DP83848CVVX National Semiconductor, DP83848CVVX Datasheet - Page 28

• Manufacturer Part Number: DP83848CVVX
• Manufacturer: National Semiconductor

Specifications of DP83848CVVX

• Lead Free Status / RoHS Status: Compliant

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4.2.2.1 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 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.
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-
Figure 8. EIA/TIA Attenuation vs. Frequency for 0, 50,
100, 130 & 150 meters of CAT 5 cable
28
tive to ensure proper conditioning of the received signal
independent of the cable length.
The DP83848C utilizes an extremely robust equalization
scheme referred as ‘Digital Adaptive Equalization.’
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.
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.