Low-Latency DFE Error Propagation Correction and Partial-Response Filter-Based Threshold Estimation for High-Speed Wireline Receivers

In analog-to-digital converter (ADC)- and digital signal processing (DSP)-based long-reach PAM-4 wireline receivers, incorrect initial threshold settings can hinder equalizer coefficient convergence and degrade signal integrity. While maximum-likelihood sequence detection mitigates decision feedback equalizer (DFE) error propagation and improves bit error rate (BER), its high latency makes it unsuitable for latency-sensitive applications. This paper proposes two circuit techniques that enhance threshold estimation and suppress DFE error propagation with minimal latency. First, a 1-D partial-response (PR) filter is introduced to reshape the received signal, inducing negative autocorrelation that improves initial threshold estimation, even when the transmitted symbols are originally uncorrelated. Second, a low-latency DFE-CURE (Correction under Uncertainty with Reverse-decision Evaluation) architecture evaluates two candidate sequences - one based on the original decision and the other based on an alternative symbol - and selects the path with the lower accumulated metric. This avoids full-sequence decoding while adding only three DSP clock cycles of latency beyond the conventional DFE, resulting in a total of five cycles after feed-forward equalization. A 56-Gb/s PAM-4 ADC/DSP-based receiver, fabricated in a 28-nm process, is evaluated under 23.1-dB channel loss. Simulations show that the 1-D PR filter reduces threshold estimation error by 83%, and DFE-CURE lowers BER from 10^-5 to 10^-6, achieving a 10× improvement.