Fileformat GDSII

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GDS II (Calma GDS II)

GDS II is a database file format which is the de facto industry standard for data exchange of integrated circuit or IC layout artwork. It is a binary file format representing planar geometric shapes, text labels, and other information about the layout in hierarchical form. The data can be used to reconstruct all or part of the artwork to be used in sharing layouts, transferring artwork between different tools, or creating photomasks.
Initially, GDS II was designed as a format used to control integrated circuit photomask plotting. Despite its limited set of features and low data density, it became the industry conventional format for transfer of IC layout data between design tools of different vendors, all of which operated with proprietary data formats. It was originally developed by Calma for its layout design software, "Graphic Data System" ("GDS") and "GDS II". Now the format is owned by Cadence Design Systems. GDS II files are usually the final output product of the IC design cycle and are given to IC foundries for IC fabrication. GDS II files were originally placed on magnetic tapes. This moment was fittingly called tape out though it is not the original root of the term. Objects contained in a GDS II file are grouped by assigning numeric attributes to them including "layer number", "datatype" or "texttype". While these attributes were designed to correspond to the "layers of material" used in manufacturing an integrated circuit, their meaning rapidly became more abstract to reflect the way that the physical layout is designed. As of October 2004, many EDA software vendors have begun to support a new format, OASIS, which may replace GDS II.

GDS II in the LayoutEditor

The GDS II file format is the default in the LayoutEditor and full supported in all existing versions of the file format. (version 3 to version 7) Some options can be set up via the setup dialog:

Handling of Layers in GDS II

The GDS II saves a layer number to each element like polygon, path, etc. By default the LayoutEditor keeps these number untouched. Optional it is possible to setup a layer mapping. With this mapping a combination of layer/datatype in the GDS II file can be maped to a layernumber in the LayoutEditor. The setup can be done via the setup dialog or via a macro.

Set Maximal Number of Points in Polygons

Version 3 of the GDS II file format limits the maximal size of polygons/path elements to 200 points. The technical limit of the file format structure is 8191 points, which is allowed in version 7. This limit can be set via the setup dialog or via a macro. If a polygon exceed this limit, it will be splitten into two or more polygon during the saving the file. The default is 8191.
As a workaround it is possible to save polygons in multi records. This is not part of the gds standard, but supported by some viewers. Activate 'gdsMultiXYRecord' to use it and avoid any splitting of polygons.

Option: Padding the Filesize to N*2048

Same old programs or tape devices can only handle GDS II file the file size is a multipy of 2048 bytes. By activating this option vie the setup dialog or via a macro all saved GDS II files will be padded to this length by add 0 at the end of the file. This option is rarely need and the default is off.

Option: Save Box as Polygon

Box element were introduced with version 4 of the GDS II file format. By activating this option by the setup dialog or via a macro all box element will be saved as a polygon. By default this option is off.

Option: Multi XY Records

Due to the block structure of the GDSII file format the maximum size of polygons is limited to 8192. Larger polygons can not be saved conform to the GDSII standard. A polygon exceed this limit will be splitted by default. However it is possible to save such polygon in multiply blocks. This method will allow unlimit number of polygon points. This extension is not part of the GDSII standard, but supported of some other GDSII programs.