|Reference||STATE OF THE ART||Stan Augarten|
|A New Method of Sensing Images|
The First 8-bit Charge-Coupled Device
What looks like an aerial shot of a football field is really one of the most important inventions in modern electronics. It is a charge-coupled device, or CCD, and it has almost single-handedly revolutionized video technology by doing away with the bulky vidicon tubes of television cameras - expensive, light-sensing vacuum tubes that were sometimes bigger than jugs of wine - and making solid-state television cameras possible. It has also led to the development of many other useful devices, such as electronic checkout terminals in supermarkets.
Unlike most of the ICs shown in this book, CCDs, which were invented by George E. Smith and W. S. Boyle, are not made out of transistors. Instead, they consist almost entirely of capacitors (specifically of the MOS variety; see p. 12). CCDs may be used as either memory chips or image detectors. In memory chips the capacitors are used to store electrons; in image detectors, to detect photons (the energy packets that comprise light) and convert them into electrical charges that can be transferred out of the chip to produce video images.
The term charge-coupled device is derived from the chip's modus operandi. Its capacitors are packed, or coupled, so tightly together that charges can be conveyed, like buckets in a fire brigade, from one capacitor to another and then to a reading station built into the chip. From there, the charges are sent in the same order in which they entered, to the host device. The charges are shunted around the chip by systematically varying the voltages of the capacitors; the presence of a charge signifies a one, its absence a zero.
In video cameras, CCDs are placed directly behind the lens. It is thanks to the invention of this chip that video cameras have become solid-state devices, with all the advantages of equipment without tubes: compactness, reliability, low cost, instant turn-on and shut down. In checkout terminals, CCDs are usually placed in lightweight, handheld wands or under the counters near the cash registers, where they can read the price codes on the merchandise moving by.
|The first 8-bit CCD, this chip consists of twenty-four closely packed MOS capacitors (the narrow rectangles in the football-field-like grid in the center). The thick rectangles at either end of the grid are input/output terminals. This chip can detect and reproduce simple images, like the letters CCD. Today's CCDs can store up to 64K bits of data. Actual size: 0.060 x 0.100 inches.|
|STATE OF THE ART
©Copyright Stan Augarten
|This book is provided for general reference. The National Museum of American History and the Smithsonian Institution make no claims as to the accuracy or completeness of this work.|
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