Optimal equalization for reducing the impact of channel group delay distortion on high-speed backplane data transmission

Channel group delay distortion represents the transmission channel's phase dispersion, which results in signal distortion and adds intersymbol interference (ISI) to the received data eyes in addition to amplitude attenuation. Despite the fact that channel group delay distortion is especially critical in high-speed backplane applications, its effects have not been discussed in detail previously in the literature. This paper presents a study of the impacts of channel group delay distortion on high-speed backplane data transmissions. Equalization strategies for reducing the impact of group delay distortion are explored. A unique bit-edge equalization (BEE) scheme is presented that reduces the impact of channel group delay distortion by compressing the data spectrum in conjunction with optimizing the sampling phase. With transmitter (TX) pre-coding, the proposed BEE employs a 5-post-tap conventional symbol-spaced FIR (SSF) filter as the TX pre-emphasis, eliminates the need for a “delay and add” duobinary filter as in the conventional duobinary transceiver, and is more compatible with the bit-centre equalization (BCE) scheme. In this work, 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 optimality of the proposed BEE in reducing the impact of channel group delay distortion and mitigating ISI is demonstrated at a data rate as high as 12 Gbps.