Image pickup device, its control method, and camera
An image pickup device, wherein a part of the carriers overflowing from the photoelectric conversion unit for a period of photoelectrically generating and accumulating the carriers may be flowed into the floating diffusion region, and a pixel signal generating unit generating a pixel signal according to the carriers stored in the photoelectric conversion unit and the carriers having overflowed into the floating diffusion region, is provided. The expansion of a dynamic range and the improvement of an image quality can be provided by controlling a ratio of the carriers flowing into the floating diffusion region to the carriers overflowing from such a photoelectric conversion unit at high accuracy.
1. A method of driving an image pickup device that includes a photoelectric conversion unit for generating carriers by photoelectric conversion and accumulating the carriers, a floating diffusion region, a transfer transistor for transferring the carriers from the photoelectric conversion unit to the floating diffusion region, a reset transistor for resetting the floating diffusion region, and a signal holding unit, the method comprising:
supplying a third gate voltage to a gate of the transfer transistor, the third gate voltage being between a first gate voltage that turns on the transfer transistor and a second gate voltage that turns off the transfer transistor;
holding a signal based on the carriers transferred during the supplying at the signal holding unit; and
resetting the floating diffusion region having the carriers transferred during the supplying,
wherein the holding is performed between the supplying and the resetting.
2. The method according to claim 1 , wherein the third gate voltage is a voltage based on an amplification degree of the pixel signal.
3. The method according to claim 1 , wherein the third gate voltage is a voltage based on a temperature.
4. The method according to claim 1 , wherein the third gate voltage is a voltage that causes a height of a potential barrier under the transfer gate between the photoelectric conversion unit and the floating diffusion region to be a lowest height among heights of potential barriers surrounding the photoelectric conversion unit.
5. The method according to claim 1 , wherein the image pickup device further includes a first element adjacent to the photoelectric conversion unit and connected to a power source, and wherein the third gate voltage is a voltage that causes a height of a potential barrier under the transfer gate to be the same as a height of a potential barrier between the photoelectric conversion unit and the first element.
6. The method according to claim 1 , wherein the image pickup device further includes a first element adjacent to the photoelectric conversion unit and connected to a power source, and wherein the method further comprises controlling a ratio of carriers flowing to the floating diffusion region to carriers flowing to the first element by supplying the third gate voltage.
7. The method according to claim 2 , wherein the amplification degree of the pixel signal is an ISO speed.
8. A method of driving an image pickup device that includes a photoelectric conversion unit for generating carriers, a floating diffusion region, a transfer transistor for transferring the carriers from the photoelectric conversion unit to the floating diffusion region, a signal holding unit, and a reset transistor for resetting the floating diffusion region, the method comprising:
supplying a third gate voltage to a gate of the transfer transistor, the third gate voltage being between a first gate voltage that turns on the transfer transistor and a second gate voltage that turns off the transfer transistor;
keeping the reset transistor turned off during supply of the third gate voltage to the gate of the transfer transistor;
holding a signal based on the carriers transferred during the supplying at the signal holding unit; and
resetting the floating diffusion region having the carriers transferred during the supplying by the reset transistor,
wherein the holding is performed between the supplying and the resetting.
9. The method according to claim 8 , wherein the third gate voltage is a voltage based on an amplification degree of the pixel signal.
10. The method according to claim 9 , wherein the amplification degree of the pixel signal is an ISO speed.
11. The method according to claim 8 , wherein the third gate voltage is a voltage based on a temperature.
12. The method according to claim 8 , wherein the third gate voltage causes a height of a potential barrier under the transfer gate between the photoelectric conversion unit and the floating diffusion region to be a lowest height among heights of potential barriers surrounding the photoelectric conversion unit.
13. The method according to claim 8 , wherein the image pickup device further includes a first element adjacent to the photoelectric conversion unit and connected to a power source, and wherein the third gate voltage is a voltage that causes a height of a potential barrier under the transfer gate to be same as a height of a potential barrier between the photoelectric conversion unit and the first element.
14. The method according to claim 13 , wherein a ratio of carriers flowing to the floating diffusion region to carriers flowing to the first element is determined by the third gate voltage.
15. The method according to claim 1 , wherein the image pickup device further includes a reset transistor, and wherein the method further comprises keeping the reset transistor turned off during supply of the third gate voltage to the gate of the transfer transistor.
16. The method according to claim 15 , wherein the holding is performed after the keeping.
17. The method according to claim 1 , wherein the resetting is not performed between the supplying and the holding.
18. The method according to claim 8 , wherein the resetting is not performed between the supplying and the holding.