Conventional approach to EM modeling requires that a designer comes up with an equivalent circuit topology based on geometry of EM structure and then tweak the values of circuit elements to obtain the best fitting response. If tweaking does not generate a good agreement with the response of the structure, the topology is discarded and a designer goes through the same process again with a new circuit topology. However, this is a very time consuming and tedious approach. This method is also heavily dependent on the designer's skill and experience.
EMtoSPICE is an EM modeling tool that generates a SPICE macromodel (or subcircuit) from a set of frequency data, allowing simulation of EM structures (or any device with known frequency data) in SPICE. EMtoSPICE accepts scattering parameters (S-parameters) in Touchstone format or raw data format. S-parameters may be obtained from a full-wave EM solver or any other EM analysis/simulation software. Measured S-parameters may also be used. A macromodel generated by EMtoSPICE may be combined with other device circuit elements in SPICE for simulation in time domain or frequency domain.
To generate a SPICE macromodel, EMtoSPICE incorporates a polynomial approximation of S-parameters. Each S-parameter is interpolated and represented as a rational function (a quotient of two polynomials), then incorporated in a macromodel using Laplace functions. EMtoSPICE generates macromodels either in HSPICEâ¢ or PSPICEâ¢ format.
EMtoSPICE does not need a full set of data to generate a macromodel. Only a limited sample of data is needed because EMtoSPICE interpolates data. This is a useful feature since a full-wave EM simulation may often require a long simulation time even with modern computing resources. Obtaining data at a small number of frequency points reduces EM simulation time. Of course, a full set of S-parameter data may be used if it is available.