Solid-state imaging device, method for driving solid-state imaging device, and electronic apparatus using an amplifier and signal lines for low and high gain
A solid-state imaging device where when the charge from a photodiode PD 11 is small, all of the charge is transferred to the feedback capacitor to obtain an output voltage amplified with a high gain due to a mirror effect created by a CTIA circuit including an amplifier arranged in a readout circuit and a feedback capacitor, while when the CTIA circuit is saturated, due to automatic reduction of the mirror effect, the remaining excessive charge is moved to a floating diffusion FD 11 having a larger capacitance to obtain an output voltage amplified with a low gain and where the obtained voltage is simultaneously output from the pixel and taken into a column sampling circuit. Due to this, a low-luminance signal can be read out with a high gain, a high-luminance signal can be read out with a low gain suppressing saturation, and in addition, signals of a high gain and low gain can be obtained by two reading operations. Further, it becomes possible to improve the lowest object illuminance performance.
1. A solid-state imaging device comprising
a pixel portion in which pixels are arranged,
a readout circuit including an amplifier capable of amplifying a pixel readout voltage read out from the pixels,
a first signal line to which a readout voltage of a low gain is output, and
a second signal line to which the output side of the amplifier is connected and a readout voltage of a high gain is output, wherein
a pixel includes
a photoelectric conversion element which accumulates a charge generated by photoelectric conversion in an accumulation period,
a transfer element capable of transferring a charge accumulated in the photoelectric conversion element in a transfer period,
a floating diffusion to which a charge accumulated in the photoelectric conversion element is transferred through the transfer element,
a source-follower element which converts the charge of the floating diffusion to a voltage signal in accordance with the charge quantity,
a reset element which resets the floating diffusion to a potential of the second signal line or a predetermined potential in a reset period, and
a feedback capacitor having one electrode connected to the floating diffusion and having another electrode connected to the second signal line, wherein
the first signal line connected to an output line of the voltage signal by the source-follower element and connected to the input side of the amplifier.
2. The solid-state imaging device according to claim 1 , wherein a capacitance of the feedback capacitor is smaller than a capacitance of the floating diffusion.
3. The solid-state imaging device according to claim 2 , wherein when the capacitance of the feedback capacitor is Cfb and the capacitance of the floating diffusion is Cfd,
the high gain is proportional to 1/Cfb, and the low gain is proportional to 1/Cfd.
4. The solid-state imaging device according to claim 1 , wherein a pixel includes a feedback element which electrically connects the feedback capacitor with the second signal line in a feedback period.
5. The solid-state imaging device according to claim 1 , wherein the pixel includes a selection element which electrically connects the output line of the voltage signal from the source-follower element with the first signal line.
6. The solid-state imaging device according to claim 1 , wherein the readout circuit includes a serial capacitor connected to an input stage of the amplifier.
7. The solid-state imaging device according to claim 1 , wherein the readout circuit includes a switch capable of selectively switching the input terminal and the output terminal of the amplifier to a connection state and disconnection state.
8. The solid-state imaging device according to claim 1 , wherein the readout circuit includes
a low gain-use sampling circuit which is connected to the first signal line and can sample the readout voltage of a low gain read out to the first signal line and
a high gain-use sampling circuit which is connected to a connection node between the output terminal of the amplifier and the second signal line and can sample the readout voltage of a high gain read out to the second signal line.
9. The solid-state imaging device according to claim 1 , wherein
the readout circuit includes
an error amplifier as the amplifier,
a serial capacitor
a switch capable of switching between a connection state and disconnection state,
a low gain-use sampling circuit which is connected to the first signal line and can sample the readout voltage of a low gain read out to the first signal line, and
a high gain-use sampling circuit which can sample the readout voltage of a high gain read out to the second signal line, and,
in the error amplifier,
the output terminal is connected to the second signal line and its connection node is connected to the high gain-use sampling circuit,
one input terminal is connected to the serial capacitor and is connected through the serial capacitor to the first signal line,
the switch is connected between the one input terminal and the output terminal, and
the other input terminal is connected to a supply line of a reference voltage.
10. The solid-state imaging device according to claim 9 , wherein the switch is held in the connection state and holds the error amplifier in a unity gain buffer state in the reset period of the pixel and a predetermined period after release of reset.
11. The solid-state imaging device according to claim 10 , wherein the switch is held in the disconnection state and releases the error amplifier from the unity gain buffer state after the predetermined period.
12. The solid-state imaging device according to claim 9 , wherein it is possible to switch the reference voltage to change settings of the ranges of high gain and low gain.
13. The solid-state imaging device according to claim 9 , wherein a clamp circuit is connected to the output side of the error amplifier.
14. The solid-state imaging device according to claim 9 , wherein the reset element connects the floating diffusion to the second signal line and resets the same to the potential of the second signal line in the reset period.
15. The solid-state imaging device according to claim 1 , having a stacked structure including
a first substrate and
a second substrate, wherein
the first substrate and the second substrate are connected through a connection portion,
on the first substrate,
at least the photoelectric conversion element and transfer element of each pixel are formed as a pixel light-receiving portion, and
on the second substrate,
at least the floating diffusion, source-follower element, reset element, and feedback capacitor of each pixel are formed as a pixel amplification and output section, and the first signal line, the second signal line, and at least a portion of the readout circuit including at least an amplifier are formed.
16. The solid-state imaging device according to claim 1 , wherein a high luminance-use capacitor is connected to the floating diffusion.
17. The solid-state imaging device according to claim 1 , wherein a circuit capable of selectively adding a predetermined capacitance is connected to the capacitance of the floating diffusion.
18. The solid-state imaging device according to claim 1 , wherein:
each pixel has
a circuit capable of selectively adding a predetermined capacitance connected to the capacitance of the floating diffusion and includes
a feedback element for electrically connecting the feedback capacitor with the second signal line in the feedback period and
a switch element for selectively connecting the connection node of the feedback capacitor and the feedback element to a predetermined power supply, and
the reset element is connected between the floating diffusion and the connection node of the feedback capacitor and the feedback element.
19. A method for driving a solid-state imaging device having
a pixel portion in which pixels are arranged,
a readout circuit including an amplifier capable of amplifying a pixel readout voltage read out from the pixels,
a first signal line to which a readout voltage of a low gain is output, and
a second signal line to which the output side of the amplifier is connected and a readout voltage of a high gain is output, wherein
a pixel includes
a photoelectric conversion element which accumulates a charge generated by photoelectric conversion in an accumulation period,
a transfer element capable of transferring a charge accumulated in the photoelectric conversion element in a transfer period,
a floating diffusion to which a charge accumulated in the photoelectric conversion element is transferred through the transfer element,
a source-follower element which converts the charge of the floating diffusion to a voltage signal in accordance with the charge quantity,
a reset element which resets the floating diffusion to the potential of the second signal line or a predetermined potential in a reset period, and
a feedback capacitor having one electrode connected to the floating diffusion and having another electrode connected to the second signal line, wherein
the first signal line connected to an output line of the voltage signal by the source-follower element and connected to the input side of the amplifier,
comprising the steps of,
when the charge from the photoelectric conversion element is small, transferring all of the charge to the feedback capacitor by a mirror effect created by a capacitive trans-impedance amplifier (CTIA) circuit including the amplifier and a feedback capacitor and thereby obtaining an output voltage amplified with a high gain and
moving remaining excessive charge to the floating diffusion having a larger capacity by automatic reduction of the mirror effect when the CTIA circuit is saturated and thereby obtaining an output voltage amplified with a low gain.
20. An electronic apparatus comprising
a solid-state imaging device and
an optical system for forming a subject image in the solid-state imaging device, wherein
the solid-state imaging device has
a pixel portion in which pixels are arranged,
a readout circuit including an amplifier capable of amplifying a pixel readout voltage read out from the pixels,
a first signal line to which a readout voltage of a low gain is output, and
a second signal line to which the output side of the amplifier is connected and a readout voltage of a high gain is output, wherein
a pixel includes
a photoelectric conversion element which accumulates a charge generated by photoelectric conversion in an accumulation period,
a transfer element capable of transferring a charge accumulated in the photoelectric conversion element in a transfer period,
a floating diffusion to which a charge accumulated in the photoelectric conversion element is transferred through the transfer element,
a source-follower element which converts the charge of the floating diffusion to a voltage signal in accordance with the charge quantity,
a reset element which resets the floating diffusion to a potential of the second signal line or a predetermined potential in a reset period, and
a feedback capacitor having one electrode connected to the floating diffusion and having another electrode connected to the second signal line, wherein
the first signal line connected to an output line of the voltage signal by the source-follower element and connected to the input side of the amplifier.