Load Capacitance

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Load Capacitance

The loadcapacitance CL is a factor for determining the "conditions"of acrystal unit when used in the oscillation circuit .In an ordingay oscillationcircuit the crystal unit is used in a range where it functions as an inductivereactance in such usage ,the oscillation circuit operates as a capacitivereactance .

In other words,when the oscillation circuit is seen from both terminals of the crystal unit,this oscillation circuit can be expressed as a series circuit of a negativeresistance -R and a capacitance CL . At that time this capacitance is calledthe load capacitance .The relationship between load capacitance and oscillationfrequency is not linear.

When the load capacitanceis small, the amount of frequency variation is large ,and when the loadcapacitance is increased, frequency variation lowers .If the load capacitanceis lessened in the oscillation circuit to secure a large allowance for theoscillation frequency ,the frequency stability will be greatly influenced evenby a small change in the circuit. The load capacitance can be chosen fromstandard values specified in the catalog. but 10-30pF is better.


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