Importance

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Abstract

An CCD image sensor includes a number of detector sites which are shielded from exposure to light so as to produce an output signal indicative of the dark current from the sensor. The output signal from the sensor is digitized into a series of multi-bit numbers. As dark current picture elements are clocked from the sensor, a logic circuit detects when any one of several least significant bits of the multi-bit digitized sensor output signal has a given logic level. A switch, controlled by the logic circuit, applies a constant current to charge a capacitor so that the voltage across the capacitor will represent the magnitude of the dark current in the sensor output signal. The capacitor voltage is subtracted from the sensor output to provide an image signal in which the effects of the dark current are compensated.

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First Claim