Automatic dark current correction

Claim 2

An automatic dark current correction device comprising a camera tube having two photosensitive areas on a single substrate, scan means for repetitively and sequentially scanning both of said photosensitive areas, the first of said sensitive areas responsive to external light incident thereon, means for preventing said external light from being incident on said second area, said first and second areas each comprising an array of PN junctions, means connected to said scan means for generating a first and second electrical signal in accordance with the duration of said first area scan and said second area scan respectively, first circuit means coupled to said tube and responsive to said first signal for providing a third electrical signal indicative of said external light, second circuit means coupled to said tube and responsive to said second signal for providing a fourth electrical signal indicative of dark current, means for storing said fourth signal for a duration of time necessary to obtain the next successive one of said third signals, and means for subtracting said fourth signal from said third signal thereby obtaining a dark current corrected signal.

Claim 3

The combination of claim 1 further including means connected between said camera and said means for storing and responsive to said second signal for delimiting said fourth signal to provide upper and lower limits to the scanning of said second area.

Claim 4

The combination of claim 1 further including a vertical scan circuit connected to said tube for providing said tube with sequential scanning of said first area and means for placing a step function into said vertical scan circuit at the end of said first area scan for shifting the beam to said second area.

Claim 5

The combination of claim 1 wherein said means for storing includes an RC circuit for averaging the series of dark current signal indications to smooth out discontinuities.

Claim 6

An automatic dark current correction device comprising a camera tube having two photosensitive areas formed in an assembly on a common substrate of a N-type material, a mosaic of P-type material arranged across the surface of said N-type material to form a plurality of PN junctions, a first portion of said PN junctions forming a first of said two areas, and a second portion of said PN junctions forming a second of said two areas, said first area having radiation incident thereon and said second area including means for shielding said second portion of PN junctions from said incident radiation, each of said first area PN junctions possessing a stored signal indicative of incident radiation and each of said second area PN junctions possessing a stored signal indicative of a dark current level, said camera tube including means for repetitively scanning said array of PN junctions for providing an output signal from each of said arrays indicative of the signal stored therein, a storage circuit coupled to said tube and responsive to the output of each successive scan for storing a corresponding signal representative of said dark current level, and means coupled to said tube and said storage circuit for repetitive subtracting each respective dark current signal from each respective incident radiation signal so as to provide an output signal corrected for dark current variation.

Claim 7

An automatic dark current correction device comprising a camera tube having two photosensitive areas formed in an assembly on a common substrate of a N-type material, a mosaic of P-type material arranged across the surface of said N-type material to form a plurality of PN junctions, a first portion of said PN junctions forming a first of said two areas, and a second portion of said PN junctions forming a second of said two areas, said first area having radiation incident thereon and said second area including means for shielding said second portion of PN junctions from said incident radiation, each of said first area PN junctions possessing a stored signal indicative of incident radiation and each of said second area PN junctions possessing a stored signal indicative of a dark current level, said camera tube including means for repetitively scanning said array of PN junctions for providing an output signal from each of said arrays indicative of the signal stored therein, a storage circuit coupled to said tube and responsive to the output of each successive scan for storing a corresponding signal representative of said dark current level, and means coupled to said tube and said storage circuit for repetitive subtracting each respective dark current signal from each respective incident radiation signal so as to provide an output signal corrected for dark current variation.