XRT73L03A Datasheet, PDF (40/62 Pages) Exar Corporation – 3 CHANNEL DS3/E3/STS-1 LINE INTERFACE UNIT

XRT73L03A
3 CHANNEL DS3/E3/STS-1 LINE INTERFACE UNIT
REV. 2.0.4
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 location
can range in amplitude from 360mVpk to
850mVpk.
3. Bellcore documents stipulate that the Receiving
Terminal must be able to receive the 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 location.
These facts are reflected in Figure 24.
Design Considerations for DS3 and STS-1 Appli-
cations
When installing equipment into environments depict-
ed in Figure 24, the system installation personnel
may be able to determine the cable length between
the local terminal equipment and the DSX-3/STSX-1
Cross-Connect Patch-Panel. The cable length be-
tween the local terminal equipment and the DSX-3/
STSX-1 Cross-Connect Patch Panel ranges between
0 and 450 feet.
It is extremely unlikely that the system installation
personnel will know the cable length between the
DSX-3/STSX-1 Cross-Connect Patch-Panel and the
remote terminal equipment. Therefore, we recom-
mend that the Receive Equalizer be enabled by set-
ting the REQEN_(n) input pin or bit-field to “1”.
The only time that the Receive Equalizer should be
disabled is when there is an off-chip equalizer in the
Receive path between the DSX-3/STSX-1 Cross-
Connect and the RTIP_(n)/RRING_(n) input pins, or
in applications where the Receiver is directly monitor-
ing the transmit output signal directly.
3.2.1.2 Design Considerations for E3 Applica-
tions
In E3 System installation, it is recommended that the
Receive Equalizer of the XRT73L03A device be en-
abled by pulling the REQEN_(n) input pins “High” or
by setting the REQEN_(n) bit-fields to “1”.
NOTE: The results of extensive testing indicates that when
the Receive Equalizer is enabled, the XRT73L03A device is
capable of receiving an E3 line signal with anywhere from 0
to 12dB of cable loss over the Industrial Temperature range.
• Design Considerations for E3 Applications or if
the Overall Cable Length is known
If during System Installation the overall cable length is
known, then in order to optimize the performance of
the XRT73L03A in terms of receive intrinsic jitter, etc.,
enable or disable the Receive Equalizer based upon
the following recommendations:
The Receive Equalizer should be turned ON if the
Receive Section of a given channel is going to re-
ceive a line signal with an overall cable length of 300
feet or greater. Conversely, turn OFF the Receive
Equalizer if the Receive Section of a given channel is
going to receive a line signal over a cable length of
less than 300 feet.
NOTES:
1. If the Receive Equalizer block is turned ON when it
is receiving a line signal over short cable length, the
received line signal may be over-equalized which
could degrade performance by increasing the
amount of jitter that exists in the recovered data
and clock signals or by creating bit-errors
2. The Receive Equalizer has been designed to
counter the frequency-dependent cable loss that a
line signal experiences as it travels from the trans-
mitting terminal to the receiving terminal. However,
the Receive Equalizer was not designed to counter
flat loss where all of the Fourier frequency compo-
nents within the line signal are subject to the same
amount of attenuation. Flat loss is handled by the
AGC block.
Disable the Receive Equalizer block by doing either of
the following.
a. Operating in the Hardware Mode
Set the REQEN_(n) input pin “Low".
b. Operating in the HOST Mode
Write a "0" to the REQEN_(n) bit-field within Com-
mand Register CR2, as illustrated below.
COMMAND REGISTER CR2-(n)
D4
D3
Reserved
ENDECDIS_(n)
X
X
3.3 CLOCK RECOVERY PLL
D2
D1
D0
ALOSDIS_(n)
DLOSDIS_(n)
REQEN_(n)
X
X
0
The purpose of the Clock Recovery PLL is to track
the incoming Dual-Rail data stream and to derive and
generate a recovered clock signal.
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