ZL30111 Data Sheet
13
Zarlink Semiconductor Inc.
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 20 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 Frequency 20 MHz
2 Tolerance as required (better than +/-50ppm)
3 Oscillation mode fundamental
4 Resonance mode parallel
5 Load capacitance as required
6 Maximum series resistance 50 Ω
Table 2 - Crystal Oscillator Specification
