4.2.2.1 Digital Adaptive Equalization and Gain Control tive to ensure proper conditioning of the received signal
independent of the cable length.
When transmitting data at high speeds over copper twisted
The DP83848I utilizes an extremely robust equalization
scheme referred as ‘Digital Adaptive Equalization.’
pair cable, frequency dependent attenuation becomes a
concern. In high-speed twisted pair signalling, the fre-
quency content of the transmitted signal can vary greatly
during normal operation based primarily on the random-
ness of the scrambled data stream. This variation in signal
attenuation caused by frequency variations must be com-
pensated to ensure the integrity of the transmission.
The Digital Equalizer removes ISI (inter symbol interfer-
ence) from the receive data stream by continuously adapt-
ing 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.
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 compensa-
tion which will over-compensate for shorter, less attenuat-
ing 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 adap-
The curves given in Figure 8 illustrate attenuation at certain
frequencies for given cable lengths. This is derived from
the worst case frequency vs. attenuation figures as speci-
fied 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 cir-
cuit.
Figure 8. EIA/TIA Attenuation vs. Frequency for 0, 50,
100, 130 & 150 meters of CAT 5 cable
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