---
name: "sim"
section: "5"
platform: "linux"
package: "magic"
version: "8.3.105+ds.1-1.1"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/sim/5"
---

# sim(5)

format of .sim files read by esim, crystal, etc.

## NAME

sim - format of .sim files read by esim, crystal, etc.

## DESCRIPTION

The simulation tools [*crystal*(1)](/crystal/1.md) and *esim*(1) accept a circuit description in **.sim** format. There is a single **.sim** file for the entire circuit, unlike Magic's [*ext*(5)](/ext/5.md) format in which there is a **.ext** file for every cell in a hierarchical design.

A **.sim** file consists of a series of lines, each of which begins with a key letter. The key letter beginning a line determines how the remainder of the line is interpreted. The following are the list of key letters understood.

- **\| units: *s* tech: *tech* format: *MIT\|LBL\|SU***

  If present, this must be the first line in the **.sim** file. It identifies the technology of this circuit as *tech* and gives a scale factor for units of linear dimension as *s*. All linear dimensions appearing in the **.sim** file are multiplied by *s* to give centimicrons. The format field signifies the sim variant. MIT and SU are compatible and understood by all tools. LBL is understood only by gemini(1).

- *type g s d l w x y **g=**gattrs **s=**sattrs **d=**dattrs*

  Defines a transistor of type *type*. Currently, *type* may be **e** or **d** for NMOS, or **p** or **n** for CMOS. The name of the node to which the gate, source, and drain of the transistor are connected are given by *g*, *s*, and *d* respectively. The length and width of the transistor are *l* and *w*. The next two tokens, *x* and *y*, are optional. If present, they give the location of a point inside the gate region of the transistor. The last three tokens are the attribute lists for the transistor gate, source, and drain. If no attributes are present for a particular terminal, the corresponding attribute list may be absent (i.e, there may be no **g=** field at all). The attribute lists *gattrs*, etc. are comma-separated lists of labels. The label names should not include any spaces, although some tools can accept label names with spaces if they are enclosed in double quotes. **In version 6.4.5 and later** the default format produced by ext2sim is SU. In this format the attribute of the gate starting with S\_ is the substrate node of the fet. The attributes of the gate, and source and substrate starting with A\_, P\_ are the area and perimeter (summed for that node only once) of the source and drain respectively. This addition to the format is backwards compatible.

- **C *n1 n2 cap***

  Defines a capacitor between nodes *n1* and *n2*. The value of the capacitor is *cap* femtofarads. **NOTE:** since many analysis tools compute transistor gate capacitance themselves from the transistor's area and perimeter, the capacitance between a node and substrate (GND!) normally does not include the capacitance from transistor gates connected to that node. If the **.sim** file was produced by [*ext2sim*(1)](/ext2sim/1.md), check the technology file that was used to produce the original **.ext** files to see whether transistor gate capacitance is included or excluded; see \`\`Magic Maintainer's Manual #2: The Technology File'' for details.

- **R *node res***

  Defines the lumped resistance of node *node* to be *res* ohms. This construct is only interpreted by a few programs.

- **r *node1 node2 res***

  Defines an explicit resistor between nodes *node1* and *node2* of resistance *res* ohms. This construct is only interpreted by a few programs.

- **N *node darea dperim parea pperim marea mperim***

  As an alternative to computed capacitances, some tools expect the total perimeter and area of the polysilicon, diffusion, and metal in each node to be reported in the **.sim** file. The **N** construct associates diffusion area *darea* (in square centimicrons) and diffusion perimeter *dperim* (in centimicrons) with node *node*, polysilicon area *parea* and perimeter *pperim*, and metal area *marea* and perimeter *mperim*. *This construct is technology dependent and obsolete.*

- **A *node attr***

  Associates attribute *attr* for node *node*. The string *attr* should contain no blanks.

- **= *node1 node2***

  Each node in a **.sim** file is named implicitly by having it appear in a transistor definition. All node names appearing in a **.sim** file are assumed to be distinct. Some tools, such as *esim*(1), recognize aliases for node names. The **=** construct allows the name *node2* to be defined as an alias for the name *node1*. Aliases defined by means of this construct may not appear anywhere else in the **.sim** file.

## SEE ALSO

[crystal(1)](/crystal/1.md), esim(1), [ext2sim(1)](/ext2sim/1.md), sim2spice(1), [ext(5)](/ext/5.md)