DS26521 datasheet(76/258 Pages) MAXIM

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DS26521 Single T1/E1/J1 Transceiver

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8.11.4 Jitter Attenuator

The DS26521 contains a jitter attenuator for each LIU that can be set to a depth of 32 or 128 bits via the JADS

(LTRCR.4) bit in the LIU Transmit 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 8-21. The jitter attenuator

can be placed in either the receive path, the transmit path, or disabled by appropriately setting the JAPS1 and

JAPS0 bits in 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 (GTCCR) 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 TCLK 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 TCLK pin if the jitter attenuator is placed in

the transmit side. If the incoming jitter exceeds either 120UIP-P (buffer depth is 128 bits) or 28UIP-P (buffer depth is

32 bits), the DS26521 sets the jitter attenuator limit trip set (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 DS26521 jitter attenuator is complaint with the following specifications shown in Table 8-34.

Table 8-34. Jitter Attenuator Standards Compliance

STANDARD

ITU-T I.431, G.703, G.736, G.823

ETS 300 011, TBR 12/12

AT&T TR62411, TR43802

TR-TSY-009, TR-TSY-253, TR-TSY-499

Figure 8-21. Jitter Attenuation

FREQUENCY (Hz)

0dB

-20dB

-40dB

-60dB

100

10K

100K

TR 62411 (Dec. 90)

Prohibited Area

ITU G.7XX

Prohibited Area

TBR12

Prohibited

Area

DS26521 Datasheet(PDF) 76 Page - Maxim Integrated Products