A pixel circuit for a ultra-low power image sensor, including: an integration node, on which a photodiode current is integrated, a comparator arranged to compare a voltage at the integration node with a reference voltage, a n+1 bits digital memory, a writing pulse signal generator arranged to generate a writing pulse signal, on the basis of the comparator output voltage and on the voltage at a memory node, the start of the pulse triggering the writing of the digital word in the n-bits digital memory part. The comparator includes a switch in series with a current source and arranged to be commanded by the voltage at the memory node so that the switch is open at the end of the pulse, so as to drastically limit the consumption of static power of the pixel circuit during the integration phase.