Transceiver Design for High-Density Links With Discontinuities Using Modal Signaling

Abstract

In high-speed chip-to-chip single-ended signaling links, far-end crosstalk presents one of the dominant noise sources, limiting the performance of the link. Diagonalizing the channel using modal decomposition has been proposed to mitigate the crosstalk, but so far only the transceiver designed for uniform low-loss homogenous media channels has been investigated. Furthermore, a practical circuit implementation of such a transceiver system will unavoidably deviate from the ideal (crosstalk-free) eigenvalue decomposition. In this paper, the impact of modal encoder/decoder coefficient quantization, random common noise, and uncorrelated noise on signal integrity is analyzed in terms of system-level performance metrics, signal-to-noise ratio at the receiver slicer, and bit error rate. Also discussed is the optimal selection of decoder coefficients with respect to the input-referred noise at the receiver. Based on these guidelines, a circuit design of a modal transceiver system over a typical memory bus with discontinuities is presented in detail. The proposed approach is verified using circuit-based link simulation, and the performance compared to several other proposed crosstalk-cancellation techniques.