About Importing and Exporting Designs

Translating CAD data between various systems can be difficult. Different CAD systems have different representations of data. For instance, some systems contain the concept of a hole and some do not. Differences in translation formats often cause data to be lost or transformed.

In Advanced Design System, translating physical designs is initiated from the layout window using the File > Import and File > Export menu commands. The program's import/export translators are highly configurable. Each translator has associated options that you can set from the Import and Export dialog boxes. These options control how the translator works. For example, with the IGES and GDSII format flatten option, a layout can be translated as a flat, non-hierarchical design. Similarly, the merge option for these formats creates two new polygons from two intersecting closed shapes.

Other options include arc conversions, treatment of holes and text, and in the layers file, specification of layer translation tables. The IGES translator has the greatest number of options because IGES is such a broad standard. System defaults are included with the product and are automatically used if no others are specified.

Translating schematic designs is initiated from the ADS Main or Schematic window using the File > Import and File > Export menu commands. Similar to the Layout translators, each schematic translator has associated options that control how the translator works.

Layout Export Considerations

Before starting a layout, you should consider how the final output could affect the layout process. Different output formats impose different restrictions. The restrictions imposed by GDSII are very different from those imposed by DXF, HPGL, Mask, or Gerber.

With all export formats, you must consider layout units and data base precision. The units and precision used in layout should match those you want in the final output.

Usually no problems are associated with translating units that are in the same measurement system (such as, mils to inches or centimeters to millimeters). However, round-off errors can occur when translating from metric-to-English units or vice versa.

Similarly, no problem is associated with translating a less precise data base resolution in the program to a more precise output resolution. However, the reverse process (such as, 0.001 Layout to 0.01 GDSII) can result in loss of data.

Available File Formats

The Import and Export commands enable you to import and export files in a variety of different formats. You can import files through Advanced Design System's Main, Schematic, or Layout window. All file export is currently done from the ADS Layout window with the exception of Intermediate File Format (IFF) files. The following table shows the available file formats and the individual import/export options.

Steps for importing and exporting these files are outlined in Importing and Exporting Schematic and Layout Designs.

DXF/DWG

The Drawing Exchange Format (DXF) was developed by Autodesk for its AutoCAD product and is widely used to transfer geometric data between systems. Like the mask file format, it provides a simple geometric representation of data. DXF files can be transferred between PC-based or UNIX-based systems. DXF is a very simple file format that can be read by most CAD programs that support DXF.

DWG is a binary format, therefore the files take less time to load and save. Advanced Design System supports importing and exporting to/from AutoCAD. AutoCAD versions 12 to 2007 are supported for import. AutoCad versions 2000, 2004 and 2007 are supported for export. Carefully consider how you want to use DXF/DWG output - including layer numbering, use of holes, and polygon shapes - before beginning your layout design. Setting up the proper layout rules in ADS can save a lot of time in generating acceptable DXF/DWG output. For specific considerations or limitations, consult your AutoCAD documentation. For details, see DXF/DWG Translator.

EGS (Archive/Generate)

Engineering Graphics System (EGS) format is a general graphics format used for capturing manually entered designs. EGS has been applied to ICs, Micro-circuits, Hybrids, and PC Board design applications. Using this format, you can easily exchange data with other programs using EGS formats.

The layout portion of Advanced Design System has adopted many of the primitive types and styles that are part of the EGS standard, but has a more enriched set of capabilities that structure information not representable in EGS. For example, EGS files cannot represent embedded arcs.

Two variations of the EGS format are:

• The Generate format is a flattened list of EGS primitives specified in the user-defined unit space. No additional information is supplied such as supplied with the Archive format.
• The Archive format is a hierarchically organized list of EGS primitives specified in the user-defined unit space. Information such as drawing shapes, layout units, database precision, and grid spacing is included.

For details, see EGS Archive Files and EGS Generate Files.

GDSII Stream

GDSII Stream Format (Calma) is an industry standard for translating final mask data to foundries. The Advanced Design System reads GDSII versions 4.0 through 6.0 and writes GDSII version 6.0.

Unlike other data formats, GDSII stream format is binary. You cannot easily view or edit a stream format file using a text editor. This format is easily translated between different CAD systems because it represents a highly restrictive data type. However, the format has a number of significant limitations; these limitations are discussed in GDSII Stream File Translator.

Gerber

Gerber refers to various data input formats that Gerber Scientific uses to drive its photoplotters. The Gerber format is used by photoplotters produced by other manufacturers also. Advanced Design System supports various types of Gerber output via mask files to either the Gerber or DXF translator. For details, see Gerber Translator.

Gerber Viewer

Gerber Viewer appears as an export file option. It is not a file format, but is placed on the export file menu so you can open the Gerber Viewer at any time. In addition, you can access the Viewer during a DXF or Gerber export (see Using the Gerber Viewer).

You can use the Gerber Viewer to view Gerber or mask files to help verify the correctness of your data. Also, you can use the Gerber Viewer to configure mask file data for photoplotting.

HPGL/2

HPGL/2 output is a subset of the HPGL/2 printer/plotter language. In Advanced Design System, you can export HPGL/2 files from the Layout window. For details, see HPGL/2 Files.

IFF

The Intermediate File Format (IFF) is an ASCII file with a simple, line-oriented command structure and a fairly rich set of constructs. This format is machine- and application-independent, thus simplifying design data transfer.

IFF files are used as the exchange mechanism when transferring designs between Advanced Design System and third-party EDA tools such as Mentor Graphics Design Architect and Cadence Analog Artist. For more information about these framework links, contact your Agilent Technologies sales representative.

For details, see IFF Files.

IGES

The Initial Graphics Exchange Specification (IGES) is an approved ANSI standard of the U.S. Department of Commerce (ANSI Y14.25M) that is used extensively throughout the computer-aided design and manufacturing world. The IGES format can represent both mechanical and electrical design data in two and three dimensions.

Because IGES is such a broad standard, the government has attempted to further define a stricter standard of IGES for the transfer of electrical design data. This standard is known as CALS specification. The CALS specification for IGES is officially contained in the military specification MIL-D-28000, Digital Representation for Communication of Product Data: IGES Application Subsets.

The Advanced Design System supports version 4.0 and 5.0 IGES formats. The program reads and writes IGES CALS Level 1 (technical illustration) and Level 3 (electrical/electronic applications) files. Level 2 (engineering drawings) is not fully supported since Level 2 is used primarily for drafting applications.

Even with the CALS standards, CAD systems accept very different IGES formats. Although it is impossible to accommodate every format, you can use a number of options to configure various IGES translators, including translators supplied by Autodesk, Mentor Graphics, and Cadence. For details, see IGES Translator.

Mask File

Mask file format is a simple flat (non-hierarchical) geometric description. The format facilitates the transfer of simple geometric data for final mask processing. Only geometric forms are described in a mask file; simulation data, element parameters, substrate definitions, and hierarchy are not included.

The Gerber and DXF translators use the mask file format as an intermediate file when converting data to Gerber and DXF. For details, see Mask Files.

MGC/PCB

MGC/PCB files are IFF files that are used exclusively for Mentor Graphics design transfers. Although this format is available from the Advanced Design System layout menu only, you can transfer both schematic and layout information.
MGC/PCB files write to a specific location each and every time. When you select this format, the filename and location of the IFF transport is determined automatically.

Netlist Files

Simulation Program with Integrated Circuit Emphasis (SPICE) is a simulation tool used by engineers throughout the world for simulating circuits of all types. Since its development at the University of California Berkeley, SPICE has been commercialized and modified by a large number of vendors and also adopted and modified by electronics companies for their own in-house use. Many designers and companies have large investments in existing subcircuits or device models described by SPICE netlists that they want to use with the Advanced Design System from Agilent Technologies.

Spectre is an EDA (Electronic Design Automation) tool produced by Cadence Design Systems, Inc. Spectre is used by engineers throughout the world for simulating circuits of all types. Many designers and companies have large investments in existing subcircuits or device models described by Spectre netlists that they want to use with the Advanced Design System (ADS) from Agilent Technologies.

For detailed information on SPICE or Spectre file import, refer to Netlist Translator for SPICE and Spectre.