Datasheet

DP83848VYB

www.ti.com

SNLS266D –MAY 2007–REVISED APRIL 2013

7.2.2.1 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 signalling, 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 DP83848VYB utilizes 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 7-4 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 7-3. EIA/TIA Attenuation vs. Frequency for 0, 50, 100, 130 & 150 Meters of CAT 5 Cable

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