A Solenoidal Basis Method For Efficient Inductance Extraction H emant Mahawar Vivek Sarin Weiping Shi Texas A&M University College Station, TX
Introduction
Background Inductance between current carrying filaments Kirchoff’s law enforced at each node
Background … Current density at a point Linear system for current and potential Inductance matrix Kirchoff’s Law
Linear System of Equations Characteristics Extremely large; R, B: sparse; L: dense Matrix-vector products with L use hierarchical approximations Solution methodology Solved by preconditioned Krylov subspace methods Robust and effective preconditioners are critical Developing good preconditioners is a challenge because system is never computed explicitly!
First Key Idea Current Components Fixed current satisfying external condition I d (left) Linear combination of cell currents (right)
Solenoidal Basis Method Linear system Solenoidal basis Basis for current that satisfies Kirchoff’s law Solenoidal basis matrix P: Current obeying Kirchoff’s law: Reduced system Solve via preconditioned Krylov subspace method
Local Solenoidal Basis Cell current k consists of unit current assigned to the four filaments of the kth cell There are four nonzeros in the kth column of P: 1, 1, -1, -1
Second Key Idea Observe: where Approximate reduced system Approximate by
Preconditioning Preconditioning involves multiplication with
Hierarchical Approximations Components of system matrix and preconditioner are dense and large Hierarchical approximations used to compute matrix-vector products with both L and Used for fast decaying Greens functions, such as 1/r (r : distance from origin) Reduced accuracy at lower cost Examples Fast Multipole Method: O(n) Barnes-Hut: O(nlogn)
FASTHENRY Uses mesh currents to generate a reduced system Approximation to reduced system computed by sparsification of inductance matrix Preconditioner derived from Sparsification strategies DIAG: self inductance of filaments only CUBE: filaments in the same oct-tree cube of FMM hierarchy SHELL: filaments within specified radius (expensive)
Experiments Benchmark problems Ground plane Wire over plane Spiral inductor Operating frequencies: 1GHz-1THz Strategy Uniform two-dimensional mesh Solenoidal function method Preconditioned GMRES for reduced system Comparison FASTHENRY with CUBE & DIAG preconditioners
Ground Plane
Problem Sizes Mesh Potential Nodes Current Filaments Linear System Solenoidal functions 33x331,0892,1123,2011,024 65x654,2258,32012,5454, x12916,64133,02449,66516, x25766,049131,584197,63365,536
Comparison with FastHenry Preconditioned GMRES Iterations (10GHz) Mesh FASTHENRY DIAG FASTHENRY CUBE Solenoidal Method 33x x x x x
Comparison … Time and Memory (10GHz) Mesh FASTHENRY DIAG FASTHENRY CUBE Solenoidal Method Time (sec) Mem (MB) Time (sec) Mem (MB) Time (sec) Mem (MB) 33x x x x x
Preconditioner Effectiveness Preconditioned GMRES iterations Mesh Filament Length Frequency (GHz) x331/ x651/ x1291/ x2561/
Wire Over Ground Plane
Comparison with FastHenry Preconditioned GMRES Iterations (10GHz) Mesh FASTHENRY DIAG FASTHENRY CUBE Solenoidal Method 33x x x x x
Comparison … Time and Memory (10GHz) Mesh FASTHENRY DIAG FASTHENRY CUBE Solenoidal Method Time (sec) Mem (MB) Time (sec) Mem (MB) Time (sec) Mem (MB) 33x x x x x
Preconditioner Effectiveness Preconditioned GMRES iterations Mesh Filament Length Frequency (GHz) x331/ x651/ x1291/ x2571/
Spiral Inductor
Preconditioner Effectiveness Preconditioned GMRES iterations Mesh Filament Length Frequency (GHz) x331/ x651/ x1291/ x2571/
Concluding Remarks Preconditioned solenoidal method is very effective for linear systems in inductance extraction Near-optimal preconditioning assures fast convergence rates that are nearly independent of frequency and mesh width Significant improvement over FASTHENRY w.r.t. time and memory Acknowledgements: National Science Foundation