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XRT7295IW

DS3/Sonet STS-1 Integrated Line Receiver

Exar Corporation 

XR-T7295

STS-1 SIGNAL REQUIREMENTS AT THE STSX

For STS-1 operation, the cross-connect is referred at the

STSX-1. Table 5 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 XR-T7295 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)

75Ω$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 5. STSX-1 Interconnection Specification

10000.....008642-ÎÎÎÎÎÎÎÎÎÎÎ1.0ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ-0.5ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ0ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ0.5ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ1.0ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ1.ÎÎÎÎÎÎÎÎÎÎÎ5 ÎÎÎÎÎÎÎÎÎÎÎ2ÎÎÎÎÎÎÎÎÎÎÎ.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 Ω resistor terminates the coaxial cable

with its characteristic impedance. The 0.01µF capacitor

to RIN couples the signal into the receive input without

disturbing the internally generated DC bias level present

on RIN. The input capacitance at the RIN pin is 2.8pF

typical (SOJ package) and 3.6pF typical (DIP package).

LOSS LIMITS FROM THE DSX-3 TO THE RECEIVE

INPUT

The signal at the cross-connect may travel through a

distribution frame, coaxial cable, connector, splitters, and

back planes before reaching the XR-T7295 device. This

section defines the maximum distribution frame and cable

loss from the cross-connect to the XR-T7295 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 XR-T7295 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

External Loop Filter Capacitor

Figure 3 shows the connection to an external 0.1µF

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 0.1µF

$ 20% is acceptable.

Rev. 1.05

9

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