A Modulo-FIR Equalizer for Wireline Communications

This paper presents a transmit-side modulo-FIR equalizer (MFE) that is suitable for future high-throughput links. In a proposed PAM transceiver architecture, forward error correction (FEC) is employed to mitigate the BER degradation by the reduced SNR. Because of the poor compatibility of a decision-feedback equalizer with the FEC system, we propose to use the MFE on the transmitter side instead, thereby avoiding a problem of error propagation. The MFE has several advantages over the conventional transmit-side equalization technique, Tomlinson-Harashima precoding (THP). The MFE predicts a modulo bit before the FIR equalizer whereas the THP equalizer calculates a modulo bit within the IIR equalizer. Hence, the overall calculation complexity is much relaxed in the MFE case, improving the operating speed. Moreover, the performance of the FIR equalizer is better than that of the IIR equalizer for handling a multiple-pole channel. By employing the MFE, the maximally achievable eye opening is improved by 30 % for PAM4 signaling, compared to the THP case.