CCDs

Charge-coupled devices (CCDs) are solid-state image sensors that convert light into an electrical signal. They consist of an array of photosensitive pixels made from silicon. When photons strike a pixel, electrons are generated and stored in a potential well. The collected charge is serially transferred across the chip by clocking the electrodes, culminating at a readout amplifier where the signal is converted to a voltage. This charge-transfer process allows high image uniformity and low readout noise.

CCDs can be front-illuminated or back-illuminated; back-illumination improves quantum efficiency, especially at shorter wavelengths. Color images are produced with color filter arrays, such as a Bayer pattern, or with separate sensors for different colors. CCDs are valued for high dynamic range and low dark current when cooled, but they require precise clocking and can be more expensive to manufacture and power-intensive than some alternatives. They are also relatively sensitive to radiation, which can degrade charge-transfer efficiency over time.

Historically, CCDs revolutionized digital imaging after their development in the 1960s and 1970s, becoming dominant in astronomy, professional imaging, and early consumer digital cameras. In recent years, complementary metal-oxide-semiconductor (CMOS) sensors have displaced CCDs in many consumer applications due to lower cost, faster readout, and on-chip processing. Nevertheless, CCDs remain in use in specialized domains requiring ultra-low noise, high dynamic range, and stable calibration, such as astronomical imaging and certain scientific instruments.