In recent years, advancements in the high-functionality and multi-functionality of image capturing apparatuses that use a CMOS image sensor or the like have been made to support various needs. Increases in pixel count and advancements in high-speed Imaging have been made to CMOS image sensors, and there is increasing demand for methods that allow for faster reading out of pixel signals.
For example, a method for performing high-speed reading out that has been in widespread use in recent years involves disposing an analog-to-digital conversion circuit (hereinafter, column ADC) every column and performing digital output, as disclosed in Japanese Patent Laid-Open No. 2005-278135. By introducing column ADCs, it becomes possible to perform digital transmission of pixel signals to outside of the image sensor, and high-speed readout has become possible following technical improvements in digital signal transmission.
On the other hand, as an example of multi-funtionalization, an image capturing apparatus capable of, for example, acquiring not only the intensity distribution of light but also the incident direction and distance information of light has been proposed. Japanese Patent No. 3774597 discloses an image sensor capable of focus detection using signals obtained from the image sensor. The image sensor has a configuration in which a photodiode (hereinafter, PD) corresponding to one micro lens is divided in two, such that each PD receives light from a different pupil surface of the taking lens. Focus detection is performed by comparing the outputs of the two PDs. A normal captured image can also be obtained by adding together the output signals from the two PDs constituting a unit pixel.
An image capturing apparatus disclosed in Japanese Patent Laid-Open No. 2009-89105 is provided with a mode for reading out focus detection signals, exposure control signals and image capture signals for live view display from a solid-state image sensor with one vertical scan of the same frame. The image capturing apparatus disclosed in Japanese Patent Laid-Open No. 2009-89105 is described as being able to perform live view display with faster focus detection control and exposure control.
However, since the signals of all of the PDs need to read out in the case of performing focus detection and exposure control in an image sensor such as disclosed in Japanese Patent No. 3774597 and Japanese Patent Laid-Open No. 2009-89105, there is a problem in that the time required to read out the signals of the PDs increases and the frame rate decreases. Even if the signal readout time is reduced by a readout method using column ADCs such as in Patent Document 1, further increases in pixel count and frame rate are expected in the future, and thus further shortening of the signal readout time is desired.