XRT75R03D_06 Datasheet, PDF (49/135 Pages) Exar Corporation – EXAR DATA SHEET FORMAT TEMPLATES

XRT75R03D
REV. 1.0.4
THREE CHANNEL E3/DS3/STS-1 LINE
The Equalizer restores the integrity of the signal and compensates for the frequency dependent attenuation of
up to 900 feet of coaxial cable (1300 feet for E3). The Equalizer also boosts the high frequency content of the
signal to reduce Inter-Symbol Interference (ISI) so that the slicer slices the signal at 50% of peak voltage to
generate Positive and Negative data.
The Equalizer can either be “IN” or “OUT” by setting the REQEN_n pin “High” or “Low” (in Hardware Mode) or
setting the REQEN_n control bit to “1” or “0” (in Host Mode).
Recommendations for Equalizer Settings:
The Equalizer has two gain settings to provide optimum equalization. In the case of normally shaped DS3/
STS-1 pulses (pulses that meet the template requirements) that has been driven through 0 to 900 feet of cable,
the Equalizer can be left “IN” by setting the REQEN_n pin to “High” (in Hardware Mode) or setting the
REQEN_n control bit to “1” (in Host Mode).
However, for square-shaped pulses such as E3 or for DS3/STS-1 high pulses (that does not meet the pulse
template requirements), it is recommended that the Equalizer be left “OUT” for cable length less than 300 feet
by setting the REQEN_n pin “Low” (in Hardware Mode) or by setting the REQEN_n control bit to “0” (in Host
Mode).This would help to prevent over-equalization of the signal and thus optimize the performance in terms of
better jitter transfer characteristics.
NOTE: The results of extensive testing indicates that even when the Equalizer was left “IN” (REQEN_n = “HIGH”),
regardless of the cable length, the integrity of the E3 signal was restored properly over 0 to 12 dB cable loss at
Industrial Temperature.
The Equalizer also contain an additional 20 dB gain stage to provide the line monitoring capability of the
resistively attenuated signals which may have 20dB flat loss. This capability can be turned on by writing a “1” to
the RxMON_n bits in the control register or by setting the RxMON pin (pin 69) “High”. However, asserting or
enabling RxMON suppresses the internal LOS circuitry and LOS will never assert nor LOS be declared when
operating with RxMON enabled.
6.1.1 Interference Tolerance:
For E3 mode, ITU-T G.703 Recommendation specifies that the receiver be able to recover error-free clock and
data in the presence of a sinusoidal interfering tone signal. For DS3 and STS-1 modes, the same
recommendation is being used. Figure 17 shows the configuration to test the interference margin for DS3/
STS1. Figure 18 shows the set up for E3.
FIGURE 18. INTERFERENCE MARGIN TEST SET UP FOR DS3/STS-1
Sine Wave
N
Generator
Attenuator
DS3 = 22.368 MHz
STS-1 = 25.92 MHz
Pattern Generator ^S
2 ²³ -1 PRBS
0 to 900 feet
Coaxial Cable
∑
DUT
XRT75R03D
Test Equipment
45