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The LXT305A receives the signal input from one twisted-
pair line on each side of a center-grounded transformer.
Positive pulses are received at RTIP and negative pulses
are received at RRING. Recovered data is output at RPOS
and RNEG, and the recovered clock is output at RCLK.
Refer to Test Specifications for LXT305A receiver timing.
The signal received at RPOS and RNEG is processed
through the peak detector and data slicers. The peak detec-
tor samples the inputs and determines the maximum value
of the received signal. A percentage of the peak value is
provided to the data slicers as a threshold level to ensure
optimum signal-to-noise ratio. For T1 applications (deter-
mined by Equalizer Control inputs EC1 - EC3
000 or
001) the threshold is set to 70% of the peak value. This
threshold is maintained above 65% for up to 15 successive
zeros over the range of specified operating conditions. For
E1 applications (EC inputs = 000 or 001) the threshold is
50%.
The receiver is capable of accurately recovering signals
with up to -13.6 dB of attenuation (from 2.4 V), corre-
sponding to a received signal level of approximately 500
mV. Maximum line length is 1500 feet of ABAM cable
(approximately 6 dB of attenuation). Regardless of re-
ceived signal level, the peak detectors are held above a
minimum level of .3 V to provide immunity from impul-
sive noise.
After processing through the data slicers, the received sig-
nal is routed to the data and clock recovery sections, and to
the receive monitor. The data and clock recovery circuits
are highly tolerant with an input jitter tolerance significant-
ly better than required by Pub 62411. Refer to Test Speci-
fications for additional information.
The receiver monitor loads a digital counter at the RCLK
frequency. The count is incremented each time a zero is
received, and reset to zero each time a one (mark) is
received. Upon receipt of 175 consecutive zeros the LOS
pin goes High, and a smooth transition replaces the RCLK
output with the MCLK. Received marks are output regard-
less of the LOS status, but the LOS pin will not reset until
the ones density reaches 12.5%. This level is based on
receipt of at least 4 ones in any 32-bit period with no more
than 15 consecutive zeros.
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