Simulating Circuits using the SPICE in National Instruments Multisim 1.1 2006/07/28 13:49:13.737 GMT-5 2006/08/03 12:08:03.370 GMT-5 Janell Rodriguez janellrodriguez@hotmail.com Erik B Luther erik.luther@ni.com Janell Rodriguez janellrodriguez@hotmail.com Erik B Luther erik.luther@ni.com This module provides a brief introduction to simulating circuits using the SPICE in National Instruments Multisim. Multisim is fully featured SPICE schematic capture and simulation tool used for circuit design, simulation, and in combination with Ultiboard for layout of custom PCBs.

Simulation Overview While a good design naturally follows from quality schematics, truly great designs can made with the help of simulation. Multisim provides powerful simulation capabilities and features which are simply unavailable in other EDA packages. Simulating a design can result in fewer design iterations and less chance of errors in the prototype stage of product development. When a design is simulated at the front end of the design process, the number of design cycles can be significantly reduced. In addition to a world-class SPICE simulator, Multisim also includes XSPICE simulation, enabling fast simulation of digital other components. Patented co-simulation techniques allow designers to simulate VHDL modeled components along with the rest of a circuit. With MultiMCU, certain microcontrollers can be simulated in the very same mixed-mode environment. MultiMCU is not available for all versions of Multisim.

Using the Interactive Simulator To begin a simulation, ensure that the circuit has all the necessary prerequisites. All circuits must include a ground reference, and a source. Once the circuit is ready for simulation, click the Run / Stop Simulation button

Run/Stop Simulation Button

or press F5. An interactive circuit simulation will begin. The settings that are used for interactive simulation can be viewed and modified by selecting Simulate/Interactive Simulation Settings.Figure 1 below illustrates some of the settings available for interactive simulation. The default end time for the simulation is 1e+30 seconds, or around 3.17e+30 billion years. By default time steps will be generated automatically.

Interactive Simulation Settings

To view results of this simulation, the measurement probe

The Measurement Probe

can be used dynamically. Simply click on the probe icon and the mouse cursor will turn into a probe. The mouse can then be moved over any net to view the following metrics: Voltage (instantaneous, peak-to-peak, RMS, and DC). Frequency. Virtual instruments can also display simulation results. Virtual instruments are covered later in this section. Multisim also provides more traditional SPICE analyses, which are run through the Grapher/Analyses List toolbar button,

Grapher/Analyses List toolbar button

or by selecting Simulate/Analyses. Analyses are described in greater detail later in this section.

Handling Simulation Errors Sooner or later, even the most experienced SPICE users will run into a SPICE simulation error. Multisim includes a simulation advisor to help discover and fix the source of troubling errors. When an error message appears such as the one in Figure 5, click the Adviser button to access the available help.

Simulation Error Log Dialog Box

Simulation Advisor

Two of the most often encountered errors are timestep errors, and singular matrix errors. below provides the most common solutions to these simulation errors.

Common Solutions to Simulation Errors