XR-T7295 Datasheet, PDF (5/20 Pages) Exar Corporation – DS3/Sonet STS-1 Integrated Line Receiver

XR-T7295
System A
ÎÎÎÎ _XR-T7296
ÎÎÎÎÎÎÎÎ ^Transmitter
0-450 ft.
0-450 ft.
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ _DSX-3
Cross
Connect
Frame
Î
or STSX-1
Type 728A
Coaxial Cable
System B
ÎÎÎÎÎ _XR-T7295
ÎÎÎÎÎÎÎÎÎÎ _Receiver
Figure 2. Application Diagram
SYSTEM DESCRIPTION
Receive Path Configurations
In the receive signal path (see Figure 1), the internal
equalizer can be included by setting REQB = 0 or
bypassed by setting REQB = 1. The equalizer bypass
option allows easy interfacing of the XR-T7295 device
into systems already containing external equalizers.
Figure 3 illustrates the receive path options.
In Case 1 of Figure 3, the signal from the DSX-3
cross-connect feeds directly into R_IN. In this mode, the
user should set REQB = 0, engaging the equalizer in the
data path. Table 1 and the following sections describe the
receive signal requirements.
In Case 2 of Figure 3, external line build-out (LBO) and
equalizer networks precede the XR-T7295 device. In this
mode, the signal at R_IN is already equalized, and the
on-chip filters should be bypassed by setting REQB=1.
The signal at R_IN must meet the amplitude limits
described in Table 1
In applications where the XR-T7295 device is used to
monitor DS3 transmitter outputs directly, the receive
equalizer should be bypassed. Again, the signal at R_IN
must meet the amplitude limits described in Table 1.
Minimum signals are for SOJ devices. Due to increased
package parasitics, add 3dB to all table values for DIP
devices.
Maximum input amplitude under all conditions is 850mV
pk.
Although system designers typically use power in dBm to
describe input levels, the XR-T7295 responds to peak
input signal amplitude. Therefore, the XR-T7295 input
signal limits are given in mV pk. Conversion factors are as
follows:
At DSX3: 390mV pk ' 0 dBm
At DSX3 + 450 ft. of cable: 310 mV pk ' 0 dBm
Data
Rate
DS3
STS-1
REQB
0
1
0
1
LOSTHR
0
V_DD/2
V_DD
0
V_DD/2
V_DD
0
V_DD/2
V_DD
0
V_DD/2
V_DD
Minimum
Signal
80
60
40
80
80
80
110
80
60
110
110
110
Unit
mV pk
mV pk
mV pk
mV pk
mV pk
mV pk
mV pk
mV pk
mV pk
mV pk
mV pK
mV pk
Table 1. Receive Input Signal Amplitude
Requirements
Rev. 1.05
5