I agree that Stefano's dissertation is a very good introduction to WDFs. Much of my own doctoral work was inspired by his excellent paper on WDF diode and op-amp modeling, which is as far as I know the first time active devices (op-amp) and complex non-series/parallel topologies (the op-amp's feedback structure) had been modeling using WDFs—a very exciting development because historically (Fettweis era) they had been associated with passive circuits only.
Most of my own papers and dissertation relate to expanding the class of circuits that can be modeled using WDFs, building on Stefano's work to enable the WDF formalism to handle complex topologies ~in general~ and circuits involving active devices ~in general~ in a systematic fashion. In my opinion, this work brings WDFs up to the same level of suitability as State Space and MNA modeling. In my opinion, WDFs are not the clear winner: each one has advantages and disadvantages which come into play in different ways in different circuits, meaning none of the formalisms is the best for ~all~ circuits. As a side effect of my topological findings, I also came up with a new technique for modeling circuits with multiple nonlinearities. Again, I would not say that the technique is ~superior~ to state-space or MNA modeling, just that it allows WDFs to be structurally compatible with multiple NLs and brings them up to a similar level of potential usefulness. It still requires a Newton solver or table lookup, just like all the other formalisms. There are also some even articles by Alberto Bernardini and Timothey Schwertdfeger that take a similar approach to handling multiple NLs, which seem to have some advantages over my technique. Here are links to some of my work on WDFs for your reference: —PhD diss, w/ most results up to 2016, TR808 bass drum as overarching case study: https://searchworks.stanford.edu/view/11891203 —IEEE article with most up-to-date and general formulation of handling complex topologies with generalized wave definition: https://www.researchgate.net/publication/325566665_Modeling_Circuits_With_Arbitrary_Topologies_and_Active_Linear_Multiports_Using_Wave_Digital_Filters —DAFx proceedings (many WDF papers including mine): https://www.dafx.de/paper-archive/ All the best, Kurt James Werner
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