ZL30110
Data Sheet
5.2.2 Crystal Oscillator
Alternatively, a Crystal Oscillator may be used. The accuracy of a crystal oscillator depends on the crystal tolerance
as well as the load capacitance tolerance. Typically, for a 25 MHz crystal specified with a 32 pF load capacitance,
each 1 pF change in load capacitance contributes approximately 9 ppm to the frequency deviation. Consequently,
capacitor tolerances and stray capacitances have a major effect on the accuracy of the oscillator frequency.
The crystal should be a fundamental mode type - not an overtone. The fundamental mode crystal permits a simpler
oscillator circuit with no additional filter components and is less likely to generate spurious responses. A typical
crystal oscillator specification is shown in Table 2.
.
1
2
3
4
5
6
Frequency
Tolerance
Oscillation mode
Resonance mode
Load capacitance
Maximum series resistance
25 MHz
as required (better than +/-50ppm)
fundamental
parallel
as required
50 Ω
Table 2 - Crystal Oscillator Specification
13
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