Glossary - alphabet order - "A"
AT crystal unit, AT cut crystal unit
This is a crystal unit that has a crystal chip that was cut at the "AT cut" angle from the quartz crystal crystallographic axis. This is one of the most widely used types of crystal units, which covers the Megahertz (MHz) band. Since this type of unit has frequency - temperature characteristics for cubic functions with inflection point near room temperature, it has excellent temperature characteristics. For description of vibration modes, see "Thickness shear vibration".
Absolute maximum rating
Absolute maximum ratings provide for items and ranges of values to prevent damage of the crystal device or critical changes in characteristics.
APR (Absolute Pull Range)
The range of frequencies that can be controlled from the nominal frequency value. In other words, APR = Frequency Control Range - Frequency Deviation (Frequency Tolerance).
A type of jitter defined in specification. See "jitter".
Allowance of oscillation
This allowance is expressed as a ratio between a crystal oscillation circuit's negative resistance and a crystal unit's CI value. It is a parameter that indicates the quality of the oscillation characteristics.
It is a thin film deposited on the surface of an optical component by evaporation to reduce surface reflections. One typical example is a single-layer made of magnesium fluoride (MgF2.) and there are also multi-layered films that further reduce reflectivity.
4 to 8 % of incident light is reflected on a glass.