ZL30101_06 Datasheet, PDF (24/35 Pages) Zarlink Semiconductor Inc – T1/E1 Stratum 3 System Synchronizer

ZL30101
Data Sheet
The output clock should be connected directly (not AC coupled) to the OSCi input of the ZL30101, and the OSCo
output should be left open as shown in Figure 11.
ZL30101
OSCi
+3.3 V
+3.3 V
20 MHz OUT
GND
0.1 µF
OSCo
No Connection
Figure 11 - Clock Oscillator Circuit
6.2.2 Crystal Oscillator
Alternatively, a crystal oscillator may be used. A complete oscillator circuit made up of a crystal, resistor and
capacitors is shown in Figure 12. The Telcordia GR1244-CORE Stratum 3 requirements for holdover stability and
freerun accuracy may not be met with this crystal oscillator circuit.
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 and circuit is shown in Table 6 and Figure 12 respectively.
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Zarlink Semiconductor Inc.