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Glossary of Terms about VCXO, TCXO, VCTCXO, TCVCXO, Crystal Oscillator
Crystal
Any crystalline material is composed of a periodic array of atoms of molecules.
The nature of the atomic bonds and structure of the periodic array will determine the properties and
physical constants of the crystal.
A crystalline material can be either polycrystalline (most ceramics) or single crystal (quartz).
Crystal Oscillator
A timing device that consists of a crystal and an oscillator circuit, providing an output waveform
at a specific reference frequency.
Duty Cycle(or Symmetry)
The measure of output waveform uniformity. The ratio of full and half cycles. For CMOS loading duty is
rated at 1/2 Vdd, and for TTL loading at 1.4 VDC.
Frequency Aging
Amount of frequency drift when operated under the specified conditions for a specified length of time.
Frequency Stability
The amount of frequency deviation from center frequency associated with a set of operation conditions, expressed in parts per million (PPM). This condition includes: Operating Temperature Range,
Supply Voltage and Output Load.
Frequency Tolerance
The permissible deviation from the nominal frequency at reference temperature (usually 25℃).
Logic Levels
Defined as the Output Voltage Logic High or "Logic 1" and the Output voltage Logic Low or "Logic 0"
Voltage "0" level (max.): +0.4 VDC TTL, +0.5 VDC HCMOS for Vdd = 5 VDC (Vdd : Supply Voltage).
Voltage "1" level (min. ): +2.4 VDC TTL, +4.5 VDC HCMOS for Vdd = 5 VDC
Nominal Frequency(Center Frequency)
The specified reference frequency of the oscillator, typically specified in MHz and KHz.
OCXO(Oven Controlled Crystal Oscillator)
A kind of oscillator that uses an oven to stabilize the frequency variation.
Operating Temperature Range
Temperature range where specification characteristics fulfilled.
This needs to be specified carefully as it impacts cost.
Output Load
The capacity of oscillator to drive other devices or the fan out. TTL devices are specified in number of
gates that can be driven. CMOS output are specified in PF.
Pull Range of VCXO
The frequency range from the nominal frequency over which the output Frequency of a VCXO under
reference conditions can be changed by means of an external DC control voltage, expressed in PPM.
Rise/Fall Time
The Rise Time is defined as the transition time from an output logic low to an output logic high. The Fall
Time is defined as the transition time from an output logic high to an output logic low.
Sine Wave
Also known as sinusoidal wave. Clipped Sine Wave is a sine wave that the upper and lower part is cut
off sliced or limited.
Start-Up Time
The specific time from oscillator power-up to the time the oscillator reaches steady oscillation.
Storage Temperature Range
Temperature range where specification characteristics can be maintained for discharged state (No input of voltage, current or power). Exposure to temperatures over this level may result in degradation or
destruction.
Supply Current(Input Current)
The amount of current consumption by an oscillator from the power supply, typically specified
in miliampere.
Supply Voltage(Input Voltage)
The DC input voltage necessary for oscillator operation. Currently 5 VDC is commonly used,
with 3.3 VDC being used in portable equipment.
TCXO(Temperature Compensated Crystal Oscillator)
A kind of oscillator that adjusts the frequency for temperature variation and commonly has an outside
adjustment for periodic calibration of frequency. This is to compensate for the aging of the crystal
over time.
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.
VCXO(Voltage Controlled Crystal Oscillator)
A kind of oscillator that has the output frequency change with a voltage change at a control pin of the
oscillator.
VCXO Linearity
Defined as the % variation in output frequency versus control voltage from a best fit straight line.
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