XRT86L30
REV. 1.0.1
SINGLE T1/E1/J1 FRAMER/LIU COMBO
By default, RxRES[1:0] is set to "None" for no external fixed resistor. If an external fixed resistor is used, the
XRT86L30 uses the parallel combination of the external fixed resistor and the internal termination as the input
impedance. See Figure 58 for a typical connection diagram using the external fixed resistor.
NOTE: Without the external resistor, the XRT86L30 meets all return loss specifications. This mode was created to add
flexibility for optimizing return loss by using a high precision external resistor.
F
IGURE 58. TYPICAL
C
ONNECTION
D
IAGRAM
U
SING ONE EXTERNAL FIXED RESISTOR
R=240Ω, 210Ω, or 150Ω
XRT86L30 LIU
RTIP
1:1
Receiver
Input
R
Line Interface T1/E1/J1
RRING
0.1µF
Internal Impedance
9.1.3
Equalizer Control
The main objective of the equalizer is to amplify an input attenuated signal to a pre-determined amplitude that
is acceptable to the peak detector circuit. Using feedback from the peak detector, the equalizer will gain the
input up to the maximum value specified by the equalizer control bits, in the appropriate channel register,
normalizing the signal. Once the signal has reached the pre-determined amplitude, the signal is then
processed within the peak detector and slicer circuit. A simplified block diagram of the equalizer and peak
detector is shown in Figure 59.
F
IGURE 59. SIMPLIFIED
B
LOCK
D
IAGRAM OF THE
EQUALIZER AND PEAK DETECTOR
Peak
Detector &
Slicer
RTIP
RRING
Rx Equalizer
Rx Equalizer
Control
9.1.4
Cable Loss Indicator
The ability to monitor the cable loss attenuation of the receiver inputs is a valuable feature. The XRT86L30
contains a per channel, read only register for cable loss indication. CLOS[5:0] is a 6-Bit binary word that
reports the value of cable loss in 1dB steps with an absolute accuracy of ±1dB. An example of -25dB cable
loss attenuation is shown in Figure 60.
F
IGURE 60. SIMPLIFIED BLOCK DIAGRAM OF THE CABLE LOSS INDICATOR
XRT86L30
-25dB Attenuated
Signal
-25dB of Cable
Loss
Equalizer and
Peak Detector
Read Only
CLOS[5:0] = 0x19h
(25dec = 19hex)
190
EXAR [ EXAR CORPORATION ]
