Various systems and methods providing high speed decoding, enhanced power
reduction and clock domain partitioning for a multi-pair gigabit Ethernet
transceiver are disclosed. ISI compensation is partitioned into two
stages; a first stage compensates ISI components induced by
characteristics of a transmitters partial response pulse shaping filter
in a demodulator, a second stage compensates ISI components induced by
characteristics of a multi-pair transmission channel in a Viterbi
decoder. High speed decoding is accomplished by reducing the DFE depth by
providing an input signal from a multiple decision feedback equalizer to
the Viterbi based on a tail value and a subset of coefficient values
received from a unit depth decision-feedback equalizer. Power reduction
is accomplished by adaptively truncating active taps in the NEXT, FEXT
and echo cancellation filters, or by disabling decoder circuitry
portions, as channel response characteristics allow. A receive clock
signal is generated such that it is synchronous in frequency with analog
sampling clock signals and has a particular phase offset with respect to
one of the sampling clock signals. This phase offset is adjusted such
that system performance degradation due to coupling of switching noise
from the digital sections to the analog sections is substantially
minimized.