XRT5997 Datasheet, PDF (27/37 Pages) Exar Corporation – Seven-Channel E1 Line Interface Unit

Capacitive-Coupling the Receiver to the Line
Figure 9, presents a recommended approach that the
user to employ when capacitive-coupling the Receive
Section to the line.
RxPOS_1
RxNEG_1
Loss of Signal - 1
U1
1
RxPOS_1
2
RxNEG_1
100
RxLOS_1
XRT5997
7
RTIP_1
C1
1
2
0.1uF
8
RRing_1
C2
1
2
0.1uF
XRT5997
1 ^R1 2
37.4
R2
37.4
J1
BNC
1
Figure 9. Recommended Schematic for Interfacing the Receive Sections of the XRT5997 Device to
the Line for 75Ω Applications (Capacitive-Coupling)
2.2 The “Receive Equalizer” Bock
After a given Channel (within the XRT5997 device) has
received the incoming line signal, via the RTIP_x and
RRing_x input pins, the first block that this signal will
pass through is the Receive Equalizer block.
frequency components. If this line signal travels over
reasonably long cable lengths, then the shape of the
pulses (which were originally square) will be distorted
and with inter-symbol interference increases.
As the line signal is transmitted from a given “Transmit-
ting” terminal, the pulse shapes (at that location) are
basically “square”. Hence, these pulses consist of a
combination of “low” and “high” frequency Fourier
components. As this line signal travels from the
“transmitting terminal” (via the coaxial cable or twisted
pair) to the receiving terminal, it will be subjected to
“frequency-dependent” loss. In other words, the higher
frequency components of the signal will be subjected
to a greater amount of attenuation than the lower
The purpose of this block is to equalize the incoming
distorted signal, due to cable loss. In essence, the
Receive Equalizer block accomplishes this by subject-
ing the received line signal to “frequency-dependent”
amplification (which attempts to counter the fre-
quency-dependent loss that the line signal has experi-
enced). By doing this, the Receive Equalizer is
attempting to restore the shape of the line signal so that
the received data can be recovered reliably.
Rev. 1.0.0
27