Patent ID: 7349018

Claim:
A method for operating a CMOS image sensor including a plurality of pixels, each of said pixels including a photo-sensor element producing charge carriers in proportion to its illumination and storage means capable of being coupled to and uncoupled from said photo-sensor element at a determined instant in order to store, on a memory node of said pixel, a measuring signal representative of said charge carriers produced by said photo-sensor element during an exposure phase, each pixel including: a first MOS transistor connected in series via its drain and source terminals, on the one hand, to a supply voltage and, on the other hand, directly to said photo-sensor element, a gate terminal of said first MOS transistor being controlled by a control signal, coupling means including first and second terminals for coupling and uncoupling said photo-sensor element and said storage means, said coupling means being a MOS coupling transistor including gate, source and drain terminals, said source and drain terminals of this coupling transistor being respectively connected to said photo-sensor element and said memory node, a second MOS transistor connected in series via its drain and source terminals, on the one hand, to a supply voltage and, on the other hand, directly to said storage means and indirectly to said photo-sensor element via said coupling means, the first and second terminals of the coupling means being respectively connected to the source terminal of the first MOS transistor and to the source terminal of the second MOS transistor; and reading means composed of a third transistor, as a source follower transistor, whose gate is connected directly to said storage means, and a fourth transistor as a line selection transistor, wherein said first or second MOS transistor is operated at least partially in weak inversion so that, during the exposure phase of said photo-sensor element, the pixel has at least partially a logarithmic response for illumination levels higher than a determined illumination level which can be zero.