DP83848YB_08 NSC [National Semiconductor], DP83848YB_08 Datasheet - Page 29

• Manufacturer Part Number: DP83848YB_08
• Manufacturer: NSC [National Semiconductor]

4.2.2.2 Base Line Wander Compensation
The DP83848YB is completely ANSI TP-PMD compliant
and includes Base Line Wander (BLW) compensation. The
BLW compensation block can successfully recover the TP-
PMD defined “killer” pattern.
BLW can generally be defined as the change in the aver-
age DC content, relatively short period over time, of an AC
coupled digital transmission over a given transmission
medium. (i.e., copper wire).
BLW results from the interaction between the low fre-
quency components of a transmitted bit stream and the fre-
quency response of the AC coupling component(s) within
the transmission system. If the low frequency content of
the digital bit stream goes below the low frequency pole of
the AC coupling transformers then the droop characteris-
tics of the transformers will dominate resulting in potentially
serious BLW.
The digital oscilloscope plot provided in Figure 9 illustrates
the severity of the BLW event that can theoretically be gen-
erated during 100BASE-TX packet transmission. This
event consists of approximately 800 mV of DC offset for a
period of 120 s. Left uncompensated, events such as this
can cause packet loss.
4.2.3 Signal Detect
The signal detect function of the DP83848YB is incorpo-
rated to meet the specifications mandated by the ANSI
Figure 9. 100BASE-TX BLW Event
29
FDDI TP-PMD Standard as well as the IEEE 802.3
100BASE-TX Standard for both voltage thresholds and tim-
ing parameters.
Note that the reception of normal 10BASE-T link pulses
and fast link pulses per IEEE 802.3u Auto-Negotiation by
the 100BASE-TX receiver do not cause the DP83848YB to
assert signal detect.
4.2.4 MLT-3 to NRZI Decoder
The DP83848YB decodes the MLT-3 information from the
Digital Adaptive Equalizer block to binary NRZI data.
4.2.5 NRZI to NRZ
In a typical application, the NRZI to NRZ decoder is
required in order to present NRZ formatted data to the
descrambler.
4.2.6 Serial to Parallel
The 100BASE-TX receiver includes a Serial to Parallel
converter which supplies 5-bit wide data symbols to the
PCS Rx state machine.
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