Image sensor pixel circuit

Abstract

Disclosed is an image sensing device having a reduced number of transistors within each imager cell as compared to prior art devices. Each imager cell includes a photosensitive element providing a photocharge responsive to incoming light, and first, second and third transistors. The first transistor is coupled to an activation line, e.g., a row select line, that carries an activation signal to a first plurality of imager cells to selectively activate cells for image data readout. This transistor transfers the photocharge towards a reference circuit node within the image cell in response to the activation signal. The second transistor is operably coupled to the first transistor, and is operative to selectively set a voltage level at the reference node. The third transistor has a control terminal coupled to the reference node, and an output terminal coupled to an output data bus common to a second plurality of image cells, e.g., a column of cells. The third transistor providing an output signal on the data line related to the reference node voltage, which is indicative of an amount of light incident upon the photosensitive element.