Integrated PAM4/NRZ N-Way Parallel Digital Unrolled Decision Feedback Equalizer (DFE)

摘要

An N-way parallel, unrolled decision feedback equalizer for a SerDes receiver can convert between four-tap PAM-2 and two-tap PAM-4 mode, maximizing hardware through the use of mode control multiplexers. Each of N interleaved parallel branches includes an ISI correction stage for generating a partial result approximating intersymbol interference and comparing the partial result to a threshold, a carry look-ahead stage for generating a second partial result based in part on previously generated partial results, and a decision feedback stage for generating a final decision based on previous branches. Mode control multiplexers can select from PAM-2 and PAM-4 operating modes, PAM-2 and MAP-4 inputs at various stages, or from single-bit PAM-2 and two-bit PAM-4 outputs. ISI correction can additionally be reformulated to incorporate comparing raw input symbols to a combination of approximated ISI and a threshold.