In the still-image imaging devices or the moving-image imaging devices available these days, the pixels of an image sensor such as a CMOS image sensor are refined to achieve multi-pixels with the aim of achieving a higher resolution. More particularly, the number of transistors constituting a pixel is reduced, and a three-transistor pixel configuration or a four-transistor pixel configuration is adopted so as to refine the pixels of the image sensor.
In the case of an image sensor having a four-transistor pixel configuration, reading of a pixel signal is performed after resetting, and the result is subjected to correlated double sampling (CDS). That makes it possible to remove the noise.
However, in the case of an image sensor having a three-transistor pixel configuration without a transfer gate, firstly reading of a pixel signal is performed followed by resetting. Hence, it becomes difficult to perform correlated double sampling. For that reason, in an image sensor having a three-transistor pixel configuration, the reset noise (kTC noise) occurring due to a reset transistor remains without being removed. Besides, in an image sensor having a three-transistor pixel configuration, the 1/f noise that occurs due to the amplifier transistor and that is superimposed on the reset voltage over long intervals of a frame period remains without being removed. For that reason, in an image sensor having a three-transistor pixel configuration, there is a poor signal-to-noise ratio (SN ratio) of the pixel signals.
Of such noises, the kTC noise can be removed by means of the active resetting method. However, removing the 1/f noise is a difficult task. Hence, there has been a demand for enabling removal of the 1/f noise and achieving enhancement in the signal-to-noise ratio of the pixel signals.