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ACS8520A

Synchronous Equipment Timing Source for Stratum 3/4E/4 and SMC Systems

Semtech Corporation 

ACS8520A SETS

ADVANCED COMMS & SENSING

FINAL

DATASHEET

Such integrators are used when alarms have to be

There is one Leaky Bucket Accumulator per input channel.

triggered either by fairly regular defect events, which

Each Leaky Bucket can select from four Configurations

occur sufficiently close together, or by defect events

(Leaky Bucket Configuration 0 to 3). Each Leaky Bucket

which occur in bursts. Events which are sufficiently

Configuration is programmable for size, alarm set and

spread out should not trigger the alarm. By adjusting the reset thresholds, and decay rate.

alarm setting threshold, the point at which the alarm is

triggered can be controlled. The point at which the alarm

is cleared depends upon the decay rate and the alarm

clearing threshold.

Each source is monitored over a 128 ms period. If, within

a 128 ms period, an irregularity occurs that is not deemed

to be due to allowable jitter/wander, then the

Accumulator is incremented.

On the alarm setting side, if several events occur close

together, each event adds to the amplitude and the alarm

will be triggered quickly; if events occur a little more

spread out, but still sufficiently close together to

overcome the decay, the alarm will be triggered

eventually. If events occur at a rate which is not sufficient

to overcome the decay, the alarm will not be triggered. On

the alarm clearing side, if no defect events occur for a

sufficient time, the amplitude will decay gradually and the

alarm will be cleared when the amplitude falls below the

The Accumulator will continue to increment up to the

point that it reaches the programmed Bucket size. The “fill

rate” of the Leaky Bucket is, therefore, 8 units/second.

The “leak rate” of the Leaky Bucket is programmable to

be in multiples of the fill rate (x 1, x 0.5, x 0.25 and

x 0.125) to give a programmable leak rate from

8 units/sec down to 1 unit/sec. A conflict between trying

to “leak” at the same time as a “fill” is avoided by

preventing a leak when a fill event occurs.

alarm clearing threshold. The ability to decay the

Disqualification of a non-selected reference source is

amplitude over time allows the importance of defect

based on inactivity, or on an out-of-band result from the

events to be reduced as time passes by. This means that, frequency monitors. The currently selected reference

in the case of isolated events, the alarm will not be set, source can be disqualified for phase, frequency, inactivity

whereas, once the alarm becomes set, it will be held on or if the source is outside the DPLL lock range. If the

until normal operation has persisted for a suitable time currently selected reference source is disqualified, the

(but if the operation is still erratic, the alarm will remain next highest priority, qualified reference source is

set). See Figure 3.

selected.

Figure 3 Inactivity and Irregularity Monitoring

Inactivities/Irregularities

Reference

Source

Leaky

Bucket

Response

Alarm

Programmable Fall Slopes

bucket_size

upper_threshold

lower_threshold

(all programmable)

F8530D_026Inact_Irreg_Mon_02

Revision 1.00/September 2007© Semtech Corp.

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