Chargecoupled

Charge-coupled devices (CCDs) are solid-state image sensors that convert light into electrical charge and move that charge across the chip by sequential clocking of electrodes. The term is sometimes written as charge-coupled device or as charge-coupled; the core idea is the coupling of charge packets between neighboring sites rather than direct readout at each pixel.

Operation centers on the collection and transfer of charge. Light exposure generates photoelectrons in each pixel’s photodiode, forming a charge packet stored in a local potential well. Clocking the gates shifts the packet toward a serial readout node, where a sense amplifier converts the charge to a voltage for digitization. Because the charge is moved across the chip rather than read out per pixel, CCDs can achieve very low readout noise and high image uniformity.

Architectures and variants include full-frame transfer, frame transfer, and interline CCDs. Back-illuminated CCDs improve quantum efficiency by exposing the photodiodes from the backside. Some devices use multiple parallel transfer registers to increase readout speed. The choice of architecture affects factors such as frame rate, fill factor, and susceptibility to smearing.

Applications and status: CCDs were dominant in astronomy, scientific imaging, and professional photography from the 1980s onward. In consumer electronics, CMOS sensors have largely supplanted CCDs due to lower power, greater integration, and cost, but CCDs remain preferred in applications requiring extremely low noise, high dynamic range, and uniformity, such as astronomical imaging and certain research instruments.