Patent ID: 6344877
Filing Date: 2002-02-05
Classification: H04N

Abstract:
An image sensor, comprising:a plurality of imager cells arranged in rows and columns, with the imager cells of a particular column being coupled to a column data line of that column, and each imager cell being operable to selectively provide an output signal indicative of one of an amount of light incident upon that imager cell and an amount of noise due to non-ideal characteristics of said each imager cell; at least one dummy pixel having a source follower field effect transistor and characteristics which are at least similar to characteristics of said each imager cell, said dummy pixel providing an output reference signal; and correlated double sampling circuitry for performing a noise sampling and a signal sampling with respect to said output signal from said each imager cell in association with said output reference signal from said dummy pixel, and image data corresponding to said each imager cell being obtained from said noise sampling and signal sampling, wherein said correlated double sampling circuitry comprises a plurality of comparators, each having a first input terminal coupled to one of said column data lines and a second input terminal connected to receive said output reference signal, and wherein said reference signal is a time varying reference signal and further comprising a plurality of up/down counters, each coupled to an output of one of said comparators and operable to count in a first direction during a first sampling interval and in an opposite direction during a second sampling interval, each up/down counter being responsive to an output of the associated comparator to stop counting when the amplitude of the time varying reference signal substantially equals the amplitude of a reset level in the first sampling interval and a signal level in the second sampling interval to thereby complete a correlated double sampling operation.