US Patent 7911512 Image sensor with readout circuit

An image sensor has an array of pixels. Each column has a first and a second column line connected to a read-reset amplifier/comparator which acts in a first mode as a unity gain buffer amplifier to reset the pixels via the first lines, and in a second mode acts as a comparator and AD converter to produce digitized reset and signal values. The reset and signal values are read out a line at a time in interleaved fashion. Reset values are stored in a memory and subsequently subtracted from the corresponding signal values. The arrangement reduces both fixed pattern and kT/C noise.