Datasheet
____________________________________________________ DS34T101, DS34T102, DS34T104, DS34T108
138 of 366
10.13.3
LIU Receiver
The LIU is configured for E1 or T1/J1 mode by setting the LTRCR.T1J1E1S bit appropriately.
10.13.3.1
Interfacing to the Line
The LIU receiver accepts incoming T1, E1 and J1 physical layer signals on the RTIP/RRING differential pair. The
receiver is designed to be fully software-selectable for E1, T1 or J1 without changing any external components.
The receiver can be transformer-coupled or capacitor-coupled to the line. Typically, the receiver interfaces to the
incoming coaxial or twisted-pair cable through a 1:1 isolation transformer. Table 10-60 specifie
s the required
characteristics of the transformer. Rx line termination (also known as impedance matching) can be internal or
external and is configurable for 75, 100, 110, or 120. For internal impedance matching, set
LRISMR.
RIMPON=1 and set LRISMR.RIMPM[2:0] to specify the impedance. For external impedance matching,
set LRISMR.
RIMPON=0, set LRISMR.RIMPM[2:0] to specify the impedance, and use external termination resistors
Rt as shown in Figure 10-68. Optionally
a 2:1 transformer can be used when LTRCR.RTR=1, but this mode is only
compatible with external termination.
10.13.3.2
Rx Sensitivity
Rx sensitivity can be adjusted for various application using LRISMR.RSMS[1:0].
10.13.3.3
Rx Signal Level Indicator
The signal strength at RTIP/RRING is reported in 2.5dB increments in LRSL.RSL[3:0]. This feature is helpful when
troubleshooting line performance problems.
10.13.3.4
Optional Monitor Mode
The LIU receiver can be used in monitoring applications, which typically have flat losses from the use of series
resistors. See Figure 10-71. In these app
lications a pre-amp stage in the receiver can be configured to apply 14dB,
20dB, 26dB, or 32dB of flat gain to compensate for the resistive losses. The monitor mode preamp is enabled by
setting LRISMR.RM
ONEN=1 and configured by LRISMR.RSMS[1:0].
Figure 10-71. Typical Rx Monitor Application
PRIMARY
T1/E1 TERMINATING
DEVICE
MONITOR
PORT JACK
T1/E1 LINE
X
F
M
R
DS34T108
Rt
Rm Rm
SECONDARY T1/E1
TERMINATING
DEVICE
10.13.3.5
Clock and Data Recovery
The LIU receiver has an active filter that reconstructs the received analog signal for the nonlinear losses that occur
in transmission. The E1CLK or T1CLK from the CLAD1 block is multiplied by 16 and used to oversample the