XRT82D20 Datasheet, PDF (17/27 Pages) Exar Corporation – SINGLE CHANNEL E1 LINE INTERFACE UNIT

XRT82D20 SINGLE CHANNEL LINE INTERFACE UNIT
REV. 1.0.7
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FIGURE 11. ILLUSTRATION OF HOW TO INTERFACE THE XRT82D20 TO THE LINE FOR 120 Ω APPLICATIONS AND
3.3V OPERATION ONLY
120 Ω Twisted Pair
1:2
120 Ω
Signal
Source
120 Ω Twisted Pair
2:1
R Load
120 Ω
866 Ω
866 Ω
RTIP
Rx Input
RRING
9.1 Ω
9.1 Ω
TTIP
Tx Output
TRING
RPOS/RData
RNEG/LCV
RClk
TVDD
AVDD
10 µF
TxLEV
TGND
AGND
+3.3 V
0.1 µF
TNEG/CODE
TPOS/TData
TClk
NOTES:
1. Figure 10 and Figure 11indicate that for 3.3 V oper-
ation, both 75 Ω and 120 Ω applications, the user
should connect a 9.1Ω resistor in series between
the TTIP/TRing outputs and the transformer.
2. Figure 10 and Figure 11indicate that the user
should use a 2 : 1 STEP-UP Transformer.
1.5 INTERFACING THE RECEIVE SECTION TO THE LINE
The design of the XRT82D20 permits the user to
transformer-couple the Receive Section to the line.
As mentioned earlier, the specifications for E1 require
75Ω termination loads, when transmitting over coaxial
cable, and 120Ω loads, when transmitting over twist-
ed-pair. Figure 12 and Figure 13 present the various
methods that the user can employ to interface the Re-
ceiver of the XRT82D20 to the line.
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