Solid-state imaging apparatus having a comparator comparing a generated reference signal with an analog signal from a pixel and its driving method

A solid-state imaging apparatus comprising:

• a pixel region wherein a plurality of pixels each outputting an analog signal by photoelectric conversion is arranged in a two dimensional matrix;
• a plurality of output lines, each arranged correspondingly to each of columns of the pixel region, and connected commonly to the pixels in a same column;
• a reference signal generating circuit for generating a reference signal changing in accordance with time;
• a comparator for comparing the reference signal with the analog signal outputted via the output line from the pixel;
• and
• a counter for counting, as a digital value, a period from a start of the comparing by the comparator until an inversion of an output signal from the comparator, wherein
• the reference signal generating circuit sets the reference signal at an offset voltage, thereafter, an input terminal of the comparator is reset, thereafter, the reference signal generating circuit resets the reference signal from the offset voltage into an initial voltage, and thereafter, the reference signal generating circuit generates the reference signal starting from the initial voltage, and the comparator starts the comparing.