Glossary of terms
Expressed in Hertz, (Hz) the frequency is the oscillator output in number of cycles per second.
Expressed in plus and minus parts per million, (±ppm) the Frequency Stability indicates the maximum allowable deviation from the stated frequency. When specifying, an oscillators' frequency stability is generally given as an ‘overall’ value, taking into account temperature variation, changes in supply voltage, 5 years ageing and drift resulting from shock and vibration.
In general, an oscillator will exhibit different performance parameters dependant upon supply voltage, therefore when performance parameters are critical be sure to state required power supply voltage.
Operating Temperature Range
The Operating Temperature Range is that temperature range over which the specified tolerance and performance parameters apply. Oscillators may often be operated without harm beyond the specified operating temperature range, but the stated specification will not necessarily apply for oscillators so used.
Storage Temperature Range
The Storage Temperature Range indicates the maximum and minimum values of temperature to which an oscillator can be subjected in the non-operational state. Exposure to temperatures outside this range may result in damage.
The Output Load parameter states the types and maximum values of loads that may be connected to an oscillator unit.
Symmetry (Duty Cycle)
Oscillator symmetry refers to the ratio between the time taken for a full cycle and that taken for a half cycle. For TTL output level oscillators these values are measured at +1.4 Volt, and at ½ VDD level for CMOS, HCMOS and Universal oscillator outputs.
The Rise Time value indicates the time taken for the output waveform to change from low voltage level to high voltage level.
The Fall Time value indicates the time taken for the output waveform to change from high voltage level to low voltage level.
Start-up Time is the time taken for an oscillator waveform to stabilise within specification after power is applied.
An oscillator with a Tri-State function allows the oscillator output to be switched on or off by means of simple logic control. The output pin of the oscillator is either at nominal frequency or at a high impedance state dependent upon the logic level on the Output Enable (OE) pin. Note that when an oscillator with enable/disable funtion implemented is in 'disable' (high impedance) mode, the internal oscillator circuit is still running, therefore power saving attributes are somewhat moderate in this mode.
An oscillator with 'Standby' function implemented, like the enable/disable function, allows the oscillator output to be switched on or off by a simple logic control circuit. However, in the case of the standby mode the oscillator powers down. This provides useful a energy saving device, particularly suitable for battery powered equipment. However, be aware that while 'standby' gives power saving over and above that of 'enable/disable', the 'standby' function implementation necessitates that the oscillator is subject to'start-up' time whenever the output is switched.
Voltage Controlled Crystal Oscillator (VCXO)
A Voltage Controlled Crystal Oscillator has its output frequency varied by means of an external control voltage. The most common application for VCXOs are in phase-locked loops, although other applications such as frequency shift keying in data transfer also require this function.
Temperature Compensated Crystal Oscillators (TCXO)
Temperature Compensated Crystal Oscillators have a highly stable frequency output over a wide operating temperature range. High stability is achieved by utilising a compensation network internally derived from measured frequency deviations during manufacture.
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