CCd

A charge-coupled device (CCD) is a solid-state image sensor that converts light into electrical charges stored in an array of photosensitive elements (pixels). It was developed in 1969 by Willard S. Boyle and George E. Smith at Bell Labs and became a foundational technology for digital imaging, notable for high sensitivity and low noise in early camera systems.

How it works: photons striking each pixel generate electron charges proportional to light intensity. These charges are collected in potential wells created by a silicon substrate. During readout, the charges are clocked sideways across the array and transferred to a common output node for amplification and digitization. This sequential transfer is the defining feature of the CCD, hence the name.

Architectures include full-frame CCDs (the entire array serves as the photosensitive area), frame-transfer CCDs (a light-sensitive area and a masked storage area), and interline transfer CCDs (vertical transfer with neighboring storage). Color information is usually obtained with a color filter array, commonly Bayer, with demosaicing performed in software or hardware. Cooling reduces dark current, enabling long exposures and higher dynamic range.

In practice, CCDs are known for excellent image quality, high quantum efficiency, and low readout noise. Drawbacks include higher cost, more power consumption, and sensitivity to radiation damage in space. They also typically require more complex clocking and can suffer from blooming when saturated. The technology has been largely supplanted in consumer photography by CMOS sensors, but remains favored in astronomy, scientific imaging, and high-end imaging where image fidelity and low noise are critical.

Related topics include back-illuminated CCDs, which increase light collection efficiency, and comparisons with CMOS sensors in terms of speed, integration, and power. CCDs continue to be used in specialized applications such as telescopes, spectrometers, and certain medical imaging devices.