Equalizer Design and Performance Trade-Offs in ADC-Based Serial Links

This paper investigates the performance benefit of using nonuniformly quantized ADCs for implementing high-speed serial receivers with decision-feedback equalization (DFE). A way of determining an optimal set of ADC thresholds to achieve the minimum bit-error rate (BER) is described, which can yield a very different set from the one that minimizes signal quantization errors. By recognizing that both the loop-unrolling DFE receiver and ADC-based DFE receiver decide each received bit based upon the result of a single slicer, an efficient architecture named reduced-slicer partial-response DFE (RS-PRDFE) receiver is proposed. The RS-PRDFE receiver eliminates redundant or unused slicers from the previous DFE receiver implementations. Both the simulation and measurement results from a 10 Gb/s ADC-based receiver fabricated in 65 nm CMOS technology and multiple backplane channels demonstrate that the RS-PRDFE can achieve the BER of a 3-4-bit uniform ADC only with 4 data slicers. Also, the combined use of linear equalizers (LEs) can further reduce the required slicer count in RS-PRDFE receivers, but only when the LEs are realized in analog domain.