
LXT972A
—
3.3V Dual-Speed Fast Ethernet Transceiver Datasheet
16
Datasheet
3.0
Functional Description
3.1
Introduction
The LXT972A is a single-port Fast Ethernet 10/100 Transceiver that supports 10Mbps and
100Mbps networks. It complies with all applicable requirements of IEEE 802.3. The LXT972A
can directly drive either a 100BASE-TX line (up to 140 meters) or a 10BASE-T line (up to 185
meters).
3.1.1
Comprehensive Functionality
The LXT972A provides a standard Media Independent Interface (MII) for 10/100 MACs. The
LXT972A performs all functions of the Physical Coding Sublayer (PCS) and Physical Media
Attachment (PMA) sublayer as defined in the IEEE 802.3 100BASE-X standard. This device also
performs all functions of the Physical Media Dependent (PMD) sublayer for 100BASE-TX
connections.
On power-up, the LXT972A reads its configuration pins to check for forced operation settings. If
not configured for forced operation, it uses auto-negotiation/parallel detection to automatically
determine line operating conditions. If the PHY device on the other side of the link supports auto-
negotiation, the LXT972A auto-negotiates with it using Fast Link Pulse (FLP) Bursts. If the PHY
partner does not support auto-negotiation, the LXT972A automatically detects the presence of
either link pulses (10Mbps PHY) or Idle symbols (100Mbps PHY) and set its operating conditions
accordingly.
The LXT972A provides half-duplex and full-duplex operation at 100Mbps and 10Mbps.
3.1.2
OSP
Architecture
Intel’s LXT972A incorporates high-efficiency Optimal Signal Processing
design techniques,
combining the best properties of digital and analog signal processing to produce a truly optimal
device.
The receiver utilizes decision feedback equalization to increase noise and cross-talk immunity by
as much as 3 dB over an ideal all-analog equalizer. Using OSP mixed-signal processing techniques
in the receive equalizer avoids the quantization noise and calculation truncation errors found in
traditional DSP-based receivers (typically complex DSP engines with A/D converters). This
results in improved receiver noise and cross-talk performance.
The OSP signal processing scheme also requires substantially less computational logic than
traditional DSP-based designs. This lowers power consumption and also reduces the logic
switching noise generated by DSP engines. This logic switching noise can be a considerable
source of EMI generated on the device
’
s power supplies.
The OSP-based LXT972A provides improved data recovery, EMI performance and low power
consumption.