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One of the great strengths of [[RF.Spice A/D]] is the ease of creating new user-defined devices or models. Most of RF.Spice's virtual blocks are indeed based on preloaded parameterized subcircuit models. You can open the Netlist code of these subcircuits, copy or modify them and package them into your own new virtual blocks. You can even convert an entire circuit into a model complete with your own symbol. There are also a number of virtual blocks whose underpinning models have been hard-coded into RF.Spice's simulation engines and device manager. An important difference between black-box virtual blocks and user-defined devices or simulation models is that virtual blocks typically use idealized devices/models and a combination of linear and nonlinear sources to minimize circuit complexity regardless of the feasibility of their hardware realization. In other words, they are primarily intended to represent functional behaviors rather than practical circuits.

== The Stages of a Macromodel Virtual Block ==