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".

Reference: Thickness shear vibration , frequency versus temperature characteristics

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.

Accumulated jitter

A type of jitter defined in specification. See "jitter".

Reference: Jitter

Ageing Aging

Example of ageing trend

This refers to the amount of change in frequency and other characteristics that occurs over time. Normally refers to the amount of variation over one year. In the case of crystal oscillators, causes of frequency variation include strain due to stress on surfaces during crystal manufacturing processes, strain due to stress that occurs at the mounting point, and changes in the package's internal gases. Crystal units that are fabricated with photolithography processing have less stress-related strain and therefore experience good ageing.

Ageing process Aging process

Generally, this is an operation or process that is performed before shipping a product in order to eliminate products that would otherwise experience early failures. In relation to crystal devices in particular, the frequency variation caused by residual strain of process is eliminated from just-finished products by this process so that the crystal devices on the market will have a more stable frequency.

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.

Anti-reflection coating

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.

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