Patent ID: 8686341

Claim:
An image sensor with active pixels comprising a matrix of pixels organized in rows and columns, the pixels of one and the same column being linked to a column conductor itself linked to a reading circuit, each pixel comprising a photodiode linked by a transfer transistor to a storage node, and a row selection transistor for linking the storage node to the column conductor or isolating it from this conductor, the sensor further comprising means for performing during one and the same cycle of integration and reading a first and a second transfer of charge from the photodiode to the storage node, the first transfer occurring after a first duration of integration, the second transfer occurring after a second duration of integration following the first duration, means for doing a first sampling, in a first sampling capacitor of the reading circuit, of the level of potential taken by the column conductor after the first transfer of charge, means for doing a second sampling, in a second capacitor of the reading circuit, of the level of potential taken by the column conductor after a reinitialization of the storage node, and means for doing a third conditional sampling in the first capacitor of a level of potential of the column conductor after the second transfer of charge, the reading circuit comprising a ramp-type analog-digital converter comprising a differential amplifier linked to the two capacitors and means for applying a linear voltage ramp to one of the capacitors, the effect of the ramp being to cause the amplifier to toggle after a variable duration dependent on the potentials sampled in the capacitors, wherein the sensor comprises means for applying firstly a provisional ramp, after the first transfer of charge, the state of the output of the amplifier at the end of the provisional ramp being used to enable or disable the third conditional sampling, and thereafter a definitive ramp after the second transfer of charge for performing a definitive analog-digital conversion of the difference between the voltages sampled in the two capacitors.