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Ngspice F.A.Q.Version 1.0
Maintened by Paolo Nenzi <p.nenzi@ieee.org>
Last update: 05/12/2001
Ngspice F.A.Q.Version 1.2
Maintained by Paolo Nenzi <p.nenzi@ieee.org>
Last update: 02-11-2003
This document contains the Frequently Asked Questions (and Answers)
for ngspice project.
______________________________________________________________________
__________________________________________________________________________
Table of Contents
@ -33,7 +33,8 @@
3. SOLUTIONS TO COMMON MISCELLANEOUS PROBLEMS
3.1 What systems are supported?
3.2 I get errors when I try to compile the source code, why?
3.3 This document didn't answer my question. Where else can I look for an answer?
3.3 This document didn't answer my question. Where else can I look for
an answer?
4. ADMINISTRATIVE INFORMATION AND ACKNOWLEDGEMENTS
4.1 Feedback
@ -44,23 +45,24 @@
______________________________________________________________________
11.. IINNTTRROODDUUCCTTIIOONN AANNDD GGEENNEERRAALL IINNFFOORRMMAATTIIOONN
1. INTRODUCTION AND GENERAL INFORMATION
11..11.. WWhhaatt iiss nnggssppiiccee??
1.1 What is ngspice ?
Ngspice is the name of a project and of a program in the project.
Spice is the famous circuit simulator developed by the CAD Group of
the University of California at Berkeley (UCB). The NG prefix has a
lot of meanings: Next Generation, New Good, etc. Choose or invent the
one you prefer. The ngspice project aims to improve the capabilities
of the Spice3 circuit simulator. The heart of the project is the
ngspice program, a circuit simulator derived from spice3f5.
The idea behind the project is to improve the capabilities of the
Spice 3f5 circuit simulator. Spice is the most famous circuit
simulator, developed at the University of California at Berkeley
(UCB), by "a cast of thousand". The NG prefix has a lot of meanings:
Next Generation, New Good, etc. Choose or invent the one you prefer.
The heart of the project is the ngspice program, a circuit simulator
derived from spice3f5.
11..22.. WWhhyy rreessuurrrreeccttiinngg BBeerrkkeelleeyy''ss SSppiiccee??
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
@ -72,119 +74,129 @@
"social" side, spice3 it's well introduced in the academic
environment.
11..33.. WWhhaatt iiss tthhee pprroojjeecctt''ss ggooaall??
The final goal of ngspice project is to develop a reliable, fast and
friendly circuit simulator for mixed signal/mixed level simulation.
Easy isn't it? ;-).
11..44.. WWhhaatt yyoouu aarree ggooiinngg ttoo ddoo??
We are going to develop a circuit simulation program. The line of
development follows two parallel paths:
1. EEnnhhaanncceemmeennttss aanndd bbuugg--ffiixxiinngg ooff tthhee oorriiggiinnaall ssppiiccee33ff55 ccooddee..
2. DDeevveellppppmmeenntt ooff aa nneeww GGPPLL''eedd ssiimmuullaattoorr..
The first phat will lead to a better spice3f5 and nothing more than
this, while the second one will bring us a new simulator,
compatible with its father but more expandable and presumably
faster and numerically stronger.
There is another project in ngspice: the development of one or more
frontend to the new simulator. One of the key issues of our project is
to let users design the front end they want, using the widget set and
the language they prefer. For this reason ngspice differs a lot from
spice3f5: in ngspice there is a clear distinction between the front
end and the back end. In ngspice the front end takes care of the
interaction with the user. It is back-end's task to maintain the
object database, to exchange data with the simulator, etc.
There are various improvements we are planning, some follows:
1. TThhee ffrraammeewwoorrkk ((oorr GGrraapphhiicc UUsseerr IInntteerrffaaccee)):: Spice is (and should
continue to be) a command line or a text tool, but this makes very
difficult to design large circuits. To overcome this difficulty, a
schematic entry tool and a waveform viewer tools are needed.
Nevertheless, there are other tools that can be useful: a parts
database, an editor which higlights the syntax, a symbol editor,
etc. Most of these program already exists in the open source world,
so they need only to be integrated in a common EDA environment.
2. DDooccuummeennttaattiioonn:: Commercial simulators have very good manuals with
tutorials, models equations explained, example of use, suggestions,
etc. This line of development has the task of providing the final
spice user with an ordered and comprehensive set of information on
the program and its features. The documentation should be useful
for the student as well as for the circuit professional.
3. IImmpprroovveemmeennttss ttoo tthhee SSppiiccee ccooddee:: This is the hard part. The target
of this direction is to make ngspice a commercial grade simulator.
This means improving it's speed, its numerical strenght, include
the latest models available and some other important features:
+o Numerical Algorithms:
+o More stable algorithms for integration (as Runge-Kutta
Methods (?) ).
+o Better convergence in Operating Point Calculation adding a
modified version of Fixed-Point Homotopy to the Newton-
Raphson algorithm,
+o Devices:
+o Behavioral device: enhance the B device of spice3 to accepts
IF THEN ELSE conditions, and digital keywords like DELAY,
HIGHV, LOWV, etc. to simulate simple digital macromodels.
+o Dynamically Loadable Devices: reduce the memory occupied by
the simulator by using shared object code for devices. Each
device is a .so library that is inserted only if the circuit
contains an element modeled by the device. If we are
simulating CMOS, we do not need BJT or SOI (in most of the
situations).
+o Code Level Modeling: let users write their devices in C and
use them in the simulator.
+o Improving device: include additional parameters to some
devices as HDIF, LDIF, etc.
+o New types of analysis, oriented to circuits syntesis and
optimization:
+o Network analysis: given four nodes, extract z,y,s and the
other double bipole paramters.
+o Monte Carlo analysis: statistical simulation based on device
tolerances.
+o Worst Case analysis: find the worst case of operation of a
given circuit based on device parameters tolerances.
+o Parametric analysis: repeat an analysis when one or more
parameters assumes different values.
+o Faster handling of sparse matrices.
+o Possibility to mesure circuit pameters, like the delay between
two nodes, etc.
+o Whatever else can be judged useful.
11..55.. LLeeggaall iissssuueess
The improved spice3f5 will be relased under the original Berkeley's
lincese. The new simulator will be released as GPL. Make ngspice a GPL
program, allow us to link a lot of good code laying on the net and
obviously contribute to the GPL community.
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 Analyis
package), the goal of nspice became less utopical: merge
spice, 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
directives:
+ 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, "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
behavior 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 have very good manuals with
tutorials, models equations explained, example of use, suggestions,
etc. Spice came with little documentation. The Spice3f manual,
available on the Internet 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 probably
never be relased under the GPL license.
11..66.. WWhhaatt mmaaiilliinngg lliissttss eexxiisstt ffoorr nnggssppiiccee??

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