Computer optimisation of circuits applied to the modelling of microwave IC passive components

A new technique for the optimisation of electrical networks has been developed whereby the computer program removes components or adds new components and nodes to a circuit in an apparently random manner in order to achieve specified performance targets. It is used to generate equivalent circuits of some microwave IC resistors, capacitors and inductors which match the measured performance of the devices over the frequency band 2¿¿18 GHz. The program minimises the difference between the calculated S-parameters of the model circuit and the measured S-parameters of the device being modelled. The model is only valid within the frequency range in which matching has occurred. Because matching is entirely mathematical, the equivalent circuit may not relate to the real physical circuit. However, computer-generated equivalent circuits may also expose parasitic or other circuit effects that have not otherwise been identified. A number of equivalent circuits are given, together with comparison graphs of the S-parameters of the model and the device. The program has devised different equivalent circuits to accommodate measured performance differences between nominally similar devices.