ACS8530 Semtech Corporation, ACS8530 Datasheet - Page 25

• Manufacturer Part Number: ACS8530
• Description: Synchronous Equipment Timing Source For Stratum 2/3E/3 Systems
• Manufacturer: Semtech Corporation

Jitter and Wander Transfer
The ACS8530 has a programmable jitter and wander
transfer characteristic. This is set by the DPLL bandwidth.
The -3 dB jitter transfer attenuation point can be set in the
range from 0.5 mHz to 70 Hz in 18 steps. The wander and
jitter transfer characteristic is shown in Figure 8. Wander
on the local oscillator clock will not have a significant
effect on the output clock whilst in Locked mode, provided
that the DPLL bandwidth is set high enough so that the
DPLL can compensate quickly enough for any frequency
changes in the crystal.
In Free-run or Holdover mode wander on the crystal is
more significant. Variation in crystal temperature or
supply voltage both cause drifts in operating frequency,
as does ageing. These effects must be limited by careful
selection of a suitable component for the local oscillator,
as specified in the section See Local Oscillator Clock.
Phase Build-out
Phase Build-out (PBO) is the function to minimize phase
transients on the output SEC clock during input reference
switching. If the currently selected input reference clock
source is lost (due to a short interruption, out of frequency
detection, or complete loss of reference) the second, next
Figure 8 TO DPLL Wander and Jitter Measured Transfer Characteristics (Jitter = 0.2 UI pk-pk)
Revision 3.01/October 2003 © Semtech Corp.
ADVANCED COMMUNICATIONS
FINAL
Page 25
highest priority reference source will be selected, and a
PBO event triggered.
ITU-T G.813
term phase transient response, resulting from a switch
from one clock source to another, with Holdover mode
entered in between, should be a maximum of 1 µs over a
15 second interval. The maximum phase transient or
jump should be less than 120 ns at a rate of change of
less than 7.5 ppm and the Holdover performance should
be better than 0.05 ppm. The ACS8530 performance is
well within this requirement. The typical phase
disturbance on clock reference source switching will be
less than 5 ns on the ACS8530.The PBO requirement, as
specified in Telcordia GR-1244-CORE
that a phase transient of greater than 3.5 µs occurring in
less than 0.1 seconds should be absorbed for Stratum 3E
level clocks. The ACS8530 can be configured to trigger a
PBO event on an input phase transient of between 1 and
3.5 µs, programmable, via Reg. 76.
The PBO operation can be set to operate automatically or
it can operate under external control. For example an
input phase jump of > 1 to 3.5 µs could be absorbed
automatically or just flagged by the device with an
interrupt raised, the external processor can then decide
when and whether to perform a PBO event to absorb the
phase disturbance. The monitoring block for detecting
[11]
states that the maximum allowable short-
ACS8530 SETS
[19]
, Section 5.7, is
DATASHEET
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