Ad conversion circuit, photoelectric conversion device, image capturing device, and mobile object

An AD conversion circuit that converts an analog signal provided to an input terminal into a digital signal, comprising:

• a continuous-time ΔΣ AD converter including an integration circuit configured to integrate a difference signal;
• a switching circuit configured to perform switching to supply an analog signal supplied to the input terminal to the continuous-time ΔΣ AD converter in a first period and to supply a voltage signal corresponding to a voltage output from the integration circuit at an end of the first period in a second period after the first period;
• and
• a holding circuit configured to hold the voltage signal corresponding to the voltage output from the integration circuit at the end of the first period and provide the voltage signal to the continuous-time ΔΣ AD converter via the switching circuit in the second period,
• wherein the continuous-time ΔΣ AD converter is configured to be able to perform gain adjustment for an analog signal input to the continuous-time ΔΣ AD converter.