A new frequency domain based methodology for signal integrity analysis

Abstract

The co-existence of two different sets of parameter definitions, requirements and specifications in the domain of digital system design; namely the time domain (TD) and frequency domain (FD), is imposing some challenges on digital system design. Those challenges are increasing with the increase in system speed and are hard to address using traditional methods. This paper proposes a new methodology to perform signal integrity (SI) analysis, fully, in frequency domain to help addressing those challenges. To perform SI analysis, fully, in FD it is required to build the correct system model, construct an efficient methodology and develop quantitative measures and relationships as well as correlation to TD quantities. The focus in this paper will be on the first two items where a system model and an efficient FD methodology are introduced and their accuracy, compared to TD simulations, is examined. Keywords-digital system design, frequency domain, signal integrity, time-domain frequency-domain correlation. I INTRODUCTIONIn the digital system domain, there are two different sets of parameters to define electrical specifications of system components as well as parameters and requirements, namely time domain (TD) and frequency domain (FD). TD parameters, such as rise time, fall time, slew rate, over and under shoot, ring back, etc. are more suitable to define the specifications of active components such as input/output (IO) driver and receiver buffers, therefore TD parameters are widely used by silicon manufacturers and designers. On the other hand, FD parameters, such as trace impedance, reflection coefficient, cross talk, etc. are more suitable to describe the spectrum and bandwidth of signals, frequency characteristics of materials and interconnect components. Hence, FD is widely used in describing the characteristics of materials, interconnect components, printed circuit boards (PCBs) and passive components in general.A typical digital electronic system is composed of a driver and a receiver, each usually contained in a package, connected to each other over an interconnect (sockets, PCB traces, vias, cables and connectors) as shown in Figure 1.Typical SI analysis aims at simulating -for developing and/or debugging a digital electronic system-electrical signal waveforms propagating from driver to receiver over the interconnect under; all, worst or statistically selected, cases of possible operating conditions. The common practice is to use a TD transient analysis tool, commercial or self-developed EDA, such as SPICE and ELDO. This common practice is inherited from the era of low speed digital system and implies the cosimulation of the passive and active system elements in the same environment, which represents an area of continuous research [2]. Figure 1: simplified general schematic for a typical digital electronics systemIn general, this co-simulation is performed by developing accurate models for the passive elements in the FD then approximating them with lumped-element equivalent models for the co-simulation, in T...