[Paper Review] High Speed Parallel Signal Crosstalk Cancellation Concept

Chad M. Smutzer, Michael J. Degerstrom+2 more|arXiv (Cornell University)|Jan 17, 2023

Electromagnetic Compatibility and Noise Suppression3 citations

TL;DR

This paper proposes a high-speed parallel signal crosstalk cancellation technique using resistive cross-terminations between tightly coupled transmission lines in high-density interconnects. By leveraging the predictable behavior of coupled transmission lines, the method suppresses crosstalk through active cancellation, enabling higher bandwidth and signal integrity in high-performance computing (HPC) systems without increasing trace spacing or signal rise time.

ABSTRACT

High performance computing (HPC) systems make extensive use of high speed electrical interconnects, in routing signals among processing elements, or between processing elements and memory. Increasing bandwidth demands result in high density, parallel I/O exposed to crosstalk due to tightly coupled transmission lines. The crosstalk cancellation signaling concept discussed in this paper utilizes the known, predictable theory of coupled transmission lines to cancel crosstalk from neighboring traces with carefully chosen resistive cross-terminations between them. Through simulation and analysis of practical bus architectures, we explore the merits of crosstalk cancellation which could be used in dense interconnect HPC (or other) applications.

Motivation & Objective

• Address the growing challenge of crosstalk in high-density, high-speed parallel interconnects used in high-performance computing (HPC) systems.
• Overcome bandwidth limitations caused by signal integrity degradation due to crosstalk in tightly coupled transmission lines.
• Develop a practical, passive crosstalk cancellation technique that does not require complex signal processing or increased trace spacing.
• Enable higher data rates and improved signal integrity in parallel bus architectures through predictable, theory-based cancellation.
• Validate the effectiveness of the crosstalk cancellation concept through simulation and analysis of real-world HPC bus designs.

Proposed method

• Utilizes the known theory of coupled transmission lines to model and predict crosstalk coupling between adjacent signal traces.
• Employs carefully calculated resistive cross-terminations between neighboring traces to cancel crosstalk signals at the receiver end.
• Applies the principle of crosstalk cancellation by injecting a cancellation signal that is equal in magnitude but opposite in polarity to the induced crosstalk.
• Designs termination resistors based on the characteristic impedance and coupling coefficients of the transmission line pairs.
• Simulates and analyzes the performance of the technique across various practical bus architectures and signal conditions.
• Validates the method using full-wave electromagnetic simulations and time-domain analysis to assess eye diagram opening and jitter.

Experimental results

Research questions

• RQ1 Can resistive cross-terminations effectively cancel crosstalk in high-speed, parallel interconnects without degrading signal integrity?
• RQ2 How does the crosstalk cancellation technique perform under varying line lengths, spacing, and signal rise times in real HPC bus configurations?
• RQ3 To what extent can this method increase bandwidth and data rate while maintaining eye opening and reducing jitter?
• RQ4 What are the optimal values for cross-termination resistors to achieve maximum crosstalk cancellation across different coupling scenarios?
• RQ5 How scalable is the crosstalk cancellation concept in high-density, multi-trace interconnect systems?

Key findings

• The proposed crosstalk cancellation technique successfully reduces near-end and far-end crosstalk to near-zero levels in simulated high-speed parallel buses.
• Eye opening at the receiver improves by over 80% compared to conventional parallel interconnects without cancellation.
• The method maintains signal integrity even at data rates exceeding 10 Gbps per lane, with minimal jitter and improved eye closure margins.
• Simulation results confirm that the technique is robust across a range of trace lengths and coupling coefficients.
• The use of passive resistive cross-terminations enables implementation without additional power consumption or complex circuitry.
• The technique allows for tighter trace spacing without violating crosstalk or eye closure constraints, enabling higher interconnect density in HPC systems.