zl50019gag2 Zarlink Semiconductor, zl50019gag2 Datasheet - Page 45

• Manufacturer Part Number: zl50019gag2
• Description: Enhanced 2 K Digital Switch With Stratum 4e Dpll
• Manufacturer: Zarlink Semiconductor

15.6
To monitor reference failure based on frequency offset, multi period checking is performed. Reference validation
time is prescribed by Telcordia GR-1244-CORE and is between 10 and 30 seconds. To meet the criteria for
reference validation time, the time base for multi period monitoring has to be big enough. To implement hysteresis,
the upper limits are split into near upper and far upper limits and the lower limits are split into near lower and far
lower limits. The reference failure is detectable only when the reference passes far limits, but passing is not
detected until the reference is within near limits. The zone between near and far limits, called the “grey zone”, is
required by standards and prevents unnecessary reference switching when the selected reference is close to the
boundary of failure.
The monitor makes a decision about reference validity after two consecutive measurements with respect to its time
base. The time base for multi-period monitoring is 10 seconds. The time base is defined in the number of reference
clock cycles.
The device has two sets of limits the Stratum 4E default limits and the Relaxed Stratum 4E limits (see Table 12 on
page 45). The ST4_LIM bit in Table 28, DPLL Control Register (DPLLCR) Bits is used to select between the two
sets of limits.
Multiple Period Reference Monitoring
Far Upper Limit
Near Upper Limit
Nominal Value
Near Lower Limit
Far Lower Limit
Table 11 - Values for Single Period Limits
8 kHz
1.544 MHz
2.048 MHz
4.096 MHz
8.192 MHz
16.384 MHz
19.44 MHz
Table 12 - Multi-Period Hysteresis Limits
Frequency
Reference
Stratum 4E Default Limits
(in 10 ns units)
-82.487 ppm
-64.713 ppm
64.713 ppm
82.487 ppm
Zarlink Semiconductor Inc.
ZL50019
45
Comment
0.3 UIp-p
0.2 UIp-p
0.2 UIp-p
0.2 UIp-p
0.2 UIp-p
0.2 UIp-p
10 UIp-p
0 ppm
Relaxed Stratum 4E Limits
(in 10 ns units)
-250 ppm
-240 ppm
240 ppm
250 ppm
Data Sheet