Method and apparatus for a pixel cell architecture having high sensitivity, low lag and electronic shutter

Abstract

An image sensing pixel cell includes a reset circuit, a capacitance, a photodiode, an amplifier circuit, and a voltage buffer. The reset circuit couples an initial voltage to a first node at an initial time, where the capacitance stores the initial voltage. The amplifier circuit is arranged to bias the photodiode at a relatively constant voltage. The voltage buffer circuit buffers the first node to produce a second voltage that corresponds to the voltage at the first node at a subsequent time. The second voltage is different from the initial voltage when a photocurrent flows in the photodiode. A pixel cell may include a shutter circuit having a closed position and an open position. The shutter circuit provides a conductive path for the photocurrent between the photodiode and a power supply connection when in the closed position. The shutter circuit provides another conductive path for the photocurrent between the photodiode and the first node when in the open position. In operation, every pixel cell in the array is reset at substantially the same time. The shutter opens for the entire pixel array to allow photocurrents to integrate on the capacitors in each pixel cell. The shutter closes and image data is read from the array of pixel cells. The image data for an image corresponds to the integrated photocurrents stored on the capacitors in the array of pixel cells.