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The minimum information needed is the Holder or Package, Frequency, and Correlation (series resonant, or load capacitance if parallel resonant).All other specifications will be per our standard specifications for the indicated holder.All specifications that differ from our standard specifications must also be supplied when ordered.
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All quartz crystal resonators have a series resonant frequency (fs, frequency of lowest impedance). At this frequency, the crystal appears resistive in the circuit.Crystals can be "pulled" from this series frequency by adding reactance (capacitance) in series with the crystal. When operated in combination with an external load capacitance (CL) the crystal oscillates in a frequency range slightly above its series resonant frequency. This is the parallel (load resonant) frequency.When ordering a parallel crystal, always specify the nominal parallel resonant frequency and the amount of load capacitance in picoFarads (pF).Alternatively, a standard value of CL (such as 20pF) can be ordered; the capacitor values are then calculated to match the crystal CL.Note that a series type will oscillate in a parallel oscillator, and vice versa. The observable difference is a frequency offset of less than + 1000ppm (0.1 %) from the nominal frequency.
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Use this formula to approximate the value of capacitors needed:CL=((C1 x C2) / (C1 + C2)) + C strayC stray is the stray capacitance in the circuit, typically 2-5pF.If the oscillation frequency is high, the capacitor values should be increased to lower the frequency. If the frequency is low, the capacitor values should be decreased, thus raising the oscillation frequency.When CL =20pF, C1 and C2 will be approximately 27-33pF each, depending on the amount of stray capacitance.
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Yes to both, but a crystal unit manufactured as a series resonant crystal will operate at a frequency higher than expected if used in a parallel resonant circuit.A crystal unit manufactured as a parallel resonant crystal will operate at a frequency lower than expected if used in a series resonant circuit.
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Yes, this industrial temperature range (-40 ºC to + 85 ºC ) is optional on most crystals. Depending on the crystal package, temperature ranges of up to -55 ºC to +105 ºC may be available.Contact ARGO's engineering department to discuss your specific requirements.
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We do not recommend that you operate a crystal outside of its specified temp 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.
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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.
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Consult with ARGO Engineering as early in your design process as possible.Remember that at some frequency which varies from manufacturer to manufacturer, the use of an overtone is mandated.Remember also that within a certain frequency range, the fundamental frequency and the overtone frequencies may overlap. In such a case, your selection may be determined by your application.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 your crystal vendor as early in the design process as possible.
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Exceeding the maximum drive level (power dissipation) of a crystal can lead to an increased rate of aging, Drive Level Dependency (DLD) problems, increased number and intensity of activity dips that can stop oscillation and, at very high drive levels, breakage of the crystal blank.
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Drive Level - HC49U crystals are typically rated 1.0mW max, while the HC49S and most SMD crystals are rated at only 0.5mW or 0.1mW maximum. See question 11 for more information on exceeding the maximum drive level of a crystal.Pullability -some applications require tuning the frequency of the oscillator, either by mechanically or electrically changing the value of load capacitance.The HC49S and surface mount crystals have less pullability than the HC49U. It is important to verify whether the HC49S or the surface mount crystal will have sufficient pull range for the application. Generally, an HC49S has one half the pullability as an HC49U.ESR - The Equivalent Series Resistance (ESR) is generally higher with the HC49S and surface mount crystals, and can cause a problem if the oscillator circuit does not have sufficient loop gain.
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I would not make the change without a thorough investigation. Some of the SMD (surface mount device) crystal units are comparable to conventional crystal units, others are not.In general, SMD's have higher resistance, differing values of shunt and motional capacitance, and are more sensitive to drive level. The pullability characteristics of these devices may differ significantly from a conventional crystal.I would recommend a fairly exhaustive qualification sequence before making the switch.
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"Activity dips" are sudden increases in the resistance of a crystal that may perturb the frequency.
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Spurs are frequency responses higher in frequency than the main response but not as high in frequency as the next regular overtone.The word "spur" is used as an abbreviation of the word "spurious" but the frequencies described by either of the two are not "spurious" at all. They are regularly occurring natural frequency responses, the amplitude of which is subject to some degree of control through crystal unit design.
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Another good question and another unequivocal "maybe.?? Usually, spurs are not a problem with crystal units intended for use in oscillator applications.
Crystal units intended for use as filters are another matter. The control and suppression of spurious responses in filter crystals is critical. If you must specify some value of spurious response suppression, PLEASE specify the test fixture to be used (IEC 60444 Pi Network is a good choice for oscillator crystals) and a reasonable frequency range over which the test is to be conducted.
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Pullability is the amount by which the frequency of a crystal will change when the circuit condition is switched from series to parallel resonance.
Pullability is also used to describe the frequency change that occurs when the load capacitance is switched from one value to another.
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The HC49U crystal utilizes a circular AT cut crystal blank. Due to their small size, most surface mount crystals use a rectangular AT strip cut crystal blank. ("Strip" refers to the rectangular shape of the blank.)
While both are AT cut blanks, several differences exist due to their different geometry. In general, given the same frequency and overtone, an AT strip cut will have a lower Shunt Capacitance (CO) and Motional Capacitance (C1) than the AT cut. Because pullability is a function of the capacitance ratio CO/C1, AT strip crystals have less pullability.
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Quartz crystals are not linear devices and they do not behave in a linear way. But, it is theoretically possible to achieve symmetrical pulling.
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Trim sensitivity is the amount by which the frequency of a crystal oscillating with a specific value of load capacitance will vary if that load capacitance is varied slightly about its nominal value.
Please see the Technical Note on Frequency Pullability for a more complete explanation.
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A good question and the answer is an unequivocal "maybe.??
If the crystal unit in question has a significant value of trim sensitivity and if a fairly stringent value of frequency tolerance is imposed, it is likely that the manufacturers tolerance on the load capacitors in use will result in actual values of load capacitance that will "pull" the crystal frequency beyond the desired tolerance.
As an example, an 18.432000 MHz crystal might easily have a trim sensitivity value at 20.0pF of +/20.0ppm/pF.
Let us suppose that a frequency tolerance of +/-10ppm is specified. If the load capacitor has a tolerance of +/-10%, or 2.0pF, it is entirely possible that an acceptable load capacitor will pull the frequency by +/-40ppm.
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The shunt capacitance (Co) is the capacitance resulting from the presence of the electrodes on the quartz plate plus the capacitance inherent in the crystal holder.
The motional capacitance is a parameter of the equivalent circuit. It is used as a means of describing the elasticity or "stiffness" of the quartz resonator.
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The differences are in size, shape and some performance characteristics. AT-cut crystal blanks are circular, and AT-strip cut crystal blanks are rectangular. Both types are AT-cuts, but several differences in performance characteristics exist because of the different geometry of the blanks.
In general, given the same frequency and overtone, the AT strip will have a lower value of Shunt Capacitance (Co) and Motional Capacitance (C1). It will also have a higher value of Effective Series Resistance (ESR) and Motional Inductance (L1). Because pullability is a function of Co and C1, AT strip cut crystals have less pullability than ocular AT cut crystals.
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使用晶體振盪前必須考慮之事項…在開始設計使用晶體振盪器前，以下問題請詳加考慮，因為這些問題將是晶體決定規格之關鍵。1. 線路上需要什麼頻率?2. 常溫下(25℃)頻率可容許多少誤差?3. 操作溫度範圍是多少?4. 在操作溫度範圍內可允許多少偏移誤差量?5. 晶體振盪在線路上是並聯或串聯振盪?6. 如是並聯振盪，負載電容是多少?7. 頻率推動變化量(pull ability)是否很重要?8. 您所需之晶體振盪器大小尺寸及包裝為何?
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A Piezoelectric Quartz Crystal Unit is an electronic component used in frequency control, filtering, and clocking applications.It consists of a quartz resonator equipped with electrodes, housed in a hermetically sealed package that provides some means of connection to a circuit.Piezoelectric Quartz Crystal Units are usually called "crystals."
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Load capacitance is defined as being the total capacitance present in an oscillator circuit as measured or calculated across the pins of the crystal socket. Load capacitance has the effect of increasing the frequency of a crystal unit.
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