Intel® Arria® 10 Transceiver PHY User Guide

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ID 683617
Date 3/28/2022
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5.1.5.6. 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). DFE amplifies the power of the high frequency components without amplifying the noise power.

Figure 231. Signal ISI


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

The DFE architecture supports eleven fixed taps.

The eleven fixed taps translate to the DFE capable of removing the ISI from the next 11 bits, beginning from the current bit.

Figure 232. Channel Pulse Response


Note: The pulse at the output of the channel shows a long decaying tail. Frequency-dependent losses and quality degradation affects other signals.
Supported modes for DFE:
  • Disabled Mode:
    • DFE disabled mode is similar to DFE manual mode, except all DFE tap values in this mode are set to zero. DFE tap values can be set in Assignment Editor/.qsf or using Avalon® memory-mapped interface.
  • Manual Mode:
    • In this mode, manual DFE tap values can be set in Assignment Editor/.qsf or using Avalon® memory-mapped interface.
  • Adaptation Enabled Mode:
    • In this adaptation mode, DFE tap values are controlled by the Adaptive Parametric Tuning Engine. This mode uses the converged DFE tap values given by the Adaptive Parametric Tuning Engine.

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