XRT5997 Datasheet, PDF (28/37 Pages) Exar Corporation – Seven-Channel E1 Line Interface Unit

XRT5997
2.3 The “Peak Detector and Slicer Block
After the incoming line signal has passed through the
Receive Equalizer block, it will next be routed to the
“Slicer” block. The purpose of the “Slicer” block is to
quantify a given bit-period (or symbol) within the incom-
ing line signal as either a “1” or a “0”.
2.3 The “LOS Detector” block
The LOS Detector block, within each channel (of the
XRT5997 device) was specifically designed to comply
with the “LOS Declaration/Clearance” requirements per
ITU-T G.775. As a consequence, the channel will
declare an LOS Condition, (by driving the “RxLOS”
output pin “high”) if the received line signal amplitude
drops to –20dB or below. Further, the channel will clear
the LOS Condition if the signal amplitude rises back up
to –15dB or above. Figure 10 presents an illustration
that depicts the signal levels at which a given channel
(within the XRT5997 device) will assert and clear LOS.
0 dB
-6 dB
-9dB
LOS Signal Must be Cleared
Maximum Cable Loss for E1
-35dB
LOS Signal may be Cleared or Declared
LOS Signal Must be Declared
Figure 10. Illustration of the Signal Levels that the Receiver Sections
(within XRT5997 device) will declare and clear LOS
Timing Requirements associated with Declaring and
Clearing the LOS Indicator. The XRT5997 device was
designed to meet the ITU-T G.775 specification timing
requirements for declaring and clearing the LOS indica-
tor. In particular, the XRT5997 device will declare an
LOS, between 10 and 255 UI (or E1 bit-periods) after
the actual time the LOS condition occurred. Further,
the XRT5997 device will clear the LOS indicator within
10 to 255 UI after restoration of the incoming line
signal. Figure 11 illustrates the LOS Declaration and
Clearance behavior, in response to first, the “Loss of
Signal” event and then afterwards, the restoration of
the signal.
Rev. 1.0.0
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