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Crystal and frequency control glossary

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Temperature vs. Frequency characteristic of a crystal resonator.


Abbreviation for transmit/receive.

Tape and reel

Refers to the packaging method used to accommodate automated pick-and-place equipment.


Temperature compensated/voltage controlled crystal oscillator is a VCXO coupled to a temperature compensation circuit allowing a variable frequency output that is also temperature compensated often used for frequency control in tactical radios, telecom timing modules (Stratum 3 Type), wireless systems reference oscillator, phase lock loop (PLL) Circuits in telecom, timing recovery, wireless base station channel or timing reference, and fiber optic timing references.


Temperature-compensated crystal oscillator often used often used for frequency control in tactical radios, telecom timing modules (Stratum 3 Type), wireless systems, and reference oscillators.


Abbreviation for time division duplex.


Any communication process that allows the transmission of information from a sender to a receiver by means of an electromagnetic or lightwave medium.

Telemetry tracking and control (TT&C)

Functions that provide for the monitoring and control of satellites.


The use of telecommunication for automatically indicating or recording measurements at a distance from the measuring instrument.

Temperature range

The minimum and maximum temperature for which the deviation from the nominal frequency will not vary by a given amount.


The terahertz, abbreviated THz, is a unit of electromagnetic (EM) wave frequency equal to one trillion hertz (1012 Hz). The terahertz is used as an indicator of the frequency of infrared (IR), visible, and ultraviolet (UV) radiation. The terahertz is not commonly used in computer and wireless technology.

Termination impedance

The impedance that should be presented to the source and load side of the filter to ensure proper performance.

Test set

A device used to measure the frequency and resistance characteristics of a quartz crystal unit. Often called a crystal impedance meter, it is abbreviated as "C.I.M."


Abbreviation for Trans European Trunked Radio or Terrestrial Trunked Radio is a set of standards developed by the European Telecommunications Standardization Institute (ETSI) that describes a common mobile radio communications infrastructure throughout Europe.

Thru Hole

A conductor used to make electrical and mechanical connection between conductive patterns on opposite sides of a printed circuit board.

Time division multiple access (TDMA)

A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to different users. TDMA is used extensively in satellite systems, local area networks, physical security systems, and combat-net radio systems.

Tolerance and stability

Three main components of frequency control product specifications are:

  1. Calibration tolerance at room temperature (25°C)
  2. Stability over the temperature range
  3. 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).


Device that accepts an input of energy in one form and produces an output of energy in some other form, with a known, fixed relationship between the input and output. One widely used class of transducers consists of devices that produce an electric output signal, e.g., microphones, phonograph cartridges, and photoelectric cells


An active semiconductor device, usually made of silicon or germanium, having three or more electrodes. The three main electrodes used are the emitter, base, and collector.


Transition region

The part of the spectrum between the passband and the stopband.


The sending and receiving of telecommunications messages through appropriate channels.

Transmission control protocol (TCP)

In the Internet Protocol suite, a standard, connection-oriented, full-duplex, host-to-host protocol used over packet-switched computer communications,

Trim effect

In a crystal oscillator, the degradation of frequency-vs.-temperature stability, and marked frequency offset, resulting from frequency adjustment which produces a rotation or distortion, or both, of the inherent frequency-vs.-temperature characteristic.

Trim sensitivity

A measure of the incremental fractional frequency change for an incremental change in the value of load capacitance. Trim sensitivity (S) is expressed in terms of PPM/pF and is calculated with the following equation: where (Ct) is the sum of the shunt capacitance (CO) and the load capacitance (CL).


The ability to adjust the frequency of an oscillator.


The tri-state function allows the oscillator to be isolated from the circuit upon application of a command signal. When this feature is activated, the output of the oscillator is in tri-state mode. The tri-state mode allows the customer to remove the oscillator from their circuit without physically removing it. Useful for tuning, testing or trouble shooting their board.

Tri-state output

An oscillator with this feature allows the output to be placed into a high impedance state. This feature is activated by the application of a logic control voltage to pin 1 of the oscillator.


Abbreviation for transistor-transistor logic.

Turning point

An AT cut crystal has a temperature vs. frequency characteristic that can be represented by a third order polynomial. The turning points are points of zero slope where the slope reverses sign. Usually there is a lower turning point around -4° C and an upper turning point around +55° C. Often ovenized oscillators hold the temperature of the crystal at the upper turning point to obtain maximum temperature stability.

Turning / turnover point - illustration

Turnover temperature

The temperature at which the frequency is at the top of the parabolic curve.


A condition existing within a quartz stone wherein the optic and/or the electric axis suddenly reverses its natural order of polarity. A single piece of quartz material, which contains both left and right handed regions, is said to be "twinned".

Type/Angle of Quartz Cut

The type and angle of a quartz cut affects the crystal device operating parameters, the most significant being frequency stability over temperature. The frequency stability is dependent upon the plane or the angle of the crystal element in relation to the crystalline axes of the crystal. The plane or angle is referred to as the crystal cut. A common type of thickness shear crystal fabricated from Y bar quartz is the AT cut. The frequency stability and operating temperature range required by the customer determine the angle of cut utilized.


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