NI Multisim: Breaking the Simulation Mold

Simulation has become established as a modern tool that provides an experimental canvas where designers and engineers can capture their circuits and harness the power of a standard PC to virtually analyze and understand their designs before going on to the more cost and time intensive prototyping stage.

Most circuit simulation is done using SPICE. However, SPICE can be a complicated language requiring a substantial investment in time, and an understanding of difficult syntax. With critical deadlines and a constant push for the evolution of their products, few professionals have the luxury of time to become experts with this powerful tool. This has caused many engineers to avoid simulation all together.

A study by National Instruments shows that 80% of engineers see the advantages of simulating within the design process, yet only 20% actually do so. The reason for this disparity is clear: traditional SPICE simulation needs to evolve to be both powerful and easy-to-use tool.

In this article you will begin to learn about the powerful simulation capabilities and ease-of-use of NI Multisim.

NIMultisim

National Instruments Multisim is a leading design platform which provides easy-to-use schematic capture, combined with powerful interactive circuit simulation software. Multisim uses a powerful and robust SPICE simulator contained in an easy-to-use and effective user interface that allows circuit analysis with the click of a button, with no need for the entry of lines of code and constant reference to a SPICE manual.

Schematic Capture

During the design process, each iteration can require numerous changes in circuit configuration and the addition of new components. Multisim uses a database of thousands of simulatable devices (Figure 1). Parts can be swapped and added to optimize and complete a design as desired; when the circuit’s schematic is finished, it is ready for simulation. Components include virtual parts, which operate based on ideal behavior, and real-world devices representing vendor-specific parts.

Figure 1. Easy Component Selection

Multisim’s drag-and-drop functionality allows easy improvements to circuits. For example, a component such as a resistor can be dropped directly onto a pre-existing net where it will automatically break and then reconnect the wire to the resistor’s pins. And if a component needs to be replaced, it can be done straight from the database without having to delete or break wires, significantly easing the drawing process. A spreadsheet view provides an interface to change any number of components at the same time, without the need to painstakingly search through schematics.

Circuit design has evolved into an industry dependent on large teams working together. The co-ordination of the group effort is essential to an effective development approach, and Multisim offers a modular system for managing such projects. Using sub-circuits, an engineer can divide and organize a design into sections within the same file, while hierarchical blocks can be used to divide a circuit into smaller separate files, allowing individuals to create, test and analyze these circuits – and then bring them together quickly and effortlessly.

Circuit Analysis

The capability of Multisim to vary and simulate representations of real components gives engineers freedom in design work, without compromising timelines and deadlines. Components are also not restricted to SPICE models, as RF and VHDL programmed devices all work seamlessly together in a process known as co-simulation.

Modeled to function and look the same as real-world devices, designers can connect virtual instruments such as oscilloscopes, IV and spectrum analyzers to their circuits to analyze simulated circuit characteristics. The transition for any engineer from their physical workbench to Multisim is easy with tools that have become second nature in the design lab. Simulated instruments such as the virtual Tektronix oscilloscope (Figure 2) have the same look and functionality as their physical counterparts.

Figure 2. Powerful Virtual Instrumentation Analysis Features

While virtual instruments are the quickest and easiest way to gain insight into the operation of circuits, designers will also want to gain a deeper understanding through more sophisticated analyses. Multisim provides several analyses including Monte Carlo, Worst Case, and Distortion Analysis. For example, Monte Carlo is a statistical technique which will perform DC, AC, or Transient analysis while randomly varying the properties of a circuit’s components during several simulated runs. The results of each simulation are output to the easy-to-use Multisim Grapher tool (Figure 3). The constraints, successes, and flaws of any electrical device within this type of random or worst case analysis provide a strong basis from which to continue, change or improve any design.

Figure 3. Multisim’s Advanced Monte Carlo Analysis Technique

Advanced Features

Multisim’s integration with National Instruments LabVIEW provides an easy way to introduce advanced real-world signals into simulation. For example, complex noise from a power source can be extremely difficult, if not impossible, to model through equations. With NI LabVIEW and data acquisition hardware, you can capture this noise and feed it directly into a Multisim simulation. NI LabVIEW can also be used to output the results of simulation as signals into the real world. By combining these real-world signals from NI LabVIEW with advanced analysis techniques in a Multisim simulation (Figure 4), engineers can gain insight into a circuit and correct design flaws long before building expensive prototypes.

Figure 4. Introduce advanced real-world signals into simulation with easy and seamless integration of Multisim and NI LabVIEW.

Once a circuit meets the specifications of a design, moving forward to PCB layout can be done with a one-click transfer to National Instruments Ultiboard (Figure 5). Ultiboard is a professional and easy-to-use PCB layout tool that generates industry standard Gerber data, as well as DXF, 3D IGES, and several other outputs. Changes to the design, both at the schematic and layout level, are coordinated so that with the click of a button, changes are annotated both in the forward and backward directions.

Figure 5. Combine Multisim with NI Ultiboard to place, route and generate Gerber data for PCB layouts.

Conclusion

Only by experimenting with and understanding the characteristics of a circuit can a design be refined and improved upon. To accomplish this, engineers have traditionally had two options; exclusively prototype, or use SPICE as an initial step to prototyping.

Simulation is a proven technique to analyze a circuit effectively. It reduces the overall number of prototypes created as well as the time and cost involved with design revisions between each of these physical models. The advantages of virtually simulating with a traditional language such as SPICE have however been overshadowed by its difficulty and complexity to use!

With its industry-leading features, graphical environment and integration with NI LabVIEW, Multisim has evolved the SPICE simulator into the easy-to-use design tool for the engineers and designers of today.

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