Charge-Coupled Device

Charge-Coupled Device (CCD), sensitive electronic device that stores packets of information as electric charge. Because of their versatility in storing charge, CCDs are often used as analog-to-digital and digital-to-analog converters and signal scramblers, but their main function is recoding information about light hitting the surface of the CCD to create light images electronically.

A CCD used for recording visual information is made of an array of photodiodes (devices that conduct electricity when light strikes them) on top of a semiconductor (a material that conducts electricity better than electrical insulators but not as well as electrical conductors). When light strikes a photodiode, an electric current proportional to the amount of light is sent to a capacitor, which stores the charge. The semiconductor processes the signal from the capacitor and sends it to a computer or other device that can analyze the data about the light that hit the CCD.

CCDs are used in facsimile machines, photocopiers (see Xerography), bar-code readers, and cameras. In astronomy CCDs have almost completely replaced photographic film as an image-capturing method. A CCD is about a hundred times more sensitive to light than photographic film or a photographic plate. The signal from a CCD is also easier than a photographic image to convert into digital code for storage in a computer.