according to claim 8 , wherein
the output unit is a transistor of a same conductivity type as that of the clipping transistor,
one of a source and a drain of the transistor is connected to the signal line,
the other one of the source and the drain of the transistor is connected to the power supply line,
the charge-voltage converter is connected to a gate of the transistor, and
the first signal and the second signal are signals output by the transistor to the signal line based on an electric potential of the gate.
10. The driving method according to claim 9 , wherein
the source and the drain of the transistor and the source and the drain of the clipping transistor are provided in a common well region.
11. The driving method according to claim 10 , wherein
the supply unit is provided in a well region separated from the well region in which the source and the drain of the transistor and the source and the drain of the clipping transistor are provided.
12. The driving method according to claim 8 , wherein
the power supply line and the second node are connected to the supply unit via a buffer,
another power supply line is connected to the second node via a switch, and
the switch and the buffer are in a parallel relation with respect to the second node.
13. The driving method according to claim 12 , wherein
the imaging apparatus includes a plurality of signal lines, a plurality of clipping units, a plurality of holding capacitances, and a plurality of switches, and
the plurality of signal lines, the plurality of clipping units, the plurality of holding capacitances, and the plurality of switches are arranged so as to respectively correspond to columns of a plurality of output units that are arrayed in a matrix.