# SPICE

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File:Spiceopus screenshot.png
Screen shot of Spice OPUS, a fork of Berkeley SPICE

SPICE (Simulation Program with Integrated Circuit Emphasis) is a general purpose analog electronic 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.

## Introduction

Integrated circuits, unlike board-level designs composed of discrete parts, are impossible to breadboard before manufacture. Further, the high costs of photolithographic 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 designs can often be breadboarded, but designers may want more information about the circuit than is available from a single mock-up. For instance, performance is affected by component manufacturing tolerances and it is helpful for designers to simulate with SPICE to predict the effect of variations of those values. Even with a breadboard, some aspects may not be accurate compared to the final printed wiring board, such as parasitic resistances and capacitances. In these cases it is common to perform Monte Carlo simulations using SPICE, a task which is impractical using calculations by hand.

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.

## Origins

SPICE was developed at the Electronics Research Laboratory of the University of California, Berkeley by Larry Nagel with direction from his research advisor, Prof. Donald Pederson. SPICE1 was largely a derivative of the CANCER program,<ref>Template:Cite journal</ref> 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 Defense 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.<ref>Template:Cite journal</ref>

SPICE1 was first presented at a conference in 1973.<ref>Nagel, L. W, and Pederson, D. O., SPICE (Simulation Program with Integrated Circuit Emphasis), Memorandum No. ERL-M382, University of California, Berkeley, Apr. 1973</ref> 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-timestep transient analysis. The real popularity of SPICE started with SPICE2<ref name=spice2>Nagel, Laurence W., SPICE2: A Computer Program to Simulate Semiconductor Circuits, Memorandum No. ERL-M520, University of California, Berkeley, May 1975</ref> in 1975. SPICE2, also coded in FORTRAN, was a much-improved program with more circuit elements, variable timestep transient analysis using either trapezoidal or the Gear integration method (also known as BDF), equation formulation via modified nodal analysis<ref>Template:Cite conference</ref> (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<ref>Quarles, Thomas L., Analysis of Performance and Convergence Issues for Circuit Simulation, Memorandum No. UCB/ERL M89/42, University of California, Berkeley, Apr. 1989.</ref> 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 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.<ref>Template:Cite news</ref> 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<ref>Vladimirescu, Andrei, SPICE -- The Third Decade, Proc. 1990 IEEE Bipolar Circuits and Technology Meeting, Minneapolis, Sept. 1990, pp. 96–101</ref>, an interactive version on a timeshare service, National CSS. The most prominent commercial versions of SPICE include HSPICE (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 behavioral 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.<ref>K. S. Kundert, The Designer’s Guide to SPICE and SPECTRE, Kluwer. Academic Publishers, Boston , 1998</ref> 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, Linx at Intel Corporation, and Pstar at NXP Semiconductor.)

## Program features and structure

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.<ref name="SPICE4">Nagel, L., Is it Time for SPICE4?, 2004 Numerical Aspects of Device and Circuit Modeling Workshop, June 23-25, 2004, Santa Fe, New Mexico. Retrieved on 2007-11-10</ref> Precursors to SPICE often had a single purpose: The BIAS<ref>Template:Cite journal</ref> program, for example, did simulation of bipolar transistor circuit operating points; the SLIC<ref>Template:Cite journal</ref> 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.

### Analyses

SPICE2 included these analyses:

• AC analysis (small-signal frequency domain analysis at the quiescent point (Q-point))
• DC analysis (nonlinear quiescent point calculation)
• DC transfer curve analysis (a sequence of nonlinear operating points calculated while sweeping an input voltage or current, or a circuit parameter)
• Noise analysis (a small signal analysis done using an adjoint matrix technique which sums uncorrelated noise currents at a chosen output point)
• Transfer function analysis (a small-signal input/output gain and impedance calculation)
• Transient analysis (time-domain large-signal solution of nonlinear differential algebraic equations)

SPICE2 also contained code for sensitivity analysis, pole-zero analysis, and small-signal distortion analysis. Analysis at various temperatures was done by automatically updating semiconductor model parameters for temperature, allowing the circuit to be simulated at temperature extremes.

Other circuit simulators have since added many analyses beyond those in SPICE2 to address changing industry requirements. Parametric sweeps were added to analyze circuit performance with changing manufacturing tolerances or operating conditions. Loop gain and stability calculations were added for analog circuits. Harmonic balance or time-domain steady state analyses were added for RF and switched-capacitor circuit design. However, a public-domain circuit simulator containing the modern analyses and features needed to become a successor in popularity to SPICE has not yet emerged.<ref name="SPICE4">second reference</ref>

### Device models

SPICE2 included many semiconductor device compact models: three levels of MOSFET model, a combined Ebers–Moll and Gummel-Poon bipolar model, a JFET model, and a model for a junction diode. In addition, it had many other elements: resistors, capacitors, inductors (including coupling), independent voltage and current sources, ideal transmission lines, and voltage and current controlled sources.

SPICE3 added more sophisticated MOSFET models, which were required due to advances in semiconductor technology. In particular, the BSIM family of models were added, which were also developed at UC Berkeley.

Commercial and industrial SPICE simulators have added many other device models as technology advanced and earlier models became inaccurate. To attempt standardization of these models so that a set of model parameters may be used in different simulators, an industry working group was formed, the Compact Model Council<ref>Template:Cite web</ref>, to choose, maintain and promote the use of standard models. The standard models today include BSIM3, BSIM4, BSIMSOI, PSP, HICUM, and MEXTRAM.

### Input and output: Netlists, schematic capture and plotting

SPICE2 took a text netlist as input and produced line-printer listings as output, which fit with the computing environment in 1975. These listings were either columns of numbers corresponding to calculated outputs (typically voltages or currents), or line-printer character "plots". SPICE3 retained the netlist for circuit description, but allowed analyses to be controlled from a command-line interface. SPICE3 also added basic X-Window plotting, as UNIX and engineering workstations became common.

Vendors and various free software projects have added schematic capture front-ends to SPICE, allowing a schematic diagram of the circuit to be drawn and the netlist to be automatically generated. Also, graphical user interfaces were added for selecting the simulations to be done and manipulating the voltage and current output vectors. In addition, very capable graphing utilities have been added to see waveforms and graphs of parametric dependencies. Several free versions of these extended programs are available, some as introductory limited packages, and some without restrictions.

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