Electronic circuit simulation usesmathematical models to replicate the behavior of an actual electronic device or circuit. Simulation software allows for the modeling of circuit operation and is an invaluable analysis tool. Due to its highly accurate modeling capability, manycolleges and universities use this type of software for the teaching ofelectronics technician andelectronics engineering programs. Electronics simulation software engages its users 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 electronic circuit designs. In particular, forintegrated circuits, the tooling (photomasks) is expensive,breadboards are impractical, and probing the behavior of internal signals is extremely difficult. Therefore, almost allIC design relies heavily on simulation. The most well known analog simulator isSPICE. Probably the best known digital simulators are those based onVerilog andVHDL.
Some electronics simulators integrate aschematic editor, a simulation engine, and an on-screenwaveform display (see Figure 1), allowing designers to rapidly modify a simulated circuit and see what effect the changes have on the output. They also typically contain extensive model and device libraries. These models typically include IC specifictransistor models such as BSIM, generic components such asresistors,capacitors,inductors andtransformers, user defined models (such as controlled current and voltage sources, or models inVerilog-A orVHDL-AMS).Printed circuit board (PCB) design requires specific models as well, such astransmission lines for the traces andIBIS models for driving and receiving electronics.
While there are strictlyanalog[2] electronics circuit simulators, popular simulators often include both analog and event-driven digital simulation[3] capabilities, and are known as mixed-mode ormixed-signal simulators if they can simulate both simultaneously.[4] An entire mixedsignal 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-drivenalgorithm 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: with primitive digital elements that use timing models and the built-in 12 or 16 state digital logic simulator, with subcircuit models that use the actual transistor topology of theintegrated circuit, and finally, with inlineBoolean logic expressions.
Exact representations are used mainly in the analysis oftransmission line andsignal 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, uses 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 forpower electronics representpiecewise linear[6] algorithms. These algorithms use an analog (linear) simulation until apower 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]
Another approach that dramatically shortens the simulation time of switch-mode converters is based on average behavioral circuits that apply the switched inductor model.[8] In this approach, the simulation is carried out on the average signals, voltages, and currents, and hence runs much faster. Another advantage of this approach is that it can carry both time domain and frequency domain simulations. The latter can be used to extract the transfer functions in open and closed loop.[9]
Process variations occur when the design isfabricated and circuit simulators often do not take these variations into account. These variations can be small, but taken together, they can change the output of a chip significantly.
Temperature variation can also be modeled to simulate the circuit's performance through temperature ranges.[10]
A common method of simulating linear circuits systems is withadmittance matrices, or Y matrices. The technique involves modeling the individual linear components as an N port admittance matrix, inserting the component Y matrix into a circuitsnodal admittance matrix, installing port terminations at nodes that contain ports, eliminating ports without nodes thoughKron reduction, converting the final Y matrix to an S or Z matrix as needed, and extracting desired measurements from the Y, Z, and/or S matrix.
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