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TECHNICAL TERMS


Offset Frequency


The frequency difference, positive or negative, (expressed in Hz) which should be added to the nominal frequency when setting the oscillator at the specified temperature (usually 25°C). The purpose is to minimize the frequency deviation over the entire operating temperature range. Each oscillator will have it's own offset frequency marked on the case. In the following example Fig 1., the dotted line shows that if the oscillator is set to nominal frequency at 25°C, the frequency deviates from -1.7 ppm to +0.3 ppm over the temperature range. By setting the frequency at 25°C to the specified offset frequency, the overall frequency deviation is reduced to ±1.0 ppm.



Frequency stability

Specified a stability vs. temperature range, for example ±1 ppm over -40°C to 85°C, this means a total peak deviation for 2 ppm over the temperature range, not referenced to the frequency at any specific temperature. If a reference, such as room temperature, is desired with a maximum allowed deviation of ±1 ppm from that reference, the specification should clearly state ±1 ppm over -40°C to 85°C referenced to the frequency @25°C. The oscillator frequency is often deliberately offset a room temperature to minimize the largest deviation from nominal frequency over the whole temperature range. Furthermore, it should be noted that the frequency vs. Temperature characteristics is not linear, perturbations in the crystal characteristics (activity dips) make it virtually impossible to guarantee exceptional stability on a per degree basis in TCXOs.


Frequency adjustment range

This range indicates the width of frequency that can be adjusted by a trimmer built in the oscillator.



Thermal hysteresis

If the frequency of a TCXO is measured at one temperature and if this temperature is changed and them returned to the original temperature and the frequency is measured again, the two frequencies will not be exactly the same. The difference between the two frequencies is called "thermally induced hysteresis". The phenomena has two components, static and dynamic. The static component is present even if the unit is allowed to stabilize at temperature for a long time. whereas the dynamic effect is a function of the rate of change of temperature and is a transient effect. The effect on a typical TCXO frequency / temperature characteristic is shown beside. Typical values are less than 0.2ppm.



Ageing

Ageing is the slow change of the oscillator frequency with time, The primary causes of mass transfer and stress relaxation mechanisms in the crystal unit can be reduced:

·by maximizing the ratio of quartz resonator mass to contamination mass,
·by minimizing the resonator frequency,
·and by carefully design and process the resonators.

SOOJUNG can offer due to its expertise very high performances.

In a well behaved oscillator the ageing rate will tend to decrease with time.



Output type and level

The TCXO product family uses the same definitions given in the Crystal Oscillator section. However, when using a direct compensation method, the TCXO offers a clipped sine wave output as a standard. This output typically draws less than 2 mA and is ideal for battery powered equipment and low cost applications.


Temperature Compensated Crystal Oscillator (TCXO)
MODEL
TC4000
TC1000
PACKAGE
1”x1”
FREQUENCY RANGE
500 KHz to 100.0 MHz
FREQUENCY STABILITY
Available
±1ppm ~ ±10ppm
±1ppm ~ ±5ppm
TEMPERATURE
RANGE
Available
-40℃ to 85℃
Frequency Adjust
±1ppm Min.
INPUT
Voltage
+5.0VDC±10%,+3.3VDC±10%
Current
(Max.)
5~50mA
(depending on Frequency. Consult Factory for critical requirements)
OUTPUT
(SQUAREWAVE)
Symmetry
40~60% @1/2 Vcc
Tr and Tf
(Max.)
15ns
"0" Level
(Max.)
10% Vdd
"1" Level
(Max.)
90% Vdd
LOGIC FAMILY
HCMOS
Aging ±2ppm 1st year,
±1ppm per thereafter (typical)
±1ppm 1st year,
±0.5ppm per thereafter (typical)
  
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