XRT7295AT Datasheet, PDF (9/18 Pages) Exar Corporation – DS3/Sonet STS-1 Integrated Line Receiver

XRT7295AT
STS-1 SIGNAL REQUIREMENTS AT THE STSX
For STS-1 operation, the cross-connect is referred at the
STSX-1. Table 4 lists the signal requirements at the
STSX-1. Instead of the DS3 isolated pulse template, an
eye diagram mask is specified for STS-1 operation
(TA-TSY-000253). The XRT7295AT correctly decodes
any transmitted signal that meets the mask shown in
Figure 6 at the STSX-1.
Parameter
Line Rate
Line Code
Test Load
Power Levels
Specification
51.84 Mbps
Bipolar with three-0 substitution (B3ZS)
75W±5%
A wide-band power level measurement
at the STSX-1 interface using a low-pass
filter with a 3dB cutoff frequency of at
least 200MHz is within -2.7 dBm and 4.7
dBm.
Table 4. STSX-1 Interconnection Specification
1.0
0.8
0.6
0.4
0.2
0-1.0
-0.5
0
0.5 1.0
1.5
2.0
Time Slots - Normalized To Peak Location
Figure 6. STSX-1 Isolated Pulse Template for Bellcore TA-TSY-000253
LINE TERMINATION AND INPUT CAPACITANCE
The recommended receive termination is shown in
Figure 3 The 75 W resistor terminates the coaxial cable
with its characteristic impedance. The 0.01mF capacitor
to R_IN couples the signal into the receive input without
disturbing the internally generated DC bias level present
on R_IN. The input capacitance at the R_IN pin is 2.8pF
typical.
LOSS LIMITS FROM THE DSX-3 TO THE RECEIVE
INPUT
The distribution frame jack may introduce 0.6 ±0.55 dB
of loss. This loss may be any combination of flat or
shaped (cable) loss.
The maximum cable distance between the point where
the transmitted signal exits the distribution frame jack and
the XRT7295AT device is 450 ft. (see Figure 2.) The
coaxial cable (Type 728A) used for specifying this
distance limitation has the loss and phase characteristics
shown in Figure 7 and Figure 8. Other cable types also
may be acceptable if distances are scaled to maintain
cable loss equivalent to Type 728A cable loss.
TIMING RECOVERY
The signal at the cross-connect may travel through a
distribution frame, coaxial cable, connector, splitters, and
back planes before reaching the XRT7295AT device.
This section defines the maximum distribution frame and
cable loss from the cross-connect to the XRT7295AT
input.
External Loop Filter Capacitor
Figure 3 shows the connection to an external 0.1mF
capacitor at the LPF1/LPF2 pins. This capacitor is part of
the PLL filter. A non-polarized, low-leakage capacitor
should be used. A ceramic capacitor with the value 0.1mF
± 20% is acceptable.
Rev.1.20
9