Simulation of interconnections in high speed integrated circuits.

The rapid development of high-speed, high-density integrated circuits has brought about a situation where the delay times and distortion of signals transmitted on the interconnections (microstrip lines) within these packages are now comparable with those of the devices in the circuit. Hence when designing high-speed digital systems the effect of signal delay, distortion, and attenuation, on these interconnections has now become a necessary part of integrated circuit design. Therefore accurate modelling and simulation of interconnects is a very important subject for research. These interconnections can create a number of problems such as signal delay, distortion, attenuation, and crosstalk between lines of close proximity. These microstrip lines have the same behaviour as exhibited by transmission lines and can therefore be described using the well-known Telegrapher's equations. A quasi-distributed equivalent circuit model describing the behaviour of such microstrip lines is implemented into the SPICE circuit simulator. This allows an investigation into lossless and lossy line characteristics and illustrates the importance of choosing the correct impedances for both the lines and devices within the integrated circuit package. The model is then extended to include crosstalk between neighbouring lines, by means of a transformation network. This study of crosstalk illustrates that logic functions lying in an intervening space between the pulse-activated lines are found to be affected more than the outside lines. The MATHEMATICA package is used for the calculation of capacitance, inductance, impedance, time delay and transformation network control parameters for any set of microstrip lines of a given geometry. The results obtained from these calculations are then used for further simulation runs using the SPICE software for different line configurations. The results obtained are seen to be consistent with all previous work conducted on coupled three line structures, and give good verification of both the Mathematica program and the SPICE equivalent circuit model.