Patent ID: 8749682
Filing Date: 2014-06-10
Classification: H04N

Abstract:
1. An image sensor having a pixel array and comprising: an input circuit comprising a first input configured to receive an analog signal from a pixel of said pixel array, the signal varying during a pixel readout period and having a first level during a first calibration period and a second level during a second read period, the input circuit further comprising a second input configured to receive a reference signal from a time varying reference circuit; two coupling capacitors; a comparator circuit configured to compare the reference signal and the analog signal; and an auto-zeroing circuit coupled across the comparator circuit, wherein the image sensor is operable such that the analog signal from the pixel and the reference signal from the time-varying reference circuit are constantly read onto respective ones of said two coupling capacitors during both the first calibration period and the second read period; and wherein said time-varying reference circuit is arranged to begin providing a ramping of said reference signal during said second read period and determine a change in magnitude of said analog signal between said first calibration period and said second read period, said time-varying reference circuit also arranged to provide said ramping of said reference signal during said first calibration period when the auto-zeroing circuit for the comparator circuit is actuated so as to compensate for any delay in onset of said ramping during said second read period.