A method is disclosed for operating an imaging device having a matrix of pixels arranged in rows and columns. A polarization voltage is generated on a gate of a main MOS transistor that is connected as diode. The main MOS transistor is coupled between a power supply voltage and a ground circuit. Prior to reading the pixels of a row of the matrix, a plurality of first capacitors are charged with the polarization voltage. The first capacitors are coupled between the gate of the main transistor and a ground node. Upon reading the pixels of the row, the first capacitors are discharged on respective gates of auxiliary transistors coupled between the columns and the ground node so as to switch on the auxiliary transistors and deliver a substantially identical polarization current to each column.