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Fig.7 Maximum driving current vs. Vibration mode Drive
level
Fig.7 shows the mechanical oscillation modes of a crystal
unit.
But without the limitation of the mechanical vibrations of a
crystal unit to some extent, the oscillation frequency stability
deteriorates or the vibrations exceeding the limit of elasticity
of a crystal wafer may cause it to be broken. Therefore, it
is necessary to limit the under limit of the drive level.
Due to the fact that the mechanical displacement of a crystal
unit whose frequency range is lower and whose vibration mode
is thickness shear or flexure mode is great, special care
is required not to break the crystal wafer.
Fig.7 shows the maximum drive current for each mode as a standard
for design.
Pullability
The pullability of a crystal to a crystal operating in the parallel
mode and is a measure of the frequency change as a function
of load capacitance. Pullability is important to the
circuit
designer who wishes to achieve several various values of load
capacitance. Aging
Quartz crystal aging applies to the cumulative change in frequency
which results in a permanent change in operating frequency
of the crystal unit. The rate of change of frequency is fastest
during the first forty-five days of operation.
Many interrelated factors are involved in aging, some of the
most common being: internal contamination, excessive drive level,
surface change of the crystal, various thermal effects, wire
fatigue and frictional wear. Proper circuit design incorporating
low operating ambient, minimum drive level, and static pre-aging
will greatly reduce all but the most severe aging problems.
Negative resistance(-R)
The negative resistance, also refer to as the degree of
oscillation allowance that can be used for judging the
quality of the circuit side oscillation motivation. The use
of a circuit which an insufficient negative resistance may
lead to such an unexpected trouble as the quartz crystal
unit failing to initiate oscillation even when power has
been switched on(Fig.8.).
Fig.8 Negative resistance
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HC-49S |
UM-1 |
SMD Crystal 5032 |
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SMD Crystal 2520 |
Crystal Oscillator Through Hole |
SMD TCXO |
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TCXO Through Hole |
SMD VCXO |
Crystal Filter 49T holder |
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ZTA Ceramic Resonator |
ZTB Ceramic Resonator |
Ceramic Filter |
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China-xtal Co., Limited.
ADD:10HO,UNIT 3,RM 601,BAISHENG HUAYUAN,4HO,ZHANGHUAN RD,
KEYUAN TOWN, ZHANGDIAN, ZIBO, SHANDONG, CHINA
Tel: 86 18678126086 Wechat: +86
18678126086
E-mail:
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