
XRT83VSH314
23
14-CHANNEL T1/E1/J1 SHORT-HAUL LINE INTERFACE UNIT
REV. 1.0.1
3.3
Jitter Attenuator
The jitter attenuator reduces phase and frequency jitter in the recovered clock if it is selected in the receive
path. The jitter attenuator uses a data FIFO (First In First Out) with a programmable depth of 32-bit or 64-bit. If
the LIU is used for line synchronization (loop timing systems), the JA should be enabled in the receive path.
When the Read and Write pointers of the FIFO are within 2-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
condition occurs, the jitter attenuator will not attenuate input jitter until the Read/Write pointer’s position is
outside the 2-Bit window. In T1 mode, the bandwidth of the JA is always set to 3Hz.
In E1 mode, the
bandwidth is programmable to either 10Hz or 1.5Hz (1.5Hz automatically selects the 64-Bit FIFO depth). The
JA has a clock delay equal to of the FIFO bit depth.
NOTE: If the LIU is used in a multiplexer/mapper application where stuffing bits are typically removed, the jitter attenuator
can be selected in the transmit path to smooth out the gapped clock. See the Transmit Section of this datasheet.
3.4
HDB3/B8ZS Decoder
In single rail mode, RPOS can decode AMI or HDB3/B8ZS signals. For E1 mode, HDB3 is defined as any
block of 4 successive zeros replaced with 000V or B00V, so that two successive V pulses are of opposite
polarity to prevent a DC component. In T1 mode, 8 successive zeros are replaced with 000VB0VB. If the
HDB3/B8ZS decoder is selected, the receive path removes the V and B pulses so that the original data is
output to RPOS.
3.4.0.1
RPOS/RNEG/RCLK
The digital output data can be programmed to either single rail or dual rail formats.
Figure 10 is a timing
diagram of a repeating "0011" pattern in single-rail mode.
Figure 11 is a timing diagram of the same fixed
pattern in dual rail mode.
FIGURE 10. SINGLE RAIL MODE WITH A FIXED REPEATING "0011" PATTERN
FIGURE 11. DUAL RAIL MODE WITH A FIXED REPEATING "0011" PATTERN
RCLK
RPOS
00
0
1
RCLK
RPOS
00
0
1
RNEG