ACS8509 데이터 시트보기 (PDF) - Semtech Corporation

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ACS8509

Synchronous Equipment Timing Source for SONET or SDH Network Elements

Semtech Corporation 

ACS8509 SETS

ADVANCED COMMUNICATIONS

FINAL

DATASHEET

the frequency outside the hold-in range for long enough to The registers sts_curr_inc_offset (address 0C, 0D, 07)

be detected, whilst the signal will also be rejected if the

eye closes sufficiently to affect the signal purity). The

“8klock” mode should be engaged for high jitter tolerance

according to these masks. All reference clock ports are

monitored for quality, including frequency offset and

general activity. Single short-term interruptions in

selected reference clocks may not cause

rearrangements, whilst longer interruptions, or multiple,

short-term interruptions, will cause rearrangements, as

will frequency offsets which are sufficiently large or

sufficiently long to cause loss-of-lock in the phase-locked

loop. The failed reference source will be removed from the

priority table and declared as unserviceable, until its

perceived quality has been restored to an acceptable

level.

report the frequency of the DPLL with respect to the

external TCXO frequency. This is a 19-bit signed number

with one LSB representing 0.0003 ppm (range of

±80 ppm). Reading this regularly can show how the

currently locked source is varying in value e.g. due to

wander on its input.

The ACS8509 performs automatic frequency monitoring

with an acceptable input frequency offset range of

±16.6 ppm. The ACS8509 DPLL has a programmable

frequency limit of ±80 ppm. If the range is programmed to

be > 16.6 ppm, the frequency monitors should be

disabled so the input reference source is not

automatically rejected as out of frequency range.

Table 7 Input Reference Source Jitter Tolerance

Jitter Tolerance

G.703

G.783

G.823

GR-1244-CORE

Frequency Monitor

Acceptance Range

±16.6 ppm

Frequency Acceptance

Range (Pull-in)

±4.6 ppm

(see Note (i))

Frequency Acceptance

Range (Hold-in)

±4.6 ppm

(see Note (i))

Frequency Acceptance

Range (Pull-out)

±4.6 ppm

(see Note (i))

±9.2 ppm

(see Note (ii))

±9.2 ppm

(see Note (ii))

±9.2 ppm

(see Note (ii))

Notes: (i) The frequency acceptance and generation range will be ±4.6 ppm around the required frequency when the external crystal

frequency accuracy is within a tolerance of ±4.6 ppm.

(ii) The fundamental acceptance range and generation range is ± 9.2 ppm with an exact external crystal frequency of 12.8 MHz. This is

the default DPLL range, the range is also programmable from 0 to 80 ppm in 0.08 ppm steps.

Revision 2.00/January 2006 © Semtech Corp.

Page 11

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