There is not one best netlist reduction technique Netlist reduction is the keyword applied to describe the process of transforming a netlist that contains parasitic elements into a second netlist of smaller size and less parasitic elements. In principle, we can claim that the smaller the netlist, the faster the simulation tool. Ideally, the reduced netlist should have exactly the same electrical behaviour as the original netlist. However, nothing is for free: there is a trade-off to be made between the accuracy of the applied algorithms and the degree of reduction. On top of the complexity challenges, the most important challenges of state-of-the-art netlist reduction tools are loopholes in the definition of exchange file formats and the lack of necessary mathematical conditions in the extraction tools. A typical example for a quasi-standard exchange file format is the DSPF (Detailed standard parasitic file) format: At the time of definition, capacitive coupling, inductance and magnetic coupling was not anticipated, and we find ourselves today with at least four different ways of defining coupling capacitors in DSPF files. These loopholes could easily be closed by using the SPEF (Standard Parasitic Exchange File) format, however main industry applications run on DSPF. While these issues are only related to the format and can be solved by developing several distinct interfaces, mathematical conditions must be respected. To name one: passivity is a necessary condition. Inductors, capacitors, resistors, even combined cannot generate energy; this is a basic physical law. Most of mathematical Model Order Reduction (MOR) algorithms start off with this condition, which might not be respected by extraction tools due to numerical inaccuracies. The direct application of the many proposed MOR algorithms are therefore generally inapplicable for industrial applications. Before reviewing today’s available techniques, we can already state that there is no universal technique usable for netlist reduction. The good news is though that EDA tools can successfully apply a combination of different techniques. We can distinguish four categories of approaches used in industrial tools: filtering, recursive star-triangle transformations, delay-oriented local operations and mathematical solutions called Model Order Reduction.
Among the techniques available to improve the speed and capacity of post-layout simulation taken parasitic components into account, netlist reduction is among the most promising techniques.
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