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Simulation Techniques for Electromagnetic Interference (EMI) and Signal Integrity (SI) in High-Speed Electronic Circuits

Luca Daniel, University of California at Berkeley
Alberto Sangiovanni-Vincentelli, University of California at Berkeley
Jacob White, Massachusetts Institute of Technology


Electromagnetic Interference (EMI) is becoming an exceptionally crucial issue in the design of modern electronic systems. Frequencies are continuously increasing, while integration trends are squeezing entire systems into extraordinary high circuit densities. In the conventional design methodology, Electromagnetic Compatibility (EMC) issues are addressed only after a prototype is built. At that stage, the traditional EMC remedies are confined to adding extrahandheld pagers, hand-held components, metal shields, metal plans, or even redesigning the entire system, with a potentially significant impact both on the cost and on the time-to-market of the products. It is our firm opinion that EMC must instead be addressed as early as possible during the design phase, and not after. EMI simulation could shorten the design time, allowing the analysis of circuits before manufacturing.

Large and expensive electronic equipment can effectively employ standard EMC solutions. But smaller, high-volume, low-priced electronic ci devices, automotive electronics and most of the embedded systems, cannot afford those costly solutions. Such devices are the most susceptible to EMI problems and the most sensitive to post-prototype EMC added costs. Unfortunately, they are also the most difficult to simulate with respect to EMI problems since they require "full-board" capabilities, and no tool is available to date for such task.

Full-board EMI simulation capability would therefore be instrumental in promptly verifying EMC compliance during the very first stages of the design of high-speed PCBs and IC-packages. For this application, we are investigating the use of Integral Equation Methods:

  1. Our research focuses on minimizing the number of unknowns needed to model each conductor in the system. We have found an alternative set of basis functions [1]-[3], requiring 16 to 20 times fewer unknowns than the classical thin filaments discretization, for the same final accuracy. In our method, we use as basis functions some of the physically admissible solutions of the diffusion equation for the current density in the interior of the conductors.

  2. We are currently implementing our method based on our new basis functions. We solve the resulting linear system using the very efficient Krylov Subspace Iterative Methods. The complexity of the algorithm is dominated by an O(N^2) matrix-vector product operation. We propose to further reduce the computational complexity of the iterative method. Fast algorithms exist for such product with complexity O(Nlog(N)). Such algorithms have been already successfully implemented in tools for the static capacitance extraction problem (FASTCAP) and for the magneto-quasi-static problem (FASTHENRY). We plan to modify and extend one of such algorithms, Precorrected-FFT, to our full-wave EMI analysis problem.

Desirable results from an EMI analysis range from the characterization of the spectrum emissions observed on a measurement sphere at 10 meters, to the generation of a model of the interconnect structures to be later interfaced with a non-linear time domain simulator.

  1. To address efficiently the first specification, we propose to use an adjoint method to calculate a set of transfer functions from the thousands of circuit inputs (e.g. the pins of the IC's) to the tens of observation points on the measurement sphere.

  2. To address the second specification, we are working on the generation of "dynamical linear systems" that mimic the same behavior of the original interconnect structure, but have a state vector orders of magnitude smaller. In [4] for instance we show how to generate guaranteed passive reduced order models from originally passive structures including dielectrics.


Publications:

L. Daniel, A. Sangiovanni-Vincentelli, J. White, Interconnect Electromagnetic Modeling using Conduction Modes as Global Basis Functions, IEEE 9th Topical Meeting on Electrical Perform. of Electronic Packages, p. 203-6, Scottsdale, AZ, 23-25 Oct. 2000. 

L. Daniel, J. White, A. Sangiovanni-Vincentelli, Interconnect Electromagnetic Modeling using Conduction Modes as Global Basis Functions, SRC TECHCON2000 (Conference Restricted to members of the Semiconductor Research Corporation), Scottsdale, AZ, Sep. 2000.  

L. Daniel, A. Sangiovanni-Vincentelli, J. White, Conduction Modes Basis Functions for Efficient Electromagnetic Analysis of On-Chip and Off-Chip Interconnect, Proceedings of the Design Automation Conference, Las Vegas, June 2001. 

L. Daniel, A. Sangiovanni-Vincentelli, J. White, Techniques for Including Dielectrics when Extracting Passive Low-Order models of High Speed Interconnect, International Conference on Computer Aided Design, San Jose, November 2001.

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