1.1 What is it?
Gnucap is a general purpose mixed analog and digital circuit simulator.
It performs nonlinear dc and transient analyses, fourier analysis, and
ac analysis linearized at an operating point. It is fully interactive
and command driven. It can also be run in batch mode. The output is
produced as it simulates. Spice compatible models for the MOSFET
(levels 1-7) and diode are included in this release.
Since it is fully interactive, it is possible to make changes and re-simulate
quickly. This makes Gnucap ideal for experimenting with circuits as you might
do in an iterative design or testing design principles as you might do in a
course on circuits.
In batch mode it is mostly Spice compatible, so it is often possible to use
the same file for both Gnucap and Spice.
The analog simulation is based on traditional nodal analysis with iteration
by Newton's method and LU decomposition. An event queue and incremental
matrix update speed up the solution considerably for large circuits and
provide some of the benefits of relaxation methods but without the drawbacks.
It also has digital devices for true mixed mode simulation. The digital
devices may be implemented as either analog subcircuits or as true digital
models. The simulator will automatically determine which to use. Networks
of digital devices are simulated as digital, with no conversions to analog
between gates. This results in digital circuits being simulated faster than
on a typical analog simulator, even with behavioral models.
Gnucap also has a simple behavioral modeling language that allows simple
behavioral descriptions of most components including capacitors and
Gnucap is an ongoing research project. It is being released in a preliminary
phase in hopes that it will be useful and that others will use it as a
thrust or base for their research.