![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_213.png)
PRELIMINARY
XRT79L71
198
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
4.3.1.9.2
Interference Margin Capability of the Receive DS3 LIU Block
The purpose of an Interference Margin Test (or specification) is to verify that the Receive DS3/E3 LIU Block
(within the XRT79L71) can tolerate a certain amount of inband noise and still properly receive a DS3 or E3
signal.
Although Interference Margin is not a specific requirement for DS3 applications, numerous customers do
inquire about the Interference Margin capabilities of our DS3 LIU Products. As a consequence, we have
specifically designed the Receive DS3/E3 LIU Block such that it will have sufficient Interference Margin in order
to meet our Customer's requirements.
This particular section documents the Interference Margin capability of the Receive DS3/E3 LIU Block, for DS3
applications.
Test Approach
The basic test configuration used for Interference Margin measurements is illustrated below in Figure 89.
The CERJAC Tester was configured to internally generate a DS3 signal, which was filled with an un-framed
2^23-1 PRBS pattern. The Transmit Output of the CERJAC 156MTS Tester was set to DSX-3. Hence, the
Tester will generate (within its output line signal) pulses that comply with the DSX-3 Isolated Pulse Template
requirements per Bellcore GR-499-CORE.
The DS3 line signal was then routed to the ME-1005 75W Coaxial Cable Simulator (from Mountain
Engineering). The Cable Simulator could either be configured to 0 or 450 feet of shaped loss into the DS3/
STS-1 line signal.
Next, this attenuated signal will be routed to one of the inputs of a summing network. The output of the
function-generator (the output frequency of which is set at half the bit-rate) will be applied to the other input.
TABLE 25: RECEIVE SENSITIVITY TEST RESULTS (DS3 APPLICATIONS)
TEST
NUMBER
POWER SUPPLY VOLTAGE
RECEIVE SENSITIVITY
COMMENTS
1
3.15V
DSX-3 + 1215 feet of Cable Loss
2
3.30V
DSX-3 + 1215 feet of Cable Loss
3
3.45V
DSX-3 + 1215 feet of Cable Loss
FIGURE 89. ILLUSTRATION OF TEST SET-UP USED TO TEST THE XRT79L71 FOR INTERFERENCE MARGIN
CERJAC
156MTS
Tester
(Transmit
Output =
DSX-3)
CERJAC
156MTS
Tester
(Transmit
Output =
DSX-3)
Flat Loss
Attenuator
Flat Loss
Attenuator
Cable
Simulator
Cable
Simulator
XRT79L71
Evaluation
Board
XRT79L71
Evaluation
Board
Function
Generator
Function
Generator