XRT83SL34 datasheet(25/80 Pages) EXAR

25 / 80 page

XRT83SL34

QUAD T1/E1/J1 SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR

PRELIMINARY

REV. P1.0.8

JITTER ATTENUATOR

To reduce phase and frequency jitter in the recovered clock, the jitter attenuator can be placed in the receive

signal path. The jitter attenuator uses a data FIFO (First In First Out) with a programmable depth that can vary

between 2x32 and 2x64. The jitter attenuator can also be placed in the transmit signal path or disabled

altogether depending upon system requirements. The jitter attenuator, other than using the master clock as

reference, requires no external components. With the jitter attenuator selected, the typical throughput delay

from input to output is 16 bits for 32 bit FIFO size or 32 bits for 64 bit FIFO size. When the read and write

pointers of the FIFO in the jitter attenuator are within two bits of over-flowing or under-flowing, the bandwidth of

the jitter attenuator is widened to track the short term input jitter, thereby avoiding data corruption. When this

situation occurs, the jitter attenuator will not attenuate input jitter until the read/write pointer’s position is outside

the two bits window. Under normal condition, the jitter transfer characteristic meets the narrow bandwidth

requirement as specified in ITU- G.736, ITU- I.431 and AT&T Pub 62411 standards.

In T1 mode the Jitter Attenuator Bandwidth is always set to 3Hz. In E1 mode, the bandwidth can be reduced

through the JABW control signal. When JABW is set “High” the bandwidth of the jitter attenuator is reduced

from 10Hz to 1.5Hz. Under this condition the FIFO length is automatically set to 64 bits and the 32 bits FIFO

length will not be available in this mode. Jitter attenuator controls are available on a per channel basis in the

Host mode and on a global basis in the Hardware mode.

GAPPED CLOCK (JA MUST BE ENABLED IN THE TRANSMIT PATH)

The XRT83SL34 LIU is ideal for multiplexer or mapper applications where the network data crosses multiple

timing domains. As the higher data rates are de-multiplexed down to T1 or E1 data, stuffing bits are removed

which can leave gaps in the incoming data stream. If the jitter attenuator is enabled in the transmit path, the

32-Bit or 64-Bit FIFO is used to smooth the gapped clock into a steady T1 or E1 output. The maximum gap

width of the 8-Channel LIU is shown in Table 2.

NOTE: If the LIU is used in a loop timing system, the jitter attenuator should be enabled in the receive path.

TABLE 2: MAXIMUM GAP WIDTH FOR MULTIPLEXER/MAPPER APPLICATIONS

FIFO DEPTH

MAXIMUM GAP WIDTH

32-Bit

20 UI

64-Bit

50 UI

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