Non-linear multi-mode time-domain hierarchical simulation approach to microwave CAD

The proposed simulation algorithm is based on the time-domain approach and can therefore cope with transients, highly non-linear problems, complex excitations and complicated oscillation patterns. All the above problems are either difficult or impossible to solve using harmonic-balance methods. Like some other advanced time-domain CAD tools, the proposed algorithm can combine non-linear, linear and behavioural analyses during the same simulation and can therefore be used for the design of mixed type analogue/digital MMICs and complete sub-systems. However, there are four main differences between the developed method and the SPICE-type simulators: (i) preservation of the circuit hierarchy during the analysis, (ii) different analysis methods for different sub-circuits (multi-mode analysis), (iii) an open structure allowing the easy addition of new simulation techniques, and (iv) substantially higher speed. The new algorithm is particularly suitable for large circuits, such as multifunction MMICs, since a circuit is decomposed into smaller subcircuits which are simulated individually and parallelly. Each subcircuit can be solved using the most appropriate technique for that sub-circuit, leading to improved efficiency and/or accuracy. The algorithm has been tested against commercial microwave CAD programs, proving its advantages.