LXT971ABC datasheet(21/90 Pages) INTEL

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LXT971A 3.3V Dual-Speed Fast Ethernet Transceiver

Datasheet

Document #: 249414

Revision #: 002

Rev. Date: August 7, 2002

3.0

Functional Description

3.1

Introduction

The LXT971A is a single-port Fast Ethernet 10/100 transceiver that supports 10 Mbps and 100

Mbps networks and complies with all applicable requirements of IEEE 802.3. The LXT971A

directly drives either a 100BASE-TX line (up to 140 meters) or a 10BASE-T line (up to 185

meters). The device also supports 100BASE-FX operation via a Low Voltage PECL (LVPECL)

interface.

3.1.1

Comprehensive Functionality

The LXT971A provides a standard Media Independent Interface (MII) for 10/100 MACs. The

LXT971A 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.

The LXT971A reads its configuration pins on power-up to check for forced operation settings. If

not configured for forced operation, the device 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 LXT971A auto-negotiates with it using Fast Link Pulse (FLP)

Bursts. If the PHY partner does not support auto-negotiation, the LXT971A automatically detects

the presence of either link pulses (10 Mbps PHY) or Idle symbols (100 Mbps PHY) and sets its

operating conditions accordingly.

The LXT971A provides half-duplex and full-duplex operation at 100 Mbps and 10 Mbps.

3.1.2

OSP™ Architecture

The LXT971A 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 LXT971A provides improved data recovery, EMI performance and low power

consumption.

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