DP83848JSQSLASHNOPB datasheet(42/84 Pages) TI1

42 / 84 page

DP83848H, DP83848J, DP83848K, DP83848M, DP83848T

SNLS250E – MAY 2008 – REVISED APRIL 2015

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6.5.1.2.3 Digital Adaptive Equalization and Gain Control

When transmitting data at high speeds over copper twisted pair cable, frequency dependent attenuation

becomes a concern. In high-speed twisted pair signaling, the frequency content of the transmitted signal

can vary greatly during normal operation based primarily on the randomness of the scrambled data

stream. This variation in signal attenuation caused by frequency variations must be compensated to

ensure the integrity of the transmission.

In order to ensure quality transmission when employing MLT-3 encoding, the compensation must be able

to adapt to various cable lengths and cable types depending on the installed environment. The selection of

long cable lengths for a given implementation, requires significant compensation which will over-

compensate for shorter, less attenuating lengths. Conversely, the selection of short or intermediate cable

lengths requiring less compensation will cause serious under-compensation for longer length cables. The

compensation or equalization must be adaptive to ensure proper conditioning of the received signal

independent of the cable length.

The DP83848x uses an extremely robust equalization scheme referred as ‘Digital Adaptive Equalization.’

The Digital Equalizer removes ISI (inter-symbol interference) from the receive data stream by continuously

adapting to provide a filter with the inverse frequency response of the channel. Equalization is combined

with an adaptive gain control stage. This enables the receive 'eye pattern' to be opened sufficiently to

allow very reliable data recovery.

The curves given in Figure 6-7 illustrate attenuation at certain frequencies for given cable lengths. This is

derived from the worst case frequency vs attenuation figures as specified in the EIA/TIA Bulletin TSB-36.

These curves indicate the significant variations in signal attenuation that must be compensated for by the

receive adaptive equalization circuit.

Figure 6-7. EIA/TIA Attenuation vs Frequency for 0, 50, 100, 130 and 150 Meters of CAT 5 Cable

6.5.1.2.4 Base Line Wander Compensation

The DP83848x 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 average DC content, relatively short period over time,

of an AC coupled digital transmission over a given transmission medium (that is, copper wire).

Detailed Description

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DP83848JSQ/NOPB Datasheet(PDF) 42 Page - Texas Instruments