SPICE, acronym of Simulation Program with Integrate Circuit Emphasis, is a circuit simulation software developed in 1975 at the University of Berkley, California, and made immediately available to the public under open source license. Afterwards, several commercial versions of the program have been realized and, among these, PSpice (developed by Microsim) is probably the most widespread. These types of software are mainly used to carry out experimental tests on an electronic circuit without having to physically implement it.

In 1999 Linear Technologies, a manufacturer of electronic components and integrated circuits, released LTSpice III (the third release of the software used for the design of its devices) under freeware license. The company was later absorbed by Analog Devices, but LTSpice, which contains an extensive library of the main devices produced by the two companies, has been constantly updated to become the most widely distributed and used circuit simulation software in the world in the industrial field.

In the era of integrated circuits, circuit simulation software has become a practically indispensable tool for electronic circuit designers. The possibility of being able to verify the specifications of a project without necessarily having to build a prototype is a very clear benefit, also from an aeconomic point of wiev.

The graphic editor of LTSpice is quite intuitive and well structured and allows you to draw the circuit using the toolbar, located at the top of the screen, where you can also find the main components (resistance, capacitance, inductance and diode). All the other components can be reached through the button depicted with a logic gate called Component. After placing the components of the circuit (including at least one generator) it is necessary to set their value and trace the connections with the Wire instrument, without forgetting to include at least one ground node.

Main LTspice tools.

Once the circuit has been set up, it is necessary to define the type of analysis to be carried out by choosing between various operating regimes: stationary, direct current, alternating current or transient. At this point you can launch the simulation with the Run command, which starts the analysis and launches the Probe application. The latter allows you to graphically display the trend of the magnitude of interest. Pressing the left mouse button on any wire displays the electrical voltage, while pressing it on the body of the component displays the current. To measure the difference in voltage between two points of the circuit, press the left mouse button on the first point and drag, holding it down, to the second point. Obviously Probe can do much more than this, but it is impossible here to go into all the features of the program, which are really many. On the web there are many tutorials both for beginners and more experienced users.

The latest version of the software (LTSpice XVII) can be downloaded directly from the developer’s website:

The program works under Windows, but Apple or Linux users can use it after installing an emulator.

Andrea Rubino

Example screen.