Glossary of Terms
Frequency: The rate at which a periodic phenomenon occurs over time. This is expressed
in kilohertz (kHz) for frequencies less than 1.0MHz, and Megahertz (MHz) for frequencies of
1.0MHz and over.
Tolerance and Stability: Three main components of frequency control product
specifications are:
- Calibration Tolerance at room temperature (25°C)
- Stability over the temperature range
- Aging
Calibration at room temperature is a measurement of the accuracy of the frequency at
+25°C. Crystal frequencies are adjusted within the stated tolerance by changing the
mass of the electrode. Lower frequencies are less sensitive to mass change and are therefore
easier to hold tighter tolerances. Tolerance and stability are measured in parts per million
(ppm).
Load Capacitance: Load Capacitance is the dynamic Capacitance of the total circuit
measured or computed across the crystal terminals.
Equivalent Series Resistance: 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 unit frequency.
Drive Level: Operating drive level is the power dissipated internally in the
crystal blank.
Aging: Aging is a general term used to describe the gradual deterioration of
the operating characteristics of a crystal unit over time.
Spurious Modes: All quartz crystals have multiple vibrational modes. Spurious
modes refer to those that are unwanted and can be a problem if the response is as strong as
the main mode.
Output Voltage Levels: In digital logic, voltage levels are referred to in terms
of logic "0" and logic "1". These levels vary depending on the type of output logic required
for the application.
Symmetry: Symmetry is defined as the ratio of amount of time the voltage is in
the logic "1" state compared to the time in the logic "0" state. The measurements are taken
at the 50% points of the voltage transition between the two logic states.
|
