Photoelectric conversion apparatus, photoelectric conversion system, and mobile object

A photoelectric conversion apparatus, comprising:

• a plurality of pixels including a first pixel and a second pixel;
• a generation unit configured to generate a first reference signal changing in potential in a first period from a first point in time to a second point in time, and a second reference signal having a gradient larger than a gradient of the first reference signal and changing in potential in a second period from a third point in time to a fourth point in time;
• and
• a plurality of analog to digital (AD) conversion units including a first AD conversion unit to which a signal from the first pixel is input, and a second AD conversion unit to which a signal from the second pixel is input,
• wherein each of the plurality of AD conversion units includes a selection circuit configured to select the first reference signal or the second reference signal, and a comparator configured to compare the first reference signal or the second reference signal selected by the selection circuit with a signal from one of the pixels,
• wherein the first period and the second period partially overlap with each other, and
• wherein the third point in time is later than the first point in time.