LAN83C183 Datasheet, PDF (28/113 Pages) SMSC Corporation – FAST ETHERNET PHYSICAL LAYER DEVICE

MLT3 encoded output data from the comparators and converts it to normal digital
data to be used for clock and data recovery.
1.2.8.2 10 MBITS/S TP RECEIVER
The 10 Mbits/s receiver detects input signals from the twisted-pair cable that are
within the template shown in Figure 1.5 The TP inputs are biased by internal resistors
and go through a low-pass filter designed to eliminate any high-frequency input
noise. The output of the receive filter goes to two different types of comparators:
squelch and zero crossing. The squelch comparator determines whether the signal
is valid, and the zero crossing comparator senses the actual data transitions after the
signal is determined to be valid. The output of the squelch comparator goes to the
squelch circuit and is also used for link pulse detection, SOI detection, and reverse
polarity detection. The output of the zero-crossing comparator is used for clock and
data recovery in the Manchester decoder.
Figure 1.5 TP Input Voltage Template (10 Mbits/s)
Short Bit
3.1 V
Slope 0.5 V/ns
585 mV
585 mV sin (π ∗ t/PW)
0
PW
Long Bit
3.1 V
Slope 0.5 V/ns
585 mV sin (π ∗ t/PW)
585 mV sin[2 π (t − PW2)/PW)]
0 PW/4
3PW/4 PW
585 mV
1.2.8.3 SQUELCH (100 MBITS/S)
The Squelch block determines if the TP input contains valid data. The 100 Mbits/s
TP squelch is one of the criteria used to determine link integrity. The squelch
comparators compare the TP inputs against fixed positive and negative thresholds,
called squelch levels. The output from the squelch comparator goes to a digital
squelch circuit, which determines whether the receive input data on that port is valid.
If the data is invalid, the receiver is in the squelched state. If the input voltage
exceeds the squelch levels at least four times with alternating polarity within a 10 µs
interval, the squelch circuit determines that the data is valid and the receiver enters
into the unsquelch state.
In the unsquelch state, the receive threshold level is reduced by approximately 30%
for noise immunity reasons and is called the unsquelch level. When the receiver is
in the unsquelch state, the input signal is considered valid.
SMSC DS – LAN83C183
28
Rev. 12/14/2000