Cross Coupling in High Speed Digital Systems

It is now well understood that the design of the signal distribution systems of high speed digital machines is as important as the design of the circuits themselves. The integrated circuit technology of today is pressing back the frontiers of speed and simultaneously providing more circuitry per unit area. A signal distribution system with suitable electrical characteristics for these high speed circuits and which is physically compatible with the circuit size is sorely needed. A candidate for such an application is the multilayer board. This paper considers the problem of cross coupling from line to line in multilayer when the excitation function is a fast rise time voltage pulse. Curves and equations are given which enable the design of a system with a given system characteristic impedance and a specified cross-coupling ratio. Experimentally obtained wave shapes from single ground plane transmission lines are given, and a practical numerical example is worked.