CCD

Definition: Charge-coupled device. Silicon integrated chip of the metal semi-conductor type: a layer of silicon oxide covers a silicon substrate with electrodes set very close together in a regular pattern (line or array according to design) over the oxide layer. These electrodes correspond to the actual sensors or pixels. Light falling on the electrodes causes a build up of electrical charge (the signal) corresponding to the amount of light and according to the voltage applied to the electrode. To read the signal charge the electrode voltages are alternately raised and reduced, which shunts the signal charge from one electrode to the another to be read off at the end of the line. So far, the process is essentially analogue: when the signal is measured, it is turned into a digital code which corresponds to the light value for the corresponding pixel. * Developed in the mid 1930s; first used in a camera in 1972, by 1980s the core technology enabling and directing the development of digital photography.

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