LTspice Genealogy - The Heritage of Simulation Ubiquity

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1969: Beginnings of CANCER (Computer Analysis of Nonlinear Circuits, Excluding Radiation)

  • CANCER began as a derivative of a program that was the class project of a series of courses taught by Ron Rohrer with the approval and encouragement of Professor Donald O. Pederson
  • Larry Nagel wrote the netlist parser and the analysis core and was student group leader
  • Lynn Weber developed a noise analysis feature that utilized adjoint network techniques
  • Bob Berry wrote the sparse matrix LU decomposition package
  • CANCER project's key features:
    • Was the first circuit simulator to utilize sparse matrix techniques
    • Used Newton-Raphson iteration method heuristically modified for bipolar circuits
    • Utilized implicit integration to accommodate widely spread time constants of an IC
    • Integrated DC operating point analysis, small-signal AC analysis and transient analysis
  • Project presented by Ron Rohrer at the 1971 ISSCC , but the code was considered partially proprietary and was never publicly released

1971: SPICE 1 (Simulation Program with IC Emphasis) - direct outgrowth of CANCER

  • Ron Rohrer leaves UC Berkeley and further development of CANCER (renamed SPICE) became Larry Nagel's Masters project with Don Pederson taking over as faculty advisor
  • KEY EVENT: Don Pederson insisted that all further work be releasable to the public domain
  • SPICE 1 release's key features:
    • Models for bipolar transistors were changed to Gummel-Poon equations
    • JFET and Shichman-Hodges MOSFET devices added (for Dave Hodges' MOSFET design class)
    • Fixed time step and strict Nodal Analysis (true voltage sources and inductors not supported)
    • DC, AC, Transient, Noise, and Sensitivity Analyses in the same program
    • Built-in models for diodes, bipolar transistors, MOSFETs, and JFETs
  • Was about 6k lines of FORTRAN at first informal limited public release in late 1971
  • Official public release was May 1972 with first formal paper presented by Don Pederson at the 16th Midwest Symposium on Circuit Theory, April 12, 1973
  • SPICE 1 becomes industry standard simulation tool running on large mainframe computers

1972: SPICE 2 begins

  • First version of SPICE 2 was Larry Nagel's Ph.D. project under Don Pederson
  • Modified Nodal Analysis (MNA) added, enabling voltage sources and inductors for the first time
  • Ellis Cohen added dynamic memory allocation
  • Adjustable time-step control added, greatly speeding most simulations
  • MOSFET and bipolar models overhauled and extended
  • Was about 8k lines of FORTRAN when first released to the public domain in late 1974
  • Larry Nagel departs for Bell Labs and his thesis becomes the SPICE 2 Users Guide

1975: Journey to SPICE 2G6 (the pinnacle FORTRAN version)

  • Ellis Cohen becomes primary contributor with later help from Andrei Vladimirescu
  • First of a series of public revision releases after Nagel's version 2B begin in 1978
  • Along the way, sub circuits, poly sources and transmission lines are added
  • Version 2G6 ends up implementing three MOSFET models:
    • MOS 1 is a simplistic model described purely by ideal square-law I-V characteristics
    • MOS 2 is an analytical model, MOS 3 is a semi-empirical model and both include second-order effects such as channel length modulation, sub threshold conduction, scattering limited velocity saturation, small-size effects, and charge-controlled capacitances
  • 2G6 released to public domain in April 1983 (and is still available today from UC Berkeley)
  • Many commercial simulators today are based on SPICE 2G6

1983: SPICE 3 begins

  • Tom Quarles begins work, writing first version in RATFOR, a C-like preprocessor for FORTRAN
  • Was fully converted to C in 1985 with first early versions released in March of that year
  • Added models: MESFET, lossy transmission line and non-ideal switch
  • Arbitrary behavioral voltage and current sources added
  • Includes polynomial capacitors, inductors and voltage controlled sources
  • Allowed the use of alphabetical node labels rather than only numbers
  • Features a graphical interface for viewing results
  • New version eliminates many convergence problems
  • Added noise, distortion and pole-zero analysis, temperature sweeping, Monte Carlo and Fourier analysis
  • Not fully compatible with SPICE 2G6
  • Was about 135,000 lines of C code at first public release in 1989
  • Final version at Berkeley, SPICE 3F5, released to public in 1993
  • XSPICE was developed at Georgia Tech as an extension to the SPICE language to allow behavioral modeling of components
    • Drastically improve the speeds of mixed-mode and digital simulations

1984: PSpice (micro Processor SPICE)

  • Developed by MicroSim to run on the first IBM PC, initially released in January 1984
  • Was the first commercial offspring of Berkeley SPICE to run directly on the PC platform
  • Was the first SPICE program to gain wide acceptance in both industry and academia
  • KEY EVENT: A zero cost (but node-limited) student version is introduced in 1988 – for the first time, SPICE becomes ubiquitous in the electrical engineering community
  • Evolved from Berkeley SPICE 2G, but added many proprietary enhancements
  • Probe, a waveform viewer module, was added when PC VGA graphics became available
  • Schematics, a graphical front end, was added much later sometime in the early 1990s

The Road To LTspice

  • 1981 Linear Technology Corporation founded
  • 1991 DOS SwitcherCAD available (equation based)
  • 1996 μPower SwitcherCAD available(simulation based)

1999: LTspice/SwitcherCAD III first released to public

2008: LTspice IV

Some possible noteworthy events/additions:

Ver 2 Jan03: graphical symbol editor hierarchical schematics Apr04: Chan inductor, undocumented behavioral inductor revealed