XRT81L27 Datasheet, PDF (25/30 Pages) Exar Corporation – SEVEN CHANNEL E1 LINE INTERFACE UNIT WITH CLOCK RECOVERY

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XRT81L27
SEVEN CHANNEL E1 LINE INTERFACE UNIT WITH CLOCK RECOVERY
REV. 1.1.0
FIGURE 12. ILLUSTRATION OF HOW TO INTERFACE THE TRANSMIT SECTIONS OF THE XRT81L27 TO THE LINE (FOR
75 OR 120Ω APPLICATIONS)
TPOS_n
TNEG_n
TTIP_n
9.1Ω
Line
Input
1:2
75Ω
Coax
TClk_n
XRT81L27
TRING_n
9.1Ω
120Ω
Twisted
Pair
3.0 THE RECEIVE SECTION
The Receive Sections of the XRT81L27 consists of
the following blocks:
• The Receive Equalizer block
• The Peak Detector and Slicer block
• The LOS Detector block
• The Receive Output Interface block
3.1 INTERFACING THE RECEIVE SECTIONS TO THE
LINE
The design of each channel (within the XRT81L27)
permits the user to transformer-couple or capacitive-
couple the Receive Section to the line. Additionally,
as mentioned earlier, the specification documents for
E1 specify 75Ω termination loads, when transmitting
over coaxial cable, and 120Ω loads, when transmit-
ting over twisted-pair. Figure 13, Figure 14 and
Figure 15 present the various methods that can be
employ to interface the Receivers (of the XRT81L27)
to the line. The receive circuits of Figure 13,
Figure 14 and Figure 15 differ in the impedance at the
inputs and the line connections.
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