Magic VLSI Layout Tool Version 8.2 *

ext2spice, exttospice

Convert extracted file(s) to a SPICE format file.


ext2spice [option] [cellname]

where option is one of the following:
[run] [runtime_options]
Run ext2spice on current cell, with command-line options (see Summary, below).
Reset to default values
format hspice|spice2|spice3|ngspice
Set output format. spice3 is the default, for compatibility with tclspice. This is a change from previous versions of magic, where the default was hspice.
rthresh [value]
Set resistance threshold value. Lumped resistances below this value will not be written to the output. The value is in ohms, or may be the keyword infinite to prohibit writing any lumped resistances to the output.
cthresh [value]
Set capacitance threshold value. The value is in femtofarads, or may be the keyword infinite to prohibit writing any parasitic capacitances to the output.
merge [merge_option]
Merge parallel devices/transistors. The valid merge options are:
Merge transistors and capacitors having the same device type and node connections and having the same width and length. Device multipliers ("M=") are output for each set of merged devices.
Merge transistors having the same node connections and having the same length. Widths are summed in the final output. Merge any capacitors having the same device type and node connections. Capacitance is summed in the final output.
Do not merge any devices.
extresist on|off
Incorporate output from the command extresist into the final SPICE file.
resistor tee [on|off]
Model resistor capacitance as a T-network. Each resistor device is split into two, with all substrate and overlap capacitance placed on the node between the two half-length devices. Without this option, resistor devices lose all parasitic capacitance information, and ext2spice may produce warnings about unknown nodes. However, use of this option may conflict with LVS (layout-vs.-schematic), when only one resistor is expected per drawn device.
subcircuit [on|off]
When set to on (the default), and if the cell selected for SPICE output has defined ports on the top level, then the cell becomes a subcircuit definition in the output, and the output has no top-level calls to any devices. This format is appropriate for including in a testbench netlist, for example. If the top-level cell does not have defined ports, then there is no way for magic to determine what the ports might be, or what order they may be in, making it impossible to generate a consistent subcircuit, so in the absence of ports, this option has no function. Ports are defined by the use of the port method for labeling input and output ports. When option subcircuit is set to off, the top-level circuit will be the top level of the netlist, and it will have no associated subcircuit definition.
subcircuit top [on|off]
This variant of the subcircuit option controls whether or not ext2spice generates a .subckt wrapper around the top-level circuit. If the top-level circuit does not have defined ports, then no .subckt wrapper will ever be generated, because ext2spice will not be able to know which nets are the ports.
subcircuit descend [on|off]
When set to off, the subcircuit descend option will not descend into any subcells below the top level, writing only the top-level circuit to the output. The default is on. This option can be useful for writing out digital circuits made from standard cells, since the digital subcircuits can usually be included from a vendor library.
scale [on|off]
When set to on, the scale value is set by the SPICE ".scale" card, recognized by some SPICE parsers. All device lengths, widths, and areas are then given in integer units (internal database units). When set to off, all device widths, lengths, and areas are given in unscaled, physical dimensions.
short [voltage|resistor|none]
Determines behavior with respect to ports with different names connected to the same net. SPICE does not have a universal method for describing a net with more than one name. A common way of handling this is by separating differently-named parts of a net with a zero-ohm ideal resistor or a zero-volt DC source. "ext2spice short" uses one of these methods to preserve duplicate port names. "ext2spice short resistor" uses the zero-ohm resistor method, which "ext2spice short voltage" uses the zero-volt source method. "ext2spice short none" reverts to the default behavior, which is to remove all port names except for one from the netlist.
hierarchy [on|off]
When set to on, magic will extract a hierarchical representation of the circuit, in which the cell hierarchy of the layout is represented in SPICE by ".subckt" macros. "ext2spice hierarchy" does not require that subcircuits have port labels. Each subcircuit will be analyzed for port connections, and port connections will be consistent in the SPICE output between the subcircuit definition (".subckt") and instantiated calls ("X") to that subcircuit.
blackbox [on|off]
When set to "on", views marked as abstract will be output as subcircuit calls ("X") but there will be no associated subcircuit definition output. A circuit is considered "abstract" if at the time of extraction it has a property named "LEFview". A cell will automatically be given this property if it is read from a LEF input file. It may also be given this property using the "property" command. In order for the blackbox view to be meaningful, the subcell must declare ports (see the "port" command).
renumber [on|off]
When set to on, subcircuit calls (see above; only used for certain options such as "subcircuit", "hierarchy", or with extracted device types "subcircuit" or "rsubcircuit") are numbered sequentially "X1", "X2", etc., as encountered by the extractor. When set to off, subcircuit calls (when used with options "subcircuit" or "hierarchy", but not applying to low-level extracted subcircuit devices) will be rendered in the SPICE output file as "X" followed by the ID (name) of the cell instance.
global [on|off]
When set to on or default, unconnected global nets of the same name in subcells are merged in the output. When set to off, such nets are left unconnected.
Name of the cell to generate output for. This item is optional; if not specified, then ext2spice generates output for the current edit cell.
Apply settings appropriate for running LVS (layout vs. schematic). These settings are as follows:
  • hierarchy on
  • format ngspice
  • cthresh infinite
  • rthresh infinite
  • renumber off
  • scale off
  • blackbox on
  • subcircuit top auto
  • global off
This command applies the settings but does not generate output (i.e., does not run ext2spice), so that settings can be overridden if necessary.
(The lvs option was introduced in version 8.2.79).
Print help information.


Without options, or with the option run, the ext2spice command converts the hierarchical extracted netlist information produced by the extract command in a series of .ext files into a flattened representation in SPICE format, used for detailed analog simulation.

runtime_options may be passed on the command line, and represent the original command-line options passed to the standalone version of ext2spice. A number of the original command-line options have been deprecated in the Tcl-based version, and some are duplicated by other ext2spice options. Valid runtime_options are:

Aggressive merging of devices. If the lengths of FET devices connected in parallel are equal, then add their widths together to form a single device. Overrides any value specified by the "ext2spice merge" command option.
Conservative merging of devices. If the lengths and widths of FET devices connected in parallel are equal, then add their widths together to form a single device. Overrides any value specified by the "ext2spice merge" command option.
-o filename
Save the output as file filename (filename must include any file extension, as there is no standard extension for SPICE files).
-j device:class [/subclass] /subsnode
Override values of resistance class, substrate resistance class, and substrate node name for device type device. Resistance classes are indexed by number and must match the definition in the technology file's extract section.
-f spice2|spice3|hspice|ngspice
Choose the output SPICE format for compatibility with different versions of SPICE.
Distribute junction areas and perimeters. The Magic extractor computes area and perimter values per node, not per device. For devices that share a node, Magic cannot distinguish between the devices (for parasitic calculations, it's not necessary to distinguish between the devices). Normally, when generating device output, Magic writes the lumped area and perimeter values along with the first device attached to a node, and sets the area and perimeter values for all remaining devices on that node to zero. The -d option causes Magic to distribute the node area and perimeter evenly among all devices attached to that node.
Don't output transistor or node attributes in the SPICE file. This option will also disable the output of information such as the area and perimeter of source and drain diffusion and the FET substrate.
Don't output nodes that aren't connected to devices (floating nodes).
Trim characters from node names when writing the output file. char should be either "#" or "!". The option may be used twice if both characters require trimming.
-y num
Select the precision for outputting capacitors. The default is 1 which means that the capacitors will be printed to a precision of 0.1 fF.
-J hier|flat
Select the source/drain area and perimeter extraction algorithm. If hier is selected then the areas and perimeters are extracted only within each subcell. For each device in a subcell the area and perimeter of its source and drain within this subcell are output. If two or more devices share a source/drain node then the total area and perimeter will be output in only one of them and the other will have 0. If flat is selected the same rules apply, only the scope of search for area and perimeter is the whole netlist. In general, flat (which is the default) will give accurate results (it will take into account shared sources/drains).
With options, the command sets various parameters affecting the output format and content.

Implementation Notes:

ext2spice is implemented as a separate loadable Tcl package, but one which depends on the presence of the standard "tclmagic" package. magic is set up with a placeholder command for ext2spice, and will automatically load the Tcl package when this command is invoked.

exttospice is an alias for ext2spice, to satisfy the grammatically anal retentive. ext2spice is also implemented as a script to be run from the shell command line, where it executes magic in batch mode (i.e., using the -dnull option) and runs the ext2spice command automatically. With this usage, the syntax is:

ext2spice [ magic_options -- ] ext2spice_runtime_options ext_file
The double-dash separates command options passed to magic on startup (such as "-T technology" to specify the technology) from those runtime options (see above) passed to the ext2spice command.

See Also:


Return to command index

Last updated: September 17, 2021 at 10:12am