zl30102 Zarlink Semiconductor, zl30102 Datasheet - Page 26

• Manufacturer Part Number: zl30102
• Description: T1/e1 Stratum 4/4e Redundant System Clock Synchronizer For Ds1/e1 And H.110
• Manufacturer: Zarlink Semiconductor

4.6
In general, clock redundancy implies that the redundant timing card DPLL tracks the output clock and/or frame
pulse of the active timing card DPLL. In case that the active timing card fails, the devices that use the active clock
and/or frame pulse must be able to switch to the redundant clock and/or frame pulse without experiencing
disruptions. Therefore the redundant signals must closely track the active signals. The ZL30102 supports this kind
of clock redundancy in various ways;
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•
•
Lock only to the active clock. The ZL30102 uses the 922 Hz loop filter bandwidth to closely track the active
clock, even in the presence of jitter on the active clock. However the active and redundant frame pulse may
not be aligned.
Lock to the active frame pulse. Both the redundant clock and frame pulse will be aligned with the active clock
and frame pulse. However the ZL30102 loop filter bandwidth is limited to 58 Hz for an 8 kHz frame pulse.
Therefore the redundant clock and frame pulse will not track the active frame pulse as closely in the
presence of jitter on the active frame pulse as with a 922 Hz loop filter bandwidth.
Lock to both the active clock and associated frame pulse. The ZL30102 uses the 922 Hz loop filter
bandwidth and thereby track the active clock and frame pulse in the presence of jitter on the active signals. It
will also align the redundant frame pulse with the active frame pulse.
Clock Redundancy Support
REF0
REF_OOR0
(internal signal)
REF_FAIL0
HOLDOVER
REF_SEL
LOCK
Note: This scenario is based on REF1 remaining good throughout the duration.
LOCK pin behaviour depends on phase and frequency offset of REF1.
Figure 16 - Automatic Reference Switching - Out-of-Range Reference Failure
Frequency Precision failure
10 to 20 s
REF0
REF1
Zarlink Semiconductor Inc.
ZL30102
26
Lock Time
Data Sheet