SPICE has the ability to simulate components ranging from the most basic passive elements such as resistors and capacitors to sophisticated semiconductor devices such as MESFETs and MOSFETs. Using these intrinsic components as the basic building blocks for larger models, designers and chip manufacturers have been able to define a truly vast and diverse number of SPICE models. Most commercially available simulators include more than 15,000 different components.
The quality of SPICE models can vary, and not all SPICE models are applicable to every application. It is important to consider this when using the models supplied with a SPICE simulation package. Using a SPICE model inappropriately can lead to inaccurate results, or even generate an error in some circumstances. One of the most common errors made by even seasoned engineers is confusing a SPICE model with a PSPICE model. PSPICE is a commercially available program that uses proprietary languages to define components and models.
A circuit must be presented to SPICE in the form of a netlist. The netlist is a text description of all circuit elements such as transistors and capacitors, and their corresponding connections. Modern schematic capture and simulation tools such as Multisim allow users to draw circuit schematics in a user-friendly environment, and automatically translate the circuit diagrams into netlists. Consider as an example the simple voltage divider circuit below. We include both netlist and corresponding circuit schematic.
Voltage Divider Netlist
* Any text after the asterisk '*' is ignored by SPICE
* Voltage Divider
vV1 1 0 12
rR1 1 2 1000
rR2 2 0 2000
.OP * perform a DC operating point analysis
Voltage Divider Schematic