XRT75R12_15 Datasheet, PDF (33/90 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER

REV. 1.0.5
XRT75R12
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH JITTER ATTENUATOR
FIGURE 19. HDB3 ENCODING FORMAT
TClk
TPDATA ^{1 0 1 1} 0 0 0 0 1 ^{0 0 0 0 0 0 0 0}
Line
Signal
10
1000V
000
B00V
1
1
V
4.4 TRANSMIT PULSE SHAPER
The Transmit Pulse Shaper converts the B3ZS encoded digital pulses into a single analog Alternate Mark
Inversion (AMI) pulse that meets the industry standard mask template requirements for STS-1 and DS3. For
E3 mode, the pulse shaper converts the HDB3 encoded pulses into a single full amplitude square shaped
pulse with very little slope. The Pulse Shaper Block also includes a Transmit Build Out Circuit, which can
either be disabled or enabled by setting the TxLEV_n bit to “1” or “0” in the control register. For DS3/STS-1
rates, the Transmit Build Out Circuit is used to shape the transmit waveform that ensures that transmit pulse
template requirements are met at the Cross-Connect system. The distance between the transmitter output and
the Cross-Connect system can be between 0 to 450 feet. For E3 rate, since the output pulse template is
measured at the secondary of the transformer and since there is no Cross-Connect system pulse template
requirements, the Transmit Build Out Circuit is always disabled. The differential line driver increases the
transmit waveform to appropriate level and drives into the 75 load as shown in Figure 20.
FIGURE 20. TRANSMIT PULSE SHAPE TEST CIRCUIT
TxPOS(n)
TxNEG(n)
TxLineClk(n)
TPData(n) ^TTIP(n)
TNData(n)
TxClk(n) _TRing(n)
R1
31.6 +1%
R2
31.6 + 1%
R3
75
1:1
4.4.1 Guidelines for using Transmit Build Out Circuit
If the distance between the transmitter and the DSX3 or STSX-1, Cross-Connect system, is less than 225 feet,
enable the Transmit Build Out Circuit by setting the TxLEV_n control bit to “0”. If the distance between the
transmitter and the DSX3 or STSX-1 is greater than 225 feet, disable the Transmit Build Out Circuit.
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