XRT73LC00 datasheet(32/53 Pages) EXAR

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XRT73LC00

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E3/DS3/STS-1 LINE INTERFACE UNIT

REV. P1.0.1

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.

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