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Library Design Guidelines
This topic contains guidelines that helps you optimize your library to reduce die size and maximize the effectiveness of the place-and-route software. These guidelines help to understand about the models the software uses and gives you some general tips on the best ways to model the cells in your library.
A properly designed cell library is one of the most important factors in obtaining optimum results from InnovusTM Digital Implementation System (Innovus). A poorly designed library can lead to increased run times, undesirable placements, poor routing, and ultimately, less than ideal performance.
The library design guidelines are written with Innovus in mind, many also apply to any advanced place-and-route tool. Try to adhere to as many of these features as possible in your library design.
Before detailing the library development guidelines, it is important for the designer of the library to keep in mind that minimizing cell sizes does not necessarily minimize the total die size. In fact, some of the suggestions can cause an increase in the size of the individual cells, but will decrease the overall die size due to reductions in routing among the cells. This topic does not detail the procedures for creating or validating your library.
There are some general rules for all cell types:
- Every logical pin must have a physical description that contains at least one port. Each port must have at least one physical geometry.
- All objects belonging to the cell must be inside the cell boundary.
- In some technologies, power and ground pins extend to the edge or outside the boundary.
- The edges of pins and blockages must be at least one half the minimum spacing away from the cell boundary.
- Minimizing cell size does not necessarily minimize die size. It is better to increase the cell size slightly to optimize routing than to minimize cell size without keeping routing considerations in mind.
For an optimal design, follow these guidelines:
- Determine the routing grid for each layer.
- Try to keep pin and blockages on routing grids.
- Ensure that pins will be accessible after all connections are made.
- Keep cell size a multiple of the greatest common denominator of grids in each direction.
- Create a site for each cell height and multiple of grid minimum.
- Create place-and-route boundaries around cells.
Related Topics
Guidelines for Defining Blockages in a Cell Library
Guidelines for Setting Cell Porosity and High Density in a Cell Library
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