It
is important to prevent light from falling onto the CCD pixels
during the readout process to avoid artifacts on the image. The most
simple method is to use a shutter in front of the CCD which is actually
raelized by the ICCD image intensifiers shutter function. Though, the
most simple kind of CCD chip which can be used is a so called
full-frame CCD, as shown in the according picture.
Frame-transfer CCD chips first transfer the collected charges very fast
into a light insensitive area, before the actual readout process
starts. The covered area is located below the CCD's sensitive surface.
Interline-transfer CCD chips only shift the pixel charges into adjacent
covered pixels, which needs only one single shifting, and thus is even
faster than the frame-transfer.
Frame-interline-transfer CCD chips combine the two latter structres to
minimize additional noise and optimize readout performance.
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The
higher the resolution of a CCD sensor with a fixed surface area, the
smaller are the pixels. The smaller the pixels are, the lower is the
signal to noise ratio. This is due to the fact that some noise sources
do not scale with the pixels surface area, as the signal does. Thus,
the higher the resolution, the lower is the signal to noise ratio.
Read more about CCD sensors here.
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