MT9042 데이터 시트보기 (PDF) - Mitel Networks
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MT9042 Datasheet PDF : 16 Pages
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MT9042
Preliminary Information
Description
Freerun
Normal
(PRI)
Normal
(SEC)
Holdover
(PRI)
Holdover
(SEC)
State
P1
P2
P3
P4a
P4b
Power On (RST=0
LOSS1=X LOSS2=X)
No change Invalid state Invalid state Invalid state Invalid state
LOSS1=0 LOSS2=0
P2
No change
P2
P2
P2
LOSS1=1 LOSS2=0
time loss < tgt
P3
P4a
No change No change
P3
ST.GD
LOSS1=1 LOSS2=0
time loss > tgt
P3
Invalid state No change
P3
P3
LOSS1=0 LOSS2=1
P2
No change
P2
P2
P2
LOSS1=1 LOSS2=1
No change
P4a
P4b
No change No change
Where : ST.GD = Start guard time; X = Don’t care
Table 4 - State Table For Automatic Input Reference Selection and Operating Mode
Locking Range and Lock Time
The locking range of the PLL is the range that the
input reference frequency can be deviated from its
nominal frequency while the output signals maintain
synchronization. The relevant value is usually
specified in parts-per-million (ppm). For both the T1
and E1 outputs, lock was maintained while an 8 kHz
input was varied between 7900 Hz to 8100 Hz
(corresponding to ±12500 ppm). This is well beyond
the required ±100 ppm. The lock range of 12500
ppm also applies to 1.544 MHz and 2.048 MHz
reference inputs.
The lock time is a measure of how long it takes the
PLL to reach steady state frequency after a
frequency step on the reference input signal. The
locking time is measured by applying an 8000 Hz
signal to the primary reference and an 8000.8 Hz
(+100 ppm) to the secondary reference. The output
is monitored with a time interval analyzer during slow
periodic rearrangements on the reference inputs.
The lock time for both the T1 and E1 outputs is
approximately 311 ms, which is well below the
required lock time of 1.0 seconds.
Holdover and Freerun Accuracy
The holdover option of the PLL provides the user
with the capability of maintaining the integrity of
output signals when the input reference signals are
lost. Holdover performance is defined as the rate of
3-102
slip (i.e., amount of slip on 60 seconds) of the 8 kHz
reference input. For both the T1 and E1 outputs the
rate of slip was measured as a function of the input
reference frequency. The results measured over an
observation period of 60 seconds, are presented in
Table 5.
Reference Input
Frequency
% of Frame Pulse Slip
8 kHz
8%
1.544 MHz
58%
2.048 Hz
58%
Table 5 - Holdover Slip Rate (60 seconds)
The freerun accuracy of the PLL is a measure of how
accurately the PLL can reproduce the desired output
frequency. The freerun accuracy is a function of
master clock frequency which must be 20 MHz ±32
ppm in order to meet AT & T TR62411 and ETSI
specifications.
Maximum Time Interval Error (MTIE)
MTIE is a measure of the rate of change of phase on
the output signal due to a step in phase on the
reference input. The specification also clearly
indicates a peak constraint on the characteristic of
the output signal. The specification is uniquely a
function of the loop bandwidth (or loop delay) of the
PLL. AT & T TR62411 clearly indicates that a
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