This paper reviews recent progress and future directions of signal integrity design for high-speed digital circuits, focusing on four areas: signal propagation on transmission lines, discontinuity modeling and characterization, measurement techniques, and link-path design and analysis.

Signal Integrity Design for High-Speed Digital Circuits: Progress and Directions

Mitigating power distribution network (PDN) noise is one of the main efforts for power integrity (PI) design in high-speed or mixed-signal circuits. Possible solutions, which are based on decoupling or isolation concept, for suppressing PDN noise on package or printed circuit board (PCB) levels are reviewed in this paper. Keeping the PDN impedance very low in a wide frequency range, except at dc, by employing a shunt capacitors, which can be in-chip, package, or PCB levels, is the first priority way for PI design. The decoupling techniques including the planes structure, surface-mounted technology decoupling capacitors, and embedded capacitors will be discussed. The isolation approach that keeps part of the PDN at high impedance is another way to reduce the PDN noise propagation. Besides the typical isolation approaches such as the etched slots and filter, the new isolation concept using electromagnetic bandgap structures will also be discussed.

Overview of Power Integrity Solutions on Package and PCB: Decoupling and EBG Isolation

This paper reviews the fundamentals and latest progress of modeling, analysis, and design technologies for signal integrity and electromagnetic compatibility on PCB and package in the past decades. Most results in this field are based on the very rich and highly educational literature produced by Prof. C. Paul in his long scientific career. The inclusion of parameters variability effects is also considered, and it is demonstrated how statistical simulations can become affordable by means of recently-introduced stochastic methods. Finally, the necessity of practical training of designers is mentioned, and an experience relying on realistic PCB demonstrators is illustrated.

Overview of Signal Integrity and EMC Design Technologies on PCB: Fundamentals and Latest Progress

Efficient multiscale electromagnetic simulations require several major challenges that need to be addressed, such as flexible and robust geometric modeling schemes, efficient and stable time-stepping methods, etc. Due to the versatile choices of spatial discretization and temporal integration, discontinuous Galerkin time-domain (DGTD) methods can be very promising in simulating transient multiscale problems. This paper provides a comprehensive review of different DGTD schemes, highlighting the fundamental issues arising in each step of constructing a DGTD system. The issues discussed include the selection of governing equations for transient electromagnetic analysis, different basis functions for spatial discretization, as well as the implementation of different time-stepping schemes. Numerical examples demonstrate the advantages of DGTD for multiscale electromagnetic simulations.

Discontinuous Galerkin Time-Domain Methods for Multiscale Electromagnetic Simulations: A Review

In this work, machine learning methods are applied to high-speed channel modeling for signal integrity analysis. Linear, support vector, and deep neural network (DNN) regressions are adopted to predict the eye-diagram metrics, taking advantage of the massive amounts of simulation data gathered from prior designs. The regression models, once successfully trained, can be used to predict the performance of high-speed channels based on various design parameters. The proposed learning-based approach saves complex circuit simulations and substantial domain knowledge altogether, in contrast to alternatives that exploit novel numerical techniques or advanced hardware to speed up traditional simulations for signal integrity analysis. Our numerical examples suggest that both support vector and DNN regressions are able to capture the nonlinearities imposed by transmitter and receiver models in high-speed channels. Overall, DNN regression is superior to support vector regression in predicting the eye-diagram metrics. Moreover, we also investigate the impact of various tunable parameters, optimization methods, and data preprocessing on both the learning speed and the prediction accuracy for the support vector and DNN regressions.

High-Speed Channel Modeling With Machine Learning Methods for Signal Integrity Analysis

Differential signaling has become a popular choice for multigigabit digital applications in favor of its low-noise generation and high common-mode noise immunity. Recalling from the full-wave solution of S-parameters, this paper presented a design methodology of analysis scheme to extract the equivalent circuits of discontinuities observed on the strongly coupled differential lines. Signal integrity effects of the bent differential transmission lines in a high-speed digital circuit were then simulated in the time domain. A dual back-to-back routing topology of bent differential lines to reduce the common-mode noise was further investigated. To alleviate the common-mode noise at the receiver, a novel compensation scheme in use of the shunt capacitance was also proposed. Furthermore, the comparison between the simulation and measured results validated the equivalent circuit model, coupled bends with compensation capacitance patch, and analysis approach

Noise reduction using compensation capacitance for bend discontinuities of differential transmission lines

An efficient Delaunay-Voronoi modeling of the power-ground planes suitable directly for SPICE compatibity is proposed to deal with the ground bounce noise and decoupling capacitors placement problems for the high-speed digital system designs. The model consists of virtual ports and triangular meshes with the lumped circuit elements, in which all the element values can be related to the mesh geometry shape by the analogy between the circuit equations and Maxwell's equations. Since the analogy fails to apply due to the singular fields near the input/output pins, the via effect of driving and sensing ports is not negligible and an analytical expression from the Hankel function is thus presented for the correction term. A simple rule has been investigated for the model with minimum lumped circuit elements to accurately represent the power-ground planes over the frequency range of interests. The full-wave simulation and measurement results verify the good correlations with the proposed models for the impedance responses of regular and defective plane shapes.

Delaunay–Voronoi Modeling of Power-Ground Planes With Source Port Correction

As the speed of signal through an interconnection increases toward the multigigabit ranges, the effects of lossy transmission lines on the signal quality of printed circuit boards becomes a critical issue. To evaluate the eye diagram and thus the signal integrity in the modern digital systems, this paper proposes a fast methodology that employs only two anti-polarity one-bit data patterns instead of the pseudo-random bit sequence as input sources to simulate the worst-case eye diagram. Analytic expressions are derived for the impulse response of the lossy transmission lines due to the skin-effect loss, while the Kramers-Kronig relations are employed to deal with the noncausal problem related to the dielectric loss. Two design graphs that can be used to rapidly predict the eye diagram characteristics versus the conductive and dielectric losses are then constructed and based on which, the maximally usable length of transmission lines under a certain signal specification can be easily acquired. At last, the time-domain simulations and experiments are implemented to verify the exactitude of proposed concept.

Fast Methodology for Determining Eye Diagram Characteristics of Lossy Transmission Lines

In contrast to the commonly employed single-ended delay lines, the employment of differential signaling may alleviate the occurrence of crosstalk and improve the signal integrity. This paper qualitatively investigates the time-domain reflection (TDR) and time-domain transmission (TDT) waveforms for the single-ended and differential delay lines with the serpentine and flat spiral routing schemes. A numerical formula is then proposed to quantitatively predict the voltage levels of the saturated near-end and far-end propagating crosstalk noises among the sections of differential delay lines. Signal waveforms and eye diagrams of the four basic routing schemes are obtained by HSPICE simulations, demonstrating that the combination of differential signaling and flat spiral layouts can exhibit the best delay-line performance. Furthermore, both the TDR and TDT measurements for differential delay lines are performed to validate the exactitude of proposed analyses.

/pdf/comparisons-between-serpentine-and-flat-spiral-delay-lines-347gqhifja.pdf

Comparisons between serpentine and flat spiral delay lines on transient reflection/transmission waveforms and eye diagrams

In the high-speed digital printed circuit board, decoupling capacitors play an important role in lowering the power-ground planes impedance leading to the ground bounce noise in I/O ports while the logic is in transition. This paper investigates the optimal placement of decoupling capacitors in suppressing the input and transfer impedances of power-ground planes. The cavity model combines with genetic algorithm (GA) here to find the design specification and the optimal placement of the decoupling capacitors.

https://www.piers.org/piersonline/vol1/2k5hz_p411.pdf

Chien-Min Lin

Papers

Noise reduction using compensation capacitance for bend discontinuities of differential transmission lines

Delaunay–Voronoi Modeling of Power-Ground Planes With Source Port Correction

Fast Methodology for Determining Eye Diagram Characteristics of Lossy Transmission Lines

Comparisons between serpentine and flat spiral delay lines on transient reflection/transmission waveforms and eye diagrams

Optimization for the Locations of Decoupling Capacitors in Suppressing the Ground Bounce by Genetic Algorithm