ACS8530 datasheet(13/152 Pages) SEMTECH

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ADVANCED COMMUNICATIONS

FINAL

DATASHEET

Revision 3.02/November 2005 © Semtech Corp.

Page 13

www.semtech.com

ACS8530 SETS

are used when alarms have to be triggered either by fairly

regular defect events, which occur sufficiently close

together, or by defect events which occur in bursts. Events

which are sufficiently spread out should not trigger the

alarm. By adjusting the 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.

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

alarm clearing threshold. The ability to decay the

amplitude over time allows the importance of defect

events to be reduced as time passes by. This means that,

in the case of isolated events, the alarm will not be set,

whereas, once the alarm becomes set, it will be held on

until normal operation has persisted for a suitable time

(but if the operation is still erratic, the alarm will remain

set). See Figure 3.

There is one Leaky Bucket Accumulator per input channel.

Each Leaky Bucket can select from four configurations

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

Configuration is programmable for size, alarm set and

reset thresholds, and decay rate.

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.

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.

Disqualification of a non-selected reference source is

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

frequency monitors. The currently selected reference

source can be disqualified for phase, frequency, inactivity

or if the source is outside the DPLL lock range. If the

currently selected reference source is disqualified, the

next highest priority, qualified reference source is

selected.

Figure 3 Inactivity and Irregularity Monitoring

F8530D_026Inact_Irreg_Mon_02

Inactivities/Irregularities

Programmable Fall Slopes

Reference

Source

Leaky

Bucket

Response

Alarm

bucket_size

upper_threshold

lower_threshold

(all programmable)

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