I347-AT4 Datasheet, PDF (28/148 Pages) Intel Corporation – Intel® Ethernet Network Connection I347-AT4 Datasheet

I347-AT4—Device Functionality
3.2.3
Receive Side Network Interface
3.2.3.1
Analog-to-Digital Converter
The I347-AT4 incorporates an advanced high speed ADC on each receive channel with
greater resolution than the ADC used in the reference model of the 802.3ab standard
committee. Higher resolution ADC results in better SNR, and therefore, lower error
rates. Proprietary architectures and design techniques result in high differential and
integral linearity, high power supply noise rejection, and low metastability error rate.
The ADC samples the input signal at 125 MHz.
3.2.3.2
Active Hybrid
The I347-AT4 employs a sophisticated on-chip hybrid to substantially reduce the near-
end echo, which is the super-imposed transmit signal on the receive signal. The hybrid
minimizes the echo to reduce the precision requirement of the digital echo canceller.
The on-chip hybrid allows both the transmitter and receiver to use the same
transformer for coupling to the twisted pair cable, which reduces the cost of the overall
system.
3.2.3.3
Echo Canceller
Residual echo not removed by the hybrid and echo due to patch cord impedance
mismatch, patch panel discontinuity, and variations in cable impedance along the
twisted pair cable result in drastic SNR degradation on the receive signal. The I347-AT4
employs a fully developed digital echo canceller to adjust for echo impairments from
more than 100 meters of cable. The echo canceller is fully adaptive to compensate for
the time varying nature of channel conditions.
3.2.3.4
NEXT Canceller
The 1000BASE-T physical layer uses all 4 pairs of wires to transmit data to reduce the
baud rate requirement to only 125 MHz. This results in significant high frequency
crosstalk between adjacent pairs of cable in the same bundle. The I347-AT4 employs 3
parallel NEXT cancellers on each receive channel to cancel any high frequency crosstalk
induced by the adjacent 3 transmitters. A fully adaptive digital filter is used to
compensate for the time varying nature of channel conditions.
3.2.3.5
Baseline Wander Canceller
Baseline wander is more problematic in the 1000BASE-T environment than in the
traditional 100BASE-TX environment due to the DC baseline shift in both the transmit
and receive signals. The I347-AT4 employs an advanced baseline wander cancellation
circuit to automatically compensate for this DC shift. It minimizes the effect of DC
baseline shift on the overall error rate.
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