XRT75R12D_06 Datasheet, PDF (35/134 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET

XRT75R12D
REV. 1.0.1 TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
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
4.3 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 75Ω 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
31.6Ω +1%
R2
31.6Ω + 1%
R3
75Ω
1:1
4.3.1 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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