XRT73LC00 Datasheet, PDF (32/53 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73LC00
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. P1.0.1
áç
PRELIMINARY
As the line signal is transmitted from a given transmit-
ting terminal, the pulse shapes at that location are ba-
sically square. These pulses consist of a combina-
tion of “Low” and “High” frequency Fourier compo-
nents. As this line signal travels from the transmitting
terminal via the coaxial cable to the receiving termi-
nal, it is subjected to frequency-dependent loss. The
higher-frequency components of the signal is subject-
ed to a greater amount of attenuation 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 origi-
nally square is distorted and inter-symbol interference
increases.
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 frequency
dependent loss that the line signal has experienced
and to restore the shape of the line signal so that the
transmitted data and clock can be recovered reliably.
3.2.1 Guidelines for Setting the Receive Equal-
izer
This data sheet presents guidelines for setting the
Receive Equalizer, for the following conditions.
1. If the overall cable length from the local Receiving
Terminal to the remote Transmitting Terminal is
NOT known.
2. If the overall cable length from the local Receiving
Terminal to the remote Transmitting Terminal is
known.
3.2.1.1 If the Overall Cable Length is NOT
Known
This section presents recommendations on what
state to set the Receive Equalizer when the overall
cable-length from the local Receiving Terminal to the
remote Transmitting Terminal is NOT known. For
DS3, STS-1 and E3 applications, enable the Receive
Equalizer by setting either the REQDIS input pin “low”
or the REQDIS bit-field to “0”. The remainder of this
section provides an explanation why we recommend
enabling the Receive Equalizer for these applications.
3.2.1.1.1 The Use of the Receive Equalizer in a
Typical DS3 or STS-1 Application
Most System Manufacturers of equipment supporting
DS3 and STS-1 lines interface their equipment to ei-
ther a DSX-3 or STSX-1 Cross-Connect. While in-
stalling their equipment the Transmit Line Build-Out
circuit is set to the proper setting that makes the
transmit output pulse compliant with the Isolated
DSX-3 or STSX-1 Pulse Template requirements. For
the XRT73LC00 this is achieved by setting the TX-
LEV input pin or bit-field to the appropriate level.
When the System Manufacturer is interfacing the Re-
ceive Section of the XRT73LC00 to the Cross-Con-
nect, they should keep aware of the following facts:
1. All DS3 or STS-1 line signals that are present at
either the DSX-3 or the STSX-1 Cross-Connect
are required to meet the Isolated Pulse Template
Requirements per Bellcore GR-499-CORE for
DS3 applications or Bellcore GR-253-CORE for
STS-1 applications.
2. Bellcore documents state that the amplitude of
these pulses at the DSX-3 or STSX-1 can range
in amplitude from 360mVpk to 850mVpk.
3. Bellcore documents stipulate that the Receiving
Terminal must be able to receive this pulse-tem-
plate compliant line signal over a cable length of
0 to 450 feet from the DSX-3 or the STSX-1
Cross Connect.
These facts are reflected in Figure 19.
29