DS3181/DS3182/DS3183/DS3184
198
10.16.3 Detailed Description
The receiver performs clock and data recovery from an alternate mark inversion (AMI) coded signal or a B3ZS- or
HDB3-coded AMI signal and monitors for loss of the incoming signal. The transmitter drives standard pulse-shape
waveforms onto 75
coaxial cable. See
Figure 10-58 for a detailed functional block diagram of the DS3/E3/STS-1
LIU. The jitter attenuator can be mapped into the receiver data path, mapped into the transmitter data path, or be
disabled. The DS3/E3/STS1 LIU conforms to the telecommunications standards listed in
Table 4-1. Figure 1-1shows the external components required for proper operation.
Figure 10-58. DS3/E3/STS-1 LIU Block Diagram
Analog
Local
Loopback
Preamp
Clock &
Data
Recovery
Line
Driver
Waveshaping
RXPn
RXNn
TXPn
TXNn
Power
Supply
squelch
Jit
te
rAt
tenuat
or
(can
be
placed
in
eit
her
t
he
receive
pat
hor
t
he
t
ransmit
pat
h)
Driver
Monitor
VDD
VSS
Automatic
Gain
Control
+
Adaptive
Equalizer
ALOS
CLKC
Clock Rate
Adapter
CLKB
CLKA
TO B3ZS/HDB3
DECODER
FROM B3ZS/HDB3
ENCODER
FROM DS3/E3/
STS-1 LINE
TO DS3/E3/STS-1
LINE
10.16.4 Transmitter
10.16.4.1 Transmit Clock
The clock used in the LIU Transmitter is typically based on either the CLAD clock or TCLKI, selected by the
CLADC bit in PORT.CR3.
10.16.4.2 Waveshaping, Line Build-Out, Line Driver
The waveshaping block converts the transmit clock, positive data, and negative data signals into a single AMI
signal with the waveshape required for interfacing to DS3/E3/STS1 lines.
Table 18-8 through
Table 18-12 and
Figure 18-9 (AC Timing Section) show the waveform template specifications and test parameters.
Because DS3 and STS-1 signals must meet the waveform templates at the cross-connect through any cable length
from 0 to 450ft, the waveshaping circuitry includes a selectable LBO feature. For cable lengths of 225ft or greater,
the TLBO configuration bit (PORT.CR2.TLBO) should be low. When TLBO is low, output pulses are driven onto the
coaxial cable without any pre-attenuation. For cable lengths less than 225ft, TLBO should be high to enable the
LBO circuitry. When TLBO is high, pulses are pre-attenuated by the LBO circuitry before being driven onto the
coaxial cable. The LBO circuitry provides attenuation that mimics the attenuation of 225ft of coaxial cable.
The transmitter line driver can be disabled and the TXPn and TXNn outputs tri-stated by asserting the LTS
configuration bit (PORT.CR2.LTS). Powering down the transmitter through the TPD configuration bit (CPU bus
mode) also tri-states the TXPn and TXNn outputs.