XRT7300
áç
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.1.1
interface the Receive Section of the XRT7300 to the
line as shown in Figure 16 or Figure 17.
FIGURE 16. RECOMMENDED SCHEMATIC FOR INTERFACING THE RECEIVE SECTION OF THE XRT7300 TO THE LINE
(TRANSFORMER-COUPLING)
RTIP
RxPOS
RxNEG
RxLineClk
RPOS
RNEG
RCLK1
R1
BNC
T2
Ω
37.5
C1
0.01uF
RxLOS
RxLOL
RLOS
RLOL
R2
1:1
Ω
37.5
RRING
FIGURE 17. RECOMMENDED SCHEMATIC FOR INTERFACING THE RECEIVE SECTION OF THE XRT7300 TO THE LINE
(CAPACITIVE-COUPLING)
C1
0.01uF
Receive Line Signal
RTIP
R1
Ω
75
C2
0.01uF
RRING
3.2 THE RECEIVE EQUALIZER BLOCK
the signal is subjected to a greater amount of attenu-
ation than the lower-frequency components. If this
line signal travels over reasonably long cable lengths
(e.g., greater than 450 feet), then the shape of the
pulses (which were originally square) is distorted and
inter-symbol interference increases.
After the XRT7300 has received the incoming line
signal via the RTIP and RRING input pins, the first
block that this signal passes through is the AGC cir-
cuit followed by the Receive Equalizer.
As the line signal is transmitted from a given transmit-
ting terminal, the pulse shapes at that location are ba-
sically square. Hence, these pulses consist of a com-
bination of “Low” and “High” frequency Fourier com-
ponents. As this line signal travels from the transmit-
ting terminal via the coaxial cable to the receiving
terminal, it is subjected to frequency-dependent loss.
In other words, the higher-frequency components of
The purpose of the Receive Equalizer is to equalize
the distortion of the incoming signal due to cable loss.
The Receive Equalizer accomplishes this by subject-
ing the received line signal to frequency-dependent
amplification (which attempts to counter the frequen-
cy dependent loss that the line signal has experi-
enced) and to restore the shape of the line signal so
26
EXAR [ EXAR CORPORATION ]
