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Crystals and Oscillators

when stability counts…

A survey of these essential electronic systems, how they work, and how they are used. Practical component values are given for each oscillator.The stability of the better RC oscillators is about 0.1%, while LC oscillators are stable up to 0.01%. If we require greater stability, the choice falls on a crystal oscillator. Certain crystalline substances, of which quartz is a prime example, have the property that they produce an electric field when they are subjected to stress and, conversely, become physically distorted when they are subjected to an electric field. This is known as the piezo-electric effect. Consequently, it is possible to cut a crystal so that it will physically vibrate at a given frequency when it is subject to an alternating electric field. Instead of the electro-magnetic resonance of the LC network, we have the electro-mechanical resonance of the piezo-electric crystal. The difference is that crystals can easily be machined to high precision, with natural frequencies as close as 10 parts per million. (ppm)
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