Claudio Siviero

Parametric macromodels of differential drivers and receivers

This paper addresses the modeling of differential drivers and receivers for the analog simulation of high-speed interconnection systems. The proposed models are based on mathematical expressions, whose parameters can be estimated from the transient responses of the modeled devices. The advantages of this macromodeling approach are: improved accuracy with respect to models based on simplified equivalent circuits of devices; improved numerical efficiency with respect to detailed transistor-level models of devices; hiding of the internal structure of devices; straightforward circuit interpretation; or implementations in analog mixed-signal simulators. The proposed methodology is demonstrated on example devices and is applied to the prediction of transient waveforms and eye diagrams of a typical low-voltage differential signaling (LVDS) data link.

Reliable eye-diagram analysis of data links via device macromodels

This paper addresses the impact of device macromodels on the accuracy of signal integrity and performance predictions for critical digital interconnecting systems. It exploits nonlinear parametric models for both single-ended and differential devices, including the effects of power supply fluctuations and receiver bit detection. The analysis demonstrates that the use of well-designed macromodels dramatically speeds up the simulation as well it preserves timing accuracy even for long bit sequences.

Behavioral Modeling of Digital Devices Via Composite Local Linear State–Space Relations

This paper addresses the generation of accurate and efficient behavioral models of digital ICs. The proposed approach is based on the approximation of the device port characteristics by means of composite local linear state-space relations whose parameters can effectively be estimated from device port transient responses via well-established system identification techniques. The proposed models have been proven to overcome some inherent limitations of the state-of-the-art models used so far, and they can effectively be implemented in any commercial tool as simulation program with integrated circuit emphasis (SPICE) subcircuits or VHDL-AMS hardware descriptions. A systematic study of the performances of the proposed state-space models is carried out on a synthetic test device. The effectiveness of the proposed approach has been demonstrated on a real application problem involving commercial devices and a data link of a mobile phone.

Behavioral macromodels of differential drivers with pre-emphasis

This paper addresses the extension of the behavioral modeling via parametric relations to differential drivers with pre-emphasis. These devices are of paramount importance to enable multi-gigabit data transmission over conventional copper interconnects. The proposed models preserve the accuracy and efficiency strengths of behavioral parametric macromodels for conventional devices. Their operation is demonstrated in a realistic simulation example involving a 3.125 Gb/s commercial driver with pre-emphasis.

Behavioral macromodels of differential drivers

This paper addresses the development of behavioral macromodels of differential drivers for the assessment of signal integrity and electromagnetic compatibility effects in high-speed digital systems. The obtained macromodels are readily implemented as SPICE-like subcircuits to be included in any circuit simulation environment. Accuracy and efficiency of macromodels are assessed by applying the proposed methodology to actual differential devices.

Locally-Stable Macromodels of Integrated Digital Devices for Multimedia Applications

This paper addresses the development of accurate and efficient behavioral models of digital integrated circuits for the assessment of high-speed systems. Device models are based on suitable parametric expressions estimated from port transient responses and are effective at system level, where the quality of functional signals and the impact of supply noise need to be simulated. A potential limitation of some state-of-the-art modeling techniques resides in hidden instabilities manifesting themselves in the use of models, without being evident in the building phase of the same models. This contribution compares three recently-proposed model structures, and selects the local-linear state-space modeling technique as an optimal candidate for the signal integrity assessment of data links. In fact, this technique combines a simple verification of the local stability of models with a limited model size and an easy implementation in commercial simulation tools. An application of the proposed methodology to a real problem involving commercial devices and a data-link of a wireless device demonstrates the validity of this approach.

Parametric Macromodels of Differential Drivers With Pre-Emphasis

This paper discusses the extraction of behavioral models of differential drivers with pre-emphasis for the assessment of signal integrity and electromagnetic compatibility effects in multigigabit data transmission systems. A suitable model structure is derived and the procedure for its estimation from port transient waveforms is illustrated. The proposed methodology is an extension of the macromodeling based on parametric relations applied to plain differential drivers. The obtained models preserve the accuracy and efficiency strengths of behavioral parametric macromodels for conventional devices. A realistic application example involving a high-speed communication path and a 3.125 Gb/s commercial driver model with pre-emphasis is presented.

Behavioral modeling of IC output buffers: a case study

This paper addresses the behavioral modeling of IC output ports by means of nonlinear parametric relations and system identification methods. The approach is applied to a commercial device and a systematic discussion of the impact of the modeling setup on the model performance is presented.

Present and future of I/O-buffer behavioral macromodels

Modern Signal and Power Integrity (SI/PI) verification flows rely on accurate models for complex I/O-buffers that drive and receive electrical signals on high-speed channels. The sheer density of modern integrated circuits makes detailed transistor-level descriptions computationally cumbersome to the point where they become unusable for system-level simulations. Fortunately, transistor-level descriptions may be replaced with more compact representations that approximate the input/output buffers behavior with considerable accuracy while providing a simulation speedup of several orders of magnitude. Known as behavioral models, surrogate models or macromodels, these computationally efficient equivalents have become a de-facto industry standard in SI/ PI simulations. This paper presents an overview of the state-of-the-art in I/O-buffer behavioral modeling, introducing the main features of both standard and emerging solutions. Open issues and future research directions are also discussed.

Macromodel-Based Iterative Solvers for Simulation of High-Speed Links With Nonlinear Terminations

Data transmission on high-speed channels may be affected by several undesired effects, including coupling from nearby interconnects, dispersion, losses, signal reflections from terminations and from internal discontinuities, and nonlinear/dynamic effects of drivers and receivers. The latter are often neglected, leading to very fast solvers, whose results may, however, be questionable when driver/receiver nonlinearities are important. This paper presents a framework for the transient analysis of complex high-speed channels with arbitrary nonlinear termination circuits. The approach is based on decoupling channel and terminations through a scattering-based waveform relaxation (WR) formulation. The channels are here cast as delay-rational macromodels, which are solved in discrete time domain through fast delayed recursive convolutions. The terminations can be either arbitrary circuits, solved by SPICE, or nonlinear behavioral macromodels, which are here formulated in discrete-time scattering representations. To overcome the known convergence issues of standard WR methods, we apply here more general iterative solution schemes, such as generalized minimal residual and biconjugate gradient stabilized, integrated into inexact Newton iterations, obtaining a set of numerical schemes with guaranteed convergence. The excellent performance of the proposed approach is illustrated on a large set of benchmarks.