Electronic circuit simulation

Electronic circuit simulation uses mathematical models to replicate the behavior of an actual electronic device or circuit. Simulation software allows for modeling of circuit operation and is an invaluable analysis tool. Due to its highly accurate modeling capability, many Colleges and Universities use this type of software for the teaching of electronics technician and electronics engineering programs. Electronics simulation software engages the user by integrating them into the learning experience. These kinds of interactions actively engage learners to analyze, synthesize, organize, and evaluate content and result in learners constructing their own knowledge^[1].

Simulating a circuit’s behavior before actually building it can greatly improve design efficiency by making faulty designs known as such, and providing insight into the behavior of electronics circuit designs. In particular, for integrated circuits, the tooling (photomasks) is expensive, breadboards are impractical, and probing the behavior of internal signals is extremely difficult. Therefore almost all IC design relies heavily on simulation. The most well known analog simulator is SPICE. Probably the best known digital simulators are those based on Verilog and VHDL.

Some electronics simulators integrate a schematic editor, a simulation engine, and on-screen waveforms (see Figure 1), and make “what-if” scenarios easy and instant. They also typically contain extensive model and device libraries. These models typically include IC specific transistor models such as BSIM, generic components such as resistors, capacitors, inductors and transformers, user defined models (such as controlled current and voltage sources, or models in Verilog-A or VHDL-AMS). Printed circuit board (PCB) design requires specific models as well, such as transmission lines for the traces and IBIS models for driving and receiving electronics.

Figure 1. CircuitLogix waveform displays.

Types

While there are strictly analog ^[2] electronics circuit simulators, popular simulators often include both analog and event-driven digital simulation^[3] capabilities, and are known as mixed-mode simulators ^[4]. This means that any simulation may contain components that are analog, event driven (digital or sampled-data), or a combination of both. An entire mixed signal analysis can be driven from one integrated schematic. All the digital models in mixed-mode simulators provide accurate specification of propagation time and rise/fall time delays.

The event driven algorithm provided by mixed-mode simulators is general purpose and supports non-digital types of data. For example, elements can use real or integer values to simulate DSP functions or sampled data filters. Because the event driven algorithm is faster than the standard SPICE matrix solution, simulation time is greatly reduced for circuits that use event driven models in place of analog models ^[5].

Mixed-mode simulation is handled on three levels; (a) with primitive digital elements that use timing models and the built-in 12 or 16 state digital logic simulator, (b) with subcircuit models that use the actual transistor topology of the integrated circuit, and finally, (c) with In-line Boolean logic expressions. An example of a mixed-mode simulator is shown in Figure 2.

Figure 2. CircuitLogix mixed-mode simulator.

Exact representations are used mainly in the analysis of transmission line and signal integrity problems where a close inspection of an IC’s I/O characteristics is needed. Boolean logic expressions are delay-less functions that are used to provide efficient logic signal processing in an analog environment. These two modeling techniques use SPICE to solve a problem while the third method, digital primitives, use mixed mode capability. Each of these methods has its merits and target applications. In fact, many simulations (particularly those which use A/D technology) call for the combination of all three approaches. No one approach alone is sufficient.

Another type of simulation used mainly for power electronics represent piecewise linear^[6] algorithms. These algorithms use an analog (linear) simulation until a power electronic switch changes its state. At this time a new analog model is calculated to be used for the next simulation period. This methodology both enhances simulation speed and stability significantly^[7].

Complexities

Often circuit simulators do not take into account the process variations that occur when the design is fabricated into silicon. These variations can be small, but taken together can change the output of a chip significantly.

Process variations occur in the manufacture of circuits in silicon.

Temperature variation can also be modeled to simulate the circuit's performance through temperature ranges.

See also

• List of free electronics circuit simulators
• Qucs
• SPICE
• Transistor models
• Verilog
• VHDL
• Yenka
• PLECS
• Livewire_(software)
• PSIM

References

1. ^ http://e-articles.info/e/a/title/Disadvantages-and-Advantages-of-Simulations-in-Online-Education/
2. ^ Mengue and Vignat,jjj Entry in the University of Marne, at Vallee
3. ^ P. Fishwick, Entry in the University of Florida
4. ^ J. Pedro and N. Carvalho, Entry in the Universidade de Aveiro, Portugal
5. ^ L. Walken and M. Bruckner, Event-Driven Multimodal Technology
6. ^ P. Pejovic, D. Maksimovic, A new algorithm for simulation of power electronic systems using piecewise-linear device models
7. ^ J. Allmeling, W. Hammer, PLECS piece-wise linear electrical circuit simulation for Simulink

External links

• Free Great Java Circuit Simulation by Paul Falstad - Free Educational Great Java Circuit Simulation
• Linear Tech's LTSpice - LTSpice analog and digital simulator, runs under Windows and Linux.
• Multisim website - Circuit simulation software from National Instruments
• CircuitLogix website - electronics circuit simulator
• Circuit Simulator Analyses - circuitdesign.info
• Electronic Circuit Simulation Applet
• GeckoCIRCUITS website - Free power electronics circuit simulator (Java Applet)