Boston College, Department of Physics

 PH351001 Contemporary Electronics Laboratory

 

In this course, you are invited to use a SPICE simulator to check your homework solutions.

SPICE (Simulation Program with Integrated Circuit Emphasis) Circuit Simulation

 

(or how to make & debug realistic virtual circuits without getting your hands dirty)

 

 

SPICE is a general purpose industry standard circuit simulator that has been in use for over 40 years, since 1973. All commercial circuits, whether they are circuits in integrated circuit chips, or printed circuit boards, are simulated using SPICE prior to making the first real circuits. Modern SPICE simulators have sophisticated Graphics User Interfaces & virtual instruments, so that you literally just draw your circuit, assign values to components (including chips), and “hook up” virtual signal sources and virtual measuring instruments (meters scopes, network analyzers, etc.)  As much as I abhor Wikipedia, the Wikipedia SPICE article is pretty good. (http://en.wikipedia.org/wiki/SPICE)

 

The way modern commercial SPICE simulators are made, they contain libraries of realistic components (resistors, capacitors, etc.) that also include vast libraries of integrated circuit chips. By “realistic”, they contain information to allow the SPICE simulator to also simulate how the circuit will perform as things like temperature change, to allow it to take into account the tolerances that the specific components you chose are manufacture to, etc. Such commercial SPICE simulators can cost tens of thousands of dollars per license (runnable installation). Many chip manufacturers however, give away for free some very good SPICE simulators that already know about a lot of generic components like resistors, capacitors, inductors, common diodes, common transistors, common op-amps, and even common digital circuits. These free SPICE simulators also contain libraries of the manufacturers’ chips, the idea being that many companies (or hobbyists) will use free SPICE simulators, often for years, before buying a commercial SPICE simulator, and then tend to use the chips in their designs that are in that free SPICE simulator’s libraries.

 

LTSPICE

 

There is a very good free SPICE simulator made by a chip company called Linear Technologies (http://www.linear.com/) called LTSPICE. LTSPICE is available in versions for Windows as well as OS X.

 

You can go to the Linear Technologies LTSPICE page ( http://www.linear.com/designtools/software/) and download the Windows or Mac (OS X) version appropriate to your PC. You can download the software without making an account on Linear’s website. LTSPICE allows you to just draw the circuit, simulate it, and see the waveforms. LTSPICE has a bunch of examples, including simulation examples of some of the chips we will work with in this course, such as the LM741 op-amp and the LM 555 Timer Chip. An screen shot of the circuit from Lab 4 being simulated in LTSPICE & displayed in their plotting panes is shown below:

 

MultiSim

A nicer SPICE simulator with a bunch of virtual instruments like virtual scopes is MultiSim. MultiSim is not free, but they do have a trial version which is good for 30 days. They also have a student edition which is around $40 for a 2-year license. A pretty good deal considering buying a non-student license is about $2800. Both the trial and student versions have limitations on the size & complexity of the circuits they will simulate, but you can do a lot within the confines of those limitations. The trial version can only be used for 30 days. The trial version includes limitations such as the impossibility to print schematics and export final Gerber files. (Gerber files are the circuit board design files you'd send to a PC board maker to make a commercial quality board for you.) The student edition limitations are listed here. An screen shot of the circuit from Lab 4 being simulated in MultiSim & displayed on a virtual scope is shown below:

 

 

 

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