Subsections B. For many years, this format was the only one of its kind and many other vendors accepted it in their systems. This is important because GDS II is a binary format that makes assumptions about integer and floating-point representations. A GDS II circuit description is a collection of cells that may contain geometry or other cell references. A library of these structures is contained in a file that consists of a library header, a sequence of structures, and a library tail. Each structure in the sequence consists of a structure header, a sequence of elements , and a structure tail.
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The Advanced Design System reads GDSII files into a layout design without circuit or schematic information, internally converting the drawing data to the current layout units. For a step-by-step tutorial, see Importing a Layout.
If the importer encounters elements on layers not present in the layer definition file, it will automatically add new layers. If new layers are added, the importer saves the revised layer definition file to disk. When transferring a file via tape, the block size must be preserved. To write fixed-block sized tapes for transfer to other systems, refer to your computer system documentation.
Note Because the GDSII stream is a block-structured binary file, it can easily be corrupted when transferring the file from one system to another. The reason for this is as follows.
The GDSII file format can contain multiple top-level instances that may or may not be related to one another. The name of that instance is reflected in the Layout title bar. In some cases, this name does not match that of the imported file. GDSII file instance names simplify the tracking of hierarchies within the file. An x appears in the box to the left of selected attributes. To select or deselect an attribute, click it.
This button invokes the Layer Editor. For Layer Editor options, see Defining Layers. The size, in layout units, for text in the imported design. The default value is 1.
See Importing a Layout for more information. For more information on the Layer Editor, see Defining Layers. Define Layers This button invokes the Layer Editor. Text Size The size, in layout units, for text in the imported design.
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While other formats have been proposed to replace it and one, OASIS, seems to be gaining some traction GDSII remains by far the main way of describing the physical layout for the masks used to build a chip. This is despite the fact that GDSII is not an open industry standard -- it was developed by Calma in the 80's and the ownership of the specification moved from Calma to GE to Valid to Cadence over the years. As you can imagine, computers and processors have come a long way since that time; the specification has some constraints which were probably based both on the limitations of the 80's era computers and also on the developer's beliefs that chips were going to be approximately the same complexity for the foreseeable future. Fortunately, the way the database was created enabled users to extend many of the dejure limitations while maintaining defacto compatibility with the actual architectural underpinnings.
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, GDSII was designed as a stream format used to control integrated circuit photomask plotting. Despite its limited set of features and low data density, it became the industry conventional stream format for transfer of IC layout data between design tools of different vendors, all of which operated with proprietary data formats. GDSII files were originally placed on magnetic tapes. This moment was fittingly called tape out though it is not the original root of the term.
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 photo masks. Despite its limited set of features and low data density, it became the industry's default format for transfer of IC layout data between design tools of different vendors, all of which at that time operated with often incompatible and proprietary data formats. Currently, the format is owned by Cadence Design Systems.