CIRCUIT

NAME
SYNOPSIS
OPTIONS
DESCRIPTION
EXAMPLE
AUTHOR
SEE ALSO

NAME

OPTIONS

-h, --help

Display a help message.

-v, --verbose

Turn on verbosity.

-q, --quiet

Don't produce informational messages. This option is cancelled by the -v option.

-s, --sfile FILE.s

Use the indicated technology file. By default, the default technology file of the current project is used.

-m, --maskdata FILE

Use the indicated maskdata file. By default, the default maskdata file of the current project is used.

-i, --ignore-preexisting

Ignore any preexisting capacitance rules present in the technology file.

-p, --precision low|medium|high

Use the given level of precision

-Z, --z-window VALUE

Set the window in the z-direction for which capacitive coupling is significant. The value should be in microns.

--no-color

Disable colored output.

The tabs tool allows the user to automatically produce capacitance rules for a given technology. See tecc(1ICD) or space(1ICD) for information on technology files. Capacitance rules enable a more efficient way of circuit extraction than full 3D extraction, at the cost of some accuracy.

When you wish to generate capacitance rules using tabs, first change your working directory to an appropriate project directory. Tabs will, by default, use the maskdata and space.def.s files of the process related to the current project. You can change this behavior by specifying the --maskdata and --sfile flags. (In case you specify both flags, you will not need to be in a project directory).

Before you run tabs, also make sure that the technology file contains no capacitance rules. You can use the --ignore-preexisting flag to ignore any capacitance rules which are already in the technology file, but obviously, you should know what you are doing.

A minimal technology file suitable for input to tabs is shown below.

unit vdimension 1e-6 conductors : # name : condition : mask : resistivity : type cond_mf : cmf : cmf : 0.045 : m cond_ms : cms : cms : 0.030 : m contacts : # name : condition : lay1 lay2 : resistivity cont_s : cva cmf cms : cmf cms : 1e-12 vdimensions : v_cmf : cmf : cmf : 1.70 0.70 v_cms : cms : cms : 2.80 0.70 dielectrics : # Dielectric consists of 5 micron thick SiO2 # (epsilon = 3.9) on a conducting plane. SiO2 3.9 0.0 air 1.0 5.0

Tabs essentially uses only the vdimensions section and the dielectrics section of the technology file. Please see tecc(1ICD) for more information on these sections.

Tabs computes rules for (vertical) area capacitances, (vertical and lateral) edge-edge capacitances, ground-capacitances, and (vertical) edge-surface capacitances. A good description of the concepts involved is given in the Space User's Manual.

The --z-window option is very useful, and should be used in all cases, except for very simple cases. It allows you to specify a maximum influence window in the z-direction. Normally, tabs takes into account the influences between all possible layers. This is, however, not very useful in realistic cases. For example, when your process contains 16 levels of metal, then the bottom-most layer of metal will, most likely, not have any significant capacitive coupling to the top-most layer. To reduce computation time, you should therefore use this option. The value given should be specified in microns. A reasonable value is 2*(h+s) where h is the maximum height of a conductor, and s is the maximum vertical spacing between two successive conductor layers. You can see what influences have been considered by tabs by inspecting the technology file after tabs has completed its computation.

The generated capacitance rules are written to the same technology file (extension .s) as used for the input. Generated rules are written to the file with a special tag, so that they can be automatically replaced when tabs is invoked another time. Hence, any pre-existing generated rules do not have to be removed from the file manually, before running tabs.

Internally, tabs uses the 3d mode of the space extractor to compute the values for the capacitance rules, using various layout patterns. When you use the --verbose option, you will be able to see the output of the extraction process.

EXAMPLE

The following example shows how tabs can be invoked.

# cd my-project-dir # tabs -Z 2.0