DFE mode is recommended for high-reflection channels, medium- to long-reach applications with high channel losses of 8 dB and above at the Nyquist frequency. DFE mode has the advantage of equalizing a channel without amplifying noise and crosstalk. Therefore, it is the best choice when crosstalk is a concern or when reflections are identified in a single-bit response analysis. In certain low-loss applications that require the use of DFE, the AGC is fixed. Please use the default Wizard settings.
DFE mode must be carefully considered in 8B/10B applications or where data scrambling is not employed. To properly adapt to data, the auto adaptation in DFE mode requires incoming data to be random. For example, in a XAUI application, the user payload data is non-scrambled and 8B/10B encoded. While the user payload is generally random, the frequency content of the data is inherently limited by the encoding, and there is nothing defined in the protocol to prevent repeated patterns from occurring. These repeated patterns can cause the auto adapting algorithms to drift away from the ideal equalization setting. Patterns with characteristics similar to PRBS7 (or higher polynomials) are sufficiently random for auto adaptation to properly choose the correct equalization setting.