ISI mitigation using bit-edge equalization in high-speed backplane data transmission

This paper presents an improved bit-edge equalization (BEE) method for mitigating intersymbol interference (ISI) in high-speed backplane applications. Using a least-mean-square (LMS) adaptive algorithm as a receiver (RX) error convergence engine, the proposed BEE method is based on equalizing only the edges of data bits with an adjustment of LMS error derivation points, which in turn changes the error information and affects filter coefficients for pulse amplitude modulation. As a result, the received channel far-end 3-level bit-edge eye diagrams can be optimized. This proposed BEE method employs a conventional symbol-spaced FIR (SSF) filter as transmitter (TX) pre-emphasis for bit-edge equalization. With TX data pre-coding, the received channel far-end 3-level signal to 2-level binary decoding only depends on the current received bit. No error propagation occurs. In this work, the proposed BEE method is compared with the bit-center equalization (BCE) method and duobinary signaling method by applying the adjustment of LMS error derivation points in all these methods. A typical Tyco 34-inch FR4 backplane channel is used as the comparison benchmark. A Matlab script based link simulation tool is used to evaluate the link performance. The simulation results demonstrate that the proposed BEE method is the most effective for mitigating ISI in relatively high-loss channels.