The importance of quartz crystal resonators in electronics results from their extremely high Q, relatively small size and excellent temperature stability.
A quartz crystal resonator uses the piezoelectric properties of quartz. The direct piezoelectric effect refers to the electric polarization of certain materials brought about by the application of mechanical stress.
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Measuring and specifying jitter using a phase noise plot for a crystal oscillator that contains only random jitter sources has several advantages over conventional time domain methods using high-speed digital sampling oscilloscopes (DSO’s).
The jitter performance of the oscillator is often much better than the combined jitter uncertainty of the DSO’s internal sampling oscillator, the DSO’s trigger point uncertainty and some questionable software techniques.
Temperature is an important factor when specifying the stability of crystal oscillators. By compensating for the effects of temperature on the oscillation frequency of the crystal, a TCXO can exhibit up to 100 times better stability over its operating temperature range than a comparable uncompensated oscillator.
Clock oscillators are the most technically simple oscillator IQD offer, the package contains a quartz wafer and also the necessary circuit to make the quartz resonate. Consequently by applying the correct power supply to the device a stable output clock waveform is provided at the output pin. IQD’s clock oscillator part numbers all contain the code SPXO. SPXO is an acronym for Simple Packaged Xtal Oscillator.
Micro Electro Mechanical Systems or MEMS as it is commonly known is the latest technology to be used in the Frequency Products market as an alternative to quartz based devices. MEMS devices use a "silicon-beam" rather than quartz as the frequency control element which provides advantages such as small package size and good environmental performance for shock and vibration.
Oven Controlled Crystal Oscillators offer frequency stabilities even tighter than those offered by a TCXO. The frequency drift of the quartz crystal due to temperature shift is reduced by heating the crystal in an oven and so holding the temperature of the quartz at a fixed point. Traditionally this technology meant physically large devices with heavy power consumptions, however technology is constantly developing and IQD are proud to offer some of the smallest OCXOs in the world. IQD uses the code OCXO to denote our oven controlled quartz crystal oscillator part numbers.
Quartz crystals are the most technically simple product IQD offer, the package contains only a piece of quartz wafer, all the supporting circuitry needed to create the oscillation must be provided by the customer’s circuit. The quartz wafer inside is cut and shaped to give a resonant frequency within the specified limits. IQD’s quartz crystal part numbers all contain the code XTAL.
Temperature Compensated Crystal Oscillators give much tighter frequency stabilities than standard clock oscillators. The frequency over temperature change of the quartz crystal is internally monitored and compensated for using a similar process to that used inside a VCXO. As a result the frequency change seen on the output is significantly reduced. Some temperature compensated voltage controlled crystal oscillators also give a further fine tuning function to allow the customer to make changes to the output frequency while the circuit is active.
Voltage Controlled Crystal Oscillators give a stable clock output waveform which can be changed via an analogue voltage input. The technology makes use of the pullability of the crystal, its change in frequency due to change in load capacitance. The voltage input is used to vary the load capacitance of the crystal circuit within the oscillator, this gives a very controllable change in output frequency which can be used to tune the device to match the exact frequency required while the circuit is active. IQD uses the code VCXO to denote our voltage controlled quartz crystal oscillator part numbers.
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Mobile communications applications require extremely accurate synchronization of the signal frequency throughout the network. Without absolute frequency stability typically within ±0.05 ppm at all points, cut-outs and failed calls will occur. To minimize frequency discrepancies, each timing device within the network is locked to an external reference source, e.g. GPS in the case of CDMA. This imposes two key requirements on each timing device: it must be able to synchronize adequately to the reference clock over its entire lifetime of ten years or more, and it must be able to hold its frequency stable for a period of 24 hours or more in the event of loss of the external reference signal.
Since its introduction the 32.768kHz miniature watch crystal has become the most popular time keeping reference ever. This application note is intended to give some guidance as to the use of quartz crystals in time keeping applications.
In almost all circumstances designers will want to use simple logic gate oscillators for this application for the sake of convenience and cost. The criteria normally applied to this type of design are that it should be accurate, low in cost and low in power consumption. Using a watch crystal and CMOS logic all these criteria can be met.
On occasion IQD receive notification from customers that they have problems receiving goods with a date code beyond a specific time period.
The purpose of this brief is to detail what can happen to a quartz based timing device while stored on the shelf and when this could cause a problem.