Circuit simulation

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The circuit simulation with computers and corresponding circuit simulation programs is accepted today in the development of electronic devices (as well as in training) standard. The functionality of simple and complex analog and digital circuits can be simulated, verified and tested with the appropriate programs - depending on the scope of the simulation model - without actually having to implement the desired circuit. However, the prerequisite for the circuit of the simulation circuit design to work correctly later (after a corresponding practical circuit board assembly or implementation in a chip) is that the real components have been simulated with sufficient accuracy when the simulation software was implemented. As a result, on the one hand, this saves time and money for developing electronic circuits and, on the other hand, helps to better understand electronics and their problems.

Types of circuit simulations

Depending on the area of ​​application, a distinction is made between various circuit simulations and their methods:

  1. The time and value continuous circuit simulation of mostly analog circuits or circuit parts. It is typical that circuits and their components are described with the underlying physical parameters and the function of individual circuit elements is described, for example, by means of differential equations . Since the circuits to be simulated are usually not too extensive, but only represent reduced equivalent circuits or parts of more complex circuits, the actual circuit is entered directly into the simulator as a network list, for example in the form of a circuit diagram . Alternatively, many programs also allow the use of a hardware description language .
  2. The time and value discrete circuit simulation of digital, clocked circuits. The main difference is that the simulation is only evaluated at certain times, usually the cycle times. States between these times are "skipped" in the simulator. Typical areas of application of such simulations are the testing and verification of complex digital circuits, as they are described using hardware description languages ​​in VHDL or Verilog .

Analog circuit simulation

Simulation of an analog circuit

For analog circuit simulation, the electronic components (e.g. resistors , capacitors , semiconductors , logic and arithmetic circuits, etc.) are represented as mathematical models. By calculating values ​​for the nodes of the circuit using network equations, a comprehensive data matrix for the simulated circuit is created. The basis of the system of equations are Kirchhoff's rules .

The evaluation of this data can be displayed during the simulation with virtual measuring and display instruments.

In addition to the pure testing of functionality, the simulated circuits can also be analyzed under the following aspects:

Since around 1970 the University of California at Berkeley has been working intensively on the first circuit simulation. In 1972 the first version of SPICE (Simulation Program with Integrated Circuit Emphasis) was published. The program is written in FORTRAN and runs on mainframes. SPICE became the standard in circuit simulation for industry and universities. In the following years SPICE was continuously developed and the manufacturers of parts and components made their own mathematical models of their products available. Some software manufacturers acquired licenses for the SPICE source code and developed their own programs for circuit simulation from this. As a result, PSpice appeared on the market in 1980 as the first simulation program for PCs.

Other programs followed such as MULTISIM from Electronics Workbench, MICROCAP, LTspice and many others. From 1985 new versions of SPICE were programmed in C. Many of the programs for circuit simulation can now be downloaded from the Internet as free software ( GPL ), shareware or free student versions. What they all have in common, however, is that a more or less current version of SPICE works in the background.

Extensions in this area consist of using hardware description languages ​​instead of network lists or circuit diagrams to model the circuit to be simulated on a higher level of abstraction. With VHDL-AMS, an attempt is made to expand the VHDL language, which was originally intended only for modeling discrete, digital circuits, to include analog circuit simulation. Currently (2007) there are already simulators for VHDL-AMS, which are in direct competition with the circuit simulators, which are mostly based on SPICE .

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