Patent ID: 6635857
Filing Date: 2003-10-21
Classification: H04N

Abstract:
An image sensing pixel cell used in a pixel cell array, comprising:(a) a reset circuit that couples an initial voltage to a first node at an initial time; (b) a capacitance substantially associated with the first node that stores the initial voltage at the initial time; (c) a photodiode; (d) a unity gain current buffer arranged to bias the photodiode at a relatively constant voltage, the unity gain current buffer comprising a transfer gate transistor and an amplifier circuit, the amplifier circuit being employed to adjust a gate voltage on the transfer gate transistor in a manner to maintain the relatively constant voltage on the photodiode, the gate voltage being adjusted based on a photocurrent flowing in the photodiode; and (e) a voltage buffer circuit that buffers the first node to produce a second voltage, the second voltage corresponds to the voltage at the first node at a subsequent time, the voltage at the first node at the subsequent time is different from the initial voltage when the photocurrent flows in the photodiode.