Driving method of solid-state imaging apparatus, solid-state imaging apparatus, and imaging system
In an amplifying type MOS sensor having a 3-transistor construction, when a frame rate is raised, an accumulation time of a frame just after the switching of a drive mode becomes short. When a gain correction is made to compensate a lack of accumulation time, a deterioration in picture quality is caused. A read out scan and a reset scan are executed in parallel in the frame before the switching of the drive mode, thereby preventing that a time period for resetting a pixel is overlapped with a time period for holding a pixel signal into a holding unit.
1. A driving method of a solid-state imaging apparatus that includes: a pixel region with pixels arranged two dimensionally, wherein each of the pixels includes a photoelectric conversion element for accumulating an electric charge according to an incident light, a floating diffusion region for holding the electric charge, a transfer unit for transferring the electric charge accumulated in the photoelectric conversion element to the floating diffusion region, a reset unit for resetting the electric charge held in the floating diffusion region, and an output unit for outputting a pixel signal according to a voltage in the floating diffusion region; and a holding unit for holding the pixel signals output from the output units, the method comprising steps of:
conducting, in a first frame, a read out scan in a first drive mode, for selecting a pixel by controlling a potential of the floating diffusion region of the pixel by a power source unit and the reset unit, and holding the pixel signal of the pixel in the holding unit; and
commencing, in a second frame following the first frame, a read out scan in a second drive mode different from the first drive mode, and
conducting a reset scan in the second drive mode, for resetting the electric charge accumulated in the photoelectric conversion element of the pixel, wherein the reset scan starts in the first frame in which the read out scan in the first drive mode is conducted, and is conducted without overlapping with a holding operation of holding the pixel signal in the holding unit within a horizontal synchronization period.
2. The driving method of a solid-state imaging apparatus according to claim 1 , wherein a length of one horizontal synchronization period in the first drive mode and a length of one horizontal synchronization period in the second drive mode are the same length, and a length of a period from a start of the horizontal synchronization period to the holding operation and a length of a period from the start of the horizontal synchronization period to a resetting operation are different.
3. The driving method of a solid-state imaging apparatus according to claim 1 , wherein a length of one horizontal blanking period in the first drive mode and a length of one horizontal blanking period in the second drive mode are a same length.
4. The driving method of a solid-state imaging apparatus according to claim 1 , wherein the electric charge, which is accumulated in the photoelectric conversion element of the pixel outputting the pixel signal and held in the holding unit by the read out scan in the second drive mode in the second frame, is reset by the reset scan starting in the second drive mode in the first frame.
5. The driving method of a solid-state imaging apparatus according to claim 1 , wherein a resetting operation for resetting the electric charge accumulated in the photoelectric conversion element in the reset scan in the second drive mode is conducted in a same time period as a selecting operation for selecting the pixel subjected to the read out scan in the first drive mode.
6. A solid-state imaging apparatus comprising:
a pixel region with pixels arranged two dimensionally, wherein each pixel includes: a photoelectric conversion element for accumulating an electric charge according to an incident light, a floating diffusion region for holding the electric charge, a transfer unit for transferring the electric charge accumulated in the photoelectric conversion element to the floating diffusion region, a reset unit for resetting the electric charge held in the floating diffusion region, and an output unit for outputting a pixel signal according to a voltage in the floating diffusion region; and
a holding unit for holding the pixel signals output from the output units;
wherein, in a first frame, a read out scan is conducted in a first drive mode, for selecting a pixel by controlling a potential of the floating diffusion region of the pixel by a power source unit and the reset unit of the pixel, and holding the pixel signal of the pixel in the holding unit,
wherein, in a second frame following the first frame, a read out scan is commenced in a second drive mode different from the first drive mode, and
wherein a reset scan is conducted in the second drive mode, for resetting the electric charge accumulated in the photoelectric conversion element, such that the reset scan starts in the first frame in which the read out scan in the first drive mode is conducted, and is conducted without overlapping with a holding operation of the pixel signal in the holding unit within a horizontal synchronization period.
7. The solid-state imaging apparatus according to claim 6 , further comprising a controller that controls a length of one horizontal synchronization period in the first drive mode and a length of one horizontal synchronization period in the second drive mode to be a same length, and controls a length of a period from a start of the horizontal synchronization period to the holding operation and a length of a period from the start of the horizontal synchronization period to a resetting operation are different.
8. The solid-state imaging apparatus according to claim 6 , wherein a length of one horizontal blanking period in the first drive mode and a length of one horizontal blanking period in the second drive mode are a same length.
9. The solid-state imaging apparatus according to claim 6 , wherein the electric charge, which is accumulated in the photoelectric conversion element of the pixel outputting the pixel signal and held in the holding unit by the read out scan in the second drive mode in the second frame, is reset by the reset scan starting in the second drive mode in the first frame.
10. The solid-state imaging apparatus according to claim 6 , further comprising a controller that controls such that a resetting operation for resetting the electric charge accumulated in the photoelectric conversion element in the reset scan in the second drive mode is conducted in a same time period as a selecting operation for selecting the pixel subjected to the read out scan in the first drive mode.
11. The solid-state imaging apparatus according to claim 6 , wherein each of the plurality of the photoelectric conversion elements is connected to a respective one of the floating diffusion regions, via a respective transfer unit.
12. The solid-state imaging apparatus according to claim 6 , wherein, for each pixel the photoelectric conversion element is a photodiode, each of the transfer unit, the reset unit, and the output unit is a MOS transistor, and the floating diffusion region is connected to a gate of the MOS transistor of the output unit as an output portion.
13. A solid-state imaging apparatus according to claim 6 , wherein the solid-state imaging apparatus is incorporated in an imaging system that includes:
an optical system for forming an image on the pixel region; and
a signal processing unit for processing a signal output from the solid-state imaging apparatus.
14. The solid-state imaging apparatus according to claim 6 , wherein the reset scan in the second drive mode is conducted in a period after setting a non-selecting state for read scanning, until selection of a pixel of a next row.