AR8031-AL1B データシートの表示（PDF） - Unspecified

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AR8031-AL1B

AR8031 Integrated 10/100/1000 Mbps Ethernet Transceiver

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2.3 Transmit Functions

Table 2-2 describes the transmit function

encoder modes.

Table 2-2. Transmit Function Encoder Modes

Encoder Mode Description

1000 BASE-T

In 1000 BASE-T mode, the AR8031

scrambles transmit data bytes

from the MAC interfaces to 9-bit

symbols and encodes them into

4D five-level PAM signals over the

four pairs of CAT5 cable.

100 BASE-TX

In 100 BASE-TX mode, 4-bit data

from the MII is 4B/5B serialized,

scrambled, and encoded to a

three-level MLT3 sequence

transmitted by the PMA.

10 BASE-Te

In 10 BASE-Te mode, the AR8031

transmits and receives

Manchester-encoded data.

2.4 Receive Functions

2.4.1 Decoder Modes

Table 2-3 describes the receive function

decoder modes.

Table 2-3. Receive Function Decoder Modes

Decoder Mode Description

1000 BASE-T

In 1000 BASE-T mode, the PMA

recovers the 4D PAM signals after

accounting for the cabling

conditions such as skew among

the four pairs, the pair swap order,

and the polarity of the pairs. The

resulting code group is decoded

into 8-bit data values. Data stream

delimiters are translated

appropriately and data is output

to the MAC interfaces.

100 BASE-TX

In 100 BASE-TX mode, the receive

data stream is recovered and

descrambled to align to the

symbol boundaries. The aligned

data is then parallelized and 5B/

4B decoded to 4-bit data. This

output runs to the MII receive

data pins after data stream

delimiters have been translated.

10 BASE-Te

In 10 BASE-Te mode, the

recovered 10 BASE-Te signal is

decoded from Manchester then

aligned.

2.4.2 Analog to Digital Converter

The AR8031 device employs an advanced high

speed ADC on each receive channel with high

resolution, which results in better SNR and

lower error rates.

2.4.3 Echo Canceller

A hybrid circuit is used to transmit and receive

simultaneously on each pair. A signal reflects

back as an echo if the transmitter is not

perfectly matched to the line. Other connector

or cable imperfections, such as patch panel

discontinuity and variations in cable

impedance along the twisted pair cable, also

result in drastic SNR degradation on the

receive signal. The AR8031 device implements

a digital echo canceller to adjust for echo and is

adaptive to compensate for the varied channel

conditions.

2.4.4 NEXT Canceller

The 1000 BASE-T physical layer uses all four

pairs of wires to transmit data. Because the four

twisted pairs are bundled together, significant

high frequency crosstalk occurs between

adjacent pairs in the bundle. The AR8031

device uses three parallel NEXT cancellers on

each receive channel to cancel high frequency

crosstalk. The AR8031 cancels NEXT by

subtracting an estimate of these signals from

the equalizer output.

2.4.5 Baseline Wander Canceller

Baseline wander results from Ethernet links

that AC-couple to the transceivers and from

AC coupling that cannot maintain voltage

levels for longer than a short time. As a result,

transmitted pulses are distorted, resulting in

erroneous sampled values for affected pulses.

Baseline wander is more problematic in the

1000 BASE-T environment than in 100 BASE-

TX due to the DC baseline shift in the transmit

and receive signals. The AR8031 device uses an

advanced baseline wander cancellation circuit

that continuously monitors and compensates

for this effect, minimizing the impact of DC

baseline shift on the overall error rate.

2.4.6 Digital Adaptive Equalizer

The digital adaptive equalizer removes inter-

symbol interference at the receiver. The digital

adaptive equalizer takes unequalized signals

from ADC output and uses a combination of

feedforward equalizer (FFE) and decision

18 • AR8031 Integrated 10/100/1000 Mbps Ethernet Transceiver

18 • August 2011

Atheros Communications, Inc.

COMPANY CONFIDENTIAL

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