Analysis of multiconductor microstrip with applications in high-speed integrated circuits

Interconnects used in high-speed integrated circuits can be modeled as multiconductor microstrip transmission lines embedded in an inhomogeneous multi-layered dielectric medium. In this work a full-wave hybrid-mode approach is used to accurately characterize the frequency dependent parameters of multiconductor microstrip. The microstrip is analyzed in the spectral domain and a Moment Method is used to find the unknown phase constants, eigencurrents, and modal characteristic impedances. These parameters are then used in a newly developed equivalent circuit model for terminated hybrid-mode multiconductor transmission line. Existing CAD packages, such as SPICE, can be used for the implementation of the model. Experimental results for digital signal propagation on terminated multiconductor microstrip are compared with theoretical simulations. Results from this full-wave based technique are compared with calculations made under the dispersionless TEM approximation and clearly show the need for a frequency dependent solution of the microstrip fields for high-speed signal applications. Interline coupling on VLSI interconnects is also addressed. The effectiveness of using isolation lines to reduce cross-talk is discussed. It is shown that such shield lines are not always useful and may lead to degradation of circuit performance in some cases.