SPICE

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SPICE (Simulation Program with Integrated Circuits Emphasis) is a general purpose analog circuit simulator. It is a powerful program that is used in IC and board level design to check the integrity of circuit designs and to predict circuit behavior.

1 Explanation
2 Origins
3 Commercial versions with significant market share
4 Open Source versions
5 See also
6 External links

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Explanation

In real-world circuits, performance is affected by component value tolerances. It is difficult for designers to predict the effect of larger value tolerances. On the other hand they want to use cheaper components with large tolerances if they wish to mass produce their products. Also in radio applications, especially UHF and microwave, parasitics cannot be ignored and must be built into a generic model of the circuit being simulated. In both these cases it is usual to perform Monte Carlo simulations which are difficult or even impossible to calculate by hand.

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Origins

SPICE was originally developed at the Electronics Research Laboratory of the University of California, Berkeley in 1975 by Larry Nagle and Donald Pederson. Versions 1 and 2 were coded in Fortran (2G.6 in 1983 was the last) and ran on mainframe computers. Versions 3 and later are coded in C, but still use a Fortran-like syntax for circuit description. Many commercial versions of SPICE have later replaced Berkeley SPICE as the industry standard. While many are still compatible with the original Berkeley syntax, commercial vendors added proprietary extensions that limit the portability of circuit descriptions and models between different vendors. Most recent versions also include a graphical user interface for constructing circuit descriptions. For digital circuits (e.g., RAM), dedicated simulators exist that run orders of magnitude faster than the traditional Spice tools.

SPICE was largely a derivative of the CANCER program presented by Ronald A. Rohrer announced in a paper at the 1971 ISSCC. CANCER was an acronym for "Computer Analysis of Nonlinear Circuits, Excluding Radiation," a hint to Berkeley's liberalism of 1960s: at these times many circuit simulators were developed under the DoD contracts that demanded the capability to evaluate the radiation hardness of a circuit. It was developed at Berkeley in the sixties, remember! The original SPICE program was released under a restrictive license, which makes it difficult for others to improve upon the original software. Berkeley SPICE continues to influence both commercial and academic offshoots of the program. A new circuit simulator, Ngspice, based on SPICE 3F5, is licensed under the old BSD license. There also exists a branch project called tclspice. Free versions are available for non-commercial use for most computing platforms. LTSPICE is a free SPICE that works on Microsoft Windows and on Linux (under Wine (software) emulator). MacSpice is available for Mac OS9 and OSX.

First versions of Berkeley SPICE used Nodal analysis. However this meant that ideal voltage sources and inductors could not be included in the circuit. Later versions are using Modified nodal analysis, which does not have this drawback. Different algorithms are used to translate all circuit analysis problems into a single or multiple simpler problems of calculating an operating point of a linear circuit. Such problems can then be solved efficiently by solving a linear simultaneous equation. For example non-linear circuits are solved using a Newton-Raphson algorithm, which linearizes non-linear elements in a circuit. Transient analysis is performed using trapezoid or Gear integration algorithm.

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