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Crystal and frequency control glossary

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OCVCXO

Oven controlled/voltage controlled crystal oscillator often used in often used in navigation system clocks, frequency standards, MTI radars, wireless base stations, telecom timing modules, precision test equipment, phase lock loop (PLL) circuits in telecom timing recovery, wireless base station channel or timing reference and fiber optic timing reference.

OCXO

Oven-controlled crystal oscillator often used in navigation system clocks, frequency standards, MTI radars, wireless base stations, telecom timing modules and precision test equipment.

Ohms

A unit of electrical resistance, defined as the resistance in a circuit in which a potential difference of one volt creates a current of one ampere; hence, 1 ohm equals 1 volt/ampere.

Omni-directional antenna

Antenna that radiates equal power in all directions in a horizontal plane.

Operating temperature range

The maximum and minimum temperatures that the crystal device can be exposed to during oscillation. Temperature range over which the crystal's characteristics are guaranteed. See storage temperature range.

Original Equipment Manufacturer (OEM)

Maker of equipment that is marketed by another vendor, usually under the name of the reseller. The OEM may only manufacture certain components, or complete computers, which are then often configured with software, and/or other hardware by the reseller.

Oscillation mode

A quartz crystal is designed to vibrate on its fundamental frequency or one of its overtones. This becomes important between the 24 MHz to 40 MHz range. Crystals in that frequency range may be made as either a high fundamental or a low 3rd overtone. Fundamental mode crystals at these frequencies become more expensive, because the quartz blank is extremely thin, difficult to handle, and subject to a higher rate of breakage in processing. If you are able to use the 3rd overtone crystal instead of the fundamental, your cost savings may be significant. As the frequency range is extended, the oscillation mode of the crystal changes to other overtones. Crystals in the range of 60-110 MHz are generally 5th overtones, while crystals in the range of 110-175 MHz generally are 7th overtones.

Oscillator

An electronic circuit that produces an output signal of a specific frequency. An oscillator generally consists of an amplifier having part of its output returned to the input by means of a feedback loop; the necessary and sufficient condition for oscillation is that the signal, in passing from input to output and back to input via the feedback loop, arrive at the input with no change in amplitude or phase. If this condition is met for only a single frequency, the output is a pure sine wave; if it is met for more than one frequency, the output is a complex wave. Some oscillators are designed to operate under certain conditions so that the output is a square wave, a triangular wave, or a pulse. In some cases, a very stable mechanical oscillator, such as a specially prepared quartz crystal, may be coupled to an electronic oscillator to enhance its frequency stability.

Output

The output of a hybrid crystal clock oscillator is a highly stable reference signal.

Output enable function

The function to change the output signal.

Output frequency

The frequency signal generated by an oscillator circuit.

Output load

The power-consuming element connected to the output of a circuit.

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.

Output wave shape

Graph of the output frequency vs. time. This can be a square, sine, or trapezoid.

Ovenized crystals

An ovenized crystal is any crystal made to operate at a temperature above the anticipated ambient temperature (typically +50°C to +110°C) in order to eliminate changes in frequency due to the change in temperature. See precision crystals.

Overshoot/Undershoot

This effect is commonly called ringing. The output voltage can exceed the steady state plateau of either the logic "0" state or the logic "1" state for a period of time. This ringing will decrease in amplitude until the steady state plateau is reached. An unmatched impedance load presented to the oscillator output causes the ringing. It becomes more pronounced as the rise/fall times decrease and the output frequency increases. Proper output loading and good R.F./Microwave transmission line techniques must be used to prevent ringing on the waveform.

Overtone order

The numbers allotted to the successive overtones of a given mode of vibration from the integral numbers commencing with the fundamental as unity.

Overtones

Crystals can vibrate at many harmonic frequencies. Frequencies, which are multiples of the lowest or fundamental frequency, are referred to as overtone frequencies. The overtones are usually referred to by the number of the overtone. An odd numbered multiple of the fundamental frequency.

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