Rainbow Electronics DS26519 - Manual (Page 102)

DS26519 16-Port T1/E1/J1 Transceiver
102 of 310
9.12.5 Jitter Attenuator
The DS26519 contains a jitter attenuator that can be set to a depth of 32 or 128 bits via the JADS bits in LIU
Transmit and Receive Control Register (
LTRCR ).
The 128-bit mode is used in applications where large excursions of wander are expected. The 32-bit mode is used
in delay sensitive applications. The characteristics of the attenuation are shown in
Figure 9-26 . The jitter attenuator
can be placed in either the receive path or the transmit path, or be disabled by appropriately setting the JAPS1 and
JAPS0 bits in the LIU Transmit and Receive Control Register (
LTRCR ).
For the jitter attenuator to operate properly, a 2.048MHz, 1.544MHz, or a multiple of up to 8x clock must be applied
at MCLK. See the Global Transceiver Clock Control Register 1 (
GTCCR1 ) for MCLK options. ITU-T specification
G.703 requires an accuracy of ±50ppm for both T1/J1 and E1 applications. TR62411 and ANSI specs require an
accuracy of ±32ppm for T1/J1 interfaces. Circuitry adjusts either the recovered clock from the clock/data recovery
block or the clock applied at the TCLKn pin to create a smooth jitter-free clock, which is used to clock data out of
the jitter attenuator FIFO. It is acceptable to provide a gapped/bursty clock at the TCLKn pin if the jitter attenuator is
placed in the transmit side. If the incoming jitter exceeds either 120UI
P-P
(buffer depth is 128-bits) or 28UI
P-P
(buffer
depth is 32 bits), then the DS26519 will set the jitter attenuator limit trip (JALTS) bit in the LIU Latched Status
Register (
LLSR .3). In T1/J1 mode, the jitter attenuator corner frequency is 3.75Hz, and in E1 mode it is 0.6Hz.
The DS26519 jitter attenuator is compliant with the following specifications shown in Table 9-43 .
Table 9-43. Jitter Attenuator Standards Compliance
Standard
ITU-T I.431, G.703, G.736, G.823
ETS 300 011, TBR 12/13
AT&T TR62411, TR43802
TR-TSY 009, TR-TSY 253, TR-TSY 499
Figure 9-26. Jitter Attenuation
FREQUENCY (Hz)
0dB
-20dB
-40dB
-60dB
1 10 100 1K 10K
JITTER
ATTENUAT
ION
(dB)
100K
TR 62411 (Dec. 90)
Prohibited Area
C
u
rv
e
B
C
ur
ve
A
ITU G.7XX
Prohibited Area TBR12
Prohibited
Area
T1 E1