zl50021 Zarlink Semiconductor, zl50021 Datasheet - Page 45

• Manufacturer Part Number: zl50021
• Description: Enhanced 4 K Digital Switch With Stratum 3 Dpll
• Manufacturer: Zarlink Semiconductor

14.2
The input jitter acceptance is specified in standards as the minimum amount of jitter of a certain frequency on the
input clock that the DPLL must accept without making cycle slips or losing lock. The lower the jitter frequency, the
larger the jitter acceptance. For jitter frequencies below a tenth of the cut-off frequency of the DPLL's jitter transfer
function, it safely can be said that any provided input jitter will be followed by the DPLL. The maximum value of jitter
tolerance for the DPLL is ±1023 UI
14.3
The corner frequency (-3 dB) of the DPLL is programmable through LPF (bits 3 - 0) in the Bandwidth Control
Register (BWCR) from 0.475 Hz to 15.5 kHz, in 16 steps. Stratum 3 requires a corner frequency of maximally 3 Hz.
The default corner frequency is 1.9 Hz.
15.0
15.1
To determine if the DPLL is locked to the input clock, a lock detector monitors the phase value output of the phase
detector, which represents the difference between input reference and output feedback clock. If the phase value is
below a certain threshold for a certain interval, the DPLL is pronounced locked to the input clock. The monitoring is
done in intervals of 4 ms. The lock detector threshold and the interval are programmable by the user through the
Lock Detector Threshold Register (LDTR) and the Lock Detector Interval Register (LDIR) respectively. See
Table 36 on page 73 and Table 37 on page 73 for the bit descriptions of the Lock Detector Threshold Register
(LDTR) and Lock Detector Interval Register (LDIR) registers respectively. The value of the Lock Detector Threshold
Register (LDTR) should be programmed with respect to the maximum expected jitter frequency and amplitude on
the selected input references.
The lock status can be monitored through the Reference Change Status Register (RCSR). See Table 41 on
page 78 for the bit description of the Reference Change Status Register (RCSR).
15.2
Several standards require that the output clock of the DPLL may not move in phase more than a certain amount. In
order to meet those standards, a special circuit maintains the phase of the DPLL output clock during reference and
mode rearrangements. The total output phase change or Maximum Timing Interval Error (MTIE) during
rearrangements is less than 31 ns per rearrangement, exceeding Stratum 3 requirements. After a large number of
reference switches, the accumulated phase error can become significant, so it is recommended to use MTIE reset
in such situations, to realign outputs to the nearest edge of the selected reference. The MTIE reset can be
programmed by setting MTR (bit 7) in the Reference Change Control Register (RCCR), as described in Table 40 on
page 76.
15.3
Besides total phase change, standards also require a certain rate of the phase change of the output clock. The
phase alignment speed is programmable by the user through a value in the Slew Rate Limit Register (SRLR) as
described in Table 38 on page 74. Stratum 3 requires that the phase alignment speed not exceed 81 ns per
1.326 ms (61ppm). The width of the register and the limiter circuitry, if not bypassed, provide a maximum phase
change alignment speed of 186 ppm.
The limiter circuitry can be bypassed by programming BLM (bit 13) in the Bandwidth Control Register (BWCR).
Bypassing limiter (combined with choice of other parameters in the BWCR register) can achieve very fast lock of
the output clock to the selected input reference. A side effect of the bypassing limiter is manifested through much
higher intrinsic jitter. Once the bypassing is stopped, the jitter characteristics are guaranteed. The phase alignment
speed default value is 56 ppm.
Input Jitter Acceptance
Jitter Transfer Function
Lock Detector
Maximum Time Interval Error (MTIE)
Phase Alignment Speed (Phase Slope)
DPLL Specific Functions and Requirements
p-p
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Zarlink Semiconductor Inc.
ZL50021
45
Data Sheet