L80227 LSI, L80227 Datasheet - Page 33

• Manufacturer Part Number: L80227
• Manufacturer: LSI

Specifications of L80227

• Lead Free Status / RoHS Status: Not Compliant

2.3.7 Twisted-Pair Transmitters
2.3.7.1 100 Mbits/s TP Transmitter
The algorithm for synchronization of the descrambler is the same as the
algorithm outlined in the IEEE 802.3 specification.
After the descrambler is synchronized, it maintains synchronization as
long as enough descrambled idle pattern ones are detected within a
given interval. To stay in synchronization, the descrambler needs to
detect at least 25 consecutive descrambled idle pattern ones in a 1 ms
interval. If 25 consecutive descrambled idle pattern ones are not
detected within the 1 ms interval, the descrambler goes out of
synchronization and restarts the synchronization process.
The descrambler is disabled for 10BASE-T operation.
This section describes the operation of the 10 and 100 Mbits/s TP
transmitters.
The TP transmitter consists of an MLT3 encoder, waveform generator,
and line driver.
The MLT3 encoder converts the NRZI data from the scrambler into a
three-level code required by IEEE 802.3. MLT3 coding uses three levels,
converting ones to transitions between the three levels, and zeros to no
transitions or changes in level.
The purpose of the waveform generator is to shape the transmit output
pulse. The waveform generator takes the MLT3 three-level encoded
waveform and uses an array of switched current sources to control the
shape of the twisted-pair output signal. The waveform generator consists
of switched current sources, a clock generator, filter, and logic. The
switched current sources control the rise and fall time as well as signal
level to meet IEEE 802.3 requirements. The output of the switched
current sources goes through a second order low-pass filter that
“smooths” the current output and removes any high-frequency
components. In this way, the waveform generator preshapes the output
waveform transmitted onto the twisted-pair cable such that the waveform
meets the pulse template requirements outlined in IEEE 802.3. The
waveform generator eliminates the need for any external filters on the TP
transmit output.
Block Diagram Description
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