[[Berkas:CCD.jpg|thumb|right|300px|CCD yang dikembangkan khusus untuk penggambaran [[ultraviolet]], dalam sebuag kemasan berikat kawat.]]
'''Alat muatan-berpasangan''' ([[bahasa Inggris]]: '''charge-coupled device''' atau '''CCD''') adalah sebuah sensor untuk merekam gambar, terdiri dari [[sirkuit terintegrasi]] berisi "array" [[kapasitor]] yang berhubungan, atau berpasangan. Di bawah kendali sirkuit luar, setiap kapasitor dapat menyalurkan [[muatan]] listriknya ke tetanggannya. CCD digunakan dalam [[fotografi digital]] dan [[astronomi]] (terutama dalam [[fotometri]]), optikal dan [[spektroskopi]] [[UV]] dan teknik kecepatan tinggi seperti [[penggambaran untung]].
When a [[photon]] strikes an [[atom]], it can elevate an electron to a higher energy level, in some cases freeing the electron from the atom. When light strikes the CCD surface, it frees electrons to move around and they accumulate in the capacitors. Those electrons are shifted along the CCD by regular electronic pulses and "counted" by a circuit which dumps the electrons from each pixel in turn into a capacitor and measures and amplifies the voltage across it, then empties the capacitor. This gives an effective black & white image of how much light has fallen on each individual pixel.
CCDs containing a single row of capacitors can be used as delay lines. An analogue [[voltage]] is applied to the first capacitor in the array, and at regular intervals a command is given to each capacitor to transfer its charge to its neighbour. Thus the entire array is shifted by one location. After a delay equal to the number of capacitors multiplied by the shift interval, the charge corresponding to the input signal arrives at the last capacitor in the array, where it is amplified to become the output signal. This process continues indefinitely, creating a signal at the output that is a delayed version of the input, with some distortion due to [[sampling frequency|sampling]]. A CCD used in this way is also known as a ''bucket-brigade delay line''. This application of CCDs has now been mostly superseded by digital delay lines.
CCDs with several rows of pixels shift the charge down in the fashion of a vertical [[shift register]] and only the last row is read out in a horizontal shift register. The speed of the measuring circuit must be enough to count out the entire bottom row, then shift the rows down and repeat for every other row, until it has read the entire frame. In [[camcorder|video cameras]] this entire process takes place about 40 times a second.
Several factors can affect whether a photon will cause an atom to release an electron: circuits on the CCD surface can block light from entering; longer wavelengths can penetrate certain depths of the CCD without interaction with the atoms; some shorter wavelengths may reflect off the surface, and so on.
Knowing how many of the photons which fall on the photoreactive surface will release an electron is an accurate measurement of the CCD's sensitivity. This figure is called "[[quantum efficiency]]" and is given as a percentage.
== Applications ==