Analog Image Storage Using Charge-Coupled Devices

Fairchild Camera and Instrument Corporation300 Robbins Lane, Syosset, L. I., New York 11791AbstractCharge -Coupled Device (CCD) area image detectors of the interline- transfer type include a design feature which enables analog imagedata to be electrically inserted into the vertical registers via a horizontal input register and, when the device is adequately cooled, this datacan be temporarily stored in the vertical registers. Such analog storage devices have been successfully used in several R & D programsperforming functions such as TV scan rate reduction, background cancellation in chopper operated pyroelectric vidicons and precision TVfield delay for image processing. The results from these programs, consolidated with other CCD technology advances, form the basis for anew program now in progress at Fairchild Camera and Instrument Corp. sponsored by the Night Vision and Electro Optical Laboratory.This program has as its objective the development of an Analog TV Scan Rate Converter and its primary storage element, a two -dimensionalanalog storage charge -coupled device containing 640 X 256 storage sites. The scan rate converter is intended to interface with TV datacompression systems and other systems which require a large two -dimensional analog memory plane.This paper describes the Analog TV Scan Rate converter and the storage CCD under development. The current status of analog imagestorage using charge -coupled devices is reviewed and potential applications are explored.IntroductionAn analog CCD memory organized as a series -parallel- series two -dimensional register, capable of storing a full frame of TV formattedinformation in analog form for periods up to ten seconds, forms the basis for the design of an Analog TV Scan Rate Converter. The con-verter is intended to provide a rugged, low power, small size, light weight buffer between a TV camera (or other RS -170 format inputsources) and a data compression encoder employed for bandwidth minimization.Analog image storage using CCD's is not limited to buffer type or scan rate conversion applications. During the past three years, aseries of R & D programs have demonstrated the feasibility of CCD analog storage in pyroelectric vidicon background cancellation andprecision TV field delay for use in real time image processing.This paper is primarily concerned with Analog Image Storage using CCD's. It is intended to inform the image -processing community ofthe technology, the results achieved to date and the on -going efforts to develop a new and highly useful tool for analog image -processing.Early ProgramsIn early analog storage programs involving charge -coupled devices, the Fairchild 488 X 380 area imaging CCD was used. When thisdevice is used in a storage mode, charge is injected directly into the vertical registers via the electrical input charge injection port andhorizontal input register. This process bypasses the "photosites" (which are opaqued in the storage mode) and allows charge to betemporarily stored in the vertical registers.To minimize dark current, the CCD was assembled with a simple thermo -electric cooler into a small hermetically sealed module asshown in Figure 1.