In the field of imaging devices comprising a detector generating electric charges in response to incident photon radiation, and an analog-to-digital conversion circuit forming means for reading the quantity of electric charges generated, an analog-to-digital conversion circuit comprises: a comparator which can switch depending on the comparison between a potential on an integration node and a predetermined threshold potential, a counter incrementing with each switch of the comparator, a counter-charge injection circuit injecting a quantity Qc of counter-charges on the integration node with each switch of the comparator, and control means which determine the quantity Qc of counter-charges injected. The analog-to-digital conversion circuit is characterized in that the control means determine the quantity Qc of counter-charges injected as a function of a value of the counter.