Roper Photometric manual Typical CCD Imager

Classical CCD The one-dimensional charge transfer concept can be extended to two Implementations dimensions. Buried channels arranged in parallel establish columns; charge

cannot migrate between columns. Along each column, charge is contained in individual potential wells by a multiphase gate structure, as discussed for the one-dimensional case. The result is a two-dimensional array of independent potential wells.

A Typical CCD Imager shows a stylized CCD imager. The large square array is the parallel register. In this example, the parallel register contains 262,144 independent potential wells, called picture elements or pixels. Each pixel is

20 µm square and contains a single charge packet.

A Typical CCD Imager

Pixel columns

				20 ∝
				One	20
				pixel	∝
	Parallel clocks
				Output node			Serial clocks
						Serial Register
10.
25						512
mm
		Parallel Register				x
		512 x 512 pixels
						1
						pixels
			10.25 mm

The serial register is along one side of the parallel register, perpendicular to the pixel columns. The serial register is itself a one-dimensional CCD. It may be masked so that incident photons cannot create charge.

Many CCD formats and aspect ratios are available; the choice of CCD is dictated by the application.

When a CCD imager is exposed to light, charge accumulates in the potential wells of the parallel register. Charge can accumulate over an extended period of time. The total amount of charge is proportional to the product of the light intensity and the exposure time. (A charge accumulation is often called an integration.) The complete charge pattern corresponds to the focused image.

Chapter 3. Advanced CCD Theory 31