Crosstalk-included PAM-4 Worst Eye Diagram Estimation Method for High-speed Serial Links

Abstract

In this paper, we first propose a crosstalk-included pulse amplitude modulation-4 (PAM-4) worst eye diagram estimation method. The proposed method is based on the conventional peak distortion analysis (PDA) method. Compared to the non-return-to-zero (NRZ), the PAM-4 has 3 single bit responses (SBRs) due to the 4-level amplitude modulation. To consider worst crosstalk effects, the main idea is to take 3-level transition crosstalk responses as input when estimating each level-transition worst eyes by the PDA. By superposition of the estimated 1-level, 2-level and 3-level worst eyes, a PAM-4 worst eye contour can be provided as an innermost contour. For verification, we compared the estimated PAM-4 worst eye diagrams with those at bit-error-ratio (BER) 10-12 by the statistical eye simulator using input output buffer information specification-algorithmic modeling interface (IBIS-AMI). We compared the results in various cases: with 1 near-end crosstalk (NEXT) aggressor (aggr); with 1 NEXT and 1 far-end crosstalk (FEXT) aggrs; with 2 NEXT and 1 FEXT aggrs. The error rates of eye widths and heights between the proposed method and the simulator were 6.3 % and 4 % respectively. Moreover, we compared the computing time. The computing time of the proposed method was within 50 ms in all the cases, however that of the simulator increases from 10.5 s to 21.7 s as the number of aggrs increases.