Patent ID: 6885396

Claim:
A circuit for reading out values of pixels from an active pixel sensor array, the circuit comprising: a first sample-and-hold circuit for sampling and storing signals from pixels in a first column; a second sample-and-hold circuit for sampling and storing signals from pixels in a second column; an operational amplifier-based charge sensing circuit, associated only with the first and second columns in the array, that selectively provides an amplified differential output signal based on signals sampled either by the first sample-and-hold circuit or the second sample-and-hold circuit; and an analog-to-digital converter, associated only with the first and second columns in the array, for converting the differential output to a corresponding digital signal using a successive approximation technique, said analog-to-digital converter including a comparator and a first binary-scaled capacitor network; wherein the capacitors in the first network share a common node coupled to a first input of the comparator, the amplified differential output signal from the charge sensing circuit is coupled to a second input of the comparator, and each of the capacitors in the first capacitor network has an associated latch circuit for storing a bit corresponding to a differential signal for a pixel sampled by the first sample-and-hold circuit while a differential signal for a pixel sampled by the second sample-and-hold circuit is amplified and converted to a corresponding digital signal.