Hardware Reference
In-Depth Information
fragile to withstand further grinding. Still, higher-frequency crystals can be achieved by
using harmonics of the fundamental frequency, resulting in crystals of up to 200MHz or
more. Even higher frequencies can be achieved by using frequency synthesizer circuits,
which use a base crystal-generated frequency fed to a circuit that then generates multiples
of frequency that can extend well into the gigahertz or terahertz range. In fact, crystal-
based frequency synthesizer circuits generate the high operating speeds of modern PCs.
Thecrystalpackages,aswellastheshapeoftheactualquartzcrystalsinsidethepackages,
canvary.Thepackagesareusuallyametalcanthatiseithercylindricaloroblonginshape,
but they can also have other shapes or be constructed of plastic or other materials (see
Figure 3.41
)
.
Figure 3.41
Crystal packages of varying shapes.
The sliver of quartz inside the package is normally disc shaped, but it is shaped like a tun-
ingforkinsomeexamples.
Figure3.42
showsacylindricalcrystalpackagewiththecover
removed, exposing the tuning fork-shaped sliver of quartz inside.
Figure 3.42
Crystal interior showing the quartz tuning fork.
