Circuit simulation is a technique to predict the behavior of a real circuit using a computer program. It replaces real components with predefined electrical models. It is not possible to conceder all the physical processes (in circuit level simulation) in the parts and all PCB parasitic so it will only reflect the specific model that is put into it. This is the reason behind that simulators can’t substitute bread boarding and prototyping. But they allow measurements of internal currents, voltages and power that in many cases are virtually not possible to do any other way.

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

Integrated circuits, unlike board-level designs composed of discrete parts, are impossible to breadboard before manufacture. Further, the high costs of photo lithographic masks and other manufacturing prerequisites make it essential to design the circuit to be as close to perfect as possible before the integrated circuit is first built. Simulating the circuit with SPICE is the industry-standard way to verify circuit operation at the transistor level before committing to manufacturing an integrated circuit.

Board-level circuit designs can often be bread boarded for testing. Even with a breadboard, some circuit properties may not be accurate compared to the final printed wiring board, such as parasitic resistances and capacitance. These parasitic components can often be estimated more accurately using SPICE simulation. Also, designers may want more information about the circuit than is available from a single mock-up. For instance, circuit performance is affected by component manufacturing tolerances. In these cases it is common to use SPICE to perform Monte Carlo simulations of the effect of component variations on performance, a task which is impractical using calculations by hand for a circuit of any appreciable complexity.

Circuit simulation programs, of which SPICE and derivatives are the most prominent, take a text netlist describing the circuit elements (transistors, resistors, capacitors, etc.) and their connections, and translate this description into equations to be solved. The general equations produced are nonlinear differential algebraic equations which are solved using implicit integration methods, Newton’s method and sparse matrix techniques

SPICE was developed at the Electronics Research Laboratory of the University of California, Berkeley by Laurence Nagel with direction from his research advisor, Prof. Donald Pederson. SPICE1 was largely a derivative of the CANCER program, which Nagel had worked on under Prof. Ronald Rohrer. 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 United States Department of Defence contracts that required the capability to evaluate the radiation hardness of a circuit. When Nagel’s original advisor, Prof. Rohrer, left Berkeley, Prof. Pederson became his advisor. Pederson insisted that CANCER, a proprietary program, be rewritten enough that restrictions could be removed and the program could be put in the public domain.

SPICE1 was first presented at a conference in 1973. SPICE1 was coded in FORTRAN and used nodal analysis to construct the circuit equations. Nodal analysis has limitations in representing inductors, floating voltage sources and the various forms of controlled sources. SPICE1 had relatively few circuit elements available and used a fixed-time step transient analysis. The real popularity of SPICE started with SPICE2 in 1975. SPICE2, also coded in FORTRAN, was a much-improved program with more circuit elements, variable time step transient analysis using either the trapezoidal (second order Adams-Moulton method) or the Gear integration method (also known as BDF), equation formulation via modified nodal analysis (avoiding the limitations of nodal analysis), and an innovative FORTRAN-based memory allocation system developed by another graduate student, Ellis Cohen. The last FORTRAN version of SPICE was 2G.6 in 1983. SPICE3 was developed by Thomas Quarles (with A. Richard Newton as advisor) in 1989. It is written in C, uses the same netlist syntax, and added X Window System plotting.

As an early open source program, SPICE was widely distributed and used. Its ubiquity became such that “to SPICE a circuit” remains synonymous with circuit simulation. SPICE source code was from the beginning distributed by UC Berkeley for a nominal charge (to cover the cost of magnetic tape). The license originally included distribution restrictions for countries not considered friendly to the USA, but the source code is currently covered by the BSD license.

SPICE inspired and served as a basis for many other circuit simulation programs, in academia, in industry, and in commercial products. The first commercial version of SPICE was ISPICE, an interactive version on a timeshare service, National CSS. The most prominent commercial versions of SPICE include HSPICE (originally commercialized by Shawn and Kim Hailey of Meta Software, but now owned by Synopsys) and PSPICE (now owned by Cadence Design Systems). The academic spinoffs of SPICE include XSPICE, developed at Georgia Tech, which added mixed analog/digital “code models” for behavioural simulation, and Cider (previously CODECS, from UC Berkeley/Oregon State Univ.) which added semiconductor device simulation. The integrated circuit industry adopted SPICE quickly, and until commercial versions became well developed many IC design houses had proprietary versions of SPICE. Today a few IC manufacturers, typically the larger companies, have groups continuing to develop SPICE-based circuit simulation programs. Among these are ADICE at Analog Devices, LTspice at Linear Technology, Mica at Freescale Semiconductor, and TISPICE at Texas Instruments. (Other companies maintain internal circuit simulators which are not directly based upon SPICE, among them PowerSpice at IBM, Titan at Qimonda, Lynx at Intel Corporation, and Pstar at NXP Semiconductor.)

SPICE became popular because it contained the analyses and models needed to design integrated circuits of the time, and was robust enough and fast enough to be practical to use. Precursors to SPICE often had a single purpose: The BIAS program, for example, did simulation of bipolar transistor circuit operating points; the SLIC program did only small-signal analyses. SPICE combined operating point solutions, transient analysis, and various small-signal analyses with the circuit elements and device models needed to successfully simulate many circuits.

Some of the popular circuit simulators are as follows:

1.            ASTAP

2.            Advanced Design System

3.            CircuitLogix

4.            CPU Sim

5.            GNU Circuit Analysis Package

6.            Gpsim

7.            ICAP/4

8.            List of free electronics circuit simulators

9.            Logisim

10.          Micro-Cap

11.          NI Multisim

12.          National Instruments Electronics Workbench Group

13.          Ngspice

14.          PSpice

15.          PowerEsim

16.          Quite Universal Circuit Simulator

17.          SPICE

18.          SapWin

19.          SmartSpice

20.          SNAP (software)

21.          Spectre Circuit Simulator

22.          SpectreRF

These simulators differs each other and are generally application specific. Most popular version of spice simulators for analog circuit simulations are PSpice offered by MicroSim but now incorporated in OrCAD of Cadence and National Instruments Multisim.