DP83849CVSSLASHNOPB datasheet(32/101 Pages) TI1

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4.2.2.2 Base Line Wander Compensation

The DP83849C 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 10 illus-

trates the severity of the BLW event that can theoretically

be generated during 100BASE-TX packet transmission.

This event consists of approximately 800 mV of DC offset

for a period of 120

µs. Left uncompensated, events such as

this can cause packet loss.

4.2.3 Signal Detect

The signal detect function of the DP83849C is incorporated

to meet the specifications mandated by the ANSI FDDI TP-

PMD Standard as well as the IEEE 802.3 100BASE-TX

Standard for both voltage thresholds and timing parame-

ters.

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 DP83849C to

assert signal detect.

4.2.4 MLT-3 to NRZI Decoder

The DP83849C 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.

Figure 10. 100BASE-TX BLW Event

DP83849CVS/NOPB Datasheet(PDF) 32 Page - Texas Instruments

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