Modeling of nonlinear active and passive devices in three-dimensional TLM networks




Cascio, Lucia

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The increase in clock rate and integration density in modem IC technology leads to complex interactions among different parts of the circuit. These interactions are poorly represented with traditional lumped circuit design methodologies. Traditional CAD tools, such as SPICE, provide very accurate models for a large variety of active devices, but their description of the passive part of the circuit is progressively becoming insuffcient, as the frequencies of the signals increase. Problems such as dispersion, crosstalk and package effects require a full electromagnetic approach in order to predict their impact on the final response of the circuit. On the other hand, the application of a full-wave numerical method for the analysis of a complete device containing nonlinear elements is not sustainable with the present computer capabilities. The spatial and time discretization steps required to accurately model the nonlinear part of the device are much smaller than those necessary to describe the distributed part of the circuit. In the present thesis, the possibility of modeling nonlinear devices with the three-dimensional TLM method has been explored; a new procedure has been successfully developed and implemented, linking the equivalent circuit representation of the nonlinear device to the transmission line model of the electromagnetic fields in the TLM network. No restrictions are applied on the size of the device, which can thus occupy more than a TLM cell. In order to model devices embedded in heterogenous media, a modification of the TLM node and relative scattering matrix has also been proposed. In view of linking the TLM field solver with a lumped element circuit CAD tool, the modified TLM scattering algorithm has remained independent of the specific device connected to the mesh. The general methodology shown in this thesis appears to be a promising approach to solve a large variety of electromagnetic problems containing nonlinear elements.



Electromagnetic theory, Nonlinear functional analysis, Microwave transmission lines