LEF (Library Exchange Format)
To generate a LEF (Library Exchange Format) file in VLSI design, you typically need the following input files and information:
Cell Layout Database(GDS)
The primary input for generating an LEF file is the cell layout database. This includes the physical layout information of the cells in the design. The layout database can be in various formats, such as GDSII (Graphic Data System) or OASIS (Open Artwork System Interchange Standard). The layout database contains information about the shapes, layers, dimensions, and connectivity of the cells.
A technology file, also known as a process design kit (PDK), is a collection of information that describes the process technology used for manufacturing the integrated circuit. The technology file provides details about the layers, layer stack-up, design rules, spacing rules, and other process-related parameters. It defines the rules and constraints that need to be followed during the design process.
Design Rule Checking (DRC) Rule File
The DRC rule file contains the design rules specific to the manufacturing process technology. It defines constraints and checks for various design parameters, such as minimum spacing, width, enclosure rules, and other geometric constraints. The DRC rule file ensures that the layout adheres to the process-specific design rules.
Layer Mapping file
A layer mapping file or document specifies the mapping of the layers in the layout database to the corresponding layers in the technology file. It defines the correspondence between the layer names used in the layout and the layer names defined in the technology file. This mapping is necessary to ensure proper layer recognition and compatibility between the layout and technology.
The LEF file also includes electrical parameters of the cells, such as pin locations, pin types (input, output, power, etc.), pin directions, and pin capacitance values. These electrical parameters are typically provided as part of a separate file, such as a Liberty file (in Liberty format) or a separate specification document.
Depending on the specific requirements, additional information may be included in the LEF file. This can include information about cell variations, different power domains, design constraints, and other design-specific details.
It’s worth noting that the exact file formats and requirements may vary depending on the specific EDA (Electronic Design Automation) tools and design methodologies being used. The input files are typically processed by design automation tools, such as layout editors, DRC tools, and LEF generation tools, to generate the final LEF file that encapsulates the physical and electrical information of the cells for use in VLSI design flows.