Liberty File

As we have seen in the previous post about the characterisation of the cell, that knowledge is going to use to understand liberty file and their relation between them.

Liberty File

The .lib file is an ASIC representation of timing and power parameters associated with a cell in a particular semiconductor technology node. These parameters are obtained by simulating the cell under the various condition and represented that data in a format called Liberty file.

Liberty file is a timing model file which contains cell delay, cell parameter, cell transistor, setup time and hold time. The file contains timing and electrical characteristics of the gate cell and the process of getting these parameters are called characterization.

The file is provided by gate library vendor or foundry if fab supplies the gate library.

There are two techniques to characterized a cell and generated .lib file: Composite Current Source (CCS) and Non-Linear Delay Model (NLDM).

The timing of the design is checked for all PVT corners. That’s means we need particular .lib file for each PVT corners.

Liberty file contains:

• Precision units 
• Slew rate 
• Max transition 
• Max Capacitance 
• Input threshold at rise time and fall time 
• Output threshold at rise time and fall time 
• Cell attributes (area, leakage power, etc.) 
• Lookup tables for different parameters (Delay, Setup, hold, etc. with different matrix)

 

At this note of discussion, I wrapped up this topic and we will meet soon with a new file. Thank you. Have a nice day!!!!