CCD

A CCD (for charge-coupled device ) is a type of electronic device generally used to detect light, in such cases, incorporating an array of tiny electronic light sensors. It provides a mechanism for unloading the sensor-data, so as to capture an image focused on the sensors as digital data. Generally, such arrays are implemented as integrated circuits. The development and adoption of such electronic light-sensing arrays constituted a revolution in astronomy: they are used in telescopes (as well as many digital cameras) where they provide the data in electronic digital form, convenient for image storage and processing, and offering the possibility of automating the whole observation process. They have improved the efficiency of astronomical observation, vastly increasing the number of images captured and their use is advantageous for remote operation of telescopes, including space probes, and for fully-automated surveys.

The term CCD actually refers to the mechanism for unloading the data: it consists of a string of (basically) identical circuit elements that each sense and store a pixel, and are coupled together such that they that can pass their data to a neighbor in lock-step (shifting the data), so after a number of such steps, all the data has been output. The typical CCD circuit is a row of these strings in parallel, on a single chip, laid out in a grid. This technology and name ("CCD") were initially designed for data storage, but the technology to charge an electronic circuit element from incident EMR was already known and easily incorporated. Unloading a CCD's data takes some time, and faster means have been developed at the expense of more complex circuitry: such faster sensors are not termed CCDs (though undoubtedly people sometimes refer to one as a "CCD"), e.g., some fall under the term CMOS sensor. Such ability to unload data faster allows more time to collect data and more frequent unloading and resetting the device, which offers a number of benefits such as allowing a faster cadence to avoid saturation.