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Crystal常見用語

* Nominal Frequency: The frequency in MHz (or KHz) assigned by the specification of the crystal unit at 25 C.
 
* Frequency Tolerance: The allowed deviation in PPM from the nominal frequency at 25 C.
 
* Stability Over Temperature: The allowed deviation in PPM over a specified operating temperature range and the
deviation is referred to the measured frequency at 25 C.
 
* Aging: Cumulative change in frequency over a certain period of time (specified in PPM per year).
 
* Load Capacitance: Effective capacitance of the complete circuit as measured across the crystal terminals. The load
capacitance must be specified when the crystal is operating in a parallel resonant (anti resonant) circuit.
 
* Series Resonance: When a crystal operates at series resonance it appears resistive in the circuit and its impedance is
near zero.
 
* Mode of Oscillation: A crystal can operate at many frequencies. This depends upon the cut, physical properties and
geometry of the crystal blank. The most common mode is fundamental. In order to generate higher frequencies,
overtones are considered. Third, fifth, seventh, or ninth overtones can be achieved by special processing and surface
finish of the crystal blank.
 
* Equivalent Series Resistance (ESR): The internal or equivalent resistance of the circuit measured at the series resonant frequency. This is the resistance the crystal presents to the operating circuit.
 
* Drive Level: The level of power (or current) dissipation in the crystal unit during operation.