Introduction to SPICE
There’s a lot of information we’ve presented in the previous sections. A lot of this relates to finding and selecting components, as well as how to place the components into your schematics. Sometimes, when you’re placing components in your schematics and you’re designing circuits, you don’t always know the best values to use for components, or if the circuit will produce the exact behavior you want to see. Some of the electrical behavior in your circuits can be calculated rather easily, but other circuits are more difficult and may require some tools to automate these calculations
This is where simulations are very important. Most ECAD programs, including professional PCB design applications, include a circuit simulator that automates many calculations you might need to perform in circuit design. As you build up your circuits, there are times where you need to evaluate its behavior to ensure the components you choose will work properly. It’s important to know when to use circuit simulations and what they can tell you about your system.
In this lesson, we’ll look at some of the basic circuit simulation tools you can use in ECAD programs, including in Altium Designer. Circuit simulations are performed while you’re creating circuits in your schematics, and you can run them repeatedly as you try out different components for your circuits. One of the benefits of these skills is that they carry over to other areas of electronics design; circuit simulations aren’t just used for PCB design.
The industry-standard simulation package is called “Simulation Program with Integrated Circuit Emphasis,” or simply SPICE. This simulation package is open source, and anyone can implement the basic SPICE algorithm in their own simulation application. The program was originally created to run as code, and you can implement SPICE in programs like MATLAB. Today, many ECAD applications use their own version of SPICE and will give it a modified name; two common packages that are taught in many universities are LTSpice and HSpice.
A SPICE simulation can be used to determine the voltage and current distributed throughout a circuit diagram. In other words, a SPICE simulation calculates the current flowing through each leg of a circuit, and the voltage drop across each component in a circuit.
Not all circuits will need simulations, but if you know you’ll need to run simulations for certain circuits, there are some strategies you can use to set up your schematics and use components to quickly run simulations and complete your designs.
Basic Components for Simulation
Remember that designs need real components if you ever want to manufacture your board. However, the best practice when running simulations is not to use real components. Instead you can use generic components, meaning components that aren’t associated with any specific MPN.
Inside Altium Designer, you can access generic components from the Simulation Generic Components library in the Components panel.