If you need to debug a simulation, if you are planning to develop your own models, or if you are using the XSPICE simulator through the Nutmeg user interface, you will need to become familiar with the circuit description language.

The previous sections presented example circuit description input files. The following sections provide more detail on XSPICE circuit descriptions with particular emphasis on the syntax for creating and using models. First, the language and syntax of the NGSPICE simulator are described and references to additional information are given. Next, XSPICE extensions to the ngspice syntax are detailed. Finally, various enhancements to NGSPICE operation are discussed including polynomial sources, arbitrary phase sources, supply ramping, matrix conditioning, convergence options, and debugging support.