CRYSTAL UNITS  TERMS, DEFINITIONS AND CHARACTERISTICS 
Term 
Reference symbol 
Definitions and characteristics 
Motional resistance

R_{1} [Ω] 
The resistance in the motional ( series ) arm of the equivalent circuit. It represents energy losses of vibrations in the resonator. Its value is according resonator type from Ohms up to hundreds of Ohms. 
Motional inductance 
L_{1} [mH, H] 
The inductance in the motional ( series ) arm of the equivalent circuit. It represents mass inertia of the resonator. Its value is according resonator type from mH up to H 
Motional capacitance 
C_{1 }[fF] 
The capacitance in the motional ( series ) arm of the equivalent circuit. It represents elasticity of the resonator. Its value is according resonator type from order of 0.1 fF up to 10 fF. 
Shunt capacitance 
C_{0} [pF] 
The capacitance in parallel with the motional arm of the equivalent circuit. It represents the resonator as a capacitor. Its value is according resonator type in order of pF. 
Quality factor

Q 
Quality factor is dimensionless parameter characterising losses of vibration energy in resonator, it can be calculated from equation:

Capacitance ratio 
r 
Capacitance ratio is the ratio of shunt capacitance to motional capacitance:
The parameters of equivalent electrical circuit determine some characteristic features of crystal units (see below). 
Motional (series) resonance frequency 
f_{s }[kHz, MHz] 
Motional ( series ) resonance frequency ( f_{s}), is the frequency, at which the susceptance of resonator is equal to 2πf_{s}C_{0}
or ( ω_{s}C_{0}) and conductance reaches maximum

Parallel resonance frequency (lossless) 
f_{p }[kHz, MHz] 
Parallel resonance frequency (lossless) is the frequency at which the reactance of resonator is equal to 1/(2πf_{s}C0)
or 1/(ω_{s}C0) and resistance reaches maximum.

Resonance frequency 
f_{r }[kHz, MHz] 
Resonance frequency is the lower of the two frequencies of the crystal unit alone, under specified conditions, at which the electrical impedance of the crystal unit is resistive 
Antiresonance frequency 
f_{a }[kHz, MHz] 
Antiresonance frequency is the higher of the two frequencies of the crystal unit alone, under specified conditions, at which the electrical impedance of the crystal unit is resistive 
Working frequency 
f_{W }[kHz, MHz] 
Working frequency is the operational frequency of the crystal unit together with associated circuits 
Load resonance frequency 
f_{L }[kHz, MHz] 
Load resonance frequency is one of the two frequencies of a crystal unit in association with a series or with a parallel load capacitance, under specified conditions at which the electrical impedance of the combination is resistive.
The load resonance frequency is the lower of the two frequencies when the load capacitance is in series and the higher when it is in parallel.
In EN 601221:2002 (IEC 601221:2002) other characteristic frequencies of the crystal unit are defined. 
Load capacitance 
C_{L} [pF] 
Load capacitance is the effective external capacitance associated with the crystal unit which determines the load resonance frequency f_{L}. It represents the influence of external circuits on resonator frequency. 
Load resonance resistance 
R_{L} [Ω, kΩ, MΩ] 
Load resonance resistance is the resistance of the crystal unit in series with a stated external capacitance at the load resonance frequency f_{L}.

Fractional load resonance frequency offset 
D_{L} 
Fractional load resonance frequency offset is the relative frequency change of resonance frequency caused by connection of load capacitance C_{L} to the crystal unit.

Fractional pulling range 

Fractional pulling range is the fractional frequency change caused by the load capacity change from value C_{L1} to C_{L2}

Pulling sensitivity 
S 
Pulling sensitivity is the fractional pulling range related to 1 pF load capacity change at specified load capacity C_{L}.

Operating temperature range 
°C 
Operating temperature range is the range of temperatures over which the crystal unit shall be within the specified tolerances 
Operable temperature range 
°C 
Operable temperature range is the range of temperatures over which the crystal unit will not sustain permanent damage though not necessarily functioning within the specified tolerances 
Storage temperature range 
°C 
Storage temperature range is the minimum and maximum temperatures, at which the crystal unit may be stored without deterioration or damage to its performance 
Reference temperature 
°C 
Reference temperature is the temperature at which certain crystal measurements are made. For controlled temperature units, the reference temperature is the midpoint of the controlled temperature range.
For noncontrolled temperature units, the reference temperature is normally 25°C ± 2°C 
Frequency tolerance
Fig. 2

[ ppm ] 
Frequency tolerance is the maximum permissible deviation of the working frequency due to a specified cause or a combination of causes.
The frequency tolerance is usually stated in parts per million (ppm =1×10^{6}) of the nominal frequency.
The tolerances normally used are defined as follows:
 deviation from nominal frequency at the reference temperature under specified conditions;
 deviation over the temperature range from the frequency at the specified reference temperature, typical temperaturefrequency dependency for AT and SC cut is shown in Fig. 2;
 deviation as a result of ageing under specified conditions;
 deviation from nominal frequency due to all causes (overall tolerance).

Level of drive 
[ µW] 
Level of drive is a measure of the conditions imposed upon the crystal unit. This may be expressed in terms of current through or power dissipated in the crystal element

Drive level dependency 
( DLD ) 
Drive level dependency is the effect of changes in drive level conditions upon the resonance resistance or frequency of the crystal unit.
This parameter can be specified by defining the ratio of resistance between two specified drive levels, or max. relative resistance and/or frequency change over specified drive level range. 
Activity dip 

Activity dip is undesirable change in the crystal unit`s load resonance frequency and/or resonance resistance,
caused by the coupling of different modes in a narrow temperature range, at a specified load capacitance and level of drive ( see EN 604447 or IEC 604447 ) 
Frequency dip 

Frequency dip is undesirable perturbation or fluctuation in the crystal frequency occurring
in a narrow temperature range as a deviation of the load resonance frequency from the smooth regular frequency temperature characteristic
described by a polynomial of up to the 5th order. It usually shows an associated resistance change and the effect is usually drive level dependent 
Hysteresis 

Hysteresis is the max. fractional frequency difference between two crystal unit frequency measurements
at reference temperature (25 °C ± 3 °C) before and after passing through full operating temperature range. 