Logic Library

7.1 Logic Library

Logic synthesis relevant information are contained in logic libraries. Logic libraries does not contain any physical information of the logic gates. Logic library is a text file. Initially its development were done by a company called “liberty” which was later got acquired by EDA company Synopsys. Hence usual extension of logic libray is .lib and is known as liberty format logic library. This is now universally accepted and used by all fabrication houses and EDA companies.

 

Logic library has timing, area and power information pertaining to all logic gates. These characteristics include information such as cell names, pin names, delay arcs, and pin loading.

 

The technology library also defines the conditions such as the maximum transition time for nets, maximum capacitance and maximim fanout loading. These conditions are called design rule constraints.

 

In addition to cell information and design rule constraints, specify the operating conditions and wire load models specific to that technology are specified in technology library.

 

Net delay models in logic libraries are calculated from different models known as:

Ø  Nonlinear delay models (NLDMs)

Ø  Composite Current Source (CCS) models

 

7.2 Basics of Logic Library (.lib)

The contents of logic library can be broadly classified as below:

Ø  Library group

Ø  Library level attributes

Ø  Environment Description

Ø  Cell description

 

7.2.1. Library group

This gives part specifies general information such as library name regarding library.