Solid state image pickup device having dual integrator

Abstract

A solid state image pickup device which performs optical measurement achieving high signal to noise ratio by separating light to be measured from unnecessary noise components comprises a photosensitive unit comprising a photoelectric converting function, a first integrator for either integrating or not integrating a signal generated on the photosensitive unit in a first capacitor connected between an input and output thereof by a first reset signal, a second integrator for either integrating or not integrating a signal in a third capacitor by a second reset signal, a switching device and a second capacitor connected in series between an output of the first integrator and an input of the second integrator, a counter circuit comprising a counting up function and a counting down function, and a timing control circuit for prior to the measurement of the light to be measured, making the first integrator to perform integration by controlling the first reset signal, setting the second integrator in non-integration state by controlling the second reset signal, setting the switching device to on, exposing on the photosensitive unit, accumulating charges in the first and second capacitors until an output voltage of the first integrator reaches a predetermined voltage, making the counter circuit to count up elapsed time, next, in a case of measuring light to be measured, making the first integrator to perform integration by controlling the first reset signal, setting the second integrator in integration state by the second reset signal, further, setting the switching device to on, exposing on the photosensitive unit, making the counter circuit to count down from the counted value of the elapsed time, at a point of the counted value reaching zero, turning off the switching device, making the second integrator not to perform integration, thereby an output signal of the second integrator is a component of the light to be measured.

Dependencies are inferred from the claim text.