L- and H-Tile Transceiver PHY User Guide

ID 683621
Date 1/30/2024
Document Table of Contents Decision Feedback Equalization (DFE)

DFE amplifies the high frequency components of a signal without amplifying the noise content. It compensates for inter-symbol interference (ISI). DFE minimizes post-cursor ISI by adding or subtracting weighted versions of the previously received bits from the current bit. DFE works in synchronization with the TX pre-emphasis and downstream RX CTLE. This enables the RX CDR to receive the correct data that was transmitted through a lossy and noisy backplane.

The DFE advantage over CTLE is improved Signal to Noise Ratio (SNR).

Figure 192. Signal ISI

The DFE circuit stores delayed versions of the data. The stored bit is multiplied by a coefficient and then added to the incoming signal. The polarity of each coefficient is programmable.

The DFE architecture supports 15 fixed taps.

The 15 fixed taps translate to the DFE capable of removing the ISI from the previous 15 bits, beginning from the current bit.

Figure 193. Channel Pulse Response
Note: The pulse at the output of the channel shows a long decaying tail. Frequency-dependent losses and quality degradation induces ISI.