Transmission properties of balanced interconnections

The author develops simple equations for computing the characteristic impedances and crosstalk of both unbalanced and balanced interconnections in a lossless, homogeneous, microstrip configuration (signal conductors above a ground plane). The equations are applied to compare the crosstalk resulting from both types of interconnections having 4-mil conductor widths when the packaging density is three signals per 54 mils. Similar comparisons for other signal packing densities and impedances are also presented. It is shown that balanced interconnections are much more immune to noise pickup. Also, they are free of ground noise and radiate relatively little. A theoretical transformation is developed in order to apply the equations to conductors having rectangular or circular cross-sections. The equations yield values which agree well with experiment, and they can also be applied to help analyze the interconnections associated with fiber-optic transceivers, monolithic microwave integrated circuits, hybrid integrated circuits, and various multichip modules. The effect of the dielectric constant on crosstalk is also discussed