1.1 What is ngspice ?

Ngspice is a mixed-level/mixed-signal circuit simulator based on three open source software packages: Spice3f5, Cider1b1 and Xspice:

• Spice3 is the most famous and used circuit simulator. It was developed University of California at Berkeley (UCB), by "a cast of thousand" (as they say).
• Cider is a mixed-level simulator that already includes Spice3f5 and adds a device simulator to it: DSIM. Cider couples the circuit level simulator to the device simulator to provide greater simulation accuracy (at the expense of greater simulation time). Critical devices can be described with technology parameters (numerical models) and non critical ones with the original spice's compact models.
• Xspice is an extension to Spice3 that provides code modeling support and simulation of digital components through an embedded event driven algorithm.
• The NG prefix has lot of meanings: Next Generation, New Good, etc. Choose or invent the one you prefer. The heart of the project is the ngspice program.

1.2 Why resurrecting Berkeley's Spice ?

Berkeley's Spice can be considered the father of most circuit simulators available today. It is an old but still good piece of software, it may not be the fastest or the most reliable but it's free, it's available in source code and most of the electrical simulators inherited it's syntax. On the more technical side, spice3 uses good numerical algorithms (most commercial implementations have only strengthened them), implements most of the models for MOSFET submicron designs and has a powerful set of analyses. On the more "social" side, spice3 it's well introduced in the academic environment.

1.3 What is the project's goal ?

The project goal evolved during project development, at first the final goal was to develop a reliable, fast and friendly circuit simulator for mixed signal/mixed level simulation. During development it become apparent that to reach the goal a complete rewrite of spice was needed. Since it was almost absurd to rewrite Spice and since a new simulator was already under development: ACS (Al's Circuit Simulator), now GNUCap (GNU Circuit Analysis package), the goal of nspice became less utopical: merge Spice3f5, Xspice and Cider into a mixed-signal/mixed-level simulator that can be used as a reliable engine.

1.4 What you are going to do ?

We are going to develop a mixed-signal/mixed-level circuit simulation program integrating three different spice based simulators: Spice, Xspice and Cider.

Xspice is a mixed-signal circuit simulator developed by GTRI (Georgia Tech Research Institute) at Georgia Institute of Technology. Xspice was originally developed as an extension over Spice3c1. Xspice introduces code modeling and a digital simulator into ngspice. The "home site" of Xspice is:

http://users.ece.gatech.edu/~mrichard/Xspice/

Cider is a mixed-level circuit and device simulator based on Spice3f5 that couples a device simulator (DSIM) to Spice. More information can be found at:

http://www-cad.eecs.berkeley.edu/Software/cider.html

The merging process is done in parallel with bug fixing and improvement of the three simulators. The improvements are concentrated into 6 directions:

• Compact models: the improvements in compact models will address mainly the implementation of additional effects not available in the original code. Device specific improvements are documented on ngspice's documentation and in the DEVICE file in project's tarball.

  Improvements that affects all devices already implemented are: "dtemp" option to set instance's temperature relative to the circuit one and "m" parallel multiplier to simulate an arbitrary number of instances of the same kind connected in parallel.

  Planned improvements are the development of a dynamic loading mechanism for compact models, to avoid loading in memory devices that are not needed, and SOAR (Safe Operating ARea) checks to identify situations in which devices are used out of their safety areas.

• Simulator's analyses: this is a low priority area. Planned improvements include the implementation of parametric analyses, to analyse the behaviour of the circuit as a parameter changes. Parameter sweep, Monte Carlo and Worst Case fall in this category. Network analysis (double bipole parameters extraction) is another planned improvement.

• Numerical analysis code: the improvements within the numerical code must be done with extreme care. Planned improvements are, the replacement of the Sparse library with the latest code Kenneth Kundert has released, available at:

  http://sourceforge.net/projects/sparse

  Other planned improvements, but with very low priority, includes the use SuperLU library as possible Sparse library replacement (the library is available at http://crd.lbl.gov/~xiaoye/SuperLU) and the introduction of continuation metohds to aid DC convergence.

• Spice language: The language used to input the circuit to the simulator has been extended and now allows the user to input parametric values for components (the numparam library). This is an experimental feature that will be improved in the future. Planned improvements includes the support for loading more than one circuit, netlist manipulation via command line (adding and removing instances) and the implementation of a command history using the libedit library, available at:

  http://sourceforge.net/projects/libedit

• Frontend: The design of a new spice frontend has not been successful and now is orphaned, since the is no interests and many free and commercial frontends are available. There is no planned improvement here.

• Documentation: Commercial simulators come with very good manuals containing tutorials, description of models equations, example of use, suggestions, etc. Spice came with little documentation. The Spice3f manual, available on the Internet has been used as the basis for the new manual. It will be constantly improved during ngspice development and integrated with the documentation accompanying Xspice and Cider. This is a very time consuming task and probably the documentation will always be left slightly behind.

1.5 Legal issues

Ngspice merges three different simulators: spice and cider are covered with the "old" BSD license, Xspice by its own license. The ngspice license will be then the BSD license.

Since the "old" BSD license is not compatible with the GPL library it is not possible to link the ngspice with GPL'ed code, as is written in:

http://www.gnu.org/philosophy/bsd.html

The group developing ngspice has written to Berkeley's copyright holders asking to change the license to the new BSD, which has the incompatibility removed, but without success.

Ngspice will not be released under GPL license and, no GPL code can be linked into ngspice (as in the original Spice3f) without breaking GPL.

1.6. What mailing lists exist for ngspice ?

There are three mailing lists dedicated to the ngspice project.

Users mailing list: <ngspice-users@lists.sourceforge.net> This list is for ngspice users, examples, problems, bug reports and general discussion on ngspice can be sent here.

Developers mailing list: <ngspice-devel@lists.sourceforge.net> The list dedicated to ngspice development. Developers shold subscribe here, to follow the program development. May be used to send patches, and technical discussion on ngspice.

Frontend mailing list: <ngspice-frontends@lists.sourceforge.net> Almost orphaned, this list should be used to discuss issues about the realization of a graphical frontend to ngspice.

Send an empty message to the following addresses to get information on subscription.

ngspice-users-help@lists.sourceforge.net

ngspice-devel-help@lists.sourceforge.net

ngspice-frontends-help@lists.sourceforge.net

1.7. Are the mailing lists archived anywhere ?

Yes, the lists are archived. There are two places where to look for archives. The project started on the IEEE Central and South Italy web server and then moved to sourceforge. Sourceforge provides an archiving service that cam be accessed via the summary page:

http://sourceforge.net/projects/ngspice

(look for the "Lists" link). Old messages from the pre-sourceforge age are available at:

http://ngspice.sourceforge.net/lists.html

1.8. What newsgroups exist for ngspice ?

There is no ngspice specific newsgroup. Anyway ngspice threads appear on newsgroups dedicated to circuit simulation and electronic design. An (incomplete) list is:

• sci.electronics.cad
• comp.lsi.cad

1.9. Where can I get a copy of ngspice ?

You can download ngspice from:

http://sourceforge.net/projects/ngspice

1.10. Where should I look on the World Wide Web for ngspice stuff?

Look at the official Ngspice Web Page:

http://ngspice.sourceforge.net

1.11. Where should I look on the World Wide Web for Spice documentation ?

There are a lot of Internet sites that have information on spice, the best way is to point to your preferred search engine. Some interesting sites are:

The Spice Home Page:

http://bwrc.eecs.berkeley.edu/Classes/IcBook/SPICE/

Xspice Page:

http://users.ece.gatech.edu/~mrichard/Xspice

Cider Page:

http://www-cad.eecs.barkeley.edu/Software/cider.html

Spice benchmarks:

http://www.cbl.ncsu.edu/pub/Benchmark_dirs

2.1. What is the current version ?

The latest version released is:

• ngspice-rework-15 (released on 10/12/2001)

The development version is:

• ngspice-rework-15pre3 (released on 28/01/2004)

2.2. What are the latest features in the current release ?