LAN8808D datasheet(27/80 Pages) MICROCHIP

27 / 80 page

LAN8808D

DS00005833C-page 27

5.0

FUNCTIONAL DESCRIPTIONS

This section provides additional details of the major features supported by the LAN8808D:

• 10BASE-T/100BASE-TX Transceiver

• 1000BASE-T Transceiver

• Auto MDI/MDIX (Pair-Swap)

• Alignment and Polarity Detection/Correction

• Wave Shaping, Slew-Rate Control, and Partial Response

• Auto-Negotiation

• LinkMD Cable Diagnostics

• Energy Efficient Ethernet (EEE)

• IEEE 802.3-2018 Frame Preemption

• Start of Frame Indication

• Signal Quality Index

• Loopbacks

• QSGMII

• MIIM (MDIO) Interface

• Interrupts

• GPIOs

• LEDs

• Power Management

• PLL/Clocks and Resets

• JTAG

5.1

10BASE-T/100BASE-TX Transceiver

5.1.1

100BASE-TX TRANSMIT

The 100BASE-TX transmit function performs parallel-to-serial conversion, 4B/5B coding, scrambling, NRZ-to-NRZI con-

version, and MLT-3 encoding and transmission.

The circuitry starts with a parallel-to-serial conversion, which converts the MII data from the MAC into a 125 MHz serial

bit stream. The data and control stream is then converted into 4B/5B coding, followed by a scrambler. The serialized

data is further converted from NRZ-to-NRZI format, and then transmitted in MLT-3 current output. The output current is

set by an external 6.04 kΩ 1% resistor for the 1:1 transformer ratio.

The output signal has a typical rise/fall time of 4 ns and complies with the ANSI TP-PMD standard regarding amplitude

balance, and overshoot. The wave-shaped 10BASE-T output is also incorporated into the 100BASE-TX transmitter.

5.1.2

100BASE-TX RECEIVE

The 100BASE-TX receiver function performs adaptive equalization, DC restoration, MLT-3-to-NRZI conversion, data

and clock recovery, NRZI-to-NRZ conversion, de-scrambling, 4B/5B decoding, and serial-to-parallel conversion.

The receiving side starts with the equalization filter to compensate for inter-symbol interference (ISI) over the twisted

pair cable. Because the amplitude loss and phase distortion are a function of the cable length, the equalizer must adjust

its characteristics to optimize performance. In this design, the variable equalizer makes an initial estimation based on

comparisons of incoming signal strength against some known cable characteristics, then tunes itself for optimization.

This is an ongoing process and self-adjusts against environmental changes such as temperature variations.

Next, the equalized signal goes through a DC-restoration and data-conversion block. The DC-restoration circuit com-

pensates for the effect of baseline wander and improves the dynamic range. The differential data conversion circuit con-

verts the MLT-3 format back to NRZI. The slicing threshold is also adaptive.

LAN8808D Datasheet(PDF) 27 Page - Microchip Technology

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