INTRODUCING THE SPICE GOALS
SPICE software has been around since the early 1970s. SPICE stands for "Simulation Program with Integrated Circuit Emphasis." Students and faculty at UC Berkeley first developed SPICE and have maintained it since. This is why some people call it "Berkeley SPICE." It has gone through three major revisions during the last 30 years.
Berkeley SPICE has become the world standard simulation engine. Almost all circuit simulation programs use the Berkeley SPICE engine as their core. This has the advantage of competition between products, but still continuity and familiarity among vendors. SPICE models need to be produced in a specific format; this makes them (more or less) interchangeable from one vendor's version of SPICE to another vendor's version. In fact, many component manufacturers supply free SPICE models of their products to encourage you to use their products in your designs.
SPICE was developed using public funding. The program is an open license. You can legally get versions free! Why should you spend $10,000 or even $99 for something you can get free?
Using the core SPICE program is cumbersome and anti-intuitive. There is no graphic input. You define your circuit using a text editor, such as Windows Notepad. Consider the following example. Figure 1 is a simple schematic and Table 1 is the SPICE file version of Fig. 1.
One line of text describes one component and how it is connected to the rest of the circuit. "R1 1 2 100.0W" tells you that R1 is a resistor, the first lead connected to node 1, the second lead is connected to node 2 and has a value of 100W ("Node" is a SPICE term for conductor). A file of a typical power amplifier would be large, difficult to edit or troubleshoot. Most (if not all) SPICE programs will come with a schematic drawing tool, called "schematic capture."
Select your components, place them on your sheet of paper, and then play connect-the-dots to wire your circuit. The software translates your graphic work into a file like the previous example to be used by the simulator. The core SPICE program comes with only a few basic components: resistors, capacitors, voltage sources, generic NPN transistor, and so on. Commercial SPICE programs come with a library of SPICE models for specific components, such as Analog Devices AD-711, TIP 32C transistor, IRF610 power FET, 12AX7 vacuum tubes. The SPICE program uses these models to predict how your circuit will behave.
When you specify a Texas Instruments TL071 op amp, you simulate the circuit using a TL071's electrical characteristics, such as bandwidth, gain, current draw, and so forth. The more accurate the model, the more accurate your simulation results will be. When evaluating a SPICE package, examine the library of components carefully.
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