zl30108 Zarlink Semiconductor, zl30108 Datasheet - Page 19

• Manufacturer Part Number: zl30108
• Description: Sonet/sdh Network Interface Dpll
• Manufacturer: Zarlink Semiconductor

7.2.2
Alternatively, a Crystal Oscillator may be used. A complete oscillator circuit made up of a crystal, resistor and
capacitors is shown in Figure 11.
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. The crystal
specification is as follows.
Crystal Oscillator
1
2
3
4
5
6
Table 6 - Typical Crystal Oscillator Specification
Frequency
Tolerance
Oscillation Mode
Resonance Mode
Load Capacitance
Maximum Series Resistance
ZL30108
The 100 Ω resistor and the 1 µH inductor may improve
stability and are optional.
Figure 11 - Crystal Oscillator Circuit
OSCi
OSCo
1 MΩ
Zarlink Semiconductor Inc.
ZL30108
100 Ω
19
20 MHz
20 MHz
As required
Fundamental
Parallel
As required
50 Ω
1 µH
Data Sheet