Definition of Terms

Frequency This is the nominal frequency of the crystal and is expressed in either kilohertz (kHz) or Megahertz (MHz) AEL Crystal Ltd. usually express MHz frequencies to 6 decimal places, and will assume any missing digits to be zeroes.

Package/Outline This defines the physical size and construction of the enclosure within which the resonator element is mounted.

Calibration Tolerance Usually expressed in parts per million (ppm) it defines how close to the nominal frequency the crystal has to be manufactured. The closer to the nominal frequency the crystal is required, the more expensive it will be to produce.

Temperature Stability The frequency of a crystal will deviate over temperature in a predictable fashion. The temperature stability also usually expressed in ppm, is the maximum deviation from the frequency at 25deg C allowed over the operating temperature range.

Operating Temperature Range Defined as the minimum and maximum temperature over which the temperature stability must be maintained. For a typical crystal the temperature range is usually symmetrical about 25deg C

Load Capacity The load capacity must be specified in conjunction with the circuit condition (Series or parallel resonant). Many oscillator circuits employ a capacitor either in series or parallel with the crystal, which will have the effect of shifting or “pulling” the crystal from its resonant frequency.   Activity or ESR A measure of the motional resistance of the crystal. The lower the figure, the better the crystal, although there are limits on what values can be achieved depending on the frequency and the package type.

DLD (Drive Level Dependancy) Whilst related to ESR, DLD refers to the effect of very low drive levels on crystal activity and start-up performance. Occasionally very high levels of ESR may be observed at very low power conditions in the order of a few nanowatts, typically observed immediately after start-up leading to unreliable operation of the crystal.

Ageing The frequency of all crystals will deteriorate over time. Ageing is defined as the maximum frequency change allowed over a certain period, usually 1 year. The ageing effect is logarithmic, with the majority of the effect being observed within the 1st 30 days.

Pullability Quartz crystals operated with a capacitor associated with them will change frequency with a variation in the value of capacity. Pullability defines the rate of change in ppm/pF

Spurious Responses All crystals will exhibit several modes of vibration simultaneously, with the desired mode being enhanced to give the required frequency characteristics. Spurious responses are the manifestation of those unwanted modes. During manufacture we aim to suppress those modes within the operating range of the crystal.

Drive Level Drive level is a measure of the power dissipation through the crystal element. The specified drive-level is the maximum drivel level allowed before permanent damage may occur to the crystal. However, the drive-level at which the crystals are tested is the minimum drive-level required to activate the crystal under normal conditions

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