Quartz Crystal FAQs
To get answers to the most general questions about our quartz crystals, please select one of the links below:
A quartz crystal is a thin slice of quartz placed between two electrodes, housed in a hermetically sealed package that provides a means of connection to a circuit. An alternating voltage applied to these electrodes causes the quartz to vibrate, or oscillate, at a particular frequency. The frequency is a function of the thickness of the crystal. By carefully polishing or lapping a crystal, it can be made to oscillate at any frequency.
Quartz crystals are basically used for stabilizing radio frequencies. Quartz crystal applications range from security cameras in airplane cargo bays to radio transmitters for tracking salmon and whales from the meters in the gas pump at your gas station to the utility meters attached to your home from your cell phone to satellite communications from WAN/LAN equipment to test instruments on the bench to instruments at the bottom of oil wells.
ICM believes quartz crystals will continue to be used as highly accurate timing and frequency control devices in increasing applications.
Crystal blanks are cut at different orientations from the bar of quartz in order to realize specific desirable characteristics. The cut is determined by the specifications of the crystal.
Aging is the change in frequency of a crystal over time. Aging can be in the positive or negative direction. Aging effect contributes to the overall frequency drift of the oscillator that the crystal is used in.
Both cuts are actually AT-cuts, but several differences in performance characteristics exist because of the different geometric configurations of the crystal blanks. The differences are in size, shape and some performance characteristics. In general, given the same frequency and overtone, the AT-strip will have less pullability, higher resistance, and wider frequency variation over temperature. The AT-cut crystal is a much more precision device.
Both AT-cuts and BT-cuts are singularly rotated "Y"-axis cuts. The BT is cut at an angle approximately opposite that of the AT. BT-cut blanks are thicker and have a parabolic frequency versus temperature curve versus the AT, which has an "S" frequency versus temperature curve.
The piezoelectric effect means that a crystal mechanically distorts if electricity is applied and a crystal generates electricity if a mechanical force is applied. It is the voltage produced between surfaces of a solid dielectric (non-conducting substance) when a mechanical stress is applied to it.
A fundamental mode crystal oscillates at a frequency determined by the physical dimensions of the quartz plate. The fundamental frequency is the lowest frequency at which a given resonator plate will oscillate. Overtones are frequencies that are approximately odd integer multiples of the fundamental.
Consult with the ICM engineering staff as early in your design process as possible. At some frequency, which varies from manufacturer to manufacturer, the use of an overtone is mandated. If you are developing an oscillator that is to be extremely stable and accurate with a high "Q" value you probably need an overtone. If you require a lot of pullability, you probably need a fundamental. Again, consult with ICM engineers as early in the design process as possible.
I have an existing crystal design that uses an HC-49/U package. What should I consider if I change to an SMD crystal?
ICM recommends that you consider crystal drive level, pullability and ESR as discussed below:
ICM recommends that you do not operate a crystal outside of its specified temperature range. The most notable change will be a greater frequency drift due to the increased temperature extremes. Another and more serious problem that can occur is activity dips. Activity dips can cause the oscillator to stop oscillating at a specific temperature.
The minimum information needed by ICM to order a crystal is the Holder or Package, Frequency, Calibration tolerance, Temperature tolerance, and the Load (series or parallel resonant).
If you have more questions about our crystals and crystal products, call us today at 1-800-725-1426, fill out our contact form, email us at email@example.com or request an online quote for International Crystal Manufacturing radio frequency control devices – quartz crystals, oscillators, QCM crystals, filters, TCXOs / VCTCXOs, and precision crystals.
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