Glossary of Crystal Terms
Glossary of Crystal Terms
Aging
Quartz crystal aging applies to the cumulative change in frequency which results
in a permanent change in operating frequency of the crystal unit. The rate of
change in frequency is fastest during the first 2 - 3 months of operation. Many
interrelated factors are involved in aging, some of the most common being: internal
contamination , excessive drive level, surface change of the crystal, various
thermal effects , etc...
Proper circuit design incorporating low operating ambients, minimum drive level
and static pre-aging will greatly reduce all but the most severe aging problems
Calibration or Adjustment Tolerance
The setting tolerance is the maximum allowable deviation from the nominal frequency at 25°C +- 3°C. It is normally specified in parts per million (ppm)
Drive Level
Drive level is the level of power dissipated in the crystal as a result of the
operating circuit. Rated or test drive level is the power at which the crystal
is specified and any deviation from the rated level will effect the crystal
performance; therefor the actual drive level should reasonable duplicate that
specified.
AT - cut crystals generally can withstand a considerable overdrive without physical
damage, however the electrical parameters are degrated at excessive drive
Equivalent Serie Resistance (ESR)
For crystal units designed to operate at series resonance, ESR is the equivalent ohmic resistance of the unit when operating in the specified crystal impedance meter adjusted for the rated drive level and tuned to the specified crystal frequency
Load Capacity ( CL)
This is an external capacitance which sets a point on the reactance curve at which the crystal will resonate. It is normal to refer to crystals which are operated with a small value of CL as "parallel resonant" and to those which are not as "series resonant"
Nominal Frequency
The nominal frequency of the crystal . This is expressed in Megahertz ( Mhz) for frequencies of 1.0 Mhz and over. Frequencies may be specified up to seven significant figures. If less are specified, then we may assume any digits that follow are zero
Operating Temperature Range
This is the temperature range over wich the quoted temperature stability is specified
Pullability
The pullabilty of a crystal refers to a crystal operating in the parallel mode and is a measure of the frequency change as a function of load capacitance. Pullability is important to the circuit designer who wishes to achieve several operating frequencies with a single crystal by means of switching various values of load capacitance
Shunt Capacity (Co)
The "static capacity" or shunt capacity of the electrodes, the holder and the leads. It is usually measured with an ungrounded case
Spurious Response
It is also possible for a crystal to vibrate at a frequency that is not related to its fundamental or overtone frequencies. Such undesired frequencies are referred to as spurious responses.Our processes are designed to minimise (not eliminate) the spurious responses and maximise the crystal activity at the desired frequency. The circuit designer should further guard against spurious responses by ensuring that the oscillator feedback circuit achieves its highest gain at the desired operating frequency
Storage Temperature Range
The temperature range in which the crystal can be stored without damage,i.e. it will resume operation as normal once it is restored to within its operable temperature range
Temperature Stability
The stability tolerance is the maximum allowable deviation from the nominal
frequency over a specified temperature range and expressed in terms of ppm.
This factor is dependent upon the angle of cut