Analog/Mixed-Signal Behavioral Modeling – When to Use What
So when to use what? The conservative style provided by Verilog-A and Verilog-AMS is useful when there are significant accuracy requirements. This approach can potentially provide a 50-100X speedup over SPICE, but it all depends on how good your modeling is. "If you're a poor modeler, there's a chance you could end up with a model that's as slow as SPICE simulation or even slower," Walter warned.
Real number modeling, also available through Verilog-AMS with the wreal data type, brings real number values into event-driven digital simulation. It thus has the speed benefits of digital simulation and can leverage the metric-driven verification methodology that's increasingly used by digital engineers. It's good when there are hard performance requirements and limited accuracy requirements. For example, wreal is very useful for full-chip mixed-signal simulations.
The following chart shows the accuracy/speed tradeoff ranges provided by various analog/mixed-signal modeling alternatives. Note that the conservative modeling style has a broad possible range, depending on how good the modeling is.