Solid state imaging device and imaging system

An imaging system comprising:

• a solid state imaging device including
• a first photoelectric conversion unit configured to generate a signal in accordance with an incident light by photoelectric conversion,
• a first transfer unit configured to transfer the signal from the first photoelectric conversion unit,
• a ramp wave generating unit that has an input node to which the signal is transferred and configured to generate a ramp wave whose voltage changes with time at a slope in accordance with a potential of the input node,
• a detection unit configured to detect a change in a relationship between a voltage of the ramp wave and a threshold voltage,
• a ramp wave reset unit configured to reset the voltage of the ramp wave when the detection unit detects a change in the relationship between the voltage of the ramp wave and the threshold voltage,
• a control unit configured to cause the detection unit to repeatedly detect a change in the relationship between the voltage of the ramp wave and the threshold voltage by repeating generation of the ramp wave by the ramp wave generating unit and the reset by the ramp wave reset unit within a predetermined period, and
• a digital value acquisition unit configured to acquire a digital value corresponding to the number of repetitions for which a change in the relationship between the voltage of the ramp wave and the threshold voltage is detected by the detection unit within the predetermined period;
• and
• an image processing unit configured to process an image signal output from the solid state imaging device.